United States Office of
Environmental Protection Radiation Programs June 1988
Agency Washington, DC 20460
Radiation
&EPA A Study of
Deep-Ocean Currents
Near the 3800 m Low-Level
Radioactive Waste
Disposal Site
May 1984 - May 1986
-------
EPA 520/1-88-007
SAIC - 87/7503/133
A STUDY OF DEEP OCEAN CURRENTS NEAR THE 3800M
LOW-LEVEL RADIOACTIVE WASTE DISPOSAL SITE
May 1984 - May 1986
By
Christopher Casagrande and Peter Hamilton
Science Applications International Corporation
Newport, Rhode Island
Prepared as an account of work sponsored by the
United States Environmental Protection Agency
under Interagency Agreement No. DW14930778-01-0
Project Officer
William R. Curtis
Analysis and Support Division
Office of Radiation Programs (ANR-461)
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
FOREWORD
Between 1946 and 1970, the United States disposed of
low-level radioactive wastes (LLW) at sites in the Atlantic and
Pacific oceans that had been designated for disposal by the
former U.S. Atomic Energy Commission.
In 1972 the Congress enacted the Marine Protection,
Research, and Sanctuaries Act (Public Law 92-532). This Act
charged the Environmental Protection Agency (EPA) with the
responsibility to develop criteria and regulations for any ocean
disposal of waste materials, including LLW.
In 1974 the EPA Office of Radiation Programs (ORP)
initiated studies at previously used LLW disposal sites to
determine whether present ocean survey technologies could
determine the fate of radioactive wastes disposed in the past.
Early studies focused on collecting sediments and marine
organisms for radionuclide analyses and evaluating the condition
of LLW packages previously disposed on the seafloor. Subsequent
studies were conducted to identify pathways and determine
mechanisms for potential transport of radionuclides from
disposal sites. Sediment resuspension and transport, due to the
effects of near-bottom ocean currents, is a potential mechanism
for dispersal of radionuclides in the deep-sea. Thus, ORP has
studied near-bottom circulation in and near disposal sites to
determine the potential for shoreward transport of LLW.
This report presents the results of a study of near-bottom
currents at the Atlantic ocean 3800 meter LLW disposal site.
Continuous measurements were obtained between 1984 and 1986 at
approximately 5, 100, 250, 400 and 1,000 meters above the
bottom. The report describes deployments and recoveries of the
Aanderra current meters, data return and processing, data
analysis, and the potential for sediment transport of
radionuclides.
The Agency invites all readers of this report to send any
comments or suggestions to Mr. David E. Janes, Director,
Analysis and Support Division, Office of Radiation Programs
(ANR-461), Environmental Protection Agency, Washington DC, 20460,
Richard J. Gpimond, Director
Office of Radiation Programs
ill
-------
PREFACE
This report presents the results of a two-year study
of deep ocean currents from May 1984 through May 1986 at the
U.S. 3800-m low-level radioactive waste disposal site near the
mouth of the Hudson Canyon. The program objectives were to
describe the currents, including their source and variability,
and deduce from the data the potential for, and direction of,
transport of contaminants from the disposal area. The study
was accomplished under an interagency agreement between the EPA
and the Minerals Management Service (MMS) which combined the
disposal area study with the on-going MMS study of physical
processes on the Mid-Atlantic slope and rise in order to gain
the maximum benefit from a larger data base.
The results show that the currents in the disposal
area range in strength from a few to 62 cm sec~l and are
principally due to the presence of low frequency topographic
Rossby waves having periods of approximately two to four weeks.
The currents generally flow towards the southwest, in line with
the general topography of the mid-Atlantic region.
The canyon acts to distort the southwest flow,
resulting in currents below the canyon rim which are aligned
with the canyon onshore-offshore axis. The direction of
currents along the canyon axis appears to be determined by the
proximity of both the Gulf Stream and the Western Boundary
Undercurrent. The currents also exhibit the Rossby wave
characteristic of bottom intensification and penetrate to the
floor of the Hudson Canyon.
During the study period, several relatively strong
current events occurred in up- and down-channel directions of
the canyon, with the strongest current (62 cm/sec) directed
up-channel (westward). The currents are sufficiently strong to
transport dissolved contaminants toward shallower water where
they could potentially be entrained by the Western Boundary
Undercurrent and transported toward Cape Hatteras. On the other
hand, particulate matter that is fine enough to be transported
by the relatively strong currents at the disposal site would
probably be deposited further up-channel, as the influence of
the Rossby wave current amplitudes decrease toward the
continental rise. Whether the particles could leave- the canyon
and reach the middle continental rise would require further study,
This report is organized into five sections, as
follows: (I) Introduction; (II) Current Measurement Program;
(III) Literature Review; (IV) Data Analysis; and (V) Summary.
References are contained in Section VI.
-------
TABLE OF CONTENTS
Page
FOREWORD iii
PREFACE v
LIST OF FIGURES viii
LIST OF TABLES xi
I. INTRODUCTION
1.1. Overview 1
II. CURRENT MEASUREMENT PROGRAM
2.1 Mooring Design and Instrumentation 6
2.2 Deployment, Rotation and
Retrieval Cruises 8
2.3 Data Return 8
2.4 Data Processing 14
III. LITERATURE REVIEW
3.1 Introduction 16
3.2 The Gulf Stream 17
3.3 Near Bottom Currents 18
IV. DATA ANALYSIS
4.1 Introduction 24
4.2 Mean Currents 24
4.3 Topographic Rossby Waves (TRWs) 25
4.4 Relationship to the Gulf Stream 37
4.5 Higher Frequency Motions 41
V. SUMMARY 45
VI. REFERENCES 48
VII. ACKNOWLEDGMENTS 51
vii
-------
LIST OF FIGURES
Figure 1-1
Figure 1-2
Figure 1-3
Figure 2-1
Figure 2-2
Figure 3-1
Figure 3-2
Figure 3-3
Figure 4-1
Figure 4-2a
Figure 4-2b
Locations (circles) of the mooring deployments
and the 3800-m low-level radioactive waste
disposal site superimposed on the bathymetry
of the Hudson Canyon (Hanselman and Ryan, 2
1983) .
Location of the U.S. 3800-m low-level radio"
active waste disposal site in relation to the
MASAR program moorings. 3
Location of the SEEP and Gulf Stream Vari-
ability programs affiliated with MASAR/EPA. 4
Design of Mooring I deployed at the 3800-m
low-level radioactive waste disposal site. 7
Time line of the deployment period and the
usable data from each instrument at the
designated nominal depth. 9
Gulf Stream north wall separation distance
from the 3 MASAR mooring lines derived from
NOAA AAVHRR satellite infrared imagery. 19
Map of MASAR study area showing near-bottom
mean current vectors from historical and
MASAR data. 21
A comparison of mean velocities and variance
ellipses at 4000 m for the western North
Atlantic. 22
7-DLP temperatures (top) and currents (bottom)
by level on Mooring I. - 26
Five month data record beginning May 29, 1984
of 40-HLP of temperatures (top) and currents
(bottom) by level on Mooring I at the 3800-m
low-level radioactive waste disposal site. 28
'Five month data record beginning September 2 6
1984 of 40-HLP of temperatures (top) and
currents (bottom) by level on Mooring I at
the 3800-m low-level radioactive waste
disposal site. 29
viii
-------
LIST OF FIGURES (CONT.)
Figure 4-2c
Figure 4-2d
Figure 4-2e
Figure 4-2f
Figure 4-3
Figure 4-4
Figure 4-5
Figure 4-6
Figure 4-7
Five month data record beginning January 1,
1985 of 40-HLP of temperatures (top) and
currents (bottom) by level on Mooring I at
the SSOO^m low-level radioactive waste
disposal site.
30
Five month data record beginning April 30, 1985
of 40-HLP of temperatures (top) and currents
(bottom) by level on Mooring I at the 3800-m
low-level radioactive waste disposal site. 31
Five month data record beginning August 28,
1985 of 40-HLP of temperatures (top) and
currents (bottom) by. level on Mooring I at the
3800-m low-level radioactive waste disposal
site. 32
Five month data record beginning January 1,
1986 of 40-HLP of temperatures (top) and
currentss (bottom) by level on Mooring I at
the 3800-m low-level radioactive waste
disposal site. 33
Spectra of (a) kinetic energy for levels I 2
(dashed) and I 4 (solid), and (b) temperature
for instrument levels I 2 (solid) and I 5
(dashed). 35
Spectra of the (a) U component and (b) V
component for I 2 (1 - solid) and I 4 or I 5
(2 - dashed). 36
Coherence and phase differences between (a)
the U components (1 - solid) and the V
components (2 - dashed), with axes rotated
30°, of I 2 and I 4, and (b) the temperature
at I 2'and I 4 or I 5. 38
Coherence and phase differences between the
U (1 - solid) and V (2 - dashed) components,
with axes rotated 30°, and the temperature at
level (a) I 2 and (b) 15. 39
Rotary spectra for (a) II clockwise component
(1 - solid) and anticlockwise component
(2 - dashed) and (b) I 4 clockwise component
(1 - solid) and anticlockwise component
(2 - dashed). 42
ix
-------
LIST OF FIGURES fCONT.l
Figure 4-8 (a) Kinetic energy spectra plotted in variance
preserving form for I 1 for 171 days beginning
November 2, 1985. 43
-------
LIST OF TABLES
Page
Table 2-1 Aanderaa Current Meter Specifications,
Model RCM-5 10
Table 2-2 EPA Cruises To Deploy, Service and Recovery
Mooring I Between February 1984 and May 1986. 11
Table 2-3 Location of EPA Mooring I from May 1984 To
May 1986. 12
Table 2-4 ^Overall 2-year EPA Mooring I Instrument
-Average Data Return By Parameter Measured
At Each Level. 13
Table 4-1 40-HLP Statistics for EPA Mooring I
47
-------
I. INTRODUCTION
1.1 Overview
In 1976, the U.S. Environmental Protection Agency
(EPA), Office of Radiation Programs, initiated a survey of the
Atlantic 3800-m radioactive dumpsite, the approximate center of
which is indicated by the triangle shown in Figure 1-1. The
objective of this survey was to determine the potential for any
possible migration of radioactive materials, dumped between 1957
and 1959, toward shore and/or productive fishing areas. However
the determination of currents in the area was not completed.
