Abrupt climate variability in the North Atlantic region: Did the icebergs do it?

Monday, 15 December 2014
Stephen Barker1, James Chen2, Xun Gong2, Lukas Jonkers1, Gregor Knorr3 and David J Thornalley4, (1)Cardiff University, Cardiff, CF24, United Kingdom, (2)Cardiff University, Cardiff, United Kingdom, (3)Alfred Wegener Institute, Bremerhaven, Germany, (4)University College London, London, United Kingdom
We present high resolution records of temperature and ice rafted debris over the last ~440Kyr from a sediment core retrieved from the NE Atlantic. Our records reveal that episodes of ice rafting typically occurred after abrupt cooling at the site. Because the site is sensitive to the earliest phases of ice rafting as recorded by other sites across the wider Atlantic, this suggests that icebergs were not the trigger for North Atlantic cold events. Moreover we find a different relationship between cooling and the arrival of rafted ice at a site ~750km to the SE of ours. We suggest that asynchronous cooling between these locations can be explained by the more gradual southward migration of the North Atlantic polar front. We describe a mechanism that can explain the occurrence of abrupt stadial events over Greenland as a non-linear response as regional cooling continues beyond the threshold necessary for sustaining ocean circulation in its ‘warm’ mode with active convection north of Iceland. Thus while the freshwater derived from melting icebergs may provide a positive feedback for enhancing and prolonging stadial conditions, it is probably not the trigger for northern stadial events.