Neogene Mass Accumulation Rate of Carbonate Sediment Across Northern Zealandia, Tasman Sea, Southwest Pacific

Sediment mass accumulation rate (MAR) is a proxy for paleoceanographic conditions, especially if biological productivity generated most of the sediment. We determine MAR records from pelagic calcareous sediments in Tasman Sea based on analysis of 11 boreholes and >3 million seismic reflection horizon picks. Seismic data from regions of 10,000–30,000 km2 around each borehole were analyzed using data from International Ocean Discovery Program Expedition 371 and other boreholes. Local MAR was affected by deepwater currents that winnowed, eroded, or deposited seafloor sediment. Therefore, it is necessary to average MARs across regions to test paleoceanographic and productivity models. MARs during the Miocene Climate optimum (18–14 Ma) were slightly lower than Quaternary values but increased on southern Lord Howe Rise at 14–13 Ma, when global climate became colder. Intensification of the Indian and East Asian monsoons at ∼8 Ma and ∼3.6 Ma approximately corresponds to the start and end, respectively, of the Biogenic Bloom, which had MARs at least double Quaternary values. On northern Lord Howe Rise, we recognize peak MARs at∼7 Ma and ∼5 Ma. There is no correlation between Neogene MAR and ocean pH or atmospheric CO2 concentration. Neogene MARs are on average higher than Quaternary values. We posit that future long‐term productivity in the southwest Pacific could be higher than Quaternary values, but new computer models that can fit our observations are required to test this hypothesis.