Correct thermo clock with update_ocean_model calls

  Store the thermodynamic clock at the start of update_ocean_model so that it
does not get incorrectly updated during purely dynamic steps. When both dynamics
and thermodynamics are stepped together, nothing is changed, but when they are
stepped separately, this correct the thermodynamic clock that is used primarily
for diagnostics.  All answers are bitwise identical in the existing test cases.

config_src/coupled_driver/ocean_model_MOM.F90

@@ -442,8 +442,12 @@ subroutine update_ocean_model(Ice_ocean_boundary, OS, Ocean_sfc, time_start_upda
   real,    optional, intent(in)    :: cycle_length !< The duration of a coupled time stepping cycle [s].
 
   ! Local variables
-  type(time_type) :: Time_seg_start ! Stores the ocean model time at the start of this call to allow
-                            ! step_MOM to temporarily change the time as seen by internal modules.
+  type(time_type) :: Time_seg_start ! Stores the dynamic or thermodynamic ocean model time at the
+                            ! start of this call to allow step_MOM to temporarily change the time
+                            ! as seen by internal modules.
+  type(time_type) :: Time_thermo_start ! Stores the ocean model thermodynamics time at the start of
+                            ! this call to allow step_MOM to temporarily change the time as seen by
+                            ! internal modules.
   type(time_type) :: Time1  ! The value of the ocean model's time at the start of a call to step_MOM.
   integer :: index_bnds(4)  ! The computational domain index bounds in the ice-ocean boundary type.
   real :: weight            ! Flux accumulation weight of the current fluxes.
@@ -563,6 +567,7 @@ subroutine update_ocean_model(Ice_ocean_boundary, OS, Ocean_sfc, time_start_upda
     call finish_MOM_initialization(OS%Time, OS%dirs, OS%MOM_CSp, OS%restart_CSp)
   endif
 
+  Time_thermo_start = OS%Time
   Time_seg_start = OS%Time ; if (do_dyn) Time_seg_start = OS%Time_dyn
   Time1 = Time_seg_start
 
@@ -576,7 +581,7 @@ subroutine update_ocean_model(Ice_ocean_boundary, OS, Ocean_sfc, time_start_upda
                   reset_therm=Ocn_fluxes_used)
   elseif (OS%single_step_call) then
     call step_MOM(OS%forces, OS%fluxes, OS%sfc_state, Time1, dt_coupling, OS%MOM_CSp, Waves=OS%Waves)
-  else
+  else  ! Step both the dynamics and thermodynamics with separate calls.
     n_max = 1 ; if (dt_coupling > OS%dt) n_max = ceiling(dt_coupling/OS%dt - 0.001)
     dt_dyn = dt_coupling / real(n_max)
     thermo_does_span_coupling = (OS%thermo_spans_coupling .and. (OS%dt_therm > 1.5*dt_coupling))
@@ -636,7 +641,7 @@ subroutine update_ocean_model(Ice_ocean_boundary, OS, Ocean_sfc, time_start_upda
 
   if (do_dyn) OS%Time_dyn = Time_seg_start + Ocean_coupling_time_step
   if (do_dyn) OS%nstep = OS%nstep + 1
-  OS%Time = Time_seg_start  ! Reset the clock to compensate for shared pointers.
+  OS%Time = Time_thermo_start  ! Reset the clock to compensate for shared pointers.
   if (do_thermo) OS%Time = OS%Time + Ocean_coupling_time_step
   if (do_thermo) OS%nstep_thermo = OS%nstep_thermo + 1