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

Resumen

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.