Future projections and past reconstructions of Antarctic Ice Sheet stability and sea‐level rise depend on knowledge of continental shelf bathymetry, which controls water circulation under floating ice and interactions between the ice shelf and seafloor. We present a bathymetry model of the Venable Ice Shelf (VIS) in the Bellingshausen Sea sector from an inversion of airborne gravity data. The new model reveals troughs up to ∼1.6 km deeper than previously mapped, providing pathways for warm Circumpolar Deep Water to access the grounding line. A bathymetric high beneath the western VIS is identified as a former pinning point. From crevasse patterns in Landsat satellite imagery, we infer intermittent grounding of the ice shelf on this high since ∼1935, and we interpret these patterns as evidence of mid‐20th century ice‐shelf thinning, in addition to a regrounding between 1970 and 1988, extending the ice‐shelf thickness record beyond the satellite era.

Circumpolar Deep Water (CDW) and Antarctic Bottom Water (AABW) play key roles in the Earth's climate system. Both water masses form critical components of the Antarctic Circumpolar Current and Meridional Overturning Circulation and therefore directly influence the large-scale redistribution of heat, nutrients and carbon. Reconstruction of past CDW transport and AABW production and export has been a key target in palaeoceanography. One promising proxy to achieve this has been the neodymium (Nd) isotope composition of seawater. The biogeochemical processes controlling Nd in the ocean, however, remain underconstrained, and modern observations of Nd isotopes in the Southern Ocean are still geographically limited. To overcome this limitation, 61 seawater samples were collected for Nd isotope and rare earth element (REE) analysis at nine stations along the Wilkes Land continental margin and in the Australian-Antarctic Basin (65 degrees S 125 degrees E) near East Antarctica. The results show that the different water masses have the following Nd isotope characteristics: Antarctic Surface Water (AASW), e Nd = -9.0 +/- 1.0 (2SD; n = 22); Modified CDW (MCDW), e Nd = -8.8 +/- 0.8 (2SD; n = 22); AABW, e Nd = -8.3 +/- 0.5 (2SD; n = 17). There is no evidence of continental REE inputs to surface waters on the Wilkes Land margin. Observed zonal variability of Nd isotope composition in AASW can be attributed to seasonal competition between the poleward flow of warm AASW from the AAG and the westward export of cold surface shelf waters by the Antarctic Slope Current. In terms of deep and bottom waters, mixing of upwelled CDW with AASW and AABW exclusively controls the Nd isotope composition of MCDW, with no indication of boundary processes modifying the Nd isotope composition of MCDW as it encroaches the shelf or slope. The regional Nd isotope signature for AABW is intermediate between published data for the Atlantic sector AABW (e Nd = -9.1 +/- 0.7) and Pacific sector AABW (e Nd = -7.4 +/- 0.9). In the absence of active convection, this Nd isotope signature can be explained by a mixture of advected AABW from the Ade lie Land coast with a more dominant component of local MCDW and CDW. The data presented in this study constitute the first Nd isotope data set in this part of the Southern Ocean and suggest conservative behaviour of Nd in proximity to the old East Antarctic continent.

The melting of the Greenland ice sheet (GrIS) is a major contributor to past and future global sea-level rise. Understanding the response of the GrIS to times in the past when temperatures were as warm or warmer than today offers insights into its current and future response to climate change. In the southwest sector, the GrIS retreated inland beyond its current margin during the (at least regionally) warmer-than-present mid-Holocene, before it readvanced to the historical maximum position during the Little Ice Age. This was then followed by a slight retreat to its current position. To investigate the timing and magnitude of southwest GrIS retreat and readvance in response to Holocene warmth, we model the response of the solid Earth and local relative sea level (RSL) to past ice sheet change. We test a suite of eleven ice sheet scenarios that are based on ICE-6G_C but are modified in the timing and magnitude of ice retreat and readvance and pair them with four different viscoelastic Earth structures. We compare model predictions to observations of paleo sea level, present-day sea-level change, and present-day vertical land motion (VLM) around Nuuk, Greenland. We find that the modeled timing and magnitude of the Holocene retreat and readvance have a significant impact on modern sea-level change and VLM in Nuuk. Models that assume a readvance approaching the southwest GrIS’ historical maximum between 2 and 1 ka are most consistent with observations. The RSL response, however, is less sensitive to the timing of the minimum GrIS extent. Nonetheless, better data-model fits are generally obtained when the minimum ice sheet extent is reached between 5 and 3 ka, within the tested range of 6-3 ka. Comparing this timing to local and regional records of temperature and ice-sheet change suggest that the evolution of the southwestern GrIS presented here was in-phase with the likely evolution of southwestern GrIS mass balance through the Holocene. Our results have implications for future ice sheet modeling studies targeting southwestern Greenland by providing additional constraints and strengthening existing ones. Moreover, this work provides a deeper understanding of the interactions between the climate and the cryosphere and thus of future ice sheet change.

