Details about the physical transformation of over 200 of the island’s coastal glaciers are documented in a new study, in which the authors anticipate environmental impacts.
A new
study of Greenland’s shrinking ice sheet reveals that many of the island’s glaciers
are not only retreating, but are also undergoing other physical changes.
Some of those changes are causing the rerouting of freshwater rivers beneath
the glaciers, where it meets the bedrock. These rivers carry nutrients into the
ocean, so this reconfiguring has the potential to impact the local
ecology as well as the human communities that depend on it.
“The coastal environment in Greenland is
undergoing a major transformation,” said Alex Gardner, a research
scientist at NASA’s Jet Propulsion Laboratory and co-author of the study. “We are already seeing new sections of the ocean and fjords
opening up as the ice sheet retreats, and now we have evidence of changes to
these freshwater flows. So losing ice is not just about changing sea level, it’s
also about reshaping Greenland’s coastline and altering the coastal ecology.”
About
80% of Greenland is blanketed by an ice sheet, also known as a continental
glacier, that reaches a thickness of up to 2.1 miles (3.4 kilometers). Multiple
studies have shown that the melting ice sheet is losing mass at an accelerating
rate due to rising atmosphere and ocean temperatures, and that the additional meltwater
is flowing into the sea.
This
study, published on Oct. 27 in the Journal of Geophysical
Research: Earth’s Surface, provides a detailed look at physical changes to 225
of Greenland’s ocean-terminating glaciers, which are narrow fingers of ice that
flow from the ice sheet interior out into the ocean. The data used in the paper
was compiled as part of a project based at JPL called Inter-mission Time Series of Land
Ice Velocity and Elevation, or ITS_LIVE,
which brings together observations of glaciers around the globe – collected by
multiple satellites between 1985 and 2015 – into a single dataset open to
scientists and the public. The satellites are all part of the Landsat program,
which has sent a total of seven spacecraft into orbit to study Earth’s surface
since 1972. Managed by NASA and the U.S. Geological Survey, Landsat data reveals
both natural and human-caused changes to Earth’s surface, and is used by land
managers and policymakers to make decisions about Earth’s changing environment
and natural resources.
Glacier flow is imperceptible to the human eye, but this animation shows glaciers in Asia moving over a span of 11 years, from 1991 to 2002. The animation is composed of false-color images from Landsat 5 and 7 spacecraft. Moving ice is gray and blue; brighter blues are changing snow and ice cover. Credit: NASA/JPL-Caltech/USGS/Earth Observatory
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Advancing
and Retreating
As
glaciers flow toward the sea – albeit too slowly to be perceptible to the eye –
they are replenished by new snowfall on the interior of the ice sheet that gets
compacted into ice. Some glaciers extend past the coastline and can break off
as icebergs. Due to rising atmospheric and ocean temperatures, the balance
between glacier melting and replenishment, as well as iceberg calving, is
changing. Over time, a glacier’s front may naturally advance or retreat, but the
new research shows that none of the 225 ocean-terminating glaciers surveyed has
substantially advanced since 2000, while 200 have retreated.
Although this is in line with other Greenland findings, the
new survey captures a trend that hasn’t been apparent in previous work: As individual
glaciers retreat, they are also changing in ways that are likely rerouting freshwater
flows under the ice. For example, glaciers change in thickness not only as
warmer air melts ice off their surfaces, but also as their flow speed changes in
response to the ice front advancing or retreating.
Both scenarios were observed in the new study, and both can
can lead to changes in the distribution of pressure beneath the ice; scientists
can infer these pressure changes based on changes in thickness analyzed in the
study. This, in turn, can change the path of a subglacial river, since water
will always take the path of least resistance, flowing in the direction of
lowest pressure.
Citing previous studies on the ecology of
Greenland, the authors note that freshwater rivers under the ice sheet deliver nutrients
(such as nitrogen, phosphorus, iron, and silica) to bays, deltas, and fjords
around Greenland. In addition, the under-ice rivers enter the ocean where the
ice and bedrock meet, which is often well below the ocean’s surface. The relatively
buoyant fresh water rises, carrying nutrient-rich deep ocean water to the
surface, where the nutrients can be consumed by phytoplankton. Research has shown
that glacial meltwater rivers directly impact the productivity of phytoplankton
– meaning the amount of biomass they produce – which serves as a foundation of
the marine food chain. Combined with the opening up of new fjords and sections
of ocean as glaciers retreat, these changes amount to a transformation of the
local environment.
“The speed of ice loss in Greenland is
stunning,” said Twila Moon, deputy lead scientist of the
National Snow and Ice Data Center and lead author on the study. “As the ice sheet edge responds
to rapid ice loss, the character and behavior of the system as a whole are
changing, with the potential to influence ecosystems and people who depend on
them.”
The changes
described in the new study seem to depend on the unique features of its environment,
such as the slope of the land that the glacier flows down, the properties of
the ocean water that touch the glacier, as well as the glacier’s interaction
with neighboring glaciers. That suggests scientists would need detailed
knowledge not only of the glacier itself, but also of the glacier’s unique
environment in order to predict how it will respond to continued ice loss.
“It makes modeling
glacial evolution far more complex when we’re trying to anticipate how these
systems will evolve both in the short term and two or three decades out,” Gardner
said. “It’s going to be more challenging than we previously thought, but
we now have a better understanding of the processes driving the variety of
responses, which will help us make better ice sheet models.”
News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov
Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0307
jane.j.lee@jpl.nasa.gov
2020-203
Source: Jet Propulsion Laboratory