Modelling the early-Holocene Laurentide Ice Sheet collapse and abrupt climate change: implications for the 8.2 ka event

Recent research suggested that the deglaciation of an ice saddle connecting three ice domes around Hudson Bay ˜8.5 ka produced a large meltwater pulse. The resulting freshwater input to the North Atlantic was proposed as having caused the most pronounced climate change event of the Holocene, the 8.2 ka event. However, modelling experiments focussing on this saddle collapse meltwater and its climatic impact have not yet been carried out. This thesis aims to establish whether such a meltwater pulse could have forced the 8.2 ka event, and if so, to better constrain the pulse through climate and ice sheet modelling.
A series of HadCM3 general circulation model -simulations was performed using idealised freshwater forcing scenarios designed to represent the centennial-length saddle collapse meltwater flux. The simulations demonstrated that the saddle collapse meltwaterwas likely the primary cause of the 8.2 ka event.
An appropriate model setup for simulating early-Holocene Laurentide Ice Sheet evolution was then developed using the BISICLES ice sheet model, and an ensemble of simulations of the period 10–7.5 ka was run. An ice saddle collapse is simulated as part of the deglaciation, and the resulting meltwater pulse is in agreement with the timing of North Atlantic surface freshening signals, but is longer and less pronounced than the forcing used in the HadCM3 scenarios that best matched the climate-proxy data.
The findings suggest that the BISICLES model setup simulates a dynamically realistic meltwater pulse, but there is a mismatch between the simulated pulse and the forcing necessary for reproducing the 8.2 ka event with HadCM3. Future work should further develop the BISICLES model setup as outlined in the thesis in order to refine the constraints of the meltwater pulse. This could allow for using the 8.2 ka event for assessing the sensitivity of general circulation models to ocean circulation perturbations.