Stable strontium isotope fractionation in marine and terrestrial environments

The work reported in this thesis applies a new isotope tracer, stable strontium isotopes (088186Sr), to address questions concerning changes in global climate that occur in response to continental weathering processes, and to constrain the modem marine geochemical Sr cycle. Stable Sr isotopes are a relatively new geochemical proxy. and as such their behaviour needs to be understood in differing forms of marine calcium carbonate, the archives from which records of past stable Sr variability in the oceans can be constructed. Foraminifera, coccoliths and corals (both aragonite and high Mg calcite) acquire aSS/MST values lighter than that of modem day seawater, (approximately 0.11, 0.05, 0.2 and 0.19 %0 lighter than seawater at _25°C respectively) providing a rneasureable offset which can be used to constrain the modern Sr outputs from the ocean and provide a better understanding of the modem Sr cycle. Using foraminifera as a sedimentary archive the first marine &88186Sr record of seawater over the last two glacial cycles has been constructed, and used to investigate changing carbonate input and output over this 145 kyr period. Modelling of the large excursion of &88186Sr to heavier values during Marine Isotope Stage (MIS) 3, reveals that this is more likely to be due to local changes in seawater or post-depositional alteration, rather then whole ocean changes. In the terrestrial environment &88!tI6Sr has been measured in the dissolved load of rivers from the Himalaya. It is found that, in general. rivers draining carbonate catchments possess lighter isotopic &88186Sr values than those from rivers draining silicates. Covariations of either 088186Sr vs. 030Si or &88/86Sr vs. l/[Sr] can be used to distinguish between rivers draining different catchment areas. iiiEThOS - Electronic Theses Online ServiceGBUnited Kingdo