Preprints
https://doi.org/10.5194/egusphere-2022-1212
https://doi.org/10.5194/egusphere-2022-1212
 
07 Nov 2022
07 Nov 2022
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

A 600-kyr reconstruction of deep Arctic seawater δ18O from benthic foraminiferal δ18O and ostracode Mg/Ca paleothermometry

Jesse R. Farmer1,2,3, Katherine J. Keller4,5, Robert K. Poirier5, Gary S. Dwyer6, Morgan F. Schaller7, Helen K. Coxall8, Matthew O'Regan8, and Thomas M. Cronin5 Jesse R. Farmer et al.
  • 1School for the Environment, University of Massachusetts Boston, Boston, MA, USA
  • 2Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 3Department of Geosciences, Princeton University, Princeton, NJ, USA
  • 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 5Florence Bascom Geoscience Center, U.S. Geological Survey, Reston, VA, USA
  • 6Division of Earth and Ocean Sciences, Nicholas School of Environment, Duke University, Durham, NC, USA
  • 7Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy NY, USA
  • 8Department of Geological Sciences, Stockholm University, Stockholm, Sweden

Abstract. The oxygen isotopic composition of benthic foraminiferal tests (δ18Ob) is one of the preeminent tools for correlating marine sediments and interpreting past terrestrial ice volume and deep-ocean temperatures. Despite the prevalence of δ18Ob applications to marine sediment cores over the Quaternary, its use is limited in the Arctic Ocean because of low benthic foraminiferal abundances, challenges with constructing independent sediment core age models, and an apparent muted amplitude of Arctic δ18Ob variability compared to open ocean records. Here we evaluate the controls on Arctic δ18Ob by using ostracode Mg/Ca paleothermometry to generate a composite record of the δ18O of seawater (δ18Osw) from fourteen sediment cores in the intermediate to deep Arctic Ocean (700–2700 m) covering the last 600 kyr. Results show that Arctic δ18Ob was generally higher than open ocean δ18Ob during interglacials but was generally equivalent to global reference records during glacial periods. The reduced glacial-interglacial Arctic δ18Ob range resulted in part from the opposing effect of temperature, with intermediate-to-deep Arctic warming during glacials counteracting the whole-ocean δ18Osw increase from expanded terrestrial ice sheets. After removing the temperature effect from δ18Ob, we find that the intermediate-to-deep Arctic experienced large (≥ 1 ‰) variations in local δ18Osw, with generally higher local δ18Osw during interglacials and lower δ18Osw during glacials. Both the magnitude and timing of low local δ18Osw intervals are inconsistent with the recent proposal of freshwater intervals in the Arctic Ocean during past glaciations. Instead, we suggest that lower local δ18Osw in the intermediate-to-deep Arctic Ocean during glaciations reflected weaker upper ocean stratification and more efficient transport of low-δ18Osw Arctic surface waters to depth by mixing and/or brine rejection.

Jesse R. Farmer et al.

Status: open (until 02 Jan 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1212', Robert F. Spielhagen, 01 Dec 2022 reply
  • CC1: 'Comment on egusphere-2022-1212', Claude Hillaire-Marcel, 05 Dec 2022 reply

Jesse R. Farmer et al.

Jesse R. Farmer et al.

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Short summary
Oxygen isotopes are used to date marine sediments via their similar large-scale ocean patterns over glacial cycles. However, the Arctic Ocean exhibits a different isotope pattern, creating uncertainty in the timing of past Arctic climate change. We find that the Arctic Ocean experienced large local oxygen isotope changes over glacial cycles. We attribute this to a breakdown of stratification during ice ages that allowed for a unique low isotope value to characterize the Arctic Ocean.