Paleoceanographic analyses are undertaken on the basis of (1) diatom abundance (number of diatoms), (2) diatom temperature (Td) values, (3) species composition, which reflects the effects of salinity of the water and mode of living, (4) number of extinct diatoms, and (5) principal component analysis, which uses the results from the previous four analytical methods for determining the composition of species.
The number of diatom valves in a given volume of sediment depends on (1) diatom productivity, (2) preservation and/or dissolution of the diatoms, and (3) dilution with terrigenous and/or other organic materials.
The warm-water (Xw) and cold-water (Xc) species have been classified according to Kanaya and Koizumi (1966). All these diatoms are living species.
Xw species are as follows:
Xc species are as follows:
The Td ratio was proposed by Kanaya and Koizumi (1966) to estimate sea-surface water temperature during the accumulation of sediments in the lower levels of a core sequence:
where Xw is the frequency of warm-water diatoms and Xc is that of cold-water diatoms. Td ranges in value from 0 to 100. Going from the subarctic region to the tropical region, Td becomes systematically larger, showing a positive correlation with sea-surface water temperature over a given geographical site in the North Pacific (Kanaya and Koizumi, 1966).
Diatom populations incorporated into the sediment of Sites 1150 and 1151 at the time of deposition include sublittoral diatoms (brackish water and meroplanktonic or tychopelagic species) and/or freshwater diatoms that are inferred to have been transported to the site by drainage from the land and downslope transport.
The core sediments include extinct diatoms that are present as a result of reworking Miocene to Pliocene sedimentary rocks on the seafloor and/or inland area. The age of these rocks are identified according to diatom biostratigraphy.
Principal component analysis of diatom species was carried out when more than six valves of a given species were found in a sample in order to statistically analyze the stratigraphic assemblage structure which reflects the effects of physiographical-ecological, phytogeographical, and evolutionary factors at the site.