scholarly journals Seasonality of sea ice controls interannual variability of summertime Ω<sub>A</sub> at the ice shelf in the Eastern Weddell Sea – an ocean acidification sensitivity study

2015 ◽  
Vol 12 (2) ◽  
pp. 1653-1687 ◽  
Author(s):  
A. Weeber ◽  
S. Swart ◽  
P. M. S. Monteiro
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Primary Production ◽  
Interannual Variability ◽  
Mixed Layer ◽  
Seasonal Cycle ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Saturation State ◽  
Anthropogenic Co2

Abstract. Increasing anthropogenic CO2 is decreasing surface water aragonite saturation state (ΩA), a growing concern for calcifying Euthecosome pteropods and its wider impact on Antarctic ecosystems. However, our understanding of the seasonal cycle and interannual variability of this vulnerable ecosystem remains limited. This study examines surface water ΩA from four consecutive summers in the Eastern Weddell Gyre (EWG) ice shelf region, and investigates the drivers and the role played by the seasonal cycle in the interannual variability of ΩA. Interannual variability in the seasonal phasing and the rate of summer sea ice thaw was found to be the primary factor explaining interannual variability in surface water ΩA. In "optimal" summers when summer sea ice thaw began in late November/early December (2008/2009 and 2010/2011), the summertime increase in ΩA was found to be 1.02, approximately double that from summers when sea ice thaw was delayed to late December (2009/2010 and 2011/2012). We propose that the two critical climate (physical-biogeochemical) sensitivities for ΩA are the timing and the rate of sea ice thaw, which has a direct impact on the mixed layer and the resulting onset and persistence of phytoplankton blooms. The strength of summertime carbonate saturation depends on seasonal changes of sea ice, stratification and primary production. The sensitivity of surface water biogeochemistry in this region to interannual changes in mixed layer – sea ice processes, suggests that future trends in climate and the seasonal cycle of sea ice, combined with rapidly increasing anthropogenic CO2 will likely be a concern for the Antarctic ice shelf ecosystem within the next few decades. If in the future, primary production is reduced and CO2 increased, our results suggest that in the EWG summertime surface water aragonite undersaturation will emerge by the middle of this century.

scholarly journals Ocean acidification state in western Antarctic surface waters: controls and interannual variability

2014 ◽  
Vol 11 (1) ◽  
pp. 57-73 ◽  
Author(s):  
M. Mattsdotter Björk ◽  
A. Fransson ◽  
A. Torstensson ◽  
M. Chierici
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Primary Production ◽  
Interannual Variability ◽  
Ross Sea ◽  
Total Alkalinity ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Saturation State ◽  
Chl A

Abstract. During four austral summers (December to January) from 2006 to 2010, we investigated the surface-water carbonate system and its controls in the western Antarctic Ocean. Measurements of total alkalinity (AT), pH and total inorganic carbon (CT) were investigated in combination with high-frequency measurements on sea-surface temperature (SST), salinity and Chl a. In all parameters we found large interannual variability due to differences in sea-ice concentration, physical processes and primary production. The main result from our observations suggests that primary production was the major control on the calcium carbonate saturation state (Ω) in austral summer for all years. This was mainly reflected in the covariance of pH and Chl a. In the sea-ice-covered parts of the study area, pH and Ω were generally low, coinciding with low Chl a concentrations. The lowest pH in situ and lowest aragonite saturation (ΩAr ~ 1.0) were observed in December 2007 in the coastal Amundsen and Ross seas near marine outflowing glaciers. These low Ω and high pH values were likely influenced by freshwater dilution. Comparing 2007 and 2010, the largest ΩAr difference was found in the eastern Ross Sea, where ΩAr was about 1.2 units lower in 2007 than in 2010. This was mainly explained by differences in Chl a (i.e primary production). In 2010 the surface water along the Ross Sea shelf was the warmest and most saline, indicating upwelling of nutrient and CO2-rich sub-surface water, likely promoting primary production leading to high Ω and pH. Results from multivariate analysis agree with our observations showing that changes in Chl a had the largest influence on the ΩAr variability. The future changes of ΩAr were estimated using reported rates of the oceanic uptake of anthropogenic CO2, combined with our data on total alkalinity, SST and salinity (summer situation). Our study suggests that the Amundsen Sea will become undersaturated with regard to aragonite about 40 yr sooner than predicted by models.

