Thanks Brian, this is super helpful. However, in comparing my GWB output to 'standard' calculators of seawater alkalinity (e.g., 'CO2calc"), I still find offsets.
I'll send a GWB example tomorrow, but you can try using a temp of 25°C, a salinity of 35 PSU (Cl- = 546; Na+ = 469; Mg++ = 53; SO4-- = 28; Ca++ = 10.3; K+ = 10.2 all in mmol/kg), then set HCO3- = 1795 umol/kg and pH = 7.80. The results should give Total Alkalinity = 2125; Tot DIC = 1950; HCO3- = 1795 (i.e., as set 'free'); CO3-- = 135; CO2(aq) = 20 (all in umol/kg). I find that GWB comes 'close' but seems to be 10, 20% (more?) off. This is a real problem with CO3--, especially. Do you find similar? (Note, this is very simple system, assumed total oxic, and with no redox chemistry.)
Is there any way to have GWB output the actual Kds it uses for any given reaction? I'd be especailly interested to see what values of k1, k2 and kH GWB is using for the carbonate system at these conditions...
Thanks a million!