North Atlantic sea-surface temperatures for the last 1.1 million years

Abstract

Summary A 1.2 Ma time series of north-east Atlantic sea-surface temperature (SST) has been assembled from the spliced record of piston core K 708-7 (0.68-0 Ma) and hydraulic piston cores taken in nearby DSDP Hole 552A (1.2–0.68 Ma). A no-analogue fauna precludes making credible SST estimates in the interval 1.2–1.1 Ma, but the record above 1.1 Ma is suitable for SST estimates and related time-series analysis. The amplitude of SST variation is considerably higher in the Brunhes than in the upper Matuyama. This is due both to colder glacial SST minima after 0.85 Ma, and to increasingly warm interglacial SST maxima from 0.7 to 0.4 Ma. The dominant periodicity in the SST signal is centred near 95 000 years; it increases in amplitude by a factor of four from the bottom of the record to the top, with the largest increase occurring between 0.7 and 0.4 Ma. This suggests a relatively gradual evolution of ‘100 000-year’ power over half a million years of the late Quaternary, rather than a single abrupt change at 0.9 Ma. Significant, but progressively smaller, spectral peaks occur at periods of 54 000, 41 000, 31 000, 23 000 and 19 000 years. Both the 54 000-year and 31 000-year signals may be a response to insolation forcing by minor obliquity terms. Long-term δ 18 O records show small responses by the ice sheets at or near these two periods, indicating the probable initial response of the climate system to these insolation rhythms. In-phase relationships between δ 18 O and SST at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag. The mechanism by which such small insolation and ice-volume signals become enhanced in the SST record is not clear.