Therefore in March, 1984, the EPA under interagency agreement
#DW14930778-01-0 with the Minerals Management Service (MMS)
contracted with Science Applications International Corporation
(SAIC) to study the currents in and around the 3800-m dumpsite
area, as SAIC was already contracted to MMS to study the Mid-
Atlantic Slope and Rise (MASAR) dynamics west of the dumpsite to
a depth of 3000 m.
This report presents the final results of the two year
current measurements effort, from May 1984 to May 1986, in which
a single EPA mooring was deployed near the Hudson Canyon to
determine the circulation effects on the 3800-m dumpsite. The
array was re-deployed four times - in May and October 1984, and
April and November 1985. Recovery occurred in May 1986.
The measurement of near-bottom currents at the 3800-m
dumpsite was part of the MASAR program. The location of the
3800-m dumpsite current measurement mooring in relation to the
MASAR moorings is shown in Figure 1-2.
The MASAR program, as part of the MMS Outer Continental
Shelf Environmental Studies (OCS) Program, focused on the
following:
• Eddies, rings, streamers, and other Gulf Stream (GS)
related events
• The Western Boundary Undercurrent (WBUC)
• Circulation in the surface layer above the main
thermocline (less than 200 m)
• The shelf/slope front
To study these dynamical processes, the MASAR principal
investigators utilized hydrography, satellite imagery, data from
affiliated programs in the area, and Eulerian current
measurements.
Several of the MASAR affiliated programs (Fig. 1-3)
also supported the dumpsite interpretative effort. These were:
-------
70°40- 39' 38'
I I
Figure 1-1. Locations (circles) of the mooring deployments and
the 3800-m low-level radioactive waste disposal site superimposed
on the bathymetry of the Hudson Canyon (Hanselman and Ryan,
1983). Positions 1, 2, 3, and 4 refer to the May and October
1984 and April and November 1985 mooring deployment positions,
respectively. The. triangle represents the center of the 3800-m
disposal site.
-------
78 W
76 W
74W
72 W
70 W
68
42 N
40 N
38 N
36 N
34 N
200m
lOOOm
2000m
- 38 N
- 36 N
78 W
76W
74W
72 W
70W
34 N
68 W
Figure 1-2. Location of the U.S. 3800-m low-level radioactive
waste disposal site in relation to the MASAR program moorings.
The triangle represents mooring I, at the 3800-m site, initially
deployed in May 1984; the circles denote MASAR moorings deployed
in February 1984 and the stars those deployed in September 1985.
-------
- 36N
34N
Figure 1-3. Location of the SEEP and Gulf Stream Variability
programs affiliated with MASAR/EPA. Circles represent current
meter moorings, boxes represent locations of Inverted Echo
Sounders (IES).
-------
The Warm-Core Rings Experiment (WCRE), funded by NSF
and conducted by the Rosenstiel School of Marine and
Atmospheric Science (RSMAS). The satellite infrared
imagery part of the program,provided much of the 10
year statistical information on Warm-Core Rings (WCRs)
used in this report.
The Gulf Stream Meander Dynamics Program, sponsored by
the National Science Foundation (NSF) and the Office of
Naval Research (ONR). This program was designed to
study the meandering processes of the Gulf Stream (GS).
The Shelf-Edge Exchange Processes (SEEP), a program
supported by the Department of Energy (DOE). The
program's objectives were to describe and quantify the
cross-shelf transport and subsequent deposition on the
slope of organic carbon.
-------
II. CURRENT MEASUREMENT PROGRAM
2.1 Mooring Design and Instrumentation
2.1.1 Mooring Design
One of the major requirements of a successful mooring
design is that the instruments attached to the mooring remain
within a predetermined depth range when subjected to
environmental conditions. The first step in the design process
is to estimate the range of current speeds expected at the
deployment sites.
Three velocity profiles (speed vs. depth) representing
low, mean, and high speed, were generated from historical data.
The mean speed profile was used to determine the initial mooring
design and the high and low profiles were applied to that design
as a check on potential vertical instrument excursions and
mooring tilt at the instrument attachment points.
Next, the mooring design was configured with the
instruments at their required depth and the mooring assumed to be
completely vertical. Sufficient flotation was calculated and
configured to maintain a positive tension in the supporting
cable; a simple summing of submerged weights provided the amount
of tension. A safety factor of two, between working and yield
strengths, was used for this mooring design.
The preliminary design was then subjected to SAIC's
Static Buoy Analysis Computer Program (SBAP). The program
computes the shape of the mooring cable when subjected to
expected ocean current forces. Confirmation of the computer
design was later analyzed by comparing the initial design with
the actual mooring performance.
The final design used at the 3800-m dumpsite is shown
in Figure 2-1. Attached to the mooring were five Aanderaa RCM-5
current meters. The meters were nominally spaced to be
approximately 5, 100, 250, 400, and 1000 m above the ocean floor.
The spacing was designed to allow comparison of currents above,
at, and below the Hudson canyon rim. The lower two instruments
were in the canyon, the third approximately level with the rim,
and the upper two situated approximately 100 and 700 m above the
rim.
The required flotation to maintain the mooring upright j
was distributed along the entire mooring length. In case 'of'
severance at some point along the mooring array, the distribution
of flotation would insure that the remaining portion functioned
normally and would rise to the surface when released by comma'nd^
-------
2898
2930'
OT
erf
w
H
W
33-
H
CM
W
°
3530
3672
3826
3920
3925
I4
80
LEGEND
STROBE AND
RADIO BEACON
16 INCH
GLASS FLOAT
AANDERAA
(CM)
PAIRED
RELEASES
ANCHOR
WHEEL
Figure 2-1. Design of Mooring I deployed at the 3800-m
level radioactive waste disposal site.
-------
2.1.2 Instrumentation
The five Aanderaa RCM-5 current meters used on
the mooring were supplied by EPA as government furnished
equipment (GFE). After twelve months of field use they
were replaced by newly calibrated RCM-5 current meters
(also GPE). All current meters were calibrated before
and after deployments in order to minimize data error.
These meters are intended for use in deep ocean
waters below the wave zone, are self-contained and record
current speed, direction, temperature, and other parameters
as configured by the user.
Each current meter was attached to a swivel and
shaft assembly mounted in-line with other mooring components
The current speed was measured by a rotor. Revolutions
were counted and averaged, and then recorded on magnetic
tape along with current direction from a magnetic compass
and water tempetature from a thermistor. Specifications
for the Aanderaa current meters are given in Table 2-1.
2.2 Deployment, Rotation, and Retrieval Cruises
During the two-year study there were five cruises
to deploy, service, and recover the EPA Mooring designated
as "I". The cruise dates, ships used and ports are shown
in Table 2-2.
Figure 1-1 shows the position of mooring "I"
near the northeast side of the canyon after each deployment.
The exact locations, determined from Loran-C navigation,
are given in table 2-3. The first three deployments were
within 500 - 600 m of each other. The fourth deployment
was situated along the southwest canyon wall to better
define in-canyon circulation. Although each mooring was
identical in design, the differences in total water depth
for each location resulted in different instrument depths.
2.3 Data Return
Total usable data, from each instrument level,
are shown in Table 2-4. A time line of deployment periods
and data obtained at each instrument level is shown in
Figure 2-2. The lowest semiannual data return occurred
during the first 6-month deployment when older-designed '
current meters were used, resulting in a variety of failures',
One meter flooded because of transducer failure. Another
meter experienced compass failure associated with in-situ
low temperatures. The compass functioned normally before
and after deployment. A third meter's battery failed.
During the second deployment period, the top meter
-------
INSTRUMENT
LEVEL/NOM DEPTH <«)
DEPLOYMENT PERIOD
I 1
I 2
I 3
I 4
I 5
2930
3530
3672
3826
3920
1 ; j
1
L
.
L_
1 1 1 1 III
MJJflSOND
1984
1
~ J L j
r — J
J L_
1 1 1 1 1 1 .1 1 ] 1 1
JFMflMJJflSOND
1985
i 1
j
i_ |
_[
1 1 1 1 1
J F M R 11
1986
KEY:
I1 CURRENT SPEED/DIRECTION
1 J TEMPERflTURE
Figure 2-2. Time line of the deployment period and the usable data from each instrument
at the designated nominal depth.
-------
Table 2-1. Aanderaa Current Meter Specifications, Model
RCM-5.
