Uninhabited for nearly 100 years, Tieke in the middle reaches of the Whanganui River, is now home to an extended family whose members trace their connection to this place back to pre-European days, when it was a centre of learning and trade. Menthods of transport may have changed, but the Whaganui and its forests continue to provide the local people with traditional foods: ell, pig, greens.
Only two-and-a-half kilometres from the Beehive, one of the most interesting conservation projects in the country is breaking ground. The Karori Wildlife Sanctuary Trust, a private community group, is setting up a "mainland island" in the former Karori Reservoir, a valley nestled between the two populous suburbs of Karori and Highbury/Brooklyn, and bordered at the top by reserves, lifestyle blocks and farms. Mainland islands have been established in a number of locations around the country by the Department of Conservation over the past decade, following success in increasing the numbers of kokako in the original Mapara "island" south of Te Kuiti. All these mainland islands rely on ongoing pest control and natural physical boundaries to keep predator numbers inside the island low. This approach wasn't possible in an urban area. The trust decided instead to build a fence—one that would exclude 14 undesirable species of mammal: possums, stoats, ferrets, cats, dogs, rabbits, hedgehogs, weasels, two species of rat, mice, deer, goats and pigs. Nobody had previously constructed such a fence. What was more, there was virtually no research into the physical capabilities of New Zealand's key predators. "For example, we didn't know how high feral cats could jump, or how well possums could climb, or how deep rats could burrow," said Stephen Fuller, the island's general manager. Fuller, an ecological consultant, coordinated a team of engineers, scientists and environmental consultants, fencing contractors and metal and wire fabricators to trial fence designs starting in early 1996. To enclose the 250 ha reserve, 8.6 kilometres of fence was going to be required—not an undertaking to be approached haphazardly. The team erected a wooden building with two compartments, separated by the test fences under trial. Animals were put on one side, food on the other. At first the animals were aided to traverse the barrier between the compartments to reach their food. Then the aids were removed, and the animals left to their own devices. One possum was videoed making 100 unsuccessful attempts to scale the fence in a single night. Over 18 months, 100 possums, nine feral cats, seven stoats, 10 Norway rats, 20 ship rats and 55 house mice pitted their strength and cunning against various designs. "The trials put the fences under more strain than they would get in the wild," noted Fuller. "After three days without food, the animals were highly motivated to beat the fence. Normally they wouldn't try so hard." The final fence design specifically avoided using electrification, the most common method used for keeping climbing animals off pest-control fences. "Our proximity to the city, and often extreme weather conditions, posed too many maintenance and operational problems for electricity," said Fuller. The fence design chosen, and now under construction, is 2.2 m high (cats can jump up to 1.85 m), and made of a mesh tightly woven from 2.5 mm high-tensile galvanised wire. The gaps in the mesh are only 6 mm by 50 mm-narrower than the head of a mouse at weaning. The fence has a shallowly buried underground skirt of the same mesh extending 400 mm out from the bottom of the fence at right angles, tests having suggested that when some animals find that they cannot get through the fence, they start digging against it. A modular design enables damaged portions to be easily replaced. The crowning glory is a distinctive "top hat," a smooth, rounded hood of galvanised zincalume which extends 250 mm out from the fence and has been shown to effectively repel possums and other climbers. The hood has also been tested to withstand Wellington's wind gusts. Secured by wooden posts at three-metre intervals, this elaborate fence costs $180 per metre in materials alone. Adding the other costs associated with construction—clearing trees, surveying, putting in drains and gates, and erection—swell the cost to $240 per metre. In preparation for construction, a four-metrewide lane was cleared along the line of the fence—three metres to be outside the wire and one metre inside—so animals don't have any climbing aids. This lane is to be kept permanently bare. Most of the fence follows the natural contour lines of the valley ridge. The steepest section is where it plunges to the valley floor, opposite the main road into the sanctuary. Staff gathered to watch one bulldozer being anchored to another and dropped down a 45-degree slope to clear the vegetation from this section. "By the time it reached the bottom, the driver had sore legs from standing on the dashboard," said Fuller. "We all cheered." The last of the perimeter was cleared in February 1999, and fence building started immediately. Construction is expected to be complete by August. The trust has launched a public campaign encouraging Wellingtonians to buy a fencepost to support the sanctuary. By June, 750 posts (each bearing the donor's name) had been purchased. So far, $6.5 million has been raised towards the $9 million total cost of the project. This fence is expected to have broader applications, and the design has been patented. "Ours is the Rolls-Royce of fences," remarked Fuller. "Other projects may need to exclude fewer types of predators, and could use our research to develop simpler fence designs." Possible uses extend beyond conservation, and the sanctuary is talking with a power station and food manufacturer, both of whom want to exclude mammals without relying on electric fencing. After the fence is completed, all mammals inside the area will be eradicated—hopefully by January 2000—and then the real excitement will begin, as native birds and reptiles are reintroduced to the valley. Wellingtonians should be hearing kiwi calling in the night within two years.
