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  • 1
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    Slope water, Gulf Stream, and seasonal influences on southern Mid-Atlantic Bight circulation during the fall-winter transition (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 110 (2005): C02009, doi:10.1029/2004JC002311.
    Description: Observations from autumn, 2000, near the shelfbreak front in the Middle Atlantic Bight are used to describe the transition from stratified summer conditions to well-mixed winter conditions over the shelf. During the observational period, the front differed dramatically from climatological conditions, with buoyant Gulf Stream water found shoreward over the sub-surface shelfbreak front. Water mass analysis shows a large number of separate water masses with shelf, slope and Gulf Stream origins. The coolest shelf water was located at the shelfbreak and may be related to “cold pool” water masses observed to the north during summer. Shoreward of this shelfbreak water mass, a mid-shelf front was present which intersected the bottom at the 50 m isobath. High volume transports were associated with both the shelfbreak and mid-shelf fronts. Transport estimates from the cross-shelf sections were approximately 1 Sverdrup, which is large relative to previous estimates of shelf transport. The foot of the front was near the 130 m isobath, much deeper than the climatological position near the 75 m isobath, however this is consistent with a recent theory relating the magnitude of alongshelf transport to the depth at which the front intersects the bottom.
    Description: The authors gratefully acknowledge support from the Duke University - University of North Carolina Oceanographic Consortium for ship time aboard the R/V Cape Hatteras. MSL also gratefully acknowledges support from the Office of Naval Research (N00014-01-1-0260).
    Keywords: Shelfbreak front ; Mid-shelf front ; Shelf transport
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Seasonal characteristics of bottom boundary layer detachment at the shelfbreak front in the Middle Atlantic Bight (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): C03049, doi:10.1029/2003JC002032.
    Description: The seasonality of various characteristics of the detached bottom boundary layer of the Middle Atlantic Bight shelfbreak front is examined using a collection of high-resolution transects across the front. The analysis follows previous methodology in which accumulated temperature change along isopycnals within the front is used to infer the location of the detached layer. The seasonal mean isopycnal at which detachment occurs (approximately 26.0 kg m−3) is fairly constant throughout the year. However, the vertical scale of the detached layer varies significantly with season, extending 60−80 m above the bottom in winter and spring, but only 20−40 m above the bottom in summer. The vertical scale is controlled by the strength and depth of the seasonal pycnocline. The observations suggest that the detached layer is capable of extending into the euphotic zone during winter and spring.
    Description: This work was funded by the Office of Naval Research under contracts N00014-01-1-0931 (C. L. and G. G.) and N00014-01-1-0772 (C. L. and G. G.) and by the National Science Foundation under grant OCE-0095261 (R. P.)
    Keywords: Bottom boundary layer ; Shelfbreak front ; Middle Atlantic Bight
    Repository Name: Woods Hole Open Access Server
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  • 3
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    A coastal current in winter : autonomous underwater vehicle observations of the coastal current east of Cape Cod (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C07030, doi:10.1029/2007JC004306.
    Description: Evolution of the coastal current structure on the shallow continental shelf east of Cape Cod was studied using autonomous underwater vehicle (AUV) surveys and moored observations during the winters of 2005 and 2006. A coastally bounded plume of relatively fresh water, characteristic of a coastal current, persisted throughout both winters despite strong mixing. Nondimensional parameter analysis classified the plume as a bottom-trapped gravity current over a moderately steep slope, placing it in the context of other buoyant coastal currents. The range of water properties within the coastal current, its spatial extent and temporal variability were characterized on the basis of the data from repeat hydrographic sections. Along-shore freshwater transport was dominated by highly variable barotropic flow driven by local wind and basin-wide pressure gradients. It eventually contributed substantially to the average southward along-shore freshwater transport, estimated at 1.1 ± 0.3 × 103 m3 s−1 in February and 1.8 ± 0.4 × 103 m3 s−1 in the first half of March 2006. The contribution of baroclinic buoyancy-driven freshwater transport was typically an order of magnitude lower during both winters. Despite the relative weakness of the baroclinic freshwater transport, the coastal current potentially had a major impact on water mass modification during the winter. Continual presence of the low-salinity plume prevented the formation of cold dense water near the coast and its export offshore. The coastal current effectively isolated the inner-shelf zone, reducing its potential role in ventilation of the intermediate layers of the Wilkinson Basin of the Gulf of Maine.
