South Georgia and the South Sandwich Islands, a UK Overseas Territory, is not normally the center of news. But then, it's not every day a 3,900 square kilometer iceberg weighing hundreds of billions of metric tons bears down on you, threatening to upset the ecological applecart.
Gliding across the Scotia Sea, iceberg A68a calved from the Larsen C Ice Shelf in Antarctica in 2017, but only entered open waters this year. Only 200 meters (656 feet) deep, it is relatively thin for a tabular iceberg of its size, say scientists. That increases the likelihood of fragmentation, but also means it's liable to clear the 300-meter (984-feet) deep continental shelf around 100 kilometers (62 miles) south of the island, allowing it to move closer to land.
Reconnaissance flights show evidence of the edges breaking up and tunnels forming in the iceberg, but researchers at the British Antarctic Survey (BAS) have noted their surprise it has stayed intact for as long as it has. Should it arrive at the island, where the iceberg grounds and in what form could have a big impact on South Georgia's penguins. Surprisingly, not all outcomes are bad.
Hypotheticals abound and the permutations are many -- precisely why scientists are so keen to observe what happens next, even if they are powerless to intervene in a worst-case scenario.
"There's no way we can deflect or blow up the iceberg," says Norman Ratcliffe, a seabird ecologist at the BAS. "It's not going to be like 'Deep Impact or 'Armageddon.' We're taking more of a 'Star Trek'-type primary directive -- we're interested in studying what the effects are."
An island made for penguins
The island's diverse ecosystem is home to albatrosses and millions of Antarctic fur seals, nearly half the world's king penguins and gentoo penguins, and around a quarter of the world's macaroni penguins. The king penguin population attracts particular attention, having grown from "the hundreds" to "at least a million" in the past century, with the colony at St Andrew's Bay now the largest in the world, says Mark Belchier, director of fisheries and environment at the government of South Georgia and the South Sandwich Islands.
Gentoos and macaronis forage for krill close to the shore and the continental shelf respectively, while king penguins eat lanternfish and swim hundreds of kilometers on foraging trips that can last 16 days during early chick rearing, Ratcliffe explains. It is laying season, he adds, raising the prospect the iceberg could arrive in a period when parents are conducting these lengthy journeys.
Although mostly amassed on the shallower north side of the island, South Georgia's penguins could soon be confronting the iceberg.
"We think it's likely that A68a will go around the southeastern end of the island's shelf before being taken along the northern side," says Sally Thorpe, an ecosystem modeler at the BAS. As of December 9, the iceberg was approximately 50 kilometers from the nearest area of continental shelf with a depth of 200 meters, according to Thorpe. Comparing A68a's position to historical iceberg data, all but one had moved onto the South Georgia shelf (some of which had grounded) or followed current flows around the edge of the shelf in an anticlockwise direction.
In 2004 a "mega-berg" called A38b lingered off the northeast coast for an extended period. But scientific data gathering at the time "was not so robust" and "it's not clear what happened to the penguins and wildlife there," says Pablo Garcia Borboroglu, founder and president of the Global Penguin Society.
This time things will be different. BAS researchers plan to operate unmanned drones to conduct aerial censuses of colonies and will attach 20-gram (0.7-ounce) GPS devices to the back feathers of king penguins and macaroni penguins, recording each bird's location every 15 minutes.
"These tags also record how deep they're diving," explains Ratcliffe, "so we'll be able to get these three-dimensional trips. We have tracking from the same sites in previous years, so we'll be able to do a before and after comparison of what happened when the 'berg arrived."
The main concern scientists have is that the iceberg could become stranded and remain intact close to colonies for a prolonged period of time.
"Not only could foraging routes of predators and the seafloor community be affected by the presence of the iceberg, there will be also be effects from the iceberg affecting local ocean circulation ... from the amount of cooler, fresh water entering the ocean as the iceberg continues to melt," says Thorpe.
Opinions vary on how the iceberg could disturb different penguin species.
"I imagine it will be bad for kings if it blocks their path to (food) rich waters offshore," says Ratcliffe. The most likely scenario is they would continue to rear their chicks, but if the food supply slowed and chicks starved, adults would then leave the colony and head far out to sea. "It is also possible that adults would abandon live chicks if their own survival was in jeopardy," Ratcliffe adds.
Belchier believes kings are unlikely to be impacted as much as other species, however he agrees with Ratcliffe that possible changes in current flow around the island could deflect krill from the penguins' usual foraging grounds. For macaronis and gentoos, that "might have an impact on ... their ability to feed their chicks regularly, so you could have problems with chick survivorship."
However, these are far from the only outcomes. The iceberg could still change path or break up significantly. It could even have a positive impact.
The iceberg is loaded with atmospheric dust and deposits from historical volcanic eruptions accumulated over thousands of years, and if it melts rapidly it could release a "pulse of nutrients" into the water, says Belchier, boosting the local ecosystem's food supply, potentially rising through the food chain to penguins. If the iceberg runs aground on the continental shelf, its disturbance of the seabed could release nutrients too.
Even in the event of a worst-case scenario and a complete breeding failure, penguins' relatively long lifespan offers plenty of opportunities to reproduce. A population decline of 5% to 10% could result from a year of breeding failure, but it would only be felt five to six years after the event -- and it is not a certainty, as less competition for resources in subsequent years could aid rearing and absorb some losses, says Ratcliffe.
Conditions would have to be "absolutely catastrophic" for penguins not to bounce back in future years, Belchier says.
Anticipating change
Not that it means researchers should be paying any less attention. The iceberg is a colossal bellwether ringing around Antarctic and sub-Antarctic territories. The Larsen Ice Shelf from which A68a broke off has degraded for decades, while key ice shelves holding back the Pine Island and Thwaites glaciers are sustaining rapid damage. Significant global sea level rise could result from their collapse.
A changing climate is already impacting penguins throughout the southern hemisphere, as their habitats alter and food stocks shift around the ocean. Globally, a nimble approach to oceasn conservation will be required in the future, suggests Borboroglu, an expert on establishing marine protected areas through his work at the Global Penguin Society.
"There is evidence oceanographic patterns are changing, so the concept of marine protected areas should adapt into a more dynamic concept in which you have to predict where the resources are going to be," he says.
"We've seen, even in penguins, changes in distribution," Borboroglu adds. "You are trying to protect something that is no longer there -- or maybe it's there now, but it won't be in 10 years. We need to adapt quickly to these changes."
In the meantime, millions of seabirds are sitting tight, as well as the international coalition of scientists watching what happens next. For all their knowledge, still no one knows exactly where this hulking piece of ice will end up.
"It's completely the luck of the draw," says Belchier.
"course" - Google News
December 11, 2020 at 06:34PM
https://ift.tt/3qIinLD
Is an iceberg weighing hundreds of billions of tons on a penguin collision course? - CNN
"course" - Google News
https://ift.tt/35q9ps5
https://ift.tt/35rCFi1
Bagikan Berita Ini
0 Response to "Is an iceberg weighing hundreds of billions of tons on a penguin collision course? - CNN"
Post a Comment