| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
Calcite test of planktonic foraminifer produced in surface ocean sinks in the water column after its death, deposits on the seafloor, and buried in the sediment. During these process, the weight of test decreases by dissolution and increases by secondary calcification. Weight loss of calcite test has been regarded as a good proxy for carbonate dissolution, however, estimation of secondary calcification is also necessary to know a true weight loss. Since secondary calcification occurs in the deep ocean, paleo-sea surface temperature (SST) and salinity (SSS) information recorded in isotope and chemical composition of test calcite would be also biased.
In order to establish the method to estimate true weight loss from and addition on initial calcite test of planktonic foraminifer, weight and oxygen / carbon isotopes analyses were conducted on 50-70 individula foraminifer tests obtained from surface water, water column, and sediments in the western North Pacific. As a result of evaluation f
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or Globigerinoides sacculifer tests,
1) G. sac produce their tests in the surface water and attach gametogenic calcite in < 400 m water depth
2) Gametogenic calcite increases test weight by~20%
3) Dissolution slightly occur during sinking process but secondary calcification does not occur in the water column
4) Significant dissolution occur on the sea floor followed by secondary calcification during burial process
Positive correlation of oxygen isotope and weight suggests a strong influence of secondary calcification to the isotope information kept in foraminifer tests. Dissolution process of formaminifer test is characterized by thinning of their wall. Strong dissolution finally break the wall of tests, which leads to a positive skewness of weight distribution of perfect foraminifer tests, because imperfect (broken) test is not counted for weight measurement. It is discovered during this research that the skewness of weight distribution is a good semi-quantitative estimator of carbonate dissolution which is independent of secondary calcification. This fact enables us to estimate a true loss of primary calcite and addition of secondary calcite from the sediment core samples, and the objective of this study to improve the paleo-SST / SSS proxy using foraminifer tests is archieved. Less
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