pCO2 box model

This package includes all code neccessary to run simulation and generate figues for the paper "Controls on Surface Water Carbonate Chemistry along North American Ocean Margins" by Cai et al.

Background and boundary conditions

To study the relationships that control surface ocean carbonate parameters and air-sea CO2 fluxes, we use a box model to representing an idealized mixed layer. The box model is simulating the carbonate systems as a homogenous surface-ocean water mass located either in the North-West Atlantic (NWA, 40.1-42.5°N, 69.2-67.5°W), South Atlantic Bight (28.3°N–29.7°N, 77.6°W–79.2°W), or the California Current System (CCS, 40.8–41.6°N, 124.5–125°W). The model is driven by realistic temperatures and salinities from the Mercator 1/12° data-assimilated General Circulation Model with a daily resolution in time[^1].

Biological production is assessed from weekly averages of daily changes in satellite derived Chlorophyll for the year 2015 using the daily MODIS aqua 4-km Level 3 product (NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group. Moderate-resolution Imaging Spectroradiometer (MODIS) Aqua Chlorophyll Data; 2018 Reprocessing. NASA OB.DAAC, Greenbelt, MD, USA. doi: data/10.5067/AQUA/MODIS/L3M/CHL/2018. Accessed on 10/02/2019) or for the year 2016 for the west coast box. We use extract daily time series for each grid cell that falls within the NWA, SAB and CCS model regions, identify all pairs of consecutive days with valid data and convert changes in Chl to a carbon flux by using a fixed C:Chl ratio of 60 (Ref63). The resulting weekly averages are interpolated to daily time series. The resulting change in DIC is significantly smaller than other sources and sinks in the current study.

Winds are prescribed to 7 m/s in the summer and 10.5 m/s in the winter, to be consistent with representative wind data from the NOAA/Seawinds blended wind data set62. Winter mixing in NWA is simulated by adding 0.1 mmol m-3 DIC daily from October through February (over 155 days). The value is based on a scaling analysis of vertical DIC gradients and diffusivity estimates in the region based on observational in 2015 in the NWA region and 2016 in the CCS. Literature values of physical vertical diffusion combined with vertical profiles of DIC from the ECOA 2015 cruse suggests that diffusive transports of DIC is negligible during summer. We use constant winds to minimize noise and to isolate the effect by changes in solubility on the carbonate system. Atmospheric pCO2 is set to 395 μatm. All carbonate equilibria and concentrations are calculated using the CO2SYS package.