Gulf Stream Axis Research Articles

Deep-water ambient sound over the Atlantis II seamounts in the Northwest Atlantica).

Ambient sound was continuously recorded for 52 days by three synchronized, single-hydrophone, near-bottom receivers. The receivers were moored at depths of 2573, 2994, and 4443 m on flanks and in a trough between the edifices of the Atlantis II seamounts. The data reveal the power spectra and intermittency of the ambient sound intensity in a 13-octave frequency band from 0.5 to 4000 Hz. Statistical distribution of sound intensity exhibits much heavier tails than in the expected exponential intensity distribution throughout the frequency band of observations. It is established with high statistical significance that the data are incompatible with the common assumption of normally distributed ambient noise in deep water. Spatial variability of the observed ambient sound appears to be controlled by the seafloor properties, bathymetric shadowing, and nonuniform distribution of the noise sources on the sea surface. Temporal variability of ambient sound is dominated by changes in the wind speed and the position of the Gulf Stream relative to the experiment site. Ambient sound intensity increases by 4-10 dB when the Gulf Stream axis is within 25 km from the receivers. The sound intensification is attributed to the effect of the Gulf Stream current on surface wave breaking.

The Gulf Stream's path and time-averaged velocity structure and transport at 68.5°W and 70.3°W

Full-ocean-depth observations of horizontal velocity, temperature and salinity along 68.5° W chiefly over the period October 2010–May 2014 are analyzed in conjunction with repeated shipboard acoustic Doppler current profiler (SADCP) upper-ocean velocity sections occupied upstream at 70.3° W and regional satellite-altimeter-based sea surface height (SSH) data to construct estimates of the time-averaged Gulf Stream velocity, property structures and transport. A stream-coordinate mean section is created from two moorings near 68.5° W where data are binned relative to distance from the Gulf Stream axis, rotated into along- and across-stream coordinates, and then averaged. Transport in the upper 600 m inferred from the moorings excluding times of large Stream axis curvature and Gulf Stream ring influences is 59.9 Sv (with 95% confidence bounds between 58.6 and 61.6 Sv). This is in good agreement with a mean constructed from the SADCP sections at 70.3° W. Relative to the mean field at 70.3° W, the velocity core of the time-averaged Stream at 68.5° W appears broader with weaker maximum speed, consistent with a companion analysis of the altimetric SSH data. The time-averaged full-ocean-depth transport inferred from the moorings is 102.1 Sv (with 95% confidence bounds between 99.1 and 106.3 Sv), which is stronger than the mean inferred from an ensemble of 10 full-depth lowered acoustic Doppler current profiler (LADCP) sections collected along the moored array. The 2010–2014 time-averaged Gulf Stream inferred from the moored observations is weaker by about 10% than the time-averaged full-ocean-depth transport reported for the late 1980s at the same location using similar procedures, with much of this difference arising from flows at depths greater than 1000 m. Satellite altimetry provides spatial and temporal context for these results and suggests that there are small-scale recirculation cells flanking the separated Gulf Stream west of the New England Seamount Chain. Gulf Stream transport, which includes throughput and recirculating components, appears to be more sensitive to changes in these recirculations at 68.5° W compared to 70.3° W.

The North Atlantic Eddy Heat Transport and Its Relation with the Vertical Tilting of the Gulf Stream Axis

AbstractCorrelations between temperature and velocity fluctuations are a significant contribution to the North Atlantic meridional heat transport, especially at the northern boundary of the subtropical gyre. In satellite observations and in a numerical model at ⅞° resolution, a localized pattern of positive eddy heat flux is found northwest of the Gulf Stream, downstream of its separation at Cape Hatteras. It is confined to the upper 500 m. A simple kinematic model of a meandering jet can explain the surface eddy flux, taking into account a spatial shift between the maximum velocity of the jet and the maximum cross-jet temperature gradient. In the Gulf Stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth. The numerical model suggests that the meandering of the Gulf Stream could account, at least in part, for the large eddy heat transport (of order 0.3 PW) near 36°N in the North Atlantic and for its compensation by the mean flow.

