Heterogeneous melting near the Thwaites Glacier grounding line.

Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment1-3. Because it is grounded below sea level4,5, Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean6,7. Recent ice-flow acceleration2,8 and retreat of the ice front8-10 and GL11,12 indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice-ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.

Corrigendum: Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

This corrects the article DOI: 10.1038/nature20136.

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier.

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line-which marks the boundary between grounded ice and floating ice shelf-is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Thus our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

Ocean forcing of glacier retreat in the western Antarctic Peninsula.

In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region.

Antarctic ice-sheet loss driven by basal melting of ice shelves.

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.

Retreating glacier fronts on the Antarctic Peninsula over the past half-century.

The continued retreat of ice shelves on the Antarctic Peninsula has been widely attributed to recent atmospheric warming, but there is little published work describing changes in glacier margin positions. We present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years. Of these glaciers, 87% have retreated and a clear boundary between mean advance and retreat has migrated progressively southward. The pattern is broadly compatible with retreat driven by atmospheric warming, but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region.

Utilization and management of multiskilled health practitioners in U.S. hospitals.

This article examines the utilization and management of multiskilled health practitioners by U.S. hospitals. Results indicate such utilization is greatest for small hospitals as well as for other not-for-profit and government nonfederal hospitals. Flexibility, efficiency, and cost containment are the major reasons for utilizing such personnel. Secondary skills added to most multiskilled workers were of a parallel or lower level. Managerial issues and implications in utilizing multiskilled workers including training, compensation, evaluation, supervision, and competency assessment are also discussed.

The multiskilled health practitioner movement: where are we and how did we get here?

Multiskilled practitioners have been in health care settings for a long time. The form multiskilled practitioners have taken has varied with the cultural, socioeconomic, and technological constructs of the times. Some multiskilled practitioners have come and gone while others, such as the medical assistant and physician assistant, have remained. The complexity and sophistication of skills being combined have increased over time as have the degree level and opportunities for dual certification. Skills have been combined both across and within disciplines. There is currently a greater number and variety of formal programs to prepare multiskilled health practitioners in educational institutions and health care facilities, and more informal on-the-job training efforts than ever before--and they are increasing. Employment of multiskilled personnel has become a survival strategy for health care institutions in this current era of cost containment. Multiskilled allied health practitioners with basic nursing skills (ie, LPN level) may also provide one step toward a solution to the nursing personnel shortage being experienced by some health care facilities. The catchword for multiskilled has become not "whether," but "how."15 It is to everyone's benefit to learn from the efforts of those with experience in implementing the multiskilled health practitioner concept for both national and international application. The National Multiskilled Health Practitioner Clearinghouse intends, through its publications, services, and resource files, to serve as the cornerstone upon which the information from those with experience can be reposited and disseminated.

Marketing physician services in an academic medical center.

As a result of recent environmental changes in the health care industry, marketing has become a vital necessity for the survival of most hospitals. Kotler's conceptual framework is used to study and evaluate an innovative program for marketing physician services in a large urban medical center. This program was quite successful in increasing admissions and referrals and won a national award in 1984.

Refractive change in hyperglycaemia: hyperopia, not myopia.

Sudden changes in refraction are well recognised feature of hyperglycaemia. A tendency towards myopia has always been associated with elevations in blood glucose. Twelve diabetic patients were found to have experienced such refractive changes. Review of their records demonstrates that hyperglycaemia produces hyperopia. A theoretical mechanism for this phenomenon is discussed.