White Patrick L, Bertrand Erin M, Spence Jenifer S, Cavaco Maria A, Parrott Claire, Waterman Stephanie, Rowland Elden, Roberts Megan E, Noah Terry, Mellett Travis, Hallé Danielle, Hamilton Andrew K, Bundy Randelle M, Didier David, Bhatia Maya P
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2G5, Canada.
Department of Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada.
ISME Commun. 2024 Mar 18;5(1):ycaf045. doi: 10.1093/ismeco/ycaf045. eCollection 2025 Jan.
Marine-terminating (i.e., tidewater) glaciers are experiencing rapid retreat. Compared to land-terminating glaciers, tidewater glaciers can entrain nutrient-rich deep seawater with buoyant glacial meltwater released at depth from the glacier terminus, fueling summertime primary productivity. We used a continuum of tidewater glaciers at various stages of retreat in the Canadian Arctic Archipelago, in Inuit Nunangat, as a natural laboratory for approximating the impacts of tidewater glacier retreat on marine primary producers and their ecological strategies. We measured phytoplankton community composition and estimated productivity along this retreat continuum and found that phytoplankton communities consist mostly of fast-growing r-strategists such as diatoms at sites with tidewater glaciers likely to be capable of deep-water nutrient upwelling. At sites without tidewater glaciers or those with tidewater glaciers that may have retreated too much to upwell deep-water nutrients, we found communities dominated by small and potentially mixotrophic flagellates, which were indicative of regenerative production and low-nutrient environments. We also observed the highest estimated diatom carbon fixation potential co-occurring with chemical signals of upwelling near a shallow tidewater glacier. These finding suggest that shoaling tidewater glaciers can be important regions of summertime productivity when they can facilitate deep-water nutrient upwelling. However, with continued retreat, tidewater glaciers will cease deep-water upwelling. Low contributions of diatoms at sites with glaciers that no longer induce deep-water upwelling show that tidewater glacier shoaling will ultimately result in reduced ecosystem productivity and shifts towards phytoplankton that employ ecological strategies for success in stratified, nutrient-poor environments, with implications for marine ecosystems adjacent to the >1000 retreating Arctic tidewater glaciers.
海洋末端（即潮水）冰川正在迅速退缩。与陆地末端冰川相比，潮水冰川能够裹挟营养丰富的深层海水，并在冰川末端深处释放出浮力较大的冰川融水，从而促进夏季初级生产力。我们将加拿大北极群岛因纽特努纳武特地区处于不同退缩阶段的一系列潮水冰川作为一个天然实验室，来估算潮水冰川退缩对海洋初级生产者及其生态策略的影响。我们沿着这条退缩连续体测量了浮游植物群落组成并估算了生产力，发现浮游植物群落主要由快速生长的r策略者组成，比如在那些可能具备深层海水营养上涌能力的潮水冰川所在地点的硅藻。在没有潮水冰川的地点，或者那些潮水冰川退缩过多以至于无法上涌深层海水营养的地点，我们发现群落以小型且可能为混合营养型的鞭毛虫为主，这表明是再生性生产和低营养环境。我们还观察到，在一条浅潮水冰川附近，估计的硅藻碳固定潜力最高值与上涌的化学信号同时出现。这些发现表明，当浅化的潮水冰川能够促进深层海水营养上涌时，它们可能是夏季生产力的重要区域。然而，随着持续退缩，潮水冰川将停止深层海水上涌。在那些冰川不再引发深层海水上涌的地点，硅藻的贡献较低，这表明潮水冰川浅化最终将导致生态系统生产力下降，并向采用在分层、贫营养环境中成功生存的生态策略的浮游植物转变，这对与1000多条正在退缩的北极潮水冰川相邻的海洋生态系统具有重要意义。
