Time-based correlation of biogenic, lithogenic, and authigenic sediment components with anthropogenic inputs in the Gulf of
Mexico NECOP study area
Nelsen, T.A., P. Blackwelder, T. Hood, B. McKee, N. Romer, C. Alvarez-Zarikian, and S. Metz
ABSTRACT
Hypotheses related to variability in seasonal hypoxic conditions, coastal nutrient enhancement, and off-shelf transport of carbon on the
Louisiana continental shelf were tested by characterization of biogenic, lithogenic and authigenic components from two shelf and one
Mississippi Canyon sediment cores, The authigenic-phase glauconite occurs above detection limits only in the core from the hypoxic area. A major increase in glauconite concentration coincident with the onset ((1940) of the increased use of commercial fertilizers in the United States. In the same hypoxic-core, benthic foraminifera species diversity decreases upcore from approximately the turn of the century to the present in a manner concurrent with glauconite and fertilizer increases. A subset of opportunistic benthic foraminifera species, known to become more prominent in stressed environments (i.e. hypoxic), increased upcore from (52% of the total population at core bottom to (90% at core top. These benthic foraminifera population and diversity changes were not apparent on a “control” core outside the area of documented hypoxia. Seaward of the shelf, in the Mississippi Canyon, coincident increases in sediment accumulation rate, percentages of coarse fraction and of organic carbon at core top indicate increased offshelf transport of carbon and other components. Quartz percentages indicate that episodic down-canyon transport has been active to core bottom (prior to the mid 1800s).