is believed to be a possible area of active deep convection and 

 water formation. Additional stations were occupied south of the 

 South Scotia Ridge as part of the Islas Orcadas hydrographic 

 section, which crossed the Circumpolar Current at 58°W. 



Description of Circumpolar Current and Polar Front down- 

 stream from Drake Passage to North Scotia Ridge/ Falkland 

 Plateau. Based on available data, e.g., the depth of the salinity 

 maximum core or relatively dynamic topography, the Circum- 

 polar Current may consist of two "cores" of large baroclinic 

 pressure gradients. The northernmost seems to continue down- 

 stream from Drake Passage along the southern flank of the 

 North Scotia Ridge to about 45°W where it crosses this Ridge. 



The southern core seems to meander downstream, probably 

 influenced by bottom topography, and perhaps divides or be- 

 comes diffused within, the central Scotia Sea. Using two vessels, 

 a series of oceanographic sections was occupied across these 

 cores and the Polar Front, from upstream of Drake Passage 

 eastward to about 43 °W. Several of these sections extended 

 far enough south to cross all of the principal baroclinic flow and 

 perhaps to reach the Weddell-Scotia Confluence. These longer 

 sections were intended to ascertain the spatial extent and struc- 

 ture of the apparent double axis of the Circumpolar Current 

 in the western Scotia Sea. 



Principal objectives of this subprogram were to describe 

 the spatial distributions of mass and properties and the relation- 

 ship of the baroclinic current structure to the Polar Front in the 

 Scotia Sea. Knowledge about this relationship within the Ant- 

 arctic Circumpolar Current system may make it possible to 

 trace or monitor spatial configurations of the Current from 

 data obtained only in the upper layer structure (such as using 

 AXBTs from aircraft). If there is a unique relationship between 

 the current axis and polar front, then detailed information on 

 the wavelike form and possible meandering, or even eddy for- 

 mation, of the northern current axis might be obtained without 

 detailed hydrographic surveys. 



Detailed descriptions of Polar Frontal Zone. The Polar 

 Front makes a large meander pattern across the North Scotia 

 Ridge between 46° to 50°W. The most commonly observed 

 position is over a deep passage at 48° to 49°W. This feature 

 is unique in that at no other region around Antartica does the 

 Front take on a north-south orientation, or even reverse direc- 

 tion (from SSE to NNW). The integrity of the front in this 

 region may be severely diminished and the area may be a major 

 source of Antarctic Intermediate Water. Hydrographic survey 

 coverage described the position and structure of the Polar Front 

 in this unusual region. 



STD data taken by Gordon in the Polar Frontal Zone 

 indicate considerable vertical structure in the upper waters. 

 Examination of this structure and the associated temperature- 

 salinity relationships indicate considerable interleaving of water 

 masses in this zone. These structures were mapped over a 

 limited area, using XBT's and STD's from two vessels. 



Future Activities. 



In 1976, the long-term arrays in Drake Passage will be 

 reset along with special deep (4000 m) pressure gauges. At this 

 time, several satellite-tracked drifting buoys will be launched. 

 Also, mixing processes at the Polar Front will be investigated 

 using a high-resolution CTD and Swallow floats. 



Climate: Long-Range Investigation, 

 Mapping, and Prediction (CLIMAP) Study 



CLIMAP research focuses on describing and explaining 

 climatic changes over the last million years. Accurate descrip- 

 tions of climatic change over the time scale will improve the 

 CLIMAP scientists' understanding of transitions between what 

 are considered to be the two stable states of global climate — 

 the ice age and temperate period. These studies will also in- 

 crease knowledge about mechanisms of climatic change by 

 comparing global climatic descriptions derived from sample 

 analyses and those produced by computer models. 



The CLIMAP Study is unique in that analyses of deep-sea 

 sediments are used as the primary source of data. Character- 

 istics that make these sediments good indicators of past climatic 

 conditions are: 



1 ) Their global extent. Studies of other materials — ice cores, 

 glacial moraine deposits, tree rings, and lake and bog sediments 

 — are geographically restricted. The global extent of deep-sea 

 sediments also adds to their value as climatic indicators because 

 of the global exchange of latent and sensible heat between the 

 ocean and the atmosphere, which plays a dominant role in 

 climate. 



2) Their relatively constant rate of accumulation. The contin- 

 uous and relatively constant rate of sediment accumulation im- 

 parts a continuity to the climatic record in sediments. Some 

 sediment records are unbroken for many thousands of years, 

 whereas other records, such as those from tree rings, provide 

 only a record of the continental atmosphere at selected sites 

 for periods extending back 6,000 years. Continuous deep-sea 

 sediment records of the past 100,000 to 1 million years are the 

 standard against which data from ice cores, pollen samples, and 

 moraine deposits are calibrated, and by which terrestrial cli- 

 matic records are seen in true perspective. 



3) Their multivariate character. Deep-sea sediments contain 

 many indicators of past environmental conditions. Interrelation- 

 ships among these indicators make possible a wide range of 

 correlative studies. For example, scores of species of plankton, 

 each responding to different combinations of environmental 

 factors in surface waters, and many benthonic species that re- 

 flect conditions at the sea bottom, are preserved as microfossils 

 in deep-sea sediments. By applying appropriate counting tech- 

 niques and multivariate transfer functions, quantitative esti- 

 mates can be made of water conditions during the life of these 

 organisms. This information is then used in numerical models 

 of paleoclimates. Oxygen isotope ratios preserved in micro- 

 fossil skeletons reflect changes in the global ice column. Min- 

 eral and chemical properties of the sediments are used to 

 determine chemical and physical properties of the water and 

 wind and current patterns. 



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