Climate threshold at the Eocene-Oligocene transition: Antarctic ice sheet influence on ocean circulation

2009 ◽  
Author(s):  
Kenneth G Miller ◽  
James D Wright ◽  
Miriam E Katz ◽  
Bridget S Wade ◽  
James V Browning ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
Antarctic Ice Sheet

The Southern Ocean and its interaction with the Antarctic Ice Sheet

Science ◽  
2020 ◽  
Vol 367 (6484) ◽  
pp. 1326-1330
Author(s):  
David M. Holland ◽  
Keith W. Nicholls ◽  
Aurora Basinski
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Thermal Structure ◽  
Ice Sheet ◽  
Major Influence ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Air Temperatures ◽  
The Antarctic ◽  
Circulation Changes

The Southern Ocean exerts a major influence on the mass balance of the Antarctic Ice Sheet, either indirectly, by its influence on air temperatures and winds, or directly, mostly through its effects on ice shelves. How much melting the ocean causes depends on the temperature of the water, which in turn is controlled by the combination of the thermal structure of the surrounding ocean and local ocean circulation, which in turn is determined largely by winds and bathymetry. As climate warms and atmospheric circulation changes, there will be follow-on changes in the ocean circulation and temperature. These consequences will affect the pace of mass loss of the Antarctic Ice Sheet.

Draining and Filling of an Interconnected Sub-glacial Lake Network in East Antarctica

2021 ◽  
Author(s):  
Anna Hogg ◽  
Noel Gourmelen ◽  
Richard Rigby ◽  
Thomas Slater
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
East Antarctica ◽  
Glacial Lake ◽  
Antarctic Ice Sheet ◽  
Geothermal Heating ◽  
Hydrological System ◽  
Subglacial Lakes ◽  
The Antarctic ◽  
The Impact

<p>The Antarctic Ice sheet is a key component of the Earth system, impacting on global sea level, ocean circulation and atmospheric processes. Meltwater is generated at the ice sheet base primarily by geothermal heating and friction associated with ice flow, and this feeds a vast network of lakes and rivers creating a unique hydrological environment. Subglacial lakes play a fundamental role in the Antarctic ice sheet hydrological system because outbursts from ‘active’ lakes can trigger, (i) change in ice speed, (ii) a burst of freshwater input into the ocean which generates buoyant meltwater plumes, and (iii) evolution of glacial landforms and sub-glacial habitats. Despite the key role that sub-glacial hydrology plays on the ice sheet environment, there are limited observations of repeat sub-glacial lake activity resulting in poor knowledge of the timing and frequency of these events. Even rarer are examples of interconnected lake activity, where the draining of one lake triggers filling of another. Observations of this nature help us better characterise these events and the impact they may have on Antarctica’s hydrological budget, and will advance our knowledge of the physical mechanism responsible for triggering this activity. In this study we analyse 9-years of CryoSat-2 radar altimetry data, to investigate a newly identified sub-glacial network in the Amery basin, East Antarctica. CryoSat-2 data was processed in ‘swath mode’, increasing the density of elevation measurements across the study area. The plane fit method was employed in 500 m by 500 m grid cells, to measure surface elevation change at relatively high spatial resolution. We identified a network of 10 active subglacial lakes in the Amery basin. 7 of these lakes, located below Lambert Glacier, show interconnected hydrological behaviour, with filling and drainage events throughout the study period. We observed ice surface height change of up to 6 meters on multiple lakes, and these observations were validated by independently acquired TanDEM-X DEM differencing. This case study is an important decade long record of hydrological activity beneath the Antarctic Ice Sheet which demonstrates the importance of high resolution swath mode measurements. In the future the Lambert lake network will be used to better understand the filling and draining life cycle of sub-glacial hydrological activity under the Antarctic Ice Sheet.</p><p></p>

scholarly journals The response of Antarctic ice volume, global sea-level and southwest Pacific Ocean circulation to orbital variations during the Pliocene to Early Pleistocene

2021 ◽  
Author(s):  
◽  
Molly O'Rourke Patterson
Keyword(s):  
Pacific Ocean ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Early Pleistocene ◽  
Ocean Drilling Program ◽  
Antarctic Ice Sheet ◽  
Southwest Pacific ◽  
Time Period ◽  
The Antarctic

