ERSEM

ERSEM (the European Regional Seas Ecosystem Model) is a mature plankton functional type model that was initially developed by a framework 3 project¹. It is related to NPZD type models but includes several refinements necessary to correctly represent the key processes of temperate shelf ecosystems; the main ones being some plankton community complexity, the microbial loop, variable nutrient stoichiometry, variable carbon : chlorophyll ratios and a comprehensive description of benthic biochemical and ecological processes^2,3,4.

Figure 1 illustrates the trophic structure of the model whose top closure is provided by a relatively simple mesozooplankton description. The units of currency of ERSEM are Carbon, Nitrogen, Phosphorus, Silicon & Oxygen.

ERSEM may be coupled to a range of hydrodynamic models in 1D (GOTM)⁵ or 3D (POLCOMS or NEMO)⁶ which provide information on T&S, mixing and circulation or run alone in ‘aquarium’ mode. Figure 2 illustrates the Atlantic Margin Model domain, the typical 3D domain currently used The resolution is ~7km with 32 sigma layers. Much effort has been applied to the evaluation of this model system^7,8,9. ERSEM, or its close relation the Biogeochemical Flux Model (BFM), have been applied to other systems including tropical upwelling and oligotrophic situations² and globally¹⁰ with some success.

ERSEM has recently been extended to include the carbonate system giving it a predictive capability for future acidification states; impacts on ecosystem processes are being coupled in, as information becomes available¹¹.

Figure 1.

Figure 2.
Image produced by: Jason Holt, POL

References:
1. Baretta et al, 1995. Neth J Sea Research 33; and 1997, J Sea Research 38 (3-4) (ERSEM special issues).
2. Blackford et al, 2004. J Mar Sys, 52, 191-215.
3. Ebenhoh et al, 1995. Neth J Sea Research 33, 423-452.
4. Ruardij et al, 1995. Neth J Sea Research 33, 453-483.
5. Allen et al, 2004. J Sea Research, 52, 1-20.
6. Allen et al, 2001. Sarsia 86, 423-440.
7. Holt et al, 2005, J Mar Sys, 57, 167-188.
8. Lewis et al, 2006, J Mar Sys, 2006, 209-224.
9. Allen et al, J Mar Sys, 68, 381-404.
10. Vichi et al, 2007, J Mar Sys, 64, 89-109 and 110-134.
11. Blackford et al 2007. J Mar Sys. 64, 229-242.

ERSEM State Variables

State variable	elements	description
Pelagic
N1	p	phosphate
N3	n	nitrate
N4	n	ammonium
N5	s	silicate
P1	cnps	diatoms
P2	cnp	flagellates
P3	cnp	picoplankton
P4	cnp	dinoflagellates
P5	cnp	Coccolithophores (not yet in 3D)
B1	cnp	bacteria
Z6	cnp	heterotrophic nanoflagellates
Z5	cnp	microzooplankton
Z4	cnp	mesozooplankton
R1	cnp	dissolved labile organics
R2	cnp	refractory labile organics
R4	cnp	small particulate organics
R6	cnps	medium particulate organics
R8	cnps	large particulate organics
O2	o	oxygen
O3	c	dissolved inorganic carbon
Benthic
K1	p	phosphate
K3	n	nitrate
K4	n	ammonium
K5	s	silicate
H1	cnp	aerobic bacteria
H2	cnp	anaerobic bacteria
Y2	cnp	deposit feeders
Y3	cnp	suspension feeder
Y4	cnp	meiobenthos
G2	o	oxygen
G3	c	dissolved inorganic carbon
D1	m	oxygen penetration depth - metres
D2	m	nitrate / sulphide horizon
Q1	cnp	dissolved organic matter
Q6	cnps	particulate organic matter
Q7	cnps	buried organic matter
Derived Carbonate System Parameters
TA		Alkalinity
pH		pH
pCO2w		Partial pressure
HCO3		Bicarbonate
CO3		Carbonate
Oma		Aragonite saturation state
Omc		Calcite saturation state