Stable carbon isotope fractionation of organic cyst-forming dinoflagellates: Evaluating the potential for a CO2 proxy

Abstract

Over the past decades, significant progress has been made regarding the quantification and mechanistic understanding of stable carbon isotope fractionation ( 13 C fractionation) in photosynthetic unicellular organisms in response to changes in the partial pressure of atmospheric CO 2 (pCO 2 ). However, hardly any data is available for organic cyst-forming dinoflagellates while this is an ecologically important group with a unique fossil record. We performed dilute batch experiments with four harmful dinoflagellate species known for their ability to form organic cysts: Alexandrium tamarense, Scrippsiella trochoidea, Gonyaulax spinifera and Protoceratium reticulatum. Cells were grown at a range of dissolved CO 2 concentrations characterizing past, modern and projected future values ($5-50 lmol L À1 ), representing atmospheric pCO 2 of 180, 380, 800 and 1200 latm. In all tested species, 13 C fractionation depends on CO 2 with a slope of up to 0.17& (lmol L) À1. Even more consistent correlations were found between 13 C fractionation and the combined effects of particulate organic carbon quota (POC quota; pg C cell À1) and CO 2 . Carbon isotope fractionation as well as its response to CO 2 is species-specific. These results may be interpreted as a first step towards a proxy for past pCO 2 based on carbon isotope ratios of fossil organic dinoflagellate cysts. However, additional culture experiments focusing on environmental variables other than pCO 2 , physiological underpinning of the recorded response, testing for possible offsets in 13 C values between cells and cysts, as well as field calibration studies are required to establish a reliable proxy.

Seasonal variability in phytoplankton stable carbon isotope ratios and bacterial carbon sources in a shallow Dutch lake

“…A relationship between fractionation values and concentrations of CO 2(aq) would thus be expected, with higher e when pCO 2(aq) is higher. This relationship has been confirmed in several studies, which have shown the response of e to changing pCO 2(aq) to be species-specific (Degens et al 1968;Mizutani and Wada 1982;Finlay 2004;Hoins et al 2015). At both sampling sites in Lake Naarden, a general seasonal trend of higher pCO 2(aq) occurring with higher e CO2-phyto ( Fig.…”

Towards quantitative environmental reconstructions from ancient non-analogue microfossil assemblages: Ecological preferences of Paleocene – Eocene dinoflagellates

“…In recent years, significant progress was made in revealing the molecular composition of the cysts (Versteegh et al, 2007;Bogus et al, 2012Bogus et al, , 2014 and efforts to analyze their stable carbon isotope composition are emerging (Sluijs et al, 2007a(Sluijs et al, , 2018van Roij et al, 2016), which may ultimately lead to development of a new pCO 2 proxy (e.g. Hoins et al, 2015).…”

Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum

“…The impact and geographical extent of this heat-stress-driven biodiversity drop, however, remain unknown, although similar heat-stress effects on marine biota may have been widespread in tropical regions . Although other stressors like stratification, salinity fluctuations, and acidification may play a role, it should be noted that dinoflagellates typically thrive under such conditions, including high CO 2 (Hoins et al, 2015). Here, we analyze the PETM from ODP Site 959 in the equatorial Atlantic ( Fig.…”