Radiocarbon dating of peat profiles from the subarctic ecoclimatic region, west-central Canada

Long-term vegetation succession and permafrost dynamics in subarctic peat plateaus of west-central Canada have been studied through detailed plant macrofossil analysis and extensive AMS radiocarbon dating of two peat profiles. Peatland inception at these sites occurred around 5800-5100 yr BP (6600-5900 cal. BP) as a result of paludification of upland forests. At the northern peat plateau site, located in the continuous permafrost zone, palaeobotanical evidence suggests that permafrost was already present under the forested upland prior to peatland development. Paludification was initiated by permafrost collapse, but re-aggradation of permafrost occurred soon after peatland inception. At the southern site, located in the discontinuous permafrost zone, the aggradation of permafrost occurred soon after peatland inception. In the peat plateaus, permafrost conditions have remained very stable until present. Sphagnum fuscum-dominated stages have alternated with more xerophytic communities characterized by ericaceous shrubs. Local peat fires have occurred, but most of these did not cause degradation of the permafrost. Starting from 2800-1100 yr BP (2900-1000 cal. BP) consistently dry surface conditions have prevailed, possibly related to continued frost heave or nearby polygon crack formation.

加拿大中西部亚北极泥炭高原的长期植被演替与永久冻土动态，已通过对两个泥炭剖面（peat profile）的详细植物大化石分析（plant macrofossil analysis）及大量加速器质谱（AMS）放射性碳定年（radiocarbon dating）展开研究。这些位点的泥炭地起始于约5800-5100年前（yr BP）（6600-5900校正年前（cal. BP）），由高地森林沼泽化（paludification）所致。位于连续永久冻土带（continuous permafrost zone）的北部泥炭高原位点，古植物学（palaeobotanical）证据表明，在泥炭地发育前，永久冻土已存在于森林覆盖的高地之下。沼泽化由永久冻土塌陷引发，但泥炭地起始后不久便发生永久冻土再聚集（re-aggradation）。位于不连续永久冻土带（discontinuous permafrost zone）的南部位点，永久冻土聚集于泥炭地起始后不久发生。在泥炭高原中，永久冻土状况至今仍保持高度稳定。锈色泥炭藓（Sphagnum fuscum）主导阶段与以杜鹃花科灌木（ericaceous shrubs）为特征的更旱生群落（xerophytic communities）交替出现。局部泥炭火灾曾发生，但多数未导致永久冻土退化。自2800-1100年前（yr BP）（2900-1000校正年前（cal. BP））起，持续干旱的地表条件占据主导，这可能与持续冻胀（frost heave）或附近多边形裂缝形成（polygon crack formation）相关。