Abstract In response to ongoing global climate change, marine ecosystems in the northwest Atlantic are experiencing one of the most drastic increases in sea surface temperatures in the world. This warming can increase water column stratification and decrease surface nutrient concentrations, in turn impacting primary productivity and phytoplankton assemblages. However, the exact impacts of these changes on sources and quality of organic matter as well as its transfers to the benthic compartment remain uncertain. This survey characterized organic matter sources and quality within a highly-stratified sub-Arctic coastal system (Saint-Pierre and Miquelon) and described its transfer towards a biomass-dominant primary consumer, the sand dollar Echinarachnius parma. This study analyzed fatty acid and stable isotope (δ13C and δ15N) composition of surface and bottom Particulate Organic Matter (s-POM and b-POM, respectively), Sedimentary Organic Matter (SOM) and sand dollar tissue along a near shore to offshore gradient during two contrasting seasons associated either with sharp or weak water column stratification (i.e. High vs Low Stratification Periods). Results revealed high relative abundances of polyunsaturated fatty acids (notably macro- and microalgae markers) in POM during the Low Stratification Period while the High Stratification Period was characterized by elevated relative abundance of saturated fatty acids indicating a higher organic matter degradation state. In addition, strong seasonal differences were also observed in food availability with four-fold higher concentrations in total suspended solids during Low vs High Stratification Periods. These results suggested thus multiple negative effects of stratification on pelagic-benthic coupling and POM quality. Lower nutrient repletion of surface waters during period of sharp stratification diminishes pelagic-benthic coupling by reducing food availability, POM quality and vertical transfer of organic matter. By contrast, the sediment-based diet of E. parma showed a low spatiotemporal variability reflecting the homogenous composition of the SOM. This study suggests that intensified water column stratification due to increasing sea surface temperatures may modify the pelagic-benthic coupling and future quality and composition of POM pools.

中文翻译：

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高度分层的亚北极海岸系统（Saint-Pierre-et-Miquelon，NW Atlantic）中有机物的来源、质量和转移

摘要 为应对持续的全球气候变化，大西洋西北部的海洋生态系统正在经历世界上海面温度最剧烈的上升之一。这种变暖会增加水柱分层并降低地表养分浓度，进而影响初级生产力和浮游植物组合。然而，这些变化对有机物质的来源和质量及其向底栖生物转移的确切影响仍不确定。该调查表征了高度分层的亚北极沿海系统（圣皮埃尔和密克隆）内的有机物质来源和质量，并描述了其向以生物质为主的初级消费者——沙元 Echinarachnius parma 的转移。本研究分析了表面和底部颗粒有机物（分别为 s-POM 和 b-POM）、沉积有机物 (SOM) 和沙元组织的脂肪酸和稳定同位素（δ13C 和 δ15N）组成，沿着近岸到近海的梯度在与尖锐或弱水柱分层相关的两个截然不同的季节（即高与低分层时期）。结果显示，低分层期间 POM 中多不饱和脂肪酸（特别是大型和微藻标记物）的相对丰度较高，而高分层时期的特征是饱和脂肪酸的相对丰度升高，表明有机物降解状态较高。此外，在低分层和高分层期间，总悬浮固体的浓度高出四倍，在食物供应方面也观察到了强烈的季节性差异。因此，这些结果表明分层对浮游-底栖耦合和 POM 质量有多重负面影响。在急剧分层期间地表水的较低营养补充通过减少食物供应、POM 质量和有机物质的垂直转移来减少远洋-底栖耦合。相比之下，E. parma 以沉积物为基础的饮食表现出较低的时空变异性，反映了 SOM 的同质成分。这项研究表明，由于海面温度升高而加剧的水柱分层可能会改变远洋-底栖耦合以及 POM 池的未来质量和组成。