By Sid Perkins
From Denver, at a meeting of the Geological Society of America
The remains of sediment-dwelling microorganisms beneath periodically oxygen-depleted ocean waters could enable scientists to determine when nearby rivers flooded for extended periods.
Huge areas of anoxic water occur offshore near the mouths of rivers, says Lisa E. Osterman of the U.S. Geological Survey in Reston, Va. These areas often form because the rivers carry large amounts of agricultural fertilizers and other nutrients into the sea, where they fuel immense blooms of algae and other plankton at the ocean’s surface (SN: 6/5/04, p. 360: Dead Waters). When those organisms die and fall to the seafloor, their natural decomposition depletes dissolved oxygen in the water.