Dataset Information

Spatiotemporal variability in the ?18O-salinity relationship of seawater across the tropical Pacific Ocean.

ABSTRACT: The relationship between salinity and the stable oxygen isotope ratio of seawater (?18Osw) is of utmost importance to the quantitative reconstruction of past changes in salinity from ?18O values of marine carbonates. This relationship is often considered to be uniform across water masses, but the constancy of the ?18Osw-salinity relationship across space and time remains uncertain, as ?18Osw responds to varying atmospheric vapor sources and pathways, while salinity does not. Here we present new ?18Osw-salinity data from sites spanning the tropical Pacific Ocean. New data from Palau, Papua New Guinea, Kiritimati, and Galápagos show slopes ranging from 0.09 ‰/psu in the Galápagos to 0.32‰/psu in Palau. The slope of the ?18Osw-salinity relationship is higher in the western tropical Pacific versus the eastern tropical Pacific in observations and in two isotope-enabled climate models. A comparison of ?18Osw-salinity relationships derived from short-term spatial surveys and multi-year time series at Papua New Guinea and Galápagos suggests spatial relationships can be substituted for temporal relationships at these sites, at least within the time period of the investigation. However, the ?18Osw-salinity relationship varied temporally at Palau, likely in response to water mass changes associated with interannual El Niño-Southern Oscillation (ENSO) variability, suggesting nonstationarity in this local ?18Osw-salinity relationship. Applying local ?18Osw-salinity relationships in a coral ?18O forward model shows that using a constant, basin-wide ?18Osw-salinity slope can both overestimate and underestimate the contribution of ?18Osw to carbonate ?18O variance at individual sites in the western tropical Pacific.

SUBMITTER: Conroy JL

PROVIDER: S-EPMC6999658 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Spatiotemporal variability in the δ18O-salinity relationship of seawater across the tropical Pacific Ocean.

Conroy Jessica L JL Thompson Diane M DM Cobb Kim M KM Noone David D Rea Solanda S LeGrande Allegra N AN

Paleoceanography 20170501 Iss 5

The relationship between salinity and the stable oxygen isotope ratio of seawater (δ18Osw) is of utmost importance to the quantitative reconstruction of past changes in salinity from δ18O values of marine carbonates. This relationship is often considered to be uniform across water masses, but the constancy of the δ18Osw-salinity relationship across space and time remains uncertain, as δ18Osw responds to varying atmosphe ...[more]

PMID: 32020985

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Project description:The tropical Eastern Pacific Fresh Pool (EPFP) has some of the highest precipitation rates and lowest sea surface salinities found in the open ocean. In addition, the sea surface salinity in the EPFP exhibits one of the strongest annual cycles in the world ocean. The region is strongly affected by the meridionally migrating Intertropical Convergence Zone and is also influenced by large-scale ocean currents and wind-driven Ekman currents. Recognizing the complexity of competing regional influences and the importance of sea surface salinity as an integrator of freshwater forcing, the Salinity Processes Upper-ocean Regional Study (SPURS) was undertaken to better understand how ocean processes and surface freshwater fluxes set surface salinity. Instrumentation on a surface mooring, deployed for 14 months near the western edge of the EPFP, allowed estimation of the surface fluxes of momentum, heat, and freshwater. Subsurface instrumentation on the mooring provided upper-ocean vertical structure and horizontal currents. These observations, along with horizontal gradients of surface salinity from the Soil Moisture Active Passive (SMAP) satellite instrument, were used to estimate the surface-layer salinity budget at the western edge of the EPFP. While the low salinity associated with the presence of the EPFP at the mooring site was sustained by heavy rainfall, it was found that seasonal variability in large-scale currents was important to controlling the transition between the "salty" and "fresh" seasons. Ekman advection was important to prolonging local high salinity as rainfall decreased. Although illuminating some key processes, the temporal variability of the surface-layer salinity budget also shows significant complexity, with processes such as surface freshwater fluxes and vertical mixing making notable contributions. The surface flux term and the terms involving mixing across the base of the surface layer oppose and nearly cancel each other throughout the deployment, such that the horizontal advection term effectively accounts for most of the variability in surface salinity at the site on monthly to seasonal timescales. Further investigation, taking advantage of additional observations during SPURS-2, will be needed to more thoroughly examine the relevant physical processes.

Dataset Information

Spatiotemporal variability in the ?18O-salinity relationship of seawater across the tropical Pacific Ocean.

Publications

Spatiotemporal variability in the δ<sup>18</sup>O-salinity relationship of seawater across the tropical Pacific Ocean.

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