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

微观的化石壳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（d11B）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有价值的见解。最近的实验表明，硫酸盐离子的加入增加了碳酸盐矿物中B的掺入量。提出的研究将探讨硫酸盐如何以及为什么增强B的掺入。它还将检查硫酸盐是否影响合成方解石的d11B。该研究将通过培养实验来评估生物源方解石的硼化学是否受到海水硫酸盐的影响。这将是对d11B和B/Ca化石记录可靠性的关键考验，因为海水硫酸盐在过去6000万年里发生了很大的变化。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。本研究结合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结合与硫酸盐（SO42−）之间的机制联系及其与生物系统的相关性。首先，我们将综合分析合成方解石中δ11B、B/Ca等微量元素（S/Ca和Na/Ca）在加入B水溶液和变量SO42−的溶液中析出。其次，我们将在添加B和/或SO42−的生长溶液中生长亚毫米尺度的方解石晶体，并使用二次离子质谱仪（SIMS）比较B和S的晶体内分布/分区。最后，我们将在不同的海水SO42−浓度下培养一种经过充分研究的底栖有孔虫。如果有孔虫δ11B和B/Ca确实对海水SO42−的变化敏感，我们将提供解释SO42−效应的方程。该奖项反映了美国国家科学基金会的法定使命，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.