Surface water temperature changes in the high latitudes of the southern hemisphere over the Last Glacial‐Interglacial Cycle

Abstract

A set of numerical equations is developed to estimate past sea surface temperatures (SST) from fossil Antarctic diatoms. These equations take into account both the biogeographic distribution and experimentally derived silica dissolution. The data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments. Factor analysis of 166 samples (124 Holocene core top and 42 artificial samples) resolved four factors. Three of these factors depend on the water mass distribution (one Subantarctic and two Antarctic assemblages); factor 4 corresponds to a “dissolution assemblage”. Inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of SST over a wide range of biosiliceous dissolution. A transfer function (DTF 166/34/4) is derived from the distribution of these factors versus summer SST. Its standard error is ± 1°C in the −1 to +10 °C summer temperature range. This transfer function is used to estimate SST changes in two southern ocean cores (43°S and 55°S) which cover the last climatic cycle. The time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios. The reconstructed SST records present strong analogies with the air temperature record over Antarctica at the Vostok site, derived from changes in the isotopic ratio of the ice. This similarity may be used to compare the oceanic isotope stratigraphy and the Vostok time scale derived from ice flow model. The oceanic time scale, if taken at face value, would indicate that large changes in ice accumulation rates occurred between warm and cold periods.

Assessing the potential for developing internal diatom‐based transfer functions for Lake Baikal

“…Diatom dissolution in Lake Baikal has a major impact on the composition of species assemblages being incorporated into the sedimentary record (Mackay et al 2000;Ryves et al in press). Nevertheless, transfer functions from dissolved assemblages are still effective tools (e.g., Pichon et al 1992), and work is currently under way to develop ''correction factors'' to provide more realistic quantitative estimates of Lake Baikal diatoms in sedimentary assemblages. Bioturbation may potentially be a problem because of the lake's oxygenated hypolimnion, which allows for diverse (and almost wholly endemic) faunal communities to inhabit the surface sediments.…”

Quaternary surface water temperature estimations: Calibration of a diatom transfer function for the Southern Ocean

“…Rank 1 (r l) presents the ranking method originally proposed by Pichon et al [1987] defining four Rank 3 (r3) avoids the somewhat arbitrary definition of species abundances in rank classes 2 and 3 of the Pichon et al [1987] ranking which depends on the maximum abundance of the individual taxa in the total sample set. An extended stepwise ranking system was carried out by separating the relative abundances in eight fixed abundance classes starting with class 0 (abundances below 0.3%), class 1 (abundances between 0.3% and 1.5%), etc., with every following class comprising the exact double percentage data (e.g., class 2; 1.5%-3%, class 3; 3%-6%; and so on; Table 1).…”

“…In order to overcome statistical problems with the overall dominance of single taxa it was proposed by Pichon et al [1987] to convert the raw diatom counting data according to a stepwise ranking system. This conversion decreases the relative weight of dominant taxa while increasing the relative weight of less abundant taxa.…”

“…This results in increasing the paleoenvironmental significance of all taxa with lower abundances. We also test other stepwise ranking systems, taking into account the possibility of counting errors or contamination of samples and the arbitrarity of the ranking method of Pichon et al [1987].…”

Glaces polaires : variations rapides du climat

“…En Antarctique, le début du ré-chauffement précède la décroissance du volume global des glaces comme l'indique aussi l'évolution des températures océaniques dans l'océan Austral [23]. Au-delà de ces points communs, l'absence de variations climatiques rapides à Vostok aussi bien au niveau de la déglaciation précédente réalisée en une seule étape, que de l'interglaciaire luimême, constitue une différence marquante entre les deux enregistrements.…”