First evidence from Lake Melville, Canada: Subglacial lake sediments underneath the Laurentide Ice Sheet?

The fjord-type Lake Melville is located in Labrador, Eastern Canada, as part of the Hamilton Inlet System. It is mainly characterised by riverine freshwater influx into its western end and intrusion of saline water from the Labrador Sea through the shallow Rigolet Narrows. Previous studies assumed that the retreating Laurentide Ice Sheet (LIS) caused the deposition of a typical glacial sediment sequence when its margin reached Lake Melville between 10,000 to 8,000 years ago (King, 1985; Syvitski and Lee, 1997). However, as suggested for other sites (e.g. Great Slave Lake; Christoffersen et al., 2008), the up to 400 m thick sediment package might contain pre-deglacial sediment because Lake Melville potentially persisted as a subglacial lake underneath the LIS. Initial measurements and lithological investigations on two selected sediment cores (~14 m and 16 m) recovered during expedition MSM84 (2019) indicate a significant change in lithology and selected sediment-physical parameters within the lowermost two meters. First 14C-dates of gastropod and bivalve remains resulted in a preliminary age model with an extrapolated basal age of ~11.6 ka cal BP, but hence pre-dating the local deglaciation. In accordance with sediment echosounder data, microscopic investigations and first XRF analysis, we assume that these initial findings point at sediment deposition in a subglacial lake environment. In a next step, we aim at significantly improving the age model by considering more 14C-samples from various sediment cores as well as conducting further multi-proxy analyses to test our hypothesis. (Poster)