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Mayet C, Testut L, Legresy B, Lescarmontier L, Lyard F, . (2013). High-resolution barotropic modeling and the calving of the Mertz Glacier, East Antarctica
. 0148-0227, 118(10), 5267–5279.
Keywords: 0732 Icebergs, 0758 Remote sensing, 4512 Currents, 4534 Hydrodynamic modeling, 9310 Antarctica, barotropic, calving, icebergs, Mertz Glacier, model,
Programme: 1050
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Jardon F P, Vivier F, Bouruet-Aubertot P, Lourenço A, Cuypers Y, Willmes S, . (2014). Ice production in Storfjorden (Svalbard) estimated from a model based on AMSR-E observations: Impact on water mass properties
. J. Geophys. Res., 119(1), 377–393.
Keywords: 0750 Sea ice, 0752 Polynas, 0758 Remote sensing, 4207 Arctic and Antarctic oceanography, 4283 Water masses, AMSR-E satellite observations, brine enriched shelf water, ice production model, polynya area, Storfjorden, supercooling water,
Programme: 1015
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Mayet C, Testut L, Legresy B, Lescarmontier L, Lyard F, . (2013). High-resolution barotropic modeling and the calving of the Mertz Glacier, East Antarctica
. J. Geophys. Res. Oceans, 118(10), 5267–5279.
Abstract: In February 2010, the Mertz Glacier Tongue (MGT) calved, releasing an 80 × 40 km iceberg. We have developed a high-resolution barotropic ocean model of the region to simulate the local circulation in response to tides and atmospheric forcing. We improved the coastline, grounding line position and built a new bathymetry using satellite imagery and older bathymetry data to derive the best available tidal model for the region. We compared this and other available models to seven different sea level observations available in the area and significantly improved the tidal solutions reaching a root sum square of 2.3 cm. This model was then run in different bathymetric configurations, considering the ice draft of the major icebergs B9B and C28, to simulate the circulation before, during, and after the calving event. The currents changed substantially in the neighborhood of the MGT and icebergs. The barotropic model with tidal and atmospheric forcing and the atmospheric wind fields allow us to evaluate the forces acting on the MGT. The sea surface slope force dominates the budget. Calving occurred when high tide and strong nontidal currents (due to atmospheric forcing) combined to lead to the monthly maximum forces exerted on the MGT (i.e., between 10 and 13 February 2010). While the forces are not unusually large at the calving time, the currents are largely enhanced in the rifting area. Therefore, processes related to these currents, like melting the ice mélange inside the rifts, should be investigated to fully explain the final stage of the calving.
Keywords: 0732 Icebergs, 0758 Remote sensing, 4512 Currents, 4534 Hydrodynamic modeling, 9310 Antarctica, barotropic, calving, icebergs, Mertz Glacier, model,
Programme: 688
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Sanial Virginie, van Beek Pieter, Lansard Bruno, d'Ovidio Francesco, Kestenare Elodie, Souhaut Marc, Zhou Meng, Blain Stéphane, . (2014). Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach
. Journal of Geophysical Research: Oceans, 119(4), 2227–2237.
Keywords: Southern Ocean, Crozet Islands, iron fertilization, radium, altimetry, GEOTRACES, 4825 Geochemistry, 4860 Radioactivity and radioisotopes, 4219 Continental shelf and slope processes, 4223 Descriptive and regional oceanography,
Programme: 1077
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Ferrari Ramiro, Provost Christine, Park Young-Hyang, Sennéchael Nathalie, Koenig Zoé, Sekma Hela, Garric Gilles, Bourdallé-Badie Romain, . (2014). Heat fluxes across the Antarctic Circumpolar Current in Drake Passage: Mean flow and eddy contributions
. Journal of Geophysical Research: Oceans, 119(9), 6381–6402.
Abstract: In contrast to a long-standing belief, observations in the Antarctic Circumpolar Current (ACC) show that mean velocity vectors rotate with depth, thus suggesting a possible importance of the time-mean flow for the local poleward heat transport. The respective contributions of the eddy and mean flows to the heat flux across the ACC in Drake Passage (DP) are investigated using recently acquired and historical time series of velocity and temperature from a total of 24 current meter moorings and outputs of a high-resolution (1/12°) model with realistic topography. Only 11 out of the 24 depth-integrated eddy heat flux estimates are found to be significant, and they are poleward. Model depth-integrated eddy heat fluxes have similar signs and amplitudes as the in situ estimates at the mooring sites. They are mostly poleward or nonsignificant, with amplitude decreasing to the south. The cross-stream temperature fluxes caused by the mean flow at the moorings have a sign that varies with location and corresponds to the opposite of the vertical velocity estimates. The depth-integrated temperature fluxes due to the mean flow in the model exhibit small spatial scales and are of opposite sign to the bottom vertical velocities. This suggests that the rotation of the mean velocity vectors with depth is mainly due to bottom topography. The rough hilly topography in DP likely promotes the small-scale vertical velocities and temperature fluxes. Eddy heat fluxes and cross-stream temperature fluxes are integrated over mass-balanced regions defined by the model transport streamlines. The contribution of the mean flow to the ocean heat fluxes across the Southern ACC Front in DP (covering about 4% of the circumpolar longitudes) is about four times as large as the eddy heat flux contribution and the sum of the two represent on the order of 10% of the heat loss to the atmosphere south of 60°S.
