Last Glacial Maximum deep water masses in southwestern Gulf of Mexico: Clues from benthic foraminifera

摘要

The repercussions of climate change during the Last Glacial Maximun (LGM) associated with changes in the structure and chemistry of abyssal waters in the southwestern Gulf of Mexico were studied by numerical analysis of benthic foraminiferal data from three sediment cores (water depth 1988-2735 m). In this context, to better understand the distribution patterns of modern benthic foraminifera in bathyal and abyssal waters of the area, species data from twelve core-tops (water depth 960-3255 m) were also analyzed. Multivariate Q-mode factor analysis separated the modern foraminiferal faunas of the North Atlantic Deep Water (NADW, deeper than ~2000 m), dominated by Nuttallides decorata, Alabaminella turgida, Ioanella tumidula, and Globocassidulina subglobosa, from those of the shallower Subantarctic Intermediate Water (AAIW) and Caribbean Midwater (CMW), characterized by the association of Bolivina lowmani, Bulimina aculeata, Alabaminella turgida, Globocassidulina subglobosa, Epistominella exigua, and E. vitrea. Although most of the species are found in the entire stratigraphic interval studied, detailed examination shows differences between the dominant LGM and Holocene assemblages, which can be traced to climate-related modifications in world ocean circulation in the LGM, particularly those of NADW. During LGM, Alabaminella turgida (a species sensitive to oxygen depletion) along with a group of dissolution-prone species such as Biloculinella irregularis and Cornuloculina inconstans, thrived in the deepest part of the study area, indicating well-oxygenated waters of glacial NADW (GNADW). As the production of GNADW ceased in the Holocene, the deep areas in the Gulf were occupied by the present NADW that contains less oxygen and more CO2. This water mass is more corrosive and precluded the presence of dissolution-prone species during the LGM, except in the most calcium carbonate- and oxygen-rich areas next to the Yucatan platform. Conditions in this area allowed the proliferation of Nuttallides decorata during the Holocene, while the N. decorata and Alabaminella turgida populations decreased in the western Gulf.