Transformation of Peat-Forming Ecosystems in a Changing Climate and Landscape on the Western Antarctic Peninsula
Thursday, 18 December 2014
The western Antarctic Peninsula (WAP) is one of three regions that have experienced the greatest warming on Earth over the recent decades. This warming has caused widespread glacier retreat and expansion of ice-free land areas. However, responses of terrestrial ecosystems to these rapid climate and landscape changes are still poorly understood. Here we used paleo records of climate and ecosystem reconstructions during the last millennium from peats on the WAP to understand climate-cryosphere-ecosystem connections. Continuing retreat of ice and permanent snow at Bonaparte Point on Anvers Island near Palmer Station and on Galindez Island near Vernadsky Station around 65°S latitude has recently exposed numerous entombed mosses and intact peatbank ecosystems that have been buried under ice and snow since the cold Little Ice Age (LIA). Radiocarbon dating indicates ages of 850-600 cal yr BP from re-exposed moss samples from near retreating ice (n=9 dates) and of 100 cal yr BP from near shrinking snow (n=5 dates). This age difference suggests that initial climate cooling and subsequent ice advance overran peatbanks immediately below the ice margin at the onset of the LIA, followed by permanent snow expansion often from low elevation upslope at the end of the LIA. Furthermore, detailed macrofossil and pollen analysis of a 35-cm-long peat core from a moss peatbank on nearby mainland Antarctic Peninsula show dramatic shifts from a waterlogged peatland dominated by pure stands of Antarctic hairgrass (Deschampsia antarctica) before the LIA to an aerobic peatbank dominated by erect mosses Polytrichum strictum and Chorisodontium aciphyllum afterwards. At present the nearest known occurrence of Deschampsia “bog peats” is in South Georgia, about 1900 km north at 54°S, a location having a mean annual temperature 6°C higher than the study region on the WAP. If we use this modern spatial relationship as an analogue, then this suggests that the pre-LIA climate was much warmer than today and appeared to support very different ecosystems on the WAP. These results imply that major ecological transformations and novel ecosystems are things to come in Antarctica by the end of this century under rapid ongoing climate warming (>0.5°C warming per decade) and widespread glacier retreat.