We employ airborne gravity data from NASA's Operation IceBridge collected in 2009–2014 to infer the bathymetry of sub–ice shelf cavities in front of Pine Island, Thwaites, Smith, and Kohler glaciers, ...West Antarctica. We use a three‐dimensional inversion constrained by multibeam echo sounding data offshore and bed topography from a mass conservation reconstruction on land. The seamless bed elevation data refine details of the Pine Island sub–ice shelf cavity, a slightly thinner cavity beneath Thwaites, and previously unknown deep (>1200 m) channels beneath the Crosson and Dotson ice shelves that shallow (500 m and 750 m, respectively) near the ice shelf fronts. These sub–ice shelf channels define the natural pathways for warm, circumpolar deep water to reach the glacier grounding lines, melt the ice shelves from below, and constrain the pattern of past and future glacial retreat.
Key Points
Deep troughs (700 m) beneath major ice shelves in the Amundsen Sea sector of Antarctica reveal pathways for warm waters to melt glaciers
Bed mapping extends in a seamless fashion from multibeam offshore to high‐resolution reconstruction inland for the first time
The data should be an important asset for ice sheet and ocean modelers and improve our understanding of this sector
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. This study uses data from three ...bottom-mounted mooring arrays to show seasonal variability and local forcing for the currents moving into and out of the Dotson ice shelf cavity. A southward flow of warm, salty water had maximum current velocities along the eastern channel slope, while northward outflows of freshened ice shelf meltwater spread at intermediate depth above the western slope. The inflow correlated with the local ocean surface stress curl. At the western slope, meltwater outflows followed the warm influx along the eastern slope with a ~2-3 month delay. Ocean circulation near Dotson Ice Shelf, affected by sea ice distribution and wind, appears to significantly control the inflow of warm water and subsequent ice shelf melting on seasonal time-scales.
Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those ...changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice-shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate.
The Getz region of West Antarctica is losing ice at an increasing rate; however, the forcing mechanisms remain unclear. Here we use satellite observations and an ice sheet model to measure the change ...in ice speed and mass balance of the drainage basin over the last 25-years. Our results show a mean increase in speed of 23.8 % between 1994 and 2018, with three glaciers accelerating by over 44 %. Speedup across the Getz basin is linear, with speedup and thinning directly correlated confirming the presence of dynamic imbalance. Since 1994, 315 Gt of ice has been lost contributing 0.9 ± 0.6 mm global mean sea level, with increased loss since 2010 caused by a snowfall reduction. Overall, dynamic imbalance accounts for two thirds of the mass loss from this region of West Antarctica over the past 25-years, with a longer-term response to ocean forcing the likely driving mechanism.
Pine Island Ice Shelf (PIIS) buttresses the Pine Island Glacier, the key contributor to sea-level rise. PIIS has thinned owing to ocean-driven melting, and its calving front has retreated, leading to ...buttressing loss. PIIS melting depends primarily on the thermocline variability in its front. Furthermore, local ocean circulation shifts adjust heat transport within Pine Island Bay (PIB), yet oceanic processes underlying the ice front retreat remain unclear. Here, we report a PIB double-gyre that moves with the PIIS calving front and hypothesise that it controls ocean heat input towards PIIS. Glacial melt generates cyclonic and anticyclonic gyres near and off PIIS, and meltwater outflows converge into the anticyclonic gyre with a deep-convex-downward thermocline. The double-gyre migrated eastward as the calving front retreated, placing the anticyclonic gyre over a shallow seafloor ridge, reducing the ocean heat input towards PIIS. Reconfigurations of meltwater-driven gyres associated with moving ice boundaries might be crucial in modulating ocean heat delivery to glacial ice.
Abstract
The mean subthermocline and intermediate zonal circulation in the tropical Pacific is investigated using a compilation of shipboard ADCP measurements and absolute geostrophic velocities ...constructed from a high-resolution 0–2000-m Argo climatology referenced to a 1000-m velocity field derived from Argo float drifts. This reference field is dominated by basinwide alternating zonal jets with a meridional wavelength of about 3°. In regions where the sampling of SADCP data is sufficient, the consistency between the two independent datasets is striking; using the Argo drift reference is crucial to capture the current structures. Two apparently distinct systems of alternating westward and eastward zonal jets are seen in both datasets equatorward of 10°: a series of low-latitude subthermocline currents (LLSCs) below the thermocline, extending from about 200 to 800 m, including the eastward Tsuchiya jets; and a series of low-latitude intermediate currents (LLICs), extending from about 700 to at least 2000 m. These systems seem to merge poleward of 10°. Both series shoal to lighter densities eastward. The subthermocline currents and their associated potential vorticity structures undergo a major shift near 155°W, suggesting some difference in the dynamic regime between the regions west and east of this longitude. Differing behaviors (the LLSCs tend to angle poleward to the east, whereas the LLICs angle slightly equatorward) suggest that these jets may be dynamically distinct, with different forcing mechanisms.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We use United Kingdom Earth System Model simulations from the Coupled Model Intercomparison Project 6 to analyze the Ross Gyre (RG) dynamics during the historical 1850–2014 period and under two ...contrasting future climate‐change scenarios. The modeled RG is relatively stable, with an extent and strength that agree with observations. The projections exhibit an eastward gyre expansion into the Amundsen‐Bellingshausen Seas that starts during the 2040s. The associated cyclonic ocean circulation enhances the onshore transport of warm Circumpolar Deep Water into the inner regional shelf, a regime change that increases the local subsurface shelf temperatures by up to 1.2°C and is independent of future forcing scenario. The RG expansion is generated by a regional ocean surface stress curl intensification associated with anthropogenic sea ice loss. If realised in reality, such a warming would strongly influence the future stability of the West Antarctic Ice Sheet.
Plain Language Summary
We use a climate model to analyze ocean changes around West Antarctica. Our results reveal a human‐driven ocean warming that increases the continental shelf temperature in the Amundsen‐Bellingshausen Seas by more than 1°C in only ∼30 years. This rapid warming is caused by the expansion of the Ross Gyre (RG), a large oceanic circulation in the region. The West Antarctic Ice Sheet is losing mass, causing sea‐level rise, with the most rapid ice losses occurring in the Amundsen‐Bellingshausen Seas. Our results suggest that an expansion of the RG could provide a mechanism whereby melt rates increase far beyond the current range. This could have an important influence on the sea‐level rise caused by this region, with global impacts.
Key Points
The UK Earth System Model produces a fairly realistic depiction of ocean conditions in West Antarctica
Future projections suggest a rapid warming of the Amundsen Sea induced by a Ross Gyre (RG) expansion that is independent of forcing scenario
The RG expansion is primarily caused by a surface stress curl intensification induced by anthropogenic trends in Antarctic sea ice
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