ALBERT

Description: Biotic gas generation from the degradation of organic carbon in marine sediments supplies and maintains gas hydrates throughout the world’s oceans. In nascent, ultraslow-spreading ocean basins, methane generation can also be abiotic, occurring during the high-temperature (〉200 °C) serpentinization of ultramafic rocks. Here, we report on the evolution of a growing Arctic gas- and gas hydrate–charged sediment drift on oceanic crust in eastern Fram Strait, a tectonically controlled, deep-water gateway between the subpolar North Atlantic and Arctic Oceans. Ultraslow-spreading ridges between northwest Svalbard and northeast Greenland permit the sustained interaction of a mid-ocean ridge transform fault and developing sediment drift, on both young (〈10 Ma) and old (〉10 Ma) oceanic crust, since the late Miocene. Geophysical data image the gas-charged drift and crustal structure and constrain the timing of a major 30 km lateral displacement of the drift across the Molloy transform fault. We describe the buildup of a 2 m.y., long-lived gas hydrate– and free gas–charged drift system on young oceanic crust that may be fed and maintained by a dominantly abiotic methane source. Ultraslow-spreading, sedimented ridge flanks represent a previously unrecognized carbon reservoir for abiotic methane that could supply and maintain deep-water methane hydrate systems throughout the Arctic.

Description: Recent studies have highlighted the dynamic behavior of marine-terminating outlet glaciers over decadal time scales, linked to both atmospheric and oceanic warming. This helps explain episodes of nearly synchronous flow acceleration, thinning, and retreat, but nonclimatic factors such as changes in fjord width and depth, can also induce rapid recession. There is support for these topographic controls on glacier retreat, but there are few long-term records to assess their significance across a population of glaciers over millennial time scales. Here we present retreat chronologies along with topographic data for eight major outlet glaciers that underwent similar climatic forcing during deglaciation of the Fennoscandian Ice Sheet (ca. 18–10 ka). Retreat rates averaged over several millennia (~30 m a –1 ) are less than half those recently observed on modern-day outlet glaciers (〉100 m a –1 ), but deglaciation was punctuated by episodes of more rapid retreat (to ~150 m a –1 ) and readvances. It is significant that phases of rapid retreat were not synchronous between glaciers and most occurred regardless of any obvious atmospheric warming. We interpret this to reflect the complex interplay between external forcing and both topographic (e.g., bathymetry, width) and glaciological factors (e.g., ice catchments) that evolve through time, but conclude that basal overdeepenings in wide fjords induce episodes of rapid retreat (〉100 m a –1 ), further exacerbated by their greater susceptibility to oceanic warming. This complicates attempts to predict the centennial-scale trajectory of outlet glaciers and suggests that modeling the interaction between neighboring catchments and the accurate description of subglacial topography beneath them are priorities for future work.

Description: During the last glacial period large parts of the Arctic, including the Barents Sea, north of Norway and Russia, were covered by ice sheets. Despite several studies indicating that melting occurred beneath much of the Barents Sea ice sheet, very few meltwater-related landforms have been identified. We document ~200 seafloor valleys in the central Barents Sea and interpret them to be tunnel valleys formed by meltwater erosion beneath an ice sheet. This is the first account of widespread networks of tunnel valleys in the Barents Sea, and confirms previous predictions that large parts of the ice sheet were warm based. The tunnel valleys are interpreted to be formed through a combination of steady-state drainage and outburst floods close to the ice margin, as a result of increased melting within a period of rapid climate warming during late deglaciation. This is the first study documenting widespread tunnel valley formation at the northern reaches of a Northern Hemisphere paleo–ice sheet, during advanced deglaciation and beneath a much reduced ice sheet. This indicates that suitable conditions for tunnel valley formation may have occurred more widely than previously reported, and emphasizes the need to properly incorporate hydrological processes in current efforts to model ice sheet response to climate warming. This study provides valuable empirical data, to which modeling results can be compared.