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Overview

Theo Murphy meeting organised by Professor Timothy Eglinton FRS, Dr Heather Graven, Professor Susan Trumbore and Professor Peter Raymond.

This meeting will bring together leading experts in the carbon cycle and global change science together with radiocarbon specialists in order to discuss the merits, feasibility and scope of a global-scale radiocarbon measurement and synthesis program for improved assessment of current, future and managed changes to the Earth's carbon cycle and greenhouse gas emissions.

Recorded audio of the presentations will be available on this page after the meeting has taken place. Meeting papers will be published in a future issue of Philosophical Transactions of the Royal Society A.

Poster Session

There will be a poster session at the meeting venue. If you would like to apply to present a poster please submit your proposed title, abstract (not more than 200 words and in third person), author list, name of the proposed presenter and institution to the Scientific Programmes team no later than Monday 25 April 2022. Please include the text 'Poster abstract submission' in the email subject line. Please note that places are limited and posters are selected at the scientific organisers' discretion. Poster abstracts will only be considered if the presenter is registered to attend the meeting.

Attending this event

This meeting is intended for researchers in relevant fields.

  • Free to attend
  • Limited places, advance registration essential

Enquiries: contact the Scientific Programmes team

Organisers

Schedule


Chair

09:05-09:35
Radiocarbon and the changing global carbon cycle

Abstract

Anthropogenically-induced climate change is directly linked with perturbations to the global carbon cycle brought on by emissions of greenhouse gases associated with fossil fuel combustion and land-use change. Radiocarbon is a powerful tool for constraining carbon sources and carbon cycle dynamics in the Anthropocene given its absence in fossil fuels, and its depletion in other “pre-aged” C reservoirs (e.g., mineral soils, permafrost, deep ocean) that exchange with atmosphere and surface biosphere on centennial or longer timescales. Recent technological advances have greatly enhanced capacities for natural-abundance 14C measurement, and these advances coincide with burgeoning 14C databases, as well as the emergence of next-generation carbon cycle and earth system models. Implementation of comprehensive 14C measurement programs designed to provide crucial constraints on models, examine underlying processes, and detect (and quantify) the pace of change, are thus timely. By way of illustration, this presentation will highlight a new initiative that seeks to develop a first, national-scale 14C inventory spanning all major carbon pools. This information will be used to assess vulnerability of, and interplay between, different C pools, as well as provide a crucial benchmark against which to gauge past and future changes in carbon stocks and to constrain carbon-cycle models.

Speakers

Professor Timothy Eglinton FRS

Department of Earth Sciences, ETH Zürich, Switzerland

09:35-09:50
Discussion
09:50-10:20
How radiocarbon could help the historical global carbon budget

Abstract

The global carbon budget assesses all components of the anthropogenic perturbation on the carbon cycle. It is now well understood that the atmospheric CO2 increase amounts to only about 50% of the global emissions from human activities (fossil fuel combustion and land use changes). The oceans and the terrestrial ecosystems are acting as carbon sinks, removing together about 50% of the anthropogenic emissions. While the mechanisms for these carbon sinks are clearly identified and relatively well quantified for the ocean, the picture is less clear for the land sink. As atmospheric CO2 increases, so does plant photosynthesis, leading to increased carbon stored in vegetation first but then in litter and soils. These increase in carbon stocks will eventually lead to an increase in ecosystem respiration.  The land sink can hence be seen as the transient imbalance between a growing photosynthesis term and a delayed growing respiration term. The lag between the growth of these fluxes is directly controlled by the residence time of carbon in vegetation and soils. Radiocarbon has the potential to help better quantifying the “active” soil carbon, that is the fraction of the global soil carbon that is already affected by the atmospheric CO2 driven perturbation. 

Speakers

Professor Pierre Friedlingstein

University of Exeter, United Kingdom

10:20-10:35
Discussion
10:35-11:00
Break
11:00-11:30
Past and future changes in atmospheric 14C and 13C

