Binge-purge Heinrich like cyclicity needs water

Abstract:

Layers of Ice-Rafted Debris (IRD) found in sediment cores from the North Atlantic are associated with quasi-periodic episodes of iceberg discharge from the Hudson Bay/Hudson Strait region. Six such so-called Heinrich events (HE) have been identified during the Last Glacial Interval (LGI). Several mechanisms for generating HE have been proposed in the literature. The most widely tested is the internally driven binge-purge model. Such binge-purge cyclicity was shown to occur in 8 out of 10 participating ice sheet models in the ISMIP HEINO model intercomparison (Calov et al., 2010). However, all but one of the participating models used purely Shallow Ice Approximation (SIA) models which are known to be inappropriate for fast ice streams, thus calling into question the validity of the model-based test of this mechanism.

Here we run the 3D glacial systems model (GSM) with an idealized North American geometry and climate representation to simulate Heinrich like Oscillations (HOs). A Latin-Hypercube ensemble of 1000 runs is used to define a high variance subset of base parameter vectors. These vectors are then in turn applied to determine the impact of three different model components: Shallow Shelf Approximation (SSA) ice streams, basal hydrology, and Glacial Isostatic Adjustment (GIA). Preliminary results indicate that when the SSA is used for ice streams (as opposed to the SIA), HOs with appropriate periodicity are suppressed unless basal hydrology is enabled in the model. Furthermore, the inclusion of simple relaxation type GIA in the model can alter the mean period between HOs by several thousand years depending on the chosen relaxation time constant.