Sediment reworking on high-latitude continental margins and its implications for palaeoceanographic studies: insights from the Norwegian-Greenland Sea

Abstract

Geological evidence indicates that sediment reworking is common around the continental margins and abyssal depths of the Norwegian-Greenland Sea, a high-latitude setting with glacier-influenced margins. Detailed analysis of 22 cores up to 5 m long, placed in context by accompanying geophysical data including high resolution sub-bottom profiles, swath bathymetry and backscatter maps, indicates that reworking is variable and ranges from debris flows and turbidity currents, to bottom-current activity, as well as iceberg scouring. Reworking by debris flows appears to be restricted mainly to the main trough-mouth fans and sediment slides. Elsewhere, turbidity-current activity frequently dominates, although iceberg ploughing down to 600 m depth and current winnowing assume increasing significance on continental shelves. Reworking in the Norwegian-Greenland Sea reflects variations in ice-sheet dynamics that, in turn, influence the rate of sediment delivery and location of depocentres. Spatial variations in the style of reworking may also reflect the influence of continental slope gradient and bedrock geology on continental shelves. The widespread nature of sediment reworking has important implications for palaeoceanographic investigations in the region, as reworking can result in erosion and disturbance of the sediment column. It is estimated that less than 7% of material delivered to the Norwegian-Greenland Sea since the Late Weichselian is derived from hemipelagic and pelagic sedimentation. This problem is significant where continuous, high-resolution records of hemipelagic and pelagic sedimentation are required, and attempts are made to correlate with other high-resolution proxy records, such as ice cores, at sub-millennial scales. Bioturbation results in the smoothing of high-resolution records and imposes a maximum resolution for sediment-core time-slices of generally 400 years or more. In the Norwegian-Greenland Sea, areas of high sedimentation such as trough-mouth fans or contourite drifts are commonly associated with extensive reworking. Identification of reworking is particularly important where attempts are made to link records of icebergrafted debris to past ice-sheet dynamics, as bottom-current winnowing and mass-flow processes can increase the concentration of coarse-grained iceberg-rafted debris. Such localized accentuation of the iceberg-rafted debris signal may lead to erroneous palaeoenvironmental interpretations. It is therefore critical that palaeoceanographic interpretations are firmly underpinned by an explicit sedimentological assessment of reworking.Sediment reworking on high-latitude continental margins is of two general styles: (1) erosion and deposition by sediment-gravity flow processes and contour/bottom currents, and (2) disturbance or 'smoothing' of the sediment record. The latter may be due to bioturbation, which disturbs the upper part of the sedimentary sequence, and iceberg scouring, which

Seafloor evidence for ice shelf flow across the Alaska–Beaufort margin of the Arctic Ocean

“…The co-existence of the slope gullies with the glacially eroded portion of the ABM (Figures 3, 5, 9 and 10), and their morphological and contextual similarity to gully systems documented on glaciated continental margins around Antarctica (Ó Cofaigh et al, 2003), East Greenland (Ó Cofaigh et al, 2002) and the Gulf of Alaska (Carlson et al, 1990), suggest that the gullies are related to glaciogenic processes. In each of the above localities, ice is inferred to have extended to the continental shelf edge during glacial periods, releasing subglacially entrained sediments and subglacial meltwater where the ice front separated from the seafloor.…”

The role of the cryosphere in source-to-sink systems

“…Relating dynamic ice fluxes (i.e., velocity) to strata formation in glacial S2S systems requires quantification of glacigenic sediment accumulation rates, which depends on resolving the sedimentary record at timescales equal to or better than the characteristic timescale of the ice response in question ( Fig. 2; Cofaigh et al, 2002). This is most easily accomplished in modern temperate, meltwater-dominated glacial systems, because sediment production is elevated and thus signal generation is the strongest, resulting in higher mass fluxes that produce the accumulation rates necessary to resolve the recent or short-timescale ice response function Dowdeswell et al, 1998;Dowdeswell and Siegert, 1999;Jaeger and Nittrouer, 1999a;Jaeger, 2002;Andresen et al, 2012;.…”

“…The most complete record often exists in the marine realm, but this setting is subject to its own internal dynamics that mute terrestrial ice signals, and often results in a record that is overprinted by oceanographic processes and tectonic preconditioning of the basin (Figs. 1 and 2; Cofaigh et al, 2002;Nygård et al, 2005;Reece et al, 2011;Andrews and Vogt, 2014;Walton et al, 2014;Romans et al, 2016-this volume). As such, the sedimentary record associated with both ice flux as well as ice sheet growth and decay can reflect both autogenic and allogenic forcing, complicating our ability to directly relate ice dynamics and sediment production to any particular climatic forcing.…”

“…In addition, the potential for ice to recycle its sedimentary record as it advances and retreats through the transfer zone results in an incomplete record of dynamics closest to the ice, and an integrated record beyond the last ice maximum extent ( Fig. 1; e.g., Faleide et al, 1996;Hebbeln et al, 1998;Anderson, 1999;Cofaigh et al, 2002;Hemming, 2004). The most complete record often exists in the marine realm, but this setting is subject to its own internal dynamics that mute terrestrial ice signals, and often results in a record that is overprinted by oceanographic processes and tectonic preconditioning of the basin (Figs.…”

Introduction: an Atlas of Submarine Glacial Landforms

“…Exceptions include, for example, reworking by deep-water currents and deep-keeled icebergs, and by slides which have remobilized slope sediments at scales ranging from fjord walls to the continental slope (e.g. Ó Cofaigh et al 2002;Haflidason et al 2004;Vanneste et al 2006;Ottesen & Dowdeswell 2009). In fact, many high-latitude shelves contain an almost unmodified set of subglacial and ice-marginal landforms which have been preserved since ice last retreated between 15 and 10 ka ago and are being buried only slowly in ice-distal low-energy interglacial environments (e.g.…”