    Description: This work was supported by the Coastal Ocean Institute of the Woods Hole Oceanographic Institution and the WHOI SeaGrant Office under grant NA06OAR4170021. G.G. was supported by the Office of Naval Research as part of the AWACS program under grant N00014-05-1-0410. A.S. was supported, in part, by WHOI Post-Doctoral Scholarship.
    Keywords: Coastal current ; Cooling ; Autonomous underwater vehicle
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Pathways of shelf water export from the Hatteras shelf and slope (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. 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 117 (2012): C08023, doi:10.1029/2012JC007995.
    Description: It has long been recognized that a massive flow of Middle Atlantic Bight (MAB) shelf water is exported to the deep ocean in the region near Cape Hatteras, North Carolina. We examine the details of this export using data from an extensive array of 26 moorings, deployed over the shelf and slope between Cape Hatteras and the Chesapeake Bay mouth (from 35° 27′ to 36° 40′ N) as part of the U.S. Department of Energy's Ocean Margins Program. Our analysis indicates that the flow of the MAB shelf-edge frontal jet, which typically extends over the MAB slope, falls victim to export over the length of the mooring array, essentially vanishing by the southern extreme of the array. By contrast, the flow of MAB shelf water entering the study region over the inner and middle shelf (to roughly the 40-m isobath) tends to experience very little loss over the extent of the OMP array. Based on our findings and those of previous studies, we hypothesize that this inner and middle shelf flow is diverted seaward upon encountering the Hatteras Front, which separates MAB and South Atlantic Bight shelf waters. Some fraction of this flow appears to return to the OMP array, moving northeastward over the upper slope en route to the deep ocean. Our analysis also suggests that the export of MAB shelf water is enhanced as the Gulf Stream approaches the shelf-edge near Diamond Shoals, a process we deem to be a high priority for future study.
    Description: The Ocean Margins Program was funded by the U.S. Department of Energy through various grants. Our analysis was supported by a grant (OCE-0926999) from the National Science Foundation.
    Description: 2013-02-21
    Keywords: Gulf Stream shelf water interaction ; Hatteras Shelf ; Shelf water export
    Repository Name: Woods Hole Open Access Server
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  • 5
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    The St. Lawrence polynya and the Bering shelf circulation : new observations and a model comparison (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C09023, doi:10.1029/2005JC003268.
    Description: Using 14 year-long instrumented moorings deployed south of St. Lawrence Island, along with oceanographic drifters, we investigate the circulation over the central Bering shelf and the role of polynyas in forming and disseminating saline waters over the shelf. We focus also on evaluating the Gawarkiewicz and Chapman [1995] model of eddy production within coastal polynyas. Principal results include: 1) The northern central shelf near-surface waters exhibit westward flow carrying low-salinity waters from the Alaskan coast in fall and early winter, with consequences for water mass formation and biological production. 2) Within the St. Lawrence polynya, the freshening effect of winter advection is about half as large as the salting effect of surface brine flux resulting from freezing. 3) Brine production over the Bering shelf occurs primarily offshore, rather than within coastal polynyas, even though ice production per unit area is much larger within the polynyas. 4) We find little evidence for the geostrophic flow adjustment predicted by recent polynya models. 5) In contrast to the theoretical prediction that dense water from the polynya is carried offshore by eddies, we find negligible cross-shelf eddy density fluxes within and surrounding the polynya and very low levels of eddy energy that decreased from fall to winter, even though dense water accumulated within the polynya and large cross-shore density gradients developed. 6) It is possible that dense polynya water was advected downstream of our array before appreciable eddy fluxes materialized.
