Interannual variability in primary productivity driven by sea-ice phenology in the Amundsen Sea polynyas, not ice shelves melting.

2021 ◽  
Author(s):  
Guillaume Liniger ◽  
Sebastien Moreau ◽  
Delphine Lannuzel ◽  
Fernando Paolo ◽  
Peter Strutton
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Primary Productivity ◽  
Net Primary Productivity ◽  
Light Availability ◽  
Southern Annular Mode ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Ice Coverage

<p>Ice shelves have been melting, thinning and retreating along the coast of West Antarctica for the past four decades, most notably in the Amundsen Sea sector. This area hosts two highly productive coastal polynyas, the Pine Island polynya and the Amundsen Sea polynya, whose opening triggers two of the largest phytoplankton blooms in the Southern Ocean. Previous work in the area suggests that ice shelf melting and thinning increases the iron content of coastal seawater, which could potentially boost ocean primary productivity locally. In this work, we use historical (1992-2017) remote sensing observations of net primary productivity, sea-ice concentration and rate of ice shelves melting to investigate the strength of this connection for these two large polynyas. We used the Abbot, Cosgrove, Pine Island, Thwaites, Dotson and Getz ice shelves for our analyses. Our initial results suggest no significant trends in net primary productivity though time but a large interannual variability for both polynyas. The basal melt rate and ice thinning seem to not be the main drivers of this interannual variability in these polynyas, but sea-ice coverage variability does seem to play a strong role, potentially allowing increased light availability and stratification. Further investigations of circumpolar deep water inputs and climate modes related to ice shelves melting such as El Niño or the southern annular mode are needed to clarify our findings. Our preliminary study points the complexity of ice-ocean systems, where several co-occurring processes influence coastal primary productivity, with consequences for carbon cycling and the climate system.</p>

scholarly journals Modeling Ocean–Cryosphere Interactions off Adélie and George V Land, East Antarctica

2017 ◽  
Vol 30 (1) ◽  
pp. 163-188 ◽  
Author(s):  
Kazuya Kusahara ◽  
Hiroyasu Hasumi ◽  
Alexander D. Fraser ◽  
Shigeru Aoki ◽  
Keishi Shimada ◽  
...  
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Ocean Circulation ◽  
Pressure System ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Coastal Polynya ◽  
Dominant Feature ◽  
Ice Production ◽  
Basal Melting

Ocean–cryosphere interactions along the Adélie and George V Land (AGVL) coast are investigated using a coupled ocean–sea ice–ice shelf model. The dominant feature of the Mertz Glacier Tongue (MGT), located at approximately 145°E, was a highly productive winter coastal polynya system, until its calving in February 2010 dramatically changed the regional “icescape.” This study examines the annual mean, seasonal, and interannual variabilities of sea ice production; basal melting of the MGT; ice shelves, large icebergs, and fast ice; Dense Shelf Water (DSW) export; and bottom water properties on the continental slope and rise, and assesses the impacts of the calving event. The interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature, which are linked to activity of the Amundsen Sea low pressure system. This is the main driver of the interannual variability of DSW exported from the AGVL region. The calving event led to a decrease in sea ice production that resulted in a decrease in the density of DSW export. Subsequently, there is extensive freshening downstream over the continental shelf and slope regions. In addition, it is found that the calving event causes a significant decrease in the mean melt rate of the MGT, resulting from a decrease in ocean heat flux into the cavity due to ocean circulation changes.

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.

scholarly journals Simulating or prescribing the influence of tides on the Amundsen Sea ice shelves

2019 ◽  
Vol 133 ◽  
pp. 44-55 ◽  
Author(s):  
Nicolas C. Jourdain ◽  
Jean-Marc Molines ◽  
Julien Le Sommer ◽  
Pierre Mathiot ◽  
Jérôme Chanut ◽  
...  
Keyword(s):  
Sea Ice ◽  
Amundsen Sea ◽  
Ice Shelves

scholarly journals Meteorological Drivers and Large-Scale Climate Forcing of West Antarctic Surface Melt

