pingos and pockmarks
mid-September, while Monterey Bay basked in late summer beach weather,
MBARI geologist Charlie Paull stood shivering at the base of a low hill,
several hundred miles north of the Arctic Circle and about a dozen miles
had just arrived and had already endured a ten-mile journey
across frigid Arctic waters in a small open boat. He later learned that
a woman had been mauled by a grizzly bear in this remote spot only a few
weeks before his arrival. But Paull was
not thinking about the cold or the bears. He was excited to see, rising
before him, one of the enigmatic geological features that had brought him to
the Arctic: a pingo.
A pingo rises from the Arctic plain
in far northern Canada.
Charlie Paull © 2003 MBARI
climbed slowly up the side of the pingo. Reaching the top, he paused at the edge of a small pond and
gazed out at the barren coastal plain, where a thin coat of moss and tundra
barely hid the solid permafrost beneath. The pingo on which he stood was
the highest point around, except, off in the distance, the low rounded
silhouette of another pingo. He had read that over a thousand of them
dotted this remote peninsula. His gaze shifted to the small pond at his
feet. Looking closely, he discovered small bubbles rising through
the water. He smiled.
thought about permafrost and ice and the current theory of how pingos
form. In most parts of the Arctic, permafrost (a layer of permanently
frozen soil) extends hundreds of meters below the earth's surface.
However, beneath Arctic lakes, the permafrost melts, leaving a region of
water-saturated soil. According to theory, a pingo is created when one
of these lakes dries up, allowing permafrost to reform at the ground
surface, trapping water underneath. As
the surface permafrost thickens, it puts pressure on the subsurface water,
which creates a bulge in the overlying permafrost—a pingo.
had his doubts about the standard theory, which focused on the fact
that pingos—or at least "pingo-like-features"—were known to exist on the
sea bottom (where lakes are rather rare). Some researchers contended that these submarine pingos had
formed on land during periods of lower sea level. However, Paull thought
this unlikely because waves and ice would have quickly eroded and
destroyed the pingos as the ocean rose around them.
suspected that the submarine pingos had formed beneath the sea, and that they
might still be forming. This was why he had come to the Arctic. About five
years before, he and fellow geologist Bill Ussler had written a National
Science Foundation (NSF) grant proposal to investigate methane
hydrates in sea-bottom sediments and their relationship to submarine
pingos. The NSF had turned down his proposal with the comment that submarine
hydrate research was not a research topic they were interested in funding.
the next few years, however, funding agencies became vitally interested in
Arctic processes, global warming, and gas in sea-bottom sediments.
Scientists learned that huge volumes of methane were locked up in oceanic
sediments, mixed with frozen water to form methane hydrates. Some even
suggested that these hydrates could have triggered extreme shifts in the
Earth's climate by suddenly releasing vast amounts of methane (a greenhouse gas) into the atmosphere.
undersea methane becoming a hot topic, Paull and Ussler decided to resubmit
their proposal. As Paull put it, they simply asked the question,
"Why don't we go and see
what it takes to get gas released from methane hydrates today?" They pointed out that the Arctic Ocean was a logical place to
such releases because hydrates in this area had been slowly warming since
the end of the last ice age, more than 10,000 years ago.
also suggested that, rather than searching the entire Arctic ocean for
dissolved gas, scientists should look for geological features that might
indicate where gas was emerging from the sediment. Submarine pingos were
one such feature. Similarly, gas might also be found around submarine pockmark fields, where the sea
bottom is scarred by hundreds of meter-deep pits in the sea floor.
time, their proposal was enthusiastically accepted. This was why Charlie Paull was
standing on a low hill, watching bubbles emerge from a shallow pond, and
A curious polar bear comes to visit
the research vessel.
This photo was not taken with a telephoto lens.
Charlie Paull © 2003 MBARI
days later, he set out in the Canadian Coast Guard vessel Nahidik, with
a goal of obtaining cross-sections through several submarine pingos using
seismic profiling—bouncing sound waves off sediment layers in the sea
bed. But these efforts were thwarted by the vagaries of drifting ice and
the very real risk of marauding polar bears climbing on board the
low-sided survey vessel. Thus, Paull had to rely on decade-old surveys as
he began the second part of his research, which focused on
obtaining sediment cores in and around submarine pingos.
before he could begin his second cruise, aboard the Canadian
icebreaker Sir Wilfred Laurier, the
challenges of the Arctic became apparent once again. Thick fog
prevented him from flying to meet the icebreaker in time for its
departure. After four days of what he called "a mild form of
purgatory," the icebreaker came to him, or at least within 200 miles
of where he was stranded, so
that the ship's helicopter could pick him up.
board the icebreaker, Paull met
Ussler, fellow MBARI researchers Rendy Keaten and Richard Whitmarsh, and
scientists from Canada and the United States
Geological Survey. Although the MBARI scientists were all new to Arctic
research, the Canadians were old hands who, according to Paull, had
"hung out together in the Beaufort Sea for years."
research in the Arctic means shoveling snow
off the deck of the research vessel... even in September!
© 2003 MBARI
spent the next three weeks dodging pack ice and shallow water while
collecting about eighty sediment cores in and around half a dozen
submarine pingos and two pockmark fields. This was their primary
mission—to take samples of mud and ice and to analyze the water and gas
within these samples. Specifically, they wanted to find out if gas was
trapped in the sediment, and if so, determine what kind of gas it was and where it was coming from.
their surprise and delight, the researchers found plenty of gas in cores
from the submarine pingos. They also used a small remotely operated
vehicle (ROV) to record video of gas bubbling out of the tops of two
submarine pingos. Encouraged by this finding, Ussler decided to try and
obtain a sample of this gas. Improvising with some decidedly low-tech
tools, including an old funnel and a large plastic syringe, he succeeded in converting the small ROV into a submarine
gas-collection system. He also used a small boat, a plastic bucket, and
his bare hands to collect gas bubbling to the sea surface—no mean feat in
frigid Arctic water.
results from the geochemical analyses are intriguing. For example, the gas
emerging from the submarine pingos appears to be nearly pure methane. This suggests that
it did not originate from a natural gas reservoir that lies deep
below the sea floor in this area. In
addition, water in the submarine pingo cores is only half as salty as water in
the surrounding sediments, suggesting that it came from buried freshwater ice
rather than from the overlying seawater.
is quick to point out that none of these early data conclusively proves that the gas and
fresh water in the pingos originated in methane hydrates. However,
the circumstantial evidence is very suggestive. His team is currently
analyzing oxygen isotopes in water from the cores, which will be compared
with oxygen isotope ratios in local seawater and groundwater.
his data still coming in and numerous cores to analyze, Paull and
his coworkers are not yet ready to advance their own theory of how pingos
form. But they are convinced that pingos and pockmarks are active features
that relate to gasses and/or liquids flowing up from the subsurface.
any luck, their research will supply another piece in the scientific
puzzle of past and present climate change. Not only that, Paull's team
will be able to provide a new perspective on a geologic feature that has
baffled geologists for generations. Not a bad result for a month's work—and half a
decade of preparation. Several months after his trip to the Arctic,
Charlie Paull is still smiling...
MBARI geologist Charlie Paull
and the Canadian icebreaker Sir Wilfred
© 2003 MBARI