Roundup: Porcupine Glacier, Patterned Ground and Ciliates

Roundup: Glacier Calving, Ciliates and the Alps

 

A calving event in Porcupine Glacier shows rapid retreat

From the American Geophysical Union: “Porcupine Glacier is a 20 km long outlet glacier of an icefield in the Hoodoo Mountains of Northern British Columbia that terminates in an expanding proglacial lake. During 2016 the glacier had a 1.2 square kilometer iceberg break off, leading to a retreat of 1.7 km in one year. This is an unusually large iceberg to calve off in a proglacial lake, the largest ever seen in British Columbia or Alaska… The retreat of this glacier is similar to a number of other glaciers in the area: Great Glacier, Chickamin Glacier, South Sawyer Glacier and Bromley Glacier. The retreat is driven by an increase in snowline/equilibrium line elevations which in 2016 is at 1700 m, similar to that on South Sawyer Glacier in 2016.”

Learn more about the retreat of Porcupine glacier, and view satellite images here.

A glacier in Kenai National Park, where Porcupine glacier is located
A glacier in Kenai National Park, where Porcupine glacier is located (Source: Dubhe/Wikimedia Commons)

 

Patterned ground exposed by glacier retreat in the Alps

From the Biology and Fertility of Soils: “Patterned ground (PG) is one of the most evident expressions of cryogenic processes affecting periglacial soils, where macroscopic, repeated variations in soil morphology seem to be associated with small-scale edaphic [impacted by soil] and vegetation gradients, potentially influencing also microbial communities. While for high-latitude environments only few studies on PG microbiology are available, the alpine context, where PG features are rarer, is almost unexplored under this point of view… These first results support the hypothesis that microbial ecology in alpine, periglacial ecosystems is driven by a complex series of environmental factors, such as lithology [study of the general physical characteristics of rocks], altitude, and cryogenic activity, acting simultaneously on community shaping both in terms of diversity and abundance.”

Learn more about glacier retreat in the Italian Alps here.

Glaciers in the Italian Alps
Glaciers in the Italian Alps (Source: Glac01 /Wikimedia Commons)

 

Microorganisms found in glacial meltwater streams

From Polar Biology: “Microbial communities living in microbial mats are known to constitute early indicators of ecosystem disturbance, but little is known about their response to environmental factors in the Antarctic. This paper presents the first major study on ciliates [single-celled animals bearing cilia] from microbial mats in streams on King George Island (Antarctica)… Samples of microbial mats for ciliate analysis were collected from three streams fed by Ecology Glacier. The species richness, abundance, and biomass of ciliates differed significantly between the stations studied, with the lowest numbers in the middle course of the stream and the highest numbers in the microhabitats closest to the glacier and at the site where the stream empties into the pond. Variables that significantly explained the variance in ciliate communities in the transects investigated were total organic carbon, total nitrogen, temperature, dissolved oxygen, and conductivity.”

Learn more about the ciliates here.

One of the glaciers on King George Island
One of the glaciers on King George Island (Source: Acaro/Wikimedia Commons).
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Precipitation Controls Retreat of Kerguelen’s Glaciers

An aerial view of the Kerguelen Islands and its glaciers (Source: NASA Earth Observatory)
An aerial view of the Kerguelen Islands and its glaciers (Source: NASA Earth Observatory)

Islands in the Indian Ocean are not the first to come to mind when glacier retreat is mentioned. However, glaciers in the Kerguelen Islands, located at sub-polar latitudes in the southern hemisphere, have been experiencing widespread and rapid retreat in recent years.

While rising temperatures are generally assumed to be the main cause of glacial retreat, a recent study published in Nature revealed that a reduction in precipitation is the dominant factor controlling the retreat of glaciers in the Cook Ice Cap on the Kerguelen. Similar conclusions were made in a study of Kilimanjaro’s melting glaciers, and this study could offer further insight into the effect of circulation changes on glaciers.

A Macaroni Penguin, one of thirty bird species that nest on the Kerguelen Islands (Source: Magnus Manske).
A Macaroni Penguin, one of thirty bird species that nest on the Kerguelen Islands (Source: Liam Quinn/Wikimedia Commons).

