Table S1.

Monthly mean normalized flux

Normalized flux	April	May	June	July	August	September	October	November	December	Year mean
fOCS, m s−1	−0.4	−0.7	−1.3	0.7	−1.6	−1.7	−0.8	−0.5	−0.4	−0.9
fOCS, mmol m−2 s−1	−9	−17	−31	18	−39	−43	−18	−10	−10	−22
fOCS/fCO2 (ERU)		−0.4	0.7	−2.0	0.8	2.4	3.7	−9.6	5.2	1.4*
fOCS/fGEP (LRU)		1.5	0.5	−0.4	1.2	1.2	0.7	6.6	9.4	1.0*

Monthly mean of ecosystem flux per molecule of OCS (f_OCS, m⋅s⁻¹); ecosystem flux per mole of OCS (f_OCS, mmol⋅m⁻²⋅s⁻¹); ratio of the flux per molecule of OCS to that of CO₂ (f_OCS/f_CO2), comparable to the ERU; and ratio of the flux per molecule of OCS to that of GEP (f_OCS/f_GEP), comparable to the LRU for daylight hours (PAR > 300 μE⋅m⁻²⋅s⁻¹). Note: Period of net OCS emission in July. This has been removed from the mean year calculation.

^*Only the growing season mean (June–October 2011, excluding July) was calculated for f_OCS/f_CO2 and f_OCS/f_GEP instead of an annual mean. Only data with u* > 0.17 m⋅s⁻¹ have been used in the calculations.