When South Canterbury's Opuha Dam hit the news in February 1997 it was for all the wrong reasons. The then partially completed dam had been breached by an unseasonal deluge, and the surge of water it released damaged a number of farms downstream. But since then the project has got back on track. The repaired dam was completed in June 1998, and is showing signs of becoming just what its builders hoped: the linchpin for economic expansion in the region. Farming intensification, power generation, ecological enhancement to downstream rivers and a boost to tourism from the creation of a 730 ha recreational lake are among the expected benefits of the project. Opuha is the largest earth dam built in New Zealand for almost 40 years. The 91 million cubic metres of water in its lake is designed to irrigate some 16,000 ha of farmland stretching from inland of Fairlie to the coastal plains between Pleasant Point, Temuka and Timaru. Indeed, the lake has been providing desperately needed water since late September 1998. The Opuha scheme also generates a peak output of 7.5 MW of electricity, equivalent to about 6 per cent of South Canterbury's annual consumption. The project is a joint venture by private and community interests in the region, including 175 farmer shareholders, local electricity lines company Alpine Energy and the Timaru and Mackenzie District Councils. Situated in the Opuha River gorge about 10 km north-east of Fairlie, the dam is 50 m high and 265 m wide at the base. It stretches 300 m across the gorge and contains about 850,000 cu. m of hard fill quarried from river terraces upstream. Construction manager Chris Hollingum says the site chosen for the dam is extremely sound geologically. The gorge walls are of hard rock, and the nearest major fault line is 12 km away. The stability of the site allowed earth to be used rather than concrete, saving several million dollars. The design incorporates some of the latest overseas innovations in dam construction, including a stepped spillway, the first of its kind in New Zealand. This dissipates the energy of the water more effectively than a conventional spillway, and is also shorter and therefore cheaper to construct, says Hollingum. In addition, the dam includes features to meet environmental and ecological requirements, including the provision of a pipe lined with small rocks to allow eels to pass upstream. Further ecological benefits will extend downstream. In past summers, the Opihi River system (of which the Opuha River is a part) has been known to dry up, stranding fish which have had to be rescued. Releasing stored winter water in summer will now allow minimum flows to be maintained, providing fish and other river life clear passage year round. The power station also breaks with tradition. Turbine and generator are housed in a concrete cylinder 17 m high, most of which is buried. The roof can be removed in about 10 minutes and the machinery lifted out with a mobile crane, saving the expense of installing a permanent heavy-duty gantry. Water reaches the power station via a 200 m-long, 2.5 m-diameter pipe from the bottom of the lake. Construction began in November 1995, when the river was diverted to the right-hand side of the gorge so the dam foundations could be laid on the left‑hand side. Later the river was diverted through a pipe to the left so the foundations could be extended across the entire width of the gorge. Once the base had been completed, the dam was built up in steps to its full height. Construction was set back more than a year by the dramatic breach of the partially completed structure on Waitangi Day 1997, following a flash flood. After this disaster, three temporary flood channels were cut at different levels on the left-hand side, designed to cope with a 1-in-200-years