Distal volcanic impacts on peatlands: palaeoecological evidence from Alaska

Despite the fact that volcanic ash (tephra) layers are found preserved in peat deposits around the world, comparatively little research has investigated the impacts of distal volcanic emissions on peatlands. This study investigates the impacts of several late-Holocene volcanic eruptions on five peatlands in southern Alaska using a palaeoecological approach. Testate amoebae analysis, peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers. Changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers. The humification results were considered unreliable because of a methodological problem, a finding which may have implications for other studies using this technique. Redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras. The most likely causes of the impacts are volcanic gases, acidic precipitation or tephra-derived leachates. The finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall. These results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change. Implications of the results for peat-based palaeoclimatic studies are discussed, as are possible directions for future research.