Source of Earth's 'big chill' discovered

Basu

study published in the August 24 issue of Science finds that water deep underground may double the amount of debris making its way into the seas. Asish Basu, professor of earth and environmental science, conducted the study in collaboration with Robert Poreda, professor of earth and environmental science; Carolyn Dowling, graduate teaching assistant in the Department of Earth and Environmental Science; and researchers from other universities.

The research findings could affect a wide range of scientific applications including study of global climate and the ocean's basic chemistry.

Basu, who has been sampling water and sediments from two of the world's largest rivers--the Ganges and the Brahmaputra of the Indian subcontinent--since the late 1990s, has been piecing together information on an event in Earth's history called the Great Cool-Down, a period 40 million years ago when the global climate changed from the steamy world of the dinosaurs to the cooler world of today and the amount of carbon dioxide gas in the atmosphere dropped significantly.

Coinciding with this cooling period was a consistent change in the ratio of two isotopes of the element strontium in the oceans' water--a change that continues to this day.

"Deep underground in the Bengal Basin, strontium concentration levels in the ground water are approximately 10 times higher than in the Ganges and Brahmaputra river waters," says Basu.

Knowing the speed the water is moving underground, Basu and his team calculated how much strontium could be leached out of the Bengal Basin and into the Indian Ocean. They calculated that about 1.4 times more strontium flows into the ocean through the groundwater than through the rivers above--easily enough to account for the 40 million-year rise.

"This means that we have to re-evaluate the residence times--the time a particular element remains in the ocean water before settling out--of various chemical elements and species," says Basu. "Most current studies on the ocean's chemistry are based on the supposition that the global rivers are the only carriers responsible for bringing in dissolved materials to the oceans. Our study changes that perception permanently."

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