Understanding and modelling the Microbial Carbon Pump under changing nutrient concentrations and temperature

海水是一种复杂的化学物质汤，包括溶解的有机物质（DOM），如糖，脂肪和氨基酸都含有碳。事实上，海洋DOM中的碳含量与大气中的二氧化碳含量大致相同。那么，这些碳是如何变成DOM的，又是什么控制着它的产生和命运呢？大气中的二氧化碳溶解在海水中，被称为浮游植物的小型单细胞生物将其转化为对其生长至关重要的有机分子。这些有机分子中的一些从健康细胞中泄漏出来，而更多的是在细胞死亡或被吃掉时释放出来的，从而形成了DOM的海洋池。许多人都熟悉这样的概念，即浮游植物支持海洋食物网，不同生物过程产生的死细胞和碎屑沉入海底，被沉积物掩埋。这一过程有效地将最初以大气CO2形式存在的碳输送到海底;这被称为“生物碳泵”（BCP）。科学家们最近才意识到的另一个过程提供了另一种去除和储存大气二氧化碳的方法。在这一过程中发挥关键作用的是更小的生物体，它们是海洋中数量最多的生命形式：细菌。细菌迅速对浮游植物释放的DOM及其相关食物网的活动采取行动，清除它们最容易用于生长的部分。经过数周和数月的时间，DOM组分的连续清除逐渐改变了剩余物质的化学性质，因此残留分子几乎不含其他值得服用的物质。这些分子，通常被定义为“难熔DOM”，在生物学上毫无价值，并被留在地球的洋流中。这里描述的过程被称为“微生物碳泵”（MCP），被认为在过去的几千年里缓慢地积累和储存了惊人数量的难降解DOM，估计为624千兆吨。这种令人难以置信的碳库目前被认为是稳定的，非生物去除过程（例如光降解）平衡了其生产。然而，最近的研究表明，由于气候变化，预计海洋表层无机营养物质的可用性会减少，这可能会改变MCP的活性，增加耐火性DOM的生产量。这意味着，海洋细菌有可能通过将更多的碳分流到难降解DOM中来减轻大气CO2的人为增加。如果这一假设得到证实，将从根本上改变我们对生物圈调节气候能力的看法，这表明海洋细菌在以前被忽视的气候活跃作用。我们必须了解这种机制是否重要的唯一方法是使用数值模型，并在不断变化的环境条件下运行它们。然而，到目前为止，没有海洋或地球系统模型帐户MCP dynamics.In本项目中，我们将进行实验室实验，以提供所需的生理信息和理解水平，使我们能够开发第一个模型描述MCP及其与营养浓度和温度的关系。这一结果将是模拟当前和未来海洋中MCP的第一个关键步骤。为了实现这一雄心勃勃的目标，该项目将汇集一个由国际公认的科学家组成的多学科团队，从化学分析师到系统生物学和生态系统建模师。项目团队将通过与N教授的合作得到加强。焦教授（厦门大学，中国）7年前在一篇开创性的论文中首次提出了MCP概念。

Seawater is a complicated soup of chemicals including dissolved organic material (DOM), such as sugars, fats and amino acids all containing carbon. In fact, there is roughly the same amount of carbon within marine DOM as there is CO2 in the atmosphere. So how did this carbon become DOM, and what controls its production and fate? Atmospheric CO2, dissolves in seawater where small single celled organisms called phytoplankton incorporate it into organic molecules essential for their growth. Some of these organic molecules leak from healthy cells, while more are released when cells die, or are eaten, creating an oceanic pool of DOM. Many people are familiar with the concept that phytoplankton support marine food webs and that dead cells and detritus generated by different biological processes sink to the seafloor to be buried in sediments. This process effectively transports carbon, originally present as atmospheric CO2, to the seafloor; this is termed the 'Biological Carbon Pump' (BCP). A separate process, which scientists have only recently become aware of, provides another way of removing and storing atmospheric CO2. The key role in this process is played by even smaller organisms which are numerically the most abundant life form in the oceans: the bacteria. Bacteria quickly act upon the DOM released from phytoplankton and the activities of their associated food web, scavenging parts they can most readily use for growth. Progressively, over weeks and months, sequential scavenging of components of DOM gradually transforms the chemical nature of the remaining material so that the residual molecules contain little else worth taking. These molecules, commonly defined as 'refractory-DOM', are biologically worthless, and are left to travel the Earth's Oceanic currents. The process described here is called the 'Microbial Carbon Pump' (MCP) and is thought to have slowly accumulated and stored a staggering amount of refractory-DOM over the past millennia, estimated to be 624 gigatonnes. This incredible reservoir of carbon is currently thought to be stable, with abiotic removal processes (e.g. photo degradation) balancing its production. However, recent studies suggest that that the projected decrease in surface ocean inorganic nutrient availability due to climate change could modify MCP activity, increasing refractory-DOM production with respect to its consumption. This implies that marine bacteria have the potential to mitigate the anthropogenic increase in atmospheric CO2 by shunting more carbon into refractory-DOM. This hypothesis, if verified, will radically change the way we think of the capacity of the biosphere to modulate climate, suggesting a previously overlooked climate-active role for marine bacteria.The only way we have to understand if this mechanism is significant is to use numerical models and run them under changing environmental conditions. However, to date, no ocean or Earth system models account for MCP dynamics.In this project, we will conduct laboratory experiments to provide the required level of physiological information and understanding needed to enable us to develop the first model describing the MCP and its relationship with nutrient concentration and temperature. This outcome will be the first critical step toward the simulation of the MCP in present and future oceans. To achieve this ambitious goal, the project will bring together a multidisciplinary team of internationally recognised scientists, from chemical analysts to system biology and ecosystem modellers. The project team will be boosted by the partnership with Prof N. Jiao (Xiamen University, China) who first proposed the MCP concept in a seminal paper 7 years ago.