Late Pleistocene Eucampia antarctica Abundance Stratigraphy in the Atlantic Sector of the Southern Ocean

Abstract

A stratigraphy based upon abundance changes in the marine diatom Eucampia antarctica (Castr.) Mangin is presented for Late Pleistocene sediments of the Atlantic sector of the Southern Ocean south of the Polar Front. This stratigraphy is directly tied to lithology and concentrations of ice-rafted detritus. We find a positive correlation between E. antarctica abundance, increased ice-rafted detritus, and silty diatomaceous sediment. Low E. antarctica counts are associated with little or no ice-rafted detritus and diatomaceous ooze. Tentative correlation with the oxygen isotope record indicates that low E. antarctica abundances are associated with Oxygen Isotope Stages 1, 5a, 5c, and 5e. Late Pleistocene Eucampia antarctica abundance stratigraphy in the Atlantic sector of the Southern Ocean INTRODUCTION The Antarctic region plays a significant role in the world climate system (Fletcher, 1969). Fletcher pointed out that ice cover in the Southern Ocean influences ocean/atmosphere heat exchange and that yearly variations in ice cover may be important in enhancing the climatic effects of minor changes in global heating. It is therefore important to be able to identify both shortand long-term climatic fluctuations in the Southern Ocean recorded in deep-sea sediments. Central to this theme is the development of high resolution stratigraphic schemes. Since foraminifera and coccoliths are largely absent from high southern latitude sediments, the responsibility for a suitable stratigraphic scheme rests with the radiolarians and diatoms. Regional stratigraphies in the deep-sea sediments based upon abundance changes of individual species (Ericson, 1961; Ericson et al., 1961; Hays et al., 1976; Morley and Hays, 1979) or morphologic changes of selected species [e.g. coiling direction in Globorotalia truncatulinoides (d'Orbigny) (Ericson and Wollin, 1956), size change in Coscinodiscus nodulifer A. Schmidt (Arrhenius, 1952; Burckle and McLaughlin, 1977)] have been used to resolve time intervals of less than 50,000 years. Within the past few years it has been possible to further refine the resolution of some of these stratigraphies by correlating them with the globally synchronous oxygen isotope record (Shackleton and Opdyke, 1973, 1976). Using such an approach, Hays et al. (1976) and Morley and Hays (1979) have resolved time intervals of less than 10,000 years with a stratigraphy based upon changes in abundance of the radiolarian Cycladophora davisiana Ehrenberg. In the Southern Ocean, and particularly south of the Polar Front, a number of diatom species show abundance variations during the Late Pleistocene (unpublished data L.H.B.). These include such well-known forms as Coscinodiscus lentiginosus Janisch, Nitzschia kerguelensis (O'Meara), and Eucampia antarctica (Castr.) Mangin. This paper describes variations in abundance of this latter species which is found in the Antarctic and sub-Antarctic regions of the Southern Ocean and is also a constituent of the displaced diatom flora entrained in the Antarctic Bottom Water (Burckle and Stanton, 1975). Five cores in the South Atlantic were selected for this study (see table 1). Four were located south of the Polar Front and one (V29-105) north of it. Although we have studied E. antarctica abundances in other sectors of the Southern Ocean, we have not yet assured ourselves that the fine details of each abundance curve are indeed correlative around the Antarctic. micropaleontology, vol. 29, no. 1, pp. 6-10, 1983 6 This content downloaded from 157.55.39.45 on Tue, 19 Jul 2016 05:50:29 UTC All use subject to http://about.jstor.org/terms