Ocean carbon cycling since the middle Miocene: testing the metabolic hypothesis

中新世中期以来的海洋碳循环：检验代谢假说

• 批准号: NE/N001621/1
• 负责人: Paul Pearson
• 金额: $ 76.59万
• 依托单位: CARDIFF UNIVERSITY
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FN001621%2F1
• 关键词: Ocean; carbon; cycling; since; middle

Respiration - the process by which organic matter (food) is broken down to provide energy, releasing carbon dioxide - is strongly temperature-dependent. For every ten degrees increase in temperature, it occurs about 2 and a half times faster. We are respiring organisms but we don't notice this because our body temperatures are regulated, but cold-blooded creatures do, and so too do the most important respirers of all in terms of global processes - the bacteria and other microbes. This is why we put food in the fridge, and why a tropical swamp is a much more biologically active place than a temperate bog. Recently there has been a dawning realization among Earth System scientists that this marked temperature-dependency of microbial metabolism must be taken into account if we are to understand some of the big global feedbacks involved in climate change, and hence we should incorporate it into Earth System computer models.One important process that helps regulate the amount of CO2 in the atmosphere occurs in the ocean, and is called the 'biological pump'. Algae photosynthesize in the photic zone at the surface, forming the base of the food chain. Most of this organic matter gets eaten up and respired in the surface layer and the CO2 is returned to the atmosphere, but a substantial proportion sinks to deeper water. Most of it does, eventually, also get broken down by bacteria, but here the CO2 released is isolated from the surface. Some of the organic matter can reach the sea floor where it can be incorporated into sediments, forming the hydrocarbon source rocks of the future. The rain of organic matter sinking to the deep sea and sediments produces a compensatory 'pump' of CO2 from the atmosphere to the ocean. Now imagine we turn up the temperature in the water column as a result of climate change. This is good news for the bacteria which use up the sinking organic matter more efficiently. Less carbon gets removed from the surface ocean hence CO2 accumulates in the atmosphere until a new balance is restored. Because CO2 is an important greenhouse gas, contributing to global warming when it is in the atmosphere, this process could theoretically accentuate the warming process, or work the other way round on a cooling planet. It is important that we understand how important this feedback is in the real world, and what knock-on effects it may have in other parts of the Earth System. We have devised a way of studying it in the Earth's past, using fossil sediments from the sea floor. We plan to take a series of sediment samples spanning the last 15 million years across the oceans to investigate the efficiency of the biological pump. The planet has cooled markedly over this period so we predict major changes to the functioning of ocean ecosystems and the biological pump. We will study the chemical composition of fossil shells of foraminifera (microscopic protists that occur in large numbers) that lived distributed through the water column. By using a combination of geochemical techniques we can establish the temperature profile, pH profile, and strength of the biological pump.To explore the data we will use a specially modified version of a state-of-the-art Earth System Model that will take into account temperature-dependency of metabolic processes. We will then use the model to investigate its impact on a range of globally important factors such as patterns of organic carbon burial and atmospheric carbon dioxide, and investigate how important these factors are for future climate change.We predict that global cooling over the last 15 million years has produced improved oxygenation and food supply in deep planktonic niches (the so-called 'twilight zone' of the ocean) and that this would have spurred evolutionary innovation at depth. We will test this idea by studying plankton abundance patterns at depth in time and space and investigating whether there has been enhanced evolution in this environment.