Abstract

The ratio of 14C/C in atmospheric CO214CO2) has changed dramatically over the Industrial Period due to human activities. Emissions of CO2 from fossil fuel combustion reduce Δ14CO2 because 14C is absent in million-year-old fossil fuels, which have been stored for much longer than the radioactive decay time of 14C. Atmospheric Δ14CO2 rapidly increased in the 1950s to 1960s because of 14C produced during nuclear bomb testing. The resulting trends in Δ14C in atmospheric CO2 are influenced not only by these human emissions but also by natural carbon exchanges that mix carbon between the atmosphere and ocean and terrestrial ecosystems. This mixing caused Δ14CO2 to return toward preindustrial levels in the first few decades after the spike from nuclear testing. More recently, as the bomb 14C excess is now mostly well mixed with the decadally overturning carbon reservoirs, fossil fuel emissions have become the main factor driving further decreases in atmospheric Δ14CO2. Presently, Δ14CO2 is dropping below the preindustrial level of 0 per mil. In the future, Δ14CO2 will continue to change. The changes are mainly determined by global fossil fuel emissions. We present simulations of future atmospheric Δ14CO2 and discuss their effect on other carbon reservoirs and various applications using 14C.

Speakers

11:30-11:45
Discussion
11:45-12:15
Lightning Talks
12:15-12:30
Discussion
12:30-13:30
Lunch

Chair

13:30-14:00
AMS and future advances in 14C measurement

Abstract

The technical evolution of Accelerator Mass Spectrometry (AMS) over the last ten years has boosted research with radioactive tracers. Dedicated high performing instruments are covering the needs of a wide user community to get reliable isotopic ratio measurements with uncertainties in the range of 10 - 20 radiocarbon years. But not only the analytic quality has increased. Several established AMS laboratories have renewed their instrumentation and new laboratories have started operation. Thus, the overall measurement capacity has now reached a volume making research possible requiring large number of individual analyses. It enables the analysis of tree ring records in annual resolution which will be most beneficial not only in the classical dating applications. The access to direct CO2 gas measurements is essential to applications that need capability of analysis of samples in the low ug range. This is of particular importance in connection with global carbon cycle studies. Radiocarbon in the ocean has also gained importance. Bomb produced radiocarbon is still traceable in the global oceans, and detailed analyses will help to reinforce the data basis on ocean circulation. Recent progress in sample preparation makes it much easier to analyse large sample series with high data quality.

Speakers

Professor Dr Hans-Arno Synal

ETH Zürich, Switzerland

14:00-14:15
Discussion
14:15-14:45
Modelling radiocarbon dynamics in the Earth system to infer process rates in the global carbon cycle

Abstract

Radiocarbon can be used as a tracer of the global carbon cycle to infer rates of exchange among different reservoirs. It can also be used to improve the representation of different processes in Earth system models (ESMs) and test their predictions. Although many ESMs do not represent radiocarbon explicitly, it is now possible to compute the dynamics of radiocarbon based on existing model output such as the Coupled Model Intercomparison (CMIP) archive. This contribution will introduce a new set of concepts and methods to obtain radiocarbon dynamics from numerical model output, and to compare radiocarbon observations in the context of an underlying distribution of carbon ages. These concepts provide new opportunities to integrate radiocarbon observations with ESMs and to better forecast future trajectories of the global carbon cycle as well as the fate of carbon of fossil fuel origin.

Speakers

Dr Carlos A. Sierra

Max Planck Institute for Biogeochemistry, Jena, Germany and Swedish University of Agricultural Sciences, Uppsala, Sweden

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Estimating Fossil CO₂ Emissions from Atmospheric Measurements of Radiocarbon in CO₂

Abstract

Fossil-derived CO₂ is completely devoid of ¹⁴C. Therefore, the ¹⁴C content of atmospheric CO₂, expressed as Δ¹⁴CO₂, is a very good estimator for recently emitted fossil CO₂. Measured gradients of Δ¹⁴CO₂ in the atmosphere can be used to disentangle fossil and non-fossil CO₂ fluxes at local, regional, and national scales. At the local scale, this can be used to estimate fossil CO₂ emissions from total CO₂ enhancements observed by other platforms such as in situ sensors and satellites. At regional and national scales, Δ¹⁴CO₂ measurements can be used to construct fossil CO₂ emission estimates with accuracy comparable to “bottom-up” inventory estimates. Besides providing an independent verification of emission inventories, such regional estimates also play a crucial role in diagnosing the terrestrial carbon cycle. Accurate atmosphere-based estimates of fossil CO₂ emissions at urban to regional scales are not possible from CO₂ measurements alone, irrespective of the measurement platform, due to interference from the land biosphere. A coordinated effort at measuring and modelling Δ¹⁴CO₂ in the atmosphere can therefore lead to accurate atmosphere-based estimates of fossil CO₂ emissions, in direct support of regional and national emission verification and mitigation efforts.

