Long-term, high-resolution measurements of environmental variability are sparse in the High Arctic. In the absence of such data, we turn to proxies recorded in the layered skeletons of the long-lived crustose coralline algae Clathromorphum compactum. Annual growth banding in this alga is dependent on several factors that include temperature, light availability, nutrients, salinity, and calcium carbonate saturation state. It has been observed that growth slows during winter as sunlight reaching the seafloor diminishes due to decreased insolation and the build-up of sea-ice, such that the relationship between sea-ice cover extent and algal growth has allowed for reconstructions of relative sea-ice variability through time. However, recent laboratory work has shown that C. compactum continue growing in complete darkness (sea-ice cover). Therefore, a more complete understanding of algal growth is necessary for the refinement of the sea-ice proxy. Here, we present the results of a ~year-long in-situ growth and environmental monitoring experiment in Arctic Bay, Nunavut, Canada (~73°N) which addresses, for the first time in situ, the gaps in our understanding of growth over an annual cycle in the High Arctic. Algal growth was assessed on a quasi-monthly basis, where specimens were subsampled to quantify monthly extension in the context of ocean temperature and light availability. By measuring extension rate through time, we observed that the algae grew on average 72 µm yr^-1, with ~54% of annual growth occurring during the sea-ice free summer months (June-September), ~25% during the winter months (November-April), and ~21% occurring during the transition months of May and October. Although winter growth slowed, we did not observe a consistent cessation of linear extension during low-or no-light months. We posit that substantial growth during the winter months at this latitude is most likely a consequence of the mobilization of stored energy (photosynthate) produced during the photosynthetically active summer months. However, we also discuss the possibility of low light-photosynthetic activity and/or dark carbon fixation, which could also facilitate extension through time. Overall, the novel growth model presented here has implications for the use of C. compactum growth for reconstructing the environment as well as for trace-element-based (typically Mg/Ca) algal chronologies.

在高北极地区，对环境变化的长期、高分辨率测量很少。在没有这些数据的情况下，我们转向记录在长寿命甲壳珊瑚藻的分层骨骼中的代理密实笼形藻。这种藻类的年生长带取决于几个因素，包括温度、光照可用性、养分、盐度和碳酸钙饱和状态。已经观察到增长 由于日照减少和海冰堆积，到达海底的阳光在冬季减慢，因此海冰覆盖范围与藻类生长之间的关系允许重建相对海冰随时间的变化。然而，最近的实验室工作表明， C.紧凑型继续在完全黑暗中生长（海冰覆盖）。因此，对于海冰代理的细化，需要更全面地了解藻类生长。在这里，我们展示了长达一年的结果原位在加拿大努纳武特 (~73°N) 北极湾进行的生长和环境监测实验首次解决了原位，我们对北极高地年度周期增长的理解存在差距。藻类生长以准月为基础进行评估，其中对样本进行二次抽样以量化海洋温度和光照可用性背景下的每月扩展。通过测量随时间的延伸率，我们观察到藻类平均生长 72 µm yr ^-1，约 54% 的年增长发生在无海冰的夏季月份（6 月至 9 月），约 25% 发生在冬季（11 月至 4 月），约 21% 发生在 5 月和 10 月的过渡月份。尽管冬季增长放缓，但我们没有观察到在低光照或无光照月份线性延伸的持续停止。我们假设在这个纬度的冬季月份的显着增长很可能是在光合作用活跃的夏季月份产生的储存能量（光合产物）的动员的结果。然而，我们还讨论了低光合作用活性和/或暗碳固定的可能性，这也可以促进随时间的延长。总的来说，这里介绍的新型增长模型对使用C.紧凑型用于重建环境以及基于微量元素（通常为 Mg/Ca）的藻类年表的生长。