Abstract
Abstract. The 8.2 ka event is the most prominent abrupt climate change in the Holocene and is often believed to result from catastrophic drainage of proglacial lakes Agassiz and Ojibway (LAO) that routed through the Hudson Bay and the Labrador Sea into the North Atlantic Ocean, and perturbed Atlantic meridional overturning circulation (MOC). One key assumption of this triggering mechanism is that the LAO freshwater drainage was dispersed over the Labrador Sea. Recent data, however, show no evidence of lowered δ18O values, indicative of low salinity, from the open Labrador Sea around 8.2 ka. Instead, negative δ18O anomalies are found close to the east coast of North America, extending as far south as Cape Hatteras, North Carolina, suggesting that the freshwater drainage may have been confined to a long stretch of continental shelf before fully mixing with North Atlantic Ocean water. Here we conduct a sensitivity study that examines the effects of a southerly drainage route on the 8.2 ka event with the ECBilt-CLIO-VECODE model. Hosing experiments of four routing scenarios, where freshwater was introduced to the Labrador Sea in the northerly route and to three different locations along the southerly route, were performed to investigate the routing effects on model responses. The modeling results show that a southerly drainage route is possible but generally yields reduced climatic consequences in comparison to those of a northerly route. This finding implies that more freshwater would be required for a southerly route than for a northerly route to produce the same climate anomaly. The implicated large amount of LAO drainage for a southerly routing scenario is in line with a recent geophysical modelling study of gravitational effects on sea-level change associated with the 8.2 ka event, which suggests that the volume of drainage might be larger than previously estimated.
Highlights
The 8.2 ka cold event is the largest abrupt climate change over the past 10 000 years documented in the Greenland ice core records (Alley et al, 1997; Kobashi et al, 2007)
The distinct oceanic responses to the R1 and R3 routes are characterized by marked decreases in the strength of meridional overturning circulation (MOC) in the North Atlantic Ocean (Fig. 3a), the GIN Sea (Fig. 3b), and meridional heat transport in the ocean at 30◦ S (Fig. 3c)
The Atlantic MOC strength of R1 route decreases by ∼5 Sv, 8 Sv, and 10 Sv for the 1.03 Sv, 2.06 Sv, and 3.09 Sv freshwater perturbation, respectively (Fig. 3a)
Summary
The 8.2 ka cold event is the largest abrupt climate change over the past 10 000 years documented in the Greenland ice core records (Alley et al, 1997; Kobashi et al, 2007). Proxy records from many parts of the world, the circum-North Atlantic region (e.g., Morrill and Jacobsen, 2005; Hughes et al, 2006; Kerschner et al, 2006; Lutz et al, 2007), suggest that this event has been broadly felt in the Northern Hemisphere. This large, abrupt, and widespread cooling event is often interpreted to result from the outburst of proglacial lakes Agassiz and Ojibway (LAO) that flooded the North Atlantic Ocean with freshwater. High-resolution records from marine archives document rapid changes in both surface and deep oceans concomitant with the catastrophic drainage of LAO (Ellison et al, 2006; Kleiven et al, 2008)
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