An inventory and topographic analysis of glaciers in the Torngat Mountains, northern Labrador, Canada

AbstractThis study presents the first complete glacier inventory of the Torngat Mountains, northern Labrador, Canada. In total, 195 glaciers and ice masses are identified, covering a total area of 24.5 ± 1.8 km2. Mapped ice masses range in size from 0.01 to 1.26 km2, with a median size of 0.08 km2. Ice masses have a median elevation of 776 m a.s.l. and span an altitudinal range of 290–1500 m a.s.l. Indications of ice flow suggest at least 105 active glaciers in the Torngat Mountains. Analysis of morphometric and topographic parameters suggests that the regional distribution of ice masses is linked to physiographic setting while the preservation of coastal ice masses at low elevation is related to local meteorological conditions. In the most coastal environments, ice masses are shown to exist below the regional glaciation level due to topographic shadowing, coastal proximity and widespread debris cover. This study provides a baseline for future change assessment.</jats:p

Proglacial groundwater storage dynamics under climate change and glacier retreat

Proglacial aquifers are an important water store in glacierised mountain catchments that supplement meltwater‐fed river flows and support freshwater ecosystems. Climate change and glacier retreat will perturb water storage in these aquifers, yet the climate‐glacier‐groundwater response cascade has rarely been studied and remains poorly understood. This study implements an integrated modelling approach that combines distributed glacio‐hydrological and groundwater models with climate change projections to evaluate the evolution of groundwater storage dynamics and surface‐groundwater exchanges in a temperate, glacierised catchment in Iceland. Focused infiltration along the meltwater‐fed Virkisá River channel is found to be an important source of groundwater recharge and is projected to provide 14%–20% of total groundwater recharge by the 2080s. The simulations highlight a mechanism by which glacier retreat could inhibit river recharge in the future due to the loss of diurnal melt cycling in the runoff hydrograph. However, the evolution of proglacial groundwater level dynamics show considerable resilience to changes in river recharge and, instead, are driven by changes in the magnitude and seasonal timing of diffuse recharge from year‐round rainfall. The majority of scenarios simulate an overall reduction in groundwater levels with a maximum 30‐day average groundwater level reduction of 1 m. The simulations replicate observational studies of baseflow to the river, where up to 15% of the 30‐day average river flow comes from groundwater outside of the melt season. This is forecast to reduce to 3%–8% by the 2080s due to increased contributions from rainfall and meltwater runoff. During the melt season, groundwater will continue to contribute 1%–3% of river flow despite significant reductions in meltwater runoff inputs. Therefore it is concluded that, in the proglacial region, groundwater will continue to provide only limited buffering of river flows as the glacier retreats

Surface melt and ponding on Larsen C Ice Shelf and the impact of föhn winds

A common precursor to ice shelf disintegration, most notably that of Larsen B Ice Shelf, is unusually intense or prolonged surface melt and the presence of surface standing water. However, there has been little research into detailed patterns of melt on ice shelves or the nature of summer melt ponds. We investigated surface melt on Larsen C Ice Shelf at high resolution using Envisat advanced synthetic aperture radar (ASAR) data and explored melt ponds in a range of satellite images. The improved spatial resolution of SAR over alternative approaches revealed anomalously long melt duration in western inlets. Meteorological modelling explained this pattern by föhn winds which were common in this region.Melt ponds are difficult to detect using optical imagery because cloud-free conditions are rare in this region and ponds quickly freeze over, but can be monitored using SAR in all weather conditions. Melt ponds up to tens of kilometres in length were common in Cabinet Inlet, where melt duration was most prolonged. The pattern of melt explains the previously observed distribution of ice shelf densification, which in parts had reached levels that preceded the collapse of Larsen B Ice Shelf, suggesting a potential role for föhn winds in promoting unstable conditions on ice shelves

Modelled glacier response to centennial temperature and precipitation trends on the Antarctic Peninsula