<p>This thesis investigates orbitally-paced variations in the extent of East Antarctic Ice Sheet (EAIS), and the “downstream” influence of these ice sheet variations on ocean circulation and sea level variability during the Pliocene and Early Pleistocene - a time period characterised by a major global cooling step that culminated in the development of a bipolar glaciated world. Three unique records are examined from (1) the Antarctic margin, (2) the southwest Pacific Ocean, and (3) shallow-marine sedimentary strata exposed in Wangnaui Basin, New Zealand.  The Integrated Ocean Drilling Program (IODP) Site U1361 recovered a continuous sedimentary Early Pliocene to Early Pleistocene (4.3 to 2.0 Ma) record from the lowermost continental rise on the Wilkes Land margin offshore of the EAIS. A facies model and stratigraphic framework were developed that allowed for the identification of glacial advances (massive and laminated mudstones) and retreats (diatom-rich mudstones) across the continental shelf, with evidence for prolonged retreats spanning several glacial to interglacial cycles throughout the Pliocene. These cycles are followed by an extensive Early Pleistocene interval (~2.6 Ma) of diatom-rich mudstone with evidence for reworking by bottom currents, interpreted to be the consequence of downslope density currents associated with increased sea ice production after 2.6 Ma. Frequency analysis on Iceberg Rafted Debris (IBRD) from Site U1361 reveals that under an Early Pliocene warm climate state (4.3 to 3.3 Ma), that ice discharge off the EAIS occurred in response to climate change paced by the 40-kyr cycles of obliquity. Whereas, the colder climate state of Late Pliocene to Early Pleistocene (3.3 to 2.0 Ma) resulted in a transferral of orbital variance to 20-kyr-duration, precession-dominated variability in IBRD preceding the development of a more stable marine-based margin of the EAIS at ~2.6 Ma, which is hypothesized to reflect the declining influence of oceanic forcing as the high-latitude Southern Ocean cooled thereby increasing the seasonal duration and extent of sea-ice. The precession-paced influence on IBRD and ice volume variability of the EAIS was strongly modulated by 100-kyr-eccentricity, which is expressed lithologically in cycles of two alternating lithofacies 1) diatom-rich mudstones and 2) massive and laminted mudstones in the Site U1361 record.  A compilation of benthic stable isotope records from Ocean Drilling Program (ODP) Site 1123 in the southwest Pacific Ocean was also developed. The δ18O record identified a 40-kyr obliquity pacing, consistent with other benthic δ18O records globally for this time period, thus allowing for an orbitally-tuned timescale to be developed for this site. Long-term trends in both the δ18O and δ13C records at ODP Site 1123 coincide with major developments of the Antarctic Ice Sheet and Northern Hemisphere glaciation at 3.33 Ma and ~2.6 Ma respectively. A gradual reduction in the deep water δ13C gradient between the southwest Pacific (ODP Site 1123) and equatorial Pacific (ODP Site 849) between 3.33 and 2.6 Ma coincides with expansion of the Antarctic Ice Sheet, enhanced Antarctic Bottom Water (AABW) production, invigorated atmospheric zonal circulation in the southern hemisphere mid-latitudes, and increased meridional sea surface temperature (SST) gradients in the Pacific Ocean.  Finally, a shallow-marine, continental margin stratigraphic section from the Turakina River Valley in the Wanganui Basin, New Zealand, was used to record local sea-level changes, dominated by orbitally-driven, global glacio-eustasy, during the mid-Pliocene interval (3.2 to 3.0 Ma). This interval was selected as it precedes the build-up of significant Northern Hemisphere Ice Sheet, thus allowing for an independent assessment of the orbtial-scale variability of Antarctic Ice Sheet volume. Grain size based proxy of percent mud was employed to reconstruct paleobathymetric changes, which displayed 100-kyr cycles consistent with ~20 m variations in local water depths during the mid-Pliocene. Combined with IBRD record from Site U1361, this reconstruction suggests that the marine margins of East Antarctica varied at orbital timescale, and provided a significant contribution to global eustatic sea-level variations during the mid Pliocene (consistent with global mean sea-level estimates of up to ~+20 m above present from related studies).</p>

Comparison of peri-Antarctic sub-shelf melt rates in coupled and uncoupled ice-sheet model simulations

2020 ◽  
Author(s):  
Lars Zipf ◽  
Charles Pelletier ◽  
Konstanze Haubner ◽  
Sainan Sun ◽  
Hugues Goosse ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
Optimal Solution ◽  
Ocean Model ◽  
Model Framework ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
First Results ◽  
Framework Conditions ◽  
The Antarctic