Variability in the Deep Western Boundary Current: Local versus remote forcing

Horizontal velocity, temperature and salinity measurements from the Line W array for the period 2004–2008 show large changes in the water mass structure and circulation of the Deep Western Boundary Current (DWBC). Fluctuations in the flow with periods from 10 to 60 days are bottom intensified: signals most likely associated with topographic Rossby waves (TRW). A fraction (∼15%) of the DWBC transport variability is caused by Gulf Stream rings and meanders. These flow anomalies are surface intensified and fluctuate at frequencies lower than the TRW. Interannual variability in the velocity field appears to be related to changes in the hydrographic properties. The dominant mode of variability is characterized by an overall freshening, cooling, a potential vorticity (PV) increase in the deep Labrador Sea Water (dLSW) and a PV decrease in the Overflow Water (OW). The variability in the flow associated with these property changes is not spatially homogeneous. Offshore (water depths larger than 3500 m) changes in the velocity are in phase with PV changes in the OW: a decrease in the OW PV is accompanied by an increase in the southward (negative) transport. Conversely, variations of the inshore flow are in phase with changes in the dLSW PV (increasing PV and decreasing transport). This trend, true for most of the record, reverses after the winter of 2007–2008. A sudden decrease of the dLSW PV is observed, with a corresponding intensification of the flow in the inner DWBC as well as a northward shift in the Gulf Stream axis.

Differences between observed and a coupled simulation of North Atlantic sea surface currents and temperature

North Atlantic sea surface temperature (SST) distributions derived from observations and a coupled model from NOAA's Geophysical Fluid Dynamics Laboratory, CM2.1, are compared to evaluate the model's ability to simulate recent (1900 to the present) oceanic surface characteristics. The North Atlantic focus will limit our analyses to spatial scales less than gyre, scales usually not addressed in previous model‐observation comparisons. Identifying model differences from observations at these scales will assist modelers in identifying problems to be considered and remedies to be applied. The properties compared are the mean annual SST, standard deviation, amplitude of the annual and semiannual harmonic, decadal meridional movements of the axis of the Gulf Stream, propagation of SST anomalies along the axis of the Gulf Stream, and 100‐year trends in SST records. Because of the dependence of SST on surface currents, observed flow from surface drifters and simulated flow from 15 m fields are also compared. The model simulates the large‐scale properties of all the variables compared. However, there are areas of differences in some variables that can be related to inadequacies in the simulated current fields. For example, the model Gulf Stream (GS) axis after separation from the western boundary is located some 100 km north of the observed axis, which contributes to an area of warmer simulated SSTs. The absence of a slope current in the same region that advects colder water from the Labrador Sea in the observations also contributes to this area of higher model SSTs. The model North Atlantic Current (NAC) is located to the east of the observed NAC contributing to a large area of SST discrepancy. The patterns of the amplitude of the annual harmonic are similar with maximum amplitude off the east coast of northern North America. The semiannual harmonic exhibits relatively large amplitudes (>1°C) north of about 55°N, a signal not found in the observations. In both the model and observations, a region of increased standard deviations encompasses the GS and NAC. The model simulates north‐south migrations of the GS core but at a longer period (20 years) than observed. The model does not simulate the SST anomalies that propagate along the observed GS and NAC. The model captures both the spatial and temporal characteristics of the Atlantic Multidecadal Oscillation. Both model and observations exhibit a dipole in trends, with positive trends in the subtropical Atlantic and negative trends in the subpolar gyre. The modeled region of negative trends is limited to the western subpolar Atlantic. The observed trends extend farther to the east.

Iceberg scours along the southern U.S. Atlantic margin

Rapid climate fluctuations associated with ice-sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice-rafted debris deposits across the North Atlantic. Iceberg transport is largely controlled by ocean surface currents; therefore, iceberg trajectories can serve as a proxy for paleo-circulation studies. Records of iceberg transport from ice-rafted debris (i.e., Heinrich layers) in the North Atlantic suggest that most icebergs released during Quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid-latitudes; however, new data suggest that there may have been an additional southerly component of transport along the western Atlantic margin. Here, we present evidence of extensive iceberg scouring across the upper slope offshore of South Carolina, ~1000 km south of the proximal ice margin during Quaternary glacial maximums. The location and orientation of the keel marks suggest that icebergs were entrained in a southwestward-flowing coastal current. At present, warm waters of the rapid, northeastward-flowing Gulf Stream bathe the upper slope off the southeastern United States. An offshore shift in the Gulf Stream axis during sea-level lowstand may have allowed glacially fed coastal currents to penetrate farther south. This may be the first evidence of iceberg rafting to subtropical latitudes in the North Atlantic.

