is assumed to be well mixed, so only one set of state variables is followed there.
Below the mixed layer, however, the values vary with both biological processes and
mixing between successive 1 m layers at realistic rates. All variable and parameter
names are given in Table 4.2.
Table 4.2 Symbols used in the model (simplified from Frost 1993).
(^) Biological and chemical state variables
P, PZ Phytoplankton carbon concentration in the mixed layer, and at depth −3 Z in the intermediate layer (mgC m
)
H,
HZ Herbivorous zooplankton carbon concentration (mgC m−3)
D,
DZ Concentration of detritus (mgC m−3)
N, NZ Nitrogenous nutrient (NO 3 or NH 4 ) concentration (mmol N m−3)
Physical environment input data (Fig. 4.8 )
I (^0) Incident solar radiation (ly day−1) (not explicit in equations shown here)
Zm Mixed-layer depth (m)
Mixed-layer temperature (°C)
Derived environmental properties
k Attenuation coefficient of irradiance (m−1) (not explicit in equations shown here)
PARZPhotosynthetically available irradiance (E m−2 day−1) at depth z
Fixed and variable parameters Value
Kv Vertical eddy diffusivity (cm^2 s−1) 0.1–1.80*
α Initial slope of phytoplankton photosynthesis vs. irradiance response (mgC [mg Chl a]
−1 [E
m−2]−1)
21.0
Pmax Maximum carbon-specific photosynthetic rate (mgC [mgC]−1 day−1) 0.47–
1.38**
ξ N : C in organic matter (mmol N m−3) 0.0126
Half-saturation constant for phytoplankton NH 4 uptake (mmol N m−3) 0.1
e Herbivore maximum specific ingestion rate (mgC [mgC]−1 day−1) 1.01–1.66†
f Half-saturation constant for herbivore ingestion (mgC m−3) 17.0
ρ 0 Herbivore grazing threshold (mgC m−3) 10.0
γ Herbivore growth efficiency 0.3
m Herbivore maximum specific mortality rate (mgC [mgC]−1 day−1) 0.30–0.50†
h Half-saturation constant for herbivore mortality (mgC m−3) 35.0
w Detrital degradation rate (fraction day−1) 0.03–0.05†