Passive tracer added to fabm.iow-spm.yaml

fabm.iow-spm.yaml

 # SPDX-FileCopyrightText: 2024 Helmholtz-Zentrum hereon GmbH
 # SPDX-License-Identifier: CC0-1.0
-# SPDX-FileContributor Ovidio Garcia Oliva <ovidio.garcia@hereon.de>instances:
+# SPDX-FileContributor Ovidio Garcia Oliva <ovidio.garcia@hereon.de>
+instances:
   spm:                               # arbitrary short name (required)
     use: true                        # optional, default = true
     long_name: spm                   # optional, default = short name
@@ -36,4 +37,14 @@
 #      pmpool: 530.0                  # bottom pool (kg m-2), default = rho*thickness_L1
 #      flufflayer: 2.65               # bottom pool (kg m-2), default = rho*thickness_fluff
     coupling:                        # optional
-    check_conservation: false        # default = false
\ No newline at end of file
+    check_conservation: false        # default = false
+  tracer:
+    use: true
+    long_name: passive_tracer
+    model: bb/passive
+    parameters:
+      vertical_velocity: 0.0            # vertical velocity (negative for settling, positive for rising) (m d-1), default = 0.0
+      specific_light_attenuation: 0.0   # specific light attenuation (m-1 (mol m-3)-1), default = 0.0
+      surface_flux: 0.0                 # surface flux (positive for into the water) (mol m-3 m d-1), default = 0.0
+    initialization:
+      c: 1.0                            # concentration (mol m-3)