The northern Antarctic Peninsula is currently undergoing rapid atmospheric warming1. Increased glacier-surface melt during the twentieth century2, 3 has contributed to ice-shelf collapse and the widespread acceleration4, thinning and recession5 of glaciers. Therefore, glaciers peripheral to the Antarctic Ice Sheet currently make a large contribution to eustatic sea-level rise6, 7, but future melting may be offset by increased precipitation8. Here we assess glacier–climate relationships both during the past and into the future, using ice-core and geological data and glacier and climate numerical model simulations. Focusing on Glacier IJR45 on James Ross Island, northeast Antarctic Peninsula, our modelling experiments show that this representative glacier is most sensitive to temperature change, not precipitation change. We determine that its most recent expansion occurred during the late Holocene ‘Little Ice Age’ and not during the warmer mid-Holocene, as previously proposed9. Simulations using a range of future Intergovernmental Panel on Climate Change climate scenarios indicate that future increases in precipitation are unlikely to offset atmospheric-warming-induced melt of peripheral Antarctic Peninsula glaciers

Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula

The Western Antarctic Peninsula has recently undergone rapid climatic warming, with associated decreases in sea ice extent and duration, and increases in precipitation and glacial discharge to the ocean. These shifts in the freshwater budget can have significant consequences on the functioning of the regional ecosystem, feedbacks on regional climate, and sea-level rise. Here we use shelf-wide oxygen isotope data from cruises in four consecutive Januaries (2011–2014) to distinguish the freshwater input from sea ice melt separately from that due to meteoric sources (precipitation plus glacial discharge). Sea ice melt distributions varied from minima in 2011 of around 0 % up to maxima in 2014 of around 4–5%. Meteoric water contribution to the marine environment is typically elevated inshore, due to local glacial discharge and orographic effects on precipitation, but this enhanced contribution was largely absent in January 2013 due to anomalously low precipitation in the last quarter of 2012. Both sea ice melt and meteoric water changes are seen to be strongly influenced by changes in regional wind forcing associated with the Southern Annular Mode and the El Niño–Southern Oscillation phenomenon, which also impact on net sea ice motion as inferred from the isotope data. A near-coastal time series of isotope data collected from Rothera Research Station reproduces well the temporal pattern of changes in sea ice melt, but less well the meteoric water changes, due to local glacial inputs and precipitation effects

Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ashley, K. E., McKay, R., Etourneau, J., Jimenez-Espejo, F. J., Condron, A., Albot, A., Crosta, X., Riesselman, C., Seki, O., Mass, G., Golledge, N. R., Gasson, E., Lowry, D. P., Barrand, N. E., Johnson, K., Bertler, N., Escutia, C., Dunbar, R., & Bendle, J. A. Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat. Climate of the Past, 17(1), (2021): 1-19, https://doi.org/10.5194/cp-17-1-2021.Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.This research has been supported by the Natural Environment Research Council (CENTA PhD; NE/L002493/1 and Standard Grant Ne/I00646X/1), Japanese Society for the Promotion of Science (JSPS/FF2/60 no. L-11523), NZ Marsden Fund (grant nos. 18-VUW-089 and 15-VUW-131), NSF (grant nos. PLR-1443347 and ACI-1548562), the U.S. Dept. of Energy (grant no. DE-SC0016105), ERC (StG ICEPROXY, 203441; ANR CLIMICE, FP7 Past4Future, 243908), L'Oréal-UNESCO New Zealand For Women in Science Fellowship, University of Otago Research Grant, the IODP U.S. Science Support Program, Spanish Ministry of Science and Innovation (grant no. CTM2017-89711-C2-1-P), and the European Union (FEDER)

The modelled surface mass balance of the Antarctic Peninsula at 5.5 km horizontal resolution.

This study presents a high-resolution (similar to 5.5 km) estimate of surface mass balance (SMB) over the period 1979-2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr(-1) in the western AP (WAP) and below 500 mm we yr(-1) in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP ice-sheet-integrated SMB, including ice shelves (an area of 4.1 x 10(5) km(2)), is estimated at 351 Gt yr(-1) with an interannual variability of 58 Gt yr(-1), which is dominated by precipitation (PR) (365 +/- 57 Gt yr(-1)). The WAP (2.4 x 10(5) km(2)) SMB (276 +/- 47 Gt yr(-1)), where PR is large (276 +/- 47 Gt yr(-1)), dominates over the EAP (1.7 x 10(5) km(2)) SMB (75 +/- 11 Gt yr(-1)) and PR (84 +/- 11 Gt yr(-1)). Total sublimation is 11 +/- 2 Gt yr(-1) and meltwater runoff into the ocean is 4 +/- 4 Gt yr(-1). There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (-0.36 Gt yr(-2))