Phytoplankton Organic Carbon and Sulfur Cycling at the Marginal Ice Edge Zone

北极浮游植物可能是二氧化碳(CO2)的汇，也是二甲基硫(DMS)的主要生产者。最大的影响预计在边缘冰区，那里的浮游植物从5月持续到9月，因为冰向北退去。在任何一个生长期，这些多产水域可以覆盖北冰洋陆架海面积的一半以上，例如巴伦支海。边缘冰区浮游植物的主要成分之一是棕囊藻，它以殖民地的形式大量生产二甲基硫。众所周知，该物种排泄高比例的新固定碳作为高分子量聚合物，以形成殖民地。后来，当硝酸盐变得有限时，它会在花期的后期大量下沉。硅藻，如妊娠海链藻，可能在夏末冰缘的水华中占主导地位，也可能先于早春的Pouchetii水华(即社会角毛藻)。Pouchetii和硅藻之间溶解有机碳的形成和细胞沉积的不同模式需要包括在生产力模型中，以了解北极陆架地区二氧化碳和二甲基硫的产生和汇。这项实地和实验室研究的目标是与挪威科学家合作，以：(1)确定Pouchetii和硅藻在冰缘水华的初级生产量、胞外固定碳比例、DMS生产量、以及颗粒碳和硫向深度的沉积：(2)利用巴伦支海10年的时间序列确定哪些是有利于每种水华类型的主要环境变量；(3)通过结合冰缘水华的碳和硫收支来估计DMS产量和二氧化碳吸收的10年时间序列。这项研究将对北极大陆架地区冰缘水华期间浮游植物对碳和硫循环的贡献的季节和年际变化提供一个初步的近似。

Arctic phytoplankton may act as a sink for carbon dioxide (CO2) and a major producer of dimethylsulfide (DMS). Maximum effects are expected in the marginal ice zone where phytoplankton blooms extend from May to September as the ice recedes northwards. These productive waters can cover more than half the area of arctic shelf seas, such as the Barents Sea, in any one growth period. One of the main components of the phytoplankton at the marginal ice zone is Phaeocystis pouchetii which, in its colonial form, is a high producer of DMS. This species is known to excrete a high proportion of newly fixed carbon as high molecular weight polymers in order to form the colony. Later, it sinks in mass in the latter stages of the bloom when nitrate becomes limiting. Diatoms, such as Thalassiosira gravida, may dominate the bloom at the ice edge late in the summer and may also precede the P. pouchetii bloom in early spring (i.e. Chaetoceros socialis). The different patterns of dissolved organic carbon formation and cell sedimentation between P. pouchetii and diatoms need to be included in productivity models for an understanding of the production and sink of CO2 and DMS in arctic shelf areas. The objectives of this field and laboratory study, in collaboration with Norwegian scientists, are to: (1) to determine the quantitative differences between P. pouchetii and diatoms blooms in the ice edge with respect to primary production, proportion of carbon fixed that is extracellular, DMS production, and sedimentation of particulate carbon and sulfur to depth: (2) to determine which are the main environmental variables that favor each type of bloom using a 10-year time series from the Barents Sea; and (3) to estimate a 10-year time series of DMS production and CO2 uptake by combining the existing time series with carbon and sulfur budgets of the ice edge blooms. This research will provide a first approximation to the seasonal and interannual variability of the phytoplankton contribution to the carbon and sulfur cycle during the ice edge bloom in arctic shelf areas.