How do Arctic microalgae thrive in the chaotic light field of in-ice and under-ice marine habitats?

对于光合作用的有机体来说，海洋极地环境是光变化最极端的环境之一。从极地的夜晚到午夜的太阳，从无冰到有冰的条件，微藻已经进化到比持续的光子缺乏和过剩更长寿。极地微藻如何在长时间的黑暗中生存，在极低的光照下生长，如何应对广泛而快速的波动，以及如何容忍过量的辐射，人们仍然知之甚少。我的研究计划将解决以下问题：1)在初冬到仲冬，冰藻和浮游植物能够实现净生长的最低光照水平是多少？2)光在海冰基质中是如何分布的，以及营养物质和食草动物是如何分布的，这种分布与海冰微物理有什么关系？3)冰下的动态光系统是如何由海冰的各种宏观特征(积雪的异质性和变质作用、脊、铅、冰期、融化池塘)形成的？4)浮游植物如何从初级生产力的角度对这种高度波动的光系统做出反应？5)考虑到放牧和其他损失过程，哪种动态光系统最有利于海冰下的生物量积累(水华)？6)在利用遥感数据估计大规模初级生产量时，如何适当地考虑中小尺度的光波动？7)北极海冰的持续变化对冰下初级生产量有何影响？这项探索拨款研究计划将包括实验室实验、实地活动和大规模遥感应用的升级方法的开发。实验室实验将旨在确定：1)在冬末和初春典型的海冰基质和上层水柱条件下微藻生长的最低光照需求，以及2)极地微藻如何应对光照的广泛和快速波动，以及光照变化和限制最终如何影响生长。在实地考察期间，将使用安装在临时内窥镜上的新型微型光学传感器和成像系统来记录塑造冰藻微尺度环境的光学、物理和化学特性。此外，将使用各种自主平台(无人机、自动水下航行器和远程操作潜航器)来描述从米到几公里的冰下光场，我们将确定初级生产对广泛观测到的光变化的空间和时间响应。最后，将制定新的升级办法，以适当考虑影响所有季节大规模光和初级生产的海冰的中小尺度特征。新的方法将应用于遥感数据，以确定泛北极初级生产的多年趋势，包括冰下的贡献。

Marine polar environments are, for photosynthesising organisms, among the most extreme in terms of variations in light. From the polar night to the midnight sun, and from ice-free to ice-covered conditions, microalgae have evolved to outlive sustained lacks and excesses of photons. How polar microalgae survive prolonged darkness, grow at extremely low levels of light, cope with wide and rapid fluctuations, and tolerate excess irradiance remain poorly understood. My research programme will address the following questions: 1) What is the minimum light level at which ice algae and phytoplankton can achieve net growth during early to mid-winter? 2) How is light distributed inside the sea-ice matrix, together with nutrients and grazers, and how does this distribution relates to sea-ice microphysics? 3) How is the under-ice dynamic light regime shaped by various macroscopic features of sea ice (snow-pack heterogeneity and metamorphism, ridges, leads, ice age, melt ponds)? 4) How do phytoplankton respond to this highly fluctuating light regime in terms of gross primary production? 5) Considering also grazing and other loss processes, which dynamic light regime is most favourable for biomass accumulation (bloom) under sea ice? 6) How to properly account for small- and medium-scale light fluctuations when estimating primary production at large scale using remote-sensing data? 7) What are the consequences, on un-der-ice primary production, of the ongoing modifications of sea ice in the Arctic? This Discovery Grant research program will include laboratory experiments, field activities, and the development of upscaling methods for large-scale remote-sensing applications. The laboratory experiments will aim at determining: 1) the minimum light requirement for microalgae growth in conditions typical of the sea-ice matrix and the upper-water column during late winter and early spring, and 2) how polar microalgae cope with wide and rapid fluctuations in light and how the light variation and limitation ultimately affect growth. During the field expeditions, new miniaturised optical sensors and imaging systems mounted onto an ad hoc endoscope will be used to document the optical, physical and chemical properties that shape the micro-scale environment of ice algae. Also, various autonomous platforms (drones, autonomous underwater vehicles and remotely operating vehicles) will be used to describe the under-ice light field at scales ranging from the metre to several kilometres, and we will determine the space and time response of primary production to the broad spectrum of observed light variations. Finally, new upscaling approaches will be developed to appropriately account for small- and medium-scale features of sea ice that affect light and primary production at large scale during all seasons. The new approaches will be applied on remote-sensing data to determine multiyear trends in pan-Arctic primary production, including the under-ice contribution.