Antarctica's Pine Island Glacier sensitive to climatic variability

A new study published in Science this month suggests the thinning of Pine Island Glacier in West Antarctica is much more susceptible to climatic and ocean variability than at first thought. Observations by a team of scientists at British Antarctic Survey, and other institutions, show large fluctuations in the ocean heat in Pine Island Bay. The team discovered that oceanic melting of the ice shelf into which the glacier flows decreased by 50 per cent between 2010 and 2012, and this may have been due to a La Nin? weather event.

Pine Island Glacier has thinned continuously during past decades driven by an acceleration in its flow. The acceleration is thought to be caused by thinning of the floating ice shelf created as the glacier slides into the sea. Understanding the processes driving ice shelf thinning and the glacier's response is key to assessing how much it will contribute to rising sea levels.

It's now known that much of the thinning is due to a deep oceanic inflow of Circumpolar Deep Water (CDW) on the continental shelf neighbouring the glacier. This warmer water then makes its way into a cavity beneath the ice shelf melting it from below.

The passage of this warmer water was made easier by the unpinning of the ice shelf from an underwater ridge. The ridge had, in effect, acted as a wall preventing warmer water from getting to the thickest part of the shelf. This ungrounding event was one of the major driving forces behind the glacier's rapid change.

In 2009, a higher CDW volume and temperature in Pine Island Bay contributed to an increase in ice shelf melting compared to the last time measurements were taken in 1994. But observations made in January 2012, and reported now in Science, show that ocean melting of the glacier was the lowest ever recorded. The top of the thermocline (the layer separating cold surface water and warm deep waters) was found to be about 250 metres deeper compared with any other year for which measurements exist.

This lowered thermocline reduces the amount of heat flowing over the ridge. High resolution simulations of the ocean circulation in the ice shelf cavity demonstrate that the ridge blocks the deepest ocean waters from reaching the thickest ice. So its presence enhances the ice shelf's sensitivity to climate variability since any changes in the thermocline can alter the amount of heat filtering through.

The fluctuations in temperature recorded by the team may be explained by particular climatic conditions. In January 2012 the dramatic cooling of the ocean around the glacier is believed to be due to an increase in easterly winds caused by a strong La Nin? event in the tropical Pacific Ocean. Normally the winds flow from the west.

The observations suggest there is a complex interplay between geological, oceanographic and climatic processes. The study stresses the importance of both local geology and climate variability in ocean melting in this region.

Lead author, Dr Pierre Dutrieux, from British Antarctic Survey (BAS) said: "We found ocean melting of the glacier was the lowest ever recorded, and less than half of that observed in 2010. This enormous, and unexpected, variability contradicts the widespread view that a simple and steady ocean warming in the region is eroding the West Antarctic Ice Sheet. These results demonstrate that the sea-level contribution of the ice sheet is influenced by climatic variability over a wide range of time scales."

Co-author, Professor Adrian Jenkins, also from BAS, added: "It is not so much the ocean variability, which is modest by comparison with many parts of the ocean, but the extreme sensitivity of the ice shelf to such modest changes in ocean properties that took us by surprise. That sensitivity is a result of a submarine ridge beneath the ice shelf that was only discovered in 2009 when an Autonomous Underwater Vehicle mapped the seabed beneath the ice. These new insights suggest that the recent history of ice shelf melting and thinning has been much more variable than hitherto suspected and susceptible to climate variability driven from the tropics."

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Bermuda on alert as storm likely to skirt island

HAMILTON, Bermuda (AP) – People in Bermuda braced Friday for a weekend of rough weather from Tropical Storm Leslie as forecasters said the system would likely regain strength and become a hurricane again while passing to the east of this Atlantic Ocean island.

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A satellite image shows Hurricane Leslie churning in the Atlantic Ocean near Bermuda on Wednesday. Leslie is projected to pass over or near Bermuda on Sunday.

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A satellite image shows Hurricane Leslie churning in the Atlantic Ocean near Bermuda on Wednesday. Leslie is projected to pass over or near Bermuda on Sunday.

The Bermuda Weather Service said the storm was on track to pass about 200 miles (321 kilometers) east-southeast of the island late Sunday afternoon as a Category 1 hurricane.

"It appears that Bermuda will be spared a direct impact," said Wayne Perinchief, the national security minister for the British territory. "However, I urge the public to remain cautious as there is the potential for the storm to re-intensify and change track, and we could experience heavy rain and winds in shower bands."

Some businesses were closing early and people crowded into shops to stock up on emergency supplies. At least one cruise ship canceled a stop in Bermuda and the airport was expected to close.

