NorESMhub · jmaerz · Dec 11, 2025 · Dec 10, 2025 · Dec 11, 2025
diff --git a/cime_config/buildnml b/cime_config/buildnml
@@ -84,6 +84,7 @@ def buildnml(case, caseroot, compname):
     hamocc_ciso               = case.get_value("HAMOCC_CISO")
     hamocc_extncycle          = case.get_value("HAMOCC_EXTNCYCLE")
     hamocc_n2oc               = case.get_value("HAMOCC_N2OC")
+    hamocc_n2o_hist           = case.get_value("HAMOCC_N2O_HIST")
     hamocc_nh3c               = case.get_value("HAMOCC_NH3C")
     hamocc_atmndepc           = case.get_value("HAMOCC_ATMNDEPC")
     hamocc_sinking_scheme     = case.get_value("HAMOCC_SINKING_SCHEME")
@@ -195,6 +196,7 @@ def buildnml(case, caseroot, compname):
         config["hamocc_ciso"] = "yes" if hamocc_ciso else "no"
         config["hamocc_extncycle"] = "yes" if hamocc_extncycle else "no"
         config["hamocc_n2oc"] = "yes" if hamocc_n2oc else "no"
+        config["hamocc_n2o_hist"] = "yes" if hamocc_n2o_hist else "no"
         config["hamocc_nh3c"] = "yes" if hamocc_nh3c else "no"
         config["hamocc_atmndepc"] = "yes" if hamocc_atmndepc else "no"
         config["hamocc_sedbypass"] = "yes" if hamocc_sedbypass else "no"

diff --git a/cime_config/config_component.xml b/cime_config/config_component.xml
@@ -188,7 +188,16 @@
     <file>env_run.xml</file>
     <desc>N2O fluxes coupled from atmosphere. Requires module ecosys and extncycle</desc>
   </entry>
-
+
+  <entry id="HAMOCC_N2O_HIST">
+    <type>logical</type>
+    <valid_values>TRUE,FALSE</valid_values>
+    <default_value>FALSE</default_value>
+    <group>run_component_blom</group>
+    <file>env_run.xml</file>
+    <desc>Provide historical N2O concentrations (uncoupled). Requires module ecosys and extncycle</desc>
+  </entry>
+
   <entry id="HAMOCC_NH3C">
     <type>logical</type>
     <valid_values>TRUE,FALSE</valid_values>

diff --git a/cime_config/namelist_definition_blom.xml b/cime_config/namelist_definition_blom.xml
@@ -3649,6 +3649,17 @@
     <desc>Switch to couple N2O fluxes to atmosphere</desc>
   </entry>
 
+  <entry id="do_n2o_hist" modify_via_xml="HAMOCC_N2O_HIST">
+    <type>logical</type>
+    <category>bgcnml</category>
+    <group>bgcnml</group>
+    <values>
+      <value>.false.</value>
+      <value hamocc_n2o_hist="yes" hamocc_extncycle="yes">.true.</value>
+    </values>
+    <desc>Switch provide atmospheric N2O in historical period (uncoupled)</desc>
+  </entry>
+
   <entry id="do_nh3_coupled" modify_via_xml="HAMOCC_NH3C">
     <type>logical</type>
     <category>bgcnml</category>

diff --git a/hamocc/meson.build b/hamocc/meson.build
@@ -7,6 +7,7 @@ sources += files(
   'mo_cyano.F90',
   'mo_dipowa.F90',
   'mo_get_cfc.F90',
+  'mo_get_n2o_hist.F90',
   'mo_hamocc4bcm.F90',
   'mo_hamocc_init.F90',
   'mo_hamocc_step.F90',