Abstract. Surface-mass-balance (SMB) and firn-densification (FD) models are widely used in altimetry studies as a tool to separate atmospheric-driven from ice-dynamics-driven ice-sheet mass changes and to partition observed volume changes into ice-mass changes and firn-air-content changes. Until now, SMB models have been principally validated based on comparison with ice core and weather station data or comparison with widely separated flight radar-survey flight lines. Firn-densification models have been primarily validated based on their ability to match net densification over decades, as recorded in firn cores, and the short-term time-dependent component of densification has rarely been evaluated at all. The advent of systematic ice-sheet-wide repeated ice-surface-height measurements from ICESat-2 (the Ice Cloud, and land Elevation Satellite, 2) allows us to measure the net surface-height change of the Greenland ice sheet at quarterly resolution and compare the measured surface-height differences directly with those predicted by three FD–SMB models: MARv3.5.11 (Modèle Atmosphérique Régional version 3.5.11) and GSFCv1.1 and GSFCv1.2 (the Goddard Space Flight Center FD–SMB models version 1.1 and 1.2). By segregating the data by season and elevation, and based on the timing and magnitude of modelled processes in areas where we expect minimal ice-dynamics-driven height changes, we investigate the models' accuracy in predicting atmospherically driven height changes. We find that while all three models do well in predicting the large seasonal changes in the low-elevation parts of the ice sheet where melt rates are highest, two of the models (MARv3.5.11 and GSFCv1.1) systematically overpredict, by around a factor of 2, the magnitude of height changes in the high-elevation parts of the ice sheet, particularly those associated with melt events. This overprediction seems to be associated with the melt sensitivity of the models in the high-elevation part of the ice sheet. The third model, GSFCv1.2, which has an updated high-elevation melt parameterization, avoids this overprediction.

Reviewed by: The Northwest Gardens of Lord & Schryver by Valencia Libby David Porter THE NORTHWEST GARDENS OF LORD & SCHRYVER by Valencia Libby Oregon State University Press, Corvallis, 2021. Illustrations, photographs, notes, bibliography, index. 256 pages. $29.95 paper Valencia Libby exhaustively recaps the lives and work of Elizabeth Lord and Edith Schryver, life partners who founded the first women-owned landscape architecture firm in the Pacific Northwest. The two women met by chance in the dining salon of an ocean liner in 1927. The voyage was the first leg on a tour of Europe’s great gardens and monuments. Their chance meeting and felicitous first encounter made them traveling companions. After docking in Edinburgh, Scotland, the tour took them across the Continent. It is easy to imagine their journey had a flavor of romantic adventure worthy of the cinema. On side trips, for example, they flew to Spain and Morocco; the Moorish gardens inspired some of their later designs. They discovered shared perceptions and tastes as they traveled. Ultimately, they believed that they would find opportunity in their profession if they started out in Oregon where Lord’s family connections could help them succeed. Schryver, daughter of an industrious entrepreneur from New York, and Lord, child of a leading family in Salem, Oregon, found much in common. Both were passionate about gardens, design, and landscape architecture. Schryver at age twenty-six was already employed in a New York firm, while Lord, age thirty-nine, was studying at Lowthorpe, a landscape program in Massachusetts that trained women professionals who could be economically independent. Gardening with her mother had sparked Lord’s horticultural interest. In 1922, her work improving the grounds of a local country club won praise, which led her to Lowthorpe and eventually Schryver. After the two women launched their firm, they cultivated clients eager to own knowledgeably conceived and constructed gardens. The firm’s early years were challenging as the Great Depression unfolded. Libby describes their fortitude facing challenges, their willingness to do the necessary work themselves, and the steady growth of their reputation for designing gardens that not only pleased the eye but also “stir the imagination” in the words of their friend Alice Brown Powell (p. 72). The book recounts the development and construction of ten private gardens in the Pacific Northwest. Undoubtedly, Lord’s social connections helped the firm succeed. During those years, they also took on public projects, such as an extensive design for Breitenbush Hot Springs in the Willamette National Forest. Also notable was their work in 1938 developing a landscape plan at historic McLoughlin House in Oregon City. Closest to their heart was the design and construction of their Salem home, Gaiety Hollow, and its gardens. Lord and Schryver’s reputation later prompted the Portland Garden Club to hire them to design its headquarters in Portland. Lord and Schryver had a notable effect on regional landscape architecture. They helped the profession build its credibility with architects, horticulturists, and contractors, making clear that women were capable practitioners in all of these areas. They brought new perspectives on garden design, incorporating novel elements they had seen in their far-ranging travels. They broadened the plant palette employed in Northwest gardens with knowledge of plants from the East Coast and other areas where they had made connections. This book will satisfy readers who are deeply interested in these women and in landscape design’s evolution through the twentieth century. [End Page 315] David Porter Gresham, Oregon Copyright © 2022 Oregon Historical Society

