Planktic foraminifera from the southwestern Atlantic (30°-60°S): Species-specific patterns in the upper 50 m
Planktic foraminifers were studied in 96 samples collected in the southwestern Atlantic (30°-60°S, along 53°W) in November 1993, mainly from depths between 0 and 50 m. Very high proportions of juveniles (unidentified) were present throughout the area, especially north of 37°S, where they accounted f...
| Main Authors: | , |
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| Language: | unknown |
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1996
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| Online Access: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_03778398_v28_n1_p53_Boltovskoy https://hdl.handle.net/20.500.12110/paper_03778398_v28_n1_p53_Boltovskoy |
| Summary: | Planktic foraminifers were studied in 96 samples collected in the southwestern Atlantic (30°-60°S, along 53°W) in November 1993, mainly from depths between 0 and 50 m. Very high proportions of juveniles (unidentified) were present throughout the area, especially north of 37°S, where they accounted for up to 70-80% of all shells recorded. For most species no clear vertical specific stratification was detected in the 0-50 m layer. Zoogeographic grouping of the 18 species identified allowed the defining of 5 distinct zones along the transect: Subtropical (north of 31°S, 80% warm water individuals); Warm-Transitional (34°-37°S, 35% warm water); Transitional (37°-49°S, 99% cold water); Subantarctic (49-55°S, 100% cold water); and Antarctic (south of 56°S, 100% cold water). Boundaries between foraminiferal assemblage zones are in good agreement with hydrological fronts described for the area. Comparison of the present data with planktic collections from the North Atlantic show large differences in the proportions of various taxa. In the 14-24°C range, G. bulloides is much more abundant in the northern hemisphere than in the southern one, whereas G. quinqueloba, G. inflata and G. rubescens show the opposite trend. On the other hand, temperature-related percentage contributions within the 14°-24°C range indicate that the preferred thermic régimes of the 9 species considered are remarkably similar in the North and South Atlantic collections compared. The southernmost planktic distributional ranges of selected warm water taxa are roughly coincident with those established previously on the basis of surface sediments, disagreements being chiefly attributable to selective dissolution on the bottom. In contrast, at the bottom percentages of cold water foraminifers (G. bulloides, G. pachyderma) are significantly enhanced with respect to their planktic populations, and their sedimentary northward limits extend well beyond their maximum ranges in the upper-layer plankton. It is suggested that submergence of these cold water ... |
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