Carbon cycling in a warming world: a deglacial test case

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences

Abstract

Projections of future climate change require us to understand the interactions between carbon and its main reservoirs, including the large natural exchanges between ocean, land and atmosphere. Studies have also shown that uncertainties in modelling the carbon cycle are as important as uncertainties in modelling the physical climate system. Thus it is vital that we develop a better quantitative understanding. The natural component of the carbon cycle has already been significantly perturbed today, so studying the natural processes before human interventions is an important additional test of our knowledge and understanding. This is particularly true when there were abrupt perturbations on the climate system that occurred on human-relevant timescales. A prime target is the transition out of the glacial period, some 20,000 years ago. The transition saw global temperatures increase by ~ 3-5C, sea level rise by 120m and atmospheric pCO2 increase by ~100ppmV. Importantly, a large portion of these changes occurred in rapid events which overprinted the long term deglacial transition.

We still do not fully understand how CO2 levels in the atmosphere increased over this time although processes that alter the balance of carbon between the ocean, land and the atmosphere are certainly critical. Indeed, the leading hypothesis to explain the major rise in atmospheric CO2 calls upon release of carbon from the deep ocean that accumulated from the decay of organic matter as it rains down through to the ocean's depths. At the same time changes in the terrestrial biosphere are thought to have contributed through processes including permafrost melting. This link between biological productivity and the exchange of carbon between its reservoirs is a timely topic given concern over the fate of anthropogenic carbon emissions - including ocean acidification and suggestions of long-term excess storage of carbon in the deep sea. However recent studies have provided data that contradict this view of carbon storage and exchange. Evidence has pointed towards climatically-triggered release of geologically-held carbon. The solid Earth contains vast reservoirs of carbon, so small changes in release have the potential to be important to the carbon budget. If release of geologic carbon is indeed sensitive to changes in the climate system, then this process may also be triggered under future climate scenarios. Constraining the potential impact of geologic carbon released in the past has the potential to provide critical new information in projecting future change.

The interdisciplinary project team proposes an ambitious programme combining field work, geochemical analyses and integrated modelling to provide specific tests of the competing hypotheses that have been used to explain the rising CO2 levels at the end of the glacial period. We will particularly focus on using radiocarbon to help diagnose the distinct sources of carbon. New data will be based on geochemical analyses on precisely dated deep-sea coral skeletons collected from locations which are key to these tests. We will mount the first Remotely Operated Vehicle research expedition to the Eastern Equatorial Pacific dedicated to systematic collections of corals from depths where release of geological carbon is hypothesised to have occurred. Our second focus will be on the North Atlantic (samples in hand) where changes in ocean circulation and linkages to isolated basins may have played a key role in releasing carbon from the deep ocean. We will integrate these data with existing knowledge and use them in conjunction with climate modelling (including intermediate complexity models and state of the art General Circulation Models) to explore which processes are most important to the Earth system in a warming world. We will also be well placed to formulate a broad synthesis of the processes controlling the carbon cycle during the most pronounced rapid warming period of recent Earth history.

Planned Impact

Beyond the scientific community, we have identified five distinct end-user groups. Through the arc of the project we will continue to seek out additional opportunities to maximize the impact of our research.


a) Galápagos National Park and INOCAR: Our proposed research sites will explore the deep submarine flanks of the Galápagos islands and platform (~3500-500m), many of which have never been observed or sampled, so the proposed study will provide key data that will enhance the conservation efforts of the Charles Darwin Research Station and Galápagos National Park. Data from the cruise will be provided to INOCAR and the Ecuadorian government to help with the design of new limits for marine protected areas in the Galápagos (see letters of support). Part of our broader impacts effort will be devoted to raising awareness of the importance of the sub-photic benthic communities to the maintenance of the overall Galápagos ecosystem.


