Marine biology
The work undertaken for this work package is dedicated to extending and improving the representation of the relevant biogeochemical cycles, key plankton functional types, particulate sinking, ballasting and dissolution processes in the GENIE model and then testing the biogeochemical hypotheses for CO2 control.
The surface mixed-layer physics of GENIE will be improved from the present very crude, constant-depth mixed layer. This will be replaced by a relatively simple scheme, such as that in the OPA GCM , in which mixed-layer depth or, equivalently, turbulence energy, depends continuously on the inputs of wind and buoyancy. Such an extension is highly appropriate for an intermediate complexity model since it gives a significantly more accurate representation with relatively minor complication to the dynamics and extremely low computational overheads. It will have the double advantage of improving the characteristics of ventilation and water-mass production, and improving the interaction of the model physics and biology, via seasonal variability of mixed-layer depth.
The simplified phytoplankton functional type models of and will be added to GENIE. These models divide the phytoplankton community into nitrogen fixers, diatoms (silicifiers) and “other algae” that regulate the major oceanic nutrient cycles (nitrogen, phosphorus and silicon). They will be coupled to the framework of biogeochemical cycles we will establish in GENIE, with particular attention to the processes of oxygen consumption and denitrification at depth, and the preservation of organic material in the long-term sedimentary record. The ecology of these models is relatively simple, but appropriate to the low grid resolution of GENIE, and the requirement for a relatively long time-step. Furthermore, extensions such as zooplankton grazing, the microbial loop and dissolved organic material, can be added as appropriate. Calcification will initially be added as a simple function of primary production, but following recent studies , which suggest mechanisms by which CaCO3 production may be regulated, the framework could be extended both to incorporate these hypotheses and, potentially, to test them.
Parameterisations of processes controlling δ13C and δ18O fractionation in plankton from work-package 2 (δ13C) and the the QUEST-Deglaciation proposal (δ18O) will be incorporated into the functional types model. Biogeochemical contributions to the glacial CO2 change will be examined by using glacial climate boundary conditions, forcing GENIE with dust fields (Fe and Si input) from previous work and QUEST Deglaciation output. The change of CO2 at Termination I will be compared with that obtained by the biogeochemically enhanced version of FAMOUS (work-package 7). We will then undertake long transient integrations using GENIE. These will take the modelled spatial pattern of Fe/Si deposition from the atmosphere for the LGM and Holocene, and scale them with EPICA iron/dust over 800 kyr (synthesised in “work-package 1”../wp1). We will examine both the direct effects of Fe and Si fertilization and the potential for Fe fertilisation of N fixation to alter the N budget of the ocean.
We will improve the water column particle dissolution scheme, with a velocity-depending sinking scheme for all particulates (rather than assumed fixed pre-determined profiles). The scheme will include the effects of ballasting of sinking organic material by associated biogenic opal and CaCO3 . This will have the flexibility to closely mimic some of the ‘standard’ prescribed power law and exponential parameterizations, giving us good traceability with previous work. A new description for the remineralization of opal within the water column will be included, which shares a common mechanistic basis with the sedimentary diagenesis model. A synthesis of sinking fluxes and their inorganic components (including atmospherically-deposited dust) in the modern ocean provides an initial calibration dataset . Ballasting mechanisms will be evaluated.