EXport Pathways Out of the Southern ocean and the Effect on anthropogenic carbon sequestration (Expose)

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes

Abstract

New approaches will be applied to a hierarchy of ocean computer model simulations to address a major issue facing climate science: how anthropogenic carbon released in the atmosphere is injected and locked away at more at 1 km below the Southern Ocean surface ? The World's oceans slow the rate of climate change by absorbing a large proportion of CO2 emission due to human activity. The Southern Ocean is cold and windy, which favours the exchange of CO2 with the atmosphere. As a result, half of the carbon sequestrated in the world's oceans has been transferred through the Southern Ocean surface, providing therefore a significant buffer for climate change.

It is proposed to study the dynamics of the connection between the ocean surface and the deep ocean interior. Are water-masses and carbon slowly and uniformly diffused toward the deep sea or conversely are there narrow and intense carbon motorways plunging in the deep sea. Sparse ocean observations tend to show the latter, but the dynamics and the localisation of these pathways have never been studied. This is at odds with the evidence that these exports have a strong and direct impact on climate. The goal of this project is to gather a variety of recently developed very powerful and complementary tools to apply to the specific question of the dynamics of the Southern Ocean carbon sequestration. Specifically, we will investigate where the currents exporting water-masses and carbon in the deep ocean layers form and what is their rate of export. But more importantly, using a variety of computer model simulations we will investigate what are the processes that control the localisation and rates of export. This is a major question if we are to predict whether Southern Ocean carbon sequestration is likely to change in the future, with dramatic impact on climate.

This project at the cross-road of physics and biogeochemistry will extract the best of each, will contribute to new insight into the dynamics of the Southern Ocean circulation and will have implications for climate feedbacks that will lead to major advances in our understanding of climate and in our ability to predict future change.

Planned Impact

Understanding regional ocean carbon storage is vital for our national and international interest through the direct impact it has on regional climate. The project will directly meet this need, by leading to major advances in our understanding of the Southern Ocean meridional overturning circulation, which is critical for transport and distribution of nutrient, carbon, heat, and freshwater and ultimately for climate. Specifically the project will deliver a better understanding of the physics that allows atmospheric anthropogenic carbon dissolved at the surface of the ocean to be locked away from the atmosphere and injected in the deep sea for hundreds to thousand years. The proposed study is a major new UK initiative in understanding the large-scale ocean circulation in the Southern Ocean and its role in climate change.
The main beneficiaries of this work are likely to be:

i. IPCC climate science, as well as modelling, biogeochemical, and fluid dynamics community: Although these are academic/science base users we list these here (in addition to the main science case), as uptake and use of our project's findings by this community are a vital pathway to achieving further impact in the user groups listed below. The benefits to the wider community will be realised through science journal publications and international science meetings, as well as through the hosting of 2-day workshop, which will bring together leading scientists from the academic sector. A key aspect of the workshop will be the interdisciplinary nature; it will bring together scientists who may not ordinarily collaborate.

ii. The Met Office Hadley Centre: the Met Office Hadley Centre is a world-leader in climate research and modelling and unique in integrating observational analysis with climate modelling, using a hierarchy of models with various configurations, to deliver policy-relevant climate science for its government clients. Our results will directly input in the representation of water-mass and carbon storage in the Southern Ocean by pointing to directions for future model improvement. These groups are tasked with developing accurate models to predict changes in air-sea exchange, ocean dynamics and thereby climate change. Ultimately the results from these models inform UK policy-makers. Thus more accurate predictions enable a better-informed decision making process.

Iii. Department of Energy and Climate Change (DECC) and Department of Environment, Food and Rural Affairs (DEFRA): DECC are responsible for advising the UK government on climate risks and developing mitigation strategies at UK, European and international scales and for international adaptation. DEFRA is responsible for advising on UK adaptation strategies. Our work contributes to their needs as positions rely on an accurate climate evidence and impacts base and the best possible projections of future changes, including the possible implications of previously unaccounted carbon cycle feedbacks. Direct communication to these institutes will be made through Emily Shuckburgh, who is presently on secondment to DECC, and by continued interactions with Chris Sear (DECC) and Pete Newman (DEFRA) after the secondment has ended.

iv. General Public: Carbon storage and sequestration are a high-profile and high-impact topic and we envisage there being considerable general interest in this topic. The general public will be engaged through an event organised locally in Cambridge, targeting of a wide range of adults who would not necessarily normally express an interested in science. We will present a hands-on experiments as well as scientific Question and Answer with a scientist using a novel and creative means of engagement (see Pathways to Impact for details). In addition to this event, we will work closely with the BAS and NERC press offices to ensure effective engagement with the media.

