Ice Covered Ecosystems - CAMbridge bay Process Studies (ICE-CAMPS)

Sea ice algae are an important contributor of primary production in the Arctic ecosystem. Within the bottom-ice environment, access to nutrients from the underlying ocean is a major factor controlling production, phenology, and taxonomic composition of ice algae. Previous studies have demonstrated that tides and currents play an important role in driving the flux of nutrients to bottom-ice algal communities when biological demand during the spring bloom is high. In this study we investigate how surface currents under land-fast, first-year ice influence nutrient supply based on stoichiometric composition, algal chlorophyll a biomass, and species composition during spring 2016, in Dease Strait, Nunavut. Stronger water dynamics over a shoaled and constricted strait dominated by tidal currents (tidal strait) supported turbulent flow more than 85% of the deployment duration in comparison to outside the tidal strait in an embayment where turbulent flow was only evidenced a small percentage (< 15%) of the time. The system appeared to be nitrate-depleted with surface water concentrations averaging 1.3 mol L–1. Increased currents were correlated significantly with a decrease in ice thickness and an increase in ice algal chlorophyll a. Furthermore, pennate diatoms dominated the ice algal community abundance with greater contribution within the strait where currents were greatest. These observations all support the existence of a greater nutrient flux to the ice bottom where currents increased towards the center of the tidal strait, resulting in an increase of bottom ice chlorophyll a biomass by 5–7 times relative to that outside of the strait. Therefore, expanding beyond the long identified biological hotspots of open water polynyas, this paper presents the argument for newly identified hotspots in regions of strong sub-ice currents but persistent ice covers, so called “invisible polynyas”.

海冰藻类是北极生态系统中初级生产的重要贡献者。在底冰环境中，从下层海洋获取营养是控制海冰藻类生产、物候期和分类组成的主要因素。先前的研究业已证明，在春季生物量激增期间，潮汐和洋流在海冰藻类群落中营养物通量驱动方面发挥着重要作用。在本研究中，我们探究了2016年春季，在努纳武特地区的戴斯海峡，陆缘固定冰下表层洋流如何根据化学计量组成、藻类叶绿素a生物量和物种组成影响营养物质的供应。在一个以潮汐洋流为主的浅窄海峡中，较之外部潮汐海峡的湾内，水流动力更强，在部署期间超过85%的时间内支持湍流流动。该系统似乎存在硝酸盐耗竭，表层水浓度平均为1.3微摩尔/升。洋流强度的增加与冰厚度减小和冰藻叶绿素a含量增加显著相关。此外，针状硅藻在海冰藻类群落丰度中占主导地位，在洋流最大的海峡中贡献更大。这些观察结果均支持在洋流增强的潮汐海峡中心区域，存在更大的营养物质通量流向冰底，使得底冰叶绿素a生物量相对于海峡外部增加了5-7倍。因此，本文不仅扩展了长期以来已知的开阔水域多边形海冰的生物热点，还提出了在强海底洋流但持续存在冰覆盖的区域存在新的热点，即所谓的“隐形多边形海冰”。