The Gulf Stream, rings and North Atlantic eddy structures from remote sensing (Altimeter and SeaWiFS)

Seasonal SeaWiFS chlorophyll a concentrations cycles and annual changes of altimeter Sea Level Anomaly are derived for the subtropical North Atlantic near ∼ 35°N and along a Gulf Stream axis. Spatial structure of SeaWiFS, is defined in terms of deviations from a local seasonal cycle and examined in relation to altimeter eddy structure. In the subtropical region near 35°N, SeaWiFS structure is evident during the spring bloom period with a scale of ∼ 430 km, or about twice the eddy scale. A Gulf Stream axis has been selected as a region where the Sea Level Anomaly variance is a maximum. Eddy propagation speeds and scales are examined. Cold-core (cyclonic) rings correspond to areas of high SeaWiFS chlorophyll a. Warm-core (anticyclonic) rings relate to areas of low chlorophyll concentration. Both SeaWiFS structure and eddy structure have a spatial scale of ∼ 450 km or twice the ring scale along the Gulf Stream axis. SeaWiFS chlorophyll anomalies and Altimeter Sea Level Anomaly structure have an overall negative correlation coefficient of r = − 0.34. Swirl currents between eddies redistribute surface chlorophyll concentrations and can spatially bias maximum and minimum concentration levels off eddy centre.

Variability of the Gulf Stream position and transport between 1992 and 1999: a re‐analysis based on a data assimilation experiment

A multivariate dataset resulting from the assimilation of sea surface height and sea surface temperature data in an ocean circulation model of the North Atlantic, is used to study the Gulf Stream position variability from October 1992 to October 1999. The analysis takes place between 75° W and 50° W and focuses on two regions, west and east of 65° W. By calculating zonal averages of the latitudinal position, a regular annual cycle of north–south oscillations of the Gulf Stream axis is identified in the eastern region, whereas inter‐annual variations dominate in the western region. An empirical orthogonal function (EOF) analysis of space–time position anomalies reveals that, even though the annual cycle dominates over the whole domain, the variability has a spatial consistency within each individual region. The assimilation dataset is further used to analyse the variability of the Gulf Stream transport towards the east. Compared to the latitudinal position analysis, the characterization of the transport variability is more complex. Semi‐annual fluctuations can be evidenced in both the regions; however, no significant correlation was found between the fluctuations of position and transport.

A cloud line over the Gulf Stream

A 1000 km long cloud‐line over the major axis of the Gulf Stream was detected in imagery from a number of satellites on April 24, 2001. Analysis of environmental conditions shows that such a cloud‐line is formed when the synoptic low‐level wind is parallel to the Gulf Stream axis and the sky is clear, conditions that rarely occur in the high‐temperature and high‐moisture Gulf Stream region. The PSU‐NCAR fifth‐generation Mesoscale Model (MM5) is used to study the cloud line. Results show that upward motion of the air in the middle of the Gulf Stream, caused by mesoscale solenoidal circulation induced by the large surface thermal gradient, is the source for the large cloud‐line formation. This cloud‐line formation mechanism is different from that of commonly observed ship cloud lines induced by ship‐stack emissions, and its extent is much longer than that of cloud lines induced by lake effects.

