backport: postpone call to start_gotm_fabm to ensure density is valid

Author: bolding

src/gotm/gotm.F90

@@ -328,18 +328,19 @@ subroutine init_gotm(t1,t2)
    call setup_restart()
 !   call init_output(title,nlev,latitude,longitude)
 
-#ifdef _FABM_
-!  Accept the current biogeochemical state and used it to compute derived diagnostics.
-   if (fabm_calc) call start_gotm_fabm(nlev)
-#endif
-
    call do_air_sea(julianday,secondsofday)
 
 !  Call stratification to make sure density has sensible value.
 !  This is needed to ensure the initial density is saved correctly, and also for FABM.
    call shear(nlev,cnpar)
    call stratification(nlev,buoy_method,dt,cnpar,nuh,gamh)
 
+#ifdef _FABM_
+!  Accept the current biogeochemical state and used it to compute derived diagnostics.
+!  This MUST be preceded with a call to stratification, in order to ensure FABM has a valid density.
+   if (fabm_calc) call start_gotm_fabm(nlev)
+#endif
+
    if (list_fields) call fm%list()
 
    LEVEL2 'done.'