Barium/calcium ratios in non-spinose planktic foraminifera: a novel proxy for reconstructing paleo-productivity

这个项目将测试一个新的假设，即生活在深海的浮游有孔虫钡钙比记录了海洋表面的生产力。该研究将量化深海浮游有孔虫（N. duterte和P. obliquiloculata）的钡地球化学与海洋沉积物中建立的古生产力代用物之间的联系。由于出口生产力与大气中的碳固存直接相关，并随厄尔尼诺-南方涛动等气候周期而变化，因此它是建立过去海洋碳循环变异性所需的关键参数。浮游有孔虫衍生的生产力指标在其他生产力指标不太可靠或受到损害的地区特别有用，例如在沉积物积累率低和/或生物矿物保存率低的地区，或在沉积物缺氧且有机碳积累率可能受到陆源影响的沿海地区。本研究的更广泛的影响包括提高基于有孔虫方解石的气候重建的效用和建立出口生产力的新代理。该项目将为一名早期职业女性研究员、一名研究生和两名本科生提供支持。首席研究员（PI）将利用她在俄勒冈科学与工业博物馆的科学传播研究员的职位提供公众宣传。实验室培养实验证实，杜氏乳藻在钙化过程中记录了海水Ba/Ca比值。然而，已发表的记录显示，Ba/Ca在深海浮游有孔虫物种的化石标本中异常高，包括N. duterte。化石标本中的Ba/Ca比值远远超过单纯用海水Ba/Ca比值解释的结果，可能是由于海洋雪等富Ba微环境的钙化所致。PI将通过在一组跨越赤道太平洋生产力梯度的沉积物岩心中生成下岩心Ba/Ca数据来评估深层栖息分类群中Ba/Ca与地表水出口生产有关的假设，并将Ba/Ca记录与现有的古生产力数据进行比较，这些数据来自同一岩心，跨越了从末次盛冰期到现在的时间间隔。并通过在保存完好和保存较差的沉积物中完成重建来评估代理的保真度。虽然初步数据表明化石有孔虫Ba/Ca比值因溶解而降低，但这些数据表明，即使在受溶解影响最严重的样品中，Ba/Ca比值仍然反映了生产力。除了生成下岩心Ba/Ca记录外，PI还将生成来自同一样品的Mg/Ca记录和稳定同位素（氧和碳）记录。该Mg/Ca数据将用于测试新开发的基于Mg的温度校准。本研究旨在扩大古海洋学上重要但未被充分利用的非棘浮游有孔虫物种Neogloboquadrina duterte和Pulleniatina obliquiloculata的效用，并开发一种新的基于有孔虫的生产力代理。高分辨率分析技术（激光烧蚀- icp - ms、同位素比质谱和溶液基icp - ms）将用于生成下岩心微量元素和稳定同位素记录。

This project will test a novel hypothesis that deeper dwelling planktic foraminiferal barium-to-calcium ratios record surface-ocean productivity. The research will quantify the link between the barium geochemistry of deeper-dwelling planktic foraminifera (N. dutertrei and P. obliquiloculata) and established paleoproductivity proxies in marine sediments. Because export productivity is directly linked to carbon sequestration from the atmosphere and varies with climate cycles such as the El Nino-Southern Oscillation, it is a key parameter required to establish carbon cycle variability in the past ocean. A planktic foraminiferal derived productivity proxy will be particularly useful in areas where other productivity proxies are less reliable or compromised, such as in areas with low sediment accumulation rates and/or low preservation of biogenic minerals, or in coastal settings where sediments become anoxic and organic carbon accumulation rates can be biased by terrestrial sources. The broader impacts of this research include improved utility of foraminiferal calcite based climate reconstructions and the establishment of a new proxy for export productivity. The project will provide support for an early career female researcher, a graduate student, and two undergraduate students. The principal investigator (PI) will utilize her position as a Science Communication Fellow at the Oregon Museum of Science and Industry to provide public outreach.Laboratory culture experiments confirm that N. dutertrei record seawater Ba/Ca ratios during calcification. Yet, published records show that Ba/Ca is unusually high in fossil specimens of the deeper dwelling planktic foraminifera species, including N. dutertrei. The Ba/Ca ratio in fossil specimens far exceeds that which can be explained by seawater Ba/Ca ratios alone and may be due to calcification in microenvironments enriched in Ba, such as marine snow. The PI will evaluate the hypothesis that Ba/Ca in deep dwelling taxa is related to export production from surface waters by generating downcore Ba/Ca data in a suite of sediment cores that span a productivity gradient across the equatorial Pacific, compare the Ba/Ca records to existing paleo-productivity data spanning the time interval from the last glacial maximum to present from the same cores, and assess the fidelity of the proxy by completing reconstructions in well-preserved and poorly-preserved sediments. While preliminary data indicate that fossil foraminifer Ba/Ca ratios are lowered by dissolution, these data suggest that Ba/Ca ratios still reflect productivity even in the samples most heavily affected by dissolution. In addition to generating downcore Ba/Ca records, the PI will generate Mg/Ca records and stable isotope records (oxygen and carbon) from the same samples. The Mg/Ca data for N. dutertrei will be used to test a newly developed Mg-based temperature calibration for N. dutertrei. This research seeks to expand the utility of the paleoceanographically important, but underutilized, non-spinose planktic foraminifera species Neogloboquadrina dutertrei and Pulleniatina obliquiloculata and develop a new foraminifer-based proxy for productivity. High-resolution analytical techniques (laser ablation-ICP-MS, isotope ratio mass spectrometry, and solution based-ICP-MS) will be used to generate the downcore trace element and stable isotope records in this study.