COSEE-West

Science 3 February 2012: Vol. 335 no. 6068 pp. 520-521 DOI: 10.1126/science.335.6068.520 News Focus Ecology Rebuilding Wetlands by Managing the Muddy Mississippi Carolyn Gramling Coastal managers and scientists have struggled to find ways to restore water flow through the wetlands of the Mississippi delta and bring back the sediment, supply of which has been cut in half by humanmade river channels, levees, and dams intended to control the river and save coastal communities from flooding. The U.S. Army Corps of Engineers opened the Morganza spillway during the 2011 Mississippi River floods to divert floodwaters, which offered a rare opportunity to conduct a large-scale natural experiment in real time. The floodwaters did carry enough sediment to help rebuild the wetlands, but that material didn't always stay where it could do the most good. However, researchers gained valuable insights-including ideas about how spillway design can help produce more targeted sediment deposits, and what volume of flow through the spillways might be required for effective wetland rebuilding.

Abstract Changes in the upwelling and degassing of carbon from the Southern Ocean form one of the leading hypotheses for the cause of glacial-interglacial changes in atmospheric carbon dioxide. We present a 25,000-year-long Southern Ocean radiocarbon record reconstructed from deep-sea corals, which shows radiocarbon-depleted waters during the glacial period and through the early deglaciation. This depletion and associated deep stratification disappeared by ~14.6 ka (thousand years ago), consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a Southern Ocean ventilation event. Given this evidence for carbon exchange in the Southern Ocean, we show that existing deep-ocean radiocarbon records from the glacial period are sufficiently depleted to explain the ~190 per mil drop in atmospheric radiocarbon between ~17 and 14.5 ka.