2019 ◽  
Vol 32 (3) ◽  
pp. 665-684 ◽  
Author(s):  
Ryan C. Scott ◽  
Julien P. Nicolas ◽  
David H. Bromwich ◽  
Joel R. Norris ◽  
Dan Lubin
Keyword(s):  
Sea Ice ◽  
Ice Sheet ◽  
Climate Forcing ◽  
West Antarctica ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
West Antarctic ◽  
Ice Concentration ◽  
Surface Melt ◽  
Marine Air

Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multidecadal reanalysis and satellite datasets. Physical drivers of ice melt are diagnosed by comparing satellite-observed melt patterns to anomalies of reanalysis near-surface air temperature, winds, and satellite-derived cloud cover, radiative fluxes, and sea ice concentration based on an Antarctic summer synoptic climatology spanning 1979–2017. Summer warming in West Antarctica is favored by Amundsen Sea (AS) blocking activity and a negative phase of the southern annular mode (SAM), which both correlate with El Niño conditions in the tropical Pacific Ocean. Extensive melt events on the Ross–Amundsen sector of the West Antarctic Ice Sheet (WAIS) are linked to persistent, intense AS blocking anticyclones, which force intrusions of marine air over the ice sheet. Surface melting is primarily driven by enhanced downwelling longwave radiation from clouds and a warm, moist atmosphere and by turbulent mixing of sensible heat to the surface by föhn winds. Since the late 1990s, concurrent with ocean-driven WAIS mass loss, summer surface melt occurrence has increased from the Amundsen Sea Embayment to the eastern Ross Ice Shelf. We link this change to increasing anticyclonic advection of marine air into West Antarctica, amplified by increasing air–sea fluxes associated with declining sea ice concentration in the coastal Ross–Amundsen Seas.

scholarly journals Evolution of the Amundsen Sea Polynya, Antarctica, 2016–2021

2021 ◽  
Author(s):  
Grant J. Macdonald ◽  
Stephen F. Ackley ◽  
Alberto M. Mestas-Nuñez
Keyword(s):  
Sea Ice ◽  
Reanalysis Data ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Annual Variations ◽  
Ice Concentration ◽  
Ice Conditions ◽  
Sar Imagery ◽  
Key Sites ◽  
Ice Production

Abstract. Polynyas are key sites of ice production during the winter and are important sites of biological activity and carbon sequestration during the summer. The Amundsen Sea Polynya (ASP) is the fourth largest Antarctic polynya, has recorded the highest primary productivity and lies in an embayment of key oceanographic significance. However, knowledge of its dynamics, and of sub-annual variations in its area and ice production, is limited. In this study we primarily utilize Sentinel-1 SAR imagery, sea ice concentration products and climate reanalysis data, along with bathymetric data, to analyze the ASP over the period November 2016–March 2021. Specifically, we analyze (i) qualitative changes in the ASP's characteristics and dynamics, and quantitative changes in (ii) summer polynya area, (iii) winter polynya area and ice production. From our analysis of SAR imagery we find that ice produced by the ASP becomes stuck in the vicinity of the polynya and sometimes flows back into the polynya, contributing to its closure and limiting further ice production. The polynya forms westward off a persistent chain of grounded icebergs that are located at the site of a bathymetric high. Grounded icebergs also influence the outflow of ice and facilitate the formation of a 'secondary polynya' at times. Additionally, unlike some polynyas, ice produced by the polynya flows westward after formation, along the coast and into the neighboring sea sector. During the summer and early winter, broader regional sea ice conditions can play an important role in the polynya. The polynya opens in all summers, but record-low sea ice conditions in 2016/17 cause it to become part of the open ocean. During the winter, an average of 78 % of ice production occurs in April–May and September–October, but large polynya events often associated with high winds can cause ice production throughout the winter. While passive microwave data or daily sea ice concentration products remain key for analyzing variations in polynya area and ice production, we find that the ability to directly observe and qualitatively analyze the polynya at a high temporal and spatial resolution with Sentinel-1 imagery provides important insights about the behavior of the polynya that are not possible with those datasets.

scholarly journals Tropical Pacific SST Drivers of Recent Antarctic Sea Ice Trends