Keywords: Antarctic Circumpolar Current, heat fluxes, Drake Passage, current meter moorings, high-resolution model, 4532 General circulation,
Programme: 1061
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Park Young-Hyang, Durand Isabelle, Kestenare Elodie, Rougier Gilles, Zhou Meng, d'Ovidio Francesco, Cotté Cédric, Lee Jae-Hak, . (2014). Polar Front around the Kerguelen Islands: An up-to-date determination and associated circulation of surface/subsurface waters (Vol. 119). Bachelor's thesis, , .
Abstract: The circulation of iron-rich shelf waters around the Kerguelen Islands plays a crucial role for a climatically important, annually recurrent phytoplankton spring bloom over the sluggish shelf region and its downstream plume area along the Antarctic circumpolar flow. However, there is a long-standing confusion about the Polar Front (PF) in the Kerguelen region due to diverse suggestions in the literature for its geographical location with an extreme difference over 10° of latitude. Based on abundant historical hydrographic data, the in situ hydrographic and current measurements during the 2011 KEOPS2 cruise, satellite chlorophyll images, and altimetry-derived surface velocity fields, we determine and validate an up-to-date location of the PF around the Kerguelen Islands. Artificial Lagrangian particle trajectories computed from altimetric velocity time series are analyzed for the possible pathways and sources of different surface/subsurface waters advected into the chlorophyll bloom area east off the islands studied during the KEOPS2 cruise. The PF location determined as the northernmost boundary of the Winter Water colder than 2°C, which is also associated with a band of strong currents, appears to be primarily controlled by topography. The PF rounds the Kerguelen Islands from the south to deflect northward along the eastern escarpment up to the northeastern corner of the Kerguelen Plateau before making its southward retroflection. It is shown that the major surface/subsurface waters found within the deep basin east of the Kerguelen Islands originate from the shelf around the Heard Island, rather than from the shallow shelf north of the Kerguelen Islands.
Keywords: Polar Front, Kerguelen, Southern Ocean, 4207 Arctic and Antarctic oceanography, 4528 Fronts and jets,
Programme: 688,1061
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Adam T. Devlin, Jiayi Pan, Hui Lin. (2020). Multi-Timescale Analysis of Tidal Variability in the Indian Ocean Using Ensemble Empirical Mode Decomposition (Vol. 125).
Abstract: Ocean tides have been observed to be changing worldwide for nonastronomical reasons, which can combine with rising mean sea level (MSL) to increase the long-term impact to coastal regions. Tides can also exhibit variability at shorter timescales, which may be correlated with short-term variability in MSL. This short-term coupling may yield higher peak water levels and increased impacts of exceedance events that may be equally significant as long-term sea level rise. Previous studies employed the tidal anomaly correlation (TAC) method to quantify the sensitivity of tides to MSL fluctuations at long-period (>20 years) tide gauges in basin-scale surveys of the Pacific and Atlantic Ocean, finding that TACs exist at most locations. The Indian Ocean also experiences significant sea level rise and tidal variability yet has been less studied due to a sparse network of tide gauges. However, since the beginning of the 21st century, more tide gauges have been established in a wider geographical range, bringing the possibility of better estimates of tidal and MSL variability. Here, we improve the TAC approach, using the ensemble empirical mode decomposition (EEMD) method to analyze tidal amplitudes and sea level at multiple frequency bands, allowing a more effective use of shorter record tide gauges and better understanding of multiple timescales of tidal variability. We apply this approach to 73 tide gauges in the Indian Ocean to better quantify tidal variability in these under-studied regions, finding that the majority of locations exhibit significant correlations of tides and MSL.
Keywords: Coastal risks Ensemble Empirical Mode Decomposition Indian Ocean Sea level variability Tidal evolution Tidal variability
Programme: 688
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Brent G. T. Else, Jeremy J. Whitehead, Virginie Galindo, Joannie Ferland, C. J. Mundy, Stephen F. Gonski, Jens K. Ehn, Søren Rysgaard, Marcel Babin. (2019). Response of the Arctic Marine Inorganic Carbon System to Ice Algae and Under-Ice Phytoplankton Blooms: A Case Study Along the Fast-Ice Edge of Baffin Bay (Vol. 124).
