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  • 1
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    Recent changes in the Labrador Sea Water within the Deep Western Boundary Current southeast of Cape Cod (2011)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 58 (2011): 1019-1030, doi:10.1016/j.dsr.2011.07.006.
    Description: Water properties measured by the central mooring in the Line W mooring array southeast of Cape Cod document a large character shift during the period of November 2001 to April 2008. The observed temperature, salinity and planetary potential vorticity (PPV) anomalies manifest changes in the formation region of the water masses present at Station W, specifically upper Labrador Sea Water (uLSW), deep Labrador Sea Water (dLSW) and Overflow Water (OW). During the observation period, the minimum in the PPV anomaly field relative to the record mean PPV profile migrated from 1500m, where it was originally found, to 700m. Temporal changes in the vertical distribution of temperature and salinity were correlated with the PPV changes. This suggests a dLSW-dominated first half of the record, versus an uLSW-dominated second half. The structure of these anomalies is consistent with observations within the Labrador Sea, and their transit time to Line W agrees well with tracer-derived times for signals spreading along the western boundary. In that context, the observed water properties at Line W in the early 2000s reflected the intense deep convection in the Labrador Sea in the mid 1990s, with less intense convection subsequently affecting lighter isopycnals. The observed velocity field is dominated by high-frequency (periods of days to months) fluctuations, however, a fraction of the velocity variability is correlated with changes in water mass properties, and indicate a gradual acceleration of the southwestward flow, with a corresponding increase in Deep Western Boundary Current transport.
    Description: Financial support for the early observations (2001-2004) was provided by the G. Unger Vetlesen Foundation. Observations collected as part of the Line Wprogram (2004-2008) were funded by the U.S. National Science Foundation (grants number OCE-0241354 and OCE-0726720) as well as funding from WHOI’s Ocean and Climate Change Institute.
    Keywords: Deep Western Boundary Current ; Labrador Sea Water ; Variability ; Transport ; Potential vorticity
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
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    Zonal circulation across 52°W in the North Atlantic (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C11008, doi:10.1029/2003JC002103.
    Description: In July–August 1997, a hydrographic/Acoustic Doppler Current Profiler (ADCP)/tracer section was occupied along 52°W in the North Atlantic as part of the World Ocean Circulation Experiment Hydrographic Program. Underway and lowered ADCP (LADCP) data have been used to reference geostrophic velocities calculated from the hydrographic data; additional (small) velocity adjustments provided by an inverse model, constraining mass and silicate transports in 17 neutral density layers, yield the absolute zonal velocity field for 52°W. We find a vigorous circulation throughout the entire section, with an unusually strong Gulf Stream (169 Sv) and southern Deep Western Boundary Current (DWBC; 64 Sv) at the time of the cruise. At the northern boundary, on the west side of the Grand Banks of Newfoundland, we find the westward flowing Labrador Current (8.6 Sv), whose continuity from the Labrador Sea, east of our section, has been disputed. Directly to the south we identify the slopewater current (12.5 Sv eastward) and northern DWBC (12.5 Sv westward). Strong departures from strictly zonal flow in the interior, which are found in the LADCP data, make it difficult to diagnose the circulation there. Isolated deep property extrema in the southern portion, associated with alternating bands of eastward and westward flow, are consistent with the idea that the rough topography of the Mid-Atlantic Ridge, directly east of our section, causes enhanced mixing of Antarctic Bottom Water properties into overlying waters with distinctly different properties. We calculate heat and freshwater fluxes crossing 52°W that exceed estimates based on air-sea exchanges by a factor of 1.7.
    Description: This work was supported by NSF grants OCE95-29607, OCE 95-31864, OCE98-18266, and OCE-0219644.
