Constraints on Overturning Strength in the North Atlantic during Times of Rapid Climate Change


OCCI Funded Project: 2006

Proposed Research

Understanding how and why Earth’s climate has been punctuated by abrupt shifts between glaciation and deglaciation is a major goal of paleoceanography.  Since the oceans play a critical role in the global climate system, it is essential to know the rate of the world ocean circulation when developing accurate climate models. Determining this rate has been a challenge, because many of the existing approaches have relied on measurement of chemical proxies to infer the rate of circulation.

We have found that fossil deep-sea coral skeletons form a high-resolution directly datable record of the deep ocean. Much like tree rings or ice cores, many species of corals have growth bands that we can count and date. The features of the bands themselves may reflect the condition of the ocean at the time the coral was alive and creating its skeleton. We can look at the thickness of each band to gauge the corals’ growth rate during a given year, giving us a general sense of ocean conditions. We can also conduct complex geochemical analyses to extract more precise information about the ocean, such as temperature or nutrient levels, at the times when the coral bands formed. Coral structures have helped us reconstruct important climate parameters such as the history of sea level change, sea surface temperature, and even storm events.

We collected thousands of samples of cold-water corals from the New England Seamounts (a chain of extinct underwater volcanoes off the New England coast) in three expeditions between 2003 and 2005. By dating the corals, we have found a surprising temporal relationship between the abundance of corals and changes in the circulation of the deep sea. Deep-sea coral populations on the New England Seamounts were abundant near the times at which we know there were major reorganizations in the climate and circulation of the North Atlantic. We do not yet know whether changes in the sea surface environment increased the production of marine life, leading to more food for corals, or whether ocean circulation changes enhanced the dispersal of coral larvae. 

This project aims to develop a method for extracting the ratio of radio-isotopes protactinium and thorium (Pa/Th) from deep sea corals as a dynamic tracer of ocean circulation rates during the last glacial period. This method has the potential to generate a well-dated, high-resolution record of North Atlantic overturning strength over the last 80,000 years that can be used to better understand the interaction between the ocean and climate during abrupt climate change events.