New evidence for Greenland ice sheet expansion beyond its present shelf break during the Mid-Pleistocene Transition

The possibility of a continuous, kilometre-thick Arctic Ocean ice shelf in the geological past has long intrigued scientists. Yet, fundamental questions surrounding the architecture, timing, and oceanic and climatic consequences of such an ice shelf remain unresolved. A pan-Arctic glaciation model has been inferred primarily from glacial landforms identified on seafloor bathymetric highs and continental shelves, as well as from geochemical proxies found in marine sediment cores.

Subsequent chronological analyses of sediment cores from these eroded regions have suggested that this pan-Arctic Ocean ice shelf developed during Marine Isotope Stage (MIS) 6, approximately 140,000 to 160,000 years ago. In contrast, more recent evidence from the eastern Fram Strait suggests the persistence of marginal sea-ice conditions and recurrent phytoplankton spring blooms across several glacial-interglacial cycles over the last 750,000 years. Nevertheless, an exception appears to occur during MIS 16, a glacial interval between ~670,000 and 620,000 years ago that remains relatively understudied in the Arctic Ocean. During this period, biomarkers indicative of sea ice and primary productivity, and planktic foraminifera are either absent or occur in extremely low concentrations in sediment cores from both the Arctic-Atlantic Gateway and the Nordic Seas. Although the full spatial extent of glacial ice during MIS 16 remains uncertain, it is thought to have rivalled that of the Last Glacial Maximum (LGM) in terms of ice volume. In this study, we present new geomorphological evidence supported by sediment core chronologies for significant Greenland ice sheet expansion during the end of the Mid Pleistocene Transitoin (MPT). The discovery of record-deep ploughmarks, in combination with a grounding zone wedge (GZW) at approximately 800 meters water depth on the Morris Jesup Rise, northeast Greenland, suggests that the Greenland/Innuitian Ice Sheet grew sufficiently to form an ice shelf extending into the central Arctic Ocean – implying an "Antarctification" of Greenland during this extreme glacial phase.