2016 ◽  
Vol 29 (24) ◽  
pp. 8931-8948 ◽  
Author(s):  
Ariaan Purich ◽  
Matthew H. England ◽  
Wenju Cai ◽  
Yoshimitsu Chikamoto ◽  
Axel Timmermann ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Climate Model ◽  
Ross Sea ◽  
Surface Wind ◽  
Tropical Pacific ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Model Simulations ◽  
Antarctic Sea Ice

Abstract A strengthening of the Amundsen Sea low from 1979 to 2013 has been shown to largely explain the observed increase in Antarctic sea ice concentration in the eastern Ross Sea and decrease in the Bellingshausen Sea. Here it is shown that while these changes are not generally seen in freely running coupled climate model simulations, they are reproduced in simulations of two independent coupled climate models: one constrained by observed sea surface temperature anomalies in the tropical Pacific and the other by observed surface wind stress in the tropics. This analysis confirms previous results and strengthens the conclusion that the phase change in the interdecadal Pacific oscillation from positive to negative over 1979–2013 contributed to the observed strengthening of the Amundsen Sea low and the associated pattern of Antarctic sea ice change during this period. New support for this conclusion is provided by simulated trends in spatial patterns of sea ice concentrations that are similar to those observed. These results highlight the importance of accounting for teleconnections from low to high latitudes in both model simulations and observations of Antarctic sea ice variability and change.

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

2013 ◽  
Vol 10 (5) ◽  
pp. 7879-7916 ◽  
Author(s):  
M. Mattsdotter Björk ◽  
A. Fransson ◽  
M. Chierici
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Interannual Variability ◽  
Chlorophyll A ◽  
Total Alkalinity ◽  
Full Description ◽  
Carbonate System ◽  
Amundsen Sea ◽  
Water Carbonate

Abstract. Each December during four years from 2006 to 2010, the surface water carbonate system was measured and investigated in the Amundsen Sea and Ross Sea, western Antarctica as part of the Oden Southern Ocean expeditions (OSO). The I/B Oden started in Punta Arenas in Chile and sailed southwest, passing through different regimes such as, the marginal/seasonal ice zone, fronts, coastal shelves, and polynyas. Discrete surface water was sampled underway for analysis of total alkalinity (AT), total dissolved inorganic carbon (CT) and pH. Two of these parameters were used together with sea-surface temperature (SST), and salinity to obtain a full description of the surface water carbonate system, including pH in situ and calcium carbonate saturation state of aragonite (ΩAr) and calcite (ΩCa). Multivariate analysis was used to investigate interannual variability and the major controls (sea-ice concentration, SST, salinity and chlorophyll a) on the variability in the carbonate system and Ω. This analysis showed that SST and chlorophyll a were the major drivers of the Ω variability in both the Amundsen and Ross seas. In 2007, the sea-ice edge was located further south and the area of the open polynya was relatively small compared to 2010. We found the lowest pH in situ (7.932) and Ω = 1 values in the sea-ice zone and in the coastal Amundsen Sea, nearby marine out flowing glaciers. In 2010, the sea-ice coverage was the largest and the areas of the open polynyas were the largest for the whole period. This year we found the lowest salinity and AT, coinciding with highest chl a. This implies that the highest ΩAr in 2010 was likely an effect of biological CO2 drawdown, which out-competed the dilution of carbonate ion concentration due to large melt water volumes. We predict and discuss future Ω values, using our data and reported rates of oceanic uptake of anthropogenic CO2, suggesting that the Amundsen Sea will become undersaturated with regard to aragonite about 20 yr sooner than predicted by models.

scholarly journals Trends in the polar sea ice coverage under climate change scenario

MAUSAM ◽  
2021 ◽  
Vol 62 (4) ◽  
pp. 609-616
Author(s):  
AMITA PRABHU ◽  
P.N. MAHAJAN ◽  
R.M. KHALADKAR
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Arctic Region ◽  
The Arctic ◽  
Change Scenario ◽  
Polar Regions ◽  
Sea Ice Extent ◽  
Ice Coverage ◽  
Satellite Microwave ◽  
The Antarctic

