SEASONAL VARIABILITY IN THE EFFICIENCY OF UPPER OCEAN CARBON EXPORT

海洋是大气中碳的主要储存地。全球碳循环的一个重要组成部分是海洋的生物碳泵（BCP），它主要是由海洋表面的有机颗粒下沉到其内部。在表层沃茨中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。一小部分被排放到深海，在数百至数千年的时间尺度上与大气层隔绝。预计BCP的规模和效率都将因气候变化而在全球范围内下降，可能导致海洋碳储存减少，从而增加大气二氧化碳水平。因此，准确量化全球BCP的规模和效率对于了解地球的碳循环和持续人为二氧化碳输入的影响至关重要。然而，目前对BCP强度的估计为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。更不确定的是什么控制着BCP的效率及其季节时间尺度上的变化。最近，PI和合著者开发了一种新的输出比率参数化（描述了上层海洋BCP的效率）。这表明BCP的效率比以前认为的要低得多。然而，我们的参数化的输出比有比较大的不确定性，在寒冷的海面温度。输出比例被认为在很大程度上是由海洋上层的浮游植物类型决定的，因为大型、密集的浮游植物下沉速度快，比小型浮游植物输出效率更高。我们的假设是，在低温下的出口率的变化是由于在高纬度地区的浮游植物水华演变的强烈的季节性，在浮游植物群落结构的时间变化的驱动。该项目将通过结合实地研究和基于卫星数据的研究，评估浮游植物大量繁殖的季节性变化如何改变亚北极地区的出口率。我们建议整理测量上层海洋颗粒有机碳通量和浮游植物群落结构，从两个高纬度地区，适当冷的SST和强烈的变化，在浮游植物水华。该项目将使用联合王国海洋酸化研究方案北极巡航（已由NERC资助的工作）和拉布拉多海巡航（此处要求提供资金）收集的数据。我们建议参加2012年5月的现有巡航（由加拿大DFO资助），以进一步测量输出通量和浮游植物群落结构。在巡航期间遇到的水华阶段和PCS的变化将用于确定水华条件的季节梯度对出口效率的影响。然后，我们将利用卫星获得的关于海面温度、水华阶段和浮游植物群落结构的数据，将从区域研究中获得的认识应用于全球出口测量数据库。然后，我们将修订出口比率的参数化，包括相关的季节性信息，并在拟议工作的最后阶段，在全球范围内应用我们修订的参数化来计算BCP幅度的新估计。该项目旨在了解对出口比率季节性变化的控制，从而减少全球BCP幅度估计的不确定性。

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.