SPI Exploratory Grants 2020

Tundra plant communities naturally occur in areas beyond the latitudinal and elevation limits of tree growth, reaching out to alpine and polar deserts and glaciers. Due to their extreme environment, these plants are small and slow growing, yet they are responsible for the accumulation of the largest terrestrial stock of organic carbon, roughly equivalent to 70% of the present day atmospheric CO2 content. With the concerning extent of arctic warming and its anticipated feedback to climate change, ecologists and biogeochemists alike have shown vivid interest in documenting tundra plant community dynamics, such as shrub and tree expansions. Yet the inherent limitations of tedious belowground research and harsh work conditions in the Arctic have precluded us from building a mechanistic understanding of the rates and magnitude of soil processes driven by such shifts in arctic plant communities.

To address this knowledge gap, our team of early career scientists launched in 2018 the project ALTER (Abisko Long-Term Ecological Research), some 200 km north of the Arctic Circle in Sweden. In our project, we adopt a functional classification approach by grouping diverse plant species into distinct vegetation types according to their symbiotic association with characteristic soil microorganisms (mycorrhizae), which in turn regulate the accumulation and degradation of soil organic carbon belowground. By doing that, we aim to characterise the ecosystem carbon sink potential, based on the dominant vegetation type, which is readily observable aboveground and can be scaled in time and space using historical photographs, vegetation maps, drone and satellite images. To implement this in the field, we selectively remove one or another vegetation type from the plant community to assess its functional role belowground in comparison to a control treatment of random plant species removal.

With the generous support of the SPI Exploratory Grant, we aim to equip our experiment for long-term monitoring of belowground vegetation and microbial dynamics. Specifically, we aim to peek into the “black box” of arctic soils and monitor non-destructively and at high spatial and temporal resolution the dynamics of fine root and hyphae production, phenology and turnover. We are convinced that this is of primary importance as in the Arctic up to 80% of living plant biomass is found belowground and fine root and microbial turnover represent a major sink of terrestrial net primary productivity. To this end, we will install minirhizotrons as the primary tool to study root dynamics in the field, micromesh exclosures to partition root vs. hyphae contribution to soil processes, in-growth bags to quantify fungal hyphae production and composition, litterbags to quantify soil organic matter decomposition vs. stabilisation, and use genetic markers to assess soil microbial diversity.

The world is currently experiencing a period of rapid and unprecedented climate warming and high-elevation and high-latitude regions are particularly affected, with rates of temperature increase two to three times higher than the global average. In line with these warming trends over recent decades, vegetation cover and diversity has increased in these regions. The increase in plant species diversity is currently mostly visible at the coldest outposts of plant life. Understanding how vegetation of arctic and alpine regions responds to climate change is therefore a pressing ecological issue on the global scale since they represent 25% of the terrestrial biosphere, are determinants of the global carbon cycle, and harbour disproportionally high rates of biodiversity.

Thirteen years after their establishment, we will resurvey the three arctic mountain summits of the GLORIA (Global Research Initiative in Alpine environments) network to quantify recent changes in plant species cover, abundance and distribution. The GLORIA monitoring network consists of targets regions, each with usually four summit sites covering vegetation along the snowline and in alpine zones. Target regions are distributed over six continents and the globally distributed alpine life zone, thus, providing a unique opportunity for a comparative and simultaneous world-wide assessment of climate-induced impacts on cold-determined ecosystems.

Within this project, we will first assess changes in vegetation along the snowline on three summits located near Zackenberg research station in Greenland. Zackenberg is the northernmost target region within the GLORIA network and has so far only been surveyed in 2008 and 2009. We will compare these changes with temperate mountain summits of the GLORIA network such as those located in the European Alps.

We will then investigate whether seeds of species colonizing arctic mountain summits are derived from short-distance dispersal along the elevational gradient or rare long-distance dispersal events using seed bank and seed germination data from elevational transects set up in 2008.

Finally, we will set up two new GLORIA transects (Downslope Plant Survey) below the highest arctic summit for further comparisons of changes in plant species distribution. Transects will allow assessment in the near future of whether vegetation changes on arctic and temperate mountain summits can be explained by the available species pool at lower elevation.

This unique dataset will therefore grant the first opportunity to assess climate-driven changes in plant species distribution and abundance on mountain summits in the Arctic. In addition, the affiliation with the GLORIA network allows for a standardized comparison of arctic vegetation changes with other tundra habitats across Europe and thus, an evaluation of the relative velocity of these changes.

Arctic rivers and especially their deltas are very dynamic environments that are vulnerable to the rapid changes the Northern regions are currently facing. The Mackenzie river in northwestern Canada is the largest source of suspended sediments and carbon to the Arctic Ocean. The abundant lakes within the Mackenzie delta are regularly flooded by the river, and lake sediments therefore record what is transported by the river and thereby provide information on processes and potential changes occurring within the river’s watershed.

The Canadian Northwest Territories have witnessed unprecedented climate change over the last decade, with dramatic increases in temperature and precipitation leading to widespread thawing of previously frozen soils (permafrost). This begs the question as to whether fluxes and characteristics of materials exported from the Mackenzie river basin have changed in response to this changing climate. We propose to collect a suite of lake sediment cores from the Mackenzie delta in order to determine whether the materials discharged by the Mackenzie River and its tributaries have responded to recent climatic change, and in particular to seek evidence for mobilization of the vast stores of carbon held in permafrost within the watershed. The latter would represent an ominous sign of large-scale perturbations to the Arctic carbon cycle.

