Deep ocean storage of heat and CO₂ in the Fram Strait, Arctic Ocean during the last glacial period

The Fram Strait is the only deep gateway between the Arctic Ocean and the Nordic Seas and thus is a key area to study past changes in ocean circulation and the marine carbon cycle. Here, we study deep ocean temperature, δ¹⁸O, carbonate chemistry (i.e., carbonate ion concentration, [CO₃^2-]), and nutrient content in the Fram Strait during the late glacial (35,000-19,000 years BP) and the Holocene based on benthic foraminiferal geochemistry and carbon cycle modelling. Our results indicate a thickening of Atlantic water penetrating into the northern Nordic Seas, forming a subsurface Atlantic intermediate water layer reaching to at least ~2600 m water depth during most of the late glacial period. The recirculating Atlantic layer was characterized by relatively high [CO₃^2-] and low δ¹³C during the late glacial, and provides evidence for a Nordic Seas source to the glacial North Atlantic intermediate water flowing at 2000-3000 m water depth, most likely via the Denmark Strait. In addition, we discuss evidence for enhanced terrestrial carbon input to the Nordic Seas at ~23.5 ka. Comparing our δ¹³C and qualitative [CO₃^2-] records with results of carbon cycle box modelling suggests that the total terrestrial CO₂ release during this carbon input event was low, slow, or directly to the atmosphere.