Attenuated carbon sequestration by Weddell Sea dense waters over the 21st century – an assessment with FESOM-REcoM

2021 ◽  
Author(s):  
Cara Nissen ◽  
Ralph Timmermann ◽  
Mario Hoppema ◽  
Judith Hauck
Keyword(s):  
Carbon Sequestration ◽  
Sea Ice ◽  
Continental Shelf ◽  
Bottom Water ◽  
Water Mass ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Deep Waters ◽  
Water Formation ◽  
Water Mass Transformation

&lt;p&gt;Deep and bottom water formation regions have long been recognized to be efficient vectors for carbon transfer to depth, leading to carbon sequestration on time scales of centuries or more. Precursors of Antarctic Bottom Water (AABW) are formed on the Weddell Sea continental shelf as a consequence of buoyancy loss of surface waters at the ice-ocean or atmosphere-ocean interface, which suggests that any change in water mass transformation rates in this area affects global carbon cycling and hence climate. Many of the models previously used to assess AABW formation in present and future climates contained only crude representations of ocean-ice shelf interaction. Numerical simulations often featured spurious deep convection in the open ocean, and changes in carbon sequestration have not yet been assessed at all. Here, we present results from the global model FESOM-REcoM, which was run on a mesh with elevated grid resolution in the Weddell Sea and which includes an explicit representation of sea ice and ice shelves. Forcing this model with ssp585 scenario output from the AWI Climate Model, we assess changes over the 21&lt;sup&gt;st&lt;/sup&gt; century in the formation and northward export of dense waters and the associated carbon fluxes within and out of the Weddell Sea. We find that the northward transport of dense deep waters (&amp;#963;&lt;sub&gt;2&lt;/sub&gt;&gt;37.2 kg m&lt;sup&gt;-3&lt;/sup&gt; below 2000 m) across the SR4 transect, which connects the tip of the Antarctic Peninsula with the eastern Weddell Sea, declines from 4 Sv to 2.9 Sv by the year 2100. Concurrently, despite the simulated continuous increase in surface ocean CO&lt;sub&gt;2&lt;/sub&gt; uptake in the Weddell Sea over the 21&lt;sup&gt;st&lt;/sup&gt; century, the carbon transported northward with dense deep waters declines from 3.5 Pg C yr&lt;sup&gt;-1&lt;/sup&gt; to 2.5 Pg C yr&lt;sup&gt;-1&lt;/sup&gt;, demonstrating the dominant role of dense water formation rates for carbon sequestration. Using the water mass transformation framework, we find that south of SR4, the formation of downwelling dense waters declines from 3.5 Sv in the 1990s to 1.6 Sv in the 2090s, a direct result of the 18% lower sea-ice formation in the area, the increased presence of modified Warm Deep Water on the continental shelf, and 50% higher ice shelf basal melt rates. Given that the reduced formation of downwelling water masses additionally occurs at lighter densities in FESOM-REcoM in the 2090s, this will directly impact the depth at which any additional oceanic carbon uptake is stored, with consequences for long-term carbon sequestration.&lt;/p&gt;

scholarly journals Variability Of Thermohaline Circulation Under An Ice Shelf

1990 ◽  
Vol 14 ◽  
pp. 338
Author(s):  
H.H. Hellmer
Keyword(s):  
Sea Ice ◽  
Boundary Conditions ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Melting Zone ◽  
Weddell Sea ◽  
Shelf Water ◽  
Ice Shelf ◽  
Grounding Line ◽  
Ice Shelf Water

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results. The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics. As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km. In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.