diff --git a/hamocc/mo_carchm.F90 b/hamocc/mo_carchm.F90
@@ -104,7 +104,7 @@ subroutine carchm(kpie,kpje,kpke,kbnd,pdlxp,pdlyp,pddpo,prho,pglat,omask,psicomo
                               iatmnco2,inatalkali,inatcalc,inatsco212,                             &
                               ks,issso14,isssc14,ipowc14,                                          &
                               iatmbromo,ibromo,iatmnh3,ianh4
-    use mo_param_bgc,   only: dremcalc,srfdic_min,c14dec,atm_co2_nat,atm_n2o
+    use mo_param_bgc,   only: dremcalc,srfdic_min,c14dec,atm_co2_nat
     use mo_vgrid,       only: dp_min,kmle,kbo,ptiestu
     use mo_carbch,      only: atm_cfc11_nh,atm_cfc11_sh,atm_cfc12_nh,atm_cfc12_sh,                 &
                               atm_sf6_nh,atm_sf6_sh,                                               &

diff --git a/hamocc/mo_control_bgc.F90 b/hamocc/mo_control_bgc.F90
@@ -58,6 +58,7 @@ module mo_control_bgc
   logical           :: l_3Dvarsedpor          = .false. ! apply spatially variable sediment porosity
   logical           :: do_ndep                = .true.  ! apply n-deposition
   logical           :: do_n2o_coupled         = .false. ! for coupled simulations, use field provided by atmosphere
+  logical           :: do_n2o_hist            = .false. ! provide historical N2O concentration in non-N2O-interactive historical sim
   logical           :: do_nh3_coupled         = .false. ! for coupled simulations, use field provided by atmosphere
   logical           :: do_rivinpt             = .true.  ! apply riverine input
   logical           :: do_sedspinup           = .false. ! apply sediment spin-up

