Current Research Areas

In our research group we seek to understand how ocean circulation has changed in the past, and how these changes relate to climate.  We have focused our work on the last glacial cycle (100,000 years) looking at changes that occur on timescales from decades to tens of thousands of years.  Some of the particular questions that have interested us are:

What was the state of the ocean circulation during the Last Glacial Maximum?  A good test of the coupled ocean-atmosphere models that are used to predict future climate is their ability to replicate past climate conditions.  The Last Glacial Maximum (LGM) is a time in the relatively recent past when atmospheric carbon dioxide concentrations were significantly lower than today.  When forced with LGM boundary conditions these models produce different circulation states, some with a weaker or shallower overturning circulation in the Atlantic Ocean and some with a strong and deeply penetrating deepwater cell.  Our paleoclimate reconstructions can help to discern which models are simulating the LGM more accurately.
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How are changes in Atlantic Ocean circulation related to abrupt climate change?  During the last ice age and on the transition out of the ice age there have been abrupt (decades or less) and large (almost modern to almost glacial) shifts in climate.  The leading hypothesis is that they result from changes in the Atlantic Ocean Circulation which carries heat from north to south.  Our reconstructions aim to document whether the hypothesized circulation changes happened in concert with abrupt climate changes.
 
How has the Tropical Pacific Ocean Climate System changed with time?  The power of the tropical Pacific to influence weather patterns around the world on interannual time scales (El Nino) is well documented.  Not as well documented is how this system has changed through time in response to changes in climate forcing such as the presence of large ice sheets, atmospheric carbon dioxide concentrations and changes in deep water circulation patterns.

How has the Antarctic Circumpolar Current changed?  Changes in the Antarctic Ocean circulation are thought to be responsible, in part, for the lower atmospheric carbon dioxide concentrations during glacial times.  We aim to understand how the density structure of the Southern Ocean responds to changes in the overlying winds, and how these changes may impact atmospheric carbon dioxide levels.
 
The behavior of the ocean and climate before the historic period has to be inferred from natural archives.  We make most of our climate reconstructions by performing analyses on marine sediments.   We perform chemical and isotopic analyses of the shells of single celled organisms called foraminifera in order to reconstruct seawater temperature, density and nutrient concentrations.  The analyses on planktonic foraminifera tell us about conditions in the upper ocean where they live.  Benthic foraminifera live on the sea floor and the composition of their shells reflects the deep water in which they calcify.
 
For more detailed information about our research please see the publications page.
 
Our research takes advantage of the breadth of climate, paleoclimate and geochemical programs and facilities at the School of Earth and Atmospheric Sciences.  Our lab is equipped with a MAT253 mass spectrometer with a Kiel Device for the automated measurement of oxygen and carbon isotopes on carbonate samples.

I welcome inquiries about undergraduate, graduate student and post-doctoral research opportunities.