Current Speed Sensor: Rotor with magnetic coupling
Output: Revolutions counted electronically
Threshold: 2.5 cm/s
Maximum: 250 cm/s
Current Direction Compass: Magnetic; coupled to external vane
assembly
Resolution: 0.35 degree
Accuracy: 7.5 degrees
Temperature Sensor: Thermistor
Resolution: 0.1% of range
Accuracy: 0.05 degree C
Time Base Source: Quartz
Accuracy: 2 sec/day
Data Storage 600 feet of 1/4 inch reel to reel magnetic
tape
Capacity: 10,000 readings
Mechanical Housing: Cu Ni Si alloy, epoxy coated
Depth: 6000 meters
Weight: 26.6 kg in air
17.3 kg in water
Sampling Interval: 30 sec - 180 min
Modes: one
10
-------
Table 2-2,
EPA Cruises To Deploy, Service and Recovery
Mooring I Between February 1984 And May 1986.
SHIP
DATES
PORT(S)
U. of Del. vessel
Cape Henlopen
NOAA vessel
Mt. Mitchell
NOAA vessel
Atlantis IV
27 - 31 May 1984
26 - 28 October 1984
29 April - 1 May 1985
SAIC contract vessel
Seaward Explorer 29 Oct. - 11 Nov. 1985
EPA vessel
Peter W. Anderson 5-10 May 1986
Lewes, DE
Sandy Hook, NJ
to Shinnecock, NY
WHOI
Morehead City, NC
to Norfolk, VA
Little Creek, VA
to Balitimore, MD
11
-------
Table 2-3.
Location Of EPA Mooring I From May 1984 To
May 1986.
Deployment:
No. Date
Location
Coordinates
Loran
TD
Water
Depth
Moor
Top
1 5/31-10/28/84
37°49.2'N 25723.6 3925 m 2898 m
70°36.2'W 42292.6
10/28/84-5/1/85
37'49.3'N
70°35.7'W
25721.4 3905 m 2879 m
42293.8
3 5/1-11/11/85
37°49.2'N
70'35.9'W
25722.7 3922 m 2895 m
42294.2
4 11/11/85-5/10/86 37C49.5'N 25723.5 3922 m 2895 m
70°37.1'W 42294.0
*NOTE: Slight variation in total water depth following each
deployment results in instrument depths.
12
-------
Table 2-4. Overall 2-year EPA Mooring I Instrument Average
Data Return By Parameter Measured At Each Level.
Nominal Current
Depth Speed &
Instrument Level Direction Temperature
II 2930 m 51% 51%
12 3530 m 75% 75%
13 3672 m 69% 69%
14 3826 m 75% 93%
15 3920 m 76% 75%
13
-------
flooded because the input/output port design (this port is used
during the pre-development check of the current meter to verify
proper operation) did not use an o-ring; later designs corrected
this problem. This first group of meters was replaced with a
second group of newer meters during the 12th month turnaround.
Subsequently, the overall data return for all meters increased
from about 58% to better than 80%.
2.4 Data Processing
The data from the four deployments were generally of
good quality with the exceptions noted below. After
transcription to nine-track computer tape, the velocity and
temperature time series were processed and checked for bad data
points using established techniques discussed in SAIC (1987).
The time series were merged together by interpolating through the
gaps caused by the rotation of the mooring at 6 month intervals.
The data were then filtered by a three-hour low pass (3-HLP)
Lanzcos kernel decimating to intervals of 1 hour, a forty-hour
low pass (40-HLP) Lanzcos kernel decimating to 6-hourly intervals
and a 7-day low pass (7-DLP) Lanczos squared kernel decimating to
1 day intervals. The latter filter was used to remove energy at
periods less than 7 days so that low frequency Topographic Rossby
Wave (TRW) motions could be presented on two-year axes. The
majority of Rossby wave energy is at periods longer than 7 days
(Thompson, 1977; Hamilton, 1984). This 7-DLP filter was also
used extensively in the analysis of the MASAR data.
The current vector time series (see Figs. 4-2a to -2f
in Section 4) were plotted with the axes rotated such that the V-
component was directed along 030'T and the orthogonal U-component
along 120°T. Rotated axes are designated in the data record
identification label as "R" for rotation along with the adjacent
number "30" designating the degree of rotation, for all direction
data in this report. Axes rotation has resulted in the V-
component being approximately parallel to the general trend of
the isobaths on the continental rise NE and SW of the Hudson
canyon and the U-component being in-line with the canyon axis.
The data recovered from instrument level I 4 in the
first and second deployments was only partially complete._ The
low temperatures of the deep ocean caused the compass to seize in
this instrument and only a speed record was obtained. For the
first and second deployment periods the record was reconstructed
by combining the direction from the nearest instrument level, I
3, and I 5 when that at level I 3 malfunctioned, with the speec}
record from level I 4. This analysis procedure has been shown to
produce a good approximation of direction in the presence of low
frequency planetary wave motions which are essentially columnar.
The results are shown in Figures 4-2a to -2c (Section 4).
Directions so constructed for level I 4 should not be used for
relatively high frequency inertial or tidal motions since there
may be large changes with depth. Thus only the low frequency
14
-------
data for the first two deployments of I 4 are used in the data
analysis section (Section 4) of this report. The columnar motion
at low frequencies was checked using data from deployments 3 and
4 with the result that the phase differences through the depth
array were not significantly different from zero.
A second problem with the data concerned the
calibration of the temperature data for deployments 1 and 2. The
temperature sensors for deployments 3 and 4 were calibrated by
Lament Doherty Geological Observatory and SAIC and are considered
accurate to the precision of the instrument. Deployments 1 and 2
used old GFE instruments which evidenced calibration drifts.
There were differences in mean temperatures between the first and
second year deployments, but variances were similar. Therefore,
temperature records from deployments 1 and 2 were post calibrated
by comparing the temperatures recorded by the older GFE
instruments at the end of deployment 2 to those recorded by the
newer replacement instruments at the beginning of deployment 3
since the recovery and redeployment time difference was only a
few hours. After this correction, the mean temperature profile
for the first year was very similar to that for the second year,
differing by about 0.02°C at maximum.
15
-------
III. LITERATURE REVIEW
3.1 Introduction
A review of the oceanography of the Mid Atlantic
continental rise was conducted as part of a previous study into
the deep currents at the 3800-m low-level radioactive waste
dumpsite (Hamilton, 1982). Major experimental studies up to 1981
were reviewed and discussed. This review is basically an
updating of the information in Hamilton (1982) and the reader is
referred to that document for background material. The 3800-m
dumpsite is about 50 km north of the mean historical position of
the north wall of the Gulf Stream at 71°W and therefore the Gulf
Stream proper generally dominates the upper part of the water
column above the main thermocline. The Gulf Stream and related
warm- and cold-core rings have been the subject of a number of
studies in the last five years.
Earlier current measurements on the continental rise of
the Mid-Atlantic Bight have shown that low frequency motions are
dominated by topographic Rossby waves (TRW) (Thompson, 1977;
Hogg, 1981; Hamilton, 1984). These are planetary wave motions,
with periods ranging from about a week to several months, which
are characterized by bottom intensification (i.e. current
amplitudes increase in magnitude with depth); columnar motions
(i.e. zero phase difference between currents at different depths
at any particular wave frequency) and the direction of
propagation is such that shallow water is on the right (i.e. to
the west at the 3800-m site) . Horizontal wavelengths are of
order 100-200 km and TRWs in the Mid-Atlantic Bight show
direction of energy propagation consistent with generation by the
Gulf Stream (GS) (Hogg, 1981). The dynamics of TRW generation by
the meandering GS are not yet well understood.
Mean near-bottom flows on the continental rise show a
consistent westward and southwestward drift following the isobath
towards Cape Hatteras. This is 'known as the Western Boundary
Undercurrent (WBUC) and recent measurements from the MASAR and
POLYMODE programs are discussed below.
The Gulf Stream leaves the continental margin and flows
into deep water at Cape Hatteras, where it becomes a free flowing
meandering jet. Time-dependent wavelike, lateral displacements
or meanders of the GS are observed along its entire path.
Northeast of Gape Hatteras, these meanders show considerable
range of periodicities (4-100 days are dominant), wavelengths
(200-600 km) and phase speeds (5-40 km d"1) . The domin/ant
meanders also grow downstream of Hatteras with a tendency to
exhibit a lengthening of period and a decrease in phase speed.
By convention, a meander crest (.trough) is defined to be the
extreme shoreward or northwards (seaward or southwards)
displacement of a downstream propagating meander.
16
-------
3.2 The Gulf Stream
Recent studies of the Gulf Stream have involved the
extensive use of SOFAR floats (Richardson et al.f 1981; Schmitz
et al., 1981; Owens, 1984; Shaw and Rossby, 1984). SOFAR floats
follow motions on surfaces of equal pressure (i.e., they are
isobaric floats) and thus are not true followers of water
particles. New developments in float technology have produced
floats that more readily follow water particles on constant
density surfaces (Rossby et al., 1985a). These are known as
"Rafos" floats and some preliminary results from these devices
placed in the Gulf Stream off Cape Hatteras have been reported
(Rossby et al., 1985b). A number of Rafos float tracks released
at a nominal depth of 500 m (corresponding to about 27 sigma-t)
in the GS off Cape Hatteras have remained within the stream for
distances of over 2000 km. Only a few transferences of floats
into slope water to the north of the GS front occurred. The
implication is that at thermocline depths, the GS is an effective
barrier to transfer of Sargasso Sea water into slope water. A
similar conclusion was arrived from an isopycnal water mass
analysis of Gulf Stream 60 hydrographic sections by Bower et al.,
(1985).
