Unit Affiliation: Geochemistry, Lamont-Doherty Earth Observatory (LDEO)
Two of the major phenomena on Earth are ice ages and volcanic eruptions. This research addresses the question how these two seemingly unrelated aspects of our planet may influence one another. One causal link between the two is the pressure exerted by ice and the oceans on Earth's interior. Volcanism is sensitive to such changes in pressure. A second causal link occurs because volcanoes are the ultimate source of natural CO2 delivered to the atmosphere, and CO2 has a marked influence on climate. During an ice age cycle, vast quantities of water are transferred between continents and oceans, eliminating thick ice sheets and changing sea level. Melting ice uncorks volcanoes, leading to a pulse of much more active continental volcanism for several thousand years. Glacially induced sea level change should influence how much Earth's interior melts beneath ocean ridges. As sea level rises and falls the amount of melt delivered to make the ocean crust should vary by about ten percent, leading to changes in the thickness of the ocean crust and the depth of the sea floor. This could be the explanation for the undulating topography of the sea floor known as abyssal hills. The changes in volcanism at ocean ridges could also lead to changes in hydrothermal activity that would influence deep sea ecosystems and affect geochemical budgets of the oceans. The large volcanic pulse following de-glaciation could add large amounts of CO2 to the atmosphere, contributing to the rapid warming that occurs at the end of ice ages. Ultimately, a better understanding of the influence of volcanic CO2 emissions on climate could provide an important context for understanding the significance of human CO2 emissions.
To test these potential relationships, we combine novel new observations with quantitative modeling. High resolution maps of the sea floor will provide the bathymetric data to test whether abyssal hills vary with climate cycles. New sediment cores near ocean ridges will reveal whether hydrothermal activity also varies with glacial cycles, and how much it varies. Sampling and analysis of the volcanic rocks of the sea floor will show how melting of Earth's interior varies over time. The sea-going work will take place on two cruises, one on a U.S. oceanographic vessel and the other in collaboration with German investigators. On land, we will collaborate with leading volcanologists from the U.S. Geological Survey to investigate the volcanic signal of Cascades volcanoes over recent glacial cycles. Newly measured ages will constrain the timing of the volcanic response to glaciation. Geochemical analyses will constraint how volcanism responds to glacial changes, and how much CO2 emissions may vary. Modeling work will investigate exactly how changes in ice sheets and sea level cause pressure changes beneath volcanic regions on land and undersea, and generate quantitative models of melting of Earth's interior and how it responds to sea level change. The final aim is an integrated model that links volcanism, CO2 and climate and tests how they may interact with one another over time periods of many glacial cycles.
In essence, we are exploring the coupling between Earth's interior and Earth's climate, perhaps discovering that even the fabric of the ocean floor may be responding to climate change ultimately caused by variations in the amount of solar energy our planet receives, and that glacial cycles are influenced by the pulse of the solid Earth.
DATASETS: This project supported a marine seafloor mapping and sediment coring expedition to the Juan de Fuca Ridge. The mapping data are available through the MGDS data repository: http://www.marine-geo.org/tools/search/entry.php?id=AT26-19
Management of the U.S. Science Support Program (USSSP) associated with the International Ocean Discovery Program (IODP)