Sea-surface temperature reconstructions for the Quaternary western Atlantic

Paleotemperature estimates calculated by the SIMMAX Modern Analog Technique are presented for two gravity cores from the Rio Grande Rise, one from the Brazil Slope, and one from the Ceara Rise. The estimates are based on comparisons between modern and fossil planktonic foraminiferal assemblages and were carried out on samples from Quaternary sediments. Estimated warm-season temperatures from the Rio Grande Rise (at approx. 30° S) range from around 19°C to 24°C, with some coincidence of warm peaks with interglacial stages. The temperature estimates (also warm-season) from the more tropical Brazil Slope (at approx. 8° S) and Ceara Rise (at approx. 4° N) cores are more stable, remaining between 26°C and 28°C throughout most of their lengths. This fairly stable situation in the tropical western Atlantic is interrupted in oxygen isotope stage 6 by a significant drop of 2-3°C in both of these cores. Temperature estimates from the uppermost samples in all cores compare very well to the modern-day measured values. Affinities of some foraminiferal species for warmer or cooler surface temperatures are identified within the temperature range of the examined samples based on their abundance values. Especially notable among the warmer species are, Globorotalia menardii, Globigerinita glutinata, Globigerinoides ruber, and Globigerinoides sacculifer. Species indicative of cooler surface temperatures include Globorotalia inflata, Globigerina bulloides, Neogloboquadrina pachyderma, and Globigerina falconensis. A cluster analysis was carried out to assist in understanding the degree of variation which occurs in the foraminiferal assemblages, and how temperature differences influence the faunal compositions of the samples. It is demonstrated that fairly similar samples may have unexpectedly different estimated temperatures due to small differences in key species and, conversely, quite different assemblages can result in similar or identical temperature estimates which confirms that other parameters than just temperature affect faunal content.