Globale Quantifizierung der CO2-Senke chemische Verwitterung und der resultierenden fluviatilen Transporte geogener gelöster Stoffe in die Randmeere
Final Report Abstract
The primary objective of the project was to quantify the CO2-consumption by chemical weathering and the fluxes of dissolved products via river systems at the global scale in a spatially explicit manner. As it was assumed, based on a literature review, that a previous global lithological map can be used for this task it turned out that a more detailed map, in resolution and properties, is needed to parameterize needed models. Thus a new global lithological map (GLiM) and a new concept was developed addressing the geochemical composition of lithological classes for the first time spatially explicitly to calculate CO2- consumption while considering trace minerals in rock formations. It turned out that these trace minerals are contributing a significant proportion to the CO2-consumption and generation of lateral dissolved geogenic matter fluxes. Based on regionally calibrated weathering models the global CO2-consumption by chemical weathering and resulting lateral fluxes of Si, Ca, Mg, Na and K into river systems was estimated as well as the liberation of phosphorous to soils and ecosystems. The derived model was implemented into a state of the art Earth System model to analyse the significance of phosphorous release by chemical weathering rates on the global carbon cycle considering projected climate scenarios. Results: Globally runoff and lithology are the main drivers of ‘natural’ chemical weathering rates, as well as soil shielding, partly controlled by long-term physical erosion processes, and temperature. The specific contribution of land cover and land use to weathering fluxes remains difficult to address, but is for developed areas of significance. Globally, soil shielding, due to either deeply weathered soils or a partly disconnection of fresh weatherable rocks from the hydrological cycle, reduces chemical weathering by about 44%, in comparison to the unlikely case that relatively unweathered rock surfaces would be exposed to the Earth’s surface as for example in case of tectonic arc areas. Rating curves suggest that about 70 % of the global weathering fluxes derive from about 10% of the land area with being South East Asia an important regional hot spot. For comparison, only 50% of the runoff is attributed to 10% of the land area. The Earth systems function of global chemical weathering rates is not linearly correlated with the runoff curve. Results support the hypothesis that seasonality and permafrost processes of thawing and freezing in arctic regions should cause an increase in weathering rates if compared to the other regions and the dominant drivers of global chemical weathering rates. Predicted fluxes from the calibrated model (not including permafrost processes) underestimates for the six largest arctic catchments weathering fluxes by 53%, while calculated fluxes from this region contribute less than 5% to the global fluxes. The contribution of trace minerals (calceous non silicate minerals like carbonates) in areas of silicate dominated lithological classes to chemical weathering fluxes was elaborated with a new technique and it is now possible to quantify their contribution to the total weathering fluxes. Trace carbonates add significantly to the fluxes from felsic plutonics, metamorphic rocks and siliciclastics in general. In addition the local phosphorous-release by chemical weathering is affected strongly by the spatial correlation between runoff, lithology, temperature and soil properties. A change in the global chemical weathering rate curve can influence the carbon cycle on geological time scales. Humid island arcs are identified as the primary hot spots of CO2-consumption by chemical weathering and weathering derived silica, phosphorous and cation fluxes. However due to their small local area, relevant regions are not represented adequately in state of the art spatially explicit Earth System models. This suggests a probable, not well constrained bias for the evaluation of the role of chemical weathering on feedback mechanisms in the Earth’s system due its influence on the coupled carbon, silicon and phosphorus cycles. Latter aspect needs to be studied in the future in more detail. Based on an analysis of land-ocean dissolved silica fluxes, about 1/3 of the chemical weathering derived fluxes are intercepted in regional seas. This finding might have impact on the identified role of silica in the biological pump affecting the global carbon cycle and needs further investigation, specifically if Earth system models are applied, which do not resolve these regional seas properly. During the project a new global lithological map was developed using additional resources which provides a significantly increased resolution (considering space and detail of description) if compared to previously applied global lithological maps. Additional layers of information were introduced, thus increasing the applicability for further research related to lateral land-ocean matter transfer in the Earth System, but also for ecosystem and hydrological studies. A further improvement of robust global estimates by more sophisticated models or even alternative purely mechanistically models covering all details of rock-soil and plant processes is hindered by the availability of reliable globally representative soil data as well as a lack of monitoring data from hotspot areas covering seasonality and the impact of extreme events like heavy storms (e.g., Typhoons).
Publications
- (2009). Bicarbonate-fluxes and CO2-consumption by chemical weathering on the Japanese Archipelago — Application of a multi-lithological model framework. Chemical Geology, 65(3/4), 237- 271
Hartmann, J.
(See online at https://doi.org/10.1016/j.chemgeo.2009.03.024) - (2009). Global CO2-consumption by chemical weathering: What is the contribution of highly active weathering regions? Global and Planetary Change, 69, 185-194
Hartmann, J., Jansen, N., Kempe, S., Dürr, H.H., Köhler, P.
(See online at https://doi.org/10.1016/j.gloplacha.2009.07.007) - (2009). Global patterns of dissolved silica export to the coastal zone: Results from a spatially explicit global model. Global Biogeochemical Cycles, 23, GB0A02, 1-13
Beusen, A.H.W., Dürr, H.H., Bouwman, A.F., Dekkers, A.L.M., Hartmann, J.
(See online at https://doi.org/10.1029/2008GB003281) - (2010). Dissolved silica mobilization in the conterminous USA. Chemical Geology 270(1-4), 90-109
Jansen, N., Hartmann, J., Lauerwald, R., Dürr, H.H., Loos, S., Middelkoop, H.
(See online at https://dx.doi.org/10.1016/j.chemgeo.2009.11.008) - (2010). Predicting riverine dissolved silica fluxes into coastal zones from a hyperactive region and analysis of their first order controls. International Journal of Earth Sciences, 99, 207-230
Hartmann, J., Jansen, N., Dürr, H.H., Harashima, A., Okubo, K., Kempe, S.
(See online at https://doi.org/10.1007/s00531-008-0381-5) - (2011). Chemical weathering rates of silicate-dominated lithological classes and associated liberation rates of phosphorus on the Japanese Archipelago - implications for global scale analysis. Chemical Geology, 287(3/4), 125-157
Hartmann, J., Moosdorf N.
(See online at https://doi.org/10.1016/j.chemgeo.2010.12.004) - (2012) The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust. International Journal of Earth Science, 1-12
Hartmann, J., Dürr, H.H., Moosdorf, N., Kempe, S., Meybeck, M.
(See online at https://doi.org/10.1007/s00531-010-0635-x) - (2012). Assessing the non-conservative fluvial fluxes of dissolved organic carbon in North America. Journal of Geophysical Research, 117(G1)
Lauerwald, R., Hartmann, J., Ludwig, W., and Moosdorf, N.
(See online at https://doi.org/10.1029/2011JG001820) - (2012). Retention of dissolved silica within the fluvial system of the conterminous USA. Biogeochemistry: 1-23
Lauerwald R., Hartmann J., Moosdorf N., Dürr H., Kempe S.
(See online at https://doi.org/10.1007/s10533-012-9754-8)
