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Ironing out the carbon cycle: Carbon burial associated with iron oxides in Arctic shelf sediments

Dr Christian Maerz (SEE), Prof Caroline Peacock (SEE), Dr Johan Faust (SEE)

Project partner(s): IsoAnalytical (CASE)

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

Summary

A key question around organic matter burial in seafloor sediments is: What controls the capability of sediments to accumulate and stabilise organic matter? Over the last few years several ground-breaking studies have highlighted the importance of highly reactive iron (hydr)oxide minerals in the sediments, suggesting that these particles might be able to bind organic matter, and possibly even transform organic carbon, rendering it resistant to degradation and thus promoting its preservation and burial. This potential process for the accumulation and stabilisation of organic matter has come to be known as the “rusty carbon sink”. However, our understanding of the coupling between reactive iron and organic matter is currently limited by a number of important questions: How much organic matter is bound to exactly which iron (hydr)oxide minerals? Are different organic compounds more susceptible to binding to iron (hydr)oxides? Do iron (hydr)oxides stabilise organic matter against microbial oxidation, and does organc matter protect iron (hydr)oxides from microbial reduction? How stable is the iron-organic matter coupling during burial into deeper sediments? And last but not least, do current methods to quantify iron-bound organic matter produce reliable data? To answer these questions Drs März, Faust and Prof Peacock are investigating exactly how iron (hydr)oxides bind and stabilise organic matter and thus protect it from degradationin the frame of several ongoing research projects at the University of Leeds.

This PhD project will provide a vital new component to these ongoing research efforts by investigating the iron-organic matter coupling from a fundamental point of view, and specifically in Arctic Ocean sediments. The Arctic is one of the most rapidly changing environments on the planet as global-warming takes hold, and a better understanding of the reactivity and cycling of organic matter, and specifically organic carbon, in this ecosystem is urgently required. As an integral part of two ongoing research projects the successful PhD student will be embedded in a vibrant and active research community, and will have the opportunity to present their research at national and international meetings, and help develop and lead a number of peer-reviewed publications. 

As a first step, the PhD student will test and improve existing methods to quantify iron-bound organic carbon by preparing reference materials containing varying amounts of different types of iron (hydr)oxides and organic compounds, and extracting them using the typically used method for iron-bound organic matter extraction. Following this fundamental approach to evaluate and improve the extraction method, the PhD student will apply the (potentially revised) extraction method to surface sediments from the Arctic Ocean to better understand how the association of iron with organic matter is controlled by variable environmental parameters (e.g., primary productivity, sea ice cover, proximity to land). Subsequently, in an attempt to quantify how stable the iron-organic coupling is in Arctic marine sediments over longer timescales (1,000s of years), the PhD student will analyse sediment samples that have been buried beneath the seafloor and have experienced early diagenetic processes. 

All analyses will be conducted in the Cohen Geochemistry labs at the University of Leeds and the student will have the opportunity to look at the iron-organic matter coupling in very fine detail using an especially powerful type of microscopy and spectroscopy available at the world-leading Diamond Light Source synchrotron facility near Oxford. Preparation of iron-organic matter reference materials is currently being developed, so the PhD student will benefit from world-leading expertise available at Leeds. A unique set of Arctic Ocean sediment samples and relevant background data has also been gathered by Drs März, Faust and collaborators, and these samples are available for investigation. For key sites, complementary data on the inorganic and organic geochemical sediment composition and macro- to microbiology can be obtained, providing the student with a unique set of multi-disciplinary background data. To study the effect of the proximity to land, sediment samples from fjords in Svalbard and northern Norway are available for this PhD project from earlier research cruises. In addition, this PhD project offers the unique opportunity to join a research expedition onboard the RRS James Clark Ross to the Barents Sea in summer 2019 to collect additional samples and data. Due to our very close collaboration with Norwegian scientists, there might be further opportunities to join research expedition to the Arctic Ocean onboard the Norwegian icebreaker Kronprins Haakon.

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Related undergraduate subjects:

  • Earth science
  • Earth system science
  • Environmental science
  • Geochemistry
  • Geological science
  • Geology
  • Geoscience