diff --git a/hamocc/mo_get_n2o_hist.F90 b/hamocc/mo_get_n2o_hist.F90
@@ -0,0 +1,123 @@
+! Copyright (C) 2020  J. Tjiputra, J. Schwinger, j maerz
+!
+! This file is part of BLOM/iHAMOCC.
+!
+! BLOM is free software: you can redistribute it and/or modify it under the
+! terms of the GNU Lesser General Public License as published by the Free
+! Software Foundation, either version 3 of the License, or (at your option)
+! any later version.
+!
+! BLOM is distributed in the hope that it will be useful, but WITHOUT ANY
+! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+! FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
+! more details.
+!
+! You should have received a copy of the GNU Lesser General Public License
+! along with BLOM. If not, see https://www.gnu.org/licenses/.
+
+module mo_get_n2o_hist
+
+  implicit none
+  private
+
+  public get_n2o_hist
+
+contains
+
+  subroutine get_n2o_hist(kplyear)
+    use mod_xc,         only: mnproc
+    use mo_kind,        only: rp
+    use mo_control_bgc, only: io_stdo_bgc
+    use mo_param1_bgc,  only: iatmn2o
+    use mo_carbch,      only: atm
+    use mo_control_bgc, only: do_n2o_hist
+
+    ! Arguments
+    integer, intent(in) :: kplyear
+
+    ! Local variables
+    integer, parameter   :: start_yr = 1750   ! first year of data
+    integer, parameter   :: nyears   = 266    ! nb of years in data
+    real(rp)             :: atm_n2o_conc(nyears)
+    integer, save        :: kplyear_old = 0
+
+    ! N2O atmospheric concentration
+    ! Meinhausen et al. 2017: Historical greenhouse gas concentrations for climate modelling (CMIP6)
+    ! generated from shared LBC_1750-2015_CMIP6_GlobAnnAvg_c180926.nc file.
+    ! First (last) data represents year 1750.5 (2015.5), units are [ppt]
+
+    data atm_n2o_conc /                                                                            &
+              273864.96875_rp, 273894.06250_rp, 273927.09375_rp, 273972.81250_rp, 274016.18750_rp, &
+              274051.12500_rp, 274079.00000_rp, 274096.03125_rp, 274129.00000_rp, 274165.09375_rp, &
+              274193.09375_rp, 274222.00000_rp, 274249.90625_rp, 274301.96875_rp, 274339.93750_rp, &
+              274371.96875_rp, 274391.90625_rp, 274426.00000_rp, 274446.81250_rp, 274468.03125_rp, &
+              274495.06250_rp, 274513.03125_rp, 274530.93750_rp, 274547.09375_rp, 274565.03125_rp, &
+              274578.96875_rp, 274593.93750_rp, 274606.06250_rp, 274617.87500_rp, 274629.00000_rp, &
+              274639.21875_rp, 274646.93750_rp, 274654.00000_rp, 274657.93750_rp, 274663.93750_rp, &
+              274669.18750_rp, 274676.03125_rp, 274678.06250_rp, 274677.00000_rp, 274678.06250_rp, &
+              274677.00000_rp, 274673.96875_rp, 274673.96875_rp, 274659.00000_rp, 274648.03125_rp, &
+              274631.03125_rp, 274615.15625_rp, 274601.00000_rp, 274584.18750_rp, 274570.03125_rp, &
+              274547.09375_rp, 274531.96875_rp, 274523.00000_rp, 274505.06250_rp, 274485.96875_rp, &
+              274465.96875_rp, 274446.81250_rp, 274428.12500_rp, 274411.12500_rp, 274383.18750_rp, &
+              274360.06250_rp, 274334.00000_rp, 274304.06250_rp, 274267.12500_rp, 274230.81250_rp, &
+              274181.00000_rp, 274143.06250_rp, 274107.12500_rp, 274070.96875_rp, 274050.09375_rp, &
+              274007.09375_rp, 273970.00000_rp, 273933.18750_rp, 273894.96875_rp, 273846.96875_rp, &
+              273786.06250_rp, 273728.06250_rp, 273677.03125_rp, 273640.87500_rp, 273602.15625_rp, &
+              273564.00000_rp, 273520.09375_rp, 273444.03125_rp, 273372.09375_rp, 273214.09375_rp, &
+              273078.96875_rp, 272953.96875_rp, 272873.18750_rp, 272866.09375_rp, 272857.96875_rp, &
+              272799.03125_rp, 272689.18750_rp, 272582.00000_rp, 272606.96875_rp, 272647.93750_rp, &
+              272640.09375_rp, 272730.00000_rp, 272812.96875_rp, 272884.96875_rp, 272953.93750_rp, &
+              273021.18750_rp, 273093.96875_rp, 273167.90625_rp, 273264.06250_rp, 273363.00000_rp, &
+              273470.00000_rp, 273578.09375_rp, 273675.06250_rp, 273756.03125_rp, 273894.96875_rp, &
+              274055.96875_rp, 274240.00000_rp, 274416.12500_rp, 274570.96875_rp, 274719.93750_rp, &
+              274880.15625_rp, 275048.21875_rp, 275212.90625_rp, 275390.96875_rp, 275561.18750_rp, &
+              275719.93750_rp, 275902.93750_rp, 276078.09375_rp, 276249.93750_rp, 276416.09375_rp, &
