Southern Ocean Dust-Climate Coupling over the Past Four Million Years

Carol Peters ・ High Meadows Environmental Institute


Daniel M. Sigman, Dusenbery Professor of Geological and Geophysical Sciences and PEI associated faculty member, and colleagues publish their research findings in Nature on August 3, 2011: “Southern Ocean Dust-Climate Coupling over the Past Four Million Years” by Alfredo Martínez-Garcia, Antoni Rosell-Melé, Samuel L. Jaccard, Walter Geibert, Daniel M. Sigman and Gerald H. Haug. PEI contacted Professor Sigman to briefly inquire about the significance of the research and important next steps.

PEI: Please explain the findings in the paper “Southern Ocean Dust-Climate Coupling over the Past Four Million Years.”

SIGMAN: The last million years of Earth’s history is distinguished by the periodic occurrence of extremely deep ice ages; ice ages that had come in the previous million years were much more mild, while most other times in the past lack any such periodic cold periods. We now know that, during the recent, extremely deep ice ages, dust input to the vast southern polar ocean was higher than at any other time yet studied. Given that modern southern ocean algae have been shown to be starved of iron, the findings bolster the argument that fertilization of the southern ocean with dust lowered the atmospheric concentration of the greenhouse gas carbon dioxide and thus helped to cause the last pulses of cooling that yielded the deepest ice ages.

PEI: What are the significant implications of these findings?

SIGMAN: It greatly strengthens the case — although it is not definitive proof — that iron fertilization of the ocean has caused past changes in atmospheric CO2 concentration.

PEI: Who will use these research findings?

SIGMAN: Beyond their significance for understanding the ocean and climate in general, these results are important background information for the effort to predict how the environment will change under human activities.

PEI: Please explain the most important next step with respect to this research.

SIGMAN: The critical next step, using methods recently developed at Princeton, is to verify the ocean’s biological response to the increases in dust supply during peak ice ages.



Daniel Sigman, a geochemist and oceanographer, came to the Department of Geosciences as a Harry Hess Postdoctoral Fellow in 1998 and joined the faculty in 2000. He is a member of PEI’s associated faculty, a researcher in the Science Group within the Carbon Mitigation Initiative (CMI) , and a member of the Energy Challenge faculty within PEI’s Grand Challenges Program.

Sigman’s interests are in the environmental dynamics of the biologically-important elements, at scales ranging from single-celled organisms to the global biosphere. His analytical focus is on the isotope ratios of nitrogen, which he uses to investigate the biogeochemistry of modern and ancient environments, the ocean in particular. He also develops and applies geochemical models of the ocean. Sigman has received many awards and honors, including the Macelwane Medal of the American Geophysical Union (2004), the Friedrich Wilhelm Bessel Award of the Alexander von Humboldt Foundation (2004), the National Science Foundation CAREER Award (2005) and a MacArthur Fellowship (2009). He has taught a number of courses for PEI’s Environmental Studies Program, including Climate: Past, Present and Future, Biogeochemistry of the Ocean and Atmosphere , and Biogeochemical Cycles in Earth History: Isotope Geochemistry of the Biologically Important Elements.