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
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
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 have changes in ocean biology
and circulation in the Antarctic contributed to changes
atmospheric carbon dioxide? The lower atmospheric
carbon dioxide content observed for glacial climate intervals is
thought to be a result of increased storage of carbon in the deep
ocean. The Southern Ocean is a region where, today, carbon
rich waters are exposed to the atmosphere and it is hypothesized
that changes in this region cause the increase in deep ocean carbon
storage. We are investigating changes in ocean circulation and
the chemical properties of deep waters that form in this critical
region in order to better evaluate these hypotheses.
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.