Geochemistry of benthic foraminifera grown under different carbonate system conditions

insights into past marine carbon cycling and water mass properties can be obtained through controlled laboratory experiments with accurate seawater carbonate system (c-system) manipulations. here, we explored the use of strontium/calcium ratio (sr/ca) of the calcite shells of benthic foraminifera as a potential seawater c-system proxy through a controlled growth experiment with two deep-sea species (bulimina marginata and cassidulina laevigata) and one intertidal species (ammonia t6). to this aim, we decoupled carbonate chemistry in controlled growth experiments, i.e., changing ph at constant dissolved inorganic carbon (dic) and changing dic at constant ph. four climatic chambers were used with different controlled concentrations of atmospheric pco2 (180 ppm, 410 ppm, 1000 ppm, 1500 ppm). our results demonstrated that low ph conditions (7.56-7.73) did not influence the survival and growth rates of the three species. however, low dic conditions (879 µmol kg-1) negatively affected b. marginata and c. laevigata through low growth rate, whereas no effect was observed for ammonia t6. our results also showed a significant positive correlation between sr/ca and the c-system (dic - bicarbonate ion concentration) for ammonia t6 and b. marginata. for these two species, the regression models were coherent with published data (existing so far only for ammonia t6) and showed overall similar slopes but different intercepts, implying species-specific effect. furthermore, the sr/ca - c-system relationship was not impacted by ontogenetic trends between chamber stages, which is a considerable advantage for paleo-applications. however, no correlation with any of the c-system parameters was observed for sr/ca in c. laevigata. this might imply either a strong species-specific effect and/or a low tolerance to laboratory conditions leading to physiological stress, thereby impacting the sr incorporation into the calcite lattice.

通过精确操控海水碳酸盐体系（C-system）的实验室实验，我们可以洞察既往海洋碳循环及水团属性。在本研究中，我们探讨了利用底栖有孔虫钙质壳中的锶/钙比例（Sr/Ca）作为海水C-system潜在代理的可行性，通过针对两种深海物种（Bulimina marginata和Cassidulina laevigata）及一种潮间带物种（Ammonia t6）的控制生长实验进行探究。为此，我们在控制生长实验中解耦了碳酸盐化学，即在恒定溶解无机碳（DIC）条件下改变pH值，以及在恒定pH值条件下改变DIC。我们使用了四个气候室，分别设置不同的控制大气CO2浓度（180 ppm、410 ppm、1000 ppm、1500 ppm）。我们的结果表明，低pH条件（7.56-7.73）并未影响三种物种的存活和生长速率。然而，低DIC条件（879 µmol kg-1）通过降低生长速率对B. marginata和C. laevigata产生了负面影响，而对Ammonia t6则未观察到任何影响。此外，我们的结果还显示，对于Ammonia t6和B. marginata，Sr/Ca与C-system（DIC-重碳酸盐离子浓度）之间存在显著的正相关关系。对于这两种物种，回归模型与已发表的数据（目前仅限于Ammonia t6）一致，整体斜率相似但截距不同，表明存在物种特异性效应。此外，Sr/Ca与C-system的关系未受到气候室阶段之间的发育趋势的影响，这对古生物学应用而言是一个显著的优点。然而，在C. laevigata中，Sr/Ca与任何C-system参数之间均未观察到相关性。这可能暗示了强烈的物种特异性效应，以及对于实验室条件低耐受性所导致的生理压力，从而影响锶在方解石晶格中的结合。