Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica

2020 ◽  
Author(s):  
Anna Wåhlin ◽  
Bastien Queste ◽  
Alastair Graham ◽  
Kelly Hogan ◽  
Lars Boehme ◽  
...  
Keyword(s):  
Water Flow ◽  
Deep Water ◽  
Autonomous Underwater Vehicle ◽  
Warm Water ◽  
Ice Shelf ◽  
Mixing Processes ◽  
Spatial Gradients ◽  
West Antarctic ◽  
Warm Deep Water ◽  
Glacier Ice

<p>The fate of the West Antarctic Ice Sheet is the largest remaining uncertainty in predicting sea-level rise through the next century, and its most vulnerable and rapidly changing outlet is Thwaites Glacier . Because the seabed slope under the glacier is retrograde (downhill inland), ice discharge from Thwaites Glacier is potentially unstable to melting of the underside of its floating ice shelf and grounding line retreat, both of which are enhanced by warm ocean water circulating underneath the ice shelf. Recent observations show surprising spatial variations in melt rates, indicating significant knowledge gaps in our understanding of the processes at the base of the ice shelf. Here we present the first direct observations of ocean temperature, salinity, and oxygen underneath Thwaites ice shelf collected by an autonomous underwater vehicle, a Kongsberg Hugin AUV. These observations show that while the western part of Thwaites has outflow of meltwater-enriched circumpolar deep water found in the main trough leading to Thwaites, the deep water (> 1000 m) underneath the central part of the ice shelf is in connection with Pine Island Bay - a previously unknown westward branch of warm deep water flow. Mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point and large spatial gradients of salinity and temperature indicate that this is a region of active mixing processes. The observations challenge conceptual models of ice-ocean interactions at glacier grounding zones and identify a main buttressing point as a vulnerable region of change currently under attack by warm water inflow from all sides: a scenario that may lead to ungrounding and retreat more quickly than previously expected.</p>

scholarly journals Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

2021 ◽  
Author(s):  
Hee Won Yang ◽  
Tae-Wan Kim ◽  
Pierre Dutrieux ◽  
A. K. Wahlin ◽  
Adrian Jenkins ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Warm Water ◽  
Western Slope ◽  
Eastern Slope ◽  
Ice Shelf ◽  
Significant Control ◽  
West Antarctic ◽  
Warm Deep Water ◽  
Basal Melting

Abstract Recent rapid thinning of West Antarctic ice shelves are believed to be caused by intrusions of warm deep water that induce basal melting and seaward meltwater export. Dotson Ice Shelf has a high basal melt rate due to southward ocean heat transport in the Dotson-Getz Trough. We deployed three bottom-moored instrument arrays along the ice shelf calving front, obtaining continuous records of temperature, salinity, and current velocity throughout 2014 and 2015. Southward deep water velocities were highest along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. Inflow warm water along the eastern slope into the sub-Dotson cavity reached a maximum of 182 MW m− 1 in Summer, 3.5 times larger than the autumn/winter values of 51 MW m− 1. The inflow correlated with the local ocean surface stress curl. At the western slope meltwater outflows were strongest during autumn and weakest in spring, following the warm influx along the eastern slope with a ~ 2–3 months delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to be a significant control on the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.

scholarly journals Pathways and modification of warm water flowing beneath Thwaites Ice Shelf, West Antarctica

2021 ◽  
Vol 7 (15) ◽  
pp. eabd7254
Author(s):  
A. K. Wåhlin ◽  
A. G. C. Graham ◽  
K. A. Hogan ◽  
B. Y. Queste ◽  
L. Boehme ◽  
...  
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Warm Water ◽  
West Antarctica ◽  
Spatial Property ◽  
Ice Shelf ◽  
Large Uncertainty ◽  
West Antarctic Ice Sheet ◽  
The North ◽  
West Antarctic ◽  
Direct Observations

Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat.

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals The role of Pine Island Glacier ice shelf basal channels in deep-water upwelling, polynyas and ocean circulation in Pine Island Bay, Antarctica

2012 ◽  
Vol 53 (60) ◽  
pp. 123-128 ◽  
Author(s):  
Kenneth D. Mankoff ◽  
Stanley S. Jacobs ◽  
Slawek M. Tulaczyk ◽  
Sharon E. Stammerjohn
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Open Water ◽  
Positive Temperature ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Buoyant Plumes ◽  
Surface Circulation ◽  
Glacier Ice ◽  
Fast Ice

