Southern outlet of the Northeast Greenland Ice Stream, NE Greenland: post-Last Glacial Maximum response to climate warming

Abstract

Abstract. The Greenland Ice Sheet (GrIS) responds rapidly to the present climate, therefore, its response to the predicted future warming is of concern. To learn more about this, decoding its behavior during past periods of warmer than present climate is important. However, due to the scarcity of marine studies reconstructing ice sheet conditions on the Northeast Greenland shelf and adjacent fjords including the position of the ice sheet over marine regions, the timing of the deglaciation, and its connection to forcing factors including the Holocene Thermal Maximum (HTM) on NE Greenland remain poorly constrained. This paper aims to use bathymetric data and the analysis of sediment gravity cores to enhance our understanding of ice dynamics of the GrIS near the southern outlet of the Northeast Greenland Ice Stream (NGIS), as well as give insight into the timing of deglaciation and provide a palaeoenvironmental reconstruction of southwestern Dove Bugt and Bessel Fjord since the Last Glacial Maximum (LGM). The swath bathymetry data displayed in this study is the first time the bathymetry for Bessel Fjord has become available. North–south oriented glacial lineations, and the absence of pronounced moraines in southwest Dove Bugt, an inner continental shelf embayment (trough), suggests the southwards and offshore flow of the southern branch of the NGIS, Storstrømmen. Sedimentological data suggests that an ice body, theorized to be the NGIS, may have retreated from the region slightly before ~11.2 ka BP (in the Preboreal period). The seabed morphology of Bessel Fjord, a fjord terminating in southern Dove Bugt, includes numerous basins, separated by thresholds. The position of basin thresholds, which include some recessional moraines, suggest that the GrIS had undergone multiple halts or readvances during deglaciation. A minimum age of 7.2 ka BP is proposed for the retreat of ice to or west of its present-day position in the Bessel Fjord catchment area. This suggests that the GrIS retreated from the marine realm in early Holocene, around the time of the onset of the Holocene Thermal Maximum in this region, a period when the mean July temperature according to Bennike et al., (2008) was at least 2–3 °C higher than at present, and remained at or west of this onshore position for the remainder of the Holocene. The transition from predominantly mud to muddy sand layers in a mid-fjord core at ~4 ka BP may be the result of increased sediment input from nearby and growing ice caps. This shift may suggest that in late Holocene (Meghalayan), a period characterized by a temperature drop to modern values, ice caps in Bessel Fjord fluctuated with greater sensitivity to climatic conditions than the NE sector of the GrIS.