© Dr Mel Murphy and Dr Emily Stevenson
This year’s Gilchrist Fieldwork Award recipient is Dr Melissa Murphy from University College London who, in partnership with Dr Emily Stevenson from the University of Cambridge, is researching whether high Arctic rivers are a source of a sink for carbon dioxide. We caught up with Mel to find out more about her research, why it’s important to improve our knowledge about climate change and a few memorable encounters she had with some polar bears.
Can you tell us a little bit more about your project on high Arctic rivers – what are you hoping to find?
This summer, Emily and I spent nearly three months sampling glacier- and snow-fed rivers draining continuous permafrost in the high Arctic Zackenberg River catchment, NE Greenland. Rivers play an important role in the long-term carbon cycle, transporting dissolved and particulate material from the chemical and physical breakdown of rocks on the continents to the oceans. These ‘weathering’ processes can both release and remove carbon dioxide (CO2) from the atmosphere, and we don’t know which of these processes dominates overall in Arctic river systems. This has huge implications for understanding whether Arctic rivers are acting as a source or sink for atmospheric CO2, and therefore, how weathering in the Arctic impacts the long-term carbon cycle and climate.
We sampled the rivers throughout the melt season as the permafrost ‘active layer’ thawed, and continued sampling well into autumn, when both the active layer, and the rivers, refroze. We were also hoping to sample the annual high discharge ‘glacial lake outburst flood’ or GLOF, which discharges almost the entire annual suspended sediment load into the fjord. But this summer was only the second time since continuous monitoring began in 1997 that the GLOF did not arrive. The unpredictability of these extreme events is likely driven by climate-induced changes, which is why it is so important to understand how the Artic is responding to climate change.
Now back in the lab, we are looking at the major, trace element and isotopic geochemistry of the dissolved and suspended sediments, which can tell us about the chemical weathering reactions taking place both within the active layer and the river itself.
Why is this research important now?
The Arctic is exceptionally vulnerable to present-day climate change, and is warming twice as fast as the global average. This ‘polar amplification’ is rapidly melting ice sheets and glaciers, which leads to sea level rise.
Climate-warming enhanced permafrost degradation is changing water flow paths and increasing permafrost slumping and collapse (called thermokarsts), which releases large quantities of sediment into coastal environments.
Together, these irreversible climate impacts are changing the nature of sediment and solutes being delivered to the oceans. In turn, this will influence the future of Earth's biogeochemical cycles and landscape evolution, as well as mineral, elemental, nutrient and carbon fluxes into the ocean and atmosphere. As the polar regions are changing so rapidly, it is important to understand the impact climate change has on the long-term carbon cycle in these environments.
© Dr Mel Murphy and Dr Emily Stevenson
Why did you choose the Zackenberg River catchment for this research project?
The Zackenberg River catchment is mountainous and glaciated, with pristine rivers draining a range of bedrock types across a relatively small area. This makes it an ideal location to understand the weathering processes in this high Arctic, permafrost-dominated and glacial environment.
We were based at the Zackenberg Research Station, one of the longest operating field research facilities in the high Arctic, which is incredibly well equipped despite how remote it is. Run by the Greenlandic government, and managed by Aarhus University, Denmark, the station has a well-established research and monitoring programme which has over 20 years of continuous climate, hydrological and permafrost thermal regime data. This historic data is essential to help us understand the effects of climate change in this region.
The Arctic is an extreme environment, how did you prepare for your fieldwork?
Working in the Arctic has its challenges, but both Emily and I are experienced at working in polar climates and sampling Arctic rivers.
We never left the station without a rifle, flare gun and radio, or leaving a copy of our planned daily route with the station manager. This season, we had eight polar bear sightings near the research station but thankfully none of the encounters required more than firing a deterrent flare to scare them off!
The nearest town is over 450 km away, so we have to be sure not to forget any field and sampling equipment. Having good quality, warm, water and wind proof clothing – and a great pair of rubber boots – is essential. Some days we would hike over 30 km, crossing rivers and walking through water logged tundra, all whilst lugging up to 20 kilos of river water, as well as our field sampling equipment, first aid kit, rifle, flare and the all-important lunch!
© Dr Mel Murphy and Dr Emily Stevenson
How did your fieldwork go, did you come across anything unexpected or difficult?
We had a really great field season, and we came home with over 150 kg of river samples! However, working in the Arctic, you need to be flexible to accommodate for any unexpected changes in the plan. The weather can change quite suddenly, and fog, rain and gale-force winds can leave you stranded in the station for days.
Surprise encounters with wildlife can also halt you in your tracks. One day we nearly stumbled upon a polar bear. Luckily, we spotted it from on top of the bridge that crosses the main Zackenberg River just before we hiked in that very direction. From the safety of the bridge, we had the unbelievable chance to witness the bear from only 200 m away. We didn’t have to fire a flare or use the rifle, as it just sat down on a snow patch and watched us curiously for a few minutes before it walked away in the direction it came from. It was a very special moment.
Your method, using unique isotope tracers, has never been applied before in a high Arctic environment. Why did you choose to use this method over others?
A big problem with using river geochemistry to assess whether a region is a CO2 source or sink, is that it is difficult to disentangle the complex weathering reactions which play different roles in the long-term carbon cycle. For example, weathering of silicate rocks acts as a long-term sink for atmospheric CO2. However, weathering of sulfide minerals produces sulfuric acid, which when in contact with carbonate rocks, releases carbon back to the atmosphere. Isotopic tracers help us to fingerprint and quantify these weathering processes.
Our samples will be analysed for dissolved and suspended sediments, including lithium, calcium, strontium and sulfur isotopes. These are unique tracers that can be used to identify silicate, carbonate and sulfide mineral weathering processes. In combination with the major and trace element geochemistry, this will allow us to determine whether this high Arctic river catchment is acting as a source or a sink for inorganic carbon, and how these processes impact atmospheric CO2, and ultimately climate.
© Dr Mel Murphy and Dr Emily Stevenson
How could your research help us to understand more about climate change?
One potential application of this research, as highlighted in the recent IPCC special report, is the potential for artificial enhancement of natural weathering processes to remove CO2 from the atmosphere in an attempt to mitigate anthropogenic CO2 emissions.
Many global climate models predict that climate change will result in intensification of the hydrological cycle. This is predicted to increase precipitation and hence river runoff, and increase the frequency and intensity of extreme events. These changes will affect weathering processes, therefore, understanding how the Arctic responds to present-day climate warming, and also how these weathering processes control CO2 removal and release in Arctic rivers is a key aim of this research. It is important to understand how these processes govern Earth’s past climate evolution (particularly over glacial-interglacial cycles), which will help us predict how Earth may respond to future climate perturbations.
The Gilchrist Fieldwork Award is a biennial grant administered by the Society and run in even years, offering £15,000 to support a challenging field research project overseas. The deadline for the 2020 applications is 22 February 2020. Find out more.
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