Last deglacial abrupt climate changes caused by meltwater pulses in the Labrador Sea

Abstract

Freshwater perturbations are often thought to be associated with abrupt climate changes during the last deglaciation, while many uncertainties remain regarding the exact timing, pathway, mechanism, and influence of meltwater release. Here, we present very well-dated and high-resolution records from the eastern Labrador Sea representing the last 19.000 years, which demonstrate abrupt changes in sea surface characteristics. Four millennial-scale meltwater events have been identified between the last 14.000 and 8.200 years based on independent biomarker proxies and X-ray fluorescence scanning data. These events are characterized by increased sea ice formation and decreased sea surface temperatures which might have occurred within a few decades. We propose these abrupt changes were triggered by meltwater pulsing into the Labrador Sea periodically, resulting from collapse of the Laurentide-Greenland Ice Sheets caused by (sub-)surface ocean warming in the Labrador Sea. Our findings provide more precise information about impact of freshwater forcing on abrupt climate changes, which may help to improve simulations for past and future changes in ocean circulation and climate.

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

“…Despite these caveats, we find our records to be consistent with previous paleoceanographic reconstructions, specifically sea‐ice and WGC reconstructions in the Labrador region (e.g., Limoges et al., 2020; Saini et al., 2020; You et al., 2023) (Figure 6). These will be discussed in Section 4.3.…”

“…These appear to be small and local signals that affected only the Labrador Shelf, as other records from the northeastern Labrador Sea do not record any meltwater pulses (You et al, 2023).…”

“…However, benthic foraminifera are not necessarily a direct indicator for sea ice (Seidenkrantz, 2013), and the more direct sea‐ice proxy IP 25 is thought to provide a more reliable signal. Reconstructions based on IP 25 and dinocysts, from the northwestern and northeastern Labrador Sea, also indicate a reduction in sea ice during this period (Gibb et al., 2015; Saini et al., 2020; You et al., 2023). These findings support our interpretation, however they do not rule out a strong LC and polar water inflow, as indicated by benthic foraminifera (Lochte et al., 2019b).…”

“…(a) Stable benthic oxygen isotopes δ 18 O (Lochte et al., 2019a), (b) Atlantic group of benthic foraminifera (adapted from Lochte et al., 2019b), (c) IP 25 accumulation rates (in μg/cm 2 /Kyr) and (d) P D IP 25 index (this study) all from the Labrador Shelf. (e) IP 25 accumulation rates (in μg/cm 2 /Kyr) and (f) P D IP 25 index from the NW Labrador Sea (You et al., 2023). (g) IP 25 accumulation rates (in μg/cm 2 /Kyr) and (h) P D IP 25 index from the NE Baffin Bay (Limoges et al., 2020; Saini et al., 2020).…”

“…Prior studies have focused on the oceanographic consequences of meltwater events caused by the final melting of the remaining ice sheets on the Canadian landmass. The link between abrupt freshwater events and sea ice has only been studied in the open northeastern Labrador Sea (You et al., 2023). The consequences of the final meltwater pulse around 8.2 Kyr BP from the LIS on sea ice over the Labrador Shelf, that is, within direct influence of the freshwater, is yet unknown.…”