GC10-Pliocene-25
https://doi.org/10.5194/egusphere-gc10-pliocene-25
The warm Pliocene: Bridging the geological data and modelling communities
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Carbon dynamics in the subarctic Pacific Ocean - diatom δ11B insights into the past

Hannah Donald1, George Swann2, and Gavin Foster1
Hannah Donald et al.
  • 1School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK
  • 2School of Geography, University of Nottingham, University Park, Nottingham, NG7 2RD, UK (george.swann@nottingham.ac.uk)

The intensification of Northern Hemisphere glaciation (iNHG) at 2.73 Ma is associated in the subarctic Pacific Ocean with an abrupt drop in opal mass accumulation rates and the development of a halocline stratification. Uncertainty, however, remains around the extent to which these changes: 1) altered carbon dynamics in the water column; and 2) contributed to a reduction in atmospheric pCO2 over this period. These issues can be resolved by applying the boron isotope (δ11B) proxy to quantify past changes in the pH and pCO2 of ambient seawater. By analysing δ11B in diatom frustules, we document a surface water increase of 0.3 to 0.5 pH units in the subarctic Pacific Ocean over the iNHG. This confirms that the development of the halocline at 2.73 Ma both reorganised the vertical water column structure and limited CO2 outgassing from the ocean interior. In conjunction with other external and internal processes, including changes in the Southern Ocean, these events would have contributed to a lowering of atmospheric pCO2 and the long-term expansion of ice sheets across the Northern Hemisphere.

This research demonstrates the potential for diatom δ11B measurements to be used to reconstruct changes in pCO2, particularly in high-latitude settings where diatom frustules are readily preserved and dominate the sediment record. Such analyses have the potential to complement δ11B measurements in foraminifera and so provide further insights into the carbon dynamics of the “warm Pliocene” and other periods of interest.

How to cite: Donald, H., Swann, G., and Foster, G.: Carbon dynamics in the subarctic Pacific Ocean - diatom δ11B insights into the past, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-25, https://doi.org/10.5194/egusphere-gc10-pliocene-25, 2022.