Shaw and Rossby (1984), using SOFAR floats, discuss GS
trajectories above and below the thermocline. Using only
portions of the float tracks that correspond to GS water masses,
they showed that the shallow 700-m level trajectories remained
within the GS and between Cape Hatteras and the New England Sea
Mounts (approximately 59°W). Thus fluid particles above the main
thermocline are advected along with the current over distances
comparable to the downstream scale of the current (i.e., the
distance between meander crests). A comparison of the deep SOFAR
float trajectories (1300 and 2000 m) with the shallow ones showed
that a continuous current does not exist below the stream.
However the deep floats do show intermittent eastward flow
related to the surface current but it is apparent that water
parcels below the thermocline can escape from the stream both
northward and southward anywhere along its path. The
intermittent deep GS may be formed by the acceleration of the
shallow stream east of Cape Hatteras. Shaw and Rossby (1984)
also provide direct evidence that large meanders and the
formation of warm- and cold-core rings can be a direct influence
on the 1300-2000-m currents. This adds substance to the ideas
that the meandering GS is the source of energy for the ubiquitous
Topographic Rossby Wave motions found in the slope region
(Luyten, 1977; Hamilton, 1984).
Gulf Stream meanders have been studied from AVHRR
thermal imagery (Halliwell and Mooers, 1983; Cornillon, 1986) and
from data provided by an array of bottom mounted inverse echo
sounders (IBS) to sense the position of the main thermocline and
thus infer the position of the GS front (Watts and Johns, 1982;
Tracey and Watts, 1986). The standard deviation of the envelope
of GS frontal positions increases linearly from Cape Hatteras to
17
-------
71°W. There is a relative minimum at about 69°W followed by
about a two-fold increase in the width envelope which then
remains relatively constant (standard deviation approximately 80
km) between 68° and 58°w (Cornillon, 1986).
Meander propagation speeds and wavelengths vary
considerably. Halliwell and Mooers (1983) found, from an EOF
analyses of GS frontal maps, that there were two dominant meander
paths downstream of Cape Hatteras. At periods greater than four
months the first meander mode was a standing wave with nodes at
Cape Hatteras and about at 38 °N, 68CW. This accounts for the
relative minimum in the GS path statistics found by Cornillon
(1986) and others. The second mode resulted from downstream
propagating meanders with periods of a few weeks to a few months.
The dominant wavelength and period averaged about 330 km and 45
days, respectively. Phase speed was about 8 cm sec"1 with some
amplitudes exceeding 200 km. These meanders exhibited a wide
range of wavelengths, periods and, propagation speeds, while
undergoing exponential growth in the first 900 km downstream of
Cape Hatteras.
Halliwell and Mooers (1983) showed that there was a
weak seasonal dependency in the path of the stream. Tracey and
Watts (1986), using IES data showed that the stream tended to be
displaced southward in winter which is also the period of highest
transport. Recently, Fu et al. (1987) showed the seasonal
variation in sea-level difference across the GS front in the Mid-
Atlantic from satellite altimeter data, which showed a good
correlation with the seasonal variation in large-scale
wind/stress curl (with a three month lag). The intense winter
cooling over the northwestern Atlantic also plays a role in the
intensification of the transport. However the MASAR study showed
there is a great deal of inter-annual variability in the path of
the stream. For most of the 1984-1985 KASAR period the GS was
displaced north of its mean position. This is illustrated by
Figure 3-1 (SAIG, 1987) which shows the distance from the shelf
break along the MASAR mooring transect (north, south and a
transect midway between) of the mean monthly position of GS
front. Large amplitude fluctuations are shown in 1982-1984 which
were not present in 1985 when the stream was closer, on average,
to the slope.
3.3 Near Bottom Currents
Near bottom flows have been generally studied with
current meters. Hendry (1982) discusses records from a zonal
array of 4 moorings along 40°30'N between 56° and 55 °W. IJhe i
instruments were 1000 m off the bottom in 5000-m water depth.,'
The mean flows were westward along the isobaths and were similar
to the westward mean flows measured along 70CW in water depths o,f
less than 4000 m (Luyten, 1977) . The westward deep mean flpw at
55 °W is probably part of the Western Boundary Undercurrent which
is observed on the upper continental rise as far as Cape
Hatteras. It was more difficult to relate the current
18
-------
qAiJ.UUAWAAAiiAUAAWAAAiU4AAAWAAA,i:.Ai6N6j^
1982 I 1983 I 1984 I 1985
Month/Year
Figure 3-1. Gulf Stream north wall separation distance from the 3 MASAR mooring lines
derived from NOAA AVHRR satellite infrared imagery. A, B, C refer to separations from
the south, middle and north lines, respectively. (from.SAIC, 1987)
-------
fluctuations to GS meanders as has been done intermittently with
deep float trajectories (Owens, 1984). Some of the temperature
perturbations at these sites could be from Gulf Stream
displacements or from the formation of cold- and warm-core rings.
Observations of near bottom currents west of 70 "W have
been considerably increased by the MASAR experiment (SAIC, 1987).
Thus, mean flows upstream and downstream of the low-level
radioactive waste sites have some degree of documentation.
Figure 3-2 shows the mean currents derived from near bottom
current meters (generally 100 - 500 m off the seafloor) from the
MASAR experiment (SAIC, 1987); the SEEP experiment (Aikman et
al.7 1987); the Rise Array experiment along 70°W and 69°30'W
(Luyten, 1977); near bottom measurements along 36 °N on four
moorings in water depths from 1600 to 3700 m off Cape Hatteras
(Casagrande, 1983) ; records 500 and 1000 m off the bottom from
five current meters moored under the GS off Cape Hatteras (Johns
and Watts, 1986); five 12-month long current meter records at 500
m and 1000 m off the bottom in the same deep GS region (Bane and
Watts, 1985) ; the EPA 2800-m dumpsite (the mean of four near-
bottom four month current records is shown, Hamilton (1982)); and
finally one additional record from Richardson's (1977) study of
the Western Boundary Undercurrent southeast of Cape Hatteras is
included. Although this latter record is only two months long,
it was 100 m off the bottom in 2600-m water depth, apparently in
the core of the WBUC.
The currents are sufficiently consistent to suggest
that the estimates of the mean are statistically significant.
The resulting pattern suggests that the strongest mean flows are
at the base of the continental slope. However, there is also a
region between the 3000 and 4000-m isobaths in the vicinity of
700-72°W where the westward along-isobath flow is relatively
stronger than in the middle of the rise. This region is just
north of the mean position of the GS front. Mean flows under the
GS (MASAR site H and the Rise Array deeper than 4000 m) tend to
be negligible or much more variable in direction with perhaps a
northward trend.
Figure 3-3 (Fofonoff and Hendry, 1985). shows the low
frequency variance ellipses of deep currents, near bottom or 4000
m whichever is shallower, superimposed on Richardson's (1983)
surface drifter trajectories. The primary data used came from
the Rise Array (Luyten, 1977), the Polymode Local Dynamics
Experiment (Owens et al., 1982), and the Polymode Arrays 1 and 2
(Schmitz, 1976; 1980). At 55"W the kinetic energy (proportional
to the area of the variance ellipses) is clearly greatest under
the GS. There is a marked decrease in variance to the east at1
approximately 45°W and south to 32°N, and to a lesser degree, to
the west at 70CW. There is also a tendency towards increasing
ellipticity of the variance ellipses to the north of the GS as
stronger bottom slopes are encountered on the continental rise.
20
-------
NTS 100-600m oil bottom
I • • • thin 6 month!
months or I o n a • r
Figure 3-2. Map of MASAR study area showing near-bottom mean current vectors from
historical and MASAR data. (from SAIC, 1987)
-------
NJ
K)
50'
80-
75-
TO
50-
4CT
VS? 0 0.5 mfs °s
•/V;/ •; i . ' cr
•:- fiNsi • s-e •.".•"<»
JO-
35-
Figure 3-3. A comparison of mean velocities and variance ellipses at 4000 m for the
western Nortli Atlantic. The approximate position of the Gulf Stream is shown by surface
drifter trajectories (Richardson, 1983). The ellipse axes are proportional to rms speeds
and are drawn to the same scale as the mean velocity vectors (from Fofonoff and Hendry,
1985) .
-------
The major axis of these ellipses appear to align with the local
isobaths.
In a number of these experiments, it has been suggested
that there may be a relationship, possibly indirect, between GS
meander motions and deep currents in the vicinity of the GS.
There is some evidence that the formation and passage of warm-
core rings in the slope sea can affect the energy levels of
deeper currents. Louis et al., (1982) detected strong shoreward
propagating topographic waves over the Scotian slope and rise.
The current oscillations occurred in bursts of 4-5 cycles which
indicated isolated deterministic forcing rather than a steady
stochastic energy flux. Louis et al., (1982) also observed
Rossby waves having baroclinic depth structures on the slope and
upper rise and predominantly barotropic at the slope-rise
junction. One of the events in the Scotian rise current meter
array was related to the formation of a small warm-core eddy at
the crest of a large GS meander due south of the moored array.
The wave field was successfully , modeled as being due to an
isolated vortex by Louis and Smith (1982). A description of the
kinematics and dynamics of a mature warm-core ring is provided by
Joyce (1984). He shows that a large warm-core ring can induce
perceptible warming as deep as 4000 m but the velocity structure
is confined to the upper 1000 m. Similar kinds of changes in
depth structure are also observed in the deep MASAR current
records from the southern Mid-Atlantic Bight (SAIC, 1987).
