SciBlogs

Archive June 2010

ANZICE Part 4: Climate Models Matthew Wood Jun 22

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PrintSuspended by string from the ceiling of my tween-years bedroom, the wooden skeletons of prehistoric reptiles jostled for space among enamel-coated Harrier jets and Hellcats, sculpted in miniature from cast plastic and balsa. And I wonder why I never had a girlfriend back then? The point is I loved models.

I clearly remember being thrilled by the way that, from my own efforts, the essence of an entire railway system and its environs could be so elegantly realised in 00 gauge. The more I knew about real train systems, and the better honed my skills of recreation became, the more life-like and satisfying were the results. In this latest episode of the podcast we’ll take a look at some models that are, at once, exactly the same as, and utterly different to, those of my childhood fancy.

Modeling has always been a vital part of science’s toolbox — physical models such as flumes or wave pools can simulate the behaviour of larger water masses, for example — but increasingly, scientific modelers are harnessing the power of super computers for virtual simulations of natural systems. Simulations are obviously the only option for predictive studies of future change, but the validity of the model in use has to be shown by its ability to recreate known situations of the present or past. Regardless of how impressive the processing power of computers becomes, scientific modeling will always rely on a foundation of rigorous empirical data collection.

The Climate Models research stream of ANZICE is figuring out at what rate polar ice shelves and the temperate glaciers of New Zealand’s Southern Alps are likely to respond to predicted short- and long-term changes in climate. Their modeling has already successfully recreated the recent and highly publicised collapses of Antarctic ice shelves, and predicts the loss of all Arctic ice shelves by 2100. An energy balance model (EBM) for the Southern Alps has helped improve the understanding of the relationship between our glaciers and the local climate system.

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New Zealand’s glaciers are proving to be highly sensitive indicators of changing atmospheric circulation, particularly the large debris-free glaciers of the West Coast such as Franz Josef. While the Southern Alps have lost 30-48% of their ice mass since the mid-19th century, many glaciers have shown an anomalous readvance since the early 1980s. This appears to be related to an increase in, and shift of, Tasman Sea anticyclones that have increased southerly airflow and led to a slight cooling of the high mountain catchments.

The long-term goal is to couple the EBM to a model that simulates the dynamics of ice sheets, thus allowing the detailed simulation of past ice extents — tying in closely with the moraine mapping and dating efforts of GNS Science’s Central South Island Glacial Geomorphology project. This powerful computer model will be able to provide quantitative paleoclimate (past temperature and precipitation) estimates for the region based on geological evidence. Bear in mind that the scientists behind these models are not stuck in some windowless room staring at a screen through square eyes 24/7. Their models are completely reliant on real-world data: weeks of intensive fieldwork are required each year, monitoring weather stations and collecting continuous measurements of mass balance change and stream discharge.

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Hailing from Melbourne, Andrew Mackintosh has a career in glaciology that has so far taken him from the Greenland ice sheet to Tasmania, from the volcanic ice fields of Iceland to East Antarctica. Now based at the Antarctic Research Centre, Andrew works closely with Brian Anderson and leads the Climate Models team of ANZICE, including 6 post-graduate students. By progressing to the second round of this year’s Marsden funding applications, the research group’s coupled energy balance-ice sheet opus is still in the running towards becoming New Zealand’s next top model.

To download the podcast for your iPod, simply search and subscribe for free through the iTunes Store. For playback on other portable media devices please download from the Journeys to the Ice homepage. Otherwise you can listen straight away by using the player below.

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Photo (c) Matthew Wood 2008

ANZICE Part 3: Southern Ocean – New Zealand Responses Matthew Wood Jun 05

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Sediment core 1New Zealand is a geographically lonely place. It is the only major landmass between the tropics and Antarctica at these longitudes, and shares the southern mid-latitudes with only Patagonia and Tasmania. As such, it is a fantastic natural laboratory for investigating oceanic and atmospheric change in the southern hemisphere.

Our country is perpetually being ground down by the elements in response to rapid uplift. Terrigenous sediment makes its way down river systems to be distributed far into the deep ocean, forming thick, continuous sedimentary sequences. While the sediment itself can appear outwardly unadorned, the real story is locked within the calcareous remains of plankton that have lived their short time in our seas and subsequently dropped to the seafloor to be entombed within the layers of mud. The geochemistry of their tiny shells can be used as proxy data for ocean temperature and salinity, and to assess changes in ocean currents over time.

Phytoplankton are autotrophs and thus live in surface waters of the ocean. When conditions are right — when the waters are sufficiently warm, well-lit and rich in nutrients — massive algal blooms may be initiated, often forming along major ocean fronts. These populations of microscopic plants may be so extensive as to be easily visible from space. Such blooms are thought to flourish during warm periods — evidence of an extreme case being the chalk deposits now exposed in the famous white cliffs of Dover, formed during the super hothouse world of the late Mesozoic. Such blooms appear to be increasing off New Zealand today: can this be attributed to global warming?

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This is one of the questions that the Southern Ocean — New Zealand Responses research stream of ANZICE is currently attempting to answer. Whether these blooms are driven primarily by ocean temperature, or by the amount of incoming solar radiation, is unknown. Answering this question is important because phytoplankton are the base of the marine food chain and so any changes at this level will propagate through the whole system. They also provide their own feedback into the climate system by producing atmospheric acids that act as condensation nuclei for clouds. The calcium carbonate tests of plankton also comprise a significant carbon sink in the deep ocean, particularly so in the Southern Ocean during glacial periods, as outlined in a very recent paper.

Along with marine microfossils in these seafloor sediments are the robust pollen grains of land plants, transported to their marine resting place by the vigours of water and wind. By coring these sediments from oceanographic research vessels, ARC scientists are able to identify changes in vegetation cover on land in response to climate change. This wealth of information is made even more valuable by the logistical challenges of sampling it. This work would not be possible without collaboration with GNS Science, NIWA and research groups abroad.

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A recently initiated study by the group is a classic case of uniformitarianism; the geological premise that the present is the key to the past. Beneath the central South Island glacial lakes are hundreds of metres of finely layered silts. It is not known what this layering represents and so it is prudent to first understand the modern day processes in these lakes before starting to make inferences about the past. Instruments have been deployed to measure what happens on a monthly basis in terms of water and sediment flux through the Lake Ohau system.

Gavin Dunbar returned to the Antarctic Research Centre in 2005 after working at the Australian National University (ANU), where he was interested in the climate history of the Western Pacific as shown in coral and speleothem geochemical records. Gavin now leads the Southern Ocean — New Zealand Responses group of ANZICE and supervises a number of post-graduate students who he has seen become experts in their own fields.

To download the podcast for your iPod, simply search and subscribe for free through the iTunes Store. For playback on other portable media devices please download from the Journeys to the Ice homepage. Otherwise you can listen straight away by using the player below.

Play Podcast Now

Satellite image from SeaWIFS. Photo (c) Matthew Wood 2006

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