Fine scale sediment structure and geochemical signature between eastern and western North Atlantic during Heinrich events 1 and 2

Abstract

a b s t r a c tHeinrich iceberg-rafting events 1 and 2 (H1 and H2) in the Labrador Sea are identified by their typical nepheloid-flow deposit sedimentary structure, high bulk carbonate, increase in iceberg-rafted detritus (IRD), and depletion of d18 O in the surface-dwelling foraminifer, Neogloboquadrina pachyderma (s). Hlayers in this region have sedimentological characteristics different than those in the North Atlantic, and are consist of IRD interspersed in pelagic sediments. High resolution 14 C-AMS dates allowed us to delineate the leads and lags in instability between different ice-streams of the former Laurentide icesheet (LIS). Our data suggest that the discharge from the Hudson Strait ice-stream was followed by Cumberland Sound ice-sheet during H1 and H2. New radiogenic isotopes from the ice-proximal and surficial sediments of the greater Hudson Strait region and Labrador Sea H0, H1 and H2 layers suggest that carbonate-rich layers were only derived from Hudson Strait, not Baffin Bay. Fine scale structure of H1 and H2 intervals in Labrador Sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central Labrador Sea. A similar pattern in the structure of H1 and H2 is observed along the western European margin. These findings contrast with North Atlantic H1 and H2 intervals, which are characterized by a peak of carbonate-rich grains, followed by a peak of quartz and volcanic grains. This comparison with North Atlantic and western European margin cores leads us to suggest that the coupling or lack thereof, between the LIS and European ice-sheet, is related to the depositional processes occurring along the margins, as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs. Any significant change in ice-sheet dynamics would be recorded close to the ice-sheet margin, while distal locations would only record extreme events. We hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope/ deep Labrador sites and the Flemish Pass site described in this contribution but requires vigorous testing.Crown

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…Furthermore, have been able to identify at least two sources for the Heinrich layers in the Labrador Sea based on source rock signatures. The complex internal structure of Heinrich events as well as the variability in the sediment source (Tripsanas and Piper, 2008b;Rashid et al, 2012;Roger et al, 2013) indicates a complex series of ice stream catchments and tributary redistribution for each event, which is consistent with the activation of a number of different ice streams (see Section 2.2).…”

“…Numerous studies have also examined potential correlations between LIS IRD events and meltwater and IRD events from other mid-latitude ice streams bordering the North Atlantic (Lekens et al, 2006;, although there is much uncertainty about whether IRD events from the eastern LIS have correlatives from other ice sheets (e.g. Fronval et al 1995;Dowdeswell et al, 1999;Hemming, 2004;Rashid et al, 2012; see also Section 2.7).…”

“…The geographic distribution of IRD depends not only on supply, but also on iceberg melting rates and transport distance, which is further controlled by oceanic and atmospheric temperatures, sea ice, winds, and ocean currents. Because the volume of IRD is not representative of the event, IRD layers from the North Atlantic cannot be used as the sole proxy for rapid and extreme calving events (Rashid et al, 2012). Furthermore, have been able to identify at least two sources for the Heinrich layers in the Labrador Sea based on source rock signatures.…”

Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets

“…6; Kehew et al, 2005;Ross et al, 2011), but has only been reported for a handful of ice streams, compared to type (1) evidence. Similarly, type (5) evidence (IRD) has perhaps been under-utilised in the literature, but can be a powerful constraint on the timing of ice stream operation (Stokes et al, 2005;Rashid et al, 2012).…”

Ice streams in the Laurentide Ice Sheet: a new mapping inventory

“…These have been interpreted to record major collapses of the ice sheet (in which ice streaming appears prominent) with inferred effects on the global climate system (Andrews, 1998;Bond et al, 1992;Heinrich, 1988;Rashid & Piper, 2007;Rashid, Saint-Ange, Barber, Smith, & Devalia, 2012). The growth in the identification of ice streams has been mirrored by attempts to test and refine numerical models of their activity in the LIS (Kaplan, Pfeffer, Sassolas, & Miller, 1999;Marshall & Clarke, 1997;Marshall, Clarke, Dyke, & Fisher, 1996;Pfeffer et al, 1997;Stokes & Tarasov, 2010;Tarasov & Peltier, 2004;Winguth, Mickelson, Colgan, & Laabs, 2004).…”