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The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat. Tidewater glaciers in fjords can advance/retreat independent of climate due to stabilization by sediments at their termini. We show that an Alaskan paleo-ice stream behaved similarly on an open shelf, suggesting that increased sediment flux may delay catastrophic retreat of outlet glaciers in a warming world. [ABSTRACT FROM AUTHOR]

Calving events of Petermann Glacier, northwest Greenland, in 2010 and 2012 reduced the length of its ice tongue by c. 25 km, allowing exploration of newly uncovered seafloor during the Petermann 2015 Expedition. This article presents the results of foraminiferal analysis and environmental data from thirteen surface sediment samples in northern Nares Strait and Petermann Fjord, including beneath the modern ice tongue. This is the first study of living foraminifera beneath an arctic ice tongue and the first modern foraminiferal data from this area. Modern assemblages were studied to constrain species environmental preferences and to improve paleoenvironmental interpretations of foraminiferal assemblages. Sub--ice tongue assemblages differed greatly from those at all other sites, with very low faunal abundances and being dominated by agglutinated fauna, likely reflecting low food supply under the ice tongue. Fjord fauna were comprised of 80 percent or more calcareous species. Notably, Elphidium clavatum is absent beneath the ice tongue although it is dominant in the fjord. Increasing primary productivity associated with the transition to mobile sea ice, diminishing influence of the Petermann Glacier meltwater with distance from the grounding line, and increased influence of south-flowing currents in Nares Strait are the important controls on the faunal assemblages. [ABSTRACT FROM AUTHOR]

Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land. [ABSTRACT FROM AUTHOR]