GOTM goes biogeochemical: Application to Gotland Sea

Transcription

1 GOTM goes biogeochemical: Application to Gotland Sea Hans Burchard 1,2, Karsten Bolding 3, and Thomas Neumann 2 hans.burchard@io-warnemuende.de 1. Bolding & Burchard Hydrodynamics, Rostock, Germany 2. Baltic Sea Research Institute Warnemünde, Germany 3. Bolding & Burchard Hydrodynamics, Asperup, Denmark MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 1/16

2 Contents Motivation Literature used Basic structure of GOTM and GOTM-BIO Rationale for using stiff solvers Neumann et al. [2002] model implemented into GOTM-BIO Application of GOTM-BIO to Gotland Basin ecosystem Conclusions MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 2/16

3 Motivation To create an environment within which any biogeochemical model can be implemented without technical problems. To allow for direct plug-in of the GOTM-BIO module into GETM and other three-dimensional models. To offer a wide choice of advection schemes (for vertical motions) and solvers for the ODE (sources and sinks) part. MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 3/16

4 Literature used Burchard, H., K. Bolding, W. Kühn, A. Meister, T. Neumann, and L. Umlauf, Description of a flexible and extendable physical-biogeochemical model system for the water column, J. Mar. Sys., submitted, Burchard, H., E. Deleersnijder, and A. Meister, Discretisation of stiff biogeochemical models for the water column with modified Patankar schemes, Ocean Dynamics, submitted, Neumann, T., W. Fennel, C. Kremp, Experimental simulations with an ecosystem model of the Baltic Sea: A nutrient load reduction experiment, Global Biogeochemical Cycles, 16, /2001GB001450, MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 4/16

5 GOTM, Challenge Aim The Idea Key features Software Fortran code Test cases Forcing How to run? Information What's New Publications list FAQ User Group Hot Links Who's Who? Guestbook GOTM is a one-dimensional numerical model developed and supported by a core team of ocean modellers. GOTM aims at simulating accurately vertical exchange processes in the marine environment where mixing is known to play a key role. GOTM is freely available under the GPL (Gnu Public License). The interested user can download the source code, a set of test cases (Papa, November, Flex,...) and a comprehensive report. You are warmly invited to join the GOTM mailing list and send any comments/questions to the GOTM team or become a GOTM contributor. The GOTM developers are grateful to their sponsors. Page " maintained by webmaster. Last update: 10/28/00 18:10:02 PPM: 10/26/00 20:48:54 MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 5/16

6 Structure of GOTM-BIO MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 6/16

7 Stiff versus explicit solvers Surface nutrient content in Northern North Sea seen with numerical different solvers: nut(z = 0) [mmol N m 3 ] th-order Runge-Kutta RK4, t = 2 h RK4, t = 1/2 h RK4, t = 20 s nut(z = 0) [mmol N m 3 ] Modified Patankar-Runge-Kutta MPRK2, t = 2 h MPRK2, t = 1/2 h RK4, t = 20 s Julian Day Julian Day 1998 Explicit solver at long time steps (left) does not obey nutrient limitation. Stiff solver (right, Burchard et al. [2003]) is stable and accurate. Note the different scales. MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 7/16

8 Neumann et al model MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 8/16

9 Gotland Basin setups 1. Basic experiment 2. Experiment with reduced background turbidity (Jerlov class II instead of Jerlov class III) 3. Experiment with no feedback of bio-turbidity to the temperature equation (no feedback versus feedback) 4. Experiment with increased diapycnal mixing (k min = J kg 1 instead k min = J kg 1 ) 5. Experiment with increased wind forcing in February and March (factor 2 applied to wind speed in February and March) MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 9/16

10 Base run: temperature MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 10/16

11 Base run: Chl-a MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 11/16

12 Base run: DIN MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 12/16

13 Base run: DIP MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 13/16

14 Base run Turbidity run: Temp. MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 14/16

15 Base run no feedback run: Temp. MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 15/16

16 Conclusions 1D models for ecosystem studied need extra parameterisations for lateral processes (important e.g. for Gotland Basin studies) Nonetheless: 1D models help to understand model sensitivities and support ecosystem model development Improvements in physical parameterisations often require changes of ecosystem model parameters. Various other biogeochemical models have already been implemented into GOTM-BIO. Module can also be used for models for early diagenesis (sediment models). The new modified Patankar approach for solving the ODE part enables solution of stiff problems. MaBenE Workshop, School of Ocean Sciences, Bangor, Wales, Nov , p. 16/16