Data from: Ice-cover is the principal driver of ecological change in High Arctic lakes and ponds

Recent climate change has been especially pronounced in the High Arctic, however, the responses of aquatic biota, such as diatoms, can be modified by site-specific environmental characteristics. To assess if climate-mediated ice cover changes affect the diatom response to climate, we used paleolimnological techniques to examine shifts in diatom assemblages from ten High Arctic lakes and ponds from Ellesmere Island and nearby Pim Island (Nunavut, Canada). The sites were divided a priori into four groups (“warm”, “cool”, “cold”, and “oasis”) based on local elevation and microclimatic differences that result in differing lengths of the ice-free season, as well as about three decades of personal observations. We characterized the species changes as a shift from Condition 1 (i.e. a generally low diversity, predominantly epipelic and epilithic diatom assemblage) to Condition 2 (i.e. a typically more diverse and ecologically complex assemblage with an increasing proportion of epiphytic species). This shift from Condition 1 to Condition 2 was a consistent pattern recorded across the sites that experienced a change in ice cover with warming. The “warm” sites are amongst the first to lose their ice covers in summer and recorded the earliest and highest magnitude changes. The “cool” sites also exhibited a shift from Condition 1 to Condition 2, but, as predicted, the timing of the response lagged the “warm” sites. Meanwhile some of the “cold” sites, which until recently still retained an ice raft in summer, only exhibited this shift in the upper-most sediments. The warmer “oasis” ponds likely supported aquatic vegetation throughout their records. Consequently, the diatoms of the “oasis” sites were characterized as high-diversity, Condition 2 assemblages throughout the record. Our results support the hypothesis that the length of the ice-free season is the principal driver of diatom assemblage responses to climate in the High Arctic, largely driven by the establishment of new aquatic habitats, resulting in increased diversity and the emergence of novel growth forms and epiphytic species.

近年来，气候变化在高北极地区表现得尤为显著；然而，水生生物群（如硅藻（diatoms））的响应会受到位点特异性环境特征的调控。为了探究气候介导的冰盖变化是否会影响硅藻对气候的响应，我们采用古湖沼学技术（paleolimnological techniques），对加拿大努纳武特地区埃尔斯米尔岛及附近皮姆岛的10个高北极湖泊与池塘中的硅藻组合变化进行了分析。基于当地海拔、微气候差异所导致的无冰期时长差异，结合近30年的实地观测经验，我们预先将这些位点划分为"温暖""凉爽""寒冷"与"绿洲"四组。我们将物种变化特征化为从状态1（即整体多样性较低、以附泥和附石硅藻为主的组合）向状态2（即通常多样性更高、生态结构更复杂，且附生硅藻占比逐渐升高的组合）的转变。这种从状态1到状态2的转变，是所有经历了气候变暖导致冰盖变化的位点均观测到的一致模式。"温暖"位点是夏季最早融冰的位点之一，其群落变化出现时间最早、变化幅度也最大。"凉爽"位点同样呈现出从状态1到状态2的转变，但正如预期，其响应时间滞后于"温暖"位点。与此同时，部分"寒冷"位点直至近年夏季仍保留浮冰，仅在最表层沉积物中出现了这种组合转变。气候更为温暖的"绿洲"池塘在整个沉积记录中均存在水生植被，因此其硅藻组合全程均表现为高多样性的状态2组合。本研究结果支持如下假说：在高北极地区，无冰期时长是调控硅藻组合对气候响应的核心驱动因子，这一过程主要由新生水生栖息地的形成所驱动，进而带来群落多样性提升以及新生长型和附生硅藻物种的出现。