The deglaciation of coastal areas of southeast Greenland

Large marine-terminating glaciers around the margins of the Greenland Ice Sheet have retreated, accelerated and thinned over the last two decades. Relatively little is known about the longer term behaviour of the Greenland Ice Sheet, yet this information is valuable for assessing the significance of modern changes. We address this by reporting 11 new beryllium-10 (10Be) exposure ages from previously uninvestigated coastal areas across southeast Greenland. The new ages are combined with existing data from the region to assess the timing of glacier retreat after the Last Glacial Maximum. The results show that deglaciation occurred first in the north of the region (~68°N) and progressed southwards. This north–south progression is attributed to the influence of the warm Irminger Current on the ice margin. Areas in the south of the region were isolated from the warm waters by the shallow bathymetry of the continental shelf. This demonstrates that oceanographic forcing paced the deglaciation of southeast Greenland through the Younger Dryas and early Holocene. In most areas of southeast Greenland bedrock ages are systematically older than their counterpart boulder samples; this offset is likely the result of inherited 10Be content in bedrock surfaces. This suggests that subglacial erosion during the last glacial cycle was insufficient to completely remove pre-existing 10Be content. Alternatively, this pattern may be the signature of a substantial retreat and advance cycle prior to final Holocene deglaciation

Investigating ice-ocean interactions in Kangerdlugssuaq Fjord over the past ∼600 years through proxy reconstructions

International audienceThere is a growing body of evidence demonstrating that changes in warm water inflow to Greenlandic fjords are linked to the rapid retreat of marine-terminating outlet glaciers. This process is thought to be responsible for a substantial component of the increased mass loss from the Greenland Ice Sheet over the last two decades. Sediment cores from glaciated fjords provide high-resolution sedimentological and biological proxy recordswhich can be used to evaluate the interplay of warm water inflow and glacier calving over timescales longer than the instrumental record.In this study, a short core (1.5m) positioned at the head of Kangerdlugssuaq fjord is investigated to establish a multi-proxy record of glacier behaviour and oceanographic conditions. The core covers the past ∼600 years, spanning back to the start of the Little Ice Age. Grain-size analysis is performed to quantify ice-rafted debris (IRD), a parameter related to the calving intensity of Kangerdlugssuaq glacier. Bottom current strength isreconstructed by measurements of the mean sortable silt; periods of vigorous current flow are assumed to be due to enhanced warm water inflow. A record of sea surface temperatures is derived from alkenone paleothermometry (Uk’ 37), and the origin of the alkenones is discussed (in situ vs. advection). Reconstructions of ice-oceaninteractions on a longer timescale provide a baseline to better understand the recent -and potentially future- retreat of marine-terminating glaciers in Greenland

Evaluating ice-rafted debris as a proxy for glacier calving in Upernavik Isfjord, NW Greenland

International audienceRecords of ice‐rafted debris (IRD) in sediments are commonly used as a proxy for iceberg production and to reconstruct past changes of glacier stability. However, the interpretation of IRD is complex as multiple processes modulate its variability. This study investigates the relationship between IRD variability and glaciological change by measuring IRD records from Upernavik Fjord and comparing these to frontal positions of Upernavik Isstrøm during the past century. Results show that the spatial variability of IRD deposition throughout the fjord is high, indicating that randomness inherent to IRD distorts the calving signal. However, we investigate whether IRD records can be combined to improve the reconstruction, as previously suggested, and show the importance of core site selection and number of cores on this approach. The outer‐fjord core compares relatively well to the observed front positions and this is reflected in the composite record: increased IRD deposition in 1937–1946, 1968–1980, and 1996–1999 occurred during periods of faster retreat. Comparison with climatic records shows that the calving episodes in the late ‘30 s/early ‘40 s and late ‘90 s are related to warm ocean and air temperatures, whereas intensified retreat and calving during the ‘70 s reflects partly an internal glacier response to the fjord geometry

A 2000-year record of ocean influence on Jakobshavn Isbræ calving activity, based on marine sediment cores

International audienc

Holocene break-up and reestablishment of the Petermann Ice Tongue, Northwest Greenland

Over the last decade, two major calving events of the Petermann Ice Tongue in Northwest Greenland have led to speculation on its future stability and contribution to further Greenland Ice Sheet mass loss. However, it has been unclear if these events are anomalous or typical within the context of limited historical observations. We extend the historical record of the floating ice tongue using the stratigraphy of Petermann Fjord sediments to provide a longer-term perspective. Computed tomography (CT) scans, X-Ray Fluorescence (XRF) scans, Ice-Rafted Debris (IRD) counts, and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites, allowing for reconstructions of past behavior of the Petermann Ice Tongue. Radiocarbon dating of foraminifera, 210Pb, and paleomagnetic secular variation (PSV) provide age control and help to address uncertainties in radiocarbon reservoir ages. A floating ice tongue in Petermann Fjord formed in late glacial time as Petermann Glacier retreated from an advanced grounded position. This paleo-ice tongue broke-up during the early Holocene when high northern latitude summer insolation was higher than present. After gradual regrowth of the ice tongue associated with regional cooling, the ice tongue reached its historical extent only within the last millennium. Little or no ice tongue was present for nearly 5000 years during the middle Holocene, when decadal mean regional temperatures are estimated to be 0.8–2.9 °C higher than preindustrial (1750 CE) and seasonal sea-ice in the Lincoln Sea was reduced. This pre-historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break-up by the mid-21st Century.The Petermann 2015 Expedition (OD1507) and this work was funded by the National Science Foundation Office of Polar Programs (Awards 1418053 to AM and JS, 1417787 to LM, and 1417784 to AJ), the Swedish Polar Research Secretariat, and a Swedish Research Council (VR) grant to MJ. Additional support to BR came from Leslie and Mark Workman at the Oregon ARCS Foundation and a Geological Society of America graduate student research grant

Supplementary_material – Supplemental material for The deglaciation of coastal areas of southeast Greenland

<p>Supplemental material, Supplementary_material for The deglaciation of coastal areas of southeast Greenland by Laurence M Dyke, Anna LC Hughes, Camilla S Andresen, Tavi Murray, John F Hiemstra, Anders A Bjørk and Ángel Rodés in The Holocene</p

Marine sediment data by Greenland marine-terminating glaciers

Source data file with basic with basic Information for all cores, including core positions, mass accumulation rates, and glaciological data for glaciers contributing meltwater to the fjords from where the cores were taken

Wangner_et_al_supplementary_information – Supplemental material for A 2000-year record of ocean influence on Jakobshavn Isbræ calving activity, based on marine sediment cores

<p>Supplemental material, Wangner_et_al_supplementary_information for A 2000-year record of ocean influence on Jakobshavn Isbræ calving activity, based on marine sediment cores by David J Wangner, Anne E Jennings, Flor Vermassen, Laurence M Dyke, Kelly A Hogan, Sabine Schmidt, Kurt H Kjær, Mads F Knudsen and Camilla S Andresen in The Holocene</p