diff --git a/src/aed_core.F90 b/src/aed_core.F90
index 8837494..24ae513 100644
--- a/src/aed_core.F90
+++ b/src/aed_core.F90
@@ -668,6 +668,8 @@ FUNCTION aed_locate_variable(name) RESULT(ret)
 !
 !-------------------------------------------------------------------------------
 !BEGIN
+   IF ( TRIM(name) == '' ) THEN ; ret = 0; RETURN ; ENDIF
+
    ret = aed_create_variable(name, '', '', .true.)
 
    IF ( ret /= 0 ) THEN
@@ -693,6 +695,8 @@ FUNCTION aed_locate_sheet_variable(name) RESULT(ret)
 !
 !-------------------------------------------------------------------------------
 !BEGIN
+   IF ( TRIM(name) == '' ) THEN ; ret = 0; RETURN ; ENDIF
+
    ret = aed_create_variable(name, '', '', .true.)
 
    IF ( ret /= 0 ) THEN
@@ -718,6 +722,8 @@ FUNCTION aed_locate_global(name) RESULT(ret)
 !
 !-------------------------------------------------------------------------------
 !BEGIN
+   IF ( TRIM(name) == '' ) THEN ; ret = 0; RETURN ; ENDIF
+
    IF ( TRIM(name) == "cell_vel" ) THEN
        ret = -1
        IF ( .NOT. host_has_cell_vel ) RETURN
@@ -740,6 +746,8 @@ FUNCTION aed_locate_sheet_global(name) RESULT(ret)
 !
 !-------------------------------------------------------------------------------
 !BEGIN
+   IF ( TRIM(name) == '' ) THEN ; ret = 0; RETURN ; ENDIF
+
    ret = aed_create_variable(name, '', '', .true.)
 
    all_vars(ret)%sheet = .true.
diff --git a/src/aed_geochemistry.F90 b/src/aed_geochemistry.F90
index 611abd8..b528689 100644
--- a/src/aed_geochemistry.F90
+++ b/src/aed_geochemistry.F90
@@ -313,18 +313,18 @@ SUBROUTINE aed_define_geochemistry(data, namlst)
    !----------------------------------------------------------------------------
    ! Register links to other modules
 
-   data%id_o_oxy = aed_locate_global(oxy_link)
+   data%id_o_oxy = aed_locate_variable(oxy_link)
 
    IF ( ph_link .EQ. '' ) THEN
      ! Register as a diagnostic variable
      data%id_pH = aed_define_diag_variable( 'pH', 'pH', 'pH')
    ELSE
      ! Link to module
-     data%id_pH = aed_locate_global(ph_link)
+     data%id_pH = aed_locate_variable(ph_link)
    ENDIF
 
    ! solution to get aed_carbon's pCO2 updated for atm exchange ...
-   data%id_c_pco2 = aed_locate_global(pco2_link)
+   data%id_c_pco2 = aed_locate_variable(pco2_link)
 
    !----------------------------------------------------------------------------
    ! Register diagnostic variables
diff --git a/src/aed_organic_matter.F90 b/src/aed_organic_matter.F90
index cade9d1..e318f0c 100644
--- a/src/aed_organic_matter.F90
+++ b/src/aed_organic_matter.F90
@@ -568,6 +568,7 @@ SUBROUTINE aed_define_organic_matter(data, namlst)
    ELSE
      data%id_Psed_pon = aed_define_diag_variable('Psed_pon','mmol/m**2/s',  'PON sedimentation')
    ENDIF
+   data%use_Psed_link_pop = Psed_pop_variable .NE. ''
    IF (data%use_Psed_link_pop) THEN
      data%id_Psed_pop = aed_locate_sheet_variable(Psed_pop_variable)
    ELSE