The significance of Atlantic Water routing in the Nordic Seas: The Holocene perspective

Abstract

The Nordic Seas are a key region for global ocean circulation, crucial in water mass exchange between the North Atlantic and the Arctic oceans, and deepwater formation. The advection of Atlantic Water (AW) to the Nordic Seas is decisive for the oceanography and climate of the region and beyond. Here, we present a set of sedimentary records, including two new cores from the western Nordic Seas to reconstruct the history of AW routing in the Nordic Seas over the Holocene. Our results show that the early Holocene (11.7–8 ka BP) thermal maximum, caused by an ‘overshoot’ of overturning circulation and high insolation, was limited to the eastern Nordic Seas, while the western part remained cold due to the meltwater blocking the spreading of AW. After 8 ka BP, the retreat of the freshwater lid allowed AW to reach the central Greenland Sea, where deep convection developed. After 5 ka BP, the increase in sea-ice export from the Arctic strengthened deep convection, which intensified the westward AW flow. A disruption of convectional activity around 2.7 ka BP, triggered by a minimum in solar activity, caused cooling and expansion of sea ice in the Nordic Seas and might have contributed to a global climatic deterioration. The overturning circulation in the Nordic Seas did not recover to its previous state until the present. We demonstrate that the rate of AW advection into the Nordic Seas alone is not enough to understand the oceanographic evolution of this area and its influence on regional or even global ocean and climate changes. The shifts in AW routing within the Nordic Seas and the rate of deep convection are also important.

Worldwide consequences of a mid-Holocene cooling in the Nordic Seas

“…The Iceland-Scotland Overflow Water flow speed also shows a distinct increase around that time (Hall et al, 2004). This indicates an intensification of the overturning circulation in the Nordic Seas probably related to the end of the widespread meltwater discharge from the Greenland Ice Sheet (GIS) (Seidenkrantz et al, 2012) and the subsequent onset of deep convection in the Greenland Sea (Telesiński et al, 2022;Thornalley et al, 2013). This increase in overturning circulation resulted in subsurface warming observed in the southernmost cores (MD95-2011 and M17730-4) at ~7.5 ka BP.…”

“…These include (Fig. 1) cores MD95-2011 (Risebrobakken et al, 2003), M17730 (Telesiński et al, 2015), M23258 (Sarnthein et al, 2003), MSM5/5-712 (Werner et al, 2013), JM10-330 (Consolaro et al, 2015), MSM5/5-723 (Müller et al, 2012) and OCE2017-GR02 (Telesiński et al, 2022).…”

“…This value was calculated with the Marine Reservoir Correction database (Reimer and Reimer, 2001) and the Marine20 curve (Heaton et al, 2022(Heaton et al, , 2020 using the same whale bones samples as those used by Mangerud et al (2006). For core GR02 no regional correction was used (Devendra et al, 2022;Telesiński et al, 2022).…”

“…Although in the southern records (MD95-2011 and M17730) the increase in N. pachyderma abundance was of lower amplitude than that around 8.2 ka BP, in the Fram Strait records the amplitude was greater and the event was even recorded in core GR02 from the continental slope of NE Greenland, in which the 8.2 ka BP event was absent. It should be kept in mind that the Fram Strait records are based on the >100µm fraction (Consolaro et al, 2018;Telesiński et al, 2022;Werner et al, 2015Werner et al, , 2013, in contrast to the >150µm fraction used in the southern cores (Risebrobakken et al, 2003;Sarnthein et al, 2003;Telesiński et al, 2015).…”

“…This increase in overturning circulation resulted in subsurface warming observed in the southernmost cores (MD95-2011 and M17730-4) at ~7.5 ka BP. However, since the main AW flow has been shifted towards the Greenland Sea (Telesiński et al, 2022), in cores located farther north (M23258-2 and in the Fram Strait), after brief initial warming at 7.8-7.9 ka BP, cooling can be observed starting shortly thereafter. Subsurface water cooling might have triggered or at least enhanced a stepwise sea-ice expansion in the eastern Fram Strait that occurred around 7 ka BP (Fig.…”