flood event. Each channel was covered over as the dam was rebuilt to its full height. Permanent flood protection is provided by the main spillway—also designed to handle a 1-in-200-years event—and a "fuse plug" near the top of the dam. The plug is designed to wash out slowly in the event of an extreme flood to let excess water over the dam. The upstream face of the dam is covered with fine shingle lower down and metre-wide boulders closer to the top as protection against wave damage. Downstream, the riverbed has been deepened by eight metres to increase the vertical water head for the turbine. Complementing the dam is a smaller weir about a kilometre downstream which can hold up to 52 hours of river flow, and this is an integral part of the whole scheme. Opuha is primarily an irrigation scheme, and power generation is a bonus. The main objective is to have a dam full of water to irrigate farms downriver when the weather turns dry, as it regularly does, and to maintain consistent minimum flows in the downstream rivers. If power demands are high in the morning and the dam is not full, water can be run through the turbine, then corralled in this pond. It will be released gradually during the rest of the day, and no more water will be taken from the main dam. Most of the water for irrigation is drawn from rivers well below the dam. When the dam is full, power is generated from the overflow continuously. No staff are situated on site, and all controls are operated remotely. Ollie Turner, former economic development officer for Timaru District Council, says the dam is central to South Canterbury's economic development. "Securing a reliable supply of water will reduce the costs of droughts and open up new diversification options for farmers," he claims. One of the most likely diversifications is expected to be the conversion of sheep and beef farms to dairying. The transition is relatively simple, and the high conversion cost is far outweighed by higher returns. Breeding ewes currently return $360 per ha, and bull beef $320—only a fraction of dairying's $3000 per ha. There is also plenty of spare capacity in local dairy company processing plants. Expansion of dairying will have a positive spin-off for dryland farmers, who stand to benefit from increased demand for off-farm grazing of dairy herds during winter. The development of intensive beef feedlots is expected to be another growth area, according to Turner, one which would generate enormous demand for extra feed. Horticulture is also likely to expand. Farmers who choose to remain with sheep and beef will benefit from the dam too, says Turner, as a reliable water supply should significantly boost gross-profit margins. This in turn will help secure a long-term future for the region's major meat-processing plants in Timaru and Pareora, along with hundreds of jobs. Vegetable processing is another sector touted as likely to see growth, with the infrastructure already in place. McCain Foods has a strong presence in the region, having taken over and expanded the former J. Wattie Foods factory at Washdyke, and Skeggs Foods operates a vegetable-processing plant at Studholme, south of Timaru. Further afield, more processing capacity is available at Talley's Ashburton plant. The considerable recreation potential of the lake for boaties and anglers is bringing additional economic gains by boosting visitor numbers in summer. Turner says economic-impact studies suggest the total annual boost to the region's economy, from higher returns to farmers and flow-on effects from this extra income, could be in excess of $20 million a year. The dam is predicted to create 400 new jobs over the next decade, mostly in primary-produce processing. The economic recovery of South Canterbury, it seems, is just around the corner.
