Roundup: Grounding Lines, Methane-Oxidizing Bacteria and Grazing Patterns

Grounding Lines of Antarctic Glaciers Show Fast Retreat

From Nature Geoscience, “Grounding lines are a key indicator of ice-sheet instability, because changes in their position reflect imbalance with the surrounding ocean and affect the flow of inland ice. Although the grounding lines of several Antarctic glaciers have retreated rapidly due to ocean-driven melting, records are too scarce to assess the scale of the imbalance. Here, we combine satellite altimeter observations of ice-elevation change and measurements of ice geometry to track grounding-line movement around the entire continent, tripling the coverage of previous surveys. Between 2010 and 2016, 22%, 3% and 10% of surveyed grounding lines in West Antarctica, East Antarctica and at the Antarctic Peninsula retreated at rates faster than 25 m yr−1 (the typical pace since the Last Glacial Maximum) and the continent has lost 1,463 km2 ± 791 km2 of grounded-ice area.”

Discover more about Antarctica’s melting situation here.

The calving front of an ice shelf in West Antarctica as seen from above (Source: NASA/Flickr)


Glacier Melt Exposes Land for Methane-Oxidizing Bacteria

From Oxford Academic: “Methane (CH4) is one of the most abundant greenhouse gases in the atmosphere and identification of its sources and sinks is crucial for the reliability of climate model outputs. Although CH4 production and consumption rates have been reported from a broad spectrum of environments, data obtained from glacier forefields are restricted to a few locations. We report the activities and diversity of Methane-Oxidizing Bacteria along a Norwegian sub-Arctic Glacier Forefield using high-throughput sequencing and gas flux measurements. The overall results showed that the methanotrophic community had similar trends of increased CH4 consumption and increased abundance as a function of soil development and time of year when glaciers retreat.”

Read more about the relationship between methane and glacier retreat here.

Methane-oxidizing Bacteria Methylosinus Trichosporium (Source: Ezra Kulczycki/ PNAS)
Methane-oxidizing Bacteria Methylosinus Trichosporium (Source: Ezra Kulczycki/ PNAS).


Grazing Patterns in Glacier-fed Wetlands

In PLOS ONE, “Grazing areas management is of utmost importance in the Andean region. In these harsh mountains, unique and productive wetlands sustained by glacial water streams are of utmost importance for feeding cattle herds during the dry season. After the colonization by the Spanish, a shift in livestock species has been observed, with the introduction of exotic species such as cows and sheep, resulting in a different impact on pastures compared to native camelid species—llamas and alpacas. Our results suggest that the access to market influenced pastoralists to reshape their herd composition, by increasing the number of sheep. They also suggest that community size increased daily grazing time in pastures, therefore intensifying the grazing pressure.”

Explore the influence of glacier meltwater on wetland size and herd composition here.

Llama in a sea of sheep grazing in a farm (Source: Brianne Hughes/ Pinterest )
A llama in a sea of sheep grazing on a farm (Source: Brianne Hughes/ Pinterest).

Post-Glacial Soils’ Star Role in Methane Cycle

The role of woodland soils in the terrestrial uptake of methane is common knowledge for most earth scientists; however, the link between the new soils, which emerge after glacier retreat, and methane uptake was only discovered in 2003. Now, a new study has brought more gravity to this finding by exposing the surprising efficiency of this process. The results are significant, considering methane is a very potent greenhouse gas. Conclusions from this study prove that glacier forelands, or the regions of land that lie at the edge of a glacier and are newly ice-free, could play a role in mitigating climate change.

Lake Near Sunnig Grat Summit in Canton or Uri, Switzerland
Lake Near Sunnig Grat Summit in Canton or Uri, Switzerland

The new study, led by doctoral candidate Eleonora Chiri at the ETH Zurich, or the Swiss Federal Institute of Technology, aimed to discover which components of glacier forefield soils determine its performance as a terrestrial sink for atmospheric methane. To answer this question, researchers collected between 12 and 15 samples of aerobic methane-oxidizing bacteria–organisms which use methane as their only source of carbon and energy–from multiple strategic locations between the Damma and Griessfirn glaciers in the Canton of Uri, Switzerland. These two glaciers were chosen because of their difference in bedrock type. Samples were assessed for four attributes: soil-atmosphere methane flux, methane oxidation activity, methane-oxidizing bacteria abundance, and bacterial variation. These measures helped the scientists to understand what types of bacteria thrive in the sample regions and how their activity affects the rate of uptake of methane in the various sampling locations. Soils collected ranged from 6 to 120 years old.

The data revealed four key trends. First of all, methane-oxidizing bacteria composition was the only factor that varied based on location; the most important influence on this factor was bedrock type. Oxidation activity was dependent on the water content of the soil. It was initially greatest in deep layers of soil, but oxidation towards the surface became more pronounced as the soil matured. Most significantly, though, researchers found that although the amount of methane from the air that was consumed by the bacteria increased with the age of the soil, a robust amount of uptake could be established as quickly as a few years after the soil became ice-free, and could reach full maturity in about a decade. Contrary to the belief that an area of glacier forefield soil could not uptake methane until it reached 80 years of maturity, the authors concluded  “alpine glacier-forefield soils investigated in this study acted as a sink for atmospheric [methane]already within <10 yr after glacial retreat.”

Field sites and sampling locations (Photo credit: Chiri et al.)
Field sites and sampling locations (Photo credit: Chiri et al.)

This research is critical to understanding the full picture of glacial retreat. On one hand, many scientists are concerned that thawing Arctic lakes will cause more methane to be released into the atmosphere. This climate change feedback loop could have catastrophic effects, since methane is a greenhouse gas 21 times more potent than carbon dioxide. Therefore, the role of methane uptake in glacier forefields could serve as a buffer for this new source of methane emissions.

In addition to the biological significance, the findings from this research have implications for climate change policy. According to the researchers, “young mountainous soils have the potential to consume substantial amounts of atmospheric methane, and should be incorporated into future estimates of global soil uptake.” Although prior mitigation policy has often focused on the role of carbon dioxide in mitigation strategies, the role of soil uptake from glacier forefields opens up a new opportunity for policymakers to claim new sources of climate change offsets. For example, in cities that have implemented greenhouse gas cap-and-trade programs, companies are allowed conservation-based forest management as a carbon offset option. Further research may indicate that the preservation of glacier forefields is also beneficial and this may present itself as an option for greenhouse gas offsets as well.

Klausenpass in Uri, Switzerland
Klausenpass in Uri, Switzerland

This study is the first step in understanding the role of glacier forefields in the balancing the global methane budget. More research is necessary to understand the magnitude and timescale of the soil-atmosphere exchange in order to obtain a full picture of this process.