Role of dust fluxes in stimulating Ethmodiscus rex giant diatom blooms in the northwestern tropical Pacific during the Last Glacial Maximum
Abstract The strontium (Sr) and neodymium (Nd) isotope compositions and clay-mineral assemblages of the lithogenic fraction of sediments in the southern Mariana Trench together with major- and trace-elements concentrations of bulk sediments have been determined to trace the sediment provenance and investigate the relationship between Asian dust input and blooms of the giant diatom Ethmodiscus rex (E. rex). Enrichment of barium (Ba) in relative to upper continental crust (UCC) and low average Rb/K ratios in all study cores point to both hydrothermal and volcaniclastic inputs to the sediments. Both the Sr-Nd isotope compositions and the clay-mineral assemblages of the lithogenic fraction reflect a two-component mixing system consisting of Mariana arc volcaniclastics and Asian eolian dust. Decreases in smectite content and kaolinite/chlorite ratio and increases in illite content and illite/kaolinite ratio just preceding the formation of laminated diatom mats (LDMs) suggest changes in the source of the eolian dust from eastern Asian deserts (EADs) to central Asian deserts (CADs) at the onset of the Last Glacial Maximum (LGM) which stimulated the blooming of E. rex giant diatom. These observations suggest a potential causal linkage among atmospheric circulation patterns, the sources of Asian eolian dust, and marine productivity. We postulate that intensified eolian dust input sourced from CADs may have played a greater role in promoting biological productivity in the oligotrophic northwestern tropical Pacific Ocean during the LGM than previously realized.