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Does the PEB index respond only to hypoxia in the Mississippi Delta, Gulf of Mexico?

Hal R. Tichenor, Stephen J. Culver, D. Reide Corbett, John P. Walsh and Martin A. Buzas
Does the PEB index respond only to hypoxia in the Mississippi Delta, Gulf of Mexico?
Journal of Foraminiferal Research (January 2016) 46 (1): 48-60


The frequency of anthropogenic seasonal hypoxia on the continental shelf west of the Mississippi Delta (the Louisiana Bight) has increased since the middle of the 20th century. This study applies the PEB index, a proxy for hypoxia, to four approximately 2 m kasten cores taken southwest of Southwest Pass of the Mississippi Delta. The PEB index is defined as the cumulative percent of Protononion atlanticum (=Nonionella atlantica of this study), Nonionella opima, Epistominella vitrea and Buliminella morgani. The PEB index varies little in the shallowest core, KC4 (59 m water depth). Assemblages were strongly dominated by PEB taxa (average 95%), due mainly to the dominance of E. vitrea (average 76%). In core KC3 (75 m), an average PEB value of 84% is also due mainly to E. vitrea (61%). The PEB index of KC3 was consistently higher above 90 cm, a level dated at 1955-1960 ( (super 210) Pb age estimate), and could reflect an increased influence of hypoxia or an increased rate of sediment accumulation associated with delta progradation. A similar trend characterizes core KC2 (87 m). The PEB index is 18% from 240 cm to 140 cm, increasing up core as the abundance of E. vitrea increases, likely due to delta progradation. Other PEB taxa, B. morgani and N. opima, increase in the top 30 cm of the core, probably due to increased hypoxia between 1952 and 1968 ( (super 210) Pb age estimate). Core KC1 (473 m) differed from shallower cores in its higher species diversity. Bolivina lowmani, Cassidulina neocarinata, and Bolivina ordinaria each comprise approximately 15% of assemblages and PEB taxa are rare (average 5%) but increase to 19% in a 30 cm interval attributed to off-shelf transport. We conclude that the PEB index is a useful indicator of anthropogenic hypoxia but dominance of E. vitrea may also be attributable to sedimentological factors related to delta progradation.

ISSN: 0096-1191
EISSN: 1943-264X
Serial Title: Journal of Foraminiferal Research
Serial Volume: 46
Serial Issue: 1
Title: Does the PEB index respond only to hypoxia in the Mississippi Delta, Gulf of Mexico?
Affiliation: East Carolina University, Department of Geological Sciences, Greenville, NC, United States
Pages: 48-60
Published: 201601
Text Language: English
Publisher: Cushman Foundation for Foraminiferal Research, Ithaca, NY, United States
References: 102
Accession Number: 2016-016606
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes 3 appendices; NSF grants OCE-0841092 and OCE-0452166
Illustration Description: illus. incl. 2 tables, sketch map
N28°30'00" - N29°00'00", W90°00'00" - W89°30'00"
Secondary Affiliation: Smithsonian Institution National Museum of Natural History, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Cushman Foundation for Foraminiferal Research. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201609
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