23
-------
IV. DATA ANALYSIS
4.1 Introduction
Motions on the lower continental rise are dominated by
Topographic Rossby Waves (TRWs), which are ubiquitous on the
continental rise and slope of the Mid-Atlantic Bight and have
been reviewed above. The Hudson Canyon 3800-m low-level
radioactive waste disposal site mooring is north of the mean
historical position of the cold wall or surface temperature front
of the GS at 70°W. However, for about two thirds of the two year
mooring I deployment period the monthly mean position of the cold
wall was north of mooring I (SAIC, 1987). The mooring was about
30' west of the position of the 4000-m Rise Array mooring
(Luyten, 1977; Thompson, 1977) deployed for nine months in 1973
and about 15' west of the northern end of the Inverted Echo
Sounder (IBS) line G from 1983 though 1984 (Tracey and Watts,
1986).
A sketch of the Hudson Canyon bathymetry (Fig. 1-1),
taken from Hanselman and Ryan (1983) , with the four mooring
deployment positions indicated, shows that the channel is about 3
km wide, steep sided with walls about 250 m high, . and a
relatively flat bottom. About 10 km southeast of the mooring
site, the channel broadens and begins to merge into the abyssal
plain at depths beyond 4000 m.
The first three deployments were on the eastern side of
the channel. The fourth deployment was deliberately placed on
the western side of the canyon (about 2 km west of the previous
locations) so as to determine if there were any differences in
flow characteristics, particularly mean currents, between the two
sides of the channel. Thus an attempt was made to determine if
there was a possibility of a residual circulation within the
canyon consisting of northwestward flow on one side and return
flow on the other side. This turns out not to be the case, and
as discussed below, the four deployments may be treated as a
single mooring at a site approximately in the middle of the
channel.
4.2 Mean Currents
Mean currents, of approximately 3-5 cm sec"1, at water
depths shallower than 4000 m along 70°W have been associated with
the edge of the WBUC (Thompson, 1977) , but mean currents in wafter
deeper than 4000 m measured by the rise array showed little
consistent westward drift. In the historical compilation of liieah
currents, Figure 3-2, relatively uniform westward drift of a few
cm sec"1 was found on the upper part of the rise.
Mooring I had relatively strong along-isobath
(southwestward) flow above the canyon of about 4 cm sec"1 which
24
-------
indicated that the site was within the WBUC. Table 4-1 shows
the statistics for currents measured during the complete two
year deployment. Mean velocity, in cm sec~l, and temperature,
in °C, are listed for each instrument level, along with the
variances (U1 denotes the deviation of the U-component of
velocity from , mean temperature
fluxes and , and eddy temperature fluxes
and , where angle brackets <> denote that the mean of the
quantity between them is calculated. The data from levels
I 1, I 3 and I 4 are broken into time segments due to instrument
failures. A comparison of the mean currents at I 2 and I 5 shows
that the I 2 mean flow is directed across the canyon, while the
I 5 mean flow, near the bottom, is directed up the canyon as
might be expected. Mean current speeds increase slightly with
depth between I 2 and I 5, reaching a maximum at 100 m above
the bottom at I 4. However, a comparison between the first and
fourth I.I deployments show that six- month means can vary
considerably between periods; a reflection of long time scales
present in TRW motions and indirect influences of the GS. The
more westward position of deployment 4 seems to make no
significant difference in the direction of mean flows compared
to earlier deployments. It appears, therefore, that the mean
flow is relatively uniform across the channel. No residual
internal horizontal circulation, due to canyon topography,
is apparent in these measurements.
The statistics in Table 4-1 also show that the
lower 400 m of the water column, effectively the depth of the
canyon, is virtually homogeneous. Only very small (differences
of 0.02°C) vertical temperature gradients T| exist between I 2
and I 5. This substantial, bottom-mixed layer, with a larger
temperature variance at I 1 than at I 2 and below, is apparently
caused by localized mixing and strong currents interacting with
the canyon topography. The maximum current speed observed was
62 cm sec'1 and westward in direction at I 4. It occurred
during the first deployment (Fig. 4-1) on approximately Julian
Day (JO) 195. This maximum speed is similar to data from a
rise array at 4000m depth (Luyten, 1977).
4.3 Topographic Rossby Waves (TRWs)
Deep water flows on the continental rise are
dominated by TRWs. Hogg (1981) showed that nearly barotropic
Rossby waves tend to dominate in water depths greater than
4000 m and bottom-trapped TRWs are more prevalent on the middle
and upper rises. Therefore, it is expected that TRWs will
dominate low frequency motions at periods longer than the Rossby
wave cut-off period given by T =(Na)-1; where N is the
Brunt-Vaisala frequency of the lower water column and a is the
bottom slope. For the general topography of the lower rise,
T is about 8-10 days. Thus, low frequency current fluctuations
have characteristic time scales longer than 10 days.
25
-------
o
u
Q
a
Q
U
M
Q
U
Q
O
n
K
0
U
in
11
11
I •
11
11
11
n
.11
•0
«
it
t.ei J
K
40 -
20 -
0 -
-20 -
-40
A
13
3826m
15 3920m
r^S*
"y^rV^tV^t
ii
12 3530m
;p - ;
-------
Important characteristics of TRWs are that the wave velocities
are bottom intensified and columnar (i.e., no phase differences
with depth). TRWs are discussed in more detail by
Thompson (1977); Hogg (1981) and Hamilton (1984). The original
theory is presented by Rhines (1970).
An important question addressed by the Hudson Canyon
current data is the degree to which TRWs propagating westward,
along the rise, influence the currents in a narrow channel cut
into the seafloor; the channel having small dimensions compared
with TRWs which have horizontal wavelengths on the order of
100-200 km and vertical scales of 2-3 km. The 7-DLP current data
presented in Figure 4-1 and the 40-HLP currents and temperature
data (Fig. 4-2 a-f) clearly show that the low-frequency motions
penetrate all the way to the floor of the canyon, increasing in
magnitude with depth. Occasional exceptions to this pattern
are discussed below.
The main influence of the canyon on TRW motions seems
to be an uncharacteristic relative rotation of current vectors
with depth. This is shown more clearly by the principal axes
calculations given in Table 4-1. The major and minor principal
axes effectively give the direction in which the variance of the
fluctuations is maximized and minimized, respectively. There
is a counter clockwise rotation of the major axis of about 20°
between I 1 and I 2 and a clockwise rotation of about 85°
between I 2 and I 5. U-component variances dominate within
the canyon, compared to almost equal U and V variances at I 1.
The time series current data plots (Fig. 4-2 a-f)
show the high degree of coherence of both the currents and the
temperature fluctuations through the water column. However,
there is considerable variability in the energy levels of the
fluctuations over the two-year period. The period from June
to August, 1984 (JD 160-240) showed energetic, generally
westward directed currents. It was also a period of large GS
meanders and the formation of a warm-core ring (WCR 84-E)
downstream (i.e. east) of the site. The month of June had a
large southward displacement of the GS at about 69-68°W which
formed a cold-core ring. This meander was present for most of
June. A large warm-'core ring began forming near 67°W with the
GS displaced southward throughout the Mid-Atlantic Bight. The
GS then interacts with newly formed WCR 84-E towards the end of
July. This causes a reduction in size of the warm-core eddy
which then propagates westward, reaching 70°W in the first part
of September (JD 250) . This is a period of relatively weak
currents (approximately 10 cm sec"1) at mooring I. At the
end of September (JD 263) the GS shifted northward due to
interaction with a cold-core ring (SAIC, 1987) east of Cape
Hatteras. (JD 263) . No strong westward currents occurred in
the months of March-April, June and August 1985 when rings 84-G,
85-B and 85-F were near 70.5° W. Direct relationships between
27
-------
oo
o
UJ
o
o
b)
Q
U
U4
Q
15
Ul
Q
O
U
Q
-40
JULIAN DAYS 1984
DAY 150 IS 5/29/1984
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
Figure 4-2a. Five month data record beginning May 29, 1984 of 40-HLP of temperatures (top)
and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° tiue (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots.
-------
KJ
O
8
O
U
Q
O
M
Q
o
w
a
U
w
U)
X
-x-/ V^-^'
II 2930m
12 3530m
13 3672m
3826m
15 3920m
40
20-
0-
-20-J
-40
II
12
13
14
15
JULIAN DAYS 198«
DAY 270 IS 9/26/1981
2930m
3530m
3672m
3826m
3920m
Figure 4-2b. Five month data record beginning September 26, 1984 of 40-HLP of temperatures
(top) and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° true (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots. There is approximately a one month overlap
from Figure 4-2a.
-------
OJ
o
o
u
Q
O
Ul
Q
8
O
o
g
II
^^7-
A,
~\ __ A
3530m
13
14 3826m
15 3920m
II
TT
— 12
40
20-
0
-40
14
2930m
3530m
3672m
3826m
3920m
JULIAN DAYS 1984
DAY 1 IS 1/1/1985
Figure 4-2c. Five month data record beginning January 1, 1985 of 40-HLP of temperatures
(top) and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° true (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots. There is approximately a one month overlap
from Figure 4-2b.
-------
u>
u
a
o
o
o
o
(3
(J
o
Q
O
o
Q
O
o
(X
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
JULIAN DAYS 1984
DAY 120 IS 4/30/1985
Figure 4-2d. Five month data record beginning April 30, 1985 of 40-HLP of temperatures
(top) and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° true (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots. There is approximately a one month overlap
from Figure 4-2c.
