δ30Si diatom and diatom fossil assemblage data from IODP Site 323-U1343 between 0.6 and 1.2 Ma

• Main Authors: Worne, Savannah, Swann, George E A, Kender, Sev, Lacey, Jack H, Leng, Melanie J
• Format: Dataset
• Language: English
• Published: PANGAEA 2021
• Subjects: Bering Sea; diatom; Mid Pleistocene Transition; MPT; Sea ice; Silicon isotopes; δ30Si; Southern Ocean; Pacific; Subarctic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.933139; https://doi.org/10.1594/PANGAEA.933139

High latitude ocean-atmosphere CO2 dynamics are considered important in glacial-interglacial climate, with deep-ocean carbon burial via the biological pump being highly variable through the Quaternary. During the Mid-Pleistocene Transition (MPT) shift to 100 kyr glacials, it has been suggested that elevated atmospheric-driven iron fertilisation and increased efficiency of the biological pump in the Southern Ocean was key in lowering atmospheric pCO2 and facilitating rapid land ice accumulation. Growing evidence suggests carbon cycling in the subarctic Pacific Ocean played a key role in late Quaternary glacials, although this has not yet been assessed during the MPT. Here, the silicon isotope composition of diatoms (δ30Sidiatom) from the high productivity upwelling region in the Bering Sea is used to assess the role of the subarctic Pacific biological pump in the MPT. Results show the “900 kyr event” was characterised by low silicic acid but high nitrate utilisation, coincident with the dominance of diatom resting spores. This indicates the region became nitrate- and light-limited, rather than iron-limited, due to the development of thick pack ice and expansion of glacial North Pacific Intermediate Water (GNPIW) which suppressed nutrient upwelling. We posit that iron fertilisation from sea ice expansion, coupled with the preferential preservation and higher cellular carbon content of diatom resting spores, increased regional carbon export and contributed to lower atmospheric pCO2. Remnant iron and remineralised silicic acid also likely propagated into the lower subarctic Pacific Ocean through GNPIW, aiding regionally high productivity once upwelling/vertical mixing was restored during deglaciations.