 2004 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. Geology; October 2004; v. 32; no. 10; p. 909–912; doi: 10.1130/G20709.1; 2 figures; 1 table. 909 Relationship between Antarctic sea ice and southwest African climate during the late Quaternary Jan-Berend W. Stuut Research Center Ocean Margins (RCOM), Universita ¨ t Bremen, Klagenfurterstraße, 28359 Bremen, Germany Xavier Crosta De ´partement Ge ´ ologie et Oce ´ anographie, UMR-CNRS 5805 EPOC, Universite ´ Bordeaux I, Avenue des Faculte ´s, 33405 Talence, France Klaas van der Borg R.J. Van de Graaff Laboratory, Utrecht University, Princetonlaan 4, 3584 CD Utrecht, Netherlands Ralph Schneider De ´partement Ge ´ ologie et Oce ´ anographie, UMR-CNRS 5805 EPOC, Universite ´ Bordeaux I, Avenue des Faculte ´s, 33405 Talence, France ABSTRACT Here we compare late Quaternary southwest African climate records from the west coast of southern Africa (published winter rainfall and trade wind intensity records from a core off the coast of Namibia) to records of Antarctic sea-ice extent. This comparison reveals coherent changes between Antarctic sea-ice extent and the southwest African win- ter rain region since 45 k.y. B.P., with enhanced winter rainfall and trade-wind vigor during periods of increased sea-ice presence. We propose an oceanic and atmospheric coupling between Antarctic sea ice and the winter rainfall zone of southwest Africa that may lead to increased desertification in the region if global warming persists. Keywords: late Quaternary, aridity, trade wind strength, grain size, dust, end-member modeling, sea ice, diatoms. INTRODUCTION The nature of late Quaternary climate var- iability in the southern part of the African con- tinent has been the subject of many studies focusing on terrestrial records from proxy data sources such as dune activity (e.g., Thomas et al., 2000), pollen (Meadows et al., 1996), mi- cromammals (Avery, 1999), and Hyrax mid- dens (Scott and Vogel, 2000). However, con- tinuous continental climate records from the subcontinent are scarce (Meadows, 2001). Eastern South African late Quaternary cli- mate, as inferred from lake sediments, was suggested to vary with precessional (23 k.y.) frequency, showing that the driving mecha- nisms for climate variability in eastern South Africa are most likely tied to changes in the Indian Ocean monsoonal system (Partridge et al., 1997). In contrast, deep-sea sediments re- covered off the coast of Namibia revealed that the driving mechanisms of the southwest Af- rican winter rainfall region probably have to be sought at high latitudes instead, because of a prominent obliquity (41 k.y., Stuut, 2001) signature in the climate records. The present- day major difference between the eastern and western parts of southern Africa is the timing of rainfall. The larger part of southern Africa is characterized by summer rainfall (60% of the mean annual precipitation) from the Indian monsoon (d’Abreton and Tyson, 1994), whereas a small part, along the southwestern coast and the adjacent escarpment, is typified by winter rainfall (70% of the mean annual precipitation, Tyson, 1986). Annual precipi- tation in the winter rainfall zone varies from 2 m in the southern mountains to 50 mm in the Namib Desert. The subhumid Mediter- ranean climate of the southwestern cape has resulted in the distinct Fynbos flora (e.g., Cowling et al., 1997), whereas the dunes of the hyperarid Namib are nearly devoid of vegetation. A very similar sharp north-south precipita- tion gradient can be observed at about the same latitudes in present-day South America, where the winter rainfall area that exists along the coast west of the Andes mountains grades from the extremely wet climate of Patagonia in the south into the hyperarid Atacama Desert in the north (e.g., Lamy et al., 2001). Late Quaternary rainfall variability in western South America is suggested to be related to the latitudinal position and intensity of the southern westerlies, in response to an en- hanced pole-to-equator thermal gradient (Heusser, 1989b; Lamy et al., 2001) and the accompanying enhanced polar vortex (Thompson and Solomon, 2002). On the basis of a conceptual model, Van Zinderen Bakker (1976) proposed a similar mechanism (an ex- panded Antarctic anticyclone causing an equa- torward shift of the westerlies and increased winter precipitation) for late Quaternary southernmost Africa as well. However, be- cause of the fact that the winter rainfall region in southwestern Africa is largely restricted to semiarid to hyperarid climates where terrestri- al proxy data sources are not readily pre- served, evidence from the region to test this model has remained elusive. Here we propose that during the late Qua- ternary, precipitation in the winter rain region of southwestern Africa was ultimately related to Antarctic sea-ice extent via its impact on the latitudinal position of the oceanic and at- mospheric fronts in the Southern Ocean (Fig. 1). We compare two late Quaternary (since 45 ka) sea-ice presence records from sediment cores located south of the Polar Front to a trade-wind intensity and winter rainfall record from a sediment core off southwest Africa (Stuut et al., 2002) (Fig. 2). The sea-ice pres- ence records are derived from a modern ana- logue technique (MAT) applied to fossil dia- tom assemblages from the Southern Ocean (Crosta et al., 1998). Sea-ice extent can be de- duced from sea-ice presence because there is a quasi-linear relationship between sea-ice presence at one location and ice concentration