Plateau vegetation on sub-Antarctic Macquarie Island

The plateau of sub-Antarctic Macquarie Island supports an open short herb, feldmark vegetation that is markedly affected by the prevailing strong westerly winds. This paper reports on a line transect survey carried out in 1980 which documents variation then apparent in species composition in this vegetation. Sixty-two species were recorded, with plant occurrences along 16 transects ranging from 16.7–99.5%. The cushion plant Azorella macquariensis Orchard was an important component of the plateau vegetation: it occurred at 14 of the 16 sites surveyed, with occurrences up to 50%. The dieback reported in Azorella macquariensis in 2008 was, by 2012, regarded as extensive and severe throughout its range. The data presented here well precede the first records of the dieback, and contribute to early descriptive data against which future developments in the plateau vegetation of Macquarie Island can be evaluated

Terrestrial vegetation and environments on Heard Island

Significantly ice-covered and with a very small flora (11 vascular species and about 60 bryophyte taxa), Heard Island is still emerging from the effects of the last glacial maximum. This study presents the results of a general vegetation survey. A baseline framework of environmental conditions that affect vegetation on the island is described and a classification (TWINSPAN) analysis based on presence/absence data of both vascular plant species and bryophyte taxa is provided. Distinct suites of taxa were identified on the island, some containing bryophytes only. Fifteen ecological groups were delineated. A discussion of ecological amplitude of import ant bryophyte and vascular plant taxa on Heard Island is included

Human impacts on sub-Antarctic terrestrial environments

Sub-Antarctic islands are some of the rarest ecosystems on the planet and therefore are highly significant. Around 200 years of human activities have left a legacy of substantial impacts. We explore these under the collective headings of resource harvesting, local impacts and habitat loss, homogenisation of biota and human-influenced climate change. Past human activities such as sealing and whaling have left seal species still in recovery phases, and infrastructure that continues to break down and pollute the local environment. Modern-day scientific stations have variously-sized footprints of buildings and tracks, and legacies of contaminants, particularly oils spills. On some islands, alien species have established and there is a range of impacts associated with such taxa ranging from transient to extensive, permanent transformation of ecosystems. Such impacts are being confounded by human-induced climate change. By projection, it is expected that both direct and indirect human impact will continue into the future. It is appropriate to plan all future human activity in ways that will minimise further burden on these ecosystems

Ridge top peats and paleolake deposits on Macquarie Island

Palynological analyses of two ridge top peat profiles on subantarctic Macquarie Island are presented and discussed. The profiles record Holocene vegetation changes In a small-scale mosaic pattern. Older records of island vegetation should be sought in valley and lake deposits. A preliminary account is given of several freshwater palaeolake deposits dating from the terminal Pleistocene and early Holocene

Pleistocene uplift and palaeoenvironments of Macquarie Island: evidence from palaeobeaches and sedimentary deposits

Macquarie Island (54°30'S, 159°00'E) is an emergent part of the Macquarie Ridge Complex composed of ocean-floor rocks of Miocene age now 4000 m above the ocean floor. A number of landforms, including palaeobeaches now above sea level (a.s.l.)on Macquarie Island, were formed by marine erosion during uplift of the island. During the last Pleistocene period of low sea level (c. 20 ka) the island was three times larger than now. Thermoluminescence (TL) dating of two palaeobeaches indicates Pleistocene ages: 172 ± 40 ka for one at 100 m a.s.l. and 340 ± 80 ka for another at 263 m a.s.l. Matching the altitude sequence of palaeobeaches on Macquarie Island with the pattern of peaks in world sea level determined from deep sea cores allows an independent estimate of beach ages. Comparison of the altitude and sea level sequences most plausibly places the 100 m palaeobeach in Oxygen Isotope Stage 5e (130-125 ka) and the 263 m palaeobeach in Stage 9 (340-330 ka), matching reasonably with the TL dates. Other palaeobeaches at about 50 m and 170-190 m a.s.l. then correlate with high sea levels. We calculate an average rate of uplift forthe island of 0.8 mma-I . At this rate, 4000 m of Macquarie Ridge uplift would have taken about five million years and the top of the island may first have emerged some 700 to 600 ka. During the six Pleistocene glacial-interglacial cycles since then, there has been periglacial rather than glacial activity on cold uplands, but conditions suitable for vegetation of the present type persisted close to sea level

The nature and importance of the sub-Antarctic

Sub-Antarctic land is a rare resource in world terms. It is appropriate to recognise the sub-Antarctic as a region distinct from the cool temperate zone to its north and the Antarctic zone to its south, a region with its own characteristics, and with significant intrinsic value and scientific importance. Appropriate protection from anthropogenic change and exploitation must be ensured for the sub-Antarctic

Terrace types and vegetation dynamics on Macquarie Island

Feldmark vegetation occurs extensively on the plateau of Macquarie Island above about 200 m. Alternating stripes of vegetation and gravel are frequently associated with terraced terrain. Detailed study of 38 terraced sites with non-windward aspects shows vegetation-terrace interaction to be active under present climatic conditions. Wind, moisture, hillslope, slope stability and vegetation all affect terrace form

An analysis of air temperature records for Macquarie Island: decadal warming, ENSO cooling and southern hemisphere circulation patterns

Macquarie Island lies close to, but on the eastern side of the boundary between the eastern (pacific) and western (India-Australia) limbs of the Southern Oscillation. Its temperature record matches that of the area east and southeast of New Zealand, rather than Tasmania. Temperature is influenced by atmospheric pressures in the Southern Ocean to the east and west, which can result in a warm northeasterly or cold southerly airflow over the island. It is a sensitive indicator of climatic trends because of its location at high latitude in a longitudinal region of frequent ridge formation and blocking in the Southern Hemisphere circulation. Temperature records for Macquarie Island (1949-86) show a trend (twice the global average), accelerating in the last 20 years with eight of the ten warmest years occuring in the last decade. The greatest average rate of warming has occurred in late summer and early autumn and the lowest in spring. In severe ENSO years the island cools. The warming is marked, in relation to the annual mean (4.8°C), and the biological effects should be considered

Landforms of aeolian, tectonic and marine origin in the Bauer Bay-Sandy Bay region of subantarctic Macquarie Island

Aeolian landforms on Macquarie lsland, in the Southern Ocean, occur above 100 m on the plateau between Bauer Bay and Sandy Bay. An extensive sand sheet, at least 6000 to 7000 years old, is wind and water eroded to produce blow-outs with bare troughs and vegetated elevated margins, Sand moved eastwards before the prevailing winds. Wind-polished bedrock on the western edge of the plateau is a relict feature. Wind-polishing of bedrock occurs today near sea level at the head of Bauer Bay. The area is tectonically active. No evidence of former glacial activity was observed. Topographic features in this area, previously regarded as glacial, are attributed to faulting. Tectonic uplift and sea-level changes are invoked to explain the formation and age of the broad and gently sloping raised marine terrace around much of the western and northern coasts. This explanation also sets constraints on the ages of the sand sheet and the cobble beach at about 100 m on the plateau east of Bauer Bay