Temporal variability of the carbon system across the Atlantic Ocean; causes and implications

Dr Peter Brown, Prof Toby Tyrrell, Dr Sue Hartman, Ms Allison Schaap
Rationale: 

Approximately 25% of the carbon dioxide (CO2) produced by human activities enters the ocean. Without this sink, the rate of CO2 buildup in the atmosphere would be larger than it is. Understanding what drives this CO2 sink and whether it will continue to operate at its current rate are key research issues, as is the associated ocean acidification. Climate models have predicted that oceanic CO2 uptake will weaken into the future but needs to be confirmed (and models refined where discrepancies occur) by high quality measurements.

However, large spatial heterogeneity exists for ocean CO2 uptake and it varies over numerous timescales (diurnal, monthly, seasonal, inter-annual) making monitoring challenging, and necessitating the use of multiple observing platforms, technologies and strategies to capture all modes of spatial and temporal variation in CO2 exchange. Coincident biogeochemical measurements where possible are also essential to help determine the relative contributions of biological and physical processes. Analysing time series data represents an important way of understanding the mechanisms driving planetary carbon cycling and offers the possibility to develop a three-dimensional picture of how ocean circulation, biological productivity, atmospheric forcing and plankton ecology combine together to regulate atmospheric CO2 uptake.

 

Methodology: 

The student will combine new observations with historical datasets from multiple sources. They will deploy carbon and biogeochemical sensors of different technologies (membrane sensors, equilibrator systems) on new Ship-Of-Opportunity (SOO) voyages (mooring servicing, hydrographic, transit cruises) that will analyse surface waters across subpolar/subtropical/tropical biomes sampling contrasting CO2 sink/source regions. This will improve our understanding of the drivers of variability over shorter timescales (diurnal/weekly/monthly/seasonal/interannual).

The lab analysis of discrete water samples collected on board (carbon, nutrients, phytoplankton) will add to historical NOC trans-Atlantic timeseries, enabling the determination of sub-decadal and decadal trends in biogeochemical datasets.

To place the new observations in spatial context (both horizontal and vertical), comparisons will be made to other measurement platforms, including high resolution long-term NOC Eulerian open-ocean observatory at Porcupine Abyssal Plain, as well as satellite-derived products and Biogeochemical Argo profiling float data. Although not all directly measure carbon, together these will provide biogeochemical information on how the ocean interior connects to the surface over wide geographical/temporal lengthscales

Ultimately, a simple model will be constructed (using BGC-Argo float, remotely sensed, fixed point and SOO-obtained data) to examine the controlling processes (mixing, biology, heat fluxes) of Atlantic air-sea CO2 fluxes, and their sensitivity to climate change and ocean acidification.

 

Location: 
NOC, Southampton
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at NOC. Specific training will include: deployment of sensors; laboratory sample analysis and interpretation; and the analysis of large-scale datasets including ships of opportunity, satellite and floats. As the project is highly multidisciplinary (applications from candidates with no oceanographic experience are welcomed) you will also be given guidance in acquiring the relevant background experience using existing University Masters lecture courses. You will be trained in the programming languages needed to carry out your dataset analyses, for instance Matlab and Python. You will present your work internationally. There will be an opportunity to participate on multiple research voyages, including the annual process study/instrumentation maintenance PAP observatory cruise.

 

Eligibility & Funding Details: 

Please check http://inspire-dtp.ac.uk/how-apply for details.

Background Reading: 

Macovei, V.A., S.E. Hartman, U. Schuster, S. Torres-Valdés, C.M. Moore, R.J. Sanders, 2020, Impact of physical and biological processes on temporal variations of the ocean carbon sink in the mid-latitude North Atlantic (2002–2016), PiO, doi.org/10.1016/j.pocean.2019.102223

Hartman, S.E., Humphreys, M.P.Kivimäe, C., Woodward, E. M. S, Kitidis, V., McGrath, T., Hydes, D.J., Greenwood,N., Hull, T. 5, Ostle, C.6, Pearce, D.J.Sivyer, D., Stewart, B.M. Walsham, P.Painter, S.C., McGovern, E., Harris,C., Griffiths,A., Smilenova, A., Clarke, J., Davis, C.Nightingale, P., 2018. Seasonality and spatial heterogeneity of the surface ocean carbonate system in the northwest European continental shelf, PiO, doi:10.1016/j.pocean.2018.02.005

Watson, A.J., Schuster, U., Bakker, D.C., Bates, N.R., Corbière, A., González-Dávila, M., Friedrich, T., Hauck, J., Heinze, C., Johannessen, T. and Körtzinger, A., 2009. Tracking the variable North Atlantic sink for atmospheric CO2. Science,326 (5958), pp.1391-1393. doi: 10.1126/science.1177394

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