Patterned quaking mire at Handspike Point, Macquarie Island

Abstract

Raised mires occur on an emerging marine terrace of Holocene age at Handspike Point, Macquarie Island, and slope seawards. Ponions of these mires are characterised by numerous, anastomosing to parallel, low peat ridges, separated by waterlogged troughs. The resulting patterns arc accentuated by the distinctive rosette plant Pleurophyllurn hookeri, which grows only on the ridges. Sampling suggests that ridge and trough patterns persist to at least l.)m depth. Pleurophy/lum colonisation appears to be a function of the difference in trough: ridge peat bulk density. As chis density ratio approaches 0.8, waterlogging decreases and Pleurophyllurn vigour is enhanced. Patterns are oriented at various angles to the present surface slopes, bur roughly parallel ro the plateau margin and normal to the regional slope of the marine terrace. The divergence between pattern and local contour orientation results from non-uniform accretion. Patterns at angles to the contours appear ro provide benefits which include enhanced water-level stability. The Handspike mires exhibit many characteristics of patterned and non-pancrned peatlands ubiquitous throughout the Northern Hemisphere, with particular similarities to eccentric domed mires of the Baltic region. Vertical accretion is estimated to average 1mm yr-1; lateral accretion appears to be in equilibrium with the emerging marine terrace.