AbstractSeveral hundred visible and thermal infrared satellite images of Antarctica’s southeast Amundsen Sea from 1986 to 2011, combined with aerial observations in 2009, show a strong inverse relation between prominent curvilinear surface depressions and the underlying basal morphology of the outer Pine Island Glacier ice shelf. Shipboard measurements near the calving front reveal positive temperature, salinity and current anomalies indicative of melt-laden, deep-water outflows near and above the larger channel termini. These buoyant plumes rise to the surface and are expressed as small polynyas in the sea ice and thermal signatures in the open water. The warm upwellings also trace the cyclonic surface circulation in Pine Island Bay. The satellite coverage suggests changing modes of ocean/ice interactions, dominated by leads along the ice shelf through 1999, fast ice and polynyas from 2000 to 2007, and larger areas of open water since 2008.

scholarly journals Brief communication: A submarine wall protecting the Amundsen Sea intensifies melting of neighboring ice shelves

2019 ◽  
Vol 13 (9) ◽  
pp. 2317-2324 ◽  
Author(s):  
Özgür Gürses ◽  
Vanessa Kolatschek ◽  
Qiang Wang ◽  
Christian Bernd Rodehacke
Keyword(s):  
Ocean Model ◽  
Warm Water ◽  
Ice Shelf ◽  
The West ◽  
Amundsen Sea ◽  
West Antarctic Ice Sheet ◽  
Ice Shelves ◽  
West Antarctic ◽  
Antarctic Continent ◽  
Subsurface Cavities

Abstract. Disintegration of ice shelves in the Amundsen Sea, in front of the West Antarctic Ice Sheet, has the potential to cause sea level rise by inducing an acceleration of ice discharge from upstream grounded ice. Moore et al. (2018) proposed that using a submarine wall to block the penetration of warm water into the subsurface cavities of these ice shelves could reduce this risk. We use a global sea ice–ocean model to show that a wall shielding the Amundsen Sea below 350 m depth successfully suppresses the inflow of warm water and reduces ice shelf melting. However, these warm water masses get redirected towards neighboring ice shelves, which reduces the net effectiveness of the wall. The ice loss is reduced by 10 %, integrated over the entire Antarctic continent.

scholarly journals Sensitivity of Circumpolar Deep Water Transport and Ice Shelf Basal Melt along the West Antarctic Peninsula to Changes in the Winds

2012 ◽  
Vol 25 (14) ◽  
pp. 4799-4816 ◽  
Author(s):  
Michael S. Dinniman ◽  
John M. Klinck ◽  
Eileen E. Hofmann
Keyword(s):  
Continental Shelf ◽  
Antarctic Peninsula ◽  
Deep Water ◽  
Constant Factor ◽  
Ice Shelf ◽  
The West ◽  
Ice Shelves ◽  
Circumpolar Deep Water ◽  
West Antarctic ◽  
West Antarctic Peninsula

Abstract Circumpolar Deep Water (CDW) can be found near the continental shelf break around most of Antarctica. Advection of this relatively warm water (up to 2°C) across the continental shelf to the base of floating ice shelves is thought to be a critical source of heat for basal melting in some locations. A high-resolution (4 km) regional ocean–sea ice–ice shelf model of the west Antarctic Peninsula (WAP) coastal ocean was used to examine the effects of changes in the winds on across-shelf CDW transport and ice shelf basal melt. Increases and decreases in the strength of the wind fields were simulated by scaling the present-day winds by a constant factor. Additional simulations considered effects of increased Antarctic Circumpolar Current (ACC) transport. Increased wind strength and ACC transport increased the amount of CDW transported onto the WAP continental shelf but did not necessarily increase CDW flux underneath the nearby ice shelves. The basal melt underneath some of the deeper ice shelves actually decreased with increased wind strength. Increased mixing over the WAP shelf due to stronger winds removed more heat from the deeper shelf waters than the additional heat gained from increased CDW volume transport. The simulation results suggest that the effect on the WAP ice shelves of the projected strengthening of the polar westerlies is not a simple matter of increased winds causing increased (or decreased) basal melt. A simple budget calculation indicated that iron associated with increased vertical mixing of CDW could significantly affect biological productivity of this region.

scholarly journals Déjà Vu? Ocean Warmth Melted Ancient West Antarctic Ice Shelf

Eos ◽  
2017 ◽  
Author(s):  
Sarah Derouin
Keyword(s):  
Ice Sheet ◽  
Warm Water ◽  
Ice Shelf ◽  
Ice Shelves ◽  
West Antarctic ◽  
Deja Vu ◽  
Seafloor Sediments ◽  
Déjà Vu

Clues in seafloor sediments reveal that relatively warm water beneath western Antarctic ice shelves, a major factor in today's massive ice sheet retreat, also fueled some past ice loss.