+              276584.87500_rp, 276734.93750_rp, 276864.09375_rp, 277002.00000_rp, 277133.00000_rp, &
+              277265.09375_rp, 277373.87500_rp, 277485.96875_rp, 277590.96875_rp, 277695.06250_rp, &
+              277794.93750_rp, 277885.00000_rp, 277994.96875_rp, 278079.84375_rp, 278190.87500_rp, &
+              278273.09375_rp, 278346.75000_rp, 278442.09375_rp, 278554.09375_rp, 278689.00000_rp, &
+              278831.00000_rp, 278938.90625_rp, 279050.96875_rp, 279163.06250_rp, 279308.12500_rp, &
+              279454.06250_rp, 279613.15625_rp, 279860.68750_rp, 280155.96875_rp, 280431.81250_rp, &
+              280704.87500_rp, 280980.00000_rp, 281276.03125_rp, 281611.12500_rp, 281949.90625_rp, &
+              282314.18750_rp, 282720.96875_rp, 283019.12500_rp, 283361.96875_rp, 283715.87500_rp, &
+              284047.00000_rp, 284311.93750_rp, 284614.96875_rp, 284805.00000_rp, 284850.93750_rp, &
+              284928.84375_rp, 285038.78125_rp, 285170.00000_rp, 285467.00000_rp, 285605.06250_rp, &
+              285652.03125_rp, 285692.09375_rp, 285740.03125_rp, 285832.84375_rp, 285891.03125_rp, &
+              285938.12500_rp, 286124.03125_rp, 286221.87500_rp, 286371.18750_rp, 286466.93750_rp, &
+              286587.03125_rp, 286747.06250_rp, 286951.00000_rp, 287190.96875_rp, 287387.12500_rp, &
+              287619.06250_rp, 287864.12500_rp, 288137.96875_rp, 288781.03125_rp, 289000.09375_rp, &
+              289227.06250_rp, 289427.12500_rp, 289510.96875_rp, 289556.21875_rp, 289598.06250_rp, &
+              289738.90625_rp, 289860.09375_rp, 290024.93750_rp, 290334.15625_rp, 290547.81250_rp, &
+              290844.03125_rp, 291186.96875_rp, 291511.90625_rp, 291772.03125_rp, 291987.00000_rp, &
+              292282.96875_rp, 292601.96875_rp, 292945.06250_rp, 293327.03125_rp, 293685.18750_rp, &
+              294045.09375_rp, 294453.18750_rp, 294859.93750_rp, 295269.03125_rp, 295681.00000_rp, &
+              296098.25000_rp, 296521.90625_rp, 296954.96875_rp, 297399.06250_rp, 297854.93750_rp, &
+              298326.12500_rp, 298813.96875_rp, 299318.84375_rp, 299844.93750_rp, 300392.90625_rp, &
+              300965.15625_rp, 301562.03125_rp, 302186.96875_rp, 302841.96875_rp, 303528.12500_rp, &
+              304247.15625_rp, 305001.96875_rp, 305792.87500_rp, 306623.90625_rp, 307831.12500_rp, &
+              308683.00000_rp, 309233.15625_rp, 309725.03125_rp, 310099.09375_rp, 310807.96875_rp, &
+              311278.90625_rp, 312298.12500_rp, 313182.93750_rp, 313906.93750_rp, 314708.84375_rp, &
+              315759.18750_rp, 316493.00000_rp, 317100.81250_rp, 317729.90625_rp, 318357.00000_rp, &
+              319130.03125_rp, 319933.15625_rp, 320645.96875_rp, 321574.84375_rp, 322274.96875_rp, &
+              323141.00000_rp, 324159.12500_rp, 325004.78125_rp, 325918.87500_rp, 326987.93750_rp, &
+              326987.93750_rp /
+
+    if (do_n2o_hist) then
+      if ((kplyear >= start_yr) .and. (kplyear < (start_yr + nyears))) then
+        atm(:,:,iatmn2o) = atm_n2o_conc(kplyear - start_yr + 1)
+
+        if (mnproc==1 .and. kplyear > kplyear_old) then
+          write(io_stdo_bgc,*) 'ATM N2O CONC=',kplyear,atm_n2o_conc(kplyear - start_yr + 1)
+          kplyear_old = kplyear
+        endif
+      endif
+    else
+      ! Remain with atm(:,:,iatmn2o) = atm_n2o as initialized in mo_ini_fields
+      return
+    endif
+
+
+  end subroutine get_n2o_hist
+
+end module mo_get_n2o_hist
+
diff --git a/hamocc/mo_hamocc4bcm.F90 b/hamocc/mo_hamocc4bcm.F90
@@ -68,6 +68,7 @@ subroutine hamocc4bcm(kpie,kpje,kpke,kbnd,kplyear,kplmon,kplday,kldtday,pdlxp,pd
     use mo_inventory_bgc, only: inventory_bgc
     use mo_sedshi,        only: sedshi
     use mo_get_cfc,       only: get_cfc
+    use mo_get_n2o_hist,  only: get_n2o_hist
     use mo_powach,        only: powach
     use mo_preftrc,       only: preftrc
     use mo_cyano,         only: cyano
@@ -187,6 +188,9 @@ subroutine hamocc4bcm(kpie,kpje,kpke,kbnd,kplyear,kplmon,kplday,kldtday,pdlxp,pd
         enddo
         !$OMP END PARALLEL DO
         if (mnproc.eq.1) write (io_stdo_bgc,*) 'iHAMOCC: getting N2O conc. from atm'
+      else
+        ! Get historical atmospheric N2O concentration, if requested via do_n2o_hist
+        call get_n2o_hist(kplyear)
       endif
       if (do_nh3_coupled) then
         !$OMP PARALLEL DO PRIVATE(i)