&lt;p&gt;Sub-shelf melting is the main driver of the mass loss of the Antarctic ice sheet. Various parametrizations exist to estimate basal melt rates within standalone ice sheet models, but they are not able to capture complex ocean circulation. Therefore, high resolution coupled ice sheet-ocean models are the ultimate approach to simulate observed sub-shelf melt rates on short time scales and thereby improve projections of future Antarctic sea level contribution.&lt;/p&gt;&lt;p&gt;Here, we present first results of a hindcast (last 30 years) of the new circumpolar coupled Southern Ocean &amp;#8211; Antarctic ice sheet configuration, developed within the framework of the PARAMOUR project. The configuration, which captures whole Antarctica, is based on the ocean and sea ice model NEMO3.6-LIM3, providing the ice sheet model with monthly sub-shelf melt rates, and the Antarctic ice sheet model f.ETISh v1.5, providing the updated ice shelf cavity geometry to the ocean model. Different difficulties are tackled for the coupling: The initialisation of the ice sheet model is optimised for the chosen resolution of 8km, which is a tradeoff between capturing the main features for the peri-Antarctic setup and respecting the model purpose as fast ice sheet model. Framework conditions for the coupling, e.g. a constant ice-ocean mask, are tested and implemented. The optimal solution to estimate sub-shelf melt for small ice shelves that are not resolved in the ocean model due to the different resolution of the ice sheet and the ocean model, is investigated.&lt;br&gt;Sub-shelf melt rates of the coupled setup are compared to those modeled by the standalone ocean model and those of the standalone ice sheet model with different sub-shelf melt rate parametrizations (ISMIP6, plume, PICO, PICOP) and the sensitivity of the response of the ice sheet for the different basal melt rate patterns are investigated.&lt;/p&gt;

scholarly journals Ice sheet response to sub-shelf melt rates in coupled and uncoupled peri-Antarctic ice-sheet model simulations

2021 ◽  
Author(s):  
Lars Zipf ◽  
Charles Pelletier ◽  
Konstanze Haubner ◽  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
Ocean Model ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Main Driver ◽  
First Results ◽  
The Impact ◽  
Ice Model

&lt;p&gt;Sub-shelf melting is the main driver of Antarctica's ice sheet mass loss. However, sub-shelf melt rate parameterizations for standalone ice models lack the capability to capture complex ocean circulation within ice shelf cavities. To overcome drawbacks of standalone models and to improve melt parameterizations, high resolution coupling of ice sheet and ocean models are capable of hindcasting past decennia and be compared to observations.&lt;/p&gt;&lt;p&gt;Here, we present first results of a hindcast (1985-2018) of the new circumpolar coupled Southern Ocean &amp;#8211; Antarctic ice sheet configuration, developed within the framework of the PARAMOUR project. The configuration is based on the ocean and sea ice model NEMO3.6-LIM3 and the ice sheet model f.ETISh v1.7. The coupling routine facilitates exchange of monthly sub-shelf melt rates (from ocean to ice model) and evolving ice shelf cavity geometry (from ice to ocean model).&lt;/p&gt;&lt;p&gt;We investigate the impact of the coupling frequency (more precisely, the frequency of updating the ice shelf cavity geometry within the ocean model) on the sub-shelf melt rates and its feedback on the ice dynamics. We further compare the sub-shelf melt rates of the coupled setup to those of the standalone ice sheet model with different sub-shelf melt rate parametrizations (ISMIP6, plume, PICO, PICOP) and investigate the sensitivity of the response of the ice sheet for the different basal melt rate patterns on decadal time scales.&lt;/p&gt;

scholarly journals The response of Antarctic ice volume, global sea-level and southwest Pacific Ocean circulation to orbital variations during the Pliocene to Early Pleistocene

2021 ◽  
Author(s):  
◽  
Molly O'Rourke Patterson
Keyword(s):  
Pacific Ocean ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Early Pleistocene ◽  
Ocean Drilling Program ◽  
Antarctic Ice Sheet ◽  
Southwest Pacific ◽  
Time Period ◽  
The Antarctic

