The Question of Black Carbon

Black carbon has only recently emerged as a known major contributor to climate change, especially for the Arctic. Formed by the incomplete combustion of fossil fuels, biofuels, and biomass, black carbon absorbs light more strongly than any other particulate matter, especially when deposited onto glaciers and snow cover. Here, it lowers their reflectivity, thereby absorbing atmospheric heat and resulting in earlier spring melt and higher temperatures.

New research, published in Atmospheric Chemistry and Physics, is attempting to address research gaps in this new but significant climate agent by quantifying and analyzing black carbon concentration and deposition in Svalbard, the major archipelago north of Norway.

The study, focusing on black carbon on the Holtedahlfonna glacier in Svalbard between 1700 and 2004, found significant rises in black carbon concentration from the 1970s until 2004 , with unprecedented levels in the 1990s.  Importantly, the study concludes that the increase in black carbon concentration “cannot be simply explained by changes in the snow accumulation rate at the glacier,” or simply by glacial melt and shrinkage in Svalbard. This indicates that black carbon was instead deposited in increasing quantities during this time period.

Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia

The study raises some puzzling differences between black carbon concentrations and deposition in Svalbard and between previous data from other Arctic regions. While Svalbard’s black carbon values increased rapidly from a low point in 1970 until 2004, reaching a high in the 1990s, black carbon analyzed in Greenland ice cores indicated generally decreasing atmospheric black carbon concentrations since 1989 in the Arctic.

This difference is likely at least partly explained by differences in the specific methodologies used in the studies, such as the operational definition of black carbon that determined which size particles were included in the study.

The Svalbard study collected its data by filtering the inner part of a 125 m deep ice core from the Holtedahlfonna glacier through a quartz fiber filter. The filtrate was analyzed using a thermal-optical method, while previous comparable studies used an SP2 (Single Particle Soot Photometer) method. The different methodologies used between studies makes it hard to assess the validity of the studies’ findings.

Indeed, previous studies on black carbon on Himalayan and European ice cores have repeatedly shown different and contracting trends when measured with different analytical methods, even when studies examined the same glaciers. This indicates a significant need for more and improved research on black carbon research in the Arctic.

Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia.
Burgerbukta Glacier, Svalbard. Courtesy of Wikipedia.

Black carbon concentrations, as the study reveals, are immensely complicated and depend on a variety of factors, such as air concentration of black carbon, the amount of precipitation, local wind drift patterns post-deposition, sublimation, and melt. Black carbon concentration can also be affected by sudden changes in snow and ice accumulation, or seasonal melt. These factors make it difficult for scientists to collect faithful data of black carbon concentration over time.

However, black carbon data in the Arctic is incredibly important: in the Arctic, black carbon is a more important warming agent than greenhouse gases. Its levels are intensely impacted from local and regional emission sources near Svalbard, such as forest and wild fires and flaring at gas wells in Russia, impacts that are difficult to accurately quantify, the researcher state.

While this study sheds light on recent trends of black carbon levels in Svalbard, it raises some key questions about the particle’s measurement, suggesting a need for further development of accurate black carbon measurement techniques and for further research on the role black carbon plays in Arctic warming.

Glacier Past Unveiled Through Sediments

Svalbard: Ny Ålesund. Note: this lake was not part of the study. Courtesy of James Stringer/Flickr
Svalbard: Ny Ålesund. Note: this lake was not part of the study. Courtesy of James Stringer/Flickr

Researchers have long used preserved sediment layers in glaciers as time records to understand the climate of the past. But now, researchers, publishing in Quaternary Science Reviews, have used lake sediments in glacier-fed Lake Hajeren in Svalbard to recreate glacier variability during the Holocene period.

The sediments, which were deposited over millennia, have been undisturbed, allowing researchers to develop a continuous and full record of glaciers as early as 11,700 calibrated Before Present (BP). The dates were calculated using radiocarbon calibration, meaning that the dates have been compared to other radiocarbon samples. Atmospheric carbon varies over time, so it does not necessarily correspond to the current Gregorian calendar. By comparing different radiocarbon samples, researchers hope to develop a more accurate dating system.

The researchers’ complete record revealed a number of new findings about the advance and presence of the Svalbard glacier. Sediments in Lake Hajeren indicated that between 3380 and 3230 cal BP there was a glacier advance that lasted more than 100 years. The glacier advance had never before been recorded.