diff --git a/hamocc/mo_hamocc_init.F90 b/hamocc/mo_hamocc_init.F90
@@ -48,7 +48,7 @@ subroutine hamocc_init(read_rest,rstfnm_hamocc)
                               lkwrbioz_off,do_n2o_coupled,do_nh3_coupled,                          &
                               ocn_co2_type, use_sedbypass, use_BOXATM, use_BROMO,use_extNcycle,    &
                               use_coupler_ndep,lTO2depremin,use_sediment_quality,ldyn_sed_age,     &
-                              linit_DOMclasses_sim
+                              linit_DOMclasses_sim,do_n2o_hist
     use mo_param1_bgc,  only: ks,init_por2octra_mapping
     use mo_param_bgc,   only: ini_parambgc,claydens,calcdens,calcwei,opaldens,opalwei,ropal,       &
                             & ini_bgctimes,sec_per_day
@@ -92,7 +92,7 @@ subroutine hamocc_init(read_rest,rstfnm_hamocc)
          &            inidic,inialk,inipo4,inioxy,inino3,inisil,inid13c,inid14c,inidom,swaclimfile,&
          &            with_dmsph,pi_ph_file,l_3Dvarsedpor,sedporfile,ocn_co2_type,use_M4AGO,       &
          &            do_n2o_coupled,do_nh3_coupled,lkwrbioz_off,lTO2depremin,shelfsea_maskfile,   &
-         &            sedqualfile,ldyn_sed_age,linit_DOMclasses_sim
+         &            sedqualfile,ldyn_sed_age,linit_DOMclasses_sim,do_n2o_hist
     !
     ! --- Set io units and some control parameters
     !

diff --git a/hamocc/mo_param_bgc.F90 b/hamocc/mo_param_bgc.F90
@@ -44,7 +44,7 @@ module mo_param_bgc
                             lkwrbioz_off,lTO2depremin,use_shelfsea_res_time,use_sediment_quality,  &
                             use_pref_tracers,use_coupler_ndep,use_river2omip,use_DOMclasses,       &
                             linit_DOMclasses_sim,ldyn_sed_age,sedspin_yr_s,sedspin_yr_e,           &
-                            sedspin_ncyc,ldtbgc
+                            sedspin_ncyc,ldtbgc,do_n2o_hist
   use mod_xc,         only: mnproc,xchalt
 
   implicit none
@@ -980,6 +980,7 @@ subroutine write_parambgc()
       call pinfo_add_entry('ldtbgc',                 real(ldtbgc))
       if (use_extNcycle) then
         call cinfo_add_entry('do_n2o_coupled',       do_n2o_coupled)
+        call cinfo_add_entry('do_n2o_hist',          do_n2o_hist)
         call cinfo_add_entry('do_nh3_coupled',       do_nh3_coupled)
       endif
       write(io_stdo_bgc,*) '* '