Mid Pleistocene climate instability in the subtropical northwestern Atlantic K. Billups a, ⁎ , C. Lindley a,1 , J. Fisler a,2 , P. Martin b a College of Marine and Earth Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 199581, United States b Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, United States Received 21 August 2005; accepted 15 June 2006 Available online 17 October 2006 Abstract We present Globigerinoides ruber, G. sacculifer and Neogloboquadrina dutertrei oxygen isotope records from northwestern subtropical Atlantic Site 1058 spanning the mid Pleistocene (∼ 600 to 400 ka). The high temporal resolution of these records (∼ 800 yr) allows us to compare millennial-scale climate signals during one of the most extreme glacial periods of the Pleistocene (Marine Isotope Stage (MIS) 12) to an earlier, less extreme glacial (MIS 14), as well as to two full interglacial intervals (MIS 13 and MIS 15). We observe excellent agreement in the timing and amplitude of variations between the surface-most dwelling species G. ruber and Northern Hemisphere insolation during the two interglacial periods. There is some expression of Northern Hemisphere insolation during glacial MIS 14; however, during the more extreme glacial MIS 12 Northern Hemisphere insolation patterns are not apparent in any of the planktonic foraminiferal δ 18 O records. Insolation remains relatively high, but δ 18 O values increase toward the characteristic δ 18 O maximum of MIS 12 in all three of the records. On the millennial-scale, all three species display their highest amplitude δ 18 O variations (with a period between 4–6 kyr) during glacial MIS 12. Suborbital-scale variability is also statistically significant during glacial MIS 14, but the amplitude is smaller. These results support hypotheses linking millennial-scale climate fluctuations to the extent of continental glaciation. We propose that the relatively high degree of sea surface instability during one of the most extreme glacial periods of the Pleistocene arises from the competing effects of strong atmospheric winds related to the presence of a large ice sheet to the north and persistently high incident solar radiation during this interval of time. © 2006 Elsevier B.V. All rights reserved. Keywords: Pleistocene; climate instability; subtropical Atlantic; stable oxygen isotopes; planktonic foraminifera 1. Introduction Numerous studies have shown that the more recent of the Pleistocene glacial intervals, those having the characteristic saw-tooth pattern and occurring on time scales of 100 kyr, are associated with high frequency climate variability (Mayewski et al., 1997; Oppo et al., 1998; Chapman and Shackleton, 1998, 1999; McManus et al., 1999; Schulz et al., 1999; Hendy and Kennett, Global and Planetary Change 54 (2006) 251 – 262 www.elsevier.com/locate/gloplacha ⁎ Correspondence author. Tel.: +1 302 6454249; fax: +1 302 645 4007. E-mail address: kbillups@udel.edu (K. Billups). 1 Now at: NOAA, Silver Spring, MD 20903. 2 Now at: Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109. 0921-8181/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gloplacha.2006.06.025