-------
uo
K)
O
I.I
0
O
Ul
O
111
O
UJ
Q
a
Q
U
10
U)
0-
-20-
-40
— ^
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
II 2930m
12 3530m
13 3672m
14 3826m
no jn uo >M
JULIAN DAYS 1984
DAY 240 IS 8/28/1985
Figure 4-2e. Five month data record beginning August 28, 1985 of 40-HLP of temperatures
(top) and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° true (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots. There is approximately a one month overlap
from Figure 4-2d.
-------
00
O
M
Q
0
O
Q
O
LI
a
o
U)
II 2930m
12 3530m
13 3672m
14 3826m
15 3920m
u
t-1
T.
O
40-
20-
0-
-20-
-40
II
12
13
14
15
JULIAN DAYS 1984
DAY 1 IS 1/1/1986
2930m
3530m
3672m
3826m
3920m
Figure 4-2f. Five month data record beginning January 1, 1986 of 40-HLP of temperatures
(top) and currents (bottom) by level on Mooring I at the 3800-m low-level radioactive waste
disposal site. Note Current sticks are referenced to 030° true (vertical up position) in
order to coincide with the orientation of isobaths Northeast and Southwest of the Hudson
Canyon and are designated by R30 on the plots. There is approximately a one month overlap
from Figure 4-2e.
-------
the position of the GS cold wall, the presence of rings, and the
character of the flow on the lower rise are not obvious from
these data, even though subtle connections involving the
generation and propagations of TRWs and the GS are thought to be
dynamically important.
Compared to the June to August, 1984 high current
period, JDs 235-335, 1985 (days 600 - 700, Fig. 4-1) had
relatively short period, weak fluctuations (<10 cm sec'1)
exhibiting northward flow along the axis of the canyon. However,
in contrast to these relatively low-energy periods, the last 5-
month deployment showed a strong eastward event (JD 10-30, 1986;
Fig. 4-2f) at I 1 which exceeds the velocities of the deeper
instruments. A similar strong eastward event, accompanied by
anticyclonic rotation of the current vectors and a sharp increase
in temperature, occurred at the beginning of the second
deployment at about JD 310, 1985 (Fig. 4-2b). Unfortunately,
current measurements at I 1 were not obtained for this event.
The unusual nature of these two strong eastward events along with
the presence of warmer water may indicate a more direct influence
of the deep GS, though this interpretation is speculative.
Examination of the satellite imagery for these two dates show
that on both occasions a GS meander crest is over the site and
thus a direct GS effect on the flow may be a reasonable
explanation of these events.
The kinetic energy spectra, in variance preserving form
for I 2 and 14, are shown in Figure 4-3. Variance preserving
spectra plots give a better feel for the distribution of
fluctuation energy or variance with frequency than conventional
log-log spectra plots, since equal areas under the curve
represent equal amounts of variance. The fluctuating kinetic
energy is greater at I 4 than at I 2, at all frequencies along
with a sharp decrease in energy at I 2 at about 0.15 cycles per
day (cpd) which corresponds to the Rossby wave cut-off frequency.
This increase in energy with depth is consistent with TRW
dynamics despite the existence of the canyon. The 18-month time
series used for these calculations resolves the major low
frequency peaks at 0.03, 0.06 and 0.075 cpd, (33, 16 and 13 day
periods, respectively). These frequencies have been associated
with Rossby waves, and GS meanders in previous studies (Hogg,
1981). A feature of Figure 4-3 is the occurrence of spectral
peaks at frequencies greater than the cut-off for currents within
the canyon (I 4) . These peaks occur at discrete frequencies
which seem to be harmonics of major low-frequency peaks. An
examination of the U and V component spectra (> 0.15 cpd) (Fig.
4-4) shows that the higher frequency harmonics are more
associated with the U than V component at I 4. The U component1
also shows increased variance with respect to the V component.
Thus, the currents are being channelized and distorted within the
canyon so that energy is transferred to the higher harmonics as
the Rossby waves propagate over this feature. There is no visual
indication from 40-HLP data (Fig. 4-2) that distinct wave motions
associated with the channel (i.e., channel modes) are being set
34
-------
Ul
KINETIC ENERGY SPECTRA
CYCLES/DAY
SPECTRA
CYCLES/DAY
(a)
(b)
Figure 4-3. Spectra of (a) kinetic energy for levels I 2 (2-dashed) and I 4 (1-solid) and (b)
temperature for instrument levels I 2 U-solid) and I 5 (2-dashed). The time series length is
548 days beginning November 2, 1984.
-------
LO
CD
SPECTRA
u
o
<
>
CYCLES/DAY
SPECTRA
CYCLES/DAY
(a)
(b)
Figure 4r4_- Spectra of the (a) U component and (b) V component for I 2 (1 - solid) and I 4
or I 5 (2 - dashed). The time series length is 548 days beginning November 2, 1984.
-------
up at frequencies greater than 0.1 cpd. This artifact of
spectral analysis is similar to the harmonics generated by the
distortion of a semi-diurnal tidal wave propagating into a
shoaling estuary.
Unlike the current velocity spectra, the temperature
spectra show decreasing variance with increasing depth (Fig.
4-3) . The current and temperature fluctuations at low
frequencies are also highly coherent and in phase throughout the
depth of the mooring (Fig. 4-5). Temperature and the U component
of current are also correlated with velocity leading temperature
by about 60° at all frequencies below 0.1 cpd (Fig. 4-6).
Usually for TRWs, temperature and currents are in quadrature
(i.e. 90e phase difference) since waves do not transport heat.
However, in the case of waves in the canyon, there is a small,
down-canyon flux of heat most clearly evident from the velocity
and temperature records at I 3, I 4, and I 5. This implies that
the distortion of the TRW wave motions by the canyon causes
horizontal mixing of temperature ,or pollutants which causes a
diffusive flux against the mean up-canyon currents.
Table 4-1 contains the 40-HLP statistics for the
longest combined records at each instrument. Of particular
interest are the Reynolds Stresses and the mean and
fluctuating components of the heat flux. The Reynolds Stress is
quite variable with the four, six-month deployments, but above
the canyon [U'V] is positive, which is consistent with Rossby
waves propagating westward and onshore. Within the canyon, the
momentum flux can change sign. This seems to be the case for the
relatively quiescent 1985 period (compare I 2 and I 5) . However
since the motions are essentially in phase between I 2 and I 5,
the change in momentum flux must be related to the distortion of
the wave motions by the canyon. Again the large variability in
all the calculated statistics is noted even though the averaging
period is six months to one year. The eddy fluxes are an order
of magnitude smaller than the mean advective heat fluxes. The
eddy fluxes oppose the advective fluxes. The T1 variances and
eddy fluxes at the upper level (I 1) exceed that of 2800-m
dumpsite (Hamilton, 1984) and are comparable within the canyon
indicating that the upslope and along slope, temperature gradients
are relatively substantial for the 4000-m depth, despite the
300-400 m deep bottom mixed layer.
4.4 Relationship to the Gulf Stream
The relationship between the Gulf Stream and deep
current motions under and north of the stream is not
straightforward. Further theoretical developments are needed
before the mechanisms of GS meandering and birth of rings, which
are thought to be the energy sources of deep Rossby wave motions,
are better understood. The relationship of deep currents to the
GS is quite subtle and only indirect connections can be suggested
in this repoirfe.
37
-------
00
00
LJ
I
OL
-I8B-
107
CYCLE'S/PAY
1M
CYCLES/DAY
(a)
(b)
Figure 4-5_. Coherence and phase differences between (a) the U components (1 - solid) and
the V components (2 - dashed), with axes rotated 30", of I 2 and I 4, and (b) the
temperatui=e at I 2 and I 4 or I 5. The time series length is 171 days beginning November
11, 1985.
-------
OJ
VO
tu
o
2
LU
tt
LJ
I
O
o
IM
CYCLES/DAY
LJ
O
LJ
o:
LJ
O
CYCLES/DAY
(a)
Figure 4-6, Coherence and phase differences between the U (1 - solid) and V (2 - dashed)
components, with axes rotated 30°, and temperature at level (a) I 2 and (b) 15. The time
series length is 548 days beginning November 2, 1984.
-------
There is some evidence that the path of the GS
influenced the TRW energy levels at mooring I and at MASAR
sites D, E, G and H (SAIC, 1987). During the first four months
of this study, the GS followed its usual path, leaving the slope
at Cape Hatteras and remaining south of the 4000-m isobath at
70°W. This was also a period of intense meander activity and
formation of a cold-core ring and a large warm-core ring,
downstream of the site, between 70° and 65°W. Energy levels
at mooring I were larger than in subsequent periods. Since
TRWs propagate westward along the bathymetry (Hogg, 1981), it
likely that the formation of a large warm-core ring, which
underwent an intense interaction with a GS meander in July 1984,
was partly responsible for the increased wave energy. Between
October 1984 and December 1985 (JD 270-720; Fig. 4-1) the GS
was further north of its historical position (Figure 3-1). In
fact, the GS front was often north of the 3800-m dumpsite during
this period. TRW fluctuations were weaker and of higher in
frequency than the earlier period. Fewer large warm-core rings
were generated in 1985 wes.t of 65°W. The propagation of three
rings into the Hudson Canyon region in the spring and summer of
1985 (84-G, 85-B and 85-F) appeared to have minimal effect, if
any, on the currents at mooring I. No bursts of energetic,
low frequency current fluctuations were observed. Meanders
of the GS were also less frequent, between 70°and 65°W, during
most of 1985.
