Nordic Seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum

Jochen Knies,Denizcan Köseoğlu,Patrycja E Jernas,Giuliana Panieri,Martin Klug,Reidulv Bøe,Valérie K Bellec,Leif Rise,Simon T Belt,Nicole Baeten

doi:10.1038/s41467-018-06252-8

Abstract

Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation. During glacial times, the occurrence of polynyas proximal to expansive ice sheets in both hemispheres has been proposed to explain limited ocean ventilation and a habitat requirement for marine and higher-trophic terrestrial fauna. Nonetheless, their existence remains equivocal, not least due to the hitherto paucity of sufficiently characteristic proxy data. Here we demonstrate polynya formation in front of the NW Eurasian ice sheets during the Last Glacial Maximum (LGM), which resulted from katabatic winds blowing seaward of the ice shelves and upwelling of warm, sub-surface Atlantic water. These polynyas sustained ice-sheet build-up, ocean ventilation, and marine productivity in an otherwise glacial Arctic desert. Following the catastrophic meltwater discharge from the collapsing ice sheets at ~17.5 ka BP, polynya formation ceased, marine productivity declined dramatically, and sea ice expanded rapidly to cover the entire Nordic Seas.

Highlights

Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation
In Antarctica, coastal polynyas are inferred to have occurred beyond the glacial ice-sheet margin, with their formation probably enhanced by offshore katabatic winds and amplified further by diurnal tides during the last glacial period and the Holocene[10,11,12]
Since the Barents Sea shelf was fully glaciated during the Last Glacial Maximum (LGM) between 26.5 and 19 ka[18,19,20], the margins were preconditioned for the formation of coastal polynyas

Summary

Introduction

Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation. Apart from their importance for deep water formation, coastal polynyas adjacent to expansive ice sheets are regional moisture sources[11,14,15,16] They are recognized as key sites for enhanced primary and secondary productivity associated with sea-ice controlled seasonal nutrient supply during advance and retreat, and represent oases for higher-trophic life in an otherwise glacial desert[17]. In contrast to previous studies, we propose the existence of an open water corridor in front of the NW Eurasian ice sheet that was controlled, primarily, by a combination of strong katabatic winds blowing seaward off the ice shelves and upwelling of relatively warm intermediate Atlantic water masses This polynya activity along the entire continental margin of the Barents Sea was the ultimate reason for weak (but constant) ocean convection and persistence of higher-trophic life in otherwise heavily sea-ice covered Nordic Seas during the LGM. With the onset of the SBIS deglaciation at ~19.5 ka, biological activity in the polynyas ceased, and stopped when the ice sheet collapsed at ~17.5 ka, triggering the formation of perennial sea ice cover over the entire Nordic Seas as a consequence of extreme freshwater modulation of the surface ocean and significant weakening of the AMOC

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Results

Conclusion