Researchers also noted that during the deglaciation period before 11,300 cal BP, glaciers in Svalbard remained, and that between 7.4 and 6.7 thousand cal BP, glaciers disappeared. It wasn’t until 4250 cal BP that glacier reformation began. The variability in glacier presence and formation can be attributed to pulses from the melting Laurentide Ice Sheet, episodes of cooling in the Atlantic and reduced isolation during summers.

“These findings highlight the climate-sensitivity of the small glaciers studied, which rapidly responded to climate shifts,” the authors wrote.

Their research contributes to a body of work looking to better understand the driving forces behind climate variability in the Arctic, the region most affected by climate change. The Arctic also has a disproportional impact on the global climate compared to other parts of the world.

Arctic response to climate change can also be used to develop climate models that estimate the impacts of global warming.

“The rapid response of the small Hajeren glaciers improves our understanding of climate variability on Svalbard, suggesting that the Holocene was punctuated by major centennial-scale perturbations,” the authors concluded. “As such, this study underlines the value of glacier-fed lake sediments in contextualizing Arctic climate dynamics.”

Photo Friday: A Snapshot of Svalbard

Svalbard is a Norwegian archipelago tucked in between Norway and the North Pole. Especially known for its views of the Northern Lights and its summer “midnight sun,” in which sunlight graces the archipelago 24 hours a day, Svalbard is also known for its glaciers, which cover around 60 percent of Svalbard’s land area.

Project Pressure, a charity documenting the world’s vanishing glaciers, posted incredible photos of Southern Svalbard’s glaciers. Project Pressure hosts a wide collection of incredible, free-to-use images, so be sure to check out their website here.

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Many thanks to Chris Arnold, the photographer of these photos. Check out his website here.


The Microscopic Life of Glaciers

Svalbard Glacier, courtesy of Airflore/Flickr.
Svalbard Glacier, courtesy of Airflore/Flickr.

Though it can be hard to imagine that cold, barren-looking glaciers are conducive to life, glaciers are actually teeming with organisms. Glacier surfaces are filled with cylindrical holes called cyroconite holes, in which melt water accumulates and micro-algae and cyanobacteria  thrive.

Now, a new study published in Biogeosciences has taken a closer look at these complex ecosystems to better understand the interactions between the organisms that inhabit this icy space. They found that Svalbard glaciers that received large quantities of deposits from local areas tended to have large amounts of microalgae. These microalgae can create large colonies to protect them from invertebrate grazers like tardigrades, minute animals also known as water bears, and other microscopic animals like rotifers and ciliates. Large microalgae colonies can protect themselves from the filtration feeding strategy used by rotifers.

The researchers studied these mini-ecosystems on four glaciers in Svalbard, a Norwegian Archipelago. Each sample had a different level of exposure to nutrients, water depth and the degree to which the cyroconite holes were isolated so that the researchers could separately analyze the effects of environmental factors and other biological interactions, such as animals grazing on the microalgae.

Under a microscope, the researchers identified the different species of tardigrades and rotifers. They also measured the density of microalgae clusters and the types of microalgae and cyanobacteria.

Colony of rotifers, courtesy of Specious Reasons/Flickr
Colony of rotifers, courtesy of Specious Reasons/Flickr

In glaciers farther away from glacier-free land, the microalgae species differed from glaciers closer to land. Species variability could be attributed to wind transport, the researchers suggest.

“We propose that selection occurs because polar cyanobacteria are often associated with dust in soil, and thus easily transported by 20 wind,” they wrote. Levels of nitrogen deposits from bird guano and tundra may also play a role in determining which species of microalgae lived where, but the researchers felt this factor was less important than wind transportation.

The species and quantities of grazers, on the other hand, did not vary much from site to site. Grazer types were also correlated with the types of microalgae found in different cyroconite holes. Rotifers tended to live around Zygnemales and Chlorococcales, while tardigrades were usually found around larger Zygnemales.

“The high abundances of tardigrades, rotifers, and ciliates, including genera with different feeding strategies, have been found and suggest a complex food web between more trophic levels than measured in the present study,” the authors wrote. “Feeding experiments and analysis of stomach contents may help to bring a more detailed picture of this yet hardly known food web.”