Stable isotopes in Darwin rainfall
Projects in this theme
During January 2013, a community sampling program was launched to collect rainfall during a monsoon ‘burst’ over Darwin. Sixteen sites were sampled repeatedly at 12 hour intervals from January 13 - 21 by a network of volunteers. It appears that rainfall data with a similar temporal and spatial coverage has not previously been collected from Northern Australia. Only the involvement of a large number of volunteers made this sampling program possible.
The two main conclusions drawn from the data are: 1. The isotopic composition varied substantially over time and could be correlated with modelled air back-trajectories; both oxygen and hydrogen isotope compositions were much "lighter' on Jan 13 when the moisture source was in Indonesia than on Jan 21 when the moisture source was directly west of Darwin and 2. The isotopic composition did not vary systematically between sites. The second observation suggests that future sampling of monsoonal rainfall from a few locations will be representative of the wider Darwin area.
One objective of collecting rainfall stable isotope data is to use stable isotopes as a tracer of water from individual rain fall events as it moves through the hydrological cycle, e.g. through soil, vegetation, groundwater and into rivers and the ocean. In addition to monsoonal rainfall, a smaller number of rain samples were obtained from thunderstorms during November - December 2012. These events had isotopic compositions that were mostly distinct from the monsoonal rainfall. Our next aim is to collect rainfall from a cyclone or tropical low as these events are known to sometimes produce extreme isotopic compositions.