To address these questions, we will apply a combination of geochemical and sedimentological techniques in order to constrain the flux, provenance, age and mobilization pathways of carbon and associated materials. Crucially, we plan to follow-up on recent field observations that hint at dramatic permafrost destabilization and release of aged carbon from tributaries of the Mackenzie. Provisional data provides only a “snapshot” from one point in time (spring season 2018), while lake sediment records provide continuous archives that will reveal whether this constitutes a “smoking gun” for a large-scale perturbation of the Arctic system.

<p>On top of every glacier and ice sheet, there is a layer of firn where snow slowly morphs into ice. This layer is characterized by open pore spaces connected to the surface, where air flow is still possible but severely restricted. Eventually, individual pores lose their connection to the atmosphere and become bubbles in the ice. The air trapped in such bubbles has been used to reconstruct the composition of the atmosphere in the past as the only archive that allows direct access to ancient air. Critically, all the air found in ice samples has to pass through the firn layer first. Because air movement in the firn is so slow, it acts as a filter and also allows separation of different gases at the molecular level mostly due to temperature gradients and gravity. Simply said, at the bottom of the firn column, heavier molecules are slightly enriched compared to lighter molecules, with respect to their abundances in the well-mixed atmosphere. The gas trapped in ice bubbles is thus slightly altered from the atmospheric composition, and understanding the processes causing the changes in the gas composition is paramount to interpreting the ice core record. To gain knowledge about these processes taking place in the firn, a number of so-called firn air campaigns have been carried out, where air from several depth levels within the firn is sampled and analyzed. However, due to the logistical constraints of field work in the polar winter, all firn air campaigns so far have taken place in the midst of summer, biasing the results. Because temperature gradients play a major role in the fractionation of gases in the firn, considering only summer data is suboptimal at best. The goal of this project is therefore to set up a semi-permanent firn air sampling installation at Dome C, close to Concordia Station. We will sample the firn air from summer through fall and winter into spring to finally get a complete picture of firn gas composition year-round. This will allow us to quantify the influence of seasonality and layering on the gas species, and to constrain the site-dependent gas trapping parameters during bubble close-off. This project is a collaboration with our colleagues from LSCE in Paris and the French Antarctic Logistics provider, IPEV.</p>

<p><strong>Images</strong></p>

<p>Photo1: A 20m firn hole for the seasonal sampling is being drilled. This hole serves as our conduit to sample firn air from 6 depths through a full 1-year seasonal cycle.</p>

<p>Photo2: After installing the air sampling tubing the firn hole is backfilled with glass beads to inhibit vertical air movement and seal to the atmosphere. The hole is located in the clean snow zone of Concordia Station to minimize contamination.</p>

<p>Photo3: The tubing from the firn hole is extended all the way to a heated container. With winter temperatures of -60 to -70C the compressor pumps and other electronics (not to mention the human operator) need a heated shelter to conduct the sampling.</p>

<p>Photo4: Romilly Harris-Stuart connecting the Bern firn sampling system in the heated container. The air sampling tubes from 6 different firn depths can be seen attached on the top left.</p>

<p>Photo5: Roxanne Jacob operating the firn sampling system. A 6L SilcoCan sampling container (lower left) is being filled to 2bar pressure with firn air.</p>

Plastic production is still increasing annually. This causes growing concern for the vast amounts of inadequately disposed debris entering the oceans globally. Plastic debris that enters the oceans is broken down by UV radiation and wave action over time. These smaller fragments are increasingly bio-available to marine species. Due to the remote and seemingly pristine nature of the Arctic, low levels of plastic pollution were expected. However, the few studies measuring plastics in the Arctic have recorded the presence of microplastics throughout the water column, in sediments, soil, snow and ingested by sea-bird and a few fish species. Studies at a greater spatial scale however are largely missing, as well as the knowledge of the exact origins and transportation pathways.

By collecting microplastic samples along the Norwegian Coast, around Svalbard, Jan Mayen and Greenland, this study aims to better understand the localisation, concentration, and composition of microplastics in Arctic waters, as well as the role the North Atlantic and Norwegian Coastal Currents in particular may play in transporting plastics into the Arctic, which is presumed to be a dead-end for the debris.

As an area of rapid environmental change due to warming, species' range shifts, altering seasons, increasing extreme weather patterns and the loss of sea ice, Arctic species are particularly vulnerable. Further stressors acting on this ecosystem may have a disproportionate impact. To that effect, the aim of this project is to both quantify concentrations of marine debris and assess which species are most likely to encounter the recorded debris. Filtering environmental DNA simultaneously to the microplastics trawls will show which species co-occur with the microplastics and gut analysis will show if the debris is indeed being taken-up into the food web. Combining these methods will allow the mapping of species presence and areas of high concentration which can highlight areas at higher risk and inform mitigation efforts.

Samples for the project will be collected on the TOPtoTOP Global Climate Expedition’s sailing vessel together with the Western Norway University of Applied Sciences and Norwegian Research Centre (NORCE).