Deglacial Variability in Okhotsk Sea Intermediate Water Ventilation and Biogeochemistry: Implications for North Pacific Nutrient Supply and Productivity

• Published in: Quaternary Science Reviews
• Main Authors: Lembke-Jene, Lester, Tiedemann, Ralf, Nürnberg, Dirk, Kokfeld, U., Kozdon, R., Max, L., Röhl, U., Gorbarenko, S. A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2017
• Subjects: Okhotsk; Pacific; okhotsk sea; Subarctic
• Online Access: https://oceanrep.geomar.de/id/eprint/36539/; https://oceanrep.geomar.de/id/eprint/36539/1/1-s2.0-S0277379117300756-main.pdf; https://oceanrep.geomar.de/id/eprint/36539/2/mmc1%2815%29.pdf; https://doi.org/10.1016/j.quascirev.2017.01.016

Highlights • Multi-proxy, multi-site reconstruction of Okhotsk Sea palaeo-productivity and mid-depth ventilation changes from 8 to 18 ka. • Link between hinterland river discharge and downstream Okhotsk Sea Intermediate Water (OSIW) ventilation/nutrient signatures. • Surplus Fe, Si(OH)4 export in OSIW during Bølling-Allerød to pelagic Pacific supported transient nutrient-replete conditions. • Subarctic and subtropical Pacific gyres disconnected during Bølling-Allerød, with restricted OSIW flow to lower latitudes. • Deglacial OSIW export and mid-depth Pacific biogeochemistry modulate millennial-scale regional CO2 source/sink conditions. The modern North Pacific plays a critical role in marine biogeochemical cycles, as an oceanic sink of CO2 and by bearing some of the most productive and least oxygenated waters of the World Ocean. The capacity to sequester CO2 is limited by efficient nutrient supply to the mixed layer, particularly from deeper water masses in the Pacific's subarctic and marginal seas. The region is in addition only weakly ventilated by North Pacific Intermediate Water (NPIW), which receives its characteristics from Okhotsk Sea Intermediate Water (OSIW). Here, we present reconstructions of intermediate water ventilation and productivity variations in the Okhotsk Sea that cover the last glacial termination between eight and 18 ka, based on a set of high-resolution sediment cores from sites directly downstream of OSIW formation. In a multi-proxy approach, we use total organic carbon (TOC), chlorin, biogenic opal, and CaCO3 concentrations as indicators for biological productivity. C/N ratios and XRF scanning-derived elemental ratios (Si/K and Fe/K), as well as chlorophycean algae counts document changes in Amur freshwater and sediment discharge that condition the OSIW. Stable carbon isotopes of epi- and shallow endobenthic foraminifera, in combination with 14C analyses of benthic and planktic foraminifera imply decreases in OSIW oxygenation during deglacial warm phases from c. 14.7 to 13 ka ...