Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo near-term significant change: Thwaites Glacier and the adjacent Amundsen Sea. Multiple lines of evidence point to an ongoing rapid loss of ice in this region in response to changing atmospheric and oceanic conditions. Models of the ice sheet's dynamic behavior indicate a potential for greatly accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone and nearby areas leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments. This scenario could occur over the next few centuries, and faster ice loss could occur through processes omitted from most ice flow models such as hydrofracture and ice cliff failure, which have been observed in recent rapid ice retreats elsewhere. Increased basal melt at the grounding zone and increased potential for hydrofracture due to enhanced surface melt could initiate a more rapid collapse of Thwaites Glacier within the next few decades.

/pdf/how-much-how-fast-a-science-review-and-outlook-for-research-1fsz116hh0.pdf

How Much, How Fast?: A Science Review and Outlook for Research on the Instability of Antarctica's Thwaites Glacier in the 21st Century

A state-of-the-art review of fate and transport of oil spills in open and ice-covered water

Over recent decades outlet glaciers of the Amundsen Sea Embayment (ASE), West Antarctica, have accelerated, thinned and retreated, and are now contributing approximately 10% to global sea level rise. All the ASE glaciers flow into ice shelves, and it is the thinning of these since the 1970s, and their ungrounding from “pinning points” that is widely held to be responsible for triggering the glaciers’ decline. These changes have been linked to the inflow of warm Circumpolar Deep Water (CDW) onto the ASE's continental shelf. CDW delivery is highly variable, and is closely related to the regional atmospheric circulation. The ASE is south of the Amundsen Sea Low (ASL), which has a large variability and which has deepened in recent decades. The ASL is influenced by the phase of the Southern Annular Mode, along with tropical climate variability. It is not currently possible to simulate such complex atmosphere-ocean-ice interactions in models, hampering prediction of future change. The current retreat could mark the beginning of an unstable phase of the ASE glaciers that, if continued, will result in collapse of the West Antarctic Ice Sheet, but numerical ice-sheet models currently lack the predictive power to answer this question. It is equally possible that the recent retreat will be short-lived and that the ASE will find a new stable state. Progress is hindered by incomplete knowledge of bed topography in the vicinity of the grounding line. Furthermore, a number of key processes are still missing or poorly represented in models of ice-flow.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016RG000532

Atmosphere-ocean-ice interactions in the Amundsen Sea Embayment, West Antarctica

Glaciological and oceanographic observations coupled with numerical models show that warm Circumpolar Deep Water (CDW) incursions onto the West Antarctic continental shelf cause melting of the undersides of floating ice shelves. Because these ice shelves buttress glaciers feeding into them, their ocean-induced thinning is driving Antarctic ice-sheet retreat today. Here we present a multi-proxy data based reconstruction of variability in CDW inflow to the Amundsen Sea sector, the most vulnerable part of the West Antarctic Ice Sheet, during the Holocene epoch (from 11.7 thousand years ago to the present). The chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced CDW upwelling, controlled by the latitudinal position of the Southern Hemisphere westerly winds, forced deglaciation of this sector from at least 10,400 years ago until 7,500 years ago—when an ice-shelf collapse may have caused rapid ice-sheet thinning further upstream—and since the 1940s. These results increase confidence in the predictive capability of current ice-sheet models.

/pdf/west-antarctic-ice-sheet-retreat-driven-by-holocene-warm-brxkkei1si.pdf

West Antarctic Ice Sheet retreat driven by Holocene warm water incursions

We present a new image compression scheme for hyperspectral images based on the newly-emerged matrix/tensor completion theory. Unlike typical transform-coding based methods, the proposed approach does not require any transform to be performed by the imaging sensor when doing on-board compression. Only a small set of pixels on a sparse set of locations on the imaging sensor needs to be captured and transmitted for each image. The decoder side relies on matrix/tensor completion for reconstructing the original images. Hence the scheme can drastically reduce the computation and bandwidth requirements on the on-board imaging sensors. Experiments show that the proposed method is able to obtain compression performance close to JPEG2000 while enjoying the afore-mentioned unique benefits.

