Sack Lunch Seminar (SLS)
SLS - Andrew Rhines (Harvard) - Dynamics and Paleoclimate Implications of the Seasonal Cycle of Accumulation in Central Greenland
| Date |
Time |
Location |
| December 4th, 2013 |
12:10pm-1:00pm |
54-915 |
Abstract:
Greenland has experienced large changes since the last glacial, with its summit warming by ~21C and tripling in annual average accumulation. Observations and paleoclimate simulations show that shifts in accumulation were not due to a simple scaling of the annual cycle, and that in fact the Holocene annual amplitudes are substantially smaller. Using pre-industrial and modern climate simulations, two mechanisms are explored to explain the greater seasonal cycle of accumulation during the glacial: a large scale dynamical response of the North Atlantic storm track to surface boundary conditions, and a regional reduction in atmospheric moisture available during winter due to greater sea ice cover. Moisture source tracking allows us to distinguish between long-range transport related to the storm track and to regional transport from the ocean surface near Greenland. Our results show that while the two mechanisms are intrinsically related, the contribution of each varies significantly with the background climate. With greater sea ice cover and the North Atlantic storm track locked to the topographically-enhanced stationary wave during the glacial, seasonal migration of the sea ice edge becomes relatively important in controlling moisture availability. In contrast, the pre-industrial climate has relatively greater transient eddy activity and is less moisture-limited by sea ice extent, so that accumulation is more strongly related to synoptic variability in the North Atlantic. These results highlight how changes in atmospheric circulation and sea ice together explain the shifts in annual mean and seasonal moisture supply to Greenland.
Based on these results, a temperature calibration is derived for stable water isotopes in the Greenland ice cores that depends on the mean background climate and takes into account changes in seasonality and moisture source. The new calibration compares favorably with independent estimates of the δ-18O-temperature relationship from the last glacial and Holocene.