Ecophysiology of DMSP and related compounds and their contributions to carbon and sulfur dynamics in Phaeocystis antarctica

Spectacular blooms of Phaeocystis antarctica in the Ross Sea, Antarctica are the source of some of the world's highest concentrations of dimethylsulfoniopropionate (DMSP) and its volatile degradation product, dimethylsulfide (DMS). The flux of DMS from the oceans to the atmosphere in this region and its subsequent gas phase oxidation generates aerosols that have a strong influence on cloud properties and possibly climate. In the oceans, DMS and DMSP are quantitatively significant components of the carbon, sulfur, and energy flows in marine food webs, especially in the Ross Sea. Despite its central role in carbon and sulfur biogeochemistry in the Ross Sea, surprisingly little is known about the physiological functions of DMSP in P. antarctica. The research will isolate and characterize DMSP lyases from P. antarctica, with the goal of obtaining amino acid and gene sequence information on these important enzymes. The physiological studies will focus on the effects of varying intensities of photosynthetically active radiation, with and without ultraviolet radiation as these are factors that we have found to be important controls on DMSP and DMS dynamics. The research also will examine the effects of prolonged darkness on the dynamics of DMSP and related compounds in P. antarctica, as survival of this species during the dark Antarctic winter and at sub-euphotic depths appears to be an important part of the Phaeocystis' ecology. A unique aspect of this work is the focus on measurements of intracellular MSA, which if detected, would provide strong evidence for in vivo radical scavenging functions for methyl sulfur compounds. The study will advance understanding of what controls DMSP cycling and ultimately DMS emissions from the Ross Sea and also provide information on what makes P. antarctica so successful in this extreme environment. The research will directly benefit and build on several interrelated ocean-atmosphere programs including the International Surface Ocean Lower Atmosphere Study (SOLAS) program. The PIs will participate in several activities involving K-12 education, High School teacher training, public education and podcasting through the auspices of the Dauphin Island Sea Lab Discovery Hall program and SUNY ESF. Two graduate students will be employed full time, and six undergraduates (2 each summer) will be trained as part of this project.

南极罗斯海海域的南极棕囊藻（Phaeocystis antarctica）大规模水华，是全球二甲基巯基丙酸内盐（dimethylsulfoniopropionate, DMSP）及其挥发性降解产物二甲基硫（dimethylsulfide, DMS）浓度最高的来源之一。该区域海洋向大气排放的DMS通量及其后续气相氧化过程生成的气溶胶，对云特性乃至气候均具有显著影响。在海洋环境中，DMS与DMSP是海洋食物网碳、硫及能量流动中具有重要量化意义的组分，在罗斯海海域尤为如此。尽管DMSP在罗斯海海域的碳、硫生物地球化学循环中扮演核心角色，但人们对南极棕囊藻中DMSP的生理功能却知之甚少。本研究将从南极棕囊藻中分离并鉴定DMSP裂解酶，目标是获取这类重要酶的氨基酸与基因序列信息。生理实验将聚焦于光合有效辐射（photosynthetically active radiation）强度变化，以及是否附加紫外线辐射对藻体的影响——我们已证实这些因素是调控DMSP与DMS动态变化的关键因子。此外，研究还将探讨长期黑暗环境对南极棕囊藻体内DMSP及其相关化合物动态的影响，因为该物种在南极冬季黑暗期及亚真光层的存活，被认为是棕囊藻生态适应性的重要组成部分。本研究的一个独特之处在于细胞内甲基磺酸（MSA）的检测与定量，若能成功检出，将为甲基硫化合物的体内自由基清除功能提供有力证据。本研究将增进我们对罗斯海海域DMSP循环调控机制以及最终DMS排放过程的理解，同时也将揭示南极棕囊藻为何能在这类极端环境中占据生存优势。本研究将直接受益于多项相关的海-气交互研究计划，包括国际表层海洋-低层大气研究计划（International Surface Ocean Lower Atmosphere Study, SOLAS）。项目负责人将通过多芬岛海洋实验室探索大厅项目（Dauphin Island Sea Lab Discovery Hall program）与纽约州立大学环境科学与林业学院（SUNY ESF）的支持，开展多项K12教育、高中教师培训、公众科普及播客制作相关活动。本项目将雇佣2名全职研究生，同时培训6名本科生（暑期各2名）参与研究工作。