The effect of temperature, salinity and growth rate on the stable hydrogen isotopic composition of long chain alkenones produced by <I>Emiliania huxleyi</I> and <I>Gephyrocapsa oceanica</I>

Abstract

Abstract. Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G. oceanica were on average depleted in D by 30‰ compared to those of E. huxleyi when grown under similar temperature and salinity conditions. The fractionation factor, α alkenones−H 2 O , ranged from 0.760 to 0.815 for E. huxleyi and from 0.741 to 0.788 for G. oceanica. There was no significant correlation of α alkenones−H 2 O with temperature but a positive linear correlation was observed between α alkenones−H 2 O and salinity with ∼3‰ change in fractionation per salinity unit and a negative correlation between α alkenones−H 2 O and growth rate. This suggests that both salinity and growth rate can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments.

Hydrogen isotopes in individual amino acids reflect differentiated pools of hydrogen from food and water in Escherichia coli

“…Fatty acids, hydrocarbons, and alkenones synthesized by plants, phytoplankton, and microbes are depleted in 2 H (i.e., have lower δ 2 H values) relative to bulk tissue. Such molecules, found in geological settings such as lake sediments, are used extensively as paleoclimate proxies and can have δ 2 H values that are 50-90‰ lower than environmental water (10,11).…”

Unusual C35 to C38 alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida)

“…The δD values of the alkenones in mid-Holocene sediments of Charlotte Harbor strongly deviate from δD values for alkenones from E. huxleyi (Schouten et al, 2006) and from values found for alkenones in other modern brackish environments studied thus far (Schwab and Sachs, 2011). The C 36 alkenones in sediments from the Black Sea were also relatively enriched in deuterium with reported values between -112‰ and -162‰ (Giosan et al, 2012) corresponding, based on co-occuring C 37 alkenones, to salinity between 20 and 30.…”

“…Controlled growth experiments with E. huxleyi have shown that the hydrogen isotopic composition of alkenones is linearly correlated with the hydrogen isotopic composition of the water they grow in (Englebrecht and Sachs, 2005). Schouten et al (2006) showed that the degree of fractionation between water and alkenone δD values by E. huxleyi and G. oceanica decreases when salinity increases. However, this salinity effect on δD was not found for alkenones produced in Chesapeake Bay by coastal haptophytes (Schwab and Sachs, 2011).…”

“…Since there are no experimental data for C 36:2 ethyl ketones, it is not possible to directly calculate corresponding salinity values. Based on the regression between δD of C 37 alkenones and salinity established by Schouten et al, 2006 for E. huxleyi and G. oceanica, measured δD values of around -100‰ suggest unrealistically high salinity values in excess of 50. Although chain length is known to affect δD values, and may explain ca.…”

“…The stable hydrogen and carbon isotopic compositions of these compounds have also been linked to past surface ocean salinity (Schouten et al, 2006;Schwab and Sachs, 2011) and pCO 2 conditions (Bidigare et al, 1997;Pagani et al, 2002), respectively. However, correct interpretation of these alkenone-based proxies requires detailed knowledge of the precursor organisms as well as development of robust calibrations.…”