ACCESS NUMBER: 30660-19930 

STUDY TITLE: Historical Reconstruction of Contaminant Loading and Biological 

Responses in the Central Gulf of Mexico Shelf Sediments 

REPORT TITLE: Historical Reconstruction of the Contaminant Loading and Biological 

Responses in the Central Gulf of Mexico Shelf Sediments 

CONTRACT NUMBER(S): 14-35-0001-30660-19930 

SPONSORING OCS REGION: Gulf of Mexico OCS Region 

APPLICABLE PLANNING AREA(S): Central Planning Area 

FISCAL YEAR(S) OF PROJECT FUNDING: FY 1996 $94,417; FY 1997 $103,257; FY 

1998 $55,163; FY 1999 $41750; FY 2000 $57,277; FY 2001 $36,121; FY 2002 

$26,104; FY 2003 $16,414 

COMPLETION DATE OF REPORT: September 2003 

COST(S): $431,587 

PROJECT MANAGER(S): R. Eugene Turner 

AFFILIATION: Louisiana State University 

ADDRESS: Coastal Marine Institute, Louisiana State University, Baton Rouge, 

Louisiana, 70803 

PRINCIPAL INVESTIGATOR(S)*: R. Eugene Turner, Edward B. Overton, Nancy N. 

Rabalais, and Barun K. Sen Gupta 

KEY WORDS: OCS environmental contaminants, trace metals, organics, pesticides, 

foraminifer, pigments 

BACKGROUND: A pervasive, continuing, and confounding feature of the OCS 

Program and continental shelf investigations involves evaluation of the relative 

influences of these oil and gas recovery efforts against a background of regional forcing 

functions, such as riverine sources, climate, and estuarine exchanges that vary 

‘naturally’ and have also changed over decades from landscape-scale influences. The 

question is whether in situ release of contaminants are as significant as the changes 

occurring from landuse changes in the Mississippi River watershed, and can they be 

detected against a background that includes a substantial natural variability. These 

influences complicate estimations of the more localized releases of oil and gas drilling 

and production operations. Whether contaminant releases are significant in terms of 

background or ‘natural’ amounts is an issue complicated by transport and degradation 

processes. 
ACCESS NUMBER: 30660-19930 

OBJECTIVES: Changes in chemical contaminants were documented in the Central 

Gulf of Mexico continental shelf sediments, the biogeochemical signature of ecosystem 

changes found within them and the biological response by the foraminiferal community. 

Changes are placed within the framework of the regional influence of the Mississippi 

River, oil and gas recovery efforts, and the natural variability of the ecosystem. The 

approach was to analyze constituents in dated sediment cores. 

DESCRIPTION: The report is divided into four (4) chapters addressing aspects of 

these questions on this shelf. Our primary analyses are of the constituents in dated 

sediments before mineral recovery activity began up to the mid-1990s. Chapter 2 

examines three main categories of pollutants or bio-indicators: total polycyclic aromatic 

hydrocarbons, or PAHs, (indicative of pyrogenic PAHs), total hopanes (indicative of 

petrogenic PAHs) and total organochlorine pesticides. Chapter 3 documents the 

regional changes in trace metals and in biological materials (carbon, nitrogen, biogenic 

silica) in time and space. Chapter 4 and Chapter 5 examine two different aspects of the 

planktonic record. 

SIGNIFICANT CONCLUSIONS: The distribution of the selected trace metals and 

organic compounds suggests a chronic contaminant loading from the river itself, from oil 

and gas exploration in the Gulf of Mexico, perhaps from natural seeps in the area, and 

the chronological usage of chlorinated agricultural pesticides. The temporal patterns in 

phytoplankton are consistent with the increased accumulation of diatom remnants in 

sediments. The increasing pigments and greater concentrations in areas where 

hypoxia is more likely to occur indicate an increase in eutrophication or a worsening of 

hypoxia or both. No definite relationship could be established between the contaminant 

concentration in sediments and the composition of foraminiferal assemblage. Deformed 

foraminifera, one indicator of extreme chemical pollution, are not present in either of the 

cores. On the other hand, the diversity and relative-abundance changes of foraminiferal 

species fit the model of progressively worsening seasonal hypoxia in the area. 

STUDY RESULTS: Analysis indicate that both OCS development and riverine sources 

exert strong influences on the sediment constituents offshore, and that these influences 

may be independent of one another. 

STUDY PRODUCT(S): Turner, R.E., E.B. Overton, N.N. Rabalais, and B.K. Sen Gupta 

(eds.). 2003. Historical reconstruction of the contaminant loading and biological 

responses in the Central Gulf of Mexico shelf sediments. U.S. Dept. of the Interior, 

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS 

Study MMS 2003-063. 131 pp.