Collaborative Research: Impact of Solar Radiation and Nutrients on Biogeochemical Cycling of DMSP and DMS in the Ross Sea, Antarctica

南大洋的地区在南半球的春季和初夏会有壮观的浮游植物水华。浮游植物的主要物种之一，附着植物南极棕囊藻，是有机硫化合物二甲基磺基丙酸盐（DMSP）的多产者，棕囊藻水华与世界上最高浓度的DMSP及其挥发性降解产物二甲基硫（DMS）有关。硫以二甲基硫的形式从海洋转移到大气中，可以影响降水的化学性质，影响云的性质，并可能影响气候。DMSP和DMS在数量上也是许多海洋食物网中碳、硫和能量流动的重要组成部分，尽管关于高纬度系统中这些过程的信息很少。该项目将研究太阳辐射和铁循环如何影响浮游植物产生DMSP和DMS，以及微生物食物网随后如何利用这些不稳定形式的有机物质。将在实地实验和实地观测中检验四个相互关联的假设：1）太阳辐射，包括由于季节性臭氧消耗而增强的紫外线-B，在确定罗斯海二甲基硫醚的净生态系统产量方面发挥着重要作用; 2）由于浮游生物群落更多地暴露于高剂量太阳辐射，浅混合层的形成促进了表层沃茨二甲基硫醚的积累; 3）DMSP的生产和周转是通过极地食物网的碳和硫通量的重要部分; 4）水华发展和导致的营养素消耗（例如，铁）将导致DMSP的高生产率和高DMS浓度和大气通量。这项研究的结果将大大提高对控制极地沃茨中DMSP和DMS浓度的基本机制的理解，从而提高我们预测从这一重要气候区域向大气中排放DMS的能力。Kieber和Kiene博士都积极地让高中生、本科生和研究生参与他们的研究，并参与针对代表性不足群体的正式项目（NSF-REU和美国化学学会-SEED）。该项目将继续开展这类教育推广活动。PI还教授本科和研究生课程，并将研究经验纳入课堂将丰富学生的学习经验。

Areas of the Southern Ocean have spectacular blooms of phytoplankton during the austral spring and early summer. One of the dominant phytoplankton species, the haptophyte Phaeocystis antarctica, is a prolific producer of the organic sulfur compound dimethylsulfoniopropionate (DMSP) and Phaeocystis blooms are associated with some of the world's highest concentrations of DMSP and its volatile degradation product, dimethylsulfide (DMS). Sulfur, in the form of DMS, is transferred from the oceans to the atmosphere and can affect the chemistry of precipitation and influence cloud properties and possibly climate. DMSP and DMS are also quantitatively significant components of the carbon, sulfur and energy flows in many marine food webs, although very little information is available on these processes in high latitude systems. This project will study how solar radiation and iron cycling affect DMSP and DMS production by phytoplankton, and the subsequent utilization of these labile forms of organic matter by the microbial food web. Four interrelated hypotheses will be tested in field-based experiments and in situ observations: 1) solar radiation, including enhanced UV-B due to seasonal ozone depletion, plays an important role in determining the net ecosystem production of DMS in the Ross Sea; 2) development of shallow mixed layers promotes the accumulation of DMS in surface waters, because of enhanced exposure of plankton communities to high doses of solar radiation; 3) DMSP production and turnover represent a significant part of the carbon and sulfur flux through polar food webs; 4) bloom development and resulting nutrient depletion (e.g., iron) will result in high production rates of DMSP and high DMS concentrations and atmospheric fluxes. Results from this study will greatly improve understanding of the underlying mechanisms controlling DMSP and DMS concentrations in polar waters, thereby improving our ability to predict DMS fluxes to the atmosphere from this important climatic region. Both Drs. Kieber and Kiene actively engage high school, undergraduate and graduate students in their research and are involved in formal programs that target underrepresented groups (NSF-REU and the American Chemical Society-SEED). This project will continue this type of educational outreach. The PIs also teach undergraduate and graduate courses and incorporation of research experiences into their classes will enrich student learning experiences.