Pigs which have grazed on the subantarctic Auckland Islands for almost 200 years are living on borrowed time. Within 10 years, if Department of Conservation plans go ahead, the animals will be eradicated. The first release, thought to be of long-snouted Asian pigs from the Philippines, took place in 1807 to provide food for shipwreck victims. When an attempt was made to farm the islands in the 1840s and '50s, more pigs were introduced, this time of English stock from the Chathams. Once farming was abandoned, the remaining pigs ran wild. For the past 150 years they have been an isolated population free from human interference. DoC, the islands' custodian, estimates that there are 500 to 1000 feral pigs on the main island. The decision to exterminate the animals is based on the extensive damage they cause to the unique plants and animals. On Enderby Island, where pigs are absent, ground-nesting seabirds are plentiful, but on the much larger Auckland Island there are only a modest number of penguins, and one or two pairs of albatross. Megaherbs, flourishing on Enderby since the removal of cattle and rabbits, are restricted to steep, inaccessible cliffs on Auckland Island. In mid January this year, the Rare Breeds Conservation Society mounted an expedition to save some of these pigs before the slaughter commenced. Twenty-two of us, including three from TV1's Country Calendar programme and a DoC representative, steamed out of Bluff aboard Sea Surveyor for the 460 km voyage-into seas so wild that even our pig dogs were thrown off colour. DoC had suggested that the pigs would be found on the open tops of 67,500 ha Auckland Island. Hunting with dogs failed to turn up any sign on the tops, but one party caught a boar and the other party a sow, both near sea level. Cages were hastily put together from wire mesh, and the pigs given sedatives and anti-biotics and left to recuperate in confinement. The following day three boars and two sows were caught close to the coast, one of the party receiving a rip in the leg from a boar in the process. This incident highlighted the difficulties of catching pigs on the island. In many places walking was easy, through an open tangle of southern rata, but elsewhere waist-high ferns or tussock totally obscured the ground. Although movement of the leaves and fronds showed where a dog had a pig bailed up, you could not see exactly how close it was or which way it was facing. Only once you got down on hands and knees under the canopy could you fully appreciate the situation. Not being able to see where you were walking was a bit of a worry. Would your next step be into a deep bog or onto a sleeping sea lion? One member leading a party on his hands and knees underneath some harsh growth was suddenly brought up short by a huge male sea lion barking not two metres from his face. Hunting on the island involved other differences from back on the mainland. These pigs did not squeal, and keeping track of the dogs was a major battle. While the dogs barked while chasing a pig, but they could not bark while they had hold of it. Noise from the waves crashing on the rocks and the wind in the trees made finding dogs holding pigs impossible at times, even at less than 100 metres' range. Radio-tracking collars were attached to dogs so we could locate them in the event of real difficulty. The pigs were completely innocent of experience about hunting. Some, in the open, just stood still until the dogs grabbed them. Most of the pigs were black, with some black and tan. Their hair was long, and in some the eyebrows had particularly long hairs. The long, dished noses dropped away from very closely spaced eyes, and the tails were long and straight to the ground. Two of our party were continually around the penned pigs and, to our delight, the pigs were feeding from their hands within a few days of capture. Hunger appeared to be the pigs' constant companion. All those captured except two young boars were in light condition—in fact, so light (35-50 kg) that a man could easily carry one. The suckling sows had only two or three teats producing milk, which told how few piglets survived, because piglets stay with the teat they first seize after birth. Over the years, the pigs have cleaned out most of the edible plants, including the striking megaherbs, and they would certainly take eggs and chicks of ground-laying birds when available, but few remain on the island. We saw pigs (and skua) devouring sea lion carcasses. Rooting damage—often significant on the mainland—is here minor, simply because there is little food to be got by digging. Food of any sort for the pigs seemed to be in short supply. One of the delights while hunting was to hear bellbirds and watch tuis bouncing through the air, catching big blowflies. One day I inadvertently left the but door open for two hours and learnt firsthand the reason that Allan W. Eden, the surveyor of the 1940s, described flies as being the single worst experience on the island. After spraying the window, I cleared one-and-a-half shovelfuls of flies off the floor l Our first pigs were captured from Port Ross at the northern end of Auckland Island, but we later took some from Carnley Harbour in the south to make our sample more representative. In total, 17 pigs were captured and, with some difficulty, transferred to Sea Surveyor. All survived the trip to Invercargill in good shape and were placed in quarantine in the old piggery of the Invercargill Hospital. The Ministry of Agriculture and Forestry treats animals reaching the mainland from the subantarctic islands as arrivals from a foreign country. They will remain in quarantine until the ministry is satisfied that they pose no danger to mainland livestock. In the meantime, they have increased magnificently in weight, and become quite sociable. The ultimate fate of these pigs is to form the nucleus of captive breeding populations, certainly in New Zealand and perhaps elsewhere in the world. Southland has decided that these subantarctic castaway animals—not just the pigs, but the cows and rabbits retrieved previously—are part of its heritage, and has formed a trust headed by Invercargill mayor Tim Shadbolt. It is expected that this trust will oversee the breeding programme and operate it for the Rare Breeds Conservation Society. Curiously, despite its indifference to the animals' fate and to all this voluntary activity, the government remains the owner of all these animals and whatever genetic potential they might hold.
