Abstract
Greenland ice cores provide excellent evidence of past abrupt climate changes. However, there is no universally accepted theory of how and why these Dansgaard-Oeschger (DO) events occur. Several mechanisms have been proposed to explain DO events, including sea ice, ice shelf buildup, ice sheets, atmospheric circulation, and meltwater changes. DO event temperature reconstructions depend on the stable water isotope ([Formula: see text]O) and nitrogen isotope measurements from Greenland ice cores: interpretation of these measurements holds the key to understanding the nature of DO events. Here, we demonstrate the primary importance of sea ice as a control on Greenland ice core [Formula: see text]O: 95% of the variability in [Formula: see text]O in southern Greenland is explained by DO event sea ice changes. Our suite of DO events, simulated using a general circulation model, accurately captures the amplitude of [Formula: see text]O enrichment during the abrupt DO event onsets. Simulated geographical variability is broadly consistent with available ice core evidence. We find an hitherto unknown sensitivity of the [Formula: see text]O paleothermometer to the magnitude of DO event temperature increase: the change in [Formula: see text]O per Kelvin temperature increase reduces with DO event amplitude. We show that this effect is controlled by precipitation seasonality.
Highlights
Greenland ice cores provide excellent evidence of past abrupt climate changes
DO event temperature reconstructions depend on the stable water isotope (δ18O) and nitrogen isotope measurements from Greenland ice cores: interpretation of these measurements holds the key to understanding the nature of DO events
We demonstrate the primary importance of sea ice as a control on Greenland ice core δ18O: 95% of the variability in δ18O in southern Greenland is explained by DO event sea ice changes
Summary
Lower δ18O–temperature coefficients occur during larger DO events (Fig. 2B) (i.e., we find a strong systematic relationship between the size of the abrupt warming and the paleothermometer coefficient at all Greenland ice core sites) This finding provides support for the idea that the paleothermometer is fundamentally dependent on the change in temperature at high latitude [32]. The seasonal cycle of precipitation and δ18O both change during a DO event; a larger proportion of precipitation falls during colder months under the warmer interstadial climate relative to the cooler stadial climate While these changes are less important in driving the majority of the geographical variability (or intercore differences) in δ18O across Greenland, compared with the pattern of near-Greenland sea ice loss, they are critical for understanding why sea ice controls on ∆δ18O vary so strongly across Greenland. Understanding these two large opposing changes, with distinctly different geographical patterns, is key to understanding Greenland DO δ18O changes
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