<p>This thesis investigates orbitally-paced variations in the extent of East Antarctic Ice Sheet (EAIS), and the “downstream” influence of these ice sheet variations on ocean circulation and sea level variability during the Pliocene and Early Pleistocene - a time period characterised by a major global cooling step that culminated in the development of a bipolar glaciated world. Three unique records are examined from (1) the Antarctic margin, (2) the southwest Pacific Ocean, and (3) shallow-marine sedimentary strata exposed in Wangnaui Basin, New Zealand.  The Integrated Ocean Drilling Program (IODP) Site U1361 recovered a continuous sedimentary Early Pliocene to Early Pleistocene (4.3 to 2.0 Ma) record from the lowermost continental rise on the Wilkes Land margin offshore of the EAIS. A facies model and stratigraphic framework were developed that allowed for the identification of glacial advances (massive and laminated mudstones) and retreats (diatom-rich mudstones) across the continental shelf, with evidence for prolonged retreats spanning several glacial to interglacial cycles throughout the Pliocene. These cycles are followed by an extensive Early Pleistocene interval (~2.6 Ma) of diatom-rich mudstone with evidence for reworking by bottom currents, interpreted to be the consequence of downslope density currents associated with increased sea ice production after 2.6 Ma. Frequency analysis on Iceberg Rafted Debris (IBRD) from Site U1361 reveals that under an Early Pliocene warm climate state (4.3 to 3.3 Ma), that ice discharge off the EAIS occurred in response to climate change paced by the 40-kyr cycles of obliquity. Whereas, the colder climate state of Late Pliocene to Early Pleistocene (3.3 to 2.0 Ma) resulted in a transferral of orbital variance to 20-kyr-duration, precession-dominated variability in IBRD preceding the development of a more stable marine-based margin of the EAIS at ~2.6 Ma, which is hypothesized to reflect the declining influence of oceanic forcing as the high-latitude Southern Ocean cooled thereby increasing the seasonal duration and extent of sea-ice. The precession-paced influence on IBRD and ice volume variability of the EAIS was strongly modulated by 100-kyr-eccentricity, which is expressed lithologically in cycles of two alternating lithofacies 1) diatom-rich mudstones and 2) massive and laminted mudstones in the Site U1361 record.  A compilation of benthic stable isotope records from Ocean Drilling Program (ODP) Site 1123 in the southwest Pacific Ocean was also developed. The δ18O record identified a 40-kyr obliquity pacing, consistent with other benthic δ18O records globally for this time period, thus allowing for an orbitally-tuned timescale to be developed for this site. Long-term trends in both the δ18O and δ13C records at ODP Site 1123 coincide with major developments of the Antarctic Ice Sheet and Northern Hemisphere glaciation at 3.33 Ma and ~2.6 Ma respectively. A gradual reduction in the deep water δ13C gradient between the southwest Pacific (ODP Site 1123) and equatorial Pacific (ODP Site 849) between 3.33 and 2.6 Ma coincides with expansion of the Antarctic Ice Sheet, enhanced Antarctic Bottom Water (AABW) production, invigorated atmospheric zonal circulation in the southern hemisphere mid-latitudes, and increased meridional sea surface temperature (SST) gradients in the Pacific Ocean.  Finally, a shallow-marine, continental margin stratigraphic section from the Turakina River Valley in the Wanganui Basin, New Zealand, was used to record local sea-level changes, dominated by orbitally-driven, global glacio-eustasy, during the mid-Pliocene interval (3.2 to 3.0 Ma). This interval was selected as it precedes the build-up of significant Northern Hemisphere Ice Sheet, thus allowing for an independent assessment of the orbtial-scale variability of Antarctic Ice Sheet volume. Grain size based proxy of percent mud was employed to reconstruct paleobathymetric changes, which displayed 100-kyr cycles consistent with ~20 m variations in local water depths during the mid-Pliocene. Combined with IBRD record from Site U1361, this reconstruction suggests that the marine margins of East Antarctica varied at orbital timescale, and provided a significant contribution to global eustatic sea-level variations during the mid Pliocene (consistent with global mean sea-level estimates of up to ~+20 m above present from related studies).</p>

scholarly journals Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics

2016 ◽  
Vol 10 (5) ◽  
pp. 2317-2328 ◽  
Author(s):  
Steven J. Phipps ◽  
Christopher J. Fogwill ◽  
Christian S. M. Turney
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Climate Model ◽  
Ice Sheet ◽  
Weddell Sea ◽  
Ocean Dynamics ◽  
Antarctic Ice Sheet ◽  
West Antarctic ◽  
Modelling Studies ◽  
East Antarctic Ice Sheet

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water (AABW) formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 °C at depth. This warming is accompanied by a Southern Ocean-wide “domino effect”, whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

Draining and Filling of an Interconnected Sub-glacial Lake Network in East Antarctica

