The major biogeochemical cycles on Earth, i.e. carbon, oxygen, water cycles, are tightly linked through processes like photosynthesis, respiration and combustion of fossil fuels by humans during the anthropocene. Combined measurements of concentrations and corresponding isotope compositions on carbon-, oxygen and hydrogen containing molecules help to disentangle relevant processes. Examples will be given that demonstrate the power of multi-parameter analyses for climate reconstructions and Earth system process understanding or to partition fossil fuel CO2 emissions by humans to involved carbon-containing reservoirs.