Constraining the application of hydrogen isotopic composition of alkenones as a salinity proxy using marine surface sediments
Weiss, G.M.; Schouten, S.; Sinninghe Damsté, J.S; Van der Meer, M.T.J. (2019). Constraining the application of hydrogen isotopic composition of alkenones as a salinity proxy using marine surface sediments. Geochim. Cosmochim. Acta 250: 34-48. https://doi.org/10.1016/j.gca.2019.01.038Additional data: In: Geochimica et Cosmochimica Acta. Elsevier: Oxford,New York etc.. ISSN 0016-7037; e-ISSN 1872-9533, more |   |
| Author keywords | Hydrogen isotopes; Alkenones; Surface sediments; Salinity |
| Authors | | Top | - Weiss, G.M., more
- Schouten, S., more
- Sinninghe Damsté, J.S, more
- Van der Meer, M.T.J., more
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| Abstract | Sea surface salinity is an essential environmental parameter necessary to understand past changes in global climate. However, reconstructing absolute salinity of the surface ocean with high enough accuracy and precision remains a complicated task. Hydrogen isotope ratios of long-chain alkenones (δ2HC37) have been shown to reflect salinity in culture studies and have been proposed as a tool to reconstruct sea surface salinity in the geologic record. The correlation between δ2HC37 – salinity in culture is prominently caused by the relationship between δ2HH2O and salinity, as well as the increase in fractionation factor α with increasing salinity. The δ2HC37 – salinity relationship in the natural environment is poorly understood. Here, surface sediments from a variety of environments covering a wide range of salinities were analyzed to constrain the environmental relationship between salinity and hydrogen isotopes of alkenones. δ2HC37 correlates significantly (r = 0.75, p < 0.0001) with annual mean salinity. Interestingly, the biological hydrogen isotope fractionation (αC37) seems independent of salinity. These findings are different from what has previously been observed in culture experiments, but align with other environmental datasets and suggest that the salinity effect on biological hydrogen isotope fractionation observed in culture is not apparent in sediments. The absence of a correlation between αC37 and salinity for marine surface sediments might be best explained by a mixing of multiple alkenone-producing species contributing to the sedimentary alkenone signal that fractionate in distinct ways. Nevertheless, sedimentary δ2HC37 ratios still correlate with salinity and δ2HH2O, suggesting that δ2HC37 ratios are useful for paleosalinity reconstructions. Our surface sediment calibration presented here can be used when different species contribute to the sedimentary alkenone pool and substantial changes in salinity are expected. |
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