Salinity and stable oxygen isotope relationship in the Southwestern Atlantic: constraints to paleoclimate reconstructions.

Andre L Belem,Ana Luiza S Albuquerque,Maria Do R Zucchi,Igor M Venancio,Yaci Gallo Alvarez,Camilla Caricchio,Tarcio Henrique R Dos Santos

doi:10.1590/0001-3765201920180226

Abstract

Stable isotopes have been widely used in the literature both to discuss current ocean circulation processes, as well as to reconstitute paleoceanographic parameters. The distribution of oxygen and deuterium stable isotopes in seawater (δ18Osw and δDsw) at the Western Tropical South Atlantic border was investigated to better understand the main fractionation processes of these isotopes and establish a regional salinity and δ18Osw relation to improve the paleoceanographic knowledge in the region. This study was conducted during a quasi-synoptic oceanographic cruise in which 98 discrete seawater samples were collected in the core of the main water masses for stable isotope analysis. A strong correlation between δ18Osw and δD was found, which made it possible to extrapolate the results for δ18Osw to δD. Although it was not possible to distinguish the water masses based only on their isotopic signatures, the water masses had a strong salinity and δ18Osw relation, and compared with previous studies, a seasonal pattern was observed. Paleosalinity differences of up to 0.2 psu between Summer and Winter are reported. Considering the limitations of the current techniques to seasonally separate the samples for the paleoceanographic studies, an intermediate Mixing Line for the Tropical South Atlantic (SSS = 1.942* δ18Osw + 34.56) was proposed to reduce the estimated errors associated with these seasonal variations.

Highlights

The isotopic fractionation of both oxygen and Earth SciencesAn Acad Bras Cienc (2019) 91(3)SALINITY-OXYGEN ISOTOPE RELATIONSHIP and Jouzel 1979, Minoura et al 1997, Thornalley et al 2010, Toledo et al 2007) in order to better understand the transition between glacial and interglacial periods
The study by Pierre et al (1991) was conducted in a narrow area between 21.9°S and 26.5°S latitude during the austral Summer, from December 1987 to January 1988 sampling from surface to ~2000 depth; whereas Ostlund et al (1987) data were obtained between October and November 1972 sampling only one full profile near 21°S and the remaining data from surface samples only along the GEOSECS section (Fig. 1)
We found a strong correlation between δ18Osw and δD that makes it possible to extrapolate the results for δ18Osw to δD

Summary

Introduction

SALINITY-OXYGEN ISOTOPE RELATIONSHIP and Jouzel 1979, Minoura et al 1997, Thornalley et al 2010, Toledo et al 2007) in order to better understand the transition between glacial and interglacial periods. Another important application of δ18Osw and δDsw is in oceanographic circulation studies (Benway and Mix 2004, Conroy et al 2014, Craig and Gordon 1965, Kroopnick 1980, 1985, Pierre 1999, Pierre et al 1991, Venancio et al 2014). Proxies for salinity are still in development, especially to reduce the sources of uncertainty (which can be up to 4 psu) due to changes in regional freshwater budgets, ocean circulation and sea ice regimes (Holloway et al 2015, Schmidt 1999)

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Discussion

Conclusion