SLS Seminar: Sophie Hines (Caltech)
"The dynamics of abrupt transitions and hysteresis in glacial ocean circulation"
High-latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard-Oeschger (DO) events. These shifts in inferred Northern Hemisphere high-latitude temperature have been linked to changes in Atlantic meridional overturning strength. Ocean overturning circulation is non-linear and models have suggested that it may exist in multiple steady state configurations. A dynamical systems approach to understanding this behavior is to look for hysteresis in the system. We do this using a time-dependent dynamical box model with four density classes and two basins that are linked by a Southern Ocean. The dynamics of the Southern Ocean region explicitly obey residual mean theory. Our model exhibits hysteresis in steady-state basin stratification as a function of North Atlantic Deep Water (NADW) formation strength. The width of the hysteresis is dependent on the relative density of NADW and the extent of sea ice in the Southern Ocean. There is evidence from the Last Glacial Maximum that ocean circulation existed in separated "two-cell" configuration and this has been hypothesized to be the result of Southern Ocean sea ice. We determine circulation configuration in our model as a function of sea ice extent, as well as NADW strength and density.
About the Speaker
Sophie Hines is a paleoceanographer interested in glacial-interglacial climate change and the role of the ocean in major climate transitions. She is working with Jess Adkins, John Eiler, and Andrew Thompson as a graduate student at Caltech. During her PhD, she has been combining precise geochemical measurements on fossil deep-sea corals with simple physical models of the ocean in order to understand changes in ocean circulation in the past.
About the Series
The Atmosphere, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmosphere, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm in 54-915. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.