Insolation vs. meltwater control of productivity and sea surface conditions off SW Greenland during the Holocene

Abstract

We address here the specific timing and amplitude of sea-surface conditions and productivity changes off SW Greenland, northern Labrador Sea, in response to the high deglacial meltwater rates, the Early Holocene maximum insolation and Neoglacial cooling. Dinocyst assemblages from sediment cores collected off Nuuk were used to set up quantitative records of sea ice cover, seasonal sea-surface temperature (SST), salinity (SSS), and primary productivity, with a centennial to millennial scale resolution. Until~10 ka BP, ice-proximal conditions are suggested by the quasi-exclusive dominance of heterotrophic taxa and low dinocyst concentrations. At about 10 ka BP, an increase in species diversity and abundance of phototrophic taxa marks the onset of interglacial conditions at a regional scale, with summer SST reaching up to 10°C between 8 and 5 ka BP, thus in phase with the Holocene Thermal Maximum as recorded in the southern Greenlandic areas/northern Labrador Sea. During this interval, low SSS but high productivity prevailed in response to high meltwater discharge and nutrient inputs from the Greenland Ice Sheet. After~5 ka BP, a decrease in phototrophic taxa marks a two-step cooling of surface waters. The first started at~5 ka BP, and the second at~3 ka BP, with a shift toward colder conditions and higher SSS suggesting reduced meltwater discharge during the Neoglacial. This second step coincides with the disappearance of the Saqqaq culture. The gap in human occupation in west Greenland, between the Dorset and the Norse settlements from 2000 to 1000 years BP, might be linked to high amplitude and high frequency variability of ocean and climate conditions.

Holocene variability in sea‐ice conditions in the eastern Baffin Bay‐Labrador Sea – A north–south biomarker transect study

“…Dinocyst‐based reconstructions in the nearby core SA13‐ST3 also indicate a slight decrease in summer primary productivity in this interval (Allan et al . 2021), in agreement with our study. Moros et al .…”

“…Based on dinocyst reconstructions in the vicinity (core SA13‐ST3), Allan et al . (2021) have reported generally low sea ice cover (<6 months per year) in the last 11 ka BP (Fig. 5B), possibly in winter months only.…”

“…2013; Allan et al . 2021), cores CC04 and CC70 (Gibb et al . 2015), and core MSM45‐19‐2 (Lochte et al .…”

“…5B), Allan et al . (2021) have reported the subsurface conditions as characterized by a slight decrease in (winter) SIC (<4 months per year) and a variably high summer primary productivity. Overall, this may indicate persistent warm subsurface conditions in this area corresponding to the final stage of the HTM.…”

Biomarker Records of Environmental Shifts on the Labrador Shelf During the Holocene

“…On the one hand, relatively warm conditions, associated with the HTM, have been found for the interval between 6.2 and 3 Kyr BP, air temperatures over Greenland remain relatively warm (Figure 7; Alley et al., 2010), warm SSTs are also reported from Baffin Bay (Allan et al., 2021; Levac, 2001) and sea ice is reported to decrease in eastern Baffin Bay (Saini et al., 2022). On the other hand, our findings indicate a cooling and increased seasonal sea ice, based on IP 25 concentrations, on the Labrador Shelf.…”