scholarly journals Nitrate supply and uptake in the Atlantic Arctic sea ice zone: seasonal cycle, mechanisms and drivers

2020 ◽  
Vol 378 (2181) ◽  
pp. 20190361 ◽  
Author(s):  
Sian F. Henley ◽  
Marie Porter ◽  
Laura Hobbs ◽  
Judith Braun ◽  
Robin Guillaume-Castel ◽  
...  
Keyword(s):  
Sea Ice ◽  
Primary Production ◽  
Arctic Ocean ◽  
Nutrient Availability ◽  
Seasonal Cycle ◽  
Nitrate Uptake ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Surface Ocean ◽  
Nitrate Supply

Nutrient supply to the surface ocean is a key factor regulating primary production in the Arctic Ocean under current conditions and with ongoing warming and sea ice losses. Here we present seasonal nitrate concentration and hydrographic data from two oceanographic moorings on the northern Barents shelf between autumn 2017 and summer 2018. The eastern mooring was sea ice-covered to varying degrees during autumn, winter and spring, and was characterized by more Arctic-like oceanographic conditions, while the western mooring was ice-free year-round and showed a greater influence of Atlantic water masses. The seasonal cycle in nitrate dynamics was similar under ice-influenced and ice-free conditions, with biological nitrate uptake beginning near-synchronously in early May, but important differences between the moorings were observed. Nitrate supply to the surface ocean preceding and during the period of rapid drawdown was greater at the ice-free more Atlantic-like western mooring, and nitrate drawdown occurred more slowly over a longer period of time. This suggests that with ongoing sea ice losses and Atlantification, the expected shift from more Arctic-like ice-influenced conditions to more Atlantic-like ice-free conditions is likely to increase nutrient availability and the duration of seasonal drawdown in this Arctic shelf region. The extent to which this increased nutrient availability and longer drawdown periods will lead to increases in total nitrate uptake, and support the projected increases in primary production, will depend on changes in upper ocean stratification and their effect on light availability to phytoplankton as changes in climate and the physical environment proceed. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

scholarly journals Ice-Core Evidence For Weddell Sea Ice Extent During The Past 200 Years

1990 ◽  
Vol 14 ◽  
pp. 350
Author(s):  
R. Mulvaney ◽  
A.P. Reid ◽  
D A. Peel
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Antarctic Peninsula ◽  
Seasonal Cycle ◽  
Global Climate ◽  
Ice Core ◽  
Weddell Sea ◽  
Sea Ice Extent ◽  
Storm Activity ◽  
The Core

A continuous, detailed, 200-years record of the anionic species, chloride, nitrate and sulphate, has been measured on an ice core from Dolleman Island (70°35.2′ S, 60°55.5′ W), Antarctic Peninsula. The site lies on the east coast of the Peninsula, and the chemistry of the core is dominated by the changing pattern of sea-ice distribution and storm activity in the Wed dell Sea. Strong annual cycles in chloride and non sea salt sulphate reflect the dominance of the seasonal cycle in sea-ice distribution in the Weddell Sea, observed in time series derived from satellite imagery since the early 1970s. However, in the case of chloride there is also an exceptionally strong interannual variability, which in many parts of the core dominates the seasonal cycle. Secular variations in the sea-ice extent appear to have a strong influence on the climate of the region and may play a major role in determining how long-term climate change in the Antarctic Peninsula relates to global climate change. The paper examines documented evidence for sea-ice extent in the Weddell Sea sector, and evaluates the usefulness of ice-core data for reconstructing this parameter in the earlier period.