Publications

10 25 50
 
Description This work is progressing well and several findings have been made so far. Primarily we have discovered that the heavily used and much published SOSE model framework is inherently unstable over long periods. While it has been heavily used to simulate the Southern Ocean for periods of 6 or less years, we have found that running this model out for 20+ years reveals significant instabilities, notably in the subpolar gyres. These tend to develop unphysical convection, leading to the model collapsing after around 10 years. Dr. Jones has made significant advances in discovering why this instability exists, as well as fixing it. It seems that freshwater fluxes from glacial run off and iceberg calving are significantly too low. This has been corrected and a free running version of SOSE, dubbed BASSOON, has been run for 30+ years without significant drift. This version now forms the basis for our experiments testing where and how key water masses move around the ocean.

He has also demonstrated that the object of the project, looking at current pathways from the southern ocean into the subtropics, occurs at a few specific locations. These appear to be in the south-east corners of the relevant gyres in the Atlantic/Indian and South Pacific. The timeframe of this transport appears to be on the order of decades, with half lives for tracers within the various ocean basins appearing to be around a decade before they are advected out of the Southern Ocean.

With the forward running pathways largely explored (and consequent research papers submitted) the project is now moving to its final phase where an adjoint model (essentially running backwards) is being used to explore how changes in surface forcing such as winds and heat fluxes can influence these export pathways.
Exploitation Route This work on correcting the gyre spin up (notably via improved representation of surface freshwater forcing and glacial runoff), will feed directly into improving the SOSE maintained by Matt Mazloff of the Scripps institute of oceanography. This is a very widely used product, so the improvements Dan is adding will be widely felt. The ultimate outcome of the project, looking at export pathways and their sensitivity to surface forcing, will be an important addition to climate models, notably those run by the UK Met Office, who will be able to compare their export strengths with those rigourously described and tested within EXPOSE.
Sectors Government, Democracy and Justice,Other

 
Description Dr. Dan Jones has made a concious effort to raise public conciousness of climate change and more specifically the Southern Ocean's role as a mediator and driver of global heat and carbon trends into the 21st century. This has been through a number of public/lay audience talks, delivered to various groups within Cambridge, including: - Co-organised and hosted Cambridge Science Festival Event "Everything you always wanted to know about climate science (but were too afraid to ask)". - Participated in "The Ocean Debate" at the 2016 Cheltenham Science Festival - Interviewed on The Naked Scientist podcast (available here: https://goo.gl/XLXwpr) - Maintained active twitter account (@DanJonesOcean), mostly science-relevant content - Interviewed for BBC Radio Cambridgeshire (recorded 7/3/16) In addition he has engaged with the Met Office on climate model development, and is showing how pathways of heat and carbon from the atmosphere into the deep ocean interior are sensitive to the parameters and setup of various climate models. It is envisaged that this work will continue into the future and as the research develops and solidifies will feed into improvements of the global coupled climate models run by the met office, and ultimately contribute to reducing the uncertainty in future climate prediction. In addition, this work has been central to developing the use of adjoint models within the UK earth sciences community. Dan Jones initiated, organised and led a workshop on the use of adjoint models for earth system sciences. This drew together many modellers from across the UK, as well as bringing in expertise from overseas. The result of this workshop has been a concerted effort by the participants to improve the supercomputing facilities within the UK to facilitate the running of adjoint models. This new technique has the potential to significantly improve our ability to attribute changes in earth systems to forcings, and thus understand the working of our planet. This work has led to an ARCHER grant to develop an optimised adjoint ocean model framework on the UK supercomuter, available for general use by the research community.
First Year Of Impact 2014
Sector Environment,Other
 
Description Dan Jones->Patrick Heimbach 
Organisation Massachusetts Institute of Technology
Country United States 
Sector Academic/University 
PI Contribution We are precipitating the development of Adjoint modelling, specifically with the MITgcm within the UK community.
Collaborator Contribution Patrick has supplied considerable expertise, time, training and code to the development of an adjoint to the MITGCM within the UK community, specifically at BAS with the intent of application to the EXPOSE project.
Impact Development of a framework for the adjoint of the MITgcm within the uk community, and wider uptake of adjoint modelling in general.
Start Year 2014
 
Description Dan->Matt Mazloff 
Organisation University of California, San Diego (UCSD)
Department Scripps Institution of Oceanography
Country United States 
Sector Academic/University 
PI Contribution Dan Jones has taken the SOSE model developed and provided by Matt Mazloff of Scripps and run in forward from its initial settings for 20+ years. This has demonstrated that this model is unstable, and rapidly develops polynyas in the Antarctic subpolar gyres. These in turn drive unphysical convection, which ultimately lead to model blow up. Dan has been working on stabilising this model and has provided much technical feedback on model setup, as well as working towards corrected and more physically based surface forcing fields, developed in conjunction wtih BAS glaciologists.
Collaborator Contribution They have provided us with the code and support nessecary to run the SOSE model on our own machines.
Impact Corrected Antarctic freshwater forcing fields.
Start Year 2013