Modeling Holocene Climate Change

Dr. Anders Carlson

Collaborators:

Gavin Schmidt (NASA GISS, Columbia, U.), Delia Oppo (WHOI), Graduate Student; Allegra LeGrande (NASA GISS, Columbia U.)

This project has multiple components comparing model output with paleoclimate data, specifically oxygen isotopes. We are using the state of the art NASA GISS coupled Atmospheric-Oceanic ModelE which tracks oxygen isotopes to simulate Holocene climate. In particular, we are investigating the influence of the lingering Laurentide Ice Sheet on climate in a 9 ka simulation and the response of the ocean-atmospheric system to the opening of Hudson Bay and the drainage of Glacial Lake Agassiz at 8.4 ka (e.g. Fig. 1).

Fig. 1. The effective climate response in five simulations (with 2.5 and 5 Sv yr of melt water introduced to the Hudson Bay) given a 40% reduction (the ensemble average) in overturning circulation. Only grid boxes with a high (0.5) goodness of fit appear. (a) SAT changes (°C). (b) Precipitation changes(mm day). (c) 18Oprecip anomalies. Increased rainfall and decreased temperature cause 18Oprecip depletions making the structure of 18Oprecip changes (‰) more complicated than either field. (d) Changes in 18Oseawater (‰) show depletion in the North Atlantic due to the depleted melt water and reduced transport of enriched seawater from the subtropics. At 60°N, increased sea ice (or reduced melting) leads to surface water enrichments. (LaGrande et al. (2006))

Other aspects of the project include a 6 ka simulation to look at insolation forcing on climate without ice sheet influences and an accelerated Holocene transient simulation. We are also conducting sensitivity tests of the climate to tropical Pacific (ENSO-like) variability.