High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch

Abstract

Many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr (orbital precession) and 100 kyr during the past 0.5 Myr (refs 1-5), whereas high-latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr (ref. 6). Little is known, however, about tropical climate variability before the mid-Pleistocene transition about 900 kyr ago, which marks the change from a climate dominated by 41-kyr cycles (when ice-age cycles and high-latitude sea surface temperature variations were dictated by changes in the Earth's obliquity) to the more recent 100-kyr cycles of ice ages. Here we analyse alkenones from marine sediments in the eastern equatorial Pacific Ocean to reconstruct sea surface temperatures and marine productivity over the past 1.8 Myr. We find that both records are dominated by the 41-kyr obliquity cycles between 1.8 and 1.2 Myr ago, with a relatively small contribution from orbital precession, and that early Pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial Pacific Ocean. We conclude that during the early Pleistocene epoch, climate variability at our study site must have been determined by high-latitude processes that were driven by orbital obliquity forcing.

The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2

“…Dwyer et al (1995) Changes in other components of the climate system indicate differing sensitivities to the changes in global ice volume and deep-water temperature that occurred during the MPT. The onset of the MPT was accompanied by decreases in sea surface temperatures (SSTs) in the North Atlantic (Ruddiman et al, 1989) and tropical-ocean upwelling regions (Schefus et al, 2004;Liu and Herbert, 2004;McClymont and Rossel-Mele, 2005) and by an increase in African (Tiedemann et al, 1994) and Asian aridity and monsoonal intensity (Clemens et al, 1996;Williams et al, 1997;Sun et al, 2006). The low-frequency component of North Atlantic SSTs and proxies of Asian and African monsoon and aridity also appeared at this time.…”

“…7b) (Liu and Herbert, 2004). In comparison, spectrograms of the two western equatorial Pacific SST records (Liu and Herbert, 2004).…”

“…7b) (Liu and Herbert, 2004). In comparison, spectrograms of the two western equatorial Pacific SST records (Liu and Herbert, 2004). Thick red line is running average of the data, (c) Alkenone record of SSTs (blue line) from the western equatorial Pacific (core MD97-2140, 2102'N) (de Garidel-Thoron et al, 2005).…”

Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

“…Specifically, these high northern latitude changes occur when intensification of the tropical and subtropical upwelling systems and increasing continental aridity have indicated more intense atmospheric circulation after 1.2 Ma [de Menocal, 1995;Durham et al, 2001;Heslop et al, 2002;Liu and Herbert, 2004;Marlow et al, 2000;McClymont and Rosell-Melé, 2005;Medina-Elizalde and Lea, 2005;Xiao and An, 1999]. The changing atmospheric circulation has been linked to an increasing meridional temperature gradient driven by circulation changes in the Southern Hemisphere, specifically by the equatorward migration of the Antarctic circumpolar current after 1.8 Ma [McClymont and Rosell-Melé, 2005;, and/or increased sea ice cover in the Southern Ocean and its effects on the temperature of the upwelling waters [Lee and Poulsen, 2006].…”

“…A shift toward a cooler climate, and the development of larger Northern Hemisphere ice sheets at $0.9 Ma, was accompanied by an increase in the duration and intensity of the glacial cycles from 41 ka to 100 ka by 0.6 Ma: the ''mid-Pleistocene climate transition'' or MPT [Imbrie et al, 1993;Mudelsee and Schulz, 1997]. In the tropics and subtropics, the MPT was marked by intensification of the Trade winds [Durham et al, 2001;Liu and Herbert, 2004;Marlow et al, 2000], Walker circulation [McClymont and Rosell-Melé, 2005;Medina-Elizalde and Lea, 2005], Asian monsoon [Heslop et al, 2002;Xiao and An, 1999], and increasing continental aridity [de Menocal, 1995;Schefuß et al, 2003]. The high latitudes also underwent transformations during the MPT, as indicated by changes in ice sheet size [Clark and Pollard, 1998], the thermohaline circulation [Oppo et al, 1995;Raymo et al, 1990;Schmieder et al, 2000], and variations to the position of the frontal systems associated with the Antarctic Circumpolar Current [Becquey and Gersonde, 2002;Diekmann and Kuhn, 2002;.…”