What is GOTM GOTM is a Public Domain

What is GOTM ? GOTM is a Public Domain water column model with a library of state-of-the-art turbulence closure models GOTM has a module with biogeochemical models ranging from NPZ-type to complex ecosystem models such as ERSEM and chemical models (IRON, ROLM) GOTM turbulence and bio modules are integrated into 3 D circulation models GOTM has a large user community GOTM has a website with source code, documentation and scenarios for download GOTM has a graphical user interface (GOTM-GUI)

Online since 1999, 50000 logins, mostly from Canada & US

GOTM Physics • Prognostic equations for current velocity, salt, temperature, turbulent kinetic energy (TKE) and TKE dissipation rate (or other length scale) • Horizontal gradients neglected or parameterised • Surface forcing via standard bulk formulae • Simple bi-modal light absorption • Effects of surface wave breaking considered • Good quantitative reproduction of field observations of turbulence

Surface dynamics in the Baltic Proper simulated with GOTM Reissmann et al. , 2007

GOTM-turb module in 3 D models • • ROMS: generic model recoded from GOTM MOM-4: turbulence module integrated POLCOMS: turbulence module integrated FVCOM: turbulence module integrated MOHID: turbulence module integrated OPA: test implementations by different groups BSH-model: implementation under work

Biogeochemical models in GOTM • Implementation constraints: – – Large number of models possible Easily extendable Large choice for numerical solvers for r. h. s. Integration into 3 D models supported • Implemented models – NPZD, Fasham, ERGOM, IRON, ROLM, ERSEM, Cyano Life Cycle, SPM, . . . • New solvers for r. h. s. developed for GOTM-BIO – Positive definite Modified Patankar solvers (Burchard et al. , 2003, 2005) – Positive definite Extended Modified Patankar solvers (Bruggeman et al. , 2006) See Burchard et al. (2006) for an overview

Surface nutrient from NPZD model in Northern North Sea with different solvers Explicit solver at long time steps (left) does not obey nutrient limitation. Stiff solver (right, Burchard et al. [2003, 2005]) is stable and accurate. Note the different scales.

GOTM-Bio in 3 D models: GETM-BFM for the North Sea Bathymetry: 6 nautical mile grid 25 vertical layers 132*114 (dry+wet) points D (m) Slide provided by Piet Ruardij (NIOZ) GETM: 3 d-hydrodynamical model BFM (<--ERSEM) 4 material cycles (C, N, P, Si) Dynamical modelling of chlorophyll Pelagic: phytoplankton, micro & mesozooplankton, bacteria Benthic: zoobenthos, aerobic & anaerobic bacteria Diagenetic processes

Surface Chlorophyll in the North Sea from GETM-BFM Simulation and animation by Piet Ruardij (NIOZ) Inga Hense & Hans Burchard

Surface nitrate before spring bloom GETM-BFM for North Sea simulation Surface nitrate in summer Bottom oxygen in late summer Results provided by Paul Mc. Cloghrie (CEFAS)