http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13332 A new map, the first based on interpretation of satellite imagery, reveals both the complexity of Australia's dunefields and their relationships with topography, climate and substrate. Of the five main sand seas, the Mallee, Strzelecki and Simpson in eastern Australia cover Quaternary sedimentary basins whereas the Great Victoria and Great Sandy dunefields in the west are formed by reworking of valley and piedmont sediments in a non-basinal landscape of low-relief ridge and valley topography. These dunefields cover large areas of the arid zone and semi-arid zone and small areas of dunes in sub-humid areas around the margins of the continent reflecting past expansion of arid climates during glacial stages of the last several glacial cycles. Several areas of low relief stand out as being largely dune-free: the limestone Nullarbor Plain, clay plains of the Georgina Basin and floodplains of rivers in the Carpentaria, Lake Eyre and Murray–Darling drainage basins where sand is rare or not transported by diminished Late Quaternary rivers. The Yilgarn Block of southwestern Australia is also surprisingly free of dunes, possibly as a result of long, deep weathering. Everywhere the history of climate change is evident in dune morphology and distribution, including large areas where the sand dune orientations are markedly divergent from modern sand moving wind directions. 2011-05-30T02:50:40.383Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13246 Maghemite (γ-Fe₂O₃) is a very common mineral at the earth’s surface and also an important material for making music and video tapes. Maghemite is usually synthesized from magnetite under oxidizing conditions after a few hours or a few days below a temperature of 300°C. The magnetic property of thermal instability and the chemical action after heating is an important character for maghemite. That is, it will become hematite in certain proportion after being heated above 250°C. Maghemite is therefore actually unable to have its Curie temperature measured. But late using synthetic sample, maghemite was further found partially thermal stable with a measurable Curie temperature ∼645°C. During our thermally magnetic experiments for a set of synthetic magnetite, we found that extra fined grain size (pseudo single domain (PSD) and small multi-domain (MD), mainly 1–10 μm) magnetite was formed to a completely thermally stable maghemite. This maghemite can also be produced by heating the same powder up to 700°C in an oven and keeping this temperature for 10 min, then cooling it down. When the generated maghemite by these two ways is heated from room temperature to 700°C, it shows almost fully reversible, or thermally stable. We used X-ray powder diffraction and Mössbauer spectroscopy to confirm the identity of this maghemite and compared its magnetic hysteresis, high temperature magnetization, low temperature thermal demagnetization, and low temperature susceptibility with those of the original preheated magnetite. Such quickly oxidized maghemite by heating to high temperature implies some types of maghemite formed in certain natural condition can carry a thermal remnant magnetization (TRM). Four types of maghemite were characterized and discussed according to their thermal stability. Among them, partially stable and fully thermally stable maghemite after heating should possess capability of carrying TRM. There is possibly a compensation of synthetizing maghemite between heating temperature and heating duration. The thermal stability of maghemite may be affected by a few factors, such as its purity (stoichiometry), heating temperature and duration. The grain size may be one of important factors. Maghemite might be similar to magnetite, having various magnetic properties corresponding to its grain size categories such as superparamagnetic (SP), single domain (SD) and MD. Low temperature measurement for PSD fine grain of synthetic magnetite shows a phenomenon of Verwey transition “suppressed”, its fundamental causes could be that the core diameter of oxidized magnetite is actually reach or approach SD size, so that its Verwey transition is shown “suppressed”. 2011-05-25T21:42:13.797Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5417 Sand dunes on the Newnes Plateau (1000 m a.s.l.), west of Sydney, were active during the Last Glacial Maximum. The scattered sand dunes are forested under the modern humid, temperate climate regime. Dune types range from parabolic to transverse lee dunes and sand sheets or patches. All point to the presence of conditions marginal for aeolian activity, made possible through wind acceleration on windward slopes, ready sand supply from the weathered sandstone of the plateau and sparse vegetation cover. Modern climate envelopes of sand dune activity in Australia predict that unrealistically drier conditions are necessary to allow wind transport at this site. Only additional impediments to plant growth, such as lower temperature and lower atmospheric carbon dioxide concentrations, appear to allow the necessary conditions for dune formation. These observations and conclusions extend our understanding of the extremes of the LGM climate in humid eastern Australia, confirming that the widespread treeless vegetation was also sparse, even in areas that today have annual rainfall above 1000 mm. 2010-01-27T22:30:35.750Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5436 The Southern Hemisphere westerlies in the southwest Pacific are known to have waxed and waned numerous times during the last two glacial cycles, though even semi-continuous histories of the westerlies extend back no more than about 20,000 years. We have good evidence for at least three scales of events. A westerly maximum occurs at the Last Glacial Maximum. There is less conclusive evidence for another westerly maximum in the late Holocene and for a minimum at ca. 11 ka. It is too early to ascribe even a cycle to these data but there are grounds to suggest that Milankovitch precessional forcing may underlie the observed pattern. There is also a quasi-2600-year cycle present in Antarctic ice cores that appears to correlate to variation in westerly flow. There is strong centennial-scale variability. In historical times, the Little Ice Age (LIA: ca. 1400–1850) was associated with a poleward shift in the circumpolar trough in the Southern Ocean, strengthened westerly circulation over Tasmania and a strengthening of southwesterly circulation and neoglaciation in southern New Zealand, while the preceding period (800–1400 AD) was less certainly marked by reduced westerly flow. From modern records we know that decadal and inter-annual variability is important (e.g. Pacific Decadal Oscillation, High Latitude Mode also known as the Antarctic Oscillation, El Niño Southern Oscillation). Only a minority of the proxies examined can identify changes on these temporal scales but data from tree-rings, ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time. Rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale. We conclude that westerly circulation is as strong now as at any time in the last glacial cycle. In addition, changes in latitudinal boundaries in the westerlies may be nearly as large in inter-annual zonal shifts (ca. 2° maximum) as in glaciation–interglaciation movements (ca. 3–4°). There is, however, reasonable evidence of strengthening/weakening across much of the westerly belt at westerly maxima/minima such as the LIA/early Holocene. 2010-01-27T22:30:22.838Z ]]>