That land is made from rock seems such a truism as to be hardly worth stating. But different landmasses are made from different types of rock, and these distinctions can be informative as to how the land was formed. Although our own patch of terra firma has a fair mixture of constituents, one is much more abundant than all the others put together: greywacke. Greywacke is a rather variable and nondescript grey rock. The word is of German origin, from grauwacke, meaning grey sandstone. While entire scientific symposia have been devoted to its definition and details, it is best described as simply a hard, grey sedimentary rock. The most important point here is that the rock is sedimentary. It formed from sand, mud, gravel, and silt that was eroded off existing land and dumped by rivers into the sea, there to be compressed over tens of millions of years. Most of the sediment was muddy sand, and most of our greywacke is now muddy sandstone. Its age varies from about 280 million years to 120 million years. But what was the preexisting land that gave rise to the sediments? Judging by the amount of greywacke in New Zealand, it must have been a sizable landmass. All the hard basement rocks of the main ranges of the North Island are greywacke—from Northland through the Hunuas, parts of Coromandel Peninsula, the Urewera, Raukumara, Kaimanawa, Ruahine and Tararua Ranges, and more. The central North Island volcanoes have merely punched through greywacke basement rock and buried it under layers of ash and ignimbrite. Greywacke has itself been eroded to form the soft and much younger papa sandstones and mudstones of Taranaki, Wanganui, Manawatu and elsewhere. In the South Island, all the central mountains are greywacke, and the Canterbury Plains are just a sheet of greywacke rubble sluiced out of the Southern Alps. Most of Marlborough, Canterbury and Otago are greywacke. Even the schists of Otago are derived from greywacke—it has just been more deeply buried, and transformed into schist. And even that is not the end of the stuff. Under much of our vast continental shelf lies more greywacke. Out to the Chathams, south to the Campbell Plateau, it is probably all greywacke. From analysis of the mineral composition of our greywacke, it has long been known that it had to derive from granitic rocks, and obviously a rock body at least as large as New Zealand in size. For three decades the hunt has focused on Antarctica, but no suitable masses of granitic rocks have been discovered there. Others have suggested that it was derived from a landmass that has now completely disappeared. Now a new suggestion has been made, although it is unlikely to be very palatable to the average Kiwi, for it suggests that Aotearoa is derived from the outwashings of north-eastern Queensland! The new hypothesis has been arrived at largely from age determinations of minerals in the greywacke. Greywacke is more than just a sedimentary rock like mudstone. It has undergone some degree of metamorphism by burial, and the combination of pressure and heating has both hardened the rock and produced new minerals. Dating these minerals gives no information about the parent rock, but the greywacke also contains minerals from the original detritus that have resisted metamorphism, and which can be dated. The best subjects for dating are those minerals that contain the common, naturally occurring radioactive elements potassium, uranium and thorium. Potassium-bearing micas and uranium-bearing zircons are readily dated using potassium-argon, argon-argon, and uranium-lead methods. The radioactive decay rates are known (and are fixed), so by measuring the amounts of the original elements and the decay products you can determine the date when the parent rock formed. This is crucial information, because it limits the search for candidate parent rocks. Christopher Adams of the Institute of Geological and Nuclear Sciences in Lower Hutt has spent 10 years painstakingly collecting, preparing and dating individual mineral grains from greywackes around the country, and in 1998 he published the results. They indicate that our greywackes formed from granitic rocks 230 to 290 million years old, with a minor mica schist component that was somewhat older, at 425 to 450 million years. These new data narrowed the search considerably. Now, rocks of a defined type and age were sought. No matching sources could be found in Antarctica, Tasmania, or south-eastern