Abstract. We have developed a ground-based Global Navigation Satellite System Reflectometry (GNSS-R) technique for monitoring water levels with a comparable precision to standard tide gauges (e.g., pressure transducers) but at a fraction of the cost and using commercial products that are straightforward to assemble. As opposed to using geodetic-standard antennas that have been used in previous GNSS-R literature, we use multiple co-located low-cost antennas to retrieve water levels via inverse modelling of Signal-to-Noise ratio data. The low-cost antennas are advantageous over geodetic-standard antennas because they are much less expensive (even when using multiple antennas in the same location) and they can be used for GNSS-R analysis over a greater range of satellite elevation angles. We validate our technique using arrays of four antennas at three test sites with variable tidal forcing and co-located operational tide gauges. The root mean square error between the GNSS-R and tide gauge measurements ranges from 0.7–1.2 cm when using all four antennas at each site. We find that using four antennas instead of a single antenna improves the precision by 30–50 % and preliminary analysis suggests that four appears to be the optimum number of co-located antennas. In order to obtain precise measurements, we find that it is important for the antennas to track GPS, GLONASS and Galileo satellites over a wide range of azimuth angles (at least 140 degrees) and elevation angles (at least 30 degrees).

George VI Sound is an ~600 km‐long curvilinear channel on the west coast of the southern Antarctic Peninsula separating Alexander Island from Palmer Land. The Sound is a geologically complex region presently covered by the George VI Ice Shelf. Here we model the bathymetry using aerogravity data. Our model is constrained by water depths from seismic measurements. We present a crustal density model for the region, propose a relocation for a major fault in the Sound, and reveal a dense body, ~200 km long, flanking the Palmer Land side. The southern half of the Sound consists of two distinct basins ~1,100 m deep, separated by a −650 m‐deep ridge. This constricting ridge presents a potential barrier to ocean circulation beneath the ice shelf and may account for observed differences in temperature‐salinity (T‐S) profiles.

Ice shelves play a critical role in the long-term stability of ice sheets through their buttressing effect. The underlying bathymetry and cavity thickness are key inputs for modelling future ice sheet evolution. However, direct observation of sub-ice-shelf bathymetry is time-consuming, logistically risky, and in some areas simply not possible. Here we use new compilations of airborne and marine gravity, radar depth sounding, and swath bathymetry to provide new estimates of sub-ice-shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier and beneath the adjacent Dotson and Crosson ice shelves. This region is of special interest, as the low-lying inland reverse slope of the Thwaites Glacier system makes it vulnerable to marine ice sheet instability, with rapid grounding line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel >800 m deep extends tens of kilometres to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves, which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these recently floated parts of the ice shelf are not yet in dynamic equilibrium with their retreated grounding line positions and the underlying ocean system, a factor which must be included in future models of this region's evolution.

Ocean melting has thinned Antarctica’s ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean–atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet.

