Global distributions of Fe, Al, Cu, and Zn contained in Earth's derma layers

To improve the usefulness and accuracy of modeling Earth's anthrobiogeochemical metal cycles, global maps at approximately 1° × 1° are produced of the concentrations and masses of Fe, Al, Cu, and Zn contained in continental sediments and soils. The maps generated utilize inverse distance weighting (IDW) and cokriging to generate new estimates for geospatially weighted mean global concentrations for these metallic micronutrients. Sediment metal concentration maps are generated from IDW of sediment samples; global soil maps are produced via cokriging upon an underlying parent rock dataset composed of both surface bedrock and sediment samples. Derived are independent estimates for the global mean concentrations in continental sediments (Fe = 3.1 wt.%, Al = 6.1 wt.%, Cu = 45 μg/g, Zn = 86 μg/g) and soils (Fe = 2.5 wt.%, Al = 3.9 wt.%, Cu = 17 μg/g, Zn = 50 μg/g). While continental sediment concentrations for Cu are within the range of previous estimates, Zn concentrations are relatively higher, ~ 20 μg/g above previous estimates. Fe and Al are slightly depleted (~ 1 wt.%) in continental sediments relative to previous estimates, likely ascribable to sampling bias and error inherent in the comparative methodologies. Besides an estimated global mean, metal concentrations in soils are also broken down by FAO soil group. Metal masses in sediments and soils remain within 30% of previous, non-spatial estimates. These maps also illustrate the discernable spatial variability across the Earth's surface. Despite data gaps, maps of metal mass show regional patterns such as the high quantities of Al in the soils and biomass of the Amazonia and Congo regions. Concentrations of metals are relatively high in the anthrosols of China. Finally, this analysis highlights those areas for which generating and providing publically available geochemical data should be prioritized. For instance, gypsisols, lixisols, and nitisols have little to no analytical data available on metal contents. A sensitivity analysis suggests that the most poorly constrained soil metal concentrations occur in the thick, old tropical soils of central Africa and the anthrosols of eastern China.

► Global maps of Fe, Al, Cu, and Zn contained in continental sediments and soils.
► Inverse distance weighting and cokriging generate new geospatially weighted estimates.
► Continental sediments: Fe = 3.1 wt.%, Al = 6.1 wt.%, Cu = 45 μg/g, and Zn = 86 μg/g.
► Soils: Fe = 2.5 wt.%, Al = 3.9 wt.%, Cu = 17 μg/g, and Zn = 50 μg/g.