Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Louise Sime / firstname.lastname@example.org / British Antarctic Survey
Co-author: Rachael Rhodes, University of Cambridge;
Peter Hopcroft, University of Bristol;
Understanding of millennial-scale DO variability of the last ice-age remains limited, with no universally accepted theory of how these extremely rapid warming events occur. The Greenland ice core d180 records constitute the archetypal record of abrupt climate variability from the last glacial period. Considerable uncertainty about the relationship between local climate and the ice-core record of d180 remains. Both in terms of the contribution of seasonality changes and the relative importance of remote versus distant environmental controls.
Here, we use modelling of d180 as a tool to help interpret the Greenland ice core records of DO-events. We perform an ensemble of multi-century isotope-enabled simulations with a coupled general circulation model, to investigate the nature of the signal contained in the d180 records. Experiments are set up using an isotope-enabled version of the Hadley Centre HadCM3 model. The set-up of our DO-type simulation to enable emulation of a salt oscillator type DO mechanism, whereby salt is progressively lost to the North Atlantic during stadial periods, and the onset of an abrupt warming when the oscillation occurs, and salt returns to the North Atlantic from the tropical Atlantic and wider global ocean. We run a set of 24 such simulations.
Our modelled d180 increases are in agreement with the magnitude of the measured Greenland ice core abrupt rises in d180. The seasonal cycle of precipitation and d180 do both change during DO event: a substantially larger proportion of precipitation falls over the ice core sites during cold months under the warmer interstadial climate. We find however that changes in precipitation seasonality are not so important in driving the majority of the geographical variability in d180 across Greenland. We also demonstrate that DO sea ice changes have a larger impact on d180 changes, compared to site temperature control.