Oceanographic conditions on the continental shelf of the Ross Sea, Antarctica, affect sea ice production, Antarctic Bottom Water formation, mass loss from the Ross Ice Shelf, and ecosystems. Since ship access to the Ross Sea is restricted by sea ice in winter, most upper ocean measurements have been acquired in summer. We report the first multiyear time series of temperature and salinity throughout the water column, obtained with autonomous profiling floats. Seven Apex floats were deployed in 2013 on the midcontinental shelf, and six Air-Launched Autonomous Micro Observer floats were deployed in late 2016, mostly near the ice shelf front. Between profiles, most floats were parked on the seabed to minimize lateral motion. Surface mixed layer temperatures, salinities, and depths, in winter were -1.8 degrees C, 34.34, and 250-500 m, respectively. Freshwater from sea ice melt in early December formed a shallow (20 m) surface mixed layer, which deepened to 50-80 m and usually warmed to above -0.5 degrees C by late January. Upper-ocean freshening continued throughout the summer, especially in the eastern Ross Sea and along the ice shelf front. This freshening requires substantial lateral advection that is dominated by inflow from melting of sea ice and ice shelves in the Amundsen Sea and by inputs from the Ross Ice Shelf. Changes in upper-ocean freshwater and heat content along the ice shelf front in summer affect cross-ice front advection, ice shelf melting, and calving processes that determine the rate of mass loss from the grounded Antarctic Ice Sheet in this sector. Plain Language Summary Measurements of temperature and salinity in coastal Antarctic waters are generally restricted to summer when sea ice disappears so that ships can operate there. Moored sensors can collect data through winter but are usually deployed below 200-300 m to minimize risk of damage from drifting icebergs. We describe a novel approach, using autonomous profilers deployed by ship and aircraft, to collect data from the seabed to the ocean surface throughout the year. We deployed 13 profilers in the Ross Sea, Antarctica. Most profilers were programmed to sit on the seabed between profiles to minimize drift and to continue profiling even when ice cover prevented their ascent to the surface. As expected, annual changes in upper-ocean temperature and salinity were closely related to seasonal changes in sea ice. However, the upper ocean continued to freshen even after the sea ice had all melted, suggesting that substantial amounts of freshwater must be coming from ice melting in the adjacent Amundsen Sea. Increasing our understanding of sources of freshwater in the Ross Sea will improve our predictions of this region's changing role in Antarctic sea ice formation, ice loss from the Antarctic Ice Sheet, and Southern Ocean ecosystems.

Over the past several decades, the Greenland Ice Sheet has been losing mass through a combination of increased surface runoff and accelerating ice flux to the ocean. Our understanding of the surface component is drawn heavily from satellite observations and climate models. The MAR (Modèle Atmosphère Régional) model is a 3D regional climate model used extensively over Greenland. Our study focuses on the surface snow and the ice down to 15-meter in depth. A light-weighted surface model for us to integrate the local observation data and force many simulations is needed. Our goal is to implement a surface-only model, derived from MAR, as a tool for understanding the glacial surface components, correlations, and MAR biases to improve projections of surface runoff. This model includes the ability to integrate observations from surface weather stations, translate the data into a model forcing format, force different simulations with various configurations or datasets, visualize model outputs, find key correlations between atmospheric drivers and modeled firn densification. In the model development, we extract the surface code from the original MAR for the simulations initialized and forced with the following snow and atmospheric fields: snow depth, temperature, density, water volume, and grain size. We then verify that the surface model generates the same outputs as the full MAR does if fetched with the identical data. The bias is checked with snowpack time-depth plots for multiple sites around Greenland, including Summit and Swiss Camp. We have found a very small bias when compared to the fully-coupled MAR. We perform quality control for the data inputs, such as replacing missing data from the station measurements, defining the max and min for each dataset, filtering out the data outliers by statistics standard deviations. As the result, our model software can provide multiple simulations in sequential and concurrent mode with user-friendly interfaces, and run robustly. The model’s first release is currently being deployed over different sites across Greenland to understand the importance of atmospheric forcing versus snow model biases in projections of future mass loss due to surface melt.

Although the Greenland ice sheet is losing mass as a whole, patterns of change on both local and regional scales are complex. Spatial statistics reveal large spatial variability of dynamic thinning rates of Greenland's marine-terminating glaciers between 2003 and 2009; only 18% of glacier thinning rates co-vary with neighboring glaciers. Most spatially-correlated thinning rates are clusters of stable glaciers in the Thule, Scoresby Sund, and Southwest regions. Conversely, where spatial-autocorrelation is low, individual glaciers are more strongly controlled by local, glacier-scale features than by regional influences. We investigate possible sources of local control of oceanic forcing by combining grounding line depths and ocean model output to estimate mean ocean heat content adjacent to 74 glaciers. Linear regression models indicate stronger correlation of dynamic thinning rates with ocean heat content compared to those with grounding line depths alone. The correlation between ocean heat and dynamic thinning is robust for all of Greenland except glaciers in the West, and strongest in the Southeast (R-2 similar to 0.81 +/- 0.15, p = 0.009), implying that glaciers with deeper grounded termini here are most sensitive to changes in ocean forcing. In the Northwest, accounting for shallow sills in the regressions improves the correlation of water depth with glacial thinning, highlighting the need for comprehensive knowledge of fjord geometry.