Biennial Observation of Carbon, Acidification, Transport and Sedimentation in the North Atlantic

The ocean, an essential element in the climate system, currently accumulates 93% of the excess heat and 31% of the excess CO2 generated by human activities. The Atlantic Meridional Overturning Circulation (AMOC) influences the climate of Europe on interannual to decadal time scales, including that of the Iberian Peninsula. The AMOC amplifies the capture of anthropogenic CO2 resulting in an average uptake rate for the North Atlantic that exceeds by 50% the average world ocean rate. In the subpolar gyre of the North Atlantic (NA), ocean acidification reaches abyssal depths (>3500 m), endangering ecosystems supported by cold water coral structures. A recent weakening of the AMOC has been reported at mid-latitudes and it is expected that the slow-down of the AMOC becomes more pronounced in the coming decades (IPCC, 2019). IPCC highlights the lack of observations to quantify the magnitude of this reduction. Therefore, observational monitoring of (present and past) ocean circulation and acidification in the NA is essential to advance in the accurate detection of the anthropogenic impact and to improve the projections of the climate models used for the IPCC reports. In this project we focus on the NA subpolar gyre (SPNA), where we propose the acquisition of new observations that will inform on the evolution of the present day and past circulations. The paleoceanographic information from this area will be crucial to establish the nature of previous changes with respect to the instrumental records in different climatic contexts.

BOCATS2, a continuation of the previous BOCATS project (2014-2017), will be a main contribution to the observation of the NA subpolar gyre by continuing the occupation of the biennial section A25-Ovide (2021 and 2023) within the framework of the international GO-SHIP programme. A particular focus will be given to the new challenge of assessing the variability of the deep circulation in the NA, improving the spatial-temporal resolution of deep currents and water mass characteristics by deploying a regional deep-ARGO array and, at a submilenary scale, using paleoceanographic data obtained in sedimentary records from key sites, such as the Bight and Charlie-Gibbs fracture zones. The high-quality observations foreseen in the SPNA will contribute to the early detection of the alteration of the carbon cycle allowing the precise estimation of the heat, CO2 and N2O storage rates and, ultimately, to find the connection between these changes and the variability of the AMOC at different time scales. The natural and anthropogenic fluxes of heat, CO2 and N2O will be evaluated, as well as the present and submillenary scale transport of sediments and biogenic elements, and the impact of acidification on these timescales by means of the analysis of CaCO3 and organic carbon fluxes to the sediment. Besides, the current ocean acidification rates will also be quantified by evaluating the present situation and establishing future projections. These new observation-based estimates will be a valuable result that will be used to validate the predictions from the models (GCMs and ESMs from CMIP5-6) for the 2°C warming scenario. Finally, special attention will be paid to the rates of elevation of aragonite saturation horizons in deep layers, where the impact on the ecosystems sustained by calcareous organisms is potentially imminent.

The objectives of the project are at the crossroad of physical oceanography (currents and water masses transports and variability), carbon cycle, and paleoceanography, so an interdisciplinary team is needed. The BOCATS2 proyect leading team is made up of researchers from CSIC (Consejo Superior de Investigaciones Científicas) and University of Vigo with different specialties (physical, chemical and geological oceanography) and supported by an LOPS-IFREMER research team with whom leadership alternates since 2010. A research team from ETHZ and CCMAR plus University of Aveiro also participates, with other institutions as University of Delaware and LOCEAN-IPSL participating. The project is therefore organised into two sub-projects, one for each institution (IIM-CSIC and UVigo), both sub-projects being in turn supported by interdisciplinary research teams. Subproject 1, or coordinator, is being leaded by Antón Velo and Fiz F. Pérez from the Marine Research Institute (IIM-CSIC) of Vigo. The coordinating project brings together a high level of interaction with international teams (France, USA, Germany and Switzerland) that contribute to the knowledge of tracers in ocean circulation. As has been the case since 2012, physical oceanography observations are based on the collaboration between the French group LOPS (Brest, IFREMER). Subproject 2 is being leaded by Guillermo Francés and Gabriel Rosón from the University of Vigo (UVigo), and collaboration in the working team of a renowned specialist on sedimentary processes associated to bottom currents from the Royal Holloway University (F.J. Hernández-Molina). The two main groups (IIM-CSIC and UVigo) have a broad collaborative experience, having participated in two previous projects, writing cross-papers, co-supervising PhD and participating in several divulgation activities.

Disciplines involved and main objectives

Fig1: Disciplines involved and main objectives


Fig2: A25-OVIDE Cruise section planned for 2021 and 2023. Bight fracture zone to be studied in 2021. Charlie-Gibbs fracture zone study planned for 2023