From December 1985 to the end of this study in
May 1986, TRW energy levels increased. The increase seems to
correspond to the GS shifting back to a more normal path at the
beginning of December. However, a very large southward meander
occurred near 68°W during December with the possible formation
of cold-core rings, similar to the meander and cold-core ring
formation in June 1984. Thus it is not clear which event, the
GS shift or the large meander, was responsible for the
increased TRW activity.
Apart from TRWs, there appeared to be two events
that could be related to the GS proper. Between JD 312 and
322 (1984) and between JD 14 and 30 (1986), see Figs. 4-2b
and 4-2f, substantial eastward flows occurred. The down-canyon
components were accompanied by relatively large increases in
temperature. Imagery -shows large meander crests moving over
the site at both times. It seems reasonable to attribute both
events to intermittent deep GS flow causing an acceleration in
lower layer currents, as discussed by Shaw and Rossby (1984).
This is substantiated in the second event since maximum
velocities occurred at I 1 rather than near bottom, as is more
usual for TRWs. The I 1 record was not available for the first
event.
GS thermocline maps, derived from an IES array
(Tracey and Watts, 1986) , clearly show a large meander
propagating eastward through the array between the middle
-------
of September and the end of November 1984 (Tracey, Cronin and
Watts, 1985). The crest arrives at the site 26-30 November, JD
270-275 about 20 days prior to the warm eastward flow event at
mooring I. The GS remains in a northern position close to the
slope for most of December. Thus, even though the correlation
with GS meander crest events is not exact, the assumption that GS
caused the eastward flow events at 4000 m seems possible.
4.5 Higher Frequency Motions
Near-inertial internal wave motions are generated
primarily by changing wind forcing at the ocean surface such as
due to the passage of storms and fronts. The waves propagate
down below the wind-mixed layer in the form of clockwise
horizontal rotating currents (looking down above) with a
periodicity close to f, the Coriolis parameter. These motions
are intermittent and thus the spectra has broad peak near f. U
and V component amplitudes are almost equal, with V leading U by
90° consistent with a constant current vector rotating at a
frequency near f. Inert ial currents were shown to be the
dominant higher frequency motions at the 2800-m dumpsite on the
upper rise (Hamilton, 1984). Maximum speeds due to inertial
oscillations approached 10 cm sec"1 on occasion with average
amplitudes 3-4 cm sec"1. The lower Hudson Canyon dumpsite is
1000 m deeper than the 2800-m site and since surface layer wind
forcing is the source of inertial currents, it is expected that
near-inertial internal waves would be more attenuated at the
greater depth. Figures 4-7 a & b show the rotary spectra for I 1
and I 4 for the last six-month deployment period. Linear
frequency axes have been used so as to emphasize the higher
frequency inertial and tidal motions. At I 1, a fairly sharp
inertial peak is observed in the clockwise rotating component at
about 1.3 cpd. A semi-diurnal (M2) spectral peak is also present
at 1.95 cpd. At I 4 both inertial and semi-diurnal tidal peaks
have become broader. The M2 tide has similar energy to that at I
1 though the anticlockwise rotary component is attenuated. The
inertial peak within the canyon is not as energetic as at I l.
The local inertial frequency, f, is 1.23 cpd for 37°50'N
latitude. Thus, the inertial peak at I 1 is about 6% higher than
f as is expected for propagating near-inertial internal waves.
Within the canyon however, the peak splits into two
with the lower frequency peak being less than f (about 1.20 cpd).
The reason for this are not clear, but the implication is that
the mean flow field contains negative (cyclonic) relative
vorticity which can support sub-inertial internal waves. The
implication is that the mean currents have horizontal shear,
possibly due to the frictional effects of the canyon walls
(Mooers, 1975).
Figure 4-8a shows the kinetic energy spectra for the
last deployment of I 1 plotted in variance preserving form, where
equal areas under the curve represent equal amounts of variance.
41
-------
N)
ROTARY SPECTRA
Q
CL
O
X
LU
O
<
>
I 2
CYCLES/DAY
(a)
ROTARY SPECTRA
I 2
CYCLES/DAY
(b)
Figure 4-7. Rotary • spectra for (a) I 1 clockwise component (1 - solid) and anticlockwise
component (2 - dashed) and (b) I 4 clockwise component (1 - solid) and anticlockwise
component (2. - dashed). The time series length is 171 days beginning November 11, 1985.
-------
KINETIC ENERGY SPECTRA
CYCLES/DAY
(a)
180
-180
I 2
CYCLES/DAY
(b)
Figure 4-8. (a) Kinetic energy spectra plotted in variance preserving form for I 1 for 171
days beginning November 2, 1985. (b) Coherence of inertial and tidal motions for the clock
wise rotary components at I 1 and I 4 for 171 days beginning November 2, 1985.
-------
It can be seen that inertial and semi-diurnal tidal peaks are
quite prominent at frequencies greater than 1 cpd but they
account for only a small proportion of the total energy which is
dominated by the low frequency TRW wave motions. The amplitude
of the M2 tidal currents is approximately 1 cm sec~^ and the
inertial currents 2-3 cm see"*. This downward propagating
internal wave kinetic energy is expected to be dispersed by the
canyon boundary layers and thus may contribute to mixing.
The coherence of inertial and tidal motions is shown in
Figure 4-8b for the clockwise rotary components at I 1 and I 4.
The tidal records show a high degree of coherence, the inertial
currents less so. The phase propagation is vertically upwards at
both frequencies as is expected for downward propagating internal
wave packets. The 60° to 90" phase differences imply a vertical
phase velocity of about 3 cm sec"-1- which is comparable to the
values calculated at the 2800-m dumpsite (Hamilton, 1984).
44
-------
V. SUMMARY
The near-bottom current and temperature fields at the
3800-m low-level radioactive waste dump site have been
investigated using data from a two-year-long mooring (May 1984-
May 1986) deployed in the lower Hudson Canyon. Aanderaa current
meters were nominally placed at about 5, 100, 250, 400, and 1000
m off the bottom. The upper two instruments were above the lip
of the canyon, the middle instrument approximately at the canyon
lip and the lower two instruments within the canyon.
The dominant motions were low frequency topographic
Rossby waves with characteristic periods of 33, 16, and 13 days.
Two-year-long records were needed to resolve the energetic longer
period motions. The wave motions were generally bottom
intensified, columnar, and penetrated to the floor of the canyon.
The effect of the canyon primarily was to distort the essentially
linear waves below the lip, introducing some non-linearity which
introduced spectral peaks at frequencies higher than the Rossby
wave cut-off (about 8 days). The average kinetic energy of the
Rossby wave motions varied by more than a factor of two with
deployment period and seemed to have a subtle relationship to the
position of the Gulf Stream. When the GS was north of its
historical mean position during most of 1985, energy levels were
approximately 40-50% lower than in either 1984 or 1986 when the
GS followed its more normal path after leaving Cape Hatteras.
However, the higher energy levels were also associated with
higher degrees of GS meander activity downstream of the site.
There were two strong eastward flow events accompanied by warmer
water that may be associated with GS meander crests overlying the
site and could be examples of the intermittent deep GS flows that
have been observed with SOFAR floats (Shaw and Rossby, 1984).
Mean currents above the canyon for the two-year period
were substantial (approximately 3.5 cm sec"1 at 230° True (T) at
400 m from the bottom) and directed to the west. Within the
canyon, mean flows (approximately 5 cm sec"1 at 100 m from the
bottom) tended to be directed more upslope (approximately 240° T)
and there was no evidence of any residualrcirculation internal to
the channel. The westward mean flows suggest that the site is on
the southern edge of Western Boundary Undercurrent (WBUC). Mean
temperatures were essentially uniform throughout the lower 400 m
of the water column, implying that the interaction of the Rossby
waves with the canyon topography generate enough mixing to
homogenize the density structure.
Higher frequency motions are weak and consist of near-
inertial and semi-diurnal internal waves with amplitudes of 2-3
and 1 cm sec"1, respectively.
The implications for disposal of pollutants is as
follows. Pollutants dissolved in the water should be subject to a
mixing through the boundary layer which is greater than the depth
45
-------
of the canyon. Maximum current speeds measured at 5 m and 100 m
from the bottom are 45 cm sec"1 and 62 cm sec"1, respectively.
Mean flows tend to be up the canyon towards the upper slope
within the canyon and westward above the canyon. Therefore,
whether a constituent is mixed above the canyon lip or remains
within the canyon, it will eventually end up in the WBUC and be
transported westward towards Cape Hatteras, similar to the fate
of dissolved constituents at the 2800-m site on the upper rise.
During the two-year study, there were two strong
(approximately 50 cm sec~i) eastward events which have been
attributed to the Gulf Stream. Such flows would transport
pollutants eastward (i.e. down-canyon) towards deeper water. The
deep Gulf Stream is an intermittent feature and thus water
particle trajectories, once out of the Gulf Stream are likely to
return northwards to the WBUC.
Once dissolved, pollutants reaching the Cape Hatteras
region via the WBUC, could be entrained into the deep GS which is
more prevalent there (Watts and Johns, 1982) and then returned
back to the WBUC downstream or further east. Alternatively, they
could remain within the WBUC and continue southwards towards the
South Atlantic. Water mass analyses implemented with some
current meter data have traced the WBUC, from its formation by
Denmark Strait overflow, to as far south as the continental slope
off the Bahamas (Fine and Molinari, 1987).
