Catastrophic ice sheet break-up surrounding Baffin Bay coincident with the Younger Dryas and the Oldest Dryas/ Bølling-Allerød interstadial

Abstract

<div> <p>The advance and retreat of the Greenland, Innuitian and Laurentide ice sheets (GIS, IIS, LIS) which surrounded Baffin Bay (West of Greenland) have been studied using numerous methods to gain insight into past ice sheet and ice stream dynamics. However, the exact timings, movements and relationships to climate events are still somewhat debated. Utilising osmium isotopes (<sup>187</sup>Os/<sup>188</sup>Os) as part of a multi-proxy strategy coupled with absolute age models, an enhanced understanding of the palaeoceanography and palaeoglaciology of this region for last ~40 kyrs is presented.</p> </div><div> <p>Carbonate-enriched layers recorded in many cores across Baffin Bay (Baffin Bay detrital carbonate - BBDC) are thought to be sourced from Palaeozoic carbonate rich rocks in the north/north-west of the bay which were covered by the IIS and LIS. Age modelling indicates that core JR175 records BBDC 0 and BBDC 1. Coincident with the BBDC events, hydrogenous <sup>187</sup>Os/<sup>188</sup>Os compositions abruptly become more radiogenic. This suggests that alongside the carbonate delivery from the north of the bay, there is also a radiogenic Os source. Radiogenic Os derives from typically older, continental inputs, such as the Archean/Proterozoic terrains of western Greenland and Baffin Island. The seemingly sudden nature (within 1000 years) of the increase in <sup>187</sup>Os/<sup>188</sup>Os would suggest a catastrophic ice sheet break-up and a period of increased iceberg discharge, or a sudden advance of the glacier outlets closer to the core site from the GIS and/or LIS.These events are also coincident with the Younger Dryas (~12.8 ka BP) and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial (~14.7 ka BP).</p> </div><div> <p>During periods of low carbonate enrichment, the <sup>187</sup>Os/<sup>188</sup>Os values are less radiogenic. We invoke this to be a baseline during lower continental erosion periods and/or iceberg delivery, and more influence of oceanic Os from the Atlantic. Indeed, during the last 10 kyrs, <sup>187</sup>Os/<sup>188</sup>Os values gradually decrease to compositions similar to the present day North Atlantic Ocean (~1.0).  This could represent increased mixing of marine Atlantic waters into Baffin Bay and/or a decrease in sediment delivery from all ice sheets representing the gradual retreat of the ice sheets through the Holocene.</p> </div><div> <p>In summary our data provide further insight into ice sheet advance, retreat, and sediment provenance within Baffin Bay during the past 40 kyrs, suggesting asynchronous behaviour of the surrounding ice sheets during theYounger Dryas and the end of the Oldest Dryas/ beginning of the Bølling–Allerød interstadial.</p> </div>