| Summary: | 碩士 === 國立中山大學 === 海洋地質研究所 === 84 === There are two parts in this study. The first part was to
confirm the reliability of planktonic foraminiferal Cd/Ca
ratios from the surface sediments. Result of Cd/Ca ratios in
the planktonic foraminiferal tests, Globigerinoides sacculifer
and Neogoloboqudrina dutertrei, from the top surface sediments
revealed a good correlation to the nutrient concentrations (
phosphate). Therefore, it is practical to apply the planktonic
foraminiferal ratios to reconstruct the changes in surface
water fertility through time. The second part of this study was
to documents the variations of paleonutrients based on the Cd/
Ca ratios in planktonic foraminiferal tests from a well AMS14C-
constrained gravity core for the last 35,000 years. The 13m
-long core, 17940-2 (20°07′N，117°23′E，w.d.1,727m) was
collected by R/V SONNE from the northern South China Sea in
1994. In general, downcore profile of Cd/Ca ratios shows a
consistent change with the mass accumulation rates of organic
carbon (TOC wt%), calcium carbonates (CaCO3 wt%) and biogenic
opal (Opal wt%). Higher Cd/Ca ratios and depletion in δ13C of
Globigerinoides ruber during last glacial maximum (22-14 ka B.
P.) to early deglaciation (∼14 ka B.P.) indicate a higher
surface fertility which might have been resulted from the
intensified vertucal mixing due to the stronger winter monsoon.
These records of biogenic fluxes also indicates a higher
productivity when surface water riched in nutrients during the
glacial times. On the contrary, the low contents of those
biogenic compositions corresponding to the high MARs in early
Holocenc might have been caused by the increased precipitation
due to stronger summer monsoon.
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