Particulate matter, if sufficiently fine grained, has a
greater propensity for sediment transport, due to the stronger
maximum currents observed, in the lower Hudson Canyon than at the
2800-m site (60 cm sec"1 versus 40 cm sec"1) . Maximum near
bottom flows were directed both up-and down-channel but with the
strongest event (JD 180-200, 1984) being directed up-channel.
Therefore, the long period fluctuations of the Rossby waves
combined with the mean currents near the canyon bottom would move
fine-grain sediments towards shallower water. Since Rossby wave
current amplitudes decrease towards the slope region, the net
result is probably deposition of any sediment possibly
contaminated with radionuclides in shallower water to the
northwest of the site. Whether sediment particles would leave
the canyon and make it to the middle continental rise
(approximately 3000-m depth) would require some model
calculations to provide guidance. The occasional deep GS event
also has enough energy to transport sediment eastward into deeper
water.
46
-------
Table 4-1
40-III.P Statistics for EPA Mooring I
Coordinate Axis Rotated 030°T
*>
Hctcr
11
U
12
13
13
14
J4
15
Period
6/14/ to
10/23/84
11/15/85
to 5/4/86
11/2/84
to 5/4/86
6/14/86
to 3/25/85
5/6/ to
H/5/85
6/14/84
to 3/01/85
5/6/85
to 5/4/86
11/2/84
to 5/4/86
cm sec
-8.12
-1.67
-1.57
-4.24
-1.91
-5.31
-3.64
-3.44
cm sue °C
-8.86 2.57
-1.23 2.58
-3.14 2.17
-4.57 2.17
-2.35 2.15
-4.82 2.17
-1.67 2.14
-2.05 2.15
56.81
46.92
23.54
73.22
17.70
104.60
40.84
47.33
65.37
53.87
37.60
44.99
30.08
59.59
31.36
39.33
29.58
35.42
4.10
23.79
-2.46
38.03
-0.24
-4.21
-20.
- 4.
- 3.
- 9.
- 4.
87 -22.77
31 - 3.17
41 - 6.«1
18 - 9.92
*
11 -.5-05
-11.52 -.10.46
- 7.
- 7.
79 - 3.57
40 - 4;4l
0.0139
0.0276
0.00293
0.00198
O.OOOH8
0.0020
0.00062
0.00049
<
0.451 0
0.505 0
0.0975 0
0.188 0
0.031 0
0.257 0
0.055 0
0.047 0
V'T'>
.400
.616
.0955
.090
.048
.151
.035
.036
-------
VI. REFERENCES
Aikman, F., H-W, Ou and R.W. Houghton, 1987. Current Variability
Across the New England Continental Shelf and Slope.
Submitted to Continental Shelf Research.
Bower, A.S., H.T. Rossby, and J.L. Lillibridge, 1985. The Gulf
Stream—Barrier or blender? J. Phys. Oceanogr., 15, 24-32.
Cornillon, P., 1986. The Effect of the New England Seamounts on
Gulf Stream Meandering as Observed from Satellite IR
Imagery. J. Phys. Oceanogr. 16, 386-389.
Fofonoff, N.P., and R.M. Hendry, 1985. Current Variability near
the Southeast Newfoundland Ridge. J. Phys. Oceanogr., 15,
963-984.
•2 - -c
Fu, L-L., J. Vazquez and M.E. Parke, 1987. Seasonal Variability
of the Gulf Stream from Satellite Altimetry. J. Geophys.
Res., 92(Cl), 749-754.
Hamilton, P., 1984. Topographic and Inertial Waves on the
Continental Rise of the Mid-Atlantic Bight. J. Geophys.
Res., 89(Cl), 695-710.
Hamilton, P., 1982. Analysis of current meter records at the
northwest Atlantic 2800 meter radioactive dumpsite, EPA
Tech. Rep. 521/1-82-002.
Halliwell, G.R., Jr., and C.N.K. Mooers, 1983. Meanders of the
Gulf Stream downstream from Cape Hatteras 1975^1978. J.
Phys. Oceanogr., 13, 1275-1292.
Hendry, R.M., 1982. On the structure of the deep Gulf Stream.
J. Mar. Res., 40, 119-142. ^ y.
Hogg, N.G., 1981. Topographic waves along 70°W on the
continental rise. J. Mar. Res. 39: 627-649.
Joyce, T.M., 1984. Velocity and Hydrographic Structure of a Gulf
Stream Warm-Core Ring. J. Phys. Oceanogr., 14, 936-947.
Louis, J.P., B.D. Petrie and P.C. Smith, 1982. Observations of
Topographiq Rossby Waves on the Continental Margin off Nova
Scotia. J. Phys. Oceanogr. 12, 47-55.
Louis, J.P., and P.C. Smith 1982. The Development of the'
Barotropic Radiation Field of an Eddy Over a Slope. J.
Phys. Oceanogr., 12, 56-73.
48
-------
Luyten, J.R., 1977. Scales of motion in the deep Gulf Stream and
across the continental rise. J. Mar. Res., 35, 49-74.
Mooers, C.N.K., 1975. Several effects of a baroclinic current on
the cross-stream propagation of inertial-internal waves.
Geophys. Fluid Dyn., 6, 245-275, 1975.
Owens, W.B., J.R. Luyten and H.L. Bryden, 1982. Moored velocity
measurements on the edge of the Gulf Stream recirculation.
J. Mar. Res., 40(Suppl.), 509-524.
Owens,.W.B., 1984. A synoptic and statistical description of the
Gulf Stream and subtropical gyre using SOFAR floats. J.
Phys. Oceanogr., 14, 104-113.
Rhines, P.B., 1970. Edge-, bottom-, and Rossby waves in a
rotating stratified fluid. Geophysical Fluid Dynamics, l:
273-302.
Richardson, P.S., 1977. On the crossover between the Gulf Stream
and the Western Boundary Undercurrent. Deep-Sea Res.
24:139-159.
Richardson, P.L., 1983. Eddy kinetic energy in the North
Atlantic from surface drifters. J. Geophys. Res., 88,
4355-4367.
Richardson, P.L., J.F. Price, W.B. Owens, W.J. Schmitz, H.T.
Rossby, A.M. Bradley, J.R. Valdes and B.C. Webb, 1981.
North Atlantic subtropical gyre: SOFAR floats tracked by
moored listening stations. Science 213, 435-437.
Richardson, P.L., 1983. Eddy kinetic energy in the North
Atlantic from surface drifters. J. Geophys. Res., 88,
4355-4367.
Rossby, T., E.R. Levine, and D.N. Conners, 1985. The isopycnal
Swallow float—A simple device for tracking water parcels in
the ocean. Progress in Oceanography, Vol. 14, Pergamon,
511-525. ,
Rossby, T., A.S. Bower, and P-T Shaw, 1985a. Particle Pathways
in the Gulf Stream. Bull. Amer. Met. Soc. 66(9), 1106-1110.
Science Applications International Corporation, 1987. Study of
Physical Processes on the U.S. Mid-Atlantic Continental
Slope and Rise. Final Report, U.S. Dept. of Interior,
Minerals Management Service, SAIC Report No. 86/7539.
Schmitz, W.J., Jr., 1976. Eddy kinetic energy in the deep
western North Atlantic. J. Geophys. Res. 81, 4981-4982.
49
-------
Schmitz, W.J., Jr., 1980. Weakly depth-dependent segments of the
North Atlantic circulation. J. Mar. Res., 38, 111-133.
Schmitz, W.J., Jr., J.F. Price, P.L. Richardson, W.B. Owens, B.C.
Webb, R.E. Cheney and H.T. Rossby, 1981. A preliminary
exploration of the Gulf Stream system with SOFAR floats. J.
Phys. Oceanogr., 11, 1194-1204.
Shaw, P-T, and H.T. Rossby, 1984. Towards a Lagrangian
description of the Gulf Stream. J. Phys. Oceanogr., 14,
528-540.
Thompson, R.O.R.Y., 1977. Observations of Rossby waves near site
D. Prog. Oceanogr., 7, 135-162.
Tracey, K.L., and D.R. Watts, 1986. On Gulf Stream meander
characteristics near Cape Hatteras. J. Geophys. Res., 91,
7587-7602.
Tracey, K.L., M. Cronin, and D.R. Watts, 1985. The Gulf Stream
Experiment: Inverted Echo Sounder Data Report for the June
1984 to May 1985 Deployment Period. University of Rhode
Island, Narragansett, RI. GSO Tech. Rept. No. 85-3.
Watts, D.R., and W.E. Johns, 1982. Gulf Stream meanders. J.
Geophys. Res., 87, 9467-9476.
50
-------
ACKNOWLEDGMENTS
Sincere appreciation is expressed to Dr. Robert W. Houghton
and the Lamont-Doherty Geological Observatory (LOGO), of
Columbia University, for the loan of five Aanderraa RCM-5
current meters. The LOGO meters were a newer-designed version
of the RCM-5 meters, specifically adapted for extended
deployment in the deep ocean environment. The overall success
of this two-year study is directly attributable to using the
current meters provided by LDGO.
Sincere .thanks are also expressed to Dr. James Lane of the
Minerals Management Service (MMS), Department of the Interior.
The two-year current measurement study, detailed in this report,
was part of a broader MMS study of physical oceanographic
processess along the U.S. mid-Atlantic slope and rise provinces.
In his role as the overall MMS project manager, Dr. Lane
provided frequent and able coordination support and assistance
to the EPA project officer.
51
------- |