The Weddell Sea Expedition 2019

2020 ◽  
Author(s):  
John Shears ◽  
Julian Dowdeswell ◽  
Freddie Ligthelm ◽  
Paul Wachter
Keyword(s):  
Sea Ice ◽  
Autonomous Underwater Vehicles ◽  
Remote Sensing Data ◽  
Open Water ◽  
Weddell Sea ◽  
Scientific Programme ◽  
Ice Shelf ◽  
Remotely Operated Vehicle ◽  
Radar Images ◽  
Ice Conditions

&lt;p&gt;The Weddell Sea Expedition 2019 (WSE) was conceived with dual aims: (i) to undertake a comprehensive international inter-disciplinary programme of science centred in the waters around Larsen C Ice Shelf, western Weddell Sea; and (ii) to search for, survey and image the wreck of Sir Ernest Shackleton&amp;#8217;s Endurance, which sank in the Weddell Sea in 1915.&amp;#160;&lt;/p&gt;&lt;p&gt;The 6-week long expedition, funded by the Flotilla Foundation, required the use of a substantial ice-strengthened vessel given the very difficult sea-ice conditions encountered in the Weddell Sea, and especially in its central and western parts. The South African ship SA Agulhas II was chartered for its Polar Class 5 icebreaking capability and design as a scientific research vessel. The expedition was equipped with state-of-the-art Autonomous Underwater Vehicles (AUVs) and a Remotely Operated Vehicle (ROV) which were capable of deployment to waters more than 3,000 m deep, thus making the Larsen C continental shelf and slope, and the Endurance wreck site, accessible. During the expedition, a suite of passive and active remote-sensing data, including TerraSAR-X radar images delivered in near real-time, was provided to the ice-pilot onboard the SA Agulhas II. These data were instrumental for safe vessel navigation in sea ice and the detection and tracking of icebergs and ice floes of scientific interest.&lt;/p&gt;&lt;p&gt;The scientific programme undertaken by the WSE was very successful and produced many new geological, geophysical, marine biological and oceanographic observations from a part of the Weddell Sea that has been little studied previously, particularly the area east of Larsen C Ice Shelf. The expedition also reached the sinking location of Shackleton&amp;#8217;s Endurance, where the presence of open-water sea ice leads allowed the deployment of an AUV to the ocean floor to try and locate and survey the wreck. Unfortunately, SA Agulhas II later lost communication with the AUV, and deteriorating weather and sea ice conditions meant that the search had to be called off.&lt;/p&gt;

Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation

2020 ◽  
Author(s):  
Frazer Christie ◽  
Toby Benham ◽  
Julian Dowdeswell
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Total Contribution ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
The Antarctic

&lt;p&gt;The Antarctic Peninsula is one of the most rapidly warming regions on Earth. There, the recent destabilization of the Larsen A and B ice shelves has been directly attributed to this warming, in concert with anomalous changes in ocean circulation. Having rapidly accelerated and retreated following the demise of Larsen A and B, the inland glaciers once feeding these ice shelves now form a significant proportion of Antarctica&amp;#8217;s total contribution to global sea-level rise, and have become an exemplar for the fate of the wider Antarctic Ice Sheet under a changing climate. Together with other indicators of glaciological instability observable from satellites, abrupt pre-collapse changes in ice shelf terminus position are believed to have presaged the imminent disintegration of Larsen A and B, which necessitates the need for routine, close observation of this sector in order to accurately forecast the future stability of the Antarctic Peninsula Ice Sheet. To date, however, detailed records of ice terminus position along this region of Antarctica only span the observational period c.1950 to 2008, despite several significant changes to the coastline over the last decade, including the calving of giant iceberg A-68a from Larsen C Ice Shelf in 2017.&lt;/p&gt;&lt;p&gt;Here, we present high-resolution, annual records of ice terminus change along the entire western Weddell Sea Sector, extending southwards from the former Larsen A Ice Shelf on the eastern Antarctic Peninsula to the periphery of Filchner Ice Shelf. Terminus positions were recovered primarily from Sentinel-1a/b, TerraSAR-X and ALOS-PALSAR SAR imagery acquired over the period 2009-2019, and were supplemented with Sentinel-2a/b, Landsat 7 ETM+ and Landsat 8 OLI optical imagery across regions of complex terrain.&lt;/p&gt;&lt;p&gt;Confounding Antarctic Ice Sheet-wide trends of increased glacial recession and mass loss over the long-term satellite era, we detect glaciological advance along 83% of the ice shelves fringing the eastern Antarctic Peninsula between 2009 and 2019. With the exception of SCAR Inlet, where the advance of its terminus position is attributable to long-lasting ice dynamical processes following the disintegration of Larsen B, this phenomenon lies in close agreement with recent observations of unchanged or arrested rates of ice flow and thinning along the coastline. Global climate reanalysis and satellite passive-microwave records reveal that this spatially homogenous advance can be attributed to an enhanced buttressing effect imparted on the eastern Antarctic Peninsula&amp;#8217;s ice shelves, governed primarily by regional-scale increases in the delivery and concentration of sea ice proximal to the coastline.&lt;/p&gt;

