New insights into the ice-covered Southern Ocean circulation from multi-altimeter combination.

2021 ◽  
Author(s):  
Matthis Auger ◽  
Jean-Baptiste Sallée ◽  
Pierre Prandi
Keyword(s):  
Southern Ocean ◽  
Sea Level ◽  
Ocean Circulation ◽  
Sea Level Anomaly ◽  
Ice Shelves ◽  
Modes Of Variability ◽  
The Past ◽  
Circulation Patterns ◽  
Polar Ocean ◽  
Global Sea Level

<p>Subtle changes in the Southern Ocean subpolar ocean circulation patterns can lead to major changes in the global overturning circulation, as well as for floating ice-shelves with critical implications for global sea-level. It is therefore crucial to carefully understand Antarctic polar ocean circulation, but the lack of ocean observation has considerably blocked our advance in this field in the past.</p><p>In this study we benefit from a new high-resolution Sea Level Anomaly (SLA) product that has been specifically constructed to document sea-level in the ice-covered Southern Ocean. This product combines up to 3 satellite altimetry missions to map SLA data daily on an equal-area grid, including the ice-covered areas of the ocean from 2013 to 2019.</p><p>Results suggest that we can map ocean features with unprecedented resolution for the region. We characterize the main features of the subpolar Southern Ocean SLA and circulation seasonal cycle, being composed of three main modes of variability, significantly impacting the dynamics of the region. We explore how they are linked with atmospheric and sea-ice forcings. Dynamics at smaller scales are investigated, by identifying the properties of mesoscale variability where possible.</p>

Causes and consequences of Southern Ocean change: the IPCC SROCC assessment

2020 ◽  
Author(s):  
Michael Meredith ◽  
Martin Sommerkorn ◽  
Sandra Cassotta ◽  
Chris Derksen ◽  
Alexey Ekaykin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Sea Level ◽  
Ocean Circulation ◽  
Global Climate ◽  
Ice Sheets ◽  
The Arctic ◽  
Polar Regions ◽  
Ice Shelves

<p>Climate change in the polar regions exerts a profound influence both locally and over all of our planet.  Physical and ecosystem changes influence societies and economies, via factors that include food provision, transport and access to non-renewable resources.  Sea level, global climate and potentially mid-latitude weather are influenced by the changing polar regions, through coupled feedback processes, sea ice changes and the melting of snow and land-based ice sheets and glaciers.</p><p>Reflecting this importance, the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) features a chapter highlighting past, ongoing and future change in the polar regions, the impacts of these changes, and the possible options for response.  The role of the polar oceans, both in determining the changes and impacts in the polar regions and in structuring the global influence, is an important component of this chapter.</p><p>With emphasis on the Southern Ocean and through comparison with the Arctic, this talk will outline key findings from the polar regions chapter of SROCC. It will synthesise the latest information on the rates, patterns and causes of changes in sea ice, ocean circulation and properties. It will assess cryospheric driving of ocean change from ice sheets, ice shelves and glaciers, and the role of the oceans in determining the past and future evolutions of polar land-based ice. The implications of these changes for climate, ecosystems, sea level and the global system will be outlined.</p>

scholarly journals Dynamic response of Antarctic Peninsula Ice Sheet to collapse of Larsen C and George VI ice shelves

2018 ◽  
Author(s):  
Clemens Schannwell ◽  
Stephen Cornford ◽  
David Pollard ◽  
Nicholas Edward Barrand
Keyword(s):  
Dynamic Response ◽  
Sea Level ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Sea Levels ◽  
The Past ◽  
Speed Up ◽  
Global Sea Level

Abstract. Ice shelf break-up and disintegration events over the past several decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause, and in turn suggests that the larger Larsen C and George VI ice shelves may undergo similar collapse in future. However, the extent to which removal of Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low (

scholarly journals Dynamic response of Antarctic Peninsula Ice Sheet to potential collapse of Larsen C and George VI ice shelves

2018 ◽  
Vol 12 (7) ◽  
pp. 2307-2326 ◽  
Author(s):  
Clemens Schannwell ◽  
Stephen Cornford ◽  
David Pollard ◽  
Nicholas E. Barrand
Keyword(s):  
Sea Level ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Sea Levels ◽  
The Past ◽  
Large Size ◽  
Speed Up ◽  
Global Sea Level

Abstract. Ice shelf break-up and disintegration events over the past 5 decades have led to speed-up, thinning, and retreat of upstream tributary glaciers and increases to rates of global sea-level rise. The southward progression of these episodes indicates a climatic cause and in turn suggests that the larger Larsen C and George VI ice shelves may undergo a similar collapse in the future. However, the extent to which removal of the Larsen C and George VI ice shelves will affect upstream tributary glaciers and add to global sea levels is unknown. Here we apply numerical ice-sheet models of varying complexity to show that the centennial sea-level commitment of Larsen C embayment glaciers following immediate shelf collapse is low (<2.5 mm to 2100, <4.2 mm to 2300). Despite its large size, Larsen C does not provide strong buttressing forces to upstream basins and its collapse does not result in large additional discharge from its tributary glaciers in any of our model scenarios. In contrast, the response of inland glaciers to a collapse of the George VI Ice Shelf may add up to 8 mm to global sea levels by 2100 and 22 mm by 2300 due in part to the mechanism of marine ice sheet instability. Our results demonstrate the varying and relative importance to sea level of the large Antarctic Peninsula ice shelves considered to present a risk of collapse.

scholarly journals Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

2020 ◽  
Vol 117 (40) ◽  
pp. 24735-24741 ◽  
Author(s):  
Stef Lhermitte ◽  
Sainan Sun ◽  
Christopher Shuman ◽  
Bert Wouters ◽  
Frank Pattyn ◽  
...  
Keyword(s):  
Sea Level ◽  
Rapid Development ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Shelf ◽  
Damage Development ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Grounding Line ◽  
Global Sea Level

Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.

