A SEVERAL CENTURY RECORD OF LOW OXYGEN CONDITIONS FROM A SEDIMENT CORE ON THE LOUISIANA CONTINENTAL SHELF

Hypoxia occurs in continental shelf subsurface waters when the uptake of oxygen by respiration exceeds its resupply. Sediment cores taken from the Louisiana shelf provide a record of hypoxic and low-oxygen conditions during the last few centuries. Our previous work established the use of the relative abundance of three low-oxygen tolerant benthic foraminifers (Pseudononion atlanticum, Epistominella vitrea, and Buliminella morgani) as a proxy for hypoxic conditions, and provided evidence for low-oxygen events that predate the start of extensive use of commercial fertilizer in the Mississippi Basin (~1950). Our research also showed that fluctuations in the amount of these low-oxygen tolerant species between 1817 AD and 1910 AD correspond with increased discharge/flooding events in the Mississippi River drainage.

Our initial record from the Louisiana shelf has been augmented by additional analyses of benthic foraminifers, carbon and nitrogen concentrations, and stable isotope compositions of sedimentary organic matter. Using a sedimentation rate extrapolated from ²¹⁰Pb data in the top 20cm, we have evidence for significant low-oxygen events extending back to around 1700 AD. Our study indicates that hypoxia is a complex natural process that has been altered by human activities.