Evidence for Pliocene North Pacific Deep Water Formation and Its Paleoproductivity Imprints

Deep-water formation plays a crucial role in global climate, yet it is absent in the modern North Pacific. However, the existence of North Pacific Deep Water (NPDW) formation during the Pliocene and its impact on the marine carbon cycle remain controversial. Here, we present high-resolution sedimentary records of authigenic neodymium isotope composition(ε_Nd), barite accumulation rates (BAR), and barite barium (Ba) isotope compositions (δ¹³⁸Ba_barite) from ODP Site 882 in the subarctic Northwest Pacific.

Our results reveal pronounced shifts in ε_Nd and Ba-proxy records synchronous with the intensification of Northern Hemisphere Glaciation. Specifically, across the ~2.73 Ma interval, seawater ε_Nd values decrease from +0.2 to -1.4, marking a shift from northern-sourced NPDW to southern-sourced Pacific Deep Water (PDW). This circulation collapse was accompanied by elevated BAR and δ¹³⁸Ba_barite values, indicating a transient peak in export production. Intriguingly, this productivity pulse is decoupled from biogenic opal accumulation, which declines during the same interval. We propose that the cessation of NPDW formation allowed the upwelling of nutrient-rich PDW. This process fueled a transient increase in export production but partly drove the ecosystem from a silicate-replete to a silicate-limited regime, or reduced nutrient burial efficiency.

In contrast to the dynamic Late Pliocene, our new data from the Early Pliocene (~4.3–3.6 Ma) show relatively stable ε_Nd and Ba-proxy records. These findings challenge previous hypotheses of an Early Pliocene circulation transition derived from Japan Sea records, suggesting that open ocean circulation in the subarctic Pacific remained stable prior to the onset of major glaciations. Our study highlights the critical role of physical circulation thresholds in regulating the efficiency of the biological carbon pump and nutrient inventory in the North Pacific.