Search

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. [ABSTRACT FROM AUTHOR]

Reveals that the climate in Greenland during the last interglacial period was characterized by a series of severe cold periods lasting from decades to centuries. Isotope and chemical analyses of the Greenland Ice-Core Project from Summit, Greenland; Effects of future global warming.

Presents a stable-isotope record for the full length of the Greenland Ice-core Proiject Summit ice core. Non-confinement of climate instability to the last glaciation; Saale-Holstein glacial cycle; Delay in the melting of the Saalean ice sheets in America and Eurasia; Rapid reorganization in the climate of the North Atlantic region.

Reveals a record of Earth's climate over the eight past ice ages and their associated interglacial periods from an ice core in Antarctica. Evidence for the past climatic instability of the last glacial cycle; Dome C record; Shift in the pattern of glacial cycles that occurred without changes in the varying seasonal distribution of sunlight that is believed to pace the ice ages.

Discusses what causes ice ages, and other episodes of violent climate change, according to a report by T. Blunier et al in the same issue. Their efforts to cross-date isotope records in ice cores from Greenland and Antarctica to within a few centuries; How they took advantage of the rapid and large swings in the methane concentration of the atmosphere during the last glacial period.