Australia. However, north-eastern Queensland contains rocks that match in both age and composition. That this region is the source for New Zealand's greywacke was further confirmed by isotopic analysis. Measuring the amounts of the various isotopes of strontium—a technique for fingerprinting rocks—indicated that Queensland rocks are the best candidates as parents for New Zealand's greywacke. Although rare, some of the dated minerals are extremely old—up to 3,100 million years—and their nearest ultimate source is thought to have been the Precambrian core of south-east China. New Zealand has come a long way! Only one question remains to be answered Queensland is 3000 kilometres distant. How did the sediment get here? It must have been transported by large river and delta systems similar to the Ganges and Orinoco Rivers of today, which drain large areas of mountainous hinterland. Perhaps they were very long rivers, but it is most unlikely that they deposited their sediment loads where New Zealand is today. Probably the New Zealand greywacke formed close to the coast of Australia, so the sediment didn't have far to travel. Subsequent to deposition, plate tectonic movement shifted us from the north-west towards the south-east. There is evidence for this trend in the movement of other rocks in the region. Some east Australian greywackes are thought to have been derived from New Guinea parent rocks, and greywackes on the Antarctic Peninsula from basement rocks in the vicinity of modern southern New Zealand. A consequence of these ideas is that the original locus of New Zealand greywacke sediments may have been subtropical. Efforts to determine and test these ideas by examining the fossils of sea life preserved in the greywacke are being carried out by me at the Institute of Geological and Nuclear Sciences. If the fossils indicate warm equatorial waters, then a near-Queensland location is indeed plausible. Indication of cooler mid-latitudinal waters would tend to support the idea of long river transport. Whatever the outcome of ongoing research, all those New Zealanders who go to Queensland are really just returning to the motherland.
That Earth's humblest materials can be transformed into sublime and beautiful objects is part of the romance of the potter's art. But it takes patience and strong hands to work such miracles. Barry Brickell, the doyen of Coromandel potters, has shaped clay dug on his property at Driving Creek for close to 40 ears. His trademark work are tall, sensuously curved sculptures, in which the clay has been laboriously kneaded and pressed into shape without the use of a potter's wheel. A single piece may take up three weeks to complete.
It was with I dismay that the staff of New Zealand Geographic received the news in 1997 that Peter Quinn, one of our main photographers, had been diagnosed with cancer. Since his first story for the magazine, on whitebaiting, in 1993, Peter had covered some big stories for us, including coal mining, the Main Trunk Line and Highway 35. (His work on the Opotiki Gisborne highway was later published in a book which has been shortlisted for the 1999 Montana Book Awards.) When initial surgery and treatment appeared to have been successful, we rejoiced with Peter and his family, and readily agreed when, on the strength of his new lease on life, he asked if he could tackle the subject of cancer as an assignment. The magazine's deputy editor, Warren Judd, was the obvious choice for the writer. Warren, who has been closely associated with New Zealand Geographic since its earliest days, has a PhD in cell biology, and had been involved in cancer research at Harvard Medical School before leading his own cancer research group at the University of Auckland. His scientific knowledge gave us the foundation on which to build our coverage. But it was Peter's own brush with mortality that made this story particularly important to us. During the 18 months it took to reach publication, we were often aware of the difficulties he was facing, both with his own health and with the challenges of illustrating this emotion-charged subject. He would sometimes spend weeks organising a particular photograph, only to have permission declined at the last moment. That this story has finally appeared in print is due in large part to Peter's unswerving commitment to the project. Here, in his own words, are his reflections on what could be described as the assignment of his life.
