implement LGM modification from Chia-Te according to Chris

source/mom/tracer.F

@@ -792,8 +792,14 @@
 !                if (k .ge. 1 .and. k .le. 10)
 !     &                  sg_bdeni = 1*sg_bdeni
                 sg_bdeni = sg_bdeni*(0.5 + lno3)*no3flag*din15flag
+#     if defined O_LGM
+                if (k .eq. 1) then
+                   sg_bdeni = 0.0
+                else if (k .eq. 2) then
+                   sg_bdeni = 0.08*sg_bdeni
+                endif
+#     endif
                 snpzd(5) = snpzd(5) + sgb*expo - sg_bdeni
-
 #    else
                 snpzd(5) = snpzd(5) + expo*sgb
 #    endif
@@ -803,13 +809,33 @@
                 fesed = fetopsed*bct*expo_p*sgb
 #    else
                 fesed = fetopsed*bct*redptn*expo*sgb
+#    endif
+! As for bdeni, also reduce sedimentary iron release from the sediment.
+#    if defined O_LGM
+                if (k .eq. 1) then
+                   fesed = 0.0
+                else if (k .eq. 2) then
+                   fesed = fesed*0.08
+                endif
 #    endif
                 bfe = fesed
                 snpzd(itdfe) = snpzd(itdfe) + fesed
                 if (t(i,k,j,io2,taum1) .lt. o2min) then
+#    if defined O_LGM
+! remineralise only the fraction of Fe as the assumed existence of the current grid cell
+! this is 0 for k.eq.1 and 0.08 for k.eq.2
+                   if (k .eq. 2) then
+                      snpzd(itdfe) = snpzd(itdfe) + expofe*sgb*0.08
+                      bfe = bfe + expofe*sgb*0.08
+                      expofe = expofe - sgb*expofe*0.08
+                   elseif (k .gt. 2) then
+#    endif
                    snpzd(itdfe) = snpzd(itdfe) + expofe*sgb
                    bfe = bfe + expofe*sgb
                    expofe = expofe - sgb*expofe
+#    if defined O_LGM
+                   endif
+#    endif
                 endif
                 rremife(i,k,j) = rremife(i,k,j) + bfe
 #    if defined O_npzd_iron_diagnostics
@@ -864,20 +890,26 @@
                 bdeni = (0.06 + 0.19*0.99
      &               **(max(t(i,k,j,io2,taum1)*1000,trcmin)
      &               - max(t(i,k,j,ino3,taum1),trcmin)))
-#   if defined O_opem
+#     if defined O_opem
      &               *max(expo_c,trcmin)
-#   else
+#     else
      &               *max(expo,trcmin)*6.625
-#   endif
+#     endif
                 bdeni = min(bdeni, expo)
                 bdeni = max(bdeni, 0.)
 
 c                if (k .ge. 1 .and. k .le. 10)
 c     &                  bdeni = sgbdfac*bdeni
                 bdeni = bdeni*(0.5 + lno3)*no3flag*din15flag
-
+#      if defined O_LGM
+                if (k .eq. 1) then
+                   bdeni = 0.0
+                else if (k .eq. 2) then
+                   bdeni = 0.08*bdeni
+                endif
+#      endif
                 snpzd(5) = snpzd(5) + expo - bdeni
-#    else
+#     else
                 snpzd(5) = snpzd(5) + expo
 #    endif
 #   endif
@@ -886,13 +918,31 @@ c     &                  bdeni = sgbdfac*bdeni
                 fesed = fetopsed*bct*expo_p
 #    else
                 fesed = fetopsed*bct*redptn*expo
+#    endif
+! As for bdeni, also reduce sedimentary iron release from the sediment.
+#    if defined O_LGM
+                if (k .eq. 1) then
+                   fesed = 0.0
+                else if (k .eq. 2) then
+                   fesed = fesed*0.08
+                endif
 #    endif
                 bfe = fesed
                 snpzd(itdfe) = snpzd(itdfe) + fesed
                 if (t(i,k,j,io2,taum1) .lt. o2min) then
+#    if defined O_LGM
+                   if (k .eq. 2) then
+                      snpzd(itdfe) = snpzd(itdfe) + expofe*0.08
+                      bfe = bfe + expofe*0.08
+                      expofe = expofe - expofe*0.08
+                   elseif (k .gt. 2) then
+#    endif
                    snpzd(itdfe) = snpzd(itdfe) + expofe
                    bfe = bfe + expofe
                    expofe = 0.
+#    if defined O_LGM
+                   endif
+#    endif
                 endif
                 rremife(i,k,j) = rremife(i,k,j) + bfe
 #    if defined O_npzd_iron_diagnostics