(Table 1) Calcium isotope composition, Mg/Ca, Sr/Ca and U/Ca ratios of calcareous cysts of Thoracosphaera heimii

We investigated the influences of temperature, salinity and pH on the calcium isotope as well as trace and minor element (uranium, strontium, magnesium) to Ca ratios on calcium carbonate cysts of the calcareous dinoflagellate species Thoracosphaera heimii grown in laboratory cultures. The natural habitat of this species is the photic zone (preferentially at the chlorophyll maximum depth) of temperate to tropical oceans, and it is abundant in deep-sea sediments over the entire Cenozoic. In our experiments, temperatures ranged from 12 to 30 °C, salinity from 36.5 to 38.8 and pH from 7.9 to 8.4. The delta44/40Ca of T. heimii cysts resembles that of other marine calcifiers, including coccolithophores, foraminifers and corals. However, its temperature sensitivity is considerably smaller and statistically insignificant, and T. heimii might serve as a recorder of changes in seawater delta44/40Ca over geologic time. The Sr/Ca ratios of T. heimii cysts show a pronounced temperature sensitivity (0.016 mmol/mol °C**-1) and have the potential to serve as a palaeo-sea surface temperature proxy. No clear temperature- and pH-dependences were observed for Mg/Ca. U/Ca seems to be influenced by temperature and pH, but the correlations change sign at 23 °C and pH 8.2, respectively.本研究通过实验室培养实验，探究了温度、盐度与pH值对实验室培养的钙甲藻（calcareous dinoflagellate）物种赫氏棘球囊藻（Thoracosphaera heimii）碳酸钙囊孢的钙同位素以及痕量与少量元素（铀、锶、镁）与钙的比值的影响。该物种的自然生境为温带至热带海洋的透光带（优先位于叶绿素最大深度处），且在整个新生代的深海沉积物中分布广泛。本实验设置的温度范围为12~30℃，盐度范围为36.5~38.8，pH值范围为7.9~8.4。赫氏棘球囊藻囊孢的δ⁴⁴/⁴⁰Ca值与其他海洋钙化生物（包括颗石藻、有孔虫以及珊瑚）的δ⁴⁴/⁴⁰Ca值相近。但该物种的温度敏感性显著更低，且在统计学上无显著意义，因此赫氏棘球囊藻可作为地质历史时期海水δ⁴⁴/⁴⁰Ca变化的记录载体。赫氏棘球囊藻囊孢的Sr/Ca比值表现出显著的温度敏感性（0.016 mmol·mol⁻¹·℃⁻¹），具备作为古海水表层温度代用指标的潜力。Mg/Ca比值未表现出明确的温度与pH依赖性。U/Ca比值似乎受温度与pH值的影响，但二者的相关性分别在23℃与pH=8.2时发生符号反转。