Osterman, L. E., U.S. Geological Survey, St. Petersburg, USA, email@example.com
Poore, R. Z., U.S. Geological Survey, St. Petersburg, USA, firstname.lastname@example.org
Swarzenski, P. W., U.S. Geological Survey, Santa Cruz, USA, email@example.com
1000 YEARS OF RECURRING NATURAL AND ANTHROPOGENIC LOW-OXYGEN WATER ON THE LOUISIANA SHELF, GULF OF MEXICO
Foraminiferal assemblages in 210Pb-dated sediment cores indicate low-oxygen bottom waters have developed seasonally over at least two-thirds of the geographic extent of the modern Louisiana “Dead Zone” since the mid-20th century. Low-oxygen bottom waters linked to anthropogenic activities extended across the Louisiana shelf after ~ 1960 and may have occurred earlier (~ 1920) in nearshore areas. Two gravity-core records indicate that low-oxygen bottom-water conditions on the Louisiana shelf have developed periodically for the last 1000 years. However, the post-1960 low-oxygen bottom-water events are more persistent, longer lasting in either frequency or duration, and impact more of the Louisiana shelf than the earlier low-oxygen bottom-water events. We conclude that the development of low-oxygen bottom waters on the Louisiana shelf is a natural process related to climatically driven variations in precipitation and resulting fluctuations in Mississippi River discharge. The natural system has been significantly modified by human activities during the last 50 to 100 years. The record indicates that modern hypoxia is more severe and more extensive than earlier naturally caused low-oxygen conditions.
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