Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries
The dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.
Purchasing an oven is not a straightforward process. It’s rather like buying a house, or a car – you need to have a look at quite a few, always want to buy ones that are more expensive than you can afford and, once you’ve made your purchase, you hope you won’t need to do it again for a long time.An oven is a real investment for a bakery business but, with the cost of energy rising, not to mention the impetus for businesses to become more ’green’, a wood-burning oven could become an increasingly popular option, not just on environmental but also money-saving grounds.Manufacturer The Bread Roll Bakery, based in Darwen, Blackburn, had the UK’s first wood-burning rack oven installed just before Christmas and is to have another installed imminently. Bakewell Ovens supplied the oven, which runs on wood pellets. These are made from natural woodchips and held together by the wood’s natural lignin, released during the pellitising process due to heat and compression, making them 100% natural.The oven itself is described as a “sustainable and ethical alternative”, and can also save bakers a huge amount in running costs. Alexander Fleck, managing director of The Bread Roll Bakery, explains that he had been within hours of signing for some gas ovens, when someone approached him with information about wood pellet ovens and he had a sudden change of heart. “The price of the ovens was about the same, but in terms of the cost of running them, you save around 60% on your fuel costs with the wood pellet version. I even spoke to one baker who had saved 70%.”Fleck says it produces a mellower and more even bake and only requires a few extra minutes maintenance per week. “It does produce ash, but this is minimal and can be used as a fertiliser for your garden,” he says.The oven is thermostatically controlled, so when it’s up to temperature, it stops feeding the pellets. There is also the flexibility to change it to a gas burner in half an hour if you run out of wood pellets.Buying an energy-efficient oven is not necessarily more expensive, and even if the outlay is greater, the money saved in energy costing means the payback period is relatively short and, from then on, you are saving money. Oven supplier Interbake suggests that the annual bill for an equivalent oven using electricity is around £20,500, whereas with a pellet oven it’s more like £7,600. However, Interbake MD David Dunne points out that the drop in the value of Sterling has had an impact on the take-up of the energy-efficient ovens it supplies. “In the last six months, the cost of the ovens has increased by 25%, due to the devaluation of the currency against the euro.”Interbake currently acts as agent for Italian manufacturer Trezza Forni, distributing its Steam Tube Deck Oven, which also uses a wood-pellet burner. “The whole concept with this type of oven is that it’s a very mellow bake and the burner heats refractory material, more or less like brickwork inside a furnace, and the furnace heats steam tubes that run throughout the baking chambers,” says Dunne.However, as the ovens are Italian, they are priced in euros and, due to the volatile currency fluctuations of late, Dunne says that, in one instance, it actually cost them money to sell one of these ovens. The company sold the machine for £56k, but, as it was manufactured abroad and had a 12-week delivery time, by the time the transaction went through, the currency fluctuations meant it actually cost Interbake money to sell it. The firm has now added a clause to orders, which states the quote in the currency it will be purchased in, based on the current exchange rate.In terms of financing new ovens, there are several opportunities for bakers. Fleck managed to secure a grant from his local council on the premise that the new oven would increase efficiency, up production and, within two years, enable the company to take on extra staff. The Carbon Trust also provided him with an interest-free loan to cover the rest. (The Carbon Trust offers interest-free loans to businesses trying to do their bit – up to £200,000 over a four-year period, but bakers need to approach them before they purchase their new bit of kit.)Wood-pellet ovens are not the only variety that can save bakers money on energy bills, however. Hamburg-based manufacturer Daub, handled by Benier in the UK, offers Thermal Roll ovens, which are currently used at bakery retailer Birds of Derby. The bakery houses four of these ovens – two specifically for rolls and small breads and two for large breads, including bloomers.The ovens, which take three racks each, use the Daub Thermal Oil heating system, whereby the oil is heated in a unit outside the oven and is then distributed through a series of radiator plates above and below each shelf in a rack oven.”The racks slide in around the radiators to give radiant baking to the products. So they can be used to bake products normally baked in deck ovens, as well as those products baked in conventional rotating rack ovens,” says Benier managing director David Marsh.Temperatures do not drop significantly when the oven is emptied or loaded and the oil has a heat capacity 2,600 times higher than hot air, reducing baking time and, in turn, energy costs by up to 25%.As Dunne says, there is a definite market for energy-efficient ovens, but the follow-through from interest to purchase has something of a drag factor, only exacerbated by the current financial climate.—-=== Case study: BIA winners go energy-efficient ===Those businesses that are building on their good fortunes by expanding their operations are putting energy-efficiency top of their wish lists. Jacksons the Bakers, last year’s winner of the BIA Quality Product Award, sponsored by Tesco, has opened a brand new facility in Chesterfield, and kitted it out with Mondial Forni ovens, featuring DOE energy-saving technology. It uses them to bake everything from morning goods and confectionery to its award-winning Traditional Steak Pie.Explained simply, Jacksons’ 32-tray oven contains 25 elements in each deck. Energy is flashed to each of the elements in a staggered fashion, so they are effectively off for up to 33% of the baking time, while offering the same bake heat. This figure can be adjusted downwards to say 20-25% if you are baking large tinned bread, which requires a bit more oomph; alternatively, you would simply raise your baking temperature to compensate, from 240?C to 260?C, and leave the oven configured to the 33% energy-saving setting.The first decision was whether to opt for gas or electric, says David Charlesworth of UK agent Norbake. “We compared the kilowatt rating of the DOE system fitted to the same oven fuelled by gas or electricity, and looked at the cost of gas against electric. We found there was still a 30% saving with the gas ovens and we decided to go with that.”If you opted for smaller ovens, such as 12-tray capacity, they could be set to a maximum of 25% energy saving. The Mondial Forni Ovens also have segmented glass doors, to cut down on heat-loss when opening, compared to a solid door.