NSFGEO-NERC: Understanding the consequences of changing phytoplankton elemental use efficiencies for global ocean biogeochemistry

本项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（UKRI/NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与自己的调查人员有关的调查人员和工作的组成部分提供资金。模拟碳和其他元素全球循环的地球系统计算机模型是我们预测未来海洋环境变化的最有价值的工具之一。然而，现有的建模方法无法真实地测试海洋温度升高将如何影响海洋微生物对通常控制其生长的限制性营养物质的需求，包括氮、磷和铁。因为这些限制性营养物质控制着海洋中光合作用的发生，它们强烈地影响着人类燃烧化石燃料产生的二氧化碳的命运。因此，确定浮游生物对营养物质的利用将如何对海洋表面的温室变暖做出反应，是科学家和决策者的首要任务。该项目支持美国的两位海洋微生物学家和英国的一位地球系统建模师之间的合作，目的是更好地了解海洋限制营养循环及其所支持的生物群落将如何对全球变暖作出反应。美国调查人员正在利用实验室培养实验、沿海海洋的野外工作和现有的过去开放海洋化学和生物学测量数据，对温度上升对营养元素利用效率（EUEs）的影响进行定量估计。EUE被定义为海洋微生物通过光合作用吸收二氧化碳的速率，单位限制营养物质在细胞中。初步结果表明，eue对温度变化高度敏感，这反过来对海洋生态系统的功能产生深远的影响。这位英国研究人员正在利用这些实验确定的值来建立一个新的地球系统模型，该模型的核心是气候变暖将如何影响重要海洋微生物群体的eue。这种新颖的方法有可能更好地估计未来随着海洋持续变暖，海洋碳吸收和营养循环将被改变的方式。更广泛的影响包括通过改进地球系统模型在海洋学和气候科学方面开辟新的科学基础，为研究生、本科生研究人员、K-12学生和博士后研究人员提供教育机会，并加强美国和英国海洋科学界之间的合作关系。主要由于缺乏机械实验数据，初级生产和全球海平面温度上升仍然没有得到很好的理解。这对地球系统建模者来说是个问题，他们正试图预测未来海洋生产力水平，这是海洋生态系统预测变化的基础，而环境决策者迫切需要这些信息。该项目通过两名美国海洋微生物学家和一名英国生物地球化学建模师之间的密切协调合作项目，解决了这一知识差距。跨学科的国际研究团队正在应用元素利用效率（EUEs）的新兴概念，将灵活的热和资源限制响应整合到新一代地球系统模型中。eue被定义为单位时间内固定的碳量，标准化为浮游植物细胞中限制资源的量，用细胞营养配额表示。初步工作表明，eue可能对未来的海洋预警非常敏感，对营养有限的海洋浮游生物组合以及海洋碳和营养生物地球化学产生重大下游影响。研究人员正在使用高通量热块方法来测量实验室浮游植物分离物在其整个热范围内的四种不同功能群中的限制性营养物质氮、磷和铁的eue。从这三种关键的限制性营养资源中获得的eue作为温度和营养胁迫程度的函数，正以迭代的方式应用于已建立的NEMO-PISCES海洋模型的以eue为中心的新版本。目前正在收集来自沿海和开放海洋地区的实地EUE数据，以便与实验室培养结果和模型输出进行比较和实地核实。该项目将通过提供对生物地球化学至关重要的海洋微生物功能群如何对当前和未来不断变化的海洋的温度变化和限制营养资源可用性作出反应的独特新见解，推进海洋全球变化生物学的学科。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。

This project is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own ivestigators and component of the work.Earth system computer models that simulate the global cycles of carbon and other elements are one of our most valuable tools to predict environmental change in the future ocean. However, existing modeling methods cannot realistically test how increasing ocean temperatures will affect the needs of marine micro-organisms for the limiting nutrients that usually control their growth, including nitrogen, phosphorus and iron. Because these limiting nutrients govern how much photosynthesis occurs in the ocean, they strongly influence the fate of carbon dioxide produced by human fossil-fuel burning. For this reason, determining how nutrient use by plankton will respond to greenhouse warming of the surface ocean is a priority for scientists and policy makers. This project supports a collaboration between two marine microbiologists in the United States and an Earth system modeler from the United Kingdom that is aiming to better understand how oceanic limiting nutrient cycles and the biological communities they support will react to global warming. The U.S. investigators are using laboratory culture experiments, field work in the coastal ocean, and existing collections of past open ocean chemistry and biology measurements to generate quantitative estimates of rising temperature effects on nutrient elemental use efficiencies (EUEs). An EUE is defined as the rate at which a marine microbe can take up carbon dioxide via photosynthesis, per unit of limiting nutrient in the cell. Preliminary results show that EUEs are highly sensitive to changing temperature, which in turn has far-reaching consequences for how ocean ecosystems function. The U.K. investigator is using these experimentally-determined values to build a new Earth system model that is centered on how warmer conditions will affect EUEs for important groups of marine micro-organisms. This novel approach has the potential to yield much better estimates of the ways that ocean carbon uptake and nutrient cycling will be altered as the ocean continues to warm in the future. Broader Impacts include breaking new scientific ground in oceanography and climate science through improved Earth system models, providing educational opportunities for graduate students, undergraduate researchers, K-12 students, and postdoctoral investigators, and strengthening collaborative ties between the marine science communities of the U.S. and the U.K.Quantitative relationships between phytoplankton nutrient limitation, primary production and globally-rising sea surface temperatures are still not well understood, largely due to a lack of mechanistic experimental data. This is problematic for Earth system modelers who are trying to project future oceanic productivity levels that underpin predicted changes in ocean ecosystems, information that is urgently needed to inform environmental policy makers. This project addresses this knowledge gap in a closely coordinated, collaborative project between two U.S. marine microbiologists and a biogeochemical modeler from the U.K. The international team of interdisciplinary researchers are applying the emergent concept of Elemental Use Efficiencies (EUEs) to integrate flexible thermal and resource limitation responses into a new generation of Earth system models. EUEs are defined as the amount of carbon fixed per unit time, normalized to the amount of a limiting resource in a phytoplankton cell, as represented by the cellular nutrient quota. Preliminary work suggests that EUEs can be very sensitive to future ocean warning, with major downstream consequences for nutrient-limited marine plankton assemblages and thus also for ocean carbon and nutrient biogeochemistry. The investigators are using high-throughput thermal block methodology to measure EUEs for the limiting nutrients nitrogen, phosphorus and iron in a diverse set of four different functional groups of laboratory phytoplankton isolates across their entire thermal ranges. EUEs obtained for these three key limiting nutrient resources as a function of temperature and degree of nutrient stress are being applied in an iterative manner to inform a novel EUE-centric version of the established NEMO-PISCES ocean model. Field EUE data from coastal and open ocean regimes are being collected for comparison to and ground-truthing of both the laboratory culture results, and the modeling output. This project will advance the discipline of ocean global change biology by providing unique new insights into how biogeochemically-critical marine microbial functional groups may respond to simultaneous shifts in temperature and limiting nutrient resource availability both today, and in the future changing ocean.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.