Atlantic inflow into the southern Nordic Seas at the onset of the LGM promotes open-ocean conditions and Fennoscandian Ice Sheet growth

the atlantic water inflow into the nordic seas has proven difficult to reconstruct for the last glacial maximum (lgm). at that time, the fennoscandian ice sheet grew potentially to its maximum extent. sea-ice free conditions in the eastern nordic seas have been proposed as an essential moisture source contributing to this build-up. it has been hypothesized that the inflow of warm and saline atlantic surface waters was important for maintaining these seasonally sea-ice free conditions in the nordic seas at that time. however, the difference between a perennially frozen ocean and a seasonally open ocean on ice sheet build-up remains unquantified. here we use, tephra-constrained surface ventilation ages from a network of marine sediment cores and model experiments, to show that atlantic inflow to the southern nordic seas likely occurred predominately via the iceland-faroe atlantic inflow pathway helping to maintain seasonal open waters at the onset of the lgm. using a numerical snow model, we further demonstrate that such open-ocean conditions may have been a factor contributing to the fennoscandian ice sheet growth with a ~150% increase in surface mass balance over norwegian coastal areas, compared to sea-ice covered conditions.

在大冰川极期（lgm）期间，北欧海域的北大西洋水流入问题一直难以重构。当时，芬兰斯堪的纳维亚冰盖可能达到了其最大范围。东北欧海域的海冰无覆盖状态被提议为构成这一增长的重要水分来源。有假设认为，温暖且盐度较高的北大西洋表层水的流入对于当时维持北欧海域的季节性无海冰状态至关重要。然而，在冰盖增长过程中，永久冻结海洋与季节性开放海洋之间的差异尚未得到量化。在本研究中，我们利用由海洋沉积岩心网络和模型实验确定的火山灰约束表面通风年龄，证明了北大西洋水流入南北欧海域很可能主要通过冰岛-法罗群岛北大西洋水流入途径发生，从而有助于在lgm初期维持季节性开放水域。通过数值雪模型，我们进一步表明，这种开放海洋条件可能是导致芬兰斯堪的纳维亚冰盖增长的因素之一，与海冰覆盖条件相比，挪威沿海地区的表面质量平衡增加了约150%。