scholarly journals Sea ice algal biomass and physiology in the Amundsen Sea, Antarctica

Elem Sci Anth ◽  
2014 ◽  
Vol 2 ◽  
Author(s):  
Kevin R. Arrigo ◽  
Zachary W. Brown ◽  
Matthew M. Mills
Keyword(s):  
Sea Ice ◽  
Photosynthetic Apparatus ◽  
Snow Accumulation ◽  
Visible Radiation ◽  
Microalgal Biomass ◽  
Amundsen Sea ◽  
Developed Surface ◽  
Phaeocystis Antarctica ◽  
Important Food Source ◽  
Time Of Year

Abstract Sea ice covers approximately 5% of the ocean surface and is one of the most extensive ecosystems on the planet. The microbial communities that live in sea ice represent an important food source for numerous organisms at a time of year when phytoplankton in the water column are scarce. Here we describe the distributions and physiology of sea ice microalgae in the poorly studied Amundsen Sea sector of the Southern Ocean. Microalgal biomass was relatively high in sea ice in the Amundsen Sea, due primarily to well developed surface communities that would have been replenished with nutrients during seawater flooding of the surface as a result of heavy snow accumulation. Elevated biomass was also occasionally observed in slush, interior, and bottom ice microhabitats throughout the region. Sea ice microalgal photophysiology appeared to be controlled by the availability of both light and nutrients. Surface communities used an active xanthophyll cycle and effective pigment sunscreens to protect themselves from harmful ultraviolet and visible radiation. Acclimation to low light microhabitats in sea ice was facilitated by enhanced pigment content per cell, greater photosynthetic accessory pigments, and increased photosynthetic efficiency. Photoacclimation was especially effective in the bottom ice community, where ready access to nutrients would have allowed ice microalgae to synthesize a more efficient photosynthetic apparatus. Surprisingly, the pigment-detected prymnesiophyte Phaeocystis antarctica was an important component of surface communities (slush and surface ponds) where its acclimation to high light may precondition it to seed phytoplankton blooms after the sea ice melts in spring.

scholarly journals A 2700-year annual timescale and accumulation history for an ice core from Roosevelt Island, West Antarctica

2019 ◽  
Vol 15 (2) ◽  
pp. 751-779 ◽  
Author(s):  
Mai Winstrup ◽  
Paul Vallelonga ◽  
Helle A. Kjær ◽  
Tyler J. Fudge ◽  
James E. Lee ◽  
...  
Keyword(s):  
Sea Ice ◽  
Accumulation Rate ◽  
Ice Core ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
West Antarctica ◽  
Sea Ice Extent ◽  
Amundsen Sea ◽  
The Core ◽  
Accumulation History

Abstract. We present a 2700-year annually resolved chronology and snow accumulation history for the Roosevelt Island Climate Evolution (RICE) ice core, Ross Ice Shelf, West Antarctica. The core adds information on past accumulation changes in an otherwise poorly constrained sector of Antarctica. The timescale was constructed by identifying annual cycles in high-resolution impurity records, and it constitutes the top part of the Roosevelt Island Ice Core Chronology 2017 (RICE17). Validation by volcanic and methane matching to the WD2014 chronology from the WAIS Divide ice core shows that the two timescales are in excellent agreement. In a companion paper, gas matching to WAIS Divide is used to extend the timescale for the deeper part of the core in which annual layers cannot be identified. Based on the annually resolved timescale, we produced a record of past snow accumulation at Roosevelt Island. The accumulation history shows that Roosevelt Island experienced slightly increasing accumulation rates between 700 BCE and 1300 CE, with an average accumulation of 0.25±0.02 m water equivalent (w.e.) per year. Since 1300 CE, trends in the accumulation rate have been consistently negative, with an acceleration in the rate of decline after the mid-17th century. The current accumulation rate at Roosevelt Island is 0.210±0.002 m w.e. yr−1 (average since 1965 CE, ±2σ), and it is rapidly declining with a trend corresponding to 0.8 mm yr−2. The decline observed since the mid-1960s is 8 times faster than the long-term decreasing trend taking place over the previous centuries, with decadal mean accumulation rates consistently being below average. Previous research has shown a strong link between Roosevelt Island accumulation rates and the location and intensity of the Amundsen Sea Low, which has a significant impact on regional sea-ice extent. The decrease in accumulation rates at Roosevelt Island may therefore be explained in terms of a recent strengthening of the ASL and the expansion of sea ice in the eastern Ross Sea. The start of the rapid decrease in RICE accumulation rates observed in 1965 CE may thus mark the onset of significant increases in regional sea-ice extent.