Tensor completion for on-board compression of hyperspectral images

Autonomous driving relies on a variety of sensors, especially radars, which have unique robustness under heavy rain/fog/snow and poor light conditions. With the rapid increase of the amount of radars used on modern vehicles, where most radars operate in the same frequency band, the risk of radar interference becomes a compelling issue. This article analyzes automotive radar interference and proposes several new approaches that combine industrial and academic expertise toward the goal of achieving interference-free autonomous driving (AD).

/pdf/radar-interference-mitigation-for-automated-driving-1g69aykgfh.pdf

Radar Interference Mitigation for Automated Driving: Exploring Proactive Strategies

The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears
to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents
transportwarm densewater ontothe shelf,channeledby bathymetric troughs leadingto the deep inner basins.
A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on
the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow
of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature
peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the
vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf
break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar
Deep Water (CDW) toward the ice shelves in the bottom layer. This bottom-intensified flow appears to be
driven by buoyancy forces rather than the shelfbreak wind. The years of 2010 and 2011 were characterized by
a comparatively stationary Amundsen Sea low, and hence there were no strong eastward winds during winter
that could drive an upwelling of warm water along the shelf break. Regardless of this, there was a persistent
flow of lower CDW in the bottom layer during the two years. The average heat transport toward the ice
shelves in the trough was estimated from the mooring data to be 0.95 TW.

Variability of Warm Deep Water Inflow in a Submarine Trough on the Amundsen Sea Shelf

We propose a compression algorithm for hyperspectral images featuring both lossy and near-lossless compression. The algorithm is based on JPEG 2000 and provides better near-lossless compression performance than 3D-CALIC. We also show that its effect on the results of selected applications is negligible and, in some cases, better than JPEG 2000.

Unified Lossy and Near-Lossless Hyperspectral Image Compression Based on JPEG 2000

Wind vector fields derived from synthetic aperture radar (SAR) sensors show variations at smaller scales than most other globally available surface wind sources. However, few studies have been devoted to the investigation of the accuracy of SAR-derived wind fields at different scales and how they compare with other wind data. In order to investigate these issues, an algorithm for the retrieval of SAR-derived wind vectors has been developed, and a quality assessment between the retrievals and in situ, scatterometer, and numerical weather model (NWM) wind data has been performed. The implemented wind retrieval algorithm detects streak features in the SAR image to estimate wind directions and inverts wind speeds using CMOD-IFR2, CMOD5, or CMOD5.N geophysical model functions. In addition, a regularization method for filtering outliers in the wind direction retrievals is used. Retrievals compared with in situ data indicated better performance at offshore locations for wind speed inversions with CMOD5.N. The bias and standard deviation for offshore regularized wind directions and CMOD5.N speeds are 9° and 25° and -0.1 and 1.4 m/s, respectively. The comparison with the scatterometer and NWM wind data has been performed for retrievals at 5-, 10-, and 20-km resolution. The results indicate a better agreement of the coarser retrievals with the reference data. Nevertheless, mapping of smaller scale features requires wind directions from the SAR image itself.

Retrieval and Quality Assessment of Wind Velocity Vectors on the Ocean With C-Band SAR

Autonomous driving relies on a variety of sensors, especially on radars, which have unique robustness under heavy rain/fog/snow and poor light conditions. With the rapid increase of the amount of radars used on modern vehicles, where most radars operate in the same frequency band, the risk of radar interference becomes a compelling issue. This article analyses automotive radar interference and proposes several new approaches, which combine industrial and academic expertise, toward the path of interference-free autonomous driving.

Gisela Carvajal

Papers

Radar Interference Mitigation for Automated Driving: Exploring Proactive Strategies

Variability of Warm Deep Water Inflow in a Submarine Trough on the Amundsen Sea Shelf

Unified Lossy and Near-Lossless Hyperspectral Image Compression Based on JPEG 2000

Retrieval and Quality Assessment of Wind Velocity Vectors on the Ocean With C-Band SAR

Radar Interference Mitigation for Automated Driving