Gulf Stream Variability and Ocean–Atmosphere Interactions*

Time series of Gulf Stream position derived from the TOPEX/Poseidon altimeter from October 1992 to November 1998 are used to investigate the lead and lag relation between the Gulf Stream path as it leaves the continental shelf and the changes in sea level pressure, surface wind stress, and sea surface temperature (SST), as given by the NCEP reanalysis. The dominant signal is a northward (southward) displacement of Gulf Stream axis 11 to 18 months after the North Atlantic Oscillation (NAO) reaches positive (negative) extrema. A SST warming (cooling) peaking north of the Gulf Stream is also seen to precede the latitudinal shifts, but it is a part of the large-scale SST anomaly tripole that is generated by the NAO fluctuations. There is no evidence that the Gulf Stream shifts have a direct impact onto the large-scale atmospheric circulation. A fast, passive response of the Gulf Stream to NAO forcing is also suggested by a corresponding analysis of the yearly mean Gulf Stream position estimated from XBT data at 200 m during 1954‐98, where the NAO primarily leads the latitudinal Gulf Stream shifts by 1 yr. The fast Gulf Stream response seems to reflect buoyancy forcing in the recirculation gyres but, as the covariability remains significant when the NAO leads by up to 9 yr, large-scale wind stress forcing may become important after a longer delay. Because of the high NAO index of the last decades, the TOPEX/Poseidon period is one of unprecedented northward excursion of the Gulf Stream in the 45-yr record, with the Gulf Stream 50‐100 km north of its climatological mean position.

Extension and Validation of a Gulf Stream Geosat Synthetic Geoid

An extended synthetic geoid for the western North Atlantic Ocean was constructed by employing Geosat altimeter data, concurrent dynamic model forecasts, and climatology. Estimates of the absolute dynamic topography from the altimeter were compared to estimates of the dynamic topography computed from independent in situ temperature measurements. The rms difference between the two topographic estimates was 0.104 m in the Gulf Stream meander and ring region, 0.081 m in the Sargasso Sea, and 0.098 m overall in this portion of the western North Atlantic ocean. The position of the mean Gulf Stream axis, the 1-σ width of the meander envelope, and the extremes of the meander envelope were determined from the altimetric data. The yearly mean AVHRR- (Advanced Very High Resolution Radiometer) derived surface north walls for 1987 and 1988 were approximately 30 km north of the yearly mean surface maximum velocity axes for the same years. This 30-km offset, however, is affected by the different satellite sampling schemes and the AVHRR data processing techniques. Separation distances derived from individual comparisons of nearly concurrent Geosat, AVHRR, and AXBT (air expendable bathythermograph) datasets result in an average (rms) offset of 17 (±12) km between the axis and the surface north wall, and an 11- (±8) km offset between the axis and the subsurface north wall. The individual axis/surface north wall offsets and their variability were found to increase with increasing anti-cyclonic curvature, consistent with the theoretical effect of centripetal acceleration on a meandering constant potential vorticity jet. This synthetic geoid, validated in portions of the western North Atlantic within a vertical accuracy of about 0.10 m, can be used with the planned Geosat Follow-On mission in the late 1990s to calculate the absolute dynamic topography in near real time.

Synthesizing the Gulf Stream Thermal Structure from XBT Data

Abstract Thirty-six XBT temperature profiles have been used in a parametric model introduced by Hendry to model the Gulf Stream's thermal structure at 65°W between 200 and 1200 dbar, with an rms residual error of 0.56°C. Velocity has been computed geostrophically relative to 1200 dbar, and has been included in calculating potential vorticity analytically from the model. The resulting potential vorticity section for 65°W has been compared with the analogous result from Hendry's parametric model at 59°W, as well as observed potential vorticity sections from 68° to 55°W. There is a significant feature in the potential vorticity structure at 65°W not found at 59°W-namely, a relative minimum in potential vorticity along isopycnals, centered at the Gulf Stream's axis and 350 dbar. The modeled potential vorticity sections are consistent with the observation including the downstream disappearance of this feature. The dynamical implications of these results are briefly discussed.

Continuous Assimilation of Geosat Altimeter Data into a Three-Dimensional Primitive Equation Gulf Stream Model

Abstract A three-dimensional data assimilation scheme is described and tested, using the Geosat altimeter data and a high-resolution, primitive equation, numerical ocean model of the Gulf Stream region. The assimilation scheme is based on an optimal interpolation approach in which data along satellite tracks are continuously interpolated horizontally and vertically into the model grid and assimilated with the model prognostic fields. Preprocessed correlations between surface elevation anomalies and subsurface temperature and salinity anomalies are used to project surface information into the deep ocean; model and data error estimates are used to optimize the assimilation. Analysis fields derived from the Navy's Optimum Thermal Interpolation System are used to initialize the model and to provide some estimate of errors. To evaluate the effectiveness of the assimilation scheme, the errors of model oceanic fields (surface elevation, Gulf Stream axis, temperature) with data assimilation are compared with erro...