    Keywords: North Atlantic Circulation ; Gulf Stream ; Deep Western Boundary Current
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Application of acoustic-doppler current profiler and expendable bathythermograph measurements to the study of the velocity structure and transport of the Gulf Stream (2015)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: We have addressed the degree to which Acoustic-Doppler Current Profiler (ADCP) and expendable bathythermograph (XBT) data can provide quantitative measurements of the velocity structure and transport of the Gulf Stream. An algorithm has been used to generate salinity from temperature and depth using an historical Temperature/Salinity relation for the NW Atlantic . Results have been simulated using CTD data and comparing real and pseudo salinity files. Errors are typically less than 2 dynamic cm for the upper 800 rn out of a total signal of 80 cm (across the Gulf Stream). When combined with ADCP data for a near-surface reference velocity, transport errors in isopycnal layers are less than about 1 Sv (106 rn3 /s), as is the difference in total transport for the upper 800 rn between real and pseudo data . The method is capable of measuring the real variability of the Gulf Stream, and when combined with altimeter data, can provide estimates of the geoid slope with oceanic errors of a few parts in 108 over horizontal scales of 500 krn .
    Description: Funding was provided by the Ocean Processes Branch of the National Aeronautics and Space Administration under grant Number NAGW 1026.
    Keywords: Endeavor (Ship: 1976-) Cruise EN86 ; Endeavor (Ship: 1976-) Cruise EN88 ; Oceanography ; Acoustic imaging
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 4
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    Description and evaluation of the Acoustic Profiling of Ocean Currents (APOC) System used on R.V. Oceanus cruise 96 on May 11-22, 1981 (2017)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: The underway current profiling system used in this study consists of a microprocessor-controlled data logger that collects and formats data from a four-beam Ametek-Straza 300 kHz acoustic Doppler current profiler, heading from the ship's gyrocompass, and navigation information from a Loran-C receiver and a satellite navigation unit. Data are recorded on magnetic tape and some real time calculations are made. The system was first used on a May, 1981 cruise aboard the R.V. OCEANUS in the western North Atlantic. Horizontal currents were profiled to depths of 100m. Time averaging is required to remove effects of ship motion. Errors in our ability to profile ocean currents are estimated to be 5-10 em s-1 for a ten-minute vector average. An intercomparison is made with a moored vector measuring current meter (VMCM). The mean difference in hourly-averaged APOC and VMCM currents over the four-hour intercomparison is a few mm s-1. Data from a variety of oceanic regimes are presented and discussed: these regimes include two Gulf Stream crossings, a warm core ring survey, and shallow water in a frontal zone to the east of Nantucket Shoals.
    Description: Prepared for NASA under Grant NAG 1-91 through NASA-Langley.
    Keywords: Acoustic imaging ; Ocean currents ; Oceanus (Ship : 1975-) Cruise OC96
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 5
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    Moored observations of the Deep Western Boundary Current in the NW Atlantic: 2004–2014 (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 7488–7505, doi:10.1002/2017JC012984.
    Description: A moored array spanning the continental slope southeast of Cape Cod sampled the equatorward-flowing Deep Western Boundary Current (DWBC) for a 10 year period: May 2004 to May 2014. Daily profiles of subinertial velocity, temperature, salinity, and neutral density are constructed for each mooring site and cross-line DWBC transport time series are derived for specified water mass layers. Time-averaged transports based on daily estimates of the flow and density fields in Stream coordinates are contrasted with those derived from the Eulerian-mean flow field, modes of DWBC transport variability are investigated through compositing, and comparisons are made to transport estimates for other latitudes. Integrating the daily velocity estimates over the neutral density range of 27.8–28.125 kg/m3 (encompassing Labrador Sea and Overflow Water layers), a mean equatorward DWBC transport of 22.8 × 106 ± 1.9 × 106 m3/s is obtained. Notably, a statistically significant trend of decreasing equatorward transport is observed in several of the DWBC components as well as the current as a whole. The largest linear change (a 4% decrease per year) is seen in the layer of Labrador Sea Water that was renewed by deep convection in the early 1990s whose transport fell from 9.0 × 106 m3/s at the beginning of the field program to 5.8 × 106 m3/s at its end. The corresponding linear fit to the combined Labrador Sea and Overflow Water DWBC transport decreases from 26.4 × 106 to 19.1 × 106 m3/s. In contrast, no long-term trend is observed in upper ocean Slope Water transport. These trends are discussed in the context of decadal observations of the North Atlantic circulation, and subpolar air-sea interaction/water mass transformation.
    Description: G. Unger Vetlesen Foundation; Woods Hole Oceanographic Institution; US National Science Foundation
    Description: 2018-03-15
    Keywords: Deep Western Boundary Current ; Atlantic Meridional Overturning Circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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