A climatology of salty intrusions over the continental shelf from Georges Bank to Cape Hatteras

Lentz, Steven J.

doi:10.1029/2003jc001859

Cited by 65 publications

(108 citation statements)

References 26 publications

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“…The tilted salinity front is a common feature at the MAB shelf break, with the upper (lower) layer of the front moving offshore (onshore). The subsurface salinity onshore intrusion has been examined by Lentz (2003), which suggested multiple potential contributors, including processes of wind forcing, eddy activity, and double diffusion.…”

Section: Mean Velocity and Thermohaline Structurementioning

confidence: 99%

“…ROMS is formulated in vertically stretched, terrain-following coordinates using algorithms described in detail by Shchepetkin and McWilliams (1998, 2003, 2005. Its computational kernel includes highorder advection and time-stepping schemes, weighted temporal averaging of the barotropic mode to reduce aliasing into the slow baroclinic motions, and conservative parabolic splines for vertical discretization.…”

Section: Modelmentioning

confidence: 99%

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Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Chen

2015

Ocean Sci.

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Abstract. A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, in situ temperature and salinity measurements in the GOM, and observed mean depth-averaged velocities. Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time-and space-continuous hindcast fields were used to depict the mean circulation, along-and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv over the Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

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Section: Mean Velocity and Thermohaline Structurementioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Chen

2015

Ocean Sci.

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“…The general circulation on the New England Shelf is part of the larger shelf circulation of the Middle Atlantic Bight, which is characterized by a southwestward along-shelf flow of relatively fresh water, with across-shelf offshore currents at the surface and bottom and onshore currents in the middle of the water column [57]. Shelf water is separated from saltier slope water by a shelf-slope front, but exchanges between these water types can occur due to frontal instabilities [31], eddies [30], warm-core ring shelf interactions [22,48], and saline intrusions at the seasonal pycnocline [56]. Locally, there is a counter-clockwise recirculation just south of MVCO, which is strongest in the summer months [50].…”

Section: Synechococcus Diversity At Mvcomentioning

confidence: 99%

Population dynamics and diversity of Synechococcus on the New England Shelf

Hunter-Cevera¹

2014

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Synechococcus is a ubiquitous marine primary producer. Our understanding of the factors that determine its abundance has been limited by available observational tools, which have not been able to resolve population dynamics at timescales that match response times of cells (hours-days). Development of an automated flow cytometer (FlowCytobot) has enabled hourly observation of Synechococcus at the Martha's Vineyard Coastal Observatory (MVCO) since 2003. In order to ascribe changes in cell abundances to either growth or loss processes, information on division rate is needed. I refined a matrix population model that relates diel changes in the distribution of cell volume to division rate and demonstrated that it provides accurate estimates of daily division rate for both cultured and natural populations. Application of the model to the 11-year MVCO time series reveals that division rate is temperature limited during winter and spring, but light limited during fall. Inferred loss rates closely follow division rate in magnitude over the entire seasonal cycle, suggesting that losses are mainly generated by biological processes. While Synechococcus cell abundance, division rate, and loss rate demonstrate striking seasonal patterns, there are also significant shorter timescale variations and important multi-year trends that may be linked to climate. Interpretation of population dynamic patterns is complicated by the diversity found within marine Synechococcus, which is partitioned into 20 genetically distinct clades. Each clade may represent an ecotype, with a distinct ecological niche. To understand how diversity may affect population dynamics, I assessed the diversity at MVCO over annual cycles with culture-independent and dependent approaches. The population at MVCO is diverse, but dominated by clade I representatives throughout the year. Other clades were only found during summer and fall. High through-put sequencing of a diversity marker allowed a more quantitative investigation into these patterns. Five main Synechococcus oligotypes that comprise the population showed seasonal abundance patterns: peaking either during the spring bloom or during late summer and fall. This pattern strongly suggests that features of seasonal abundance are affected by the underlying diversity structure. Synechococcus abundance patterns result from a complex interplay among seasonal environmental changes, diversity, and biological losses.

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“…Shelf waters are warm in summer (208C near the surface) and cold (58C) in winter (e.g., Bigelow 1933;Mayer et al 1979;Beardsley and Boicourt 1981;Beardsley et al 1985;Butman and Beardsley 1987). This seasonal variation in water temperature is primarily caused by a seasonal variation in surface heat flux with solar heating warming the ocean in springsummer and latent and sensible heat loss cooling the ocean in fall-winter (e.g., Austin and Lentz 1999;Flagg et al 2002;Bignami and Hopkins 2003;Lentz et al 2003a;Fewings et al 2008;Lentz et al 2010, manuscript submitted to J. Geophys. Res., hereafter LSP).…”

Section: Introductionmentioning

confidence: 99%

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

Lentz

2010

Journal of Physical Oceanography

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The mean heat and salt balances over the Middle Atlantic Bight continental shelf are investigated by testing the hypothesis that surface fluxes of heat or freshwater are balanced by along-isobath fluxes resulting from the mean, depth-averaged, along-isobath flow acting on the mean, depth-averaged, along-isobath temperature or salinity gradient. This hypothesized balance is equivalent in a Lagrangian frame to a column of water, for example, warming because of surface heating as it is advected southward along isobath by the mean flow.Mean depth-averaged temperatures increase from north to south along isobath at a rate of 28C (1000 km) 21at midshelf, which is consistent with the hypothesized balance and mean surface heat flux estimates from the 50-yr NCEP Reanalysis. However, mean surface heat flux estimates from the higher-resolution 20-yr Objectively Analyzed Air-Sea Fluxes (OAFlux) reanalysis are too small to balance the along-isobath heat flux divergence implying a cross-shelf heat flux convergence. It is unclear which surface heat flux estimate, NCEP or OAFlux, is more accurate. The cross-shelf heat flux convergence resulting from the mean cross-shelf circulation is too small to balance the along-isobath heat flux divergence. Mean depth-averaged salinities increase from north to south along isobath at a rate of 1 (psu) (1000 km) 21at midshelf. Mean precipitation and evaporation rates nearly balance so that the net freshwater flux is too small by more than an order of magnitude to account for the observed along-isobath increase in salinity. The cross-shelf salt flux divergence resulting from the mean cross-shelf circulation has the wrong sign to balance the divergence in the along-isobath salt flux. These results imply there must be an onshore ''eddy'' salt flux resulting from the time-dependent current and salinity variability. The along-isobath temperature and salinity gradients compensate for each other so that the mean, depthaveraged, along-isobath density gradient is approximately zero. This suggests that there may be a feedback between the along-isobath density gradient and the onshore salt and heat fluxes that maintains the density gradient near zero.

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A climatology of salty intrusions over the continental shelf from Georges Bank to Cape Hatteras

Cited by 65 publications

References 26 publications

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Population dynamics and diversity of Synechococcus on the New England Shelf

The Mean Along-Isobath Heat and Salt Balances over the Middle Atlantic Bight Continental Shelf

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