The role of sea-ice in millennial-scale climate variability

Abstract:

Changes in high-latitude sea-ice cover play an important role in many hypotheses regarding the cause of millennial-scale climate variability, mechanisms to impact global climate, and to explain the rapid return from stadial to interstadial conditions. However, clear proxy evidence for a response of high-latitude sea-ice cover to millennial-scale climate variability is, with a few exceptions, lacking. Here I present a novel record of millennial-scale climate variability and sea-ice cover in the Labrador Sea for the last 65 ka. Using the abundance of the sea-ice biomarker IP25, I show that during the early glacial (65-60 ka) sea-ice was absent from the core location, in-line with the present-day situation. As climate cooled, sea ice occasionally influenced the study site. During the LGM sea-ice cover expanded and the sea-ice margin was located close to the core site as shown by the high concentration of IP25. However, the record fails to demonstrate a direct response of sea-ice cover to Heinrich Events, which were clearly identified in the record by a high concentration of ice-rafted debris from the Hudson area. For example, sea-ice cover appears to have retreated during H2 and expanded directly afterwards, opposite to what is expected. These results demonstrate that at least in the Labrador Sea, sea-ice appears insensitive to millennial-scale climate variability, questioning our fundamental understanding of an important component of the climate system and its role in explaining the mechanisms that cause millennial-scale climate variability.