The Impact of Bottom Water Temperature on Glacial Retreat and Methane Release in Storfjorden Trough, NW Barents Sea

Abstract:

The Barents Sea is a shelf sea that connects the North Atlantic and Arctic oceans, and is a key area for the study of ocean circulation-ice sheet interactions during the Last Glacial Maximum (LGM), during which the Barents Sea was covered by a 3 km-thick marine-based ice sheet. Release of methane at the seafloor is widespread in the area, and is closely linked to changing pressure and bottom-water temperature (BWT) conditions since the last deglaciation. Here, we study core HH18-1059GC, located in Storfjorden Trough (NW Barents Sea) at 382 m water depth. Our 4.15 m long record spans the last deglaciation through to the Holocene and aligns with other reference cores from the area, allowing comparisons between methane-influenced records and unaffected records. We reconstruct BWTs using Mg/Ca of benthic foraminifera to study the relation between temperature variations, methane release from the seafloor, and glacial retreat. Previous studies show that an increase in BWT can affect both the stability of the ice sheet (through increased sub-surface melting at the grounding line) and methane seepage (via the dissociation of gas hydrates “buried” in the sediment or by changing the position of the gas hydrate stability zone). Our Mg/Ca results show BWTs varied between 5 and 7°C during the last deglaciation, reaching a maximum during Heinrich Event 1 (19-15.6 kyr BP). The BWT decreased and stabilized during the Holocene at ~3°C, except at around 6 kyr BP when the BWT increased to ~5.5°C. Coupled ice-sheet-hydrate stability modeling indicates that the warming events during ~11 kyr BP and ~6 kyr BP accelerated the dissociation of methane hydrates within the sediments, contributing to enhanced methane release at the seafloor.