Reconstructing paleosalinity from δ 18 O:Coupled model simulations of the Last Glacial Maximum, Last Interglacial and Late Holocene

• Published in: Quaternary Science Reviews
• Main Authors: Holloway, Max D., Sime, Louise C., Singarayer, Joy S., Tindall, Julia C., Valdes, Paul J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Isotopes; Last Glacial Maximum; Last Interglacial; Oxygen-18; Paleoceanography; Paleosalinity; Indian; Pacific; North Atlantic; Sea ice
• Online Access: https://hdl.handle.net/1983/a0e330b0-db66-4339-a435-426ede727ff3; https://research-information.bris.ac.uk/en/publications/a0e330b0-db66-4339-a435-426ede727ff3; https://doi.org/10.1016/j.quascirev.2015.07.007; https://research-information.bris.ac.uk/ws/files/80785840/QSR_final_revised.pdf; http://www.scopus.com/inward/record.url?scp=84949645191&partnerID=8YFLogxK

Reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation. A widely used method of determining past salinity uses oxygen isotope (δ Ow ) residuals after the extraction of the global ice volume and temperature components. This method relies on a constant relationship between δ Ow and salinity throughout time. Here we use the isotope-enabled fully coupled General Circulation Model (GCM) HadCM3 to test the application of spatially and time-independent relationships in the reconstruction of past ocean salinity. Simulations of the Late Holocene (LH), Last Glacial Maximum (LGM), and Last Interglacial (LIG) climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates (δ Oc ), which primarily reflect δ Ow and temperature. We find that HadCM3 produces an accurate representation of the surface ocean δ Oc distribution for the LH and LGM. Our simulations show considerable variability in spatial and temporal δ Ow -salinity relationships. Spatial gradients are generally shallower but within ~50% of the actual simulated LH to LGM and LH to LIG temporal gradients and temporal gradients calculated from multi-decadal variability are generally shallower than both spatial and actual simulated gradients. The largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets, ocean circulation, and sea ice regimes. These can cause errors in salinity estimates exceeding 4 psu. Our results suggest that paleosalinity reconstructions in the South Atlantic, Indian and Tropical Pacific Oceans should be most robust, since these regions exhibit relatively constant δ Ow -salinity relationships across spatial and temporal scales. Largest uncertainties will affect North Atlantic and high latitude paleosalinity reconstructions. Finally, the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography, such as the North Atlantic, without additional ...