Stable barium isotope ratios (δ¹³⁸Ba) have been proposed as a powerful proxy for the marine biological carbon pump (BCP) and ocean circulation. However, the scarcity of continuous, multi-million-year sedimentary archives limits our understanding of long-term Ba biogeochemical cycling. Hydrogenetic ferromanganese deposits (FMDs) offer continuous paleo-records, yet the mechanism governing Ba incorporation into FMDs, whether from dissolved ambient seawater or sinking particulate barite, remains unresolved. Here, we show that modern North Pacific FMD surface scrapings (δ¹³⁸Ba = +0.03 ± 0.11‰) inherently reflect the light isotopic signature of pelagic barite rather than ambient heavy near-bottom seawater (δ¹³⁸Ba = +0.23 ± 0.06‰). These data demonstrate that FMDs predominantly sequester pelagic barite through direct structural inheritance without measurable isotope fractionation. Building on this mechanistic framework, we present a continuous ~21-Myr δ¹³⁸Ba_FMD record from a North Pacific FMD, and compare this record with Ba concentrations, as well as neodymium and iron isotopes to disentangle the driving mechanisms for North Pacific Ba biogeochemical cycling since the Miocene. Our record reveals two distinct regimes: a middle Miocene (~18–10 Ma) phase where locally intensified upwelling enhanced nutrient utilization, driving δ¹³⁸Ba_FMD toward markedly heavier values; and the remaining late Cenozoic intervals dynamically modulated by basin-scale aeolian iron fertilization, where westerly-driven dust pulses triggered positive δ¹³⁸Ba_FMD excursions, alternating with lighter signatures during periods of reduced dust delivery linked to the latitudinal shifts of the westerlies. These findings establish δ¹³⁸Ba_FMD as a robust proxy for past oceanic Ba cycling, highlighting the profound sensitivity of the ocean's BCP to tectonic and climate-driven nutrient redistribution.

暂无