SedimentologyMy research is focused on reconstructing past environments using climate proxies preserved in marine sediments. Marine sediments are deposited like pages of a book, carrying information about the world with them to the seafloor. When we collect a sediment core for analysis, we get a history of the earth with the oldest part of the story at the bottom. The first part of translating this story from mud to science begins with understanding how the sediments were transported and deposited.
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Chronostratigraphy
In paleoenvironmental science, as in life, timing really is everything. Knowing when something happened is the first step to figuring out why it happened. To that end I apply a variety of standard and novel techniques, both radioisotopic and geomagnetic, to establish temporal frameworks, or 'chronostratigraphies' for marine environmental records on scales of decades to millions of years. |
Ocean Circulation
In addition to providing a home for whales and recreation for surfers, the ocean is the largest naturally 'active' reservoir of CO2 on the planet. Changes in the rate of deep water formation and/or ventilation of the interior ocean can have a profound impact on the carbon content of the atmosphere, moderating or enhancing the greenhouse effect. Currently, the ocean is absorbing more than 20% of anthropogenic CO2 emissions, although this capacity is decreasing as the oceans warm and become more acidic. Due in part to the high heat capacity of water, ocean circulation is also a highly important to distributing energy from the low latitudes to the poles. I use 14C and other environmental tracers to reconstruct changes in prehistoric ocean ventilation and circulation as well as understand how those changes influence heat distribution and the carbon cycle.
Marine Productivity and Hypoxia
Changes in marine primary productivity fuel the 'biological pump' of carbon into the interior ocean. This process is tremendously efficient, and impacts both on the CO2 content of the atmosphere as well as the level of oxygenation of the interior ocean. Periods of high primary productivity can drive ocean hypoxia, via the respiration of bacteria breaking down large amounts of organic matter sinking to the sea floor. Hypoxia in turn can have a profound effect on marine life, including economically important species such as crab and bottom fish. I use a variety of techniques to understand when periods of ocean hypoxia have occurred in the past and what has caused them.
The ice sheets on both Antarctica and Greenland have 'marine terminating' outlet glaciers, meaning their ice flows all the way to the ocean. The ocean is of course warmer than ice, but the extent to which it is warmer has a profound impact on the stability of the outlet glaciers as well as the larger ice sheets. Rapidly melting ice can in turn introduce sufficient fresh water at high latitudes to disrupt ocean thermohaline circulation. These interactions between the oceans and glacial systems thus influence global heat distribution and the carbon cycle. I study past periods when the ocean dynamically interacted with the surviving ice sheets of Greenland, Antarctica, and the extinct ice sheets of North America, to learn lessons about these feedbacks applicable to future climate change and sea level rise.