    Description: This work was supported by National Science Foundation grant OCE9730697 to the University of Alaska and grant OCE9730823 to the University of Washington. S. M. acknowledges the support of the National Science Foundation under OCE9811097 and of NASA under grant NNG04GM69G. The University of Hamburg contributions were funded by the Bundesminister für Bildung und Wissenschaft. Funding for the drifter deployment was made possible by the North Pacific Research Board, grant NPMRI T2130. Manuscript preparation was additionally supported by Office of Naval Research grants N00014-99-1-0345 and N00014-02-1-0305 to the University of Washington.
    Repository Name: Woods Hole Open Access Server
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  • 6
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    A coastal current in winter : 2. Wind forcing and cooling of a coastal current east of Cape Cod (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C10014, doi:10.1029/2008JC004750.
    Description: The combined effect of cooling and wind-driven buoyancy flux (WDBF) on a buoyant coastal current east of Cape Cod is investigated using observations and process-oriented numerical modeling. Theoretical considerations show that with the moderately strong surface density gradients observed in the Outer Cape Cod Coastal Current, WDBF can substantially exceed the buoyancy loss due to cooling, especially during intense winter storms. Evidence of deep convection associated with strong negative WDBF during downwelling-favorable winds is clearly seen in the moored observations. A simplified two-dimensional numerical model is used to illustrate the evolution of wind- and buoyancy-driven cross-shelf overturning circulation in response to surface cooling and episodic storm events. The simulation confirms that WDBF plays an important role in driving subduction of cold surface water at the offshore surface outcrop of the coastal current font. The presence of the coastal current is also shown to block onshore Ekman transport. As a result, the downwelling circulation in a cross-shore plane is predicted to have a complex multicell structure, in which exchange between the inner shelf and midshelf is restricted. The downwelling circulation has a major impact on the cross-shelf origin of cold, dense shelf waters contributing to intermediate layers of the Wilkinson Basin of the Gulf of Maine.
    Description: This work was supported by the Coastal Ocean Institute of the Woods Hole Oceanographic Institution and the WHOI SeaGrant Office under grant NA06OAR4170021. G.G. was supported by the Office of Naval Research as part of the AWACS program under grant N00014-05-1-0410. A.S. was supported, in part, by WHOI Post-Doctoral Scholarship.
    Keywords: Coastal current ; Wind-driven buoyancy flux (WDBF) ; Cooling
    Repository Name: Woods Hole Open Access Server
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  • 7
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    A large-amplitude meander of the shelfbreak front during summer south of New England : observations from the Shelfbreak PRIMER experiment (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): C03006, doi:10.1029/2002JC001468.
    Description: In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e-folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s−1, and an amplitude of 15 km (30 km from crest to trough). Along-front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s−1, although subject to significant along-front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s−1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.
    Description: This work was performed under grants N-00014-95-1-0575 and N-00014-98-1-0059. as part of the ONR Shelfbreak PRIMER Initiative. Some additional analysis and writing was done under ONR grants N-00014-00-1-0931 and N-00014-01-1-0247.
    Keywords: Shelfbreak front ; Cross-shelf exchange ; Frontal dynamics
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Shelfbreak frontal eddies over the continental slope north of Cape Hatteras (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. 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 114 (2009): C02017, doi:10.1029/2007JC004642.
    Description: Shelfbreak and slope eddies have been implicated as important agents in the exchange of water between the shelf and slope domains of the Middle Atlantic Bight (MAB). Here we present temperature, salinity, and velocity data from a series of shipboard transects that intercepted a rich eddy field over the slope of the southern MAB. Attention is focused on a well-sampled cyclonic eddy, of roughly 60-km diameter and 300-m depth, that translated southward at 0.1 m s−1. The eddy was composed of a mix of water masses including MAB shelf and slope water, Gulf Stream water, and water from the MAB shelfbreak front. Gradient Richardson numbers suggest that these water masses were subject to vigorous turbulent vertical mixing. The transport of shelfbreak frontal water contained within the eddy was substantial. In the upper 100 m, shelfbreak frontal water comprised ∼75% of the eddy's volume. This frontal water fraction moved southward with a transport of ∼0.4 Sv, comparable with the volume transport within the shelfbreak frontal jet. A number of factors indicate that this highly energetic eddy, with maximum azimuthal velocity of 0.7 m s−1, was generated through instability of the shelfbreak frontal jet. The eddy had apparently developed rapidly (in 〈3 days), consistent with models of eddy generation through baroclinic instability of the shelfbreak frontal jet. The eddy's potential temperature/salinity (θ/S) properties and energy density closely matched the θ/S properties and energy density found in the frontal jet to the north of the eddy.
