Biogeochemical river inputs for global ocean models (RivR2O)

1. General Description The data uploaded here are synthesis products for yearly means of preindustrial C, N and P exports to the ocean and their historical evolutions, which are ready-to-use for global ocean models. They will serve as biogeochemical river inputs in the River-2-Ocean Model Intercomparison Study (R2O MIP). The files cover >10000 global catchments which can be read as lists with coordinates, or as gridded netcdf files. They cover the compounds DIC, DOC, POC, DIP and DIN. The assumed pre-industrial era is assumed to be pre-1900, whereas historical data will cover 1901-2020. 1.1. Preindustrial inputs and their transformations The files are for preindustrial river inputs can be downloaded as netcdf (r2o_riverinputs_preindustrial.nc), or as catchment lists (DIC,DOC,POC,DIN: riverexports_list_CN.csv , DIP: riverexports_list_P.csv) with given coordinates. They quantify yearly means for every catchment without a significant anthropogenic perturbation. They were constructed in the following ways DIC, DOC, POC Preindustrial DIC, DOC and POC were obtained by subtracting the estimated anthropogenic perturbation for every catchment, which was determined for the 1901-2020 time period by Tian et al. (2022), from the synthesis of present-day exports by Liu et al. (2024). We further accounted for a DOC source in the tropics (+0.06 Pg C yr-1), and a sink in the Northern Hemisphere (-0.03 Pg C yr-1) based on Regnier et al. (2022). A fraction of POC was also removed from the dataset due to models misrepresenting burial on shelf (see R2O MIP protocol). Groundwater discharge of DIC (0.016 Pg C yr-1) was distributed globally homogeneously to every river mouth. Globally, these amount to 497 DIC yr-1, 255 DOC yr-1 and 94 POC yr-1 to the ocean for the preindustrial time period. DIN The DIN product averages over three three river N exports models (ORCHIDEE-NLAT, Ma et al., in review; DLEM, Tian et al., 2023; IMAGE-GNM, Beusen et al., 2016) for every catchment. The resulting preindustrial DIN load to the ocean is 11 Tg N yr-1. DIP The DIP product averages catchment estimates from IMAGE-GNM(Beusen et al., 2016) and Lacroix et al. (2020). The resulting preindustrial DIP load to the ocean is 2.19 Tg P yr-1. 1.2. Anthropogenic Perturbation (1901-2020) Not yet available, to be added. 2. Use for modelers within the R2O MIP We only briefly describe most important information on how to apply the river input data here and refer to the official R2O MIP protocol for more detail on our general simulation guidelines. We firstly recommend the addition of two terrestrial dissolved organic carbon pools in the ocean models: tDOC semi-labile (DOC_sl) and tDOC semi-refractory (DOC_sr). Their only source should be that of the river inputs, which are given separately in the river inputs files, and it should be degraded with a first order constant of k_sl = 1 / 1.5yr and k_sr = 1/20yr (based on Hansell et al., 2012). The other tDOC compound given in the dataset, tDOC labile (tdoc_l), is assumed to be rapidly degraded and should therefore be added to the ocean model DIC pool. The inputs should be added to the closest ocean model grid points where the ocean model has freshwater inputs. Note that the inputs are given as Tg C/N/P per year, and this should be taken into account in the addition of the inputs at the model timestep. We recommend scaling the inputs to the seasonality of the freshwater inputs. The inputs from the riverine files should be added to the corresponding pool based on the following table: River Input (as given in r2o_riverinputs_preindustrial.nc) Global sum Ocean Model Pool DIC -> 497 Tg C yr-1 DIC & Alkalinity (1:1 ratio, see R2O MIP protocol) DOC_l -> 124 Tg C yr-1 DIC DOC_sl -> 109 Tg C yr-1 DOC_sl (new ocean model pool) and associated nutrients (DON, DOP, see protocol) DOC_sr -> 12 Tg C yr-1 DOC_sr (new ocean model pool) and associated nutrients (DON, DOP, see protocol) POC -> 94 Tg C yr-1 POC and associated nutrients (PON, POP, see protocol) DIP -> 2.19 Tg P yr-1 DIP / Phosphate DIN -> 11 Tg N yr-1 DIN / Nitrate 3. References Beusen, A. H. W., Bouwman, A. F., Van Beek, L. P. H., Mogollón, J. M., and Middelburg, J. J.: Global riverine N and P transport to ocean increased during the 20th century despite increased retention along the aquatic continuum, Biogeosciences, 13, 2441–2451, https://doi.org/10.5194/bg-13-2441-2016, 2016. Hansell, D. A., C. A. Carlson, and R. Schlitzer (2012), Net removal of major marine dissolved organic carbon fractions in the subsurface ocean, Global Biogeochem. Cycles, 26, GB1016, doi:10.1029/2011GB004069. Lacroix, F., Ilyina, T., and Hartmann, J.: Oceanic CO2 outgassing and biological production hotspots induced by pre-industrial river loads of nutrients and carbon in a global modeling approach, Biogeosciences, 17, 55–88, https://doi.org/10.5194/bg-17-55-2020, 2020. Liu et al. (2024). Global riverine land-to-ocean carbon export constrained by observations and multi-model assessment, Nature Geoscience, https://www.nature.com/articles/s41561-024-01524-z Ma, M., Zhang, H., Lauerwald, R., Ciais, P., and Regnier, P.: Estimating lateral nitrogen transfer through the global river network using a land surface model, Earth Syst. Dynam. Discuss. [preprint], https://doi.org/10.5194/esd-2024-29, in review, 2024. Regnier, P., Resplandy, L., Najjar, R.G. et al. The land-to-ocean loops of the global carbon cycle. Nature 603, 401–410 (2022). https://doi.org/10.1038/s41586-021-04339-9 Tian, H., Yao, Y., Li, Y., Shi, H., Pan, S., Najjar, R. G., et al. (2023). Increased terrestrial carbon export and CO2 evasion from global inland waters since the preindustrial era. Global Biogeochemical Cycles, 37, e2023GB007776. https://doi.org/10.1029/2023GB007776