GENIE:Biogeochem:FAQs:3

How do I work out how much freshwater I am adding in my hosing experiment (i.e. how do I convert between Sverdrups and psu*ocean cell mass per year)?
The 'biogem_force_flux_ocn_S*.dat files allow you to manipulate ocean circulation by salinity forcing (i.e. do a freshwater hosing experiment; see here for details). The units of this forcing in these files are - psu*ocean cell mass per year. As most published papers use units of Sverdrups (1Sv = 10^6 m3 s-1) to describe estimates of ocean freshwater influx, it is useful to be able to convert between these units. In the examples files here there is a negative salinity forcing of -1e17 psu*ocean cell mass per year in 11 of the ocean surface grid boxes. To calculate what this is in units of Sverdrups see below:

1 Sv = 10^6 m3 s-1 = 3.156x10^13 m3 yr-1

Volume of the surface boxes in the equal area 36x36x8 continental config is 0.6875x10^14 m3

Therefore, 1 Sv is a fractional box dilution (== freshwater replacement) rate of 0.459 per year (= 3.156x10^13/0.6875x10^14)

The integrated salinity content of a surface box = 2.466x10^18 psu kg (assuming mean salinity = 34.902 psu and a 36x36x8 surface box mass = 0.7065x10^17 kg)

Therefore, a -1.132x10^18 psu kg salinity flux is equivalent to a 1 Sv freshwater flux

So, -1e17 psu*mass per year = 0.088 Sv of freshwater

and therefore the total freshwater flux adding up the 11 cells is 0.968 Sv.