layer, overlain by a layer of early Crustaceous pelagic sediments. 

 This is in turn overlain by a sequence of strong seismic reflectors 

 thought to be early-to-middle Tertiary turbidites. Pelagic sedimen- 

 tation again dominated the sedimentary sequence of the gulf in Late 

 Miocene and Pliocene time. 



Paleoclimatology and the Paleo-Oceanographic History of the 

 Oceans 



The sediments that accumulate slowly on the floors of the ocean 

 basins provide indications of both the climate and oceanographic 

 conditions present at the time of their deposition. Thus, analyses of 

 the mineralogy, chemical composition, and fossils preserved in the 

 sediments give a valuable insight into the changes that have 

 occurred in the oceans and atmosphere during the last 1 or 2 hundred 

 million years. 



NSF's climate, long-range mapping and prediction (CLIMAP) 

 Program has been examining climatic conditions of the last 700,000 

 years, the period of the most recent ice age on Earth. Using statistical 

 techniques that allow the distribution and relative abundance of 

 fossils in deep-sea sediments to be related to sea-surface 

 temperatures and salinity at their time of deposition, scientists in 

 this program have produced a map of sea-surface temperatures 

 18,000 years ago. This is an important point during the last ice age 

 because it marks the time of most extensive ice cover. This map 

 provides the data needed to reconstruct the climate of the world 

 during the last ice age, because ocean temperatures play an 

 important role in driving atmospheric circulation. Data from this 

 map are being used by atmospheric scientists in numerical models of 

 paleoclimates. 



Temperature distributions in the ocean 18,000 years ago show 

 some striking differences from those of today's ocean. The change in 

 midlatitude regions reaches and sometimes exceeds 10° C. Low 

 latitude changes are about 20° C, and some subtropical areas show 

 no change. There was apprently a marked equatorward displace- 

 ment of oceanographic polar fronts in the North and South Atlantic 

 and South Pacific oceans, but not in the North Pacific. Steepened 

 thermal gradients across these fronts apparently marked the axis of 

 intensified westerly winds in both hemispheres. A zonal band of 

 wind-blown, continentally derived quartz has been found to shift 

 southward during glacial times in response to the changing wind 

 conditions. 



Sediments for the last few hundred thousand years can, for the 

 most part, be obtained with standard coring techniques. To study the 

 climatic history recorded in older sediments, however, drill dores 



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