1. Arctic Ocean Model Intercomparison Project, 14th Workshop, Woods Hole 20-25.10.2010
Modeling of influence of organic matter production and destruction on the carbonate system seasonal changes in the Arctic waters
Evgeny Yakushev, Kai Sørensen,
Norwegian Institute for Water Research (NIVA), Oslo, Norway
This work aimed in studying of the role of seasonality of the biogeochemical processes of organic matter production and decay in the seasonal changes of the carbonate system (pH, pCO2, aragonite saturation). Data received at a transect Tromsø – Spitsbergen with a Ferrybox equipped SOOP vessel (Fig. 1, 2)was used for verification. A 2D simplified vertical model was used to parameterize the hydrophysical processes of at a Coast-Open Arctic section (Fig. 3, 4). The biogeochemical processes were parameterized using OxyDep, simplified biogeochemical model aiming time scales seasonal and larger, that considered inorganic nutrient (NUT), dissolved (DOM) and particular (POM) organic matter and biota (BIO). Dissolved inorganic carbon (DIC) and alkalinity (Alk) were considered as independent model parameters. DIC changes were correlated with NUT using Redfield ratio, Alk was changed in the marine boundary of the modeled transect. The carbonate system equilibration was considered as a fast process and calculated at every time step using the iteration procedure. The carbonate system modeling was described on the base of standard approach (Roy et al., 1993, Wanninkoff, 1992, Dickson, 2010).
According to the model estimates the summer formation of DOC and POC and their further destruction can play a compatible role in the carbonate system seasonal dynamics. Modeled seasonal variations of pH (~0.2) are close to the observed ones t, i.e in February and in August (pH(Tot)).The received results allowed to demonstrate that the upper layer water pCO2 varies from 480 ppm in winter to minimum values of 280 ppm during the OM production period. Therefore the summer invasion of CO2 should be replaced by the winter evasion. The received results can be helpful for planning of expedition studies and analyzing of the archived field data, as well as for elaborating of the interannual and multidecadal changes models.
FIG.1. Ship of opportunity system in
Norwegian waters
Seasonal variabiity of the model components in the water column in case of absence (top) and present (bottom) of annual changes of density stratification.
FIG. 2. Distribution and variability of pH at the transect Tromso-Longyerbyen in February, May and August
NUT
POM
DOM
BIO
OXY
DIC
Alk pH
HCO3-
CO3--
pCO2
The carbonate system equilibration was considered as a fast process, and pH was calculated at every integration time step using Gauss iteration procedure. 10
depth levels
4 columns
Flux from
river
Seasonal changes
of T, S, NUT
at marine
boundary
Flux from atmosphere
400 km X 200 m
- carbonic acid dissociation constants according to (Roy et al., 1993),
- gas exchange following (Wanninkoff, 1992).
Variable
Meaning
Units
BIO
that is all the biota from bacteria to fish. BIO grows due to photosynthesis, loses inorganic matter due to respiration, and loses total (particulate and dissolved) organic matter due to methabolism, mortality, cannibalism etc.
μM N
NUT
that is the oxydized forms of nutrients (i.e. NO3 and NO2 for N), that don’t need additional oxygen for nitrification
POM
that is all kinds of labile particulate organic matter
DOM
that is all kinds of labile dissolved organic matter and reduced forms of inorganic nutrients (i.e. NH4 and Urea for N).
OXY
concentrations of dissolved oxygen, that, changed with the formation and mineralization of the organic matter following the Redfield ratio
μM O
FIG. 3. A simplified hydrophysical 2D vertical model of a coastal zone circulation aiming to test the biogeochemical and chemical sources models with forcing from the coast, atmosphere and the open sea.
FIG. 5 OxyDep, a simplified biogeochemical model aiming time scales seasonal and larger, coupled with carbonate system
OM production and decay lead to seasonal transformation of C between inorganic TIC and organic C: biota, detritus (POM) dissolved (DOM) that affect pH.
Modelled seasonal variations of pH (~0.2) are close to the observed ones at Tromsø-Longyearbyen transect, i.e in February and in August (pH(Tot), in situ).
This effect should be taken into consideration while analyzing the archive data and estimating interannual variability.
FIG 4. NODC data for the seasonal changes of T, S, Alk and NO3 (winter data in grey symbols and summer data in color) and parameterized winter and summer distributions.
Aknowledgements: This work was supported by KLIF and NIVA.