Coral skeleton-bound nitrogen isotopes reconstruct patterns of upwelling on the Great Barrier Reef

Hanieh Tohidi Farid, Southern Cross university, Southern Cross Geoscience, Lismore, Australia and Dirk Erler, Southern Cross University, Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Lismore, NSW, Australia
Abstract:
On the outer Great Barrier Reef (GBR), upwelling is thought to play an important role in sustaining biological productivity. However our understanding of temperate nutrient supply through upwelling is limited to a few years at best. Here we use the nitrogen (N) isotopic composition of coral skeletal-bound organic matter to reconstