Abstract
Abstract. Over the last decade, hydrogen isotopes of long-chain alkenones have been shown to be a promising proxy for reconstructing paleo sea surface salinity due to a strong hydrogen isotope fractionation response to salinity across different environmental conditions. However, to date, the decoupling of the effects of alkalinity and salinity, parameters that co-vary in the surface ocean, on hydrogen isotope fractionation of alkenones has not been assessed. Furthermore, as the alkenone-producing haptophyte, Emiliania huxleyi, is known to grow in large blooms under high light intensities, the effect of salinity on hydrogen isotope fractionation under these high irradiances is important to constrain before using δDC37 to reconstruct paleosalinity. Batch cultures of the marine haptophyte E. huxleyi strain CCMP 1516 were grown to investigate the hydrogen isotope fractionation response to salinity at high light intensity and independently assess the effects of salinity and alkalinity under low-light conditions. Our results suggest that alkalinity does not significantly influence hydrogen isotope fractionation of alkenones, but salinity does have a strong effect. Additionally, no significant difference was observed between the fractionation responses to salinity recorded in alkenones grown under both high- and low-light conditions. Comparison with previous studies suggests that the fractionation response to salinity in culture is similar under different environmental conditions, strengthening the use of hydrogen isotope fractionation as a paleosalinity proxy.
Highlights
Ocean circulation plays a strong role in global heat and moisture transport (Rahmstorf, 2002) and is controlled in part by differences in temperature and salinity, known as thermohaline circulation
Ano-longer-calcifying strain of E. huxleyi was grown under high-light conditions over a salinity range from 25 to 35 with constant alkalinity in our high-light experiment, and low-light conditions over a salinity range from 26 to 42 with an alkalinity range of 1.4–4.6 mM in our alkalinity–salinity experiment
Our results show that the response in hydrogen isotopic fractionation of alkenones to salinity is statistically similar across different E. huxleyi strains and under different growth conditions, including low- and highlight conditions
Summary
Ocean circulation plays a strong role in global heat and moisture transport (Rahmstorf, 2002) and is controlled in part by differences in temperature and salinity, known as thermohaline circulation Knowing these parameters is important to reconstruct ocean circulation in the geological past, which leads to a more robust understanding of our climate system. The isotopic ratios of oxygen (δ18O) and hydrogen (δD) of water are strongly tied to these environmental parameters (Craig and Gordon, 1965) Increasing evaporation causes both enrichment in heavy isotopes (Clark and Fritz, 1997) and an increase in surface water salinity. A depleted isotopic signature is found for most precipitationfed rivers and lakes (i.e., meteoric waters) As these waters drain into the ocean and mix with seawater, the SSS is low-
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