The impacts of glacial runoff and pCO₂ on centennial-to millennial-scale climate variability during the last glacial cycle

Love, Ryan (2021) The impacts of glacial runoff and pCO₂ on centennial-to millennial-scale climate variability during the last glacial cycle. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Freshwater is hypothesized to have a critical role in previous centennial-to millennial-scale climate variability(CMCV),e.g. Dansgaard Oeschger events, the Younger Dryas, and may play a central role in future climate change as ice sheet and glacier melt accelerates. Similarly, anthropogenic climate change demonstrates the need to understand the impact of carbon dioxide (pCO₂) on climate variability. The relationship between freshwater and rapid climate change in the paleoclimate records has been a subject of intense study, but past approaches have generally relied upon an approximation of freshwater entering the oceans via wide bands in the North Atlantic in `hosing' experiments. This design element of hosing experiments, which supports the relationship between freshwater and climate cooling, artificially amplifies the climate response by introducing freshwater directly over sites of deep water formation. As well, previous studies have yet to characterize the role of either pCO₂ or freshwater on CMCV under appropriate boundary conditions. This thesis explores the impact two likely controls of CMCV, freshwater and pCO₂ concentrations. I achieve this by first determining where coastally released freshwater is transported using an eddy permitting ocean model configured for the the Younger Dryas interval during the last deglaciation. It is found that by explicitly resolving features important for the transport of coastally released freshwater, such as mesoscale eddies, that hosing overestimates the amount of freshwater transported to sites of deepwater formation by 2-4x. Next, using these results I then derive a novel method of freshwater injection, the freshwater fingerprint, and examine the relative climate impact of different freshwater injection distributions. In comparing the fingerprint method against both conventional band hosing and regional injection methods I conclude that the fingerprint methodology allows for emulation of some features of the eddy permitting representation in a coarse resolution coupled climate model. Finally, I examine the impact that pCO₂ and freshwater has on a specific form of CMCV, Dansgaard-Oeschger events during Marine Isotope Stage 3 (MIS3), with boundary conditions consistent with the MIS3 interval. When examining characteristics of CMCV I find that both increasing freshwater and decreasing carbon dioxide levels lead to similar changes in interstadial & stadial durations.

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