Effects of Past Global Change on Life (1995)
Chapter: ABSTRACT
12
Biotic Responses to Temperature and Salinity Changes During Last Deglaciation, Gulf of Mexico
BENJAMIN P. FLOWER and JAMES P. KENNETT
University of California, Santa Barbara
ABSTRACT
Understanding the biotic response to past global change provides insights into past and present Earth systems. Marine sedimentary records of the last deglaciation centered at 11,000 14C years ago (ka) are particularly promising in contributing to understanding and predicting the biotic effects of anthropogenic environmental changes. Fossil assemblages of plankton preserved in marine sediments represent an often underutilized source of paleoenvironmental information. Relative abundances of different species and their morphology vary dynamically in response to environmental change. Numerous studies have exploited the sensitivity of marine plankton assemblages to environmental changes in the last glacial ocean by transforming downcore relative abundances directly into quantitative estimates of surface temperature, salinity, and other parameters.
In some areas with unique oceanographic characteristics, transform functions do not provide reliable surface temperature and salinity estimates during times of great environmental change in the geologic past, so-called "no analog situations." For instance, planktonic foraminiferal assemblages during the last deglaciation in the Gulf of Mexico were influenced considerably by surface water salinities much lower than at present. Detailed oxygen isotopic and faunal analyses of radiometrically dated cores from the Orca Basin, Gulf of Mexico, illustrate the response of planktonic foraminifera to temperature and salinity changes in a marginal basin that amplified deglacial environmental change. Warm-water planktonic foraminifera began to replace cold-water forms in response to early deglacial warming at 14 ka, and the euryhaline form Globigerinoides ruber dominated during an episode of low-salinity meltwater influx into the Gulf of Mexico from 14 to 11.4 ka. Warm-water forms increased in abundance at 13 ka. A brief reappearance of cool species assemblages associated with the last glacial episode documents the presence of Younger Dryas cooling between 11.4 and 10.2 ka in the Gulf of Mexico. Late deglacial
