New Approaches to Measuring and Understanding the Effects of Ultraviolet Radiation on Photosynthesis by Antarctic Phytoplankton

与南极臭氧洞相关的紫外线b辐射（UV-B, 280-320）的增加已被证明会抑制浮游植物的光合作用，但对水柱产生的总体影响仍是一个有争议的问题，需要继续进行研究。调查还显示，即使在南极平流层臭氧的“正常”水平上，UV-B和UV-A （320-400 nm）似乎对水柱产生强烈影响。紫外线在浮游植物初级生产的生态学中的作用在过去可能没有得到充分的认识，而在垂直混合存在的情况下，紫外线对初级生产的估计可能特别重要。本研究主要通过定义抑制紫外线的生物加权函数来量化紫外线对南极浮游植物光合作用的影响。过去，人们利用实验室培养物将光合作用描述为紫外线和可见光的作用。对南极麦克默多站的自然组合进行的进一步实验表明，生物加权函数与光照历史密切相关。最近，在南大洋开阔水域进行的测量证实，浮游植物组合对紫外线的敏感性有很大的变化。研究还发现，南极浮游植物对光合作用的抑制在小时的时间尺度上逐渐加重，没有恢复的迹象。即使在良好的条件下，光合作用能力的丧失也会持续几个小时不变。这与实验室培养和一些自然组合形成对比，这些组合在暴露于紫外线下时迅速达到稳定的光合作用速率，反映了损害和恢复过程之间的平衡。紫外线引起的损伤的缓慢逆转对水柱光合作用具有深远的影响，特别是在垂直混合过程中。迄今为止的结果已用于模拟紫外线、臭氧消耗和垂直混合对南极水域光合作用的影响。数据表明，正常水平的紫外线可对天然浮游植物产生重大影响，臭氧消耗和垂直混合可加剧这种影响。然而，关键问题仍然没有得到很好的解决，这些问题是本建议的重点。新的理论和实验方法将用于研究威德尔-斯科舍汇合处的开放水域和帕尔默站附近的沿海水域的紫外线反应。特别地，将在几分钟到几天的时间尺度上测量紫外线抑制和恢复的动力学。将计算南大洋中上层和沿海浮游植物之间生物加权函数的变异性。结果将提供在原地和改变后的紫外线照射下光合作用的绝对估计；扩大已确定生物加权函数的组合范围；并阐明抑制和恢复动力学应如何在混合层模型中表示。

Neale 9615342 Increases in ultraviolet-B radiation (UV-B, 280-320) associated with the Antarctic ozone hole have been shown to inhibit the photosynthesis of phytoplankton, but the overall effect on water column production is still a matter of debate and continued investigation. Investigations have also revealed that even at "normal" levels of Antarctic stratospheric ozone, UV-B and UV-A (320-400 nm) appear to have strong effects on water column production. The role of UV in the ecology of phytoplankton primary production has probably been underappreciated in the past and could be particularly important to the estimation of primary production in the presence of vertical mixing. This research focuses on quantifying UV effects on photosynthesis of Antarctic phytoplankton by defining biological weighting functions for UV-inhibition. In the past, techniques were developed to describe photosynthesis as a function of UV and visible irradiance using laboratory cultures. Further experimentation with natural assemblages from McMurdo Station in Antarctica showed that biological weighting functions are strongly related to light history. Most recently, measurements in the open waters of the Southern Ocean confirmed that there is substantial variability in the susceptibility of phytoplankton assemblages to UV. It was also discovered that inhibition of photosynthesis in Antarctic phytoplankton got progressively worse on the time scale of hours, with no evidence of recovery. Even under benign conditions, losses of photosynthetic capability persisted unchanged for several hours. This was in contrast with laboratory cultures and some natural assemblages which quickly attained a steady- state rate of photosynthesis during exposure to UV, reflecting a balance between damage and recovery processes. Slow reversal of UV-induced damage has profound consequences for water-column photosynthesis, especially during vertical mixing. Results to date have been used to model th e influence of UV, ozone depletion and vertical mixing on photosynthesis in Antarctic waters. Data indicate that normal levels of UV can have a significant impact on natural phytoplankton and that the effects can be exacerbated by ozone depletion as well as vertical mixing. Critical questions remain poorly resolved, however, and these are the focus of the present proposal. New theoretical and experimental approaches will be used to investigate UV responses in both the open waters of the Weddell-Scotia confluence and coastal waters near Palmer Station. In particular, measurements will be made of the kinetics of UV inhibition and recovery on time scales ranging from minutes to days. Variability in biological weighting functions between will be calculated for pelagic and coastal phytoplankton in the Southern Ocean. The results will provide absolute estimates of photosynthesis under in situ, as well as under altered, UV irradiance; broaden the range of assemblages for which biological weighting functions have been determined; and clarify how kinetics of inhibition and recovery should be represented in mixed layer models.