scholarly journals Search for the Little Ice Age in Southern Ocean Sea-Ice Records

1990 ◽  
Vol 14 ◽  
pp. 221-225 ◽  
Author(s):  
Claire L. Parkinson
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Little Ice Age ◽  
Weddell Sea ◽  
Ice Age ◽  
Amundsen Sea ◽  
Ice Edge ◽  
Time Of Year ◽  
Sea Ice Edge ◽  
Eastern Weddell Sea

Records from the expeditions of Cook, Bellingshausen, Wilkes, and Ross in the late 18th and early 19th centuries have been examined for the information they provide on locations of the Southern Ocean sea-ice edge during the period of the late Little Ice Age in much of the Northern Hemisphere. When these locations are compared with satellite-derived ice edge locations in the mid 1970s, there is a suggestion of particularly heavy ice covers in the eastern Weddell Sea in December 1772, in the Amundsen Sea in March 1839, and perhaps, on the basis of an isolated observation, in a portion of the western Weddell Sea in January 1820. However, overall no strong Little Ice Age signal is found for the sea ice of the Southern Ocean. Many of the observations from the four expeditions indicate sea-ice edge locations that lie within the range of ice edge locations at the same time of year in the mid 1970s, and a few of the observations suggest a less extensive ice cover than in the 1970s.

scholarly journals Search for the Little Ice Age in Southern Ocean Sea-Ice Records

1990 ◽  
Vol 14 ◽  
pp. 221-225 ◽  
Author(s):  
Claire L. Parkinson
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Little Ice Age ◽  
Weddell Sea ◽  
Ice Age ◽  
Amundsen Sea ◽  
Ice Edge ◽  
Time Of Year ◽  
Sea Ice Edge ◽  
Eastern Weddell Sea

Records from the expeditions of Cook, Bellingshausen, Wilkes, and Ross in the late 18th and early 19th centuries have been examined for the information they provide on locations of the Southern Ocean sea-ice edge during the period of the late Little Ice Age in much of the Northern Hemisphere. When these locations are compared with satellite-derived ice edge locations in the mid 1970s, there is a suggestion of particularly heavy ice covers in the eastern Weddell Sea in December 1772, in the Amundsen Sea in March 1839, and perhaps, on the basis of an isolated observation, in a portion of the western Weddell Sea in January 1820. However, overall no strong Little Ice Age signal is found for the sea ice of the Southern Ocean. Many of the observations from the four expeditions indicate sea-ice edge locations that lie within the range of ice edge locations at the same time of year in the mid 1970s, and a few of the observations suggest a less extensive ice cover than in the 1970s.

scholarly journals Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation

2021 ◽  
Author(s):  
Quentin Dalaiden ◽  
Hugues Goosse ◽  
Jeanne Rezsohazy ◽  
Elizabeth R. Thomas
Keyword(s):  
Data Assimilation ◽  
Sea Ice ◽  
Ross Sea ◽  
Snow Accumulation ◽  
The West ◽  
Sea Ice Extent ◽  
Amundsen Sea ◽  
The Past ◽  
West Antarctic

