US EPA

2496036 

Journal Article 

Tracking past sedimentary records of oxygen depletion in coastal waters: Use of the Ammonia-Elphidium foraminiferal index 

Sen Gupta, BK; Platon, E 

2006 

Yes 

Journal of Coastal Research
ISSN: 0749-0208
EISSN: 1551-5036 

1351-1355 

WOS:000202961500023 

The Ammonia-Elphidium foraminiferal index (A-E index) was first used in 1996 on the Louisiana inner continental shelf as a paleohypoxia tracer in the sedimentary record. This index, based on relative abundances of Ammonia and Elphidium (widespread and well-preserved taxa in coastal sediments), was considered a proxy for oxygen depletion because (1) Ammonia is more tolerant to prolonged oxygen depletion than Elphidium- and (2) the A-E index correlated well with organic carbon in surface sediment. A direct correlation between the A-E index and the level of bottom-water oxygen was found later in an independent study in Long Island Sound. Recent data generated by several workers confirm that the A-E index is a dependable tracer of historical paleohypoxia in coastal areas of rapid sedimentation. In cores taken from 10-30 rn depths in the nor-them Gulf of Mexico, the increasing trend of the A-E index reflects a worsening spring and summer oxygen stress over much of the 20(th) century. In Long Island Sound and Chesapeake Bay, the index traces an increase in hypoxia in water depths <25 m that began in the early 1970s. Overall, present data from the southeastern and eastern U.S. indicate that the A-E index is an excellent tracker of coastal paleohypoxia on a decadal scale (and, in exceptional cases, on an annual scale) when an undisturbed, continuous record of sedimentation is available, and when the effects of possible co-varying factors (e.g. salinity) are minimal. 

hypoxia; paleohypoxia; benthic foraminifera