To better understand and appreciate your own country, there is nothing quite as good as a long trip overseas. By the same token, an understanding of how our weather works can be enriched by a long look at what goes on in some far corner of the Earth, such as the South Pole. Antarctica has a reputation as one of the stormiest places on Earth—and storms are typically associated with heavy precipitation. Paradoxically, however, much of Antarctica receives such a small amount of snow that it qualifies as a desert. On the high plateau of the interior less than 50 mm of snow (equivalent to 5 mm of rain) falls each year. On the coast the average precipitation is mostly between 100 and 400 mm, although a few areas have as much as 1000 mm, notably the area just west of the Antarctic Peninsula, bordering the Bellingshausen Sea, which is a favoured area for depressions to make landfall. The main reason for Antarctica's lack of precipitation is the extremely cold air temperatures. The amount of water vapour air is able to contain depends on its temperature. The warmer the air, the more water it can hold. For example, air with a temperature of 25°C and 100 per cent humidity (such as might approach New Zealand from the tropics in summer) contains 20 grams of gaseous water per kilogram. Air with a temperature of 5°C and the same humidity approaching Invercargill from the south in winter has only 5 grams of gaseous water per kilogram. But at the South Pole, air at -50°C and 100 per cent humidity contains less than one tenth of a gram of gaseous water per kilogram. When this air at the pole is cooled further, some of its gaseous water changes to ice, forming tiny crystals that fall slowly to the ground. Since the amount of water available is minute, the gaps between the crystals are so large that no cloud is visible, and the ice crystals fall from a blue sky. Known as "diamond dust," the falling ice crystals give rise to a rich variety of optical phenomena in the sky, including arcs, circles and sun pillars. There are several reasons it is so cold in Antarctica. Most obviously, the sunlight is less intense there, since it strikes the Earth's surface at an oblique angle, and fewer of the Sun's rays reach each square metre of the surface compared with the situation at the tropics. Also, by falling obliquely, the Sun's rays have a greater amount of the Earth's atmosphere to cross in order to reach sea level in the Antarctic, and so a greater portion of the sunlight is scattered by molecules in the atmosphere. Even so, in summer the sun shines 24 hours a day, and the total amount of sunlight reaching the surface in the course of a day is greater than in the tropics. However, almost all of Antarctica is covered in snow or ice, which acts like a mirror, reflecting the vast majority of the incoming sunlight straight back to space. It is this loss of sunlight that intensifies the cold and has allowed 30 million cubic kilometres of ice to build up over a continent that was once home to beech forests. Over a large part of east Antarctica the ice is more than three kilometres thick, and this also contributes to the low temperatures of the ice surface, because the higher the altitude, the lower the air temperature. Once sunlight begins to wane, in the second half of summer, the temperature begins to fall as the ice surface radiates more heat away to space than it absorbs from the sunlight. To warm-blooded beings such as ourselves, it may seem strange to think of a freezing surface radiating heat, but all things do so, unless they are cooled to -273°C, which is absolute zero. The temperature of the ice surface does not fall this far, even though the sun never shines for months on end in winter. Instead, once the surface air temperature has fallen to around -70°C, a state of equilibrium is reached between heat radiated downwards from the atmosphere in the night sky and heat radiated away from the surface. At this point the cold ice has cooled a thin layer of air just above it. About 500 metres up, the air temperature is some 25°C warmer, and downward radiation from this air prevents the surface cooling further. Air in the cold layer is much denser than the air above or, more importantly, the air at a similar altitude immediately adjacent to the continent. So, with the help of gravity, the cold air tends to slide off the sides of the continent down to the sea. In Antarctica, the downslope flow of cold air, known as a katabatic wind, is channelled by the terrain and can reach speeds of 150 kph or more. By this stage the wind will have picked up large quantities of snow lying on the surface, thus forming a blizzard, with a visibility of only a few metres. When the wind is strong it tends to blow the sea-ice away from land, creating large areas of open water known as polynyas. As the cold air blows across the polynya it chills the surface water, causing new sea-ice to form, which in turn is blown away. As the sea-ice forms, it leaves behind salt-enriched water, which is dense and consequently sinks to the sea-floor. Over thousands of years this water makes its way north, and eventually