Speakers

Dr Sourish Basu

Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt MD, USA

16:00-16:15
Discussion
16:15-16:45
Lightning Talks
16:45-17:00
Discussion

Chair

Professor Timothy Eglinton FRS

Department of Earth Sciences, ETH Zürich, Switzerland

09:00-09:30
Radiocarbon and permafrost dynamics

Abstract

Soils in the northern permafrost region store 1,460 to 1,600 petagrams of organic carbon, almost twice the amount contained in the atmosphere. Permafrost thaw and the microbial decomposition of organic carbon is considered one of the largest positive feedbacks from terrestrial ecosystems to climate in a warmer world. Yet, the rate of release is highly uncertain but crucial for predicting the strength and timing of this carbon cycle feedback. This was studied in a tundra landscape undergoing widespread permafrost thaw, where net ecosystem carbon exchange and the radiocarbon age of ecosystem respiration were measured to determine the influence of old carbon loss on ecosystem carbon balance. Sustained transfers of carbon to the atmosphere must come from old carbon, which forms the bulk of the permafrost carbon pool that accumulated over thousands of years. Isotope partitioning of respiration sources using radiocarbon revealed highest old carbon release with increased thaw and where soils became drier. These data document significant losses of soil carbon with permafrost thaw that, over decadal time scales that could make permafrost a large biospheric carbon source in a warmer world. This will also be influenced by site soil moisture/drainage that is an indirect consequence of changing permafrost.

Speakers

Professor Dr Ted Schuur

Northern Arizona University, Flagstaff, USA

09:30-09:45
Discussion
09:45-10:15
Radiocarbon and the Cycling of Dissolved Organic Matter (DOM)

Abstract

The >5000-year radiocarbon age of much of the 630±30 Pg C marine dissolved organic carbon (DOC) reservoir remains an enigma in the marine carbon cycle. Current models hypothesize that radiocarbon (14C) depleted DOC (DOCr) is present as a uniform reservoir with a constant 14C signature throughout the ocean that is the result of the persistence of DOCr over multiple ocean mixing cycles. However, key requirements of this model, including direct observations of DOCr with similar 14C signatures in the surface and deep ocean, have never been demonstrated. Furthermore, the diversity of radiocarbon signatures in marine DOM remains unconstrained. Studies have fractionated DOM into operationally defined fractions to interrogate the radiocarbon distribution in DOM, while others have approached this problem using mixing models to reproduce the signatures observed during the serial oxidation of DOM and DOM fractions. Some of these analyses provide conflicting results. A few studies have also attempted compound specific radiocarbon measurements and these have primarily targeted the most labile fraction, demonstrating unequivocally that recently produced DOM does accumulate. This talk will summarise previous results, identify what is still unknown, and discuss where opportunities exist for making progress toward constraining the cycling of carbon through marine DOM.

Speakers

Professor Lihini Aluwihare

Scripps Institution of Oceanography, UC San Diego, San Diego, USA

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Recent changes in ocean DI14C and implications for ocean circulation

Abstract

Anthropogenic perturbations from fossil fuel burning and nuclear bomb testing have created a useful transient tracer of ocean circulation from measurements and modelling of dissolved 14C. The atmospheric 14C/C ratio (∆14C) peaked in the early 1960s and has decreased now to nearly pre-bomb levels. We present the first analysis of a new decade of observations from 2007 to 2016 which gives a comprehensive overview of the changes in ocean ∆14C since the 1990s. Surface ocean ∆14C decreased from the 2000s to 2010s at a similar rate as from the 1990s to 2000s (20‰/decade). In contrast to the period from the 1990s to the 2000s when denser waters gained 14C from the continued downward ventilation of bomb 14C, the extent of positive ∆14C between the 2000s to 2010s is much reduced. Comparison to two ocean models, the Community Earth System Model v2 (CESM2) and the Estimating the Climate and Circulation of the Ocean v4 (ECCOv4), shows evidence from ∆14C of decadal variability in the ventilation of Southern Ocean intermediate waters. The decrease in surface tracers from the 2000s to the 2010s is consistently stronger in observations than in these models, which may result from a reduction in vertical transport and mixing due to stratification.

