Southern Ocean dust–climate coupling over the past four million years

Abstract

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles. So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles, providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

“…S2). This new age model is generally in good agreement with the original ages proposed by Venz and Hodell 2002 (65) using benthic δ 18 O stratigraphy (Fig. S3).…”

Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica

“…(ODP Site 1090; Martínez-Garcia et al, 2011) and 41°N in the North Atlantic (IODP Site U1313; Naafs et al, 2010). These subpolar records diverge after ~3.5 Ma and exhibit opposing trends across the large positive δ18O excursion associated with theM2 glacial advance at 3.3 Ma (Lisiecki and Raymo, 2005).…”

“…Pliocene continental configuration overlay from NASA GISS Panoply Data Viewer; SST anomaly data from Dowsett et al (2009). C) SST anomaly of subantarctic Atlantic Site 1090 (Martínez-Garcia et al, 2011), plotted as in panel A. D) AND-1B glacial proximity curve of , plotted against age.…”

“…In its present glaciated state, Antarctica amplifies the Southern Hemisphere meridional thermal gradient, enhancing atmospheric circulation (Lemke et al, 1980;Flohn, 1984;Raphael, 2003) and generating strong, cold winds that contribute to the formation of Antarctic bottom water by cooling surface waters and sustaining sea ice production (Gordon, 2009). Wind intensification may also contribute to an increase in the fertility of Southern Ocean surface waters, by increasing surface circulation and upwelling at frontal zones, and by transporting iron-rich dust from the continents (Martin, 1990;Martínez-Garcia et al, 2011). On geological timescales, polar ice sheets strongly influence regional and global sea level, planetary albedo, continental weathering rates, and ocean and atmospheric chemistry.…”

Orbital variations in planktonic foraminifera assemblages from the Ionian Sea during the Middle Pleistocene Transition

“…Researchers have documented a series of phenomena associated to the MPT: an increase in ice sheet volume, sea surface temperature (SST) cooling in the oceans, variations in the Atlantic Meridional Overturning Circulation (AMOC), a significant drop in the CO 2 atmospheric levels, stronger African and Asian monsoon activity and increased dust deposition in the Southern Ocean (e.g. Ruddimann et al, 1989;Mix et al, 1995;Venz and Hodell, 2002;Hodell et al, 2003;Schefus et al, 2004;Lisiecki and Raymo, 2005;McClymont and Rosell-Melè, 2005;Clark et al, 2006;Sun et al, 2006;Martínez-Garcia et al, 2011).…”