Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya

2013 ◽  
Vol 6 (3) ◽  
pp. 235-240 ◽  
Author(s):  
Kay I. Ohshima ◽  
Yasushi Fukamachi ◽  
Guy D. Williams ◽  
Sohey Nihashi ◽  
Fabien Roquet ◽  
...  
Keyword(s):  
Sea Ice ◽  
Bottom Water ◽  
Ice Formation ◽  
Antarctic Bottom Water ◽  
Water Production

scholarly journals A Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley, East Antarctica

2014 ◽  
Vol 44 (11) ◽  
pp. 2921-2937 ◽  
Author(s):  
Yoshihiro Nakayama ◽  
Kay I. Ohshima ◽  
Yoshimasa Matsumura ◽  
Yasushi Fukamachi ◽  
Hiroyasu Hasumi
Keyword(s):  
Sea Ice ◽  
Continental Slope ◽  
Bottom Water ◽  
Heat Budget ◽  
East Antarctica ◽  
Salt Flux ◽  
Ice Formation ◽  
Minor Importance ◽  
Antarctic Bottom Water ◽  
Dense Water

Abstract At several locations around Antarctica, dense water is formed as a result of intense sea ice formation. When this dense water becomes sufficiently denser than the surrounding water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense water. Descending pathways of dense water are largely determined by the topography; most dense water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the most important factor in the formation of AABW off Cape Darnley, and the existence of depressions is of only minor importance for the flux of CDBW. The mechanism responsible for the periodic downslope flow of dense water is further analyzed using an idealized model setup. The period of dense water outflow is regulated primarily by the topographic beta effect.

Recent recovery of Antarctic Bottom Water formation in the Ross Sea driven by climate anomalies

2021 ◽  
Author(s):  
Alessandro Silvano ◽  
Annie Foppert ◽  
Steve Rintoul ◽  
Paul Holland ◽  
Takeshi Tamura ◽  
...  
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Bottom Water ◽  
Ross Sea ◽  
Ice Sheet ◽  
Ice Formation ◽  
Depth Range ◽  
Antarctic Bottom Water ◽  
Climate Anomalies ◽  
The Antarctic

<div> <div> <div> <p>Antarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation, ventilates the abyssal ocean and sequesters heat and carbon on multidecadal to millennial timescales. AABW originates on the Antarctic continental shelf, where strong winter cooling and brine released during sea ice formation produce Dense Shelf Water, which sinks to the deep ocean. The salinity, density and volume of AABW have decreased over the last 50 years, with the most marked changes observed in the Ross Sea. These changes have been attributed to increased melting of the Antarctic Ice Sheet. Here we use in situ observations to document a recovery in the salinity, density and thickness (that is, depth range) of AABW formed in the Ross Sea, with properties in 2018–2019 similar to those observed in the 1990s. The recovery was caused by increased sea ice formation on the continental shelf. Increased sea ice formation was triggered by anomalous wind forcing associated with the unusual combination of positive Southern Annular Mode and extreme El Niño conditions between 2015 and 2018. Our study highlights the sensitivity of AABW formation to remote forcing and shows that climate anomalies can drive episodic increases in local sea ice formation that counter the tendency for increased ice-sheet melt to reduce AABW formation.</p> </div> </div> </div>

Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene

2001 ◽  
Vol 179 (1-2) ◽  
pp. 1-8 ◽  
Author(s):  
Peter T. Harris ◽  
Giuliano Brancolini ◽  
Leanne Armand ◽  
Martina Busetti ◽  
Robin J. Beaman ◽  
...  
Keyword(s):  
Steady State ◽  
Continental Shelf ◽  
Bottom Water ◽  
Antarctic Bottom Water ◽  
Water Production ◽  
The Holocene

scholarly journals On deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

Ocean Science ◽  
2017 ◽  
Vol 13 (6) ◽  
pp. 851-872 ◽  
Author(s):  
Wilton Aguiar ◽  
Mauricio M. Mata ◽  
Rodrigo Kerr
Keyword(s):  
Sea Ice ◽  
Bottom Water ◽  
Deep Convection ◽  
Open Ocean ◽  
Weddell Sea ◽  
Ocean Dynamics ◽  
Antarctic Bottom Water ◽  
Ocean Reanalysis ◽  
Reanalysis Product ◽  
Warm Deep Water

Abstract. Open ocean deep convection is a common source of error in the representation of Antarctic Bottom Water (AABW) formation in ocean general circulation models. Although those events are well described in non-assimilatory ocean simulations, the recent appearance of a massive open ocean polynya in the Estimating the Circulation and Climate of the Ocean Phase II reanalysis product (ECCO2) raises questions on which mechanisms are responsible for those spurious events and whether they are also present in other state-of-the-art assimilatory reanalysis products. To investigate this issue, we evaluate how three recently released high-resolution ocean reanalysis products form AABW in their simulations. We found that two of the products create AABW by open ocean deep convection events in the Weddell Sea that are triggered by the interaction of sea ice with the Warm Deep Water, which shows that the assimilation of sea ice is not enough to avoid the appearance of open ocean polynyas. The third reanalysis, My Ocean University Reading UR025.4, creates AABW using a rather dynamically accurate mechanism. The UR025.4 product depicts both continental shelf convection and the export of Dense Shelf Water to the open ocean. Although the accuracy of the AABW formation in this reanalysis product represents an advancement in the representation of the Southern Ocean dynamics, the differences between the real and simulated processes suggest that substantial improvements in the ocean reanalysis products are still needed to accurately represent AABW formation.

