Archive for the ‘About’ Category

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Polar firn aquifers: Why are we doing this?

November 16, 2018

Often when people envision Greenland and Antarctica, they see desolate, snow-filled lands; and in general, that is pretty accurate. Other than a few coastal towns and seasonal base camps, these lands are uninhabited, except for a few tough species of animals. And, of course, there is lots of snow. As snowfall settles, it compacts under the weight of new snow and the battering ram of the wind. This compacted older snow, at least one winter old, is called firn—still porous, but between fresh snow and glacial ice in density.

Where we are going to in Antarctica the firn has a special feature. These regions are known for very warm summer conditions, with lots of melting and lots of snowfall over the course of the year. The summer melt can percolate through the snow and firn grains to form a water-saturated layer that sits above the denser glacier ice. Like a well in sandstone, this is a kind of aquifer in the firn, almost like a natural snow cone. Without the syrup.

Firn aquifers have been observed on a few mountain glaciers, usually for just part of the year, but never on ice sheets until a discovery on the Greenland Ice Sheet in April of 2011. Since then, NASA Operation Ice Bridge data has mapped their extent over several regions of Greenland. In some parts of Greenland, they appear to persist for decades.

More recently, a mapping algorithm using satellite data correctly located the firn aquifers in Greenland. We applied the same method to Antarctica—and there they were, a signal in the data just like Greenland’s aquifer areas. Antarctica’s potential for firn aquifers is at present unconfirmed, yet application of a similar technique indicates that they likely exist in coastal and ice shelf regions that have climate conditions similar to firn aquifer areas in Greenland. That is what we are going to check out.

Firn aquifers are important because they could cause a kind of water-driven fracturing on ice sheets or ice shelves called hydrofracture, where water seeps into cracks in the ice and breaks them open, leading to a speed-up of a glacier or crumbling of an ice shelf. This kind of fracturing has led to some spectacular break-ups in Antarctica, or significant acceleration of glaciers in Greenland.

The objective of the Antarctic Firn Aquifer expedition is to verify the presence of firn aquifers on the Antarctic Ice Sheet by surveying two key sites on the Antarctic Peninsula: the Wilkins Ice Shelf and the southern George VI Ice Shelf. These field sites were identified using our mapping method and data from two satellite microwave instruments: a C-band radar scatterometer (EUMETSAT’s Advanced SCATterometer – ASCAT) and an L-band microwave radiometer (aboard NASA’s Soil Moisture Active Passive Satellite–SMAP). The longer wavelength of ASCAT and SMAP microwaves, and their sensitivity to the presence of liquid meltwater, allow them to see firn aquifers on ice sheets or ice shelves as deep as ~60 meters (200 feet). Over time, distinct patterns in the microwave signals can be used to distinguish firn aquifers from areas that do not store meltwater at depth.

 

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Introduction

January 1, 2016

For the past six Antarctic field seasons that usually run from November through February, Ted Scambos and colleagues have been posting updates about their expedition to the Larsen Ice Shelf region, as part of the National Science Foundation (NSF)-funded Larsen Ice Shelf System Antractica (LARISSA) project. LARISSA’s goal is to understand the causes and consequences of a rapidly changing part of Antarctica, from climate to ice to ocean and the seabed below, and then to the ecosystem evolving and adapting to the change.

This season, we return to the Antarctic Peninsula where a large plate of ice is on the brink of collapse, and test a new instrument on a frozen Colorado lake. The instrument (an ‘AMIGOS-II’, upgraded from the devices already operating in Antarctica) is designed to make combined measurements of weather, ice conditions, and ocean currents and temperature from atop an ice shelf or sea ice. The Antarctic field work is first, and then we’ll shift over to track the instrument expedition in February.

About the expedition

Who are we?

Where are we going?

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Antarctica for one, please.

November 2, 2011

Ted writes:

I’m beginning to feel like some kind of migrating bird. For the past three years, like clockwork, as the calendar passes Halloween and heads into the leafless days of November, I find myself boarding planes and flying south. Once again, I’m at South America’s jumping off point for Antarctica, Punta Arenas, Chile. Usually I have someone from our team with me, like the redoubtable Terry Haran, or the indomitable Rob Bauer, or the highly toutable Jenn Bohlander, but this year it’s just me. Me, and some top-drawer assistants at the British Antarctic Survey base, Rothera (I have yet to meet them).

I’ve heard Punta’s climate described as windy sunshine, and it’s a description that sticks. I’ve been here 4 or 5 of the calendar months, and the only question one seems to ask about the weather is, “How windy is it now?”  The answer ranges from “Kinda,” to “Holy vacuum cleaner, Batman!” A bad hair day here means actually having your hair blown off. There is an occasional spritz of stinging rain, but for the most part it is intense sunshine, scudding low clouds, haggard-looking llamas and, well, wind.

The goal this year for the LARISSA Glaciology project is to repair and upgrade two of the installed measurement stations (a GPS station on a rocky cape, and our AMIGOS compadres sitting on the Scar Inlet shelf, a remnant we suspect will someday disintegrate like the Larsen B Ice Shelf did nearly ten years ago. We don’t plan to visit the other AMIGOS, on Flask Glacier, although it now sits up to its mechanical neck in snow. (Later, we will return for it, too.) The most important part of this year’s visit is to install a new system, with a much better camera, on a cliff overlooking the Scar Inlet shelf. The camera will provide a series of images showing how the ice front and surface change during a summer, and hopefully some details of the processes during a break-up. All the gear is already waiting down in Rothera.  If we can manage this installation, it could be a fantastic record of one of the big open questions in glaciology: how does an ice shelf disintegrate? But we have to get it set up out there first. I suppose I should mention the name of the cliff is Cape Disappointment. Not a good omen. Stay tuned.

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