The Kerguelen Islands are among the most isolated places on Earth. Located on the seaway between South Africa and Antarctica, they are only accessible by boat and serve as a nesting ground for many bird species, such as the Macaroni Penguin. Glaciers cover about 500 square kilometers of the islands, and the loss of ice from these glaciers was among the most serious in the world in the 2000s, according to the study mentioned above.

Uncertainty surrounding the effects of climatic changes on glaciers in the southern mid-latitudes is particularly high due to a lack of observational data on glaciers and ice caps. Along with a lack of full modeling studies, this has led to the general assumption that warming is the main driver of glacial loss, as is the case in the northern mid-latitudes.

A team of scientists led by Vincent Favier, a researcher at Université Grenoble Alpes, set out to test the hypothesis that glacial retreat on the Kerguelen was largely due to increasing temperatures. The Cook Ice Cap was a suitable site for study because it is mainly made up of glaciers, which links its mass variations more strongly to climate variations than other ice caps at similar latitudes. In addition,  the availability of long term climate and glaciological observations in the region made it possible to produce accurate models of glacial mass balance from 1850-2011.

A glaciologist uses a steam drill to make a hole in the ice of the Cook Ice Cap to set up an ablation stake (Source: Vincent Favier).
A glaciologist uses a steam drill to make a hole in the ice of the Cook Ice Cap to set up an ablation stake (Source: Vincent Favier).

Using a combination of field data, satellite data, and climate and glacial models, the team was able to attribute 77% of ice loss since the 1960s to atmospheric drying, with temperature increases only amplifying the losses. The researchers used the decade between 1950 and 1960 as a reference period for glacial mass and modelled changes in glacial mass using different hypothetical temperature and precipitation values.

1000 different simulations were run, revealing that dryness is the dominant influence on glacier wastage despite the increase in temperatures in the Kerguelen since the 1960s. The dominant influence of precipitation is particularly evident in glacier mass balance trends between 1963-1975, when both temperatures and mass balance increased. This seemingly paradoxical observation was due to higher levels of precipitation experienced during this period.

Precipitation over the Kerguelen is influenced by the north-south movement of wind belt in the middle latitudes of the Southern Hemisphere – the Southern Annular Mode (SAM). It brings stormy weather to the Kerguelen when it is in a more northerly position, also known as its negative phase. Since 1975, the SAM has been in southerly positions more frequently, increasing atmospheric dryness over the Kerguelen. This is associated with ozone layer depletion and increases in greenhouse gas emissions, suggesting that the frequency of positive phases of SAM is likely to increase over the course of the century and worsen glacier retreat in the Kerguelen.

The terminus of a glacier at the southern end of Cook Ice Cap (Source: B. Navez)
The terminus of a glacier at the southern end of Cook Ice Cap (Source: B. Navez)

Darker surfaces exposed by this loss of glacial ice could exacerbate melting in what is known as the ice-albedo negative feedback mechanism. These surfaces absorb more heat than light colored surfaces like ice, amplifying the effects of temperature changes on glacier loss.

As the SAM is a hemispheric feature, other glaciers within similar latitudes may also have been affected. As Favier explained in an interview with GlacierHub, “We chose this location because we believe it is an example of what is occurring under the same latitude but at other longitudes, in particular in New Zealand… Indeed, this drying trend is suggested at a large scale in the mid latitudes.” However, the lack of long-term sets of observational data for other locations at similar latitudes makes it difficult to determine possible effects, he said.

The difficulty of determining the effects of these changes on other locations within similar latitudes is exacerbated by the poor simulation of temperature and precipitation patterns over the Kerguelen in climate models used by the Intergovermental Panel on Climate Change. 95% of the models used by Favier and his colleagues to model patterns of glacial mass loss in the Kerguelen underestimated glacial mass losses at Cook Ice Cap. As such, projections of ice losses in the southern mid-latitudes based on model simulations should be used with great caution, particularly in areas where circulation changes are expected.

While glacier retreat is usually associated with increasing temperatures, it seems that circulation changes are important too. Remote locations like the Kerguelen Islands can offer clues about some of the impacts of climate change.

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