Abstract
Trace elements and their isotopes are powerful proxies for reconstructing past changes in Earth’s ocean-atmosphere system, including carbon and climate cycling. This arises due to their intertwined behaviour within these systems and their preservation in oceanic sediments. The use of these elemental and isotopic proxies is reliant on a robust understanding of their biogeochemical cycling and oceanic mass balance. Importantly, the riverine input is the primary source of most trace elements into the ocean, and yet there remain significant uncertainties in the elemental and isotopic composition of this flux. This is problematic for forecasting future-climate scenarios, where the prerequisite for accurate predictions is well-defined controls on the riverine supply of trace elements and their isotopes. In this thesis, the elemental composition of 25 elements, the 87Sr/86Sr signature representing the strontium isotope weathering regime proxy, and the 238U/235U composition representing the uranium isotope paleo-redox proxy were quantified in 16 rivers spanning a wide range of climatic, tectonic and weathering conditions in the South Island of New Zealand. These datasets are combined with modelling and statistical approaches to provide improved, quantitative constraints on the effect of variable mineral weathering patterns and mineralogical sources on the dissolved riverine inventory of trace elements and trace element isotopes that are globally relevant for the rivers with elemental concentrations down to ultra-trace (pM) levels. The results of this thesis contribute to an improved understanding of the biogeochemical cycles of trace elements and their isotopes and facilitate improved, higher accuracy reconstructions of past changes in Earth’s ocean-atmosphere system.