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How the polar ocean gets rid of CO2: Blue carbon burial in Arctic and Antarctic shelf seas

Dr Christian März (SEE), Dr Caroline Peacock (SEE), Dr Rob Newton (SEE),  Dr Johan Faust (SEE), Dr David Barnes (British Antarctic Survey)

Project partner(s): British Antarctic Survey (CASE)

Contact email: c.maerz@leeds.ac.uk

Background

Earth’s climate is currently undergoing unprecedented changes, with the Arctic and west Antarctic experiencing drastic environmental perturbations. Loss of sea ice, destabilisation of icesheets, and ocean acidification are only a few examples of how increasing amounts of the greenhouse gas CO2 in the atmosphere impact the marine environment. In this context, the world’s oceans, including their organisms and sediments, play an important role as they take up huge amounts of atmospheric CO2 and sequester it as so-called “blue carbon”.

One of the most important ways that CO2 is naturally removed from the atmosphere is through its incorporation into organic biomass. This happens mainly through production by photosyntheic algae in the sunlit layers of the oceans. Once these algae die, part of their remains sink to the seafloor and get buried as organic matter into the sediments, removing CO2 (in the form of organic carbon) from the atmosphere-ocean system for millions of years. However, the burial rate of this organic carbon is spatially and temporally variable, and depends on various environmental parameters, including rates of microbial degradation in the sediment, sedimentation rates, or the activity of burrowing organisms at the seafloor. Recently, it has further been proposed that part of the organic carbon in marine surface sediments is bound to iron and manganese (oxyhydr)oxides, which might further enhance its preservation.

Figure 1: Seafloor image taken by BAS Shallow Underwater Camera System (SUCS), ~1x1 m (courtesy DKA Barnes)

Another important pathway of CO2 removel into marine sediments is carbon incorporation by macrobiota that live at the seafloor (e.g., inorganic carbon precipitated as calcium carbonate shells by benthic organisms like molluscs or bivalves, or organic carbon incorporated into heavily skeletalised fauna like corals) (Fig. 1). This carbon is buried into the sediments once the organisms die, and - in contrast to non-bound organic carbon settling through the water column - is not prone to microbial degradation. It can thus be an important carbon sink in ocean regions dominated by carbonate-precipitating benthic fauna.

In the frame of several ongoing research projects (The Changing Arctic Ocean Seafloor, ChAOS, http://www.changing-arctic-ocean.ac.uk/?page_id=199; Antarctic Seabed Carbon Capture Change, ASCCC, http://www.asccc.co.uk/), Drs März, Barnes and Faust are collecting data and samples to estimate the organic and inorganic components of blue carbon burial in various parts of the Arctic Ocean and the seas around Antarctica, with a focus on shallow shelf environments (Fig. 2). 

Figure 2: Scientists onboard the RRS James Clark Ross in the Barents Sea, summer 2017 (März sitting, Faust kneeling, Barnes in yellow coat; courtesy of J Faust)

Such environments in both northern and southern high latitudes are not only highly productive, but also have relatively high sedimentation rates, making them important carbon burial grounds. A major gap in our understanding of this carbon burial in high latitude ocean sediments has been a lack of comparison between the inorganic and organic components of blue carbon, partly due to limited collaboration between benthic geochemists (who mainly focus on organic carbon burial in sediments) and biologists (who mainly focus on inorganic carbon accumulation at the seafloor). This project offers a unique opportunity to combine approaches, expertise and data from both disciplines, to compile and compare carbon burial rates in some of the most understudied parts of our oceans that are most seriously affected by modern climate change. In addition to carbon, the project will study the fate and burial rates of organic and inorganic nitrogen in the same sediment samples, as nitrogen is currently the biolimiting nutrient in the Arctic Ocean, and its increased removal to the seabed could have implications for the carbon cycle as well.

Objectives

1)   Determining quantity and accumulation rates of inorganic and organic carbon and nitrogen in Arctic and west Antarctic shelf sediments using geochemical tools.

2)   Determining the quantity of blue carbon in Arctic and Antarctic shelf locations by applying an image analysis software to seafloor pictures taken with a benthic camera lander system.

