Late Quaternary Foraminifera From Lower Bathyal and Abyssal Sediments, Gulf of Mexico: A Record of Paleoceanographic Change.

Abstract

Striking late Quaternary surface- and deep-water oceanographic changes and a link to North Atlantic thermohaline circulation are identified by analyses of high-resolution, benthic and planktic foraminiferal census data from the lower bathyal and abyssal Gulf of Mexico (GOM). The recognized environmental, watermass, preservation, and productivity signals reveal a detailed paleoenvironmental and paleoceanographic history. A paleoceanographic model developed for surface and deep waters of the abyssal Gulf describes a four-stage sequence of oceanographic changes from the Last Glacial Maximum (LGM) to the present. Compared to present-day surface waters, those of LGM were nutrient-enriched and had reduced productivity. The influx of glacial meltwater into the Gulf, identified by increases in Globigerinoides ruber and Neogloboquadrina dutertrei, caused a reduction in salinity and an increase in nutrients (leading to higher surface-water productivity), and possibly initiated a period of surface- and bottom-water instability that continued into the middle or late Holocene. Planktic foraminifera do not indicate that GOM surface waters cooled to full-glacial conditions during the Younger Dryas interval. Compositional changes in Gulf Basin Water (GBW) from LGM to the present, with a period of bottom-water instability in between, reflect changing source areas for intermediate- and deep-water formation in the Atlantic. Glacial North Atlantic Intermediate Water (GNAIW), indicated by high relative abundances of the Oridorsalis tener species group, Ioanella tumidula, and Eggerella bradyi, strongly influenced glacial GBW during LGM and most of the Meltwater/Younger Dryas intervals. From the late Holocene to the present, a stronger influence of upper North Atlantic Deep Water (UNADW), indicated by high relative abundances of Cibicides wuellerstorfi, is evident. Between these two intervals, the influence of both GNAIW and UNADW is present, probably reflecting bottom-water reorganization. Relative abundances of several dissolution-prone benthic species (e.g. Biloculinella irregularis, Hoeglundina elegans), and of various dissolution-prone and dissolution-resistant planktic species indicate diminished bottom-water corrosivity during glacial intervals, again reflecting a significant change in GBW.