CoccolitHophore controls on ocean ALKalinitY (CHALKY)

每年在北大西洋，全球碳循环的关键区域，巨大面积的地表水在夏季变成绿松石。这种现象与独特的微观藻类-颗石藻的生长和死亡有关。颗石藻用碳酸钙（称为颗石）的鳞片覆盖它们的细胞，这些鳞片在内部产生并排列成细胞周围的外骨骼。在某些条件下，例如当营养缺乏或病毒感染细胞时，这些球孢子会大量脱落。由于其独特的光学特性和巨大的丰度，它们将水变成乳白色的绿松石色，可以从太空中检测到。这些绿松石色的沃茨（称为“白色水”）是颗石藻聚集的地方，它们已经积累了数万亿，被认为是颗石藻的水华。颗石藻通过钙化形成颗石藻，产生二氧化碳，并通过消耗碱度降低海洋的pH值。当海洋表面的球石消失时，它会降低海洋吸收更多二氧化碳的能力。通过这种方式，“白色沃茨”被认为会导致海洋碳汇的显著减少。然而，我们现在怀疑这些“白色沃茨”不是密集的颗石藻钙化或生长的区域，而是衰老和碎屑物质积累的区域。已经发现，在“白色沃茨”之外，颗石藻生长得更快，钙化得更多，最近我们发现，它们也被部分消化碳酸钙的小动物（浮游动物）大量吃草。通过这种方式，颗石体碳酸钙在表面沃茨中的再循环似乎比以前认为的要多得多，并且与它们相关的碱度可能保留在表面海洋中。然而，我们几乎没有这些不同过程（生长，死亡和下沉）的平衡的耦合测量，从而了解颗石藻如何控制海洋碱度。这代表了全球海洋碳循环的一个主要不确定性，全球碳预算和地球系统模型难以纳入碳酸钙或准确复制海水碱度的观测结果。“颗石藻对海洋碱度的控制”（CHALKY）项目旨在通过量化颗石藻生产和损失过程的平衡及其对碳循环和海气CO2通量的影响，填补这一关键的知识空白。我们将评估生态相互作用和对海水化学的影响，同时改进对颗石藻的原位和遥感光学探测，使我们能够利用地球观测数据将我们的见解扩展到全球海洋，并在历史上使用现有的卫星数据集。CHALKY将首次同时量化颗石藻碳酸钙生产（消耗碱度），病毒裂解（保留碱度），浮游动物放牧（也保留碱度）和沉入海洋内部的通量（去除碱度）。我们将看看这些过程的平衡在从晚春到夏季的过渡，当现场和卫星数据告诉我们，颗石藻是最活跃的。我们将联合收割机与测量海洋化学和原位光学特性的自主平台和最先进的传感器相结合，进行研究巡航。通过在海水碳酸盐化学和碳循环的背景下量化关键的增长和损失过程，CHALKY将更准确地反映生物学如何影响海水吸收二氧化碳的能力，从而使观测和模型更加匹配，并将碳酸钙纳入全球碳预算。

Each year in the North Atlantic Ocean, a key region for the global carbon cycle, immense areas of surface water turn turquoise in summer. This phenomenon relates to the growth and death of unique microscopic algae - coccolithophores. Coccolithophores cover their cells with scales of calcium carbonate (called coccoliths), produced internally and arranged into an exoskeleton around the cell. Under certain conditions, for example when nutrients are scarce or viruses infect cells, these coccoliths are shed in huge numbers. Due to their unique optical properties and immense abundance, they turn the water a milky turquoise colour and can be detected from space. These turquoise waters (termed 'white waters') are where coccoliths have accumulated in their trillions and have been considered as coccolithophore blooms.Coccolithophores form coccoliths through calcification, which produces CO2 and reduces the pH of the ocean by consuming alkalinity. When coccoliths are lost from the surface ocean, it reduces the capacity of the ocean to absorb more CO2. In this way, 'white waters' are thought to lead to significant reductions in the ocean's carbon sink. However, we now suspect that these 'white waters' are not areas of intensive coccolithophore calcification or growth, rather they are regions of senescence and an accumulation of detrital material. Coccolithophores have been found to grow faster and calcify more outside of the 'white waters' and more recently we have found that they are also heavily grazed by small animals (zooplankton) who partly digest the calcium carbonate. In this way, coccolithophore calcium carbonate appears to be recycled far more in surface waters than previously thought and the alkalinity they are associated with may be retained in the surface ocean. However, we have few coupled measurements of the balance of these different processes (growth, death and sinking) with which to take an informed view of how coccolithophores control ocean alkalinity. This represents a major uncertainty in the global marine C-cycle, with global C budgets and Earth System Models struggling to incorporate calcium carbonate or accurately replicate observations of seawater alkalinity. The 'coccolithophore controls on ocean alkalinity' (CHALKY) project aims to fill this critical knowledge gap by quantifying the balance of coccolithophore production and loss processes and their impact on C-cycling and air-sea CO2 fluxes. Our assessment of ecological interactions and impacts on seawater chemistry will be carried out while improving in situ and remotely sensed optical detection of coccolithophores to allow us to use Earth Observation data to scale our insights to the global ocean and historically using existing satellite data sets. CHALKY will, for the first time, concurrently quantify coccolithophore calcium carbonate production (consuming alkalinity), viral lysis (retaining alkalinity), zooplankton grazing (also retaining alkalinity) and sinking fluxes into the ocean's interior (removing alkalinity). We will look at the balance of these processes during the transition from late-spring to summer, when in situ and satellite data informs us that coccolithophores are most active. We combine a research cruise measuring these processes with autonomous platforms and state-of-the-art sensors measuring ocean chemistry and in situ optical properties. By quantifying the key growth and loss processes, within the context of seawater carbonate chemistry and C-cycling, CHALKY will inform a more accurate representation of how biology impacts the ability of seawater to absorb CO2, allowing closer matching of observations and models and inclusion of calcium carbonate in global C budgets.