Weathering and transport
We will develop source-to-sink routines of the flow of weathered material through the Earth System, incorporating both chemical and physical processes. These routines will be developed initially for integration within GENIE. However following the example of the GLIMMER ice-sheet component, the model’s interface will be generic to allow straightforward coupling with the Hadley Centre suite of models. Production modelling will primarily concentrate on terrestrial weathering under tropical, temperate and glacial regimes. The fluxes of both chemical (Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, DIN, DOC, DON, DOP, Fe, Ge and Si) and physical (i.e. sediment, incorporating estimates of bioavailable P and Fe) weathering products will then feed into a range of transport modules including fluvial, aeolian, glacial and oceanic components. Several of these routing schemes are already operational within GENIE and the Hadley Centre models and others will be developed elsewhere within QUEST and GENIEfy. Coupling these transport routines to oceanic sediment deposition will be tackled in collaboration with WP5
Sub-aerial/sub-aqueous weathering will be incorporated as routines within the MOSES/TRIFFID land-surface component of GENIE. Its coupling under the simple EMBM atmosphere will be improved in collaboration with GENIEfy. MOSES/TRIFFID and GLIMMER (see WP2) both exist within GENIE and the Hadley Centre models so that developments within WP6 will benefit both modelling communities. The primary controls on large-scale weathering patterns are available within both ESMs, namely climatic quantities such as temperature and precipitation, as well as vegetation and soil cover. The activity will develop a sub-grid parameterization procedure to incorporate the effect of topography on erosion due to both altitude and slope. The weathering processes of differing Earth-surface geologies will be incorporated using a mask approach. We will also develop a terrestrial equivalent of GENIE’s synthetic core module to facilitate the comparison of the model’s land surface predictions with paleao-data.
Several attempts have already been made at incorporating sub-glacial erosion and sediment transport processes within an ice sheet model. We will incorporate suitable modules into the GLIMMER ice-sheet model, which operates at a finer spatial resolution than the ESM into which it is embedded.
This work package will rely on close co-operation with activities within QUEST Deglaciation that will inform the method we employ to advect dust (containing Fe and Si) and d18O through our simple model atmosphere (EMBM). Generic tools for input and interpolation of wind fields from dynamical atmosphere models will be included in the GENIE framework in collaboration with GENIEfy. Wind fields, dust and d18O from the IGCM (on-line, asynchronous coupling) or FAMOUS (off-line, interpolation between extreme states) will be used in the EMBM.
The glaciological pathways of sediment transport though the Earth System will be completed by developing parameterizations for iceberg production, transport across the oceans surface and eventual melt (sediment deposition). Several alternative frameworks exist for iceberg modelling including Lagrangian and Eulerian formulations. It may also be necessary to improve the current fluvial transport algorithm within GENIE which assumes instantaneous downstream routing.
We intend to validate our integrated weathering and transport model in three phases. The first involves forcing using present-day observed climatology and land-cover patterns, with the aim of reproducing observed sediment and chemical yields. A secondary aspect of this phase will be the validation of our iceberg model for the present day. In the succeeding phases of validation, first observed land cover and then observed climatology will be replaced by model-generated fields. It is likely that this process will focus attention on GENIE’s ability to simulate precipitation and wind patterns.