b) General Public - Project Website and Public Lectures and Events: Our project provides an excellent opportunity for public engagement regarding the protection of deep marine ecosystems, the carbon cycle and associated climate change. This effort will be linked with existing and new outreach websites. We will publicise our research through public talks, Facebook and Twitter, providing links to the website and our latest talks, press releases, and papers. Results will also be posted on the websites of participant organisations, e.g. through the Cabot Institute at UoB.


c) Undergraduates: Undergraduate students will be engaged directly in the project through hands-on laboratory and modelling expertise, helping them to develop a passion for scientific endeavour, and a deep knowledge of the research field. Summer projects and final year projects provide a great opportunity for advisors and students to integrate education and research beyond the classroom, advance discovery and understanding, while providing training on solving scientiroblems and laboratory skills. Where possible, undergraduates will be included in the field program. Major findings will also be posted on the UoB Departmental Facebook pages and included in lecture material at UoB and in the departments of collaborating Universities, allowing the wider undergraduate community to maintain awareness of cutting-edge research activities.


d) Training and mentoring of two PDRAs: This project will enhance the career development of two PDRAs. PIs LFR and PV have excellent track records in actively training and advising postdoctoral scholars.


e) Supporting Women in STEM: The proposal supports a mid-career female investigator who will provide mentorship and role models for junior women in STEM subjects. We will include sections on our websites that touch on how women provide leadership in STEM subjects, from being Chief Scientist on a research cruise, to leading research teams as well as the paths taken to get here. Efforts will be made to include female undergraduates in the project through direct internships and through outreach presentations. Impact will be assessed by website traffic and event attendance.

Publications

10 25 50
 
Description The project has focussed on two main areas so far:

(a) Increasing the spatial and temporal resolution of deglacial radiocarbon records. We have established that the low latitude Atlantic and Pacific oceans exhibited similar radiocarbon patterns during deglaciation, and that their geochemical composition was also similar to the Southern Ocean. These findings are suggestive of a Southern Ocean source feeding the low latitude oceans. We have carried out dating work on corals from the Greenland Margin and Orphan Knoll. Whilst there are deglacial corals on Orphan Knoll, the oldest samples from Greenland Margin extend back to the early Holocene, potentially reflecting the melt back of the ices sheets, and sealevel rise.

(b) Compiling and increasing data from the Last Glacial Maximum (LGM) as a reference for modelling and interpretation of the deglaciation. Within these data we have established a distinct shift in Atlantic circulation within the LGM which would not be resolvable in sedimentary records.

Planning of the research expedition to the Eastern Equatorial Pacific is underway, and is currently scheduled for early 2021.
Exploitation Route These data will be of value to climate modelers and paleoclimate specialists, as well as those interested in the development of deep sea ecosystems.
Sectors Education,Environment

 
Description Dan Fornari - WHOI 
Organisation Woods Hole Oceanographic Institution
Country United States 
Sector Charity/Non Profit 
PI Contribution We will provide collaborative access to the research expedition
Collaborator Contribution Fornari will form part of the expedition team bringing expertise in mapping and imaging
Impact No outcomes yet, although papers submitted. Multidiscplinary - marine geology, oceanography, geochemistry
Start Year 2015
 
Description Mathis Hain - UC Santa Barbara 
Organisation University of California, Santa Barbara
Country United States 
Sector Academic/University 
PI Contribution Observations and analyses to contribute to modelling
Collaborator Contribution UCSB will use modelling to test observations and ideas from the proposal
Impact Observations and modelling. A paper has been submitted, but yet to receive reviews.
Start Year 2019
 
Description Herdman Symposium 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact Seminar as part of the Herman Symposium organised by Undergradute Students at the University of Liverpool open to public.
Year(s) Of Engagement Activity 2020
 
Description Public talk - Boston Aquarium 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Large publich outreach talk 'The Carlson Lecture' organised by MIT at the Boston Aquarium, also live streamed and available on line.
Year(s) Of Engagement Activity 2019
URL https://www.youtube.com/watch?v=gVsv0Xn4YhQ