scholarly journals Inflow of Warm Circumpolar Deep Water in the Central Amundsen Shelf*

2010 ◽  
Vol 40 (6) ◽  
pp. 1427-1434 ◽  
Author(s):  
A. K. Wåhlin ◽  
X. Yuan ◽  
G. Björk ◽  
C. Nohr
Keyword(s):  
Deep Water ◽  
Water Mass ◽  
Acoustic Doppler Current Profiler ◽  
Intermediate Water ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Circumpolar Deep Water ◽  
Ice Melt ◽  
West Antarctic ◽  
Glacier Ice

Abstract The thinning and acceleration of the West Antarctic Ice Sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf. A hydrographic section including lowered acoustic Doppler current profiler measurements showing such an inflow in the channel leading to the Getz and Dotson Ice Shelves is presented here. The flow rate was 0.3–0.4 Sv (1 Sv ≡ 106 m3 s−1), and the subsurface heat loss was estimated to be 1.2–1.6 TW. Assuming that the inflow persists throughout the year, it corresponds to an ice melt of 110–130 km3 yr−1, which exceeds recent estimates of the net ice glacier ice volume loss in the Amundsen Sea. The results also show a 100–150-m-thick intermediate water mass consisting of Circumpolar Deep Water that has been modified (cooled and freshened) by subsurface melting of ice shelves and/or icebergs. This water mass has not previously been reported in the region, possibly because of the paucity of historical data.

scholarly journals Some Implications of Ekman Layer Dynamics for Cross-Shelf Exchange in the Amundsen Sea

2012 ◽  
Vol 42 (9) ◽  
pp. 1461-1474 ◽  
Author(s):  
A. K. Wåhlin ◽  
R. D. Muench ◽  
L. Arneborg ◽  
G. Björk ◽  
H. K. Ha ◽  
...  
Keyword(s):  
Deep Water ◽  
Bottom Layer ◽  
Shelf Break ◽  
Ekman Transport ◽  
Shelf Area ◽  
Amundsen Sea ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Warm Deep Water ◽  
Slope Currents

Abstract The exchange of warm, salty seawater across the continental shelves off West Antarctica leads to subsurface glacial melting at the interface between the ocean and the West Antarctic Ice Sheet. One mechanism that contributes to the cross-shelf transport is Ekman transport induced by along-slope currents over the slope and shelf break. An investigation of this process is applied to the Amundsen Sea shelfbreak region, using recently acquired and historical field data to guide the analyses. Along-slope currents were observed at transects across the eastern and western reaches of the Amundsen slope. Currents in the east flowed eastward, and currents farther west flowed westward. Under the eastward-flowing currents, hydrographic isolines sloped upward paralleling the seabed. In this layer, declining buoyancy forces rather than friction were bringing the velocity to zero at the seabed. The basin water in the eastern part of the shelf was dominated by water originating from 800–1000-m depth off shelf, suggesting that transport of such water across the shelf frequently occurs. The authors show that arrested Ekman layers mechanism can supply deep water to the shelf break in the eastern section, where it has access to the shelf. Because no unmodified off-shelf water was found on the shelf in the western part, bottom layer Ekman transport does not appear a likely mechanism for delivery of warm deep water to the western shelf area. Warming of the warm bottom water was most pronounced on the western shelf, where the deep-water temperature increased by 0.6°C during the past decade.

scholarly journals Pine Island glacier ice shelf melt distributed at kilometre scales

2013 ◽  
Vol 7 (5) ◽  
pp. 1543-1555 ◽  
Author(s):  
P. Dutrieux ◽  
D. G. Vaughan ◽  
H. F. J. Corr ◽  
A. Jenkins ◽  
P. R. Holland ◽  
...  
Keyword(s):  
High Resolution ◽  
Sea Level ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Ice Streams ◽  
West Antarctic ◽  
Grounding Line ◽  
Glacier Ice ◽  
Basal Melting ◽  
Broad Scale

Abstract. By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise. Much of this ice loss is from Pine Island Glacier, which has thinned since at least 1992, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line. Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems. Here, a Lagrangian methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow. At the broad scale, melt rates of up to 100 m yr−1 occur near the grounding line, reducing to 30 m yr−1 just 20 km downstream. Between 2008 and 2011, basal melting was largely compensated by ice advection, allowing us to estimate an average loss of ice to the ocean of 87 km3 yr−1, in close agreement with 2009 oceanographically constrained estimates. At smaller scales, a network of basal channels typically 500 m to 3 km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt. Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them. Kilometre-scale variations in melt are a key component of the complex ice–ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very high resolution models, are required to predict the sea-level contribution of the region.

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