Collaborative Research: Effects of sulfate on boron incorporation into calcite: Relevance and implications for foraminiferal boron isotope and B/Ca paleo-proxies.

显微镜下的贝壳化石可以提供过去海洋化学的记录。这些化石的硼钙比（B/Ca）和硼同位素组成（d 11 B）被广泛用于记录海水pH和碳化学。这些记录为了解过去大气二氧化碳和全球碳循环的变化提供了宝贵的见解。最近的实验表明，硫酸根离子的加入增加了结合到碳酸盐矿物中的B的量。拟议的研究将探讨如何和为什么B掺入增强硫酸盐。它还将检查硫酸盐是否影响合成方解石的d11 B。该研究将使用培养实验来评估生物方解石的硼化学是否受到海水硫酸盐的影响。这将是对d11 B和B/Ca化石记录可靠性的一个关键测试，因为海水硫酸盐在过去6000万年中发生了巨大变化。该项目还将为研究生和本科生提供培训，并向当地社区开展教育推广活动。本研究整合了无机方解石沉淀实验和有孔虫培养，以底栖有孔虫为模式生物，研究B掺入和硫酸盐（SO 42 −）之间的机制联系及其与生物系统的相关性。首先，我们将综合分析在添加水溶液B和不同量的SO 42 −的溶液中沉淀的合成方解石的δ 11 B、B/Ca和其他微量元素（S/Ca和Na/Ca）。其次，我们将在添加了B和/或SO 42-水溶液的生长溶液中生长亚毫米级方解石晶体，并使用二次离子质谱仪（西姆斯）比较B和S的晶体内分布/环带。最后，我们将在各种海水SO 42 −浓度下培养一种经过充分研究的底栖有孔虫。如果有孔虫δ 11 B和B/Ca确实对海水SO 42 −的变化敏感，我们将提供计算SO 42 −效应的公式。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Microscopic fossil shells can provide records of ocean chemistry in the past. The boron to calcium ratio (B/Ca) and boron isotopic composition (d11B) of such fossils are widely used to record seawater pH and carbon chemistry. These records provide valuable insights into past changes in atmospheric carbon dioxide and the global carbon cycle. Recent experiments show that the addition of sulfate ions increases the amount of B incorporated into carbonate minerals. The proposed study will explore how and why B incorporation is enhanced by sulfate. It also will examine if sulfate influences the d11B of synthetic calcite. And the study will use culture experiments to assess whether the boron chemistry of biogenic calcite is impacted by seawater sulfate. This will be a crucial test of the reliability of d11B and B/Ca fossil records, since seawater sulfate has varied substantially over the last 60 million years. The project also will provide training for graduate and undergraduate students and educational outreach activities to local communities. This study integrates inorganic calcite precipitation experiments and foraminiferal culturing to investigate the mechanistic link between B incorporation and sulfate (SO42−) and its relevance to biological systems using benthic foraminifers as the model organism. First, we will comprehensively analyze δ11B, B/Ca and other trace elements (S/Ca and Na/Ca) of synthetic calcite precipitated in solutions added with aqueous B and variable amounts of SO42−. Second, we will grow sub-mm scale calcite crystals in growth solutions added with aqueous B and/or SO42−, and compare the intra-crystal distribution/zonation of B and S using a secondary ion mass spectrometer (SIMS). Finally, we will culture a well-studied species of benthic foraminifera under various seawater SO42− concentrations. If foraminiferal δ11B and B/Ca are indeed sensitive to changes in seawater SO42−, we will provide the equations to account for the SO42− effect.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.