The development in the satellite microwave technology during the past three decades has offered an opportunity to the scientific community to access the sea ice data over the polar regions, which was otherwise inaccessible for continuous monitoring by any other means. The present study focuses on the trends in the Sea Ice Extent (SIE) over different sectors of the Arctic and the Antarctic regions and the interannual variability in their extremes. In general, the data over the period (1979-2007) reveal marked interannual variability in the sea ice cover with an increasing and the decreasing trend over the Antarctic and the Arctic region respectively. Over the southern hemisphere, only the Bellingshausen and Amundsen Seas sector shows an exceptional decreasing trend. However, in the northern hemisphere, all the sectors show a decreasing trend, with the Kara and Barents Seas sector being the most prominent one. Although, the decreasing trend of the SIE over the Arctic could be attributed to the global warming, an intriguing question still remains as to why the other polar region shows a different behaviour.

scholarly journals Aspects of intraseasonal variability of Antarctic sea ice in austral winter related to ENSO and SAM events

2017 ◽  
Vol 63 (241) ◽  
pp. 838-846 ◽  
Author(s):  
KENJI BABA ◽  
JAMES RENWICK
Keyword(s):  
Sea Ice ◽  
El Nino ◽  
Intraseasonal Variability ◽  
Southern Annular Mode ◽  
Wave Number ◽  
Austral Winter ◽  
Sea Ice Concentration ◽  
Annular Mode ◽  
Antarctic Sea Ice ◽  
Ice Concentration

ABSTRACTWe performed an Empirical Orthogonal Function (EOF) analysis to assess the intraseasonal variability of 5–60 day band-pass filtered Antarctic sea-ice concentration in austral winter using a 20-year daily dataset from 1995 to 2014. Zonal wave number 3 dominated in the Antarctic, especially so across the west Antarctic. Results showed the coexistence of stationary and propagating wave components. A spectral analysis of the first two principal components (PCs) showed a similar structure for periods up to 15 days but generally more power in PC1 at longer periods. Regression analysis upon atmospheric fields using the first two PCs of sea-ice concentration showed a coherent wave number 3 pattern. The spatial phase delay between the sea-ice and mean sea-level pressure patterns suggests that meridional flow and associated temperature advection are important for modulating the sea-ice field. EOF analyses carried out separately for El Niño, La Niña and neutral years, and for Southern Annular Mode positive, negative and neutral periods, suggest that the spatial patterns of wave number 3 shift between subsets. The results also indicate that El Niño-Southern Oscillation and Southern Annular Mode affect stationary wave interactions between sea-ice and atmospheric fields on intraseasonal timescales.

scholarly journals Antarctic Sea Ice Climatology, Variability, and Late Twentieth-Century Change in CCSM4

2012 ◽  
Vol 25 (14) ◽  
pp. 4817-4838 ◽  
Author(s):  
Laura Landrum ◽  
Marika M. Holland ◽  
David P. Schneider ◽  
Elizabeth Hunke
Keyword(s):  
Twentieth Century ◽  
Sea Ice ◽  
Southern Oscillation ◽  
Austral Summer ◽  
Southern Annular Mode ◽  
Cold Bias ◽  
Sea Ice Concentration ◽  
Climate System Model ◽  
Modes Of Variability ◽  
Antarctic Sea Ice

Abstract A preindustrial control run and an ensemble of twentieth-century integrations of the Community Climate System Model, version 4 (CCSM4), are evaluated for Antarctic sea ice climatology, modes of variability, trends, and covariance with related physical variables such as surface temperature and sea level pressure. Compared to observations, the mean ice cover is too extensive in all months. This is in part related to excessively strong westerly winds over ~50°–60°S, which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the Southern Ocean. In spite of these biases in the climatology, the model’s sea ice variability compares well to observations. The leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the Atlantic and Pacific sectors. Both the El Niño–Southern Oscillation and the southern annular mode (SAM) project onto this mode. In twentieth-century integrations, Antarctic sea ice area exhibits significant decreasing annual trends in all six ensemble members from 1950 to 2005, in apparent contrast to observations that suggest a modest ice area increase since 1979. Two ensemble members show insignificant changes when restricted to 1979–2005. The ensemble mean shows a significant increase in the austral summer SAM index over 1960–2005 and 1979–2005 that compares well with the observed SAM trend. However, Antarctic warming and sea ice loss in the model are closely connected to each other and not to the trend in the SAM.

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