SEASONAL VARIABILITY IN THE EFFICIENCY OF UPPER OCEAN CARBON EXPORT

海洋是大气碳的主要储存库。全球碳循环的一个重要组成部分是海洋的生物碳泵(BCP)，它主要由有机颗粒从表层海洋下沉到海洋内部。在表层水域通过浮游植物初级生产产生的物质中，大部分在上层海洋中循环使用。一小部分被输出到深海，并以数百到数千年的时间尺度隔离，远离与大气的进一步接触。预计BCP的规模和效率都将随着气候变化而在全球范围内下降，这可能会导致海洋碳储量减少，从而增加大气中的二氧化碳水平。因此，准确地量化全球BCP的大小和效率对于了解地球的碳循环和持续的人为二氧化碳输入的影响至关重要。然而，目前对BCP强度的估计是4倍，这表明尽管进行了30多年的研究，但尚未就其强度达成共识。更不确定的是，是什么控制了BCP的效率及其在季节性时间尺度上的变化。最近，PI和合著者开发了一个新的出口比率参数(描述上层海洋BCP的效率)。这表明BCP的效率比之前认为的要低得多。然而，我们对出口比率的参数化在较冷的海面温度下具有较大的不确定性。出口比率被认为在很大程度上是由上层海洋中存在的浮游植物的类型推动的，因为大型、密集的浮游植物下沉速度快，出口效率高于较小的浮游生物。我们的假设是，低温下出口比率的变化是由于高纬度浮游植物水华演化的强烈季节性，由浮游植物群落结构的时间变化驱动。该项目将通过现场研究和基于卫星数据的研究相结合，评估浮游植物水华的季节变化如何改变次北极地区的出口比率。我们建议整理两个高纬度地区的上层海洋颗粒有机碳通量和同步浮游植物群落结构的测量结果，这些地区的SST适宜较低，浮游植物水华的变异性很强。该项目将使用英国海洋酸化研究计划前往北极的邮轮(工作已由NERC资助)和前往拉布拉多海的邮轮收集的数据，这里要求提供资金。我们建议在2012年5月参加一个现有的邮轮(由DFO加拿大资助)，以额外测量出口流量和浮游植物群落结构。将利用水华阶段的变化和巡航期间遇到的初级保健系统来确定水华条件的季节梯度对出口效率的影响。然后，我们将把从区域研究中获得的理解应用于全球出口测量数据库，利用卫星获取的关于海洋表面温度、水华盛发期和浮游植物群落结构的数据。然后，我们将制定修订后的出口比率参数，包括相关的季节性信息，并在拟议工作的最后阶段，将修订后的参数应用于全球，以计算BCP规模的新估计。该项目旨在了解对出口比率季节性变化的控制，从而减少估计全球贸易顺差幅度的不确定性。

The oceans are a major repository for atmospheric carbon. An important component of the global carbon cycle is the ocean's biological carbon pump (BCP), which is dominated by the sinking of organic particles from the surface ocean to its interior. Of the material generated via phytoplankton primary production in surface waters, most is recycled in the upper ocean. A small fraction is exported to the deep ocean and sequestered away from further contact with the atmosphere on timescales of hundreds to thousands of years. Both the size and efficiency of the BCP are predicted to decline globally in response to climate change, potentially resulting in reduced ocean carbon storage and hence increased atmospheric carbon dioxide levels. Therefore, accurately quantifying the magnitude and efficiency of the global BCP is essential to understanding the Earth's carbon cycle and the impact of continued anthropogenic inputs of carbon dioxide. However, current estimates of the strength of the BCP range 4-fold, suggesting that despite more than 30 years of study, no consensus on its magnitude has yet been reached. There is even more uncertainty about what controls the efficiency of the BCP and its variability on seasonal timescales.Recently, a new parameterisation of the export ratio (which describes the efficiency of the upper ocean BCP) was developed by the PI and co-authors. This suggested that the BCP efficiency was substantially lower than previously thought. However, our parameterisation of the export ratio has relatively large uncertainty at cold sea surface temperature. The export ratio is thought to be driven in large part by the type of phytoplankton present in the upper ocean, because large, dense phytoplankton sink rapidly and export more efficiently than smaller plankton. Our hypothesis is that the variability in export ratio at low temperatures is due to strong seasonality in phytoplankton bloom evolution at high latitudes, driven by temporal shifts in phytoplankton community structure. This project will assess how seasonal variability of the phytoplankton bloom alters the export ratio in the sub-Arctic through a combination of in situ and satellite data based studies. We propose to collate measurements of upper ocean particulate organic carbon flux and simultaneous phytoplankton community structure from two high latitude regions with suitably cold SST and strong variability in phytoplankton blooms. This project will use data to be collected on a UK Ocean Acidification Research Programme cruise to the Arctic (work already funded by NERC), and on a cruise to the Labrador Sea, for which funds are requested here. We propose to participate in an existing cruise in May 2012 (funded by DFO Canada) to take additional measurements of export flux and phytoplankton community structure. The variability in bloom stage and PCS encountered during the cruises will be used to determine the impact of seasonal gradients in bloom conditions on the export efficiency. We will then apply the understanding gained from the regional studies to a global database of export measurements, using satellite-derived data on sea surface temperature, bloom stage and phytoplankton community structure. We will then develop a revised parameterisation of the export ratio, including relevant seasonal information and in the final stage of the proposed work, apply our revised parameterisation globally to calculate a new estimate of the magnitude of the BCP. The project aims to gain understanding of controls on seasonal variability in the export ratio, and hence reduce uncertainty in the estimate of global BCP magnitude.