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

该项目将测试一个新的假设，即更深的居住南极有孔虫钡钙比记录表面海洋生产力。这项研究将量化生活在更深处的寒武纪有孔虫（N。dutertrei和P. dutertrei），并建立了海洋沉积物的古生产力代用指标。由于出口生产力与大气中的碳固存直接相关，并随着厄尔尼诺-南方涛动等气候周期而变化，因此它是确定过去海洋碳循环变异性所需的一个关键参数。在其他生产力代用指标不太可靠或受到损害的地区，如沉积物积累率低和/或生物矿物保存率低的地区，或沉积物缺氧和有机碳积累率可能受陆源影响的沿海地区，南极有孔虫生产力代用指标将特别有用。这项研究的更广泛的影响包括提高有孔虫方解石为基础的气候重建和建立一个新的代理出口生产力的效用。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助。主要研究者（PI）将利用她在俄勒冈州科学与工业博物馆的科学传播研究员职位提供公共宣传。dutertrei记录海水中的Ba/Ca比值在钙化。然而，已发表的记录表明，Ba/Ca在更深居住的浮游有孔虫物种的化石标本中异常高，包括N。dutertrei。化石标本中的Ba/Ca比远远超过了海水Ba/Ca比，可能是由于富含Ba的微环境（如海洋雪）中的钙化。PI将通过在一套跨越赤道太平洋生产力梯度的沉积物岩心中生成下芯Ba/Ca数据，评估深海生物分类群中Ba/Ca与地表沃茨输出生产力相关的假设，将Ba/Ca记录与相同岩心中从末次冰期最大期到现在的时间间隔内的现有古生产力数据进行比较，并通过在保存良好和保存不良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，化石有孔虫的Ba/Ca比降低溶解，这些数据表明，Ba/Ca比仍然反映生产力，即使在样品中最严重的溶解影响。除了生成下钻Ba/Ca记录外，PI还将从相同样品中生成Mg/Ca记录和稳定同位素记录（氧和碳）。N. dutertrei将被用来测试一个新开发的镁基温度校准N。dutertrei。这项研究旨在扩大古海洋学上重要的，但未充分利用的，非刺的浮游有孔虫物种Neogloboquadrina dutertrei和Pulleniatina pulliloculata的效用，并开发一个新的有孔虫为基础的生产力代理。高分辨率分析技术（激光烧蚀-ICP-MS、同位素比质谱法和基于溶液的ICP-MS）将用于生成本研究中的底层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.