Magnitude of the 8.2 ka event freshwater forcing based on stable isotope modelling and comparison to future Greenland melting

Abstract

The northern hemisphere experienced an abrupt cold event ~ 8200 years ago (the 8.2 ka event) that was triggered by the release of meltwater into the Labrador Sea, and resulting in a weakening of the poleward oceanic heat transport. Although this event has been considered a possible analogue for future ocean circulation changes due to the projected Greenland Ice Sheet (GIS) melting, large uncertainties in the amount and rate of freshwater released during the 8.2 ka event make such a comparison difficult. In this study, we compare sea surface temperatures and oxygen isotope ratios from 28 isotope-enabled model simulations with 35 paleoproxy records to constrain the meltwater released during the 8.2 ka event. Our results suggest that a combination of 5.3 m of meltwater in sea level rise equivalent (SLR) released over a thousand years, with a short intensification over ~ 130 years (an additional 2.2 m of equivalent SLR) due to routing of the Canadian river discharge, best reproduces the proxy anomalies. Our estimate is of the same order of magnitude as projected future GIS melting rates under the high emission scenario RCP8.5.

No Consistent Simulated Trends in the Atlantic Meridional Overturning Circulation for the Past 6,000 Years

“…All the simulations that start in the early Holocene (CCSM3, HadCM3, KCM, and CESM1.2.1) show stronger changes in AMOC prior to 8 ka than afterward. The early Holocene saw the 8.2 ka event with a large amount of meltwater entering into the Labrador Sea (e.g., Barber et al, 1999;Matero et al, 2017) through three possible freshwater sources: the sudden discharge of Lake Agassiz, the altered route of the continental freshwater in the North America due to the Laurentide ice sheet melting, and the continuous retreat of Laurentide ice sheet and meltwater release from 9 to 6 ka BP (Aguiar et al, 2021). However, the different forcings imposed in the simulations (Table 1) mean that only CCSM3 responds directly to a changed meltwater flux.…”

“…is gradual until industrialization and very rapid afterward (He, 2011;Tian et al, 2022). The decaying ice-sheets released meltwater throughout the early Holocene (Argus et al, 2014;Peltier et al, 2015), with an abrupt release into the Labrador Sea during the 8.2 ka event (Aguiar et al, 2021). Reconstructions also show variations in anthropogenic land-use, total solar irradiance (Vieira et al, 2011), and volcanic activity (Kobashi et al, 2017) that was particularly strong at 8.6-8 and 7.5-7 ka BP.…”

A sequence of abrupt climatic fluctuations in the north-eastern Caribbean related to the 8.2 ka event

“…At the end of the last deglaciation, North Atlantic meltwater pulses from the retreating Laurentide ice sheet triggered a chain of oceanic and atmospheric responses including temporary slow-downs or even collapses of the Atlantic Meridional Overturning Circulation (AMOC) and hemispheric-scale alterations of the atmospheric circulation (Dean et al, 2002; Morrill et al, 2013; Thomas et al, 2007). Studying these pronounced meltwater pulses of the past, helps to understand how North Atlantic freshwater influxes affect the ocean-atmosphere coupled system on basin, hemispheric, and near global scales (Aguiar et al, 2021; Alley et al, 1997; Bitz et al, 2007; Carlson, 2010). The so-called 8.2 ka event that lasted up to 150 years was the most pronounced climate anomaly during the Holocene.…”

Southeastern United States Hydroclimate During Holocene Abrupt Climate Events: Evidence From New Stalagmite Isotopic Records From Alabama

“…The possibility that SE US hydroclimate could respond to abrupt climate change resulting from AMOC shifts exists but remains to be examined with empirical observations. The YD (12.9-11.7 ka; Rasmussen et al, 2014), the 8.2 ka (Alley & Ágústsdóttir, 2005) and the Little Ice Age (LIA, CE 1400-1900Matthes, 1939) cooling events are hypothesized to be associated with AMOC slowdown/ shutdown (Aguiar et al, 2021;Alley & Ágústsdóttir, 2005;Broecker et al, 1989;Thomas et al, 2007;Wagner et al, 2013), and they provide a testbed to examine subtropical hydroclimate responses to ocean thermohaline circulation shifts. Paleoclimate and model results support the hypothesis that thermohaline circulation changes triggered the YD and 8.2 ka cooling events (Bard et al, 2000;Lea et al, 2003;LeGrande et al, 2006;Peterson & Haug, 2006;Renssen et al, 2002), and were associated with the LIA (Lund et al, 2006).…”