| dc.description.abstract | Since the 1950s, low-oxygen (hypoxic) conditions have developed in the northern Gulf of Mexico (GoM) due to increased nutrient flux from the Mississippi River. Despite the threat hypoxia poses to profitable fisheries and the extensive studies of the Louisiana Shelf, few studies have examined hypoxia on the Texas Shelf. Low-oxygen conditions on the Texas Shelf may be driven by regional processes such as the western migration of freshwater from the Mississippi–Atchafalaya plume, and thus linked to the Mississippi River nutrient fluxes, or driven by local processes like freshwater runoff and, thus, developed independently. Here, I use variation in benthic foraminiferal faunas from 210Pb-dated sedimentary cores to assess the temporal extent and severity of hypoxia on the Texas Shelf over the past ~150 years for comparison with Louisiana Shelf studies. Benthic foraminifera are sensitive to oxygen levels, and assemblages from surface sediments reflect present-day hypoxic conditions near Port Aransas, Texas. I reconstructed oxygenation over the past ~150 years in two sediment cores near Port Aransas using the full faunal assemblages and three benthic foraminiferal oxygenation proxies: the PEB index based upon the relative abundance of three hypoxia-tolerant foraminifers (Pseudononion atlanticum, Epistominella vitrea, and Buliminella morgani), the PEBn index (PEB taxa + Nonionella opima), and the A-E index based upon the relative dominance of Ammonia to Elphidium species. Additionally, I integrated oxygen and carbon isotope measurements performed on Elphidium excavatum, to examine shifts in salinity and organic matter remineralization in the sediments. Here, I found that hypoxic conditions have persisted on the Texas Shelf near Mustang Island since the ~1950s, as indicated by variation in the full faunal assemblages and the foraminiferal indices. Secular increases in hypoxia may be related to Mississippi–Atchafalaya plume however the most extreme hypoxic events may be driven by Nueces River discharge during flooding events. | en |
