Samples from Ocean Drilling Program Hole 893A were analyzed for paleotemperatures by determining the "Uk37" unsaturation index at about 3 k.y. resolution over the past 162 ka. Values of the unsaturation index at Hole 893A range from 0.415 to 0.696, corresponding to a total range in estimated paleotemperature of 8°C. Most of the variance is paced by the 41 k.y. obliquity cycle, although 100 k.y. eccentricity and 21 k.y. precessional components are present as well. The pattern of alkenone unsaturation indices over time is quite different from that produced by planktonic foraminiferal paleoclimatic proxies. We conclude that the alkenone record approximates the history of sea-surface temperature in the Santa Barbara Basin over the time period studied. Alkenone data suggest that Santa Barbara Basin sea-surface temperatures exceeded present values by about 4° during oxygen isotope Stage 5e. The Younger Dryas event may be represented as a 3° cooling that spanned several k.y. The predominance of the obliquity cycle in inferred glacial-interglacial changes in sea-surface temperature most likely reflects a real divergence of North Pacific sea-surface temperature from the classical picture of glacial-interglacial change based on oxygen isotope analyses. Alkenone abundances in the sediment vary by nearly two orders of magnitude. High abundances coincide with laminated facies, suggesting that oxygen content of basinal waters plays an important role in the preservation of these compounds.
Date of initial receipt: 6 September 1994
Date of acceptance: 13 February 1995
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