Constructing a 1.5-million-year time series of magmatic and hydrothermal activity at the Juan de Fuca ridge

Ocean ridges are the sites of 80% of Earth’s volcanism. These features emit carbon dioxide and exert an important control on the chemical composition of the oceans through deep sea hot springs. The volcanoes are aligned along the 60,000 kilometer long ocean ridge system, where plates spread apart to create the sea floor.

Studies of these volcanoes have been restricted to recent volcanic activity, because as the plates spread apart the volcanoes are covered by sediment and become inaccessible. For this reason, there is a present day snapshot of ocean ridge volcanism, but little possibility to study how it varies with one of the most important parameters of Earth science—time.

Many aspects of geological phenomena cannot be understood without knowledge of their variations through time, called “time series”. For example, time series of climate show that that Earth passes into and out of ice ages, and that global warming is happening. New discoveries now permit the construction time series for ocean ridges by taking sediment cores along transects perpendicular to ocean ridges.

The cores will be used to study volcanic glass that is preserved in the sediment. In particular, the time series will allow tests of the hypothesis that ice age cycles may influence cycles of ocean ridge volcanism and associated hydrothermal activity. Cruises to the Juan de Fuca ridge just off the coasts of Oregon and Washington will permit time series of one million years or more to be obtained for the first time.

This project will provide support for undergraduate students to participate in the research cruise. In addition, the project will support an international conference and contribute to a museum exhibit at the Harvard Museum of Natural History.

The European Research Council (ERC) has awarded a research grant for the scientific analyses to investigate time-series of ridge processes through a systematic coring program along transects perpendicular to the Juan de Fuca Ridge. The ERC grant to four principle investigators (three at GEOMAR in Germany and one at Harvard) did not include funding for collecting the sediment cores at sea.

This proposal funds the ship time to obtain the necessary samples. A preliminary 11 day leg with the AUV SENTRY will obtain sediment thickness as well as high resolution bathymetry to guide the coring. Then, a 21 day leg will carry out 70 cores on three transects, two to the west of the ridge at different distances from the ridge transform intersection, and one to the east.

The cruise would produce the first continuous, co-registered time series of glass compositions, hydrothermal activity and bathymetry over the 0 to 1Ma time scales. Time-series of basalt and sediment compositions at ocean ridges have been inaccessible because sea floor is rapidly covered by sediment and basalts are altered or have low potassium contents, making dating problematic.

The 104-106-year time scale in particular is central for testing a host of hypotheses for mid-ocean ridges, from the existence and time scales of tectonic/magmatic cycles, to the continuity of magma chambers and hydrothermal systems, to possible relationships between glacial cycles and ridge processes since the Pleistocene. Preliminary data from cores near the ridge axis show that each core is likely to preserve 50-100ka time series of fresh glasses with interesting variations.

Closely spaced cores will be used to obtain overlapping time series with the aim of constructing a long a continuous time series back to one million years. The Juan de Fuca region has the benefit of previous cores that show robust age models are possible. The program includes sediment geochemistry for age models and hydrothermal activity, major and trace elements of glasses, radiogenic isotope analyses, volcanological evaluation, modeling of mantle melting, and quantitative statistical and time-series modeling.

This program holds the promise of opening new frontiers of time and methodology that may have far-reaching implications for the investigation and understanding of ocean ridges. Broader impacts include training multiple graduate students and post-docs in state of the art techniques, education and participation of Harvard undergraduates on the cruises, an international conference on interactions between glacial cycles and solid earth processes, and an exhibit at the Harvard Natural History Museum which receives more than 250,000 visitors per year including many K-12 students.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.