Human activities have caused atmospheric CO2 levels to increase dramatically, but their growth has been slowed by the oceans absorbing approximately one quarter of this anthropogenic carbon (Canth). Globally, the North Atlantic (NA) Ocean stores the highest quantities of Canth, due to local CO2 uptake from the atmosphere, and large-scale ocean currents, particularly the Atlantic Meridional Overturning Circulation (AMOC) delivering waters high in Canth to northern locations where they cool, get denser and sink to great depths away from contact with the atmosphere.

Nevertheless, the balance of contributions to NA Canth accumulation from air-sea CO2 fluxes and ocean transports is not well constrained. Models project that the size of this carbon sink will reduce in the coming decades despite continued atmospheric CO2 increases, as surface warming increases stratification, decreases CO2 solubility, and AMOC weakening slows the transport of dense waters to depth. However, there is substantial model spread regarding flux peak, and decline timing.

The balance between air-sea fluxes and ocean transports to North Atlantic Canth accumulation is therefore not well constrained both now and into the future, and subject to large uncertainties. ROCCA will address these fundamental knowledge gaps. This will be through:

  • generating new high-resolution estimates of Canth transports across the subtropical and subpolar boundaries of the North Atlantic, relying on the outputs from the RAPID and OSNAP transport mooring arrays, to identify how they co-vary with AMOC,
  • determining the regional Canth accumulation rate from assorted data products and data-assimilating model outputs,
  • calculating contributions from local air-sea fluxes, including those derived from contemporary surface CO2 measurements, and anthropogenic CO2 fluxes derived from transport divergence estimates,
  • evaluating CMIP6 models for how carbon is accumulating in the North Atlantic, constraining model performance and uncertainty in future projections.

Our findings will help improve the accuracy of climate models, which is crucial for predicting the effects of climate change, forming new understanding of how the AMOC and the carbon system interlink.

PI: Dr Pete Brown, National Oceanography Centre
Email: peter.brown at noc.ac.uk

Dates
–
Funding

NERC – Strategic Research; US National Science Foundation (NSF)

Aim

The ROCCA project is led by Dr Pete Brown (NOC). Using our expertise in measuring and examining carbon uptake, transport and storage, and anthropogenic carbon accumulation in the NA oceanic region, we will extend the Canth transport analysis performed in this area, generate a complementary time series, determine and evaluate the evolving Canth column accumulation and better constrain the contribution of air-sea Canth fluxes in order to determine the drivers of anthropogenic carbon accumulation in the NA. In close collaboration with the modeling team, sensitivity responses to circulation variations and trends will be tested to determine how the drivers will change into the future with AMOC change.

Oceanographic sampling (sensor and mooring equipment)