Data Assimilation in a Quasi-geostrophic Open-Ocean Model of the Gulf Stream Region Using the Adjoint Method

The method of adjoint data assimilation is applied in a quasi-geostrophic (QG) open-ocean model of the Gulf Stream region. The results of data assimilation experiments are presented in which simulated AXBT and satellite altimeter observations are assimilated into the QG model. The adjoint data assimilation scheme has the ability to correct for large errors in the speed and position of the Gulf Stream jet. These experiments provide valuable insight into the dynamics of the assimilation procedure, and highlight the limitations of the adjoint method in the Gulf Stream region. The adjoint variables of the linearized QG model are approximations of the Green's functions of the adjoint equations. By examining maps of the adjoint variables, one can determine the domain of influence of individual observations. The results of assimilation experiments in which GEOSAT sea surface height observations are assimilated into the QG model are also presented. The results of the GEOSAT assimilation experiments can be interpreted using the insight gained from the simulated data assimilation experiments. It is found that not only can the adjoint method correct the position of the Gulf Stream axis, but it can also reconstruct observed features present in the real ocean (such as Gulf Stream rings) which were originally absent in the model.

Observations and EOF Analysis of Low-Frequency Variability in the Western Part of the Gulf Stream Recirculation

Abstract This study of low-frequency oceanic variability is based on data collected during the Long Term Upper Ocean Study (LOTUS), which was a two year program of (mainly) moored meteorological and oceanographic measurements. The mooring arrays were centered at 34°N, 70°W over the Hatteras Abyssal Plain. With a distance of about 300 km to the mean Gulf Stream axis and the continental slope, LOTUS was the most northern and western long-term mooring site in the Gulf Stream recirculation region to date. The observed low-frequency variability is dominated by zonally elongated motions of the secular time scale (periods <100 days) even great depths (4000 m). In contrast to observations in other parts of the recirculation region, the spectral shapes are strongly depth dependent. The vertical structure of the variability was examined by EOF analysis. Different kinds of EOFs were tested; the best representation of the observed variability was obtained by an EOF representing a undirectional nonrotating (with depth...

On Gulf Stream variability and meanders over the Blake Plateau at 30°N

Current and temperature variability of the Gulf Stream at 30°N was observed with a subsurface array of current meter moorings from August 1980 to October 1981. Energetic current fluctuations in the 2–14 day period band accounted for 45–70% of the total observed variability. Flow perturbations in the cyclonic shear zone tended to have a cyclonic sense of rotation and were 180° out of phase from anticyclonic flow perturbations within the anticyclonic shear region. These fluctuations appear to result from northward propagating wave‐like meanders of the Gulf Stream axis. The fluctuations do not appear to be directly related to local wind forcing. Observations of near‐bottom flow on the Blake Plateau east of the Gulf Stream showed periods of prolonged southward currents lasting up to 40 days with speeds in excess of 30 cm s−1. The mean flow was also southward due to these strong events. The source of the southward flow is unknown. It may be connected to cold‐core eddies that are not detectable in the surface with remote sensing or possibly a remnant of the southward undercurrent that has been observed beneath the Gulf Stream off Cape Hatteras and on the deep slope of the Blake Escarpment.