There was no widespread panic because the island, a wealthy offshore financial haven and tourist destination, has strong building codes and is accustomed to storms.

The U.S. National Hurricane Center in Miami said Leslie resumed forward movement Friday after staying stationary overnight. Late Friday, the storm had top sustained winds of 65 mph (100 kph), below the hurricane threshold of 74 mph (120 kph).

The storm was about 360 miles (575 kilometers) south-southeast of Bermuda and was moving north at 3 mph (6 kph). The U.S. center said it would likely strengthen Saturday and Sunday, adding that Leslie also was expected to begin gradually increasing its forward speed.

Out in the middle of the Atlantic, Hurricane Michael was a category 2 storm with maximum sustained winds of 100 mph (160 kph). On Thursday, it was briefly the first Category 3 of the Atlantic hurricane season.

Michael was moving northwest at 6 mph (9 kph) over the open ocean and was not a threat to land. It was about 940 miles (1,515 kilometers) west-southwest of the Azores.

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Irene flooding left Vt. home on unexpected island (AP)

BETHEL, Vt. – June Tierney and Kellie Burke never envisioned island living in the Vermont woods, but Tropical Storm Irene had other ideas.

Their home, a two-story, natural-sided saltbox, was a rural idyll on a wooded 10-acre lot off a dirt road, with a stairway leading from their backyard down a steep bank to Gilead Brook, a small stream.

When Irene blew through Vermont on Aug. 28, the brook became a raging torrent. After the storm, the main part of it had moved around to the other side of the house, leaving a smaller stream still flowing along its old bed.

Now Tierney, a 47-year-old lawyer who works for the state board that regulates utilities, and Burke, 48-year-old high school librarian, have to cross a ford — a new, narrow road that dips into the old stream and has no guardrails — to get home, and face an uncertain future. They wonder if they should cut their losses and move.

Their biggest worry is whether the next time the river runs wild, it will take the house with it.

"If we stay we're facing a huge expense to try to secure the property," Tierney said. And there's no long-term guarantee it will succeed. She quoted one stream-flow expert the couple consulted: "That river really wants your land."

The months since the storm have been a whirl of talks with their homeowners' and flood insurance companies, getting the ford built across the old stream bed, pricing what a real bridge would cost ($164,000), applying for assistance from the Federal Emergency Management Agency and accepting with gratitude an outpouring of help from neighbors and friends.

"People have been so helpful. It's been an inspiration," Burke said.

For a time, Tierney and Burke worried that their status as a lesbian couple married under Vermont law might cause a snag in getting assistance from a federal government that doesn't recognize such marriages. So far, they've had no problems.

When the brook swirled around the house, it undermined a barn, which had to be demolished. It turned what had been their wooded property into a wasteland of felled trees, root balls, boulders and silt. And it left a line of debris that came to within a few feet of the front porch.

The homeowners' insurance paid $20,000 on the barn. Flood insurance wasn't available because there was no damage to the house, Tierney said. They got the maximum emergency grant from FEMA — $30,200, half of which paid the cost of the ford — essentially a low-lying causeway across the old stream with culverts carrying water underneath — and to study the feasibility of building a new bridge.

Now the question is whether the couple will be eligible for grant money under a federally backed program that pays property owners living in the most flood-prone areas to abandon their homes and move.

They've been relying on their professional skills to work their way through the crisis.

Burke, the librarian, researched the program, while Tierney put her legal skills to researching the arcane federal regulations governing eligibility for the grants. Officials initially told her and Burke that they would get no help because their home was not harmed.

Tierney wrote in a long email to state and federal officials — she calls it her brief — that the category of eligible properties extends to one like hers that are at risk of future flooding because of how the storm changed the topography of the surrounding land.

Even if she and Burke lose in these arguments, she wants that to have been a just result, Tierney said. "When economic disaster follows natural disaster, we at least have to know it's because of the shortcomings of the program, and not because it's been misconstrued."

Tierney and Burke say it's very likely they'll have to leave the home they've shared for 13 of their 25 years together, but don't want to sell it, because that would just leave someone else facing the same risks.

"This is a potentially lethal setting," Tierney said. "It's not fit for human habitation."

Burke called the need to move "very sad." Since the flood, "it's not been easy to live here, but it's our home."

Tierney noted that like the town of Bethel, Gilead Brook takes its name from the Bible, where it's not a stream, but a mountain of testimony, of witness. Living in a home that now appears to have been built in the wrong place, she said, "We've literally been bearing witness to what it means to try to reconcile nature's intentions with those of human beings."

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