Abstract The West Antarctic climate has witnessed large changes during the second half of the 20th century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determination of whether they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and δ 18 O and tree-ring width records situated in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data assimilation method. This ultimately provides a complete spatial reconstruction over the west Antarctic region. Our reconstruction reproduces well the main characteristics of the observed changes over the instrumental period. We show that the observed sea-ice reduction in the Bellingshausen-Amundsen Sea sector over the satellite era is part of a long-term trend, starting at around 1850 CE, while the sea-ice expansion in the Ross Sea sector has only started around 1950 CE. Furthermore, according to our reconstruction, the Amundsen Sea Low pressure (ASL) displays no significant linear trend in its strength or position over 1850--1950 CE but becomes stronger and shifts eastward afterwards. The year-to-year sea-ice variations in the Ross Sea sector are strongly related to the ASL variability over the past two centuries, including the recent trends. By contrast, the link between ASL and sea-ice in the Bellingshausen-Amundsen Sea sector changes with time, being stronger in recent decades than before. Our reconstruction also suggests that the continental response to the variability of the ASL may not be stationary over time, being significantly affected by modification of the mean circulation. Finally, we show that the widespread warming since 1958 CE in West Antarctica is unusual in the context of past 200 years and is explained by both the deeper ASL and the positive phase of the Southern Annular Mode.

scholarly journals Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation 

2021 ◽  
Author(s):  
Quentin Dalaiden ◽  
Hugues Goosse ◽  
Jeanne Rezsohazy ◽  
Elizabeth R. Thomas
Keyword(s):  
Data Assimilation ◽  
Sea Ice ◽  
Ross Sea ◽  
Snow Accumulation ◽  
The West ◽  
Sea Ice Extent ◽  
Amundsen Sea ◽  
The Past ◽  
West Antarctic

<p>Ocean and ice sheet in the West Antarctic sector have witnessed large climate changes during the second half of the 20<sup>th</sup> century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determining if they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and δ<sup>18</sup>O) and tree-ring width sites located in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data assimilation method. This ultimately provides a complete spatial reconstruction over the west Antarctic region. Our reconstruction reproduces well the main characteristics of the observed changes over the instrumental period. We show that the observed sea-ice reduction in the Bellingshausen-Amundsen Sea sector over the satellite era is part of a long-term trend, starting at around 1850 CE, while the sea-ice expansion in the Ross Sea sector has only started around 1950 CE. Furthermore, according to our reconstruction, the Amundsen Sea Low pressure (ASL) displays no significant linear trend in its strength or position over 1850-1950 CE but becomes stronger and shifts eastward afterwards. The year-to-year sea-ice variations in the Ross Sea sector are strongly related to the ASL variability over the past two centuries, including the recent trends. By contrast, the link between ASL and sea ice the Bellingshausen-Amundsen Sea sector changes with time, being stronger in recent decades than before, Our reconstruction also suggests that the continental response to the variability of the ASL may not be stationary over time, being significantly affected by modification of the mean circulation. Finally, we show that the widespread warming since 1958 CE in West Antarctica is unusual in the context of past 200 years and is explained by both the deeper ASL and the positive phase of the Southern Annular Mode.</p>

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.

scholarly journals The Amundsen Sea Low: Variability, Change, and Impact on Antarctic Climate

2016 ◽  
Vol 97 (1) ◽  
pp. 111-121 ◽  
Author(s):  
M. N. Raphael ◽  
G. J. Marshall ◽  
J. Turner ◽  
R. L. Fogt ◽  
D. Schneider ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Ross Sea ◽  
Ice Core ◽  
Meridional Wind ◽  
West Antarctica ◽  
Sea Ice Extent ◽  
Amundsen Sea ◽  
West Antarctic ◽  
Climate Model Simulations

Abstract The Amundsen Sea low (ASL) is a climatological low pressure center that exerts considerable influence on the climate of West Antarctica. Its potential to explain important recent changes in Antarctic climate, for example, in temperature and sea ice extent, means that it has become the focus of an increasing number of studies. Here, the authors summarize the current understanding of the ASL, using reanalysis datasets to analyze recent variability and trends, as well as ice-core chemistry and climate model projections, to examine past and future changes in the ASL, respectively. The ASL has deepened in recent decades, affecting the climate through its influence on the regional meridional wind field, which controls the advection of moisture and heat into the continent. Deepening of the ASL in spring is consistent with observed West Antarctic warming and greater sea ice extent in the Ross Sea. Climate model simulations for recent decades indicate that this deepening is mediated by tropical variability while climate model projections through the twenty-first century suggest that the ASL will deepen in some seasons in response to greenhouse gas concentration increases.

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.

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