Subglacial discharge controls seasonal variations in the thermal structure of a glacial lake in Patagonia

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Despite its importance, seasonal lake temperature variations are poorly understood because taking long-term measurements near the front of calving glaciers is challenging. To investigate the thermal structure and its seasonal variations, we performed year-around temperature and current measurement at depths of 58–392 m in Lago Grey, a 410-m-deep glacial lake in Patagonia. The measurement revealed critical impacts of subglacial discharge on the lake thermal condition. Water below a depth of ~100 m showed the coldest temperature in mid-summer, under the influence of glacial discharge, whereas temperature in the upper layer followed a seasonal variation of air temperature. The boundary of the lower and upper layers was controlled by the depth of a sill which blocks outflow of dense and cold glacial meltwater. Our data implies that subglacial discharge and bathymetry dictate mass loss and the retreat of lake-terminating glaciers. The cold lakewater hinders underwater melting and facilitates formation of a floating terminus.

Undertaking Adventure to Make Sense of Subglacial Plumes

Novel observations and inventive analyses of glacial discharge in Greenland have revealed new insights into the irregular and chaotic nature of ice-ocean interactions at glacial calving fronts.

Aurora Basin, the weak underbelly of East Antarctica

<p>Containing ~52 m sea level rise equivalent ice mass (SLRe), the East Antarctic Ice Sheet (EAIS) is a major component of the global sea level budget; yet, uncertainty remains in how this ice sheet will respond to enhanced atmospheric and oceanic thermal forcing through the turn of the century. To address this uncertainty, we model the most dynamic catchments of EAIS out to 2100 using the Ice Sheet System Model. We employ three basal melt rate parameterizations to resolve ice-ocean interactions and force our model with anomalies in both surface mass balance and ocean thermal forcing from both CMIP5 and CMIP6 model output. We find that this sector of EAIS gains approximately 10 mm SLRe by 2100 under high emission scenarios (RCP8.5 and SSP585), and loses mass under low emission scenarios (RCP2.6). All basins within the domain either gain mass or are in near mass balance through the 86-year experimental period, except the Aurora Subglacial Basin. The primary region of mass loss in this basin is located within 50 km upstream of Totten Glacier’s grounding line, which loses up to 6 mm SLRe by 2100. Glacial discharge from Totten is modulated by buttress supplied by a 10 km ice plain, located along the southern-most end of Totten’s grounding line. This ice plain is sensitive to brief changes in ocean temperature and once ungrounded, glacial discharge from Totten accelerates by up to 70% of it present day configuration. In all, we present plausible bounds on the contribution of a large sector of EAIS to global sea level rise out to the end of the century and target Totten as the most vulnerable glacier in this region. In doing so, we reduce uncertainty in century-scale global sea level projections and help steer scientific focus to the most dynamic regions of EAIS.</p>

Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.

Beavers as Agents of Landscape Change

Beavers ingeniously alter environments to suit their needs of predator protection and food access, creating widespread effects on surface waters throughout their range. Beaver are thus considered the quintessential ecosystem engineer. They “engineer” landscapes largely by building dams across low-order streams to retain water. Dam building changes a wide range of ecological, hydrologic, and geomorphic processes that transform rivers into complex wetland systems capable of supporting a diversity of aquatic and terrestrial species. Although less studied, beavers live in and can significantly impact landscape processes in large rivers, wetlands, and lakes and unexpected places like landslides, brackish deltas, and glacial discharge environments. The earliest works on beaver are from a time when beaver were very much still being trapped to supply the fashion market in Europe with pelts (c. late 1800s to early 1900s). Works from this period primarily document the natural history of beaver. Research interest in beaver waned for several decades, coincident with low beaver populations. In the 1980s and 1990s, however, researcher interest in beaver was again piqued, which led to a little over a decade of studies documenting a range of ecosystem effects of beaver. Research on beaver ecosystem engineering was reinvigorated again in the mid- to late-2000s, coincident with rewilding efforts in Europe, beaver use in stream restoration activities in the United States, and rapid spread of the exotic, invasive beaver population in Tierra del Fuego. This encyclopedia entry provides a summary of the hydrogeomorphic processes known to be beaver-mediated, as well as the state of knowledge of how beaver form stream valleys and shape wetland ecosystems. Included are brief annotations of key literature. Ecological and biogeochemical impacts of beaver ponds are extensive, but a full description of them are beyond the scope of this annotated bibliography. The topic could benefit from greater synergistic and integrative research among biologists, geomorphologists, ecologists, and hydrologists.

Decadal Changes in Glacial Discharge in the High Alps

A new statistical analysis of daily, glacial runoff cycles offers a unique way of examining how Alpine glaciers have responded since the onset of rapid regional warming in the 1980s.

Subglacial Water Can Accelerate East Antarctic Glacier Flow

Airborne radar from the Recovery Glacier system demonstrates the importance of characterizing the underlying causes of ice flow speedup to understand how glacial discharge could change in the future.

Glacial Meltwater Plumes Support Greenland Phytoplankton Blooms

Field measurements from the Bowdoin Glacier show that entrainment of deep water into upwelling glacial discharge delivers crucial nutrients to the surface of the surrounding fjord.