呼吸作用——有机物（食物）分解以提供能量并释放二氧化碳的过程——强烈依赖于温度。温度每升高10度，其速度就会加快2.5倍。我们是呼吸有机体，但我们没有注意到这一点，因为我们的体温是受调节的，但冷血动物有，就全球过程而言，最重要的呼吸器官——细菌和其他微生物——也有。这就是为什么我们把食物放在冰箱里，也是为什么热带沼泽比温带沼泽更具有生物活性。最近，地球系统的科学家们逐渐认识到，如果我们要了解与气候变化有关的一些重大的全球反馈，就必须考虑到微生物代谢的这种明显的温度依赖性，因此我们应该把它纳入地球系统的计算机模型中。一个有助于调节大气中二氧化碳含量的重要过程发生在海洋中，被称为“生物泵”。藻类在表面的光带进行光合作用，形成食物链的底部。大部分有机物质在表层被吸收和呼吸，二氧化碳返回大气，但相当一部分沉入更深的水。其中大部分最终也会被细菌分解，但这里释放的二氧化碳与表面隔绝。一些有机物可以到达海底，在那里它可以被合并成沉积物，形成未来的烃源岩。下沉到深海的有机物质雨和沉积物产生了一个从大气到海洋的补偿性的二氧化碳“泵”。现在想象一下，由于气候变化，我们提高了水柱的温度。这对细菌来说是个好消息，因为它们能更有效地利用下沉的有机物。从海洋表面去除的碳较少，因此二氧化碳在大气中积累，直到恢复新的平衡。因为二氧化碳是一种重要的温室气体，当它存在于大气中时，会导致全球变暖，理论上，这一过程可能会加剧变暖过程，或者在一个冷却的星球上反过来。重要的是，我们要了解这种反馈在现实世界中的重要性，以及它在地球系统其他部分可能产生的连锁反应。我们设计了一种研究地球过去的方法，利用海底的化石沉积物。我们计划从过去1500万年的海洋中采集一系列沉积物样本，以调查生物泵的效率。在此期间，地球明显变冷，因此我们预测海洋生态系统和生物泵的功能将发生重大变化。我们将研究分布在水柱中的有孔虫（大量出现的微观原生生物）化石壳的化学成分。通过结合使用地球化学技术，我们可以建立生物泵的温度分布、pH分布和强度。为了研究这些数据，我们将使用一个经过特别修改的最先进的地球系统模型，该模型将考虑到代谢过程的温度依赖性。然后，我们将使用该模型来研究其对一系列全球重要因素的影响，如有机碳埋藏模式和大气二氧化碳，并研究这些因素对未来气候变化的重要性。我们预测，在过去的1500万年里，全球变冷已经改善了深海浮游生物生态位（所谓的海洋“暮光地带”）的氧合和食物供应，这将刺激深海的进化创新。我们将通过研究浮游生物在时间和空间深处的丰度模式，并调查在这种环境中是否有增强的进化来验证这一想法。

项目成果

Future-proofing the Cenozoic macroperforate planktonic foraminifera phylogeny of Aze & others (2011).

• DOI: 10.1371/journal.pone.0204625
• 发表时间: 2018
• 期刊: PloS one
• 影响因子: 3.7
• 作者: Fordham BG;Aze T;Haller C;Zehady AK;Pearson PN;Ogg JG;Wade BS
• 通讯作者: Wade BS

Late Neogene evolution of modern deep-dwelling plankton

现代深栖浮游生物的新近纪晚期演化

• DOI: 10.5194/bg-2021-230
• 发表时间: 2021
• 作者: Boscolo-Galazzo F

Calibration of key temperature-dependent ocean microbial processes in the cGENIE.muffin Earth system model

• DOI: 10.5194/gmd-2019-344
• 发表时间: 2020-02
• 期刊: Geoscientific Model Development Discussions
• 作者: K. Crichton;Jamie D. Wilson;A. Ridgwell;P. Pearson

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

• DOI: 10.5194/cp-17-2223-2021
• 发表时间: 2021-10-21
• 期刊: CLIMATE OF THE PAST
• 影响因子: 4.3
• 作者: Crichton, Katherine A.;Ridgwell, Andy;Pearson, Paul N.
• 通讯作者: Pearson, Paul N.

Temperature controls carbon cycling and biological evolution in the ocean twilight zone

• DOI: 10.1126/science.abb6643
• 发表时间: 2021-03-12
• 期刊: SCIENCE
• 影响因子: 56.9
• 作者: Boscolo-Galazzo, Flavia;Crichton, Katherine A.;Pearson, Paul N.
• 通讯作者: Pearson, Paul N.