• journal_title：The Journal of Foraminiferal Research
• Contributor：Charlotte A. Brunner ; Jennifer M. Beall ; Samuel J. Bentley ; Yoko Furukawa
• Publisher：Cushman Foundation for Foraminiferal Research
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2113/36.2.95
• journal_abbrev：Journal of Foraminiferal Research
• issn：0096-1191
• volume：36
• issue：2
• firstpage：95
• section：Articles

Foraminiferal proxies of hypoxia indicate apparent low oxygen to hypoxic conditions in several hotspots in the Mississippi Bight. The foraminiferal hypoxia proxies, the Ammonia to Elphidium (A/E) index and the Pseudononion-Epistominella-Buliminella (PEB) index, were tabulated from three sets of core tops collected in 1951–1956. Additionally, the oxygenation history of a site near the Balize delta was evaluated over the past one hundred years based on A/E and PEB indices and size distributions of pyrite framboids in a gravity core dated by ²¹⁰Pb geochronology.

The results from the 1950’s core-top collections show apparent, recurrent low-oxygen to hypoxic bottom water on the inner shelf at hotspot locales seaward of the Mississippi-Alabama barrier islands and the eastern distributaries of the Balize delta. Specifically, the A/E index exceeds 90% on the inner shelf seaward of Horn and Dauphin islands, both of the Mississippi-Alabama barrier islands, and a center between Pass à Loutre and Main Pass of the Balize delta. In partial support of these results are reports of present-day low oxygen to hypoxic concentrations in bottom waters associated with seasonally high surface chlorophyll a and seasonal strengthening of a brackish-water cap at these locales. In contrast, the PEB index in core tops suggests good oxygenation at mid-shelf depths >30 m. The PEB index, size distributions of framboidal pyrite, and other indicators in a gravity core 44 km northeast of Pass à Loutre indicate no clear change in conditions over the past century, constraining the seaward extent of the hotspot near the Balize delta.