scholarly journals Antarctic Bottom Water production from the Vincennes Bay Polynya, East Antarctica

2014 ◽  
Vol 41 (10) ◽  
pp. 3528-3534 ◽  
Author(s):  
Yujiro Kitade ◽  
Keishi Shimada ◽  
Takeshi Tamura ◽  
Guy D. Williams ◽  
Shigeru Aoki ◽  
...  
Keyword(s):  
Bottom Water ◽  
East Antarctica ◽  
Antarctic Bottom Water ◽  
Water Production

Bottom water production and its links with the thermohaline circulation

2004 ◽  
Vol 16 (4) ◽  
pp. 427-437 ◽  
Author(s):  
STANLEY S. JACOBS
Keyword(s):  
Temporal Variability ◽  
Bottom Water ◽  
Thermohaline Circulation ◽  
World Ocean ◽  
Antarctic Bottom Water ◽  
Water Production ◽  
Ongoing Work ◽  
Antarctic Continental Shelf ◽  
The World ◽  
The Antarctic

For more than a century it has been known that the abyssal basins of the world ocean are primarily occupied by relatively cold and fresh waters that originate in the Southern Ocean. Their distinguishing characteristics are acquired by exposure of surface and shelf waters to ‘ventilation’ by the polar atmosphere and to the melting and freezing of ice over and near the Antarctic continental shelf. Subsequent mixing with deep water over the continental slope results in ‘Bottom Water’ that forms the southern sinking limb of the global ‘Thermohaline Circulation.’ Over recent decades, oceanographers have wrestled with a variety of bottom water and thermohaline circulation problems, ranging from basic definitions to forcing and formation sites, source components and properties, generation processes and rates, mixing and sinking, pathways and transports. A brief review of these efforts indicates both advances and anomalies in our understanding of Antarctic Bottom Water production and circulation. Examples from ongoing work illustrate increasing interest in the temporal variability of bottom water in relation to climate change.

Antarctic Bottom Water Variability in a Coupled Climate Model

2008 ◽  
Vol 38 (9) ◽  
pp. 1870-1893 ◽  
Author(s):  
Agus Santoso ◽  
Matthew H. England
Keyword(s):  
Sea Ice ◽  
Deep Water ◽  
Bottom Water ◽  
Climate Model ◽  
Weddell Sea ◽  
Antarctic Bottom Water ◽  
Coupled Climate Model ◽  
Atlantic Sector ◽  
Free Region ◽  
Warm Deep Water

Abstract The natural variability of the Weddell Sea variety of Antarctic Bottom Water (AABW) is examined in a long-term integration of a coupled climate model. Examination of passive tracer concentrations suggests that the model AABW is predominantly sourced in the Weddell Sea. The maximum rate of the Atlantic sector Antarctic overturning (ψatl) is shown to effectively represent the outflow of Weddell Sea deep and bottom waters and the compensating inflow of Warm Deep Water (WDW). The variability of ψatl is found to be driven by surface density variability, which is in turn controlled by sea surface salinity (SSS). This suggests that SSS is a better proxy than SST for post-Holocene paleoclimate reconstructions of the AABW overturning rate. Heat–salt budget and composite analyses reveal that during years of high Weddell Sea salinity, there is an increased removal of summertime sea ice by enhanced wind-driven ice drift, resulting in increased solar radiation absorbed into the ocean. The larger ice-free region in summer then leads to enhanced air–sea heat loss, more rapid ice growth, and therefore greater brine rejection during winter. Together with a negative feedback mechanism involving anomalous WDW inflow and sea ice melting, this results in positively correlated θ–S anomalies that in turn drive anomalous convection, impacting AABW variability. Analysis of the propagation of θ–S anomalies is conducted along an isopycnal surface marking the separation boundary between AABW and the overlying Circumpolar Deep Water. Empirical orthogonal function analyses reveal propagation of θ–S anomalies from the Weddell Sea into the Atlantic interior with the dominant modes characterized by fluctuations on interannual to centennial time scales. Although salinity variability is dominated by along-isopycnal propagation, θ variability is dominated by isopycnal heaving, which implies propagation of density anomalies with the speed of baroclinic waves.

Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 138-151 ◽  
Author(s):  
M. O. Jeffries ◽  
K. Morris ◽  
W.F. Weeks ◽  
A. P. Worby
Keyword(s):  
Sea Ice ◽  
Isotopic Composition ◽  
Snow Cover ◽  
Sea Water ◽  
Ice Cores ◽  
Ice Cover ◽  
Snow Accumulation ◽  
Ice Formation ◽  
Frazil Ice ◽  
Core Sets

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

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