Radiocarbon ages and diatom abundance in samples obtained from Qarlikturvik Valley, Bylot Island

The formation of many arctic wetlands is associated with the occurrence of polygon-patterned permafrost. Existing scenarios to describe and explain surface landforms in arctic wetlands (low-center and high-center polygons and polygon ponds) invoke competing hypotheses: a cyclic succession (the thaw-lake hypothesis) or a linear succession (terrestrialization). Both hypotheses infer the predictable development of polygon-patterned wetlands over millennia. However, very few studies have applied paleoecological techniques to reconstruct long-term succession in tundra wetlands and thereby test the validity of existing hypotheses. This paper uses the paleoecological record of diatoms to investigate long-term development of individual polygons in a High Arctic wetland. Two landform processes were examined: (1) the millennial-scale development of a polygon-pond, and (2) the transition from low-center to erosive high-center polygons. Diatom assemblages were quantified from habitats associated with contrasting landforms in the present-day landscape, and used as an analog to reconstruct past transitions between polygon types. On the basis of this evidence, the paleoecological record does not support either of the existing models describing the predictable succession of polygon landforms in an arctic wetland. Our results indicate a need for greater paleoecological understanding, in combination with in situ observations in present-day geomorphology, in order to identify patterns of polygon wetland development and elucidate the long-term drivers of these landform transitions.

多数北极湿地的形成与多边形多年冻土（polygon-patterned permafrost）的发育存在紧密关联。现有用于描述和解释北极湿地地表地貌（低中心多边形、高中心多边形及多边形池塘）的研究，提出了两类相互竞争的假说：一类为循环演替路径（融湖假说（thaw-lake hypothesis）），另一类为线性演替路径（陆地化作用（terrestrialization））。两类假说均认为，多边形湿地会在千年尺度上呈现可预测的发育轨迹。然而，目前极少有研究运用古生态技术（paleoecological techniques）重建苔原湿地（tundra wetlands）的长期演替过程，以此验证现有假说的合理性。本研究借助硅藻（diatoms）的古生态记录，探究高北极（High Arctic）地区一处湿地中单个多边形地貌的长期发育过程。研究考察了两类地貌演化过程：（1）多边形池塘的千年尺度发育历程；（2）低中心多边形向侵蚀型高中心多边形的转变过程。研究人员对当前景观中不同地貌类型对应的生境开展了硅藻组合定量分析，并将其作为类比参照，用以重建不同多边形类型之间的历史转变过程。基于上述研究证据，古生态记录并不支持现有两类描述北极湿地多边形地貌可预测演替的模型。本研究结果表明，需结合更多古生态研究与当前地貌学的原位观测数据，方能明确多边形湿地的发育模式，并阐明这类地貌转变的长期驱动机制。