rises again in the North Atlantic, where it influences the climate of the northern hemisphere. As well as being factories producing large amounts of sea-ice and cold salty water, polynyas also serve as refuges for wildlife. Ironically, the early explorers sought out the open waters of the polynyas, because they enabled them to approach close to the coast, little realising that they had thereby chosen areas with the most frequent blizzards. The Australian scientist Douglas Mawson was one of the first to appreciate the true fury of the katabatic wind, when he wintered over at Cape Denison in 1912. He vividly recorded his experience in his book The Home of the Blizzard: "The climate proved to be little more than one continuous blizzard the year round; a hurricane of wind roaring for weeks together, pausing for breath only at odd hours." Even during the pauses, it turned out that the wind had only lifted above the surface where it continued to roar along, spawning occasional whirlwinds which wandered over the landscape wreaking their own havoc on whatever they touched. Because it was so cold, the snow crystals in one storm were so light that it was possible to walk through the fallen snow even though it was over a metre deep. So much air was trapped in the snow that the huskies could breathe in it. They soon gave up the effort of leaping to the surface, like dolphins, when they moved around, and just ploughed through it, their progress indicated by a wave moving along the snow surface. The cold of Antarctica poses considerable problems for the plants and animals that live there—problems they have solved in a variety of ways. The fish have antifreeze to prevent ice crystals forming in their blood in the sub-zero water temperatures. Warm-blooded animals, such as seals and penguins, have thick layers of insulation to keep out the cold, and tend to have large bodies, as this maximises heat production while minimising heat loss. Emperor penguins are so large that they must breed in deep winter, incubating the eggs on top of their feet, in order for their chicks to grow enough during the summer to be able to survive the next winter. Food is harder to come by on land, so the animals that spend all their time there are a good deal smaller. The largest is a tiny insect, the Antarctic springtail, which is about one millimetre long, and is full of polyalcohols, which enable it to survive cooling to –30°C. There is one tiny plant that keeps out of the wind by growing inside rocks, but only a few millimetres under the surface, so as to still get enough sunlight for photosynthesis. So what does this strange world—so different from New Zealand—have to do with our weather? The answer is: "Plenty!" The general circulation of the atmosphere over the whole Earth works like a heat engine. The warm land and ocean surfaces in the tropics provide heat to the atmosphere, which it carries towards the poles. There it is transferred to the rocks and ice, which radiate it away to space. Because of the Earth's rotation, the air currents moving heat poleward are deflected from a north-south direction to become westerlies in the latitudes where New Zealand lies, giving us a climate that is not too hot and not too cold. Also, the Antarctic continent is not symmetrical about the pole, but juts out on one side, with its highest point some 10 degrees of latitude away from the pole. This bulge induces a large-scale wave pattern into the westerlies, which, as it waxes and wanes, promotes the development and decay of lows and highs near New Zealand. And, of course, the Antarctic is the source of cold air for some of our best southerly outbreaks, bringing joy to skiers in winter.
Len Castle has shaped clay for 52 years, making pottery which reflects his deep fascination for the New Zealand landscape. He has travelled widely, camera in hand, seeking nature's most dramatic expressions. But of all the landscapes that inspire him, it is the volcanic zones that exert the strongest pull.
Mark Scott discovers the attractions of sheepdog trails and jam-making.
Ever since his best friend died from cancer, Rex Innis of Hikutaia has let the Cancer Society pick daffodils from his plot to sell for its annual appeal each spring. Sooner or later, cancer invades most of our lives-unbidden, unwelcome and heavy with menace, the body in mutiny against itself, Regardless of whether the disease strikes us or someone we love, life will never be the same.
What an improbable animal is the seahorse! With a horse's head, a possum's tail, eyes like tiny glass fishbowls and fins that wave like chiffon frills, the shy creatures have intrigued and delighted us since ancient times. But these thoroughbreds of the sea are now in danger of their lives. Ground up for medicines, sold, sightless and stiff, as souvenirs, captured alive for home aquariums, seahorses in many parts of the world have a hard ride ahead of them. A combination of public awareness and aquacultural research-some of it being conducted in this country-may yet turn the tide for these fascinating animals.
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