1. Norwegian Institute for Water Research, Oslo, Norway
14th AOMIP Workshop, WHOI,
On modeling of biogeochemical processes in oxygen-deficient and anoxic conditions
Yakushev E.V.
Norwegian Institute for Water Research, Oslo, Norway

2. Why the Arctic?
“Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning” (Diaz, Rozenberg, 2008)
Fjord systems: existing oxygen depletion in the coastal regions.

3. Oxygen depletion
Oxygen-deficient < 80% of sat.
Hypoxic < 30% of sat.
Suboxic < 10 μM (~3%) O2
Oxygen detection limit
“formal” 3 μM
“reachable?” 1 μM
Anoxic/Sufidic (H2S >0.3 μM)
A "healthy" aquatic environment should seldom experience DO less than 80%

4. Anoxic conditions in the water column
Rivers and rains
low So/oo
high So/oo
fresh water outflow
Sill
marine water Inflow
Formation of Halocline / Pycnocline

5. Anoxic conditions in the water columnOM
Mixing occurs down to halocline
Maximum depth of mixing (CIL in the Black Sea)
Weak turbulent transport of O2 exists to the deeper layer
O2 is using up for the OM decomposition

6. Anoxic conditions in the water column
Formation of
anoxia
H2S + NH4, Mn(II), Fe(II), CH4…
Flux of OM is not balanced by the flux of O2
and OM is decomposed with other electron-acceptors (NO3, Mn(IV), Fe(III), SO4, CO2…)

7. Redox interfaces structure
gradO2, NO3max,
PO4max
PO4min, NO2min, O2,NO3
Mn2+, NH4, CH4, S0
H2S, gradPO4max
Black Sea
Turbidity layer

8. Anoxic conditions in the water column
Baerumsbassenget
Drammensfjord (Richards, 1965)
Bunnefjord

9. Oslofjord

11. Oslo Fjord

12. Oslo Fjord

13. Hunnbunn

15. Anoxic conditions in the water column
H2S

16. Hunnbunn vertical structure
May 2o09
August 2o09

17. Process dependent of oxygen conditions
OXIC
> 62.5 μM
HYPOXIC
<62.5 μM
>10 μM
SUBOXIC
<10 μM
>0 μM
ANOXIC
=0 μM
Oxic mineralization of OM and nitrification +
Denitrification
/anammox
Oxydation of reduced species of S, Mn, Fe, C, N
Sulfatereduction,
resuction of oxydised
species of S, Mn, Fe, C
Mortality caused by low oxygen
Synthesis of OM

20. N+O model
NO3
NO2
NH4
Norg N2 O2
Goal: to study the process of formation of anoxic (O2=0 ) conditions
Am = KAm [Norg] – ammonification
Nf1 = KNf1 [NH4] fNf(O2) – nitrification 1
Nf2 = KNf2 [NO2] fNf (O2) – nitrification 2
Nr1 = KNr1 [NO3] fNr (O2) – nitratereduction 1
Nr2 = KNr2 [NO2] fNr (O2) – nitratereduction 2
Dn = KDn[NO2] fDn (O2) – denitrification
Sources:
RNorg= -Am
RNH4 = Am - Nf1+ Nr2
RNO2 = Nf1 - Nf2 + Nr1
RNO3 = Nf2 - Nr1 – Dn
RO2 = -m12 Am - m10 Nf1 –
-m11 Nf2 + m21 Nr1+ m21Nr2
Dependence of rates of processes on О2

21. N+O model
Anoxic conditions due to OM flux and restricted aeration of deep waters.
Necessity of parameterization of cycles of several elements
(Yakushev, 1992)

22. ROLM biogeochemical model
NO3
NO2
NH4
PON N2 O2
DON

23. ROLM biogeochemical model
NO3
NO2
NH4
PON N2 O2
SO4
S2O3 S0
H2S
DON

24. ROLM biogeochemical model
Phy
Zoo
NO3
NO2
NH4
PON N2 O2
SO4
S2O3 S0
H2S
DON
Bacteria
Ox.Aut
Ox.Het
Anox.Aut
Anox.Het

25. ROLM biogeochemical model
Phy
Zoo
PO4
POP
DOP
NO3
NO2
NH4
PON N2 O2
SO4
S2O3 S0
H2S
DON
Bacteria
Ox.Aut
Ox.Het
Anox.Aut
Anox.Het

26. ROLM biogeochemical model
Phy
Zoo
PO4
POP
DOP
NO3
NO2
NH4
PON N2 O2
Mn2+
Mn3+
SO4
S2O3 S0
H2S
DON
Fe2+
Fe3+
Bacteria
Ox.Aut
Ox.Het
Anox.Aut
Anox.Het
Mn4+

27. Scheme of calculations:
T,S, weather conditions
1D GOTM
T,S, light
Turbulence, sinking
Integration
Biogeochemical
changes
Parameterized biogeochemical
properties of the intrusions
ROLM
GOTM (General Ocean Turbulence Model), Burchard et al., 1999 (

28. Vertically balanced structure:
Gotland μM
4-5 μM m-1 O2
25 μM
3-4 μM m-1
Mn(II)
Mn(III)+Mn(IV) μM
300 μM
3-4 μM m-1
H2S
Black Sea
Model

29. Vertically balanced structure
3 m suboxic zone
PO4 minimum
Oxidized Mn maxima between O2 and H2S
Mn-oxidation: μM d-1 (Tebo, 1991, Schippers et al.,2005)
Kz=3.5x10-6, m2 s-1
WMn = 7.5 m d-1 Mn(II)|150 m = 10 μM
Mn-reduction: μM d-1 (Nealson et al.,1991)

30. Low mixing: Kz=1x10-6, m2 s-1 well-defined suboxic layer
small PO4 minimum
small Mn(III) and Mn(IV) maxima
low Mn-transformation rates
~ Central Black Sea

31. Large mixing: Kz=3.5x10-5, m2 s-1
c- layer
large PO4 minimum
large Mn(III) and Mn(IV) maxima
high Mn-transformation rates
~ Bosphorus region and the Black Sea RIM current

33. Modeling of oxygen-depletion processes in the Arctic:
Conclusions
Modeling of oxygen-depletion processes in the Arctic:
Open Arctic – no (climate will probably not create oxygen-minimum zones …)
Coastal regions and fjord system –yes (climate forced decreased mixing, permafrost …)
Open for collaboration/coupling with 3D regional models

34. THANK YOU!

35. Thank you !