Impact of sea ice variability on the oxygen isotope content of seawater under glacial and interglacial conditions

Records of temporal variability in the oxygen isotopic composition of biogenic carbonates (δ18Oc) from ocean sediment cores inform our understanding of past continental ice volume and ocean temperatures. Interpretation of δ18Ocvariability typically neglects changes due to factors other than ice volume and temperature. Here we investigate whether glacial‐interglacial changes in sea ice, which fractionates seawater during its formation, could shift the isotopic value of seawater—in the deep ocean (affecting benthic foraminiferal δ18Oc and thereby potentially impacting oxygen isotope based sea level reconstructions) or in surface waters (affecting planktic foraminiferal δ18Oc). We simulate glacial and interglacial states with the isotope‐enabled University of Victoria Earth System Climate Model and perform a global analysis. Distinct patterns of sea ice production emerge for the glacial versus interglacial states. We find no substantive shift in δ18Ow in model deep or bottom waters due to the simulated interglacial‐glacial sea ice variability. Small isotopic shifts due to sea ice variability are concentrated in the model's surface waters of the Northern Hemisphere, specifically in the Labrador Sea and northeastern North Atlantic. Key Points Sea ice imparts unique interglacial & glacial 3D isotopic signatures to seawater Interglacial-glacial sea ice variability produces negligible shifts in d18Ow Results don't support impact to sea level estimates or sea ice brine hypothesis