Quantitative Evaluation of Paleoproductivity of Diatom Mats from Tropical West Pacific during the Last Glacial Maximum (LGM)

The organic carbon flux to deep ocean, dominated by the bloom of giant "shade flora" diatoms via "fall dump" in stratified ocean, could rival or even exceed that of "spring bloom" diatoms. The giant "shade flora" diatoms played a significant role in the global climate transition and ocean carbon reservoir change in the Quaternary, which could be exploited by the paleoproductivity, one of most important factors in the ocean carbon cycle systems. We tried to estimate the paleoproductivity of laminated Ethmodiscus rex diatom mats (LDM) from tropical West Pacific during the Last Glacial Maximum (LGM), based on the data of opal, total organic carbon and biogenic barium from Core WPD-03 located in the eastern Philippine Sea. Primary productivity, organic carbon rain rates, burial productivity during the LDM deposition were estimated to average 248.42 g·m^-2·a^-1, 61.93 g·m^-2·a^-1 and 5.27 g·m^-2·a^-1, respectively, of which the primary productivity is comparable to those of some modern continent-margin upwelling zones, correcting low primary productivity with a largely stratified ocean and supporting substantial contribution of giant "shade flora" diatoms to the production and export of organic carbon in the world ocean. However, the unreasonable estimations for the export productivity by the empirical formulas in base of photic zone suggest that a caution must be taken to assess the "deep" productivity represented by giant "shade flora" diatoms, which should be distinguishable from classic "surface" productivity characterized by common diatoms. The high levels of productivity of LDM were consistent with the blooming conditions of dust silicon inputs and reducing depositional environments.