Journal Article

Bølling‐Allerød Productivity in the Subarctic Pacific Driven by Seasonal Upwelling

Sipala, M. R., Caissie, B., Addison, J., Blackburn, T., Marcantonio, F., Ravelo, A. C., DeLong, K. A., Stroynowski, Z.

2025

Overview

The Bølling‐Allerød deglacial event is marked by high diatom productivity and opal deposition throughout the subarctic Pacific. This opal could either constitute a strengthened biological pump and thus carbon sequestration, or a weakened biological pump and release of marine‐sequestered CO2 to the atmosphere. We quantify silicic acid supply at IODP Site U1340 in the Bering Sea using biogenic opal and δ30Si of Coscinodiscus, a diatom genus. These records, along with diatom environmental indicators, suggest the Bølling‐Allerød had high silicic acid availability related to a shift from stratification to seasonal upwelling dynamics. We thus propose the primary cause of the high productivity event was increased macronutrient supply from vertical exchange that injected old, nutrient‐rich, CO2‐rich waters into the surface. Enhanced CO2 release from the subarctic Pacific may help explain critical intervals of CO2 rise that occur at the onsets of the Bølling‐Allerød and PreBoreal. Plain Language Summary The subarctic Pacific experienced a period of remarkably high primary productivity from 14.7 to 12.9 thousand years ago. The growth and burial of diatoms, single‐celled algae with opal cell walls, deposited an opal‐rich layer in marine sediments across the entire region, including our site in the southern Bering Sea. To determine the cause of this productivity, we analyzed diatom opal and the diatom species present. The silicon isotopic composition of the opal suggests surface nutrients were more abundant during the high‐productivity event. This points to an increased connection between surface waters, where algae grow, and deep waters, which are rich in nutrients. The species present suggest deep mixing occurred each winter followed by a large spring bloom, indicating a different mode of oceanic circulation than the modern ocean. Summer production may have been limited by the rate of iron delivery, similar to the modern ocean. The combined effect of increased mixing and iron limitation is that, despite high productivity which sequestered some carbon, these events represent times when the subarctic Pacific was a net source of carbon to the atmosphere. The carbon released from the subarctic Pacific occurred during critical intervals of global change which ended the last glacial age. Key Points Diatom silicon isotopes suggest increased silicic acid availability during Bølling‐Allerød productivity in subarctic Pacific Diatom indicators suggest increased upwelling and iron limitation during high productivity events in the Subarctic Pacific Vertical mixing during the Bølling‐Allerød made the subarctic Pacific a source of atmospheric CO2 which contributed to global deglaciation

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Algae / Atmosphere / Carbon / Carbon dioxide / Carbon sequestration / Cell walls / Deep water / diatom / Diatoms / Environmental indicators / geochemistry / Intervals / Iron / Isotope composition / Marine microorganisms / Marine sediments / Nutrient release / Nutrients / Ocean circulation / Oceans / Opal / paleoceanography / paleoclimate / Plankton / Primary production / Productivity / Sediments / Silicic acid / Silicon / Silicon isotopes / Stratification / Surface water / Upwelling / Upwelling dynamics