Observation of an Anticyclonic Eddy near the Continental Shelf Break South of New England

Abstract. Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140–148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200–300 m are used to estimate the ocean heat content (400→50 MJ m−2), flux (50–200 W m−2 loss) and sea ice growth rates (maximum of 7.5–12.5 cm day−1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992–2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

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Mesoscale, tidal and seasonal/interannual drivers of the Weddell Sea overturning circulation

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0320.1 ◽

2021 ◽

Keyword(s):

Continental Shelf ◽

Shelf Break ◽

Weddell Sea ◽

Global Ocean ◽

Mean Flow ◽

Ice Shelf ◽

Overturning Circulation ◽

Global Circulation ◽

Interannual Fluctuations ◽

Continental Shelf Break

Abstract The Weddell Sea supplies 40–50% of the Antarctic BottomWaters that fill the global ocean abyss, and therefore exerts significant influence over global circulation and climate. Previous studies have identified a range of different processes that may contribute to dense shelf water (DSW) formation and export on the southern Weddell Sea continental shelf. However, the relative importance of these processes has not been quantified, which hampers prioritization of observational deployments and development of model parameterizations in this region. In this study a high-resolution (1/12°) regional model of the southern Weddell Sea is used to quantify the overturning circulation and decompose it into contributions due to multi-annual mean flows, seasonal/interannual variability, tides, and other sub-monthly variability. It is shown that tides primarily influence the overturning by changing the melt rate of the Filchner-Ronne Ice Shelf (FRIS). The resulting ~0.2 Sv decrease in DSW transport is comparable to the magnitude of the overturning in the FRIS cavity, but small compared to DSW export across the continental shelf break. Seasonal/interannual fluctuations exert a modest influence on the overturning circulation due to the relatively short (8-year) analysis period. Analysis of the transient energy budget indicates that the non-tidal, sub-monthly variability is primarily baroclinically-generated eddies associated with dense overflows. These eddies play a comparable role to the mean flow in exporting dense shelf waters across the continental shelf break, and account for 100% of the transfer of heat onto the continental shelf. The eddy component of the overturning is sensitive to model resolution, decreasing by a factor of ~2 as the horizontal grid spacing is refined from 1/3° to 1/12°.

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Gulf Stream Ring Water Intrusion on the Mid-Atlantic Bight Continental Shelf Break Affects Microbially Driven Carbon Cycling

Frontiers in Marine Science ◽

10.3389/fmars.2019.00394 ◽

2019 ◽

Vol 6 ◽

Cited By ~ 5

Author(s):

Adrienne Hoarfrost ◽

John Paul Balmonte ◽

Sherif Ghobrial ◽

Kai Ziervogel ◽

John Bane ◽

...

Keyword(s):

Continental Shelf ◽

Carbon Cycling ◽

Gulf Stream ◽

Shelf Break ◽

Water Intrusion ◽

Continental Shelf Break

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Upwelling by internal tides and kelvin waves at the continental shelf break on the Great Barrier Reef

Marine and Freshwater Research ◽

10.1071/mf9830065 ◽

1983 ◽

Vol 34 (1) ◽

pp. 65 ◽

Cited By ~ 55

Author(s):

E Wolanski ◽

GL Pickard

Keyword(s):

Continental Shelf ◽

Great Barrier Reef ◽

Low Frequency ◽

Kelvin Waves ◽

Shelf Break ◽

Internal Tides ◽

Wind Component ◽

Barrier Reef ◽

Tidal Period ◽

Continental Shelf Break

A time series of 50 days duration was obtained of sea levels and winds and of temperature and currents at six depths from 27 to 104 m at 18�19'S.,147�21'E. on the continental shelf break between the Great Barrier Reef and the Coral Sea. The sea-level signal had a predominantly mixed solar and lunar semidiurnal tidal period. The currents consisted of a semidiurnal tidal component oriented primarily cross-shelf, except near the sea floor, superimposed on a low-frequency, predominantly longshore, southward component, coherent with depth, in geostrophic balance, and modulated by the longshore wind component Large fluctuations in temperature were observed, consisting of a low-frequency component, possibly generated by internal Kelvin waves, and iiucruarions of predominantiy solar semidiurnai iidai period. The latter fiiictuations are interpreted as evidence of internal tides of amplitude up to 110 m that may be generated by the interaction of the longshore currents with topographic irregularities in the shelf. It is suggested that, during any long-term studies of water properties near the shelf break, some additional monitoring of short-term temporal variations should be carried out to avoid data aliasing by internal tides. The bottom boundary layer appears to be very active in vertical mixing. Internal tides may be very important in introducing other water components, e.g. nutrients, to the outer Great Barrier Reef.