Blake Plateau: Control of Miocene sedimentation patterns by large-scale shifts of the Gulf Stream axis

Research Article| May 01, 1982 Blake Plateau: Control of Miocene sedimentation patterns by large-scale shifts of the Gulf Stream axis Paul R. Pinet; Paul R. Pinet 1U.S. Geological Survey, and Department of Geology, Colgate University, Hamilton, New York 13346 Search for other works by this author on: GSW Google Scholar Peter Popenoe Peter Popenoe 2U.S. Geological Survey, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar Author and Article Information Paul R. Pinet 1U.S. Geological Survey, and Department of Geology, Colgate University, Hamilton, New York 13346 Peter Popenoe 2U.S. Geological Survey, Woods Hole, Massachusetts 02543 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1982) 10 (5): 257–259. https://doi.org/10.1130/0091-7613(1982)10<257:BPCOMS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul R. Pinet, Peter Popenoe; Blake Plateau: Control of Miocene sedimentation patterns by large-scale shifts of the Gulf Stream axis. Geology 1982;; 10 (5): 257–259. doi: https://doi.org/10.1130/0091-7613(1982)10<257:BPCOMS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The distribution of buried channel networks within Cenozoic sequences of the Blake Plateau and their correlation with global sea-level oscillations indicate that the Gulf Stream axis shifted landward against the Florida-Hatteras Slope during sea-level high-stands and seaward across the central Blake Plateau during sea-level lowstands. A sedimentation model incorporating axial shifts of the Gulf Stream successfully predicts the Miocene stratigraphy of the Florida-Hatteras Slope and Blake Plateau as defined by seismic and drill-hole data. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Effect of Large-Scale Shifts of Gulf Stream on Miocene Sedimentation Patterns of Southeastern U.S. Continental Margin: ABSTRACT

A broad scour band bordered by zones of nondeposition is present today beneath the high-velocity core of the Gulf Stream; deposition takes place on either side of the scour band where bottom currents are weaker. Because the Gulf Stream serves as a barrier to the seaward dispersal of river-derived detritus, deposits are compositionally zoned; clastic sediment blankets the Florida-Hatteras shelf and slope and carbonate oozes, the Blake Plateau. Similar bands of erosion and nondeposition are observed in buried Cenozoic deposits across the Blake Plateau and under the shelf. The character and areal distribution of these bands suggest earlier Gulf Stream tracks. The vertical and horizontal distribution of these unconformities and their timing coincident with high and low stands of sea level as mapped by Vail suggest that they result from a dynamic response of the Gulf Stream to global sea-level oscillations and that the Gulf Stream axis shifts landward against the Florida-Hatteras slope during high stands of sea level and seaward across the central Blake Plateau during low stands of sea level. As a consequence, a complex sedimentary record is produced in which the scour band and sedimentary facies shift landward with deepening water and seaward with shoaling water. This hypothesis was tested with a sedimentation model based on Vail's sea-level curve for the Miocene. The model successfully predicts the distribution of sedimentary facies, location of depocenters, and disposition of major unconformities within the Miocene section of the region as defined by seismic reflection profiles and drill-hole data from nine well sites. These results suggest that large-scale shifts in the position of the Gulf Stream have exerted the primary control on sedimentation patterns along this sector of the continental margin. End_of_Article - Last_Page 1669------------

On the crossover between the Gulf Stream and the Western Boundary Undercurrent

Abstract To determine how the Gulf Stream and Western Boundary Undercurrent cross each other near Cape Hatteras, six current meters were moored from May to July 1971 along a line normal to the Gulf Stream axis and 100 m above the ocean floor in depths from 1200 to 4200 m. Peak velocities of the six records (including one of 47 cm s −1 and the mean velocities of four of the deepest records (2800 to 4000m ) were in the southwest quadrant. During the observations the Gulf Stream did not extend to the bottom in this area except in brief current reversals to the northeast. The Western Boundary Undercurrent flowed southwest under the Gulf Stream parallel to the bottom contours. The transport of the undercurrent, estimated using two geostrophic velocity sections and deep current meter observations, was 24 × 10 6 m 3 s −1 .

Measurements of a Small Near-Bottom Cyclonic Circulation Near the Gulf Stream Axis

Data from near-bottom current meters moored in a small triangular array (25 km/side) plus hydrographic sections reveal the presence of a near-bottom cyclonic circulation with a radius of 50 km and velocity of 10 cm/s just north of the Gulf Stream near 50°W. The circulation extends to at least 1350 m from the ocean floor and was observed over a period of 9 days during which time it moved southward toward the Stream with speeds of 0.5–15 cm/s. The strength of the circulation decreases somewhat with distance from the bottom.