2020 ◽  
Author(s):  
Anna Hogg ◽  
Noel Gourmelen ◽  
Richard Rigby ◽  
Thomas Slater
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
East Antarctica ◽  
Glacial Lake ◽  
Antarctic Ice Sheet ◽  
Geothermal Heating ◽  
Hydrological System ◽  
Subglacial Lakes ◽  
The Antarctic ◽  
The Impact

&lt;p&gt;The Antarctic Ice sheet is a key component of the Earth system, impacting on global sea level, ocean circulation and atmospheric processes. Meltwater is generated at the ice sheet base primarily by geothermal heating and friction associated with ice flow, and this feeds a vast network of lakes and rivers creating a unique hydrological environment. Subglacial lakes play a fundamental role in the Antarctic ice sheet hydrological system because outbursts from &amp;#8216;active&amp;#8217; lakes can trigger, (i) change in ice speed, (ii) a burst of freshwater input into the ocean which generates buoyant meltwater plumes, and (iii) evolution of glacial landforms and sub-glacial habitats. Despite the key role that sub-glacial hydrology plays on the ice sheet environment, there are limited observations of repeat sub-glacial lake activity resulting in poor knowledge of the timing and frequency of these events. Even rarer are examples of interconnected lake activity, where the draining of one lake triggers filling of another. Observations of this nature help us better characterise these events and the impact they may have on Antarctica&amp;#8217;s hydrological budget, and will advance our knowledge of the physical mechanism responsible for triggering this activity. In this study we analyse 9-years of CryoSat-2 radar altimetry data, to investigate a newly identified sub-glacial network in the Amery basin, East Antarctica. CryoSat-2 data was processed in &amp;#8216;swath mode&amp;#8217;, increasing the density of elevation measurements across the study area. The plane fit method was employed in 500 m by 500 m grid cells, to measure surface elevation change at relatively high spatial resolution. We identified a network of 10 active subglacial lakes in the Amery basin. 7 of these lakes, located below Lambert Glacier, show interconnected hydrological behaviour, with filling and drainage events throughout the study period. We observed ice surface height change of up to 6 meters on multiple lakes, and these observations were validated by independently acquired TanDEM-X DEM differencing. This case study is an important decade long record of hydrological activity beneath the Antarctic Ice Sheet which demonstrates the importance of high resolution swath mode measurements. In the future the Lambert lake network will be used to better understand the filling and draining life cycle of sub-glacial hydrological activity under the Antarctic Ice Sheet.&lt;/p&gt;

IODP Exp. 374 provides clues into the Antarctic Ice Sheet contribution to sea level changes

2021 ◽  
Author(s):  
Laura De Santis ◽  
Denise Kulhanek ◽  
Robert McKay
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ross Sea ◽  
Ice Sheet ◽  
Outer Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
Global Sea Level ◽  
The Antarctic

&lt;p&gt;The five sites drilled during International Ocean Discovery Program (IODP) Expedition 374 recovered the distal geological component of a Neogene latitudinal and depth transect across the Ross Sea continental shelf, slope and rise, that can be combined with previous records of ANDRILL and the Deep Sea Drilling Project Leg 28. This transect provides clues into the ocean and atmospheric forcings on marine ice sheet instabilities and provides new direct constraints for reconstructing the Antarctic Ice Sheet contribution to global sea level change. Site U1521 recovered a middle Miocene record that allows identification of the different processes that lead to the expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. This site also recovered a semi-continuous, expanded, high-resolution record of the Miocene Climatic Optimum in an ice-proximal location. Site U1522 recovered a Pleistocene to upper Miocene sequence from the outer shelf, dating the step-wise continental shelf&amp;#8211;wide expansion and coalescing of marine-based ice streams from West Antarctica. Thin diatom-rich mudstone and diatomite beds were recovered in some intervals that provide snapshot records of a deglaciated outer shelf environment in the late Miocene. Site U1523 targeted a Miocene to Pleistocene sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time. Changes in ASC vigor is a key control on regulating heat flux onto the continental shelf, making the ASC a key control on ice sheet mass balance. Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon. The upper ~50 m at Site U1525 belong to a large trough-mouth fan deposited to the west of the site. The lower 100 m at Site U1525 and the entire 400 m succession of sediment at Site U1524 recovered near-continuous records of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. Analyses of Exp. 374 sediments is ongoing, but following initial shipboard characterization, the intial results of sample analysis, the correlation between downhole synthetic logs and the associated seismic sections provide insight into the ages and the processes of erosion and deposition of glacial and marine strata. Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming.&amp;#160;&lt;/p&gt;

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