Rapid glacial advance reconstructed during the time of Norse occupation
in Greenland

Date:
March 25, 2022
Source:
Geological Society of America
Summary:
The Greenland Ice Sheet is the second largest ice body in the
world, and it has the potential to contribute significantly to
global sea-level rise in a warming global climate. Understanding the
long-term record of the Greenland Ice Sheet, including both records
of glacial advance and retreat, is critical in validating approaches
that model future ice-sheet scenarios. However, this reconstruction
can be extremely challenging. A new study has reconstructed the
advance of one of the largest tidewater glaciers in Greenland to
provide a better understanding of long-term glacial dynamics.



FULL STORY ==========================================================================
The Greenland Ice Sheet is the second largest ice body in the world,
and it has the potential to contribute significantly to global sea-level
rise in a warming global climate. Understanding the long-term record of
the Greenland Ice Sheet, including both records of glacial advance and
retreat, is critical in validating approaches that model future ice-sheet scenarios. However, this reconstruction can be extremely challenging. A
new study published Thursday in the journal Geology reconstructed the
advance of one of the largest tidewater glaciers in Greenland to provide
a better understanding of long-term glacial dynamics.


==========================================================================
"In the news, we're very used to hearing about glacial retreat, and that's because in a warming climate scenario -- which is what we're in at the
moment - - we generally document ice masses retreating. However, we also
want to understand how glaciers react if there is a climate cooling and subsequent advance. To do this, we need to reconstruct glacier geometry
from the past," said Danni Pearce, co-lead author of the study.

An interdisciplinary team of researchers studied the advance of Kangiata Nunaata Sermia (KNS) -- the largest tidewater glacier in southwest
Greenland - - during a period of cooling when the Norse had settlements
in Greenland.

Differing from glaciers that are strictly on land, tidewater glaciers
extend and flow all the way to the ocean or a sea, where they can then
calve and break up into icebergs.

Reconstructing the advance of glaciers can be exceptionally difficult,
because the glacier typically destroys or reworks everything in its
path as it advances forward. The research team undertook multiple field
seasons in Greenland, traveling on foot to remote sites -- many of which
hadn't been visited since the 1930s -- to try and uncover the record of
KNS advance.

"When we went out into the field, we had absolutely no idea whether the evidence would be there or not, so I was incredibly nervous. Though
we did a huge amount of planning beforehand, until you go out into
the field you don't know what you're going to find," said James Lea,
the other co-lead author of the study.

By traveling on foot, the research team was able to more closely examine
and explore sites that otherwise may have been missed if traveling
by helicopter.

The team's planning paid off, and the sedimentary sequences they studied
and sampled held the clues they were looking for to date and track the
advance of the glacier.



==========================================================================
The research team found that during the twelfth and thirteenth centuries
CE, KNS advanced at least 15 km, at a rate of ~115 m/yr. This rate of
advance is comparable to modern rates of glacial retreat observed over
the past ~200 years, indicating that when climate is cooler glaciers can advance equally as fast as they are currently retreating. The glacier
reached its maximum extent by 1761 CE during the Little Ice Age,
culminating in a total advance of ~20 km.

Since then, KNS has retreated ~23 km to its present position.

The period when the glacier was advancing coincided with when the Norse
were present in Greenland. Prior to its maximum extent during the Little
Ice Age, the researchers found that KNS advanced to a location within
only 5 km of a Norse farmstead.

"Even though KNS was rapidly coming down the fjord, it did not seem to
affect the Norse, which we found really unusual," said Pearce. "So the
team started to think about the surrounding environment and the amount
of iceberg production in the fjord during that time. At the moment, the
fjord is completely filled with icebergs, making boat access challenging,
and we know from historical record that it has been like this for the
last 200 years while the glacier has been retreating. However, for KNS
to advance at 115 m/yr, it needed to hang onto its ice and could not
have been producing a lot of icebergs. So we actually think that the
fjord would have looked very different with few icebergs, which allowed
the Norse far more easy access to this site for farming, hunting, and
fishing." In the 1930s, archaeologists who visited the site hypothesized
that conditions in the fjord must have been different from the present
day in order for the Norse to have occupied the site, and this current
research study provides data to support these long-held ideas.

"So we have this counterintuitive notion that climate cooling and glacier advance might have actually helped the Norse in this specific circumstance
and allowed them to navigate more of the fjord more easily," said Lea.

The Norse left Greenland during the fifteenth century CE, and these
results are consistent with the idea that a cooling climate was likely
not the cause of their exodus; rather, a combination of economic factors
likely led the Norse to abandon Greenland.

The results from this research reconstructing rapid glacial advance are
also shown to be consistent with the ways ice sheet models work, which
brings confidence to the projections from these models. Having accurate
models and projections are crucial in understanding and preparing for
future scenarios of continued retreat of the Greenland Ice Sheet and
associated sea-level rise.

"Melt from Greenland not only impacts sea-level change but also the
ecology around the ice sheets, fisheries, the biological productivity
of the oceans - - how much algae is growing. And also because the types
of glaciers we're looking at produce icebergs these can cause hazards
to shipping and trade, especially if the Northwest Passage opens up as
it is expected to," said James Lea.

Pearce added, "Our research shows that climate cooling can change iceberg calving behavior and drive glacier advance at rates just as rapid as
current retreat. It also shows how resilient the Greenlandic Norse were
to the changing environmental conditions. Such adaptation can give us
hope for the changes we may face over the coming century.''

========================================================================== Story Source: Materials provided by Geological_Society_of_America. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Danni M. Pearce, James M. Lea, Douglas W.F. Mair, Brice R. Rea,
J. Edward
Schofield, Nicholas A. Kamenos, Kathryn M. Schoenrock, Lukasz
Stachnik, Bonnie Lewis, Iestyn Barr, Ruth Mottram. Greenland
tidewater glacier advanced rapidly during era of Norse
settlement. Geology, 2022; DOI: 10.1130/G49644.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220325093923.htm

--- up 3 weeks, 4 days, 10 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)