The role of Northeast Pacific meltwater events in deglacial climate change

Abstract

Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events.

Sediment controls dynamic behavior of a Cordilleran Ice Stream at the Last Glacial Maximum

“…Temperate tidewater glaciers can enhance their stability by building submarine morainal banks at the terminus, which both reduce buoyancy forces and insulate the ice from warm erosive seawater 3,13 . SST began to steadily rise~17 ka, exceeding those previously observed in the LGM 46 ; however, BIS appears to switch from the TGC and begin its terminal retreat earlier, around 17.6 ka cal BP. This timing suggests that the trigger for terminal retreat may be related to rapid sea level rise, increased subglacial meltwater erosion (Fig.…”

Deglacial to Holocene variability in surface water characteristics and major floods in the Beaufort Sea

“…78 and references therein). A recent model simulation suggests that if the Bering Strait partially opened at the start of YD 45 , some of the freshwater from the Northeast Pacific could be transported through the Arctic Ocean to the Nordic seas, contributing to a collapse of the AMOC 78 .…”

A mild Younger Dryas recorded in southeastern Alaska

“…Be ages from the Ahklun Mountains in southern Alaska indicate that glacier culminations occurred in the early and/or middle YD and constrain the age of a late-glacial moraine to 12.52 ± 0.24 yr BP (Young et al 2019), providing further support for climatic amelioration prior to the end of the chronozone. Furthermore, δ 18 O values of planktonic foraminifera from the Gulf of Alaska show the most positive, or coldest, values during the early/mid YD, followed by decreasing values indicative of modest warming until 11,700 cal yr BP, when rapid warming occurs (Praetorius et al 2020).…”

“…Climate during the Younger Dryas (YD) chronozone (~12,900 and~11,700 cal yr BP; Rasmussen et al 2006) is linked to a breakdown of thermohaline circulation in the North Atlantic (Broecker, Peteet, and Rind 1985;Broecker et al 1989), resulting in severe cooling of that region (Broecker, Peteet, and Rind 1985;Bohncke 1993;Isarin and Renssen 1999;Clark et al 2009). Modeling experiments (Mikolajewicz et al 1997;Okumura et al 2009) and foraminiferal oxygen isotope records from the Gulf of Alaska (Praetorius et al 2020) indicate coeval cooling of the North Pacific by both oceanic and atmospheric pathways. Lake records in southeastern Alaska also record cooling that is roughly synchronous with the YD in the North Atlantic (Engstrom, Hansen, and Wright 1990;Hansen and Engstrom 1996).…”