3)   Comparing estimates of organic carbon and blue carbon as determined by geochemical analyses of sediments and the analyses of seafloor images.

Comparing carbon and nitrogen parameters from the Arctic and Antarctic, and building a budget of carbon and nitrogen burial in high latitude shelf seas.

Approach & training

Figure 3: Megacorer tubes filled with ~35 cm of sediment from the Barents Sea, including a sponge in the left tube (courtesy of J Faust)

For this project, samples and data have been gathered by Drs März, Barnes and Faust and collaborators in the frame of the ongoing ChAOS and ASCCC projects. These are available at the University of Leeds and the British Antarctic Survey (BAS), and comprise high-resolution images from selected sites on both the Arctic and Antarctic seafloor (Fig. 1) as well as sediment samples (down to ~35 cm depth) at the locations where the images were taken (Fig. 3). For key sites, complementary data on the inorganic and organic geochemical sediment composition and macro- to microbiology can be obtained from collaborators on the ChAOS and ASCCC projects, providing the student with a unique set of multi-disciplinary background data. In addition, this PhD project likely offers the unique opportunity to join an expedition onboard the RRS James Clark Ross to the Barents Sea in summer 2019 (possibly also during summer 2018) to collect additional samples and data. The analytical approach will be two-fold, with a geochemistry-focused part at the University of Leeds (Cohen Geochemistry Laboratories), and a biology- and image analysis-focused part at BAS.

The geochemical component to this project will include analyses of the bulk sediment samples (organic/inorganic carbon and organic/inorganic nitrogen contents and isotopes, led by Dr Newton) and sequential leaching methods to extract different metal phases and the associated carbon fractions (led by Drs März and Faust). Selected samples, and analogue samples created in the laboratory, will be analysed at very high spatial and chemical resolution using the latest synchrotron nanoprobes, to further investigate the mineral-organic couplings and how these might promote carbon stabilization and burial (led by Dr Peacock).

The biological component of the project will involve several visits to BAS, where the student will be trained by Dr Barnes in processing seafloor imagery and carbon per age/per species calculations from biota samples. BAS has benthic biota samples from around shelf Antarctic seas, which the student will have access to for both training (identification of key species) and sample processing (carbon calculations). BAS also has additional training resources including an ambient aquarium with living Antarctic benthic fauna, a bank of images of biota and a polar-centric library. This project will focus on samples collected from west Antarctic shelf seas which are hotspots of sea ice loss.

The student will be trained in geochemical procedures and analyses by Drs März, Newton, Peacock and Faust who have substantial experience in extracting different metal phases from sediment samples and total acid digestions, analysis of dissolved phases using AAS, ICP-OES and ICP-MS and of solid samples using XRD, CN combustion analysis and IRMS, and synchrotron-based spectroscopy. Hands-on training and support will further be provided by highly qualified technicians in the Cohen Laboratories. At BAS, Dr Barnes will provide practical training and expertise into both Antarctic shelf systems in general, and into blue carbon burial and the required image analysis techniques in particular. The successful candidate will have access to a wide range of training workshops (scientific writing and presentation skills, statistics, science communication and outreach), and will be supported by the supervisors in preparing conference presentations and peer-reviewed publications. Additional perks of this project include the close links to several larger, multi-disciplinary and multi-institutional projects that involve shipboard expeditions to the polar oceans, providing the student with a unique opportunity for networking and seagoing experience.

Student qualification

The successful candidate should have an excellent degree in an Earth Science or closely related subject, or Environmental Sciences discipline, a strong background and keen interest in fieldwork, analytical skills and interdisciplinary research, ideally experience in conducting a research project and presenting research results to the wider scientific community.

For further information, please contact

Dr Christian März

Associate Professor in Biogeochemistry

School of Earth & Environment

University of Leeds

LS2 9JT Leeds

United Kingdom

Email: c.maerz@leeds.ac.uk

Phone: 0113 34 31504

Homepage: http://www.see.leeds.ac.uk/people/c.maerz

Twitter: ChAOS@Arctic_Seafloor

Related undergraduate subjects:

  • Earth science
  • Earth system science
  • Environmental science
  • Geochemistry
  • Geological science
  • Geology
  • Geoscience
  • Natural sciences
  • Oceanography