Detailed depth profiles of232Th in deep‐sea ferromanganese nodules and encrustations often show a subsurface maximum followed by a drastic inward decrease to a certain depth before levelling out. Length scales of this feature vary among the profiles but are proportional to growth rates of the specimens, suggesting that the profiles record changes in oceanic232Th flux with time. Consideration of the nodule chronology, the history of eolian accumulation recorded in sediment cores, and the marine geochemical behavior and budget of232Th leads us to propose that232Th in nodules/crusts is of eolian origin. The drastic inward decrease of232Th is a reflection of increase in the wind borne dust flux induced by the Northern Hemisphere glaciation beginning 2–3 Ma. The subsurface232Th peak may indicate the decline of eolian flux since 0.1–0
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