scholarly journals The importance of diurnal processes for the Seasonal cycle of Sea-ice microwave brightness temperatures during early Summer in the Weddell Sea, Antarctica

2006 ◽  
Vol 44 ◽  
pp. 297-302 ◽  
Author(s):  
Sascha Willmes ◽  
Jörg Bareiss ◽  
Christian Haas ◽  
Marcel Nicolaus
Keyword(s):  
Sea Ice ◽  
Seasonal Cycle ◽  
Meteorological Data ◽  
Austral Summer ◽  
Early Summer ◽  
Arctic Sea Ice ◽  
Weddell Sea ◽  
Brightness Temperatures ◽  
Antarctic Sea Ice ◽  
Dominant Feature

AbstractOver the perennial Sea ice in the western and central Weddell Sea, Antarctica, the onset of Summer is accompanied by a Significant decrease of Sea-ice brightness temperatures (Tb) as observed by passive-microwave radiometers Such as the Special Sensor Microwave/Imager (SSM/I). The Summer-specific Tb drop is the dominant feature in the seasonal cycle of Tb data and represents a conspicuous difference to most Arctic Sea-ice regions, where the onset of Summer is mostly marked by a rise in Tb. Data from a 5 week drift Station through the western Weddell Sea in the 2004/05 austral Summer, Ice Station POLarstern (IsPOL), helped with identifying the characteristic processes for Antarctic Sea ice. In Situ glaciological and meteorological data, in combination with SSM/I Swath Satellite data, indicate that the cycle of repeated diurnal thawing and refreezing of Snow (‘freeze–thaw cycles’) is the dominant process in the Summer Season, with the absence of complete Snow wetting. The resulting metamorphous Snow with increased grain Size, as well as the formation of ice layers, leads to decreasing emissivity, enhanced volume Scattering and increased backscatter. This causes the Summer Tb drop.

scholarly journals Ice platelets below Weddell Sea landfast sea ice

2015 ◽  
Vol 56 (69) ◽  
pp. 175-190 ◽  
Author(s):  
Mario Hoppmann ◽  
Marcel Nicolaus ◽  
Stephan Paul ◽  
Priska A. Hunkeler ◽  
Günther Heinemann ◽  
...  
Keyword(s):  
Sea Ice ◽  
Volume Fraction ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Platelet Volume ◽  
Local Maxima ◽  
Model Studies ◽  
Warm Surface Water ◽  
Fast Ice ◽  
Landfast Sea Ice

AbstractBasal melt of ice shelves may lead to an accumulation of disc-shaped ice platelets underneath nearby sea ice, to form a sub-ice platelet layer. Here we present the seasonal cycle of sea ice attached to the Ekström Ice Shelf, Antarctica, and the underlying platelet layer in 2012. Ice platelets emerged from the cavity and interacted with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout winter and spring led to an average platelet-layer thickness of 4 m by December 2012, with local maxima of up to 10 m. The additional buoyancy partly prevented surface flooding and snow-ice formation, despite a thick snow cover. Subsequent thinning of the platelet layer from December onwards was associated with an inflow of warm surface water. The combination of model studies with observed fast-ice thickness revealed an average ice-volume fraction in the platelet layer of 0.25 ± 0.1. We found that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice was equivalent to more than one-fifth of the annual basal melt volume under the Ekström Ice Shelf.

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