Collaborative Research: Attachment/Detachment of Algae to/from Sea Ice: Mechanisms and Consequences for Biogenic Fluxes and Polar Ecosystems

冰藻与外聚物（EPS）的关系以及EPS在其他形式的微生物粘附中的作用表明，EPS在藻类对冰的附着中起重要作用。有证据表明，藻类以局部脉动的形式离开冰面，这种依附关系似乎在季节性冰融化期间偶尔被克服。有证据表明，有几种物理机制可以将藻类从冰中分离出来，但目前还不存在能够预测藻类从冰中释放出来的定量数据。提供的资金用于支持在特殊设计的冰槽中进行的受控实验室实验与在AK Barrow附近沿海快冰底部社区的实地观察相结合的研究。这项研究将研究冰藻是如何附着在冰上的，可能导致藻类从冰中流出的物理过程，以及不同条件下从冰中释放的颗粒的生物地球化学特征。EPS在藻类附着在海冰上的作用将在实验中进行评估，实验使用的是由冰藻类定居的人工制造的海冰。将比较富含EPS的冰和化学降解EPS的冰在融化过程中藻类通量的时间过程。额外的实验将集中在可能引发藻类从海冰中释放的四种具体机制上：a)密度过高和附着地点的丧失，b)表面融水冲刷，c)光吸收引起的局部加热，d)冰下流。每种机制都将通过实验分离出来，以确定其对实验冰盖外藻类通量的影响。对于每种机制，从冰中触发藻类脉冲所需的最小条件将被量化，以便与实地观测进行比较。在这些实验中，还将测量从冰中释放的颗粒的生物地球化学相关特征，包括：大小、下沉速度、有机碳、有机氮、叶绿素和EPS浓度。在建议的研究中，每年都建议进行补充性的实地研究。冰和水柱中藻类丰度的时间序列将用于确定释放事件。与四种提出的分离机制相关的物理变量的时间序列进行比较，可以评估可能触发脉冲的因素。附着在冰层上的藻类在冰雪覆盖的海洋中构成了重要的初级产品。因此，了解与它们附着和脱离冰相关的过程将增强我们对极地海洋食物网、其空间变异性及其对全球气候变化的潜在响应的理解。

The association of ice algae with exopolymeric substances (EPS) and the role of EPS in other forms of microbial adhesion, suggest that EPS are important in algal attachment to ice. This attachment appears to be episodically overcome during seasonal ice melt, based on evidence that algae leave the ice in local pulses. Evidence suggests several physical mechanisms that detach algae from ice, but quantitative data that would allow prediction of algal release from ice do not exist. Funds are provided to support research that combines controlled laboratory experiments in specially-designed ice tanks with field observations of coastal fast-ice bottom communities near Barrow, AK. The research will address how ice algae attach to ice, the physical processes that may cause flux of algae out of the ice, and the biogeochemical characteristics of particles released from ice under different conditions.The role of EPS in attachment of algae to sea ice will be assessed in experiments using artificially-created, sea-ice sheets colonized by ice algae. The time course of algal flux from the ice during melting will be compared between ice enriched in EPS and ice with chemically-degraded EPS. Additional experiments will focus on four specific mechanisms that potentially trigger the release of algae from sea ice: a) excess density and loss of attachment sites, b) flushing by surface meltwater, c) local heating due to light absorption, and d) under-ice currents. Each mechanism will be experimentally isolated to determine its impact on algal flux out of experimental ice sheets. For each mechanism, the minimal conditions necessary to trigger an algal pulse from the ice will be quantified for comparison with field observations. During these experiments, biogeochemically-relevant characteristics of the particles released from the ice will also be measured, including: size, sinking rate, and organic carbon, organic nitrogen, chlorophyll, and EPS concentrations. Complementary field studies are proposed in each year of the proposed research. Time series of algal abundance in the ice and water column will be used to identify release events. Comparison to time series of physical variables relevant to the four proposed detachment mechanisms will allow assessment of the factors that may have triggered the pulses.Algae that are attached to the ice form a significant portion of the primary production in ice-covered seas. Thus, understanding the processes associated with their attachment to and detachment from the ice will enhance our understanding of the food web of polar seas, its spatial variability, and its potential response to global climate change.