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.

Supraglacial Streams and Rivers

2019 ◽  
Vol 47 (1) ◽  
pp. 421-452 ◽  
Author(s):  
Lincoln H Pitcher ◽  
Laurence C. Smith
Keyword(s):  
Sea Level ◽  
Transport Processes ◽  
Future Research ◽  
Sea Level Changes ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Shelves ◽  
Streams And Rivers ◽  
Ice Surface ◽  
Global Sea Level

Supraglacial meltwater channels that flow on the surfaces of glaciers, ice sheets, and ice shelves connect ice surface climatology with subglacial processes, ice dynamics, and eustatic sea level changes. Their important role in transferring water and heat across and into ice is currently absent from models of surface mass balance and runoff contributions to global sea level rise. Furthermore, relatively little is known about the genesis, evolution, hydrology, hydraulics, and morphology of supraglacial rivers, and a first synthesis and review of published research on these unusual features is lacking. To that end, we review their ( a) known geographical distribution; ( b) formation, morphology, and sediment transport processes; ( c) hydrology and hydraulics; and ( d) impact on ice sheet surface energy balance, heat exchange, basal conditions, and ice shelf stability. We conclude with a synthesis of key knowledge gaps and provide recommendations for future research. ▪ Supraglacial streams and rivers transfer water and heat on glaciers, connecting climate with subglacial hydrology, ice sliding, and global sea level. ▪ Ice surface melting may expand under a warming climate, darkening the ice surface and further increasing melt.

Sea-level driven acceleration in coastal forest retreat

Geology ◽  
2019 ◽  
Vol 47 (12) ◽  
pp. 1151-1155 ◽  
Author(s):  
Nathalie W. Schieder ◽  
Matthew L. Kirwan
Keyword(s):  
Sea Level ◽  
Atlantic Coast ◽  
The United States ◽  
Ecosystem Change ◽  
Coastal Forest ◽  
The Past ◽  
Dead Trees ◽  
Adult Trees ◽  
Primary Determinant ◽  
Global Sea Level

Abstract Ghost forests, consisting of dead trees adjacent to marshes, are a striking feature of low-lying coastal and estuarine landscapes, and they represent the migration of coastal ecosystems with relative sea-level rise (RSLR). Although ghost forests have been observed along many coastal margins, rates of ecosystem change and their dependence on RSLR remain poorly constrained. Here, we reconstructed forest retreat rates using sediment coring and historical imagery at five sites along the Mid-Atlantic coast of the United States, a hotspot for accelerated RSLR. We found that the elevation of the marsh-forest boundary generally increased with RSLR over the past 2000 yr, and that retreat accelerated concurrently with the late 19th century acceleration in global sea level. Lateral retreat rates increased through time for most sampling intervals over the past 150 yr, and modern lateral retreat rates are 2 to 14 times faster than pre-industrial rates at all sites. Substantial deviations between RSLR and forest response are consistent with previous observations that episodic disturbance facilitates the mortality of adult trees. Nevertheless, our work suggests that RSLR is the primary determinant of coastal forest extent, and that ghost forests represent a direct and prominent visual indicator of climate change.

scholarly journals Can the Subtropical North Atlantic permanent thermocline be observed from space?

2002 ◽  
Vol 82 (5) ◽  
pp. 709-728 ◽  
Author(s):  
Robin Pingree ◽  
Yu-Heng Kuo ◽  
Carlos Garcia-Soto
Keyword(s):  
Sea Level ◽  
Ocean Circulation ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Remotely Sensed ◽  
Ocean Currents ◽  
Maximum Temperature ◽  
Altimeter Data ◽  
Sea Level Anomaly

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for ∼2/3 of the temperature variance or vertical displacement of isotherms at a depth of ∼550 m in the Subtropical North Atlantic Ocean near 32·5°N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for ∼3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as −×650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data time series in the Subtropical North Atlantic at 32·5°N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25°W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

Global Sea Level Trend in the Past Century

Science ◽  
1982 ◽  
Vol 215 (4540) ◽  
pp. 1611-1614 ◽  
Author(s):  
V. GORNITZ ◽  
S. LEBEDEFF ◽  
J. HANSEN
Keyword(s):  
Sea Level ◽  
Past Century ◽  
The Past ◽  
Sea Level Trend ◽  
Global Sea Level

scholarly journals Sea level under climate change: Understanding the links between the past and the future

2021 ◽  
Author(s):  
Keven Roy ◽  
Nicole S. Khan ◽  
Timothy A. Shaw ◽  
Robert E. Kopp ◽  
Benjamin P. Horton
Keyword(s):  
Climate Change ◽  
Sea Level ◽  
Water Volume ◽  
Sea Levels ◽  
Global Average ◽  
Flood Risks ◽  
The Past ◽  
Recent Climate ◽  
Global Sea Level ◽  
Global And Local

Rising global sea level, a consequence of climate change, results from an increase in the world ocean’s water volume and mass. Recent climate warming is responsible for producing the highest rate of global average sea-level rise of the past few millennia, and this rate will accelerate through the 21st century and beyond, exposing low-lying islands and coastal regions to significant flood risks. The flood risks can be compounded or diminished locally because changes in sea level are not uniform. In this review, we briefly discuss ice sheets as drivers of global and local sea levels, and how they could evolve under modern climate change. We underline some of the impacts of sea level change on coastal communities, and emphasize that local sea-level projections can be very different from estimates of the global average.

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