Speakers

Joanna Lester

Imperial College London, United Kingdom

11:30-11:45
Discussion
11:45-12:15
Paleo-carbon cycle perspectives from radiocarbon

Abstract

Along with improving the accuracy of the radiocarbon chronometer, recording the natural variations of 14C is essential for our understanding of climate processes, solar activity, geophysics, and the biogeochemical carbon cycle. Marine radiocarbon integrates the influences of changing radiocarbon production, air-sea gas exchange at the sea surface, transport times within the ocean interior, and the mixing of water parcels with different transit times from the sea surface, and different sea-surface sources. The study of the variations of 14C in marine archives such as reef or deep-sea cores makes it possible to complete the calibration of the radiocarbon as well as to quantify the variations of the carbon cycle by comparing the atmospheric and oceanic series. Over the last decade, the possibility to date extremely small amounts of carbonates has allowed new research possibilities, but also led to the discovery of new sources of complexity, unaccounted or neglected previously. This implies revisiting and modifying a significant proportion of 14C records obtained previously. This revolution is similar to previous ones linked to other technological improvements (e.g., switch from beta counting to AMS for 14C in the 80s and from alpha counting to mass spectrometry for U-Th in the 90s).

Speakers

12:15-12:30
Discussion
12:30-13:30
Lunch

Chair

Professor Dr Susan Trumbore

MPI Biogeochemistry Jena, Germany

13:30-14:00
Prospects and challenges to monitor fossil CO2 at the European scale

Abstract

The European Integrated Carbon Observation System (ICOS) collects atmospheric air samples at 17 sites and analyses their 14CO2 activity as part of its atmospheric observation program. These samples allow for monitoring atmospheric 14CO2 trends and determining the amount of CO2 recently added to the atmosphere by fossil fuel combustion (ffCO2). This talk presents the latest ICOS 14CO2 data and discusses how they are affected by nuclear or local 14C emissions. We discuss possible correction or avoidance approaches and their associated uncertainties. Furthermore, the talk addresses the potential role that a 14CO2 observation network could play for the currently emerging satellite-based Copernicus CO2 Monitoring and Verification System and presents new results for using CO and NOx as fossil fuel CO2 surrogate tracers.

Speakers

14:00-14:15
Discussion
14:15-14:45
Radiocarbon in urban regions

Abstract

All nations have committed to reducing their greenhouse gas emissions through the Paris Agreement and their Nationally Determined Contributions.  While the policy directives are at the national level, the policies needed to meet these obligations are enacted at local scales.   Cities are therefore often leading the way in greenhouse gas emission mitigation efforts, both to address the climate challenge and for the many associated co-benefits.  To achieve these goals, detailed local emissions information resolved in space, time and by source sector, is needed both to assess the potential of carbon mitigation strategies and evaluate the success of such strategies.

State-of-the-art methods for determining local emissions use a combination of bottom-up inventory methods based on activity data and atmospheric observations of greenhouse gases.  A key challenge to atmospheric observations is that it is difficult to distinguish natural and anthropogenic CO2 emissions from concentration measurements alone. Radiocarbon observations resolve this challenge by separating fossil fuel derived CO2 (CO2ff) from other CO2 sources.  Studies from Indianapolis, Sacramento and Auckland demonstrate the application of radiocarbon observations to infer urban CO2ff fluxes and show that urban CO2ff emissions can be determined to better than 10% uncertainty.

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Using radiocarbon to understand opportunities and challenges for soil carbon sequestration

Abstract

Soils are the largest terrestrial pool of carbon and a large fraction of that carbon actively cycles between the soil and atmosphere. Even small land use, land management and climatic perturbations can have a large impact on the annual flux between the atmosphere and the soil. Radiocarbon measurements of bulk soil organic matter and various fractions of soil organic matter have revealed fundamental insights into the rate of loss or accumulation of soil carbon on human relevant time scales. These measurements have greatly improved our conceptual understanding of soil carbon cycling and have helped constrain numerical models of the soil carbon cycle. In this presentation, I will highlight several examples where radiocarbon has uniquely informed soil carbon cycle science and discuss where radiocarbon measurements can be better utilized to address emerging questions around soil carbon management for climatic benefits. 

Speakers

16:00-16:15
Discussion
16:15-17:00
Panel discussion and overview

Speakers

Professor Timothy Eglinton FRS

Department of Earth Sciences, ETH Zürich, Switzerland

Professor Dr Susan Trumbore

MPI Biogeochemistry Jena, Germany