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Instability and Mixing of Zonal Jets along an Idealized Continental Shelf Break

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0213.1 ◽

2015 ◽

Vol 45 (9) ◽

pp. 2315-2338 ◽

Cited By ~ 15

Author(s):

Alon Stern ◽

Louis-Philippe Nadeau ◽

David Holland

Keyword(s):

Continental Shelf ◽

Baroclinic Instability ◽

Equation Model ◽

Shelf Break ◽

The Other ◽

Vertical Shear ◽

Zonal Jets ◽

Topographic Slope ◽

West Antarctic ◽

Continental Shelf Break

AbstractThe interaction between an Antarctic Circumpolar Current–like channel flow and a continental shelf break is considered using eddy-permitting simulations of a quasigeostrophic and a primitive equation model. The experimental setup is motivated by the continental shelf of the West Antarctic Peninsula. Numerical experiments are performed to study how the width and slope of an idealized continental shelf topography affect the characteristics of the flow. The main focus is on the regime where the shelfbreak width is slightly greater than the eddy scale. In this regime, a strong baroclinic jet develops on the shelf break because of the locally stabilizing effect of the topographic slope. The velocity of this jet is set at first order by the gradient of the background barotropic geostrophic contours, which is dominated by the slope of the topography. At statistical equilibrium, an aperiodic cycle is observed. Initially, over a long stable period, an upper-layer jet develops over the shelf break. Once the vertical shear reaches the critical condition for baroclinic instability, the jet becomes unstable and drifts away from the shelf break. The cross-shelf mixing is intrinsically linked with the jet drifting, as most of the meridional flux occurs during this instability period. Investigation of the zonal momentum budget reveals that a strong Reynolds stress divergence inversion across the jet is associated with a drifting event, accelerating one flank of the jet and decelerating the other. The hypothesis that jet drifting may be due to one flank of the jet being more baroclinically unstable than the other is tested using topographic profiles with variable curvatures.

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Exploring the impact of atmospheric forcing and basal drag on the Antarctic Ice Sheet under Last Glacial Maximum conditions

The Cryosphere ◽

10.5194/tc-15-215-2021 ◽

2021 ◽

Vol 15 (1) ◽

pp. 215-231

Author(s):

Javier Blasco ◽

Jorge Alvarez-Solas ◽

Alexander Robinson ◽

Marisa Montoya

Keyword(s):

Boundary Conditions ◽

Continental Shelf ◽

Last Glacial Maximum ◽

Ice Sheets ◽

Ice Sheet ◽

Shelf Break ◽

Ice Volume ◽

Basal Friction ◽

The Antarctic ◽

Continental Shelf Break

Abstract. Little is known about the distribution of ice in the Antarctic Ice Sheet (AIS) during the Last Glacial Maximum (LGM). Whereas marine and terrestrial geological data indicate that the grounded ice advanced to a position close to the continental-shelf break, the total ice volume is unclear. Glacial boundary conditions are potentially important sources of uncertainty, in particular basal friction and climatic boundary conditions. Basal friction exerts a strong control on the large-scale dynamics of the ice sheet and thus affects its size and is not well constrained. Glacial climatic boundary conditions determine the net accumulation and ice temperature and are also poorly known. Here we explore the effect of the uncertainty in both features on the total simulated ice storage of the AIS at the LGM. For this purpose we use a hybrid ice sheet shelf model that is forced with different basal drag choices and glacial background climatic conditions obtained from the LGM ensemble climate simulations of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). Overall, we find that the spread in the simulated ice volume for the tested basal drag parameterizations is about the same range as for the different general circulation model (GCM) forcings (4 to 6 m sea level equivalent). For a wide range of plausible basal friction configurations, the simulated ice dynamics vary widely but all simulations produce fully extended ice sheets towards the continental-shelf break. More dynamically active ice sheets correspond to lower ice volumes, while they remain consistent with the available constraints on ice extent. Thus, this work points to the possibility of an AIS with very active ice streams during the LGM. In addition, we find that the surface boundary temperature field plays a crucial role in determining the ice extent through its effect on viscosity. For ice sheets of a similar extent and comparable dynamics, we find that the precipitation field determines the total AIS volume. However, precipitation is highly uncertain. Climatic fields simulated by climate models show more precipitation in coastal regions than a spatially uniform anomaly, which can lead to larger ice volumes. Our results strongly support using these paleoclimatic fields to simulate and study the LGM and potentially other time periods like the last interglacial. However, their accuracy must be assessed as well, as differences between climate model forcing lead to a large spread in the simulated ice volume and extension.

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