Abstract: Past research in seasonally ice-covered Arctic seas has suggested that ice algae play a role in reducing dissolved inorganic carbon (DIC) during spring, preconditioning surface waters to low dissolved CO2 (pCO2sw), and uptake of atmospheric CO2 during the ice-free season. The potential role of under-ice phytoplankton blooms on DIC and pCO2sw has not often been considered. In this study we examined the inorganic carbon system beneath landfast sea ice starting midway through a bottom ice algae bloom and concluding in the early stages of an under-ice phytoplankton bloom. During most of the ice algae bloom we observed a slight increase in DIC/pCO2sw in surface waters, as opposed to the expected reduction. Biomass calculations confirm that the role of ice algae on DIC/pCO2sw in the study region were minor and that this null result may be widely applicable. During snow melt, we observed an under-ice phytoplankton bloom (to 10 mg/m3 Chl a) that did reduce DIC and pCO2sw. We conclude that under-ice phytoplankton blooms are an important biological mechanism that may predispose some Arctic seas to act as a CO2 sink at the time of ice breakup. We also found that pCO2sw was undersaturated at the study location even at the beginning of our sampling period, consistent with several other studies that have measured under-ice pCO2sw in late winter or early spring. Finally, we present the first measurements of carbonate saturation states for this region, which may be useful for assessing the vulnerability of a local soft-shelled clam fishery to ocean acidification.
Keywords: air-sea CO2 exchange arctic dissolved inorganic carbon pCO2 phytoplankton sea ice
Programme: 1164
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François Fripiat, Daniel M. Sigman, Guillaume Massé, Jean-Louis Tison. (2015). High turnover rates indicated by changes in the fixed N forms and their stable isotopes in Antarctic landfast sea ice (Vol. 120).
Abstract: We report concentration and nitrogen and oxygen isotopic measurements of nitrate, total dissolved nitrogen, and particulate nitrogen from Antarctic landfast sea ice, covering almost the complete seasonal cycle of sea ice growth and decay (from April to November). When sea ice forms in autumn, ice algae growth depletes nitrate and accumulates organic N within the ice. Subsequent low biological activity in winter imposes minor variations in the partitioning of fixed N. In early spring, the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed N within sea ice, up to 20 times higher than in the underlying seawater. At this time, remineralization and nitrification also accelerate, yielding nitrate concentrations up to 5 times higher than in seawater. Nitrate δ15N and δ18O are both elevated, indicating a near-balance between nitrification and nitrate assimilation. These findings require high microbially mediated turnover rates for the large fixed N pools, including nitrate. When sea ice warms in the spring, ice algae grow through the full thickness of the ice. The warming stratifies the brine network, which limits the exchange with seawater, causing the once-elevated nitrate pool to be nearly completely depleted. The nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment, affecting its N cycling (e.g., allowing for nitrification) and impacting algal physiology (e.g., as reflected in the N and O isotope effects of nitrate assimilation).
Keywords: Antarctic isotopes nitrogen nutrients sea ice
Programme: 1010
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N. Ribeiro, L. Herraiz-Borreguero, S. R. Rintoul, C. R. McMahon, M. Hindell, R. Harcourt, G. Williams. (2021). Warm Modified Circumpolar Deep Water Intrusions Drive Ice Shelf Melt and Inhibit Dense Shelf Water Formation in Vincennes Bay, East Antarctica (Vol. 126).
Abstract: Antarctic Bottom Water (AABW) production supplies the deep limb of the global overturning circulation and ventilates the deep ocean. While the Weddell and Ross Seas are recognized as key sites for AABW production, additional sources have been discovered in coastal polynya regions around East Antarctica, most recently at Vincennes Bay. Vincennes Bay, despite encompassing two distinct polynya regions, is considered the weakest source, producing Dense Shelf Water (DSW) only just dense enough to contribute to the lighter density classes of AABW found offshore. Here we provide the first detailed oceanographic observations of the continental shelf in Vincennes Bay (104-111°E), using CTD data from instrumented elephant seals spanning from February to November of 2012. We find that Vincennes Bay has East Antarctica’s warmest recorded intrusions of modified Circumpolar Deep Water (mCDW) and that warm mCDW drives basal melt under Vanderford and Underwood ice shelves. Our study also provides the first direct observational evidence for the inflow of meltwater to this region, which increases stratification and hinders DSW formation, and thus AABW production. The Vincennes Bay glaciers, together with the Totten Glacier, drain part of the Aurora Basin, which holds up to 7 m of sea level rise equivalent. Our results highlight the vulnerability of the East Antarctic Ice Sheet to intrusions of mCDW.
Keywords: AABW Antarctic Coastal Circulation Antarctic Margins basal melt mCDW intrusions seal CTD
Programme: 109
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