The effect of temperature and salinity 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 per mil compared to those of E. huxleyi when grown under similar conditions. The fractionation factor, αalkenones-H2O, 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 αalkenones-H2O with temperature but a positive linear correlation was observed between αalkenones-H2O and salinity with ~3 per mil change in fractionation per salinity unit. This suggests that salinity can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments and, vice versa, that δD can possibly be used as a proxy to estimate paleosalinity.

How dry was the Mediterranean during the Messinian salinity crisis?

“…The conditions seem to be much different from the recent-times Mediterranean Sea where, since the last interglacial, the recorded δD alkenone varied between − 185‰ and −210‰ (van der Meer et al, 2007). Regardless of the applied calibration (Englebrecht and Sachs, 2005;Paul, 2002;Schouten et al, 2005;Schwab and Sachs, 2011;van der Meer et al, 2015;Sachs and Kawka, 2015), our δD alkenone results indicate extreme evaporation prevailing during stage 2 (halite) and 3 (Upper Gypsum). Still, similarly to alkenone based SST reconstructions (Prahl and Wakeham, 1987), there are limitations when calculating δD water from δD alkenone , since e.g.…”

“…The δD composition of the alkenones reflects predominantly the δD of the water they live in (Englebrecht and Sachs, 2005;Schouten et al, 2005;Paul, 2002), although values are also influenced by salinity , growth rate (Schouten et al, 2005;Van der Meer et al, 2015;Sachs and Kawka, 2015) and probably irradiance (Pagani, 2002;Van der Meer et al, 2015). Therefore δD alkenone was used as a proxy to reconstruct δD water (Englebrecht and Sachs, 2005;Schouten et al, 2005;Paul, 2002;Schwab and Sachs, 2011), which in turn closely reflects seawater salinity.…”

“…The δD composition of the alkenones reflects predominantly the δD of the water they live in (Englebrecht and Sachs, 2005;Schouten et al, 2005;Paul, 2002), although values are also influenced by salinity , growth rate (Schouten et al, 2005;Van der Meer et al, 2015;Sachs and Kawka, 2015) and probably irradiance (Pagani, 2002;Van der Meer et al, 2015). Therefore δD alkenone was used as a proxy to reconstruct δD water (Englebrecht and Sachs, 2005;Schouten et al, 2005;Paul, 2002;Schwab and Sachs, 2011), which in turn closely reflects seawater salinity. The existing records of measured δD on alkenones produced in the present day ocean range from approximately −181‰ in the warm Sargasso Sea (at 31°N) (Englebrecht and Sachs, 2005) to approximately − 200‰ in the temperate Chesapeake Bay (at 43°N) (Schwab and Sachs, 2011).…”

Spatial and temporal dynamics of water isotopes in the riverine‐marine mixing zone along the German Baltic Sea coast

“…Those were used to retrospectively predict the whereabouts of migrating fish (Brennan et al, 2019; Torniainen et al, 2017; Trueman et al, 2012), and to assign fish to discrete, geographically segregated stocks (Matta et al, 2010). With respect to aquatic plants or algae, their cellular lipid compounds have been shown to track the hydrogen isotopic signature of the ambient water, but with a potential additional influence of varying salinity (Aichner et al, 2017; Häggi et al, 2015; He et al, 2020; Ladd & Sachs, 2015, 2017; Sachs & Schwab, 2011; Schouten et al, 2006). These dependencies have frequently been applied in paleoclimatic studies, for reconstruction of past hydrological conditions and salinities (e.g.…”

Impact of metabolism and temperature on 2H/1H fractionation in lipids of marine bacterium Shewanella piezotolerans WP3

“…Still, the variations associated with these factors are rather small (~ 10-20‰) compared with metabolisms. Temperature is one of the most important environmental factors, and culture studies have demonstrated its impacts on hydrogen isotope composition of lipids in phototroph and archaea (Schouten et al, 2006;Dirghangi and Pagani, 2013a). Until now, however, there have been no cultures focusing on whether or not temperature can affect lipid hydrogen isotopes in heterotrophic bacteria, if so, by what relationship between fractionations and growth temperatures.…”