    Description: This work was supported by the U.S. National Science Foundation through grant OCE-03-27249.
    Keywords: Frontal eddies
    Repository Name: Woods Hole Open Access Server
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  • 9
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    A survival analysis of the gulf stream warm core rings (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. 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 125(10),(2020): e2020JC016507, https://doi.org/10.1029/2020JC016507.
    Description: Survival of Gulf Stream (GS) warm core rings (WCRs) was investigated using a census consisting of a total of 961 rings formed during the period 1980–2017. Kaplan‐Meier survival probability and Cox hazard proportional models were used for the analysis. The survival analysis was performed for rings formed in four 5° zones between 75° W and 55° W. The radius, latitude, and distance from the shelf‐break of a WCR at formation all had a significant effect on the survival of WCRs. A pattern of higher survival was observed in WCRs formed in Zone 2 (70°–65° W) or Zone 3 (65°–60° W) and then demised in Zone 1 (75°–70° W). Survival probability of the WCRs increased to more than 70% for those formed within a latitude band from 39.5° to 41.5° N. Survival probability is reduced when the WCRs are formed near the New England Seamounts.
    Description: We are grateful for financial supports from NOAA (NA11NOS0120038), NSF (OCE‐1851242), SMAST, and UMass Dartmouth. G. G. was supported by NSF under grant OCE‐1851261.
    Description: 2021-04-14
    Keywords: Gulf Stream ; Warm core rings ; Survival analysis
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Mesoscale and submesoscale shelf-ocean exchanges initialize an advective marine heatwave (2022)
    American Geophysical Union
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    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2022. 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 127(1), (2022): e2021JC017927, https://doi.org/10.1029/2021JC017927.
    Description: Observations and high-resolution numerical modeling are used to investigate the dynamical processes related to the initiation of an advective Marine Heatwave in the Middle Atlantic Bight of the Northwest Atlantic continental shelf. Both the observations and the model identify two significant cross-shelf intrusions in November 2016 and January 2017, with the latter inducing large-magnitude water mass anomalies across the shelf. Model prognostic fields reveal the importance of the combination of cyclonic eddies or ringlets and upwelling-favorable winds in producing the large-distance cross-shelf penetration and temperature/salinity anomalies. The cyclonic eddies in close proximity to the shelfbreak set up local along-isobath pressure gradients and provide favorable conditions for the intensification of the shelfbreak front, both processes driving cross-isobath intrusions of warm, salty offshore water onto the outer continental shelf. Subsequently, strong and persistent upwelling-favorable winds drive a rapid, bottom intensified cross-shelf penetration in January 2017 composed of the anomalous water mass off the shelfbreak. The along-shelf settings including realistic representation of bathymetric features are essential in the characteristics of the cross-shelf penetration. The results highlight the importance of smaller scale cyclonic eddies and the intricacy of the interplay between multiple processes to drive significant cross-shelf events.
    Description: This work was supported by Woods Hole Oceanographic Institution (WHOI) Independent Research and Development (IR&D) award and National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) Climate Variability and Predictability (CVP) program under grant NA20OAR4310398. Numerical modeling work was conducted at WHOI High-Performance Computing cluster Poseidon with startup support to Ke Chen.
    Description: 2022-06-08
    Keywords: Drivers of Marine heatwave ; Warm core rings and cyclonic eddies ; Shelfbreak front and frontogenesis ; Pressure gradient setup ; Wind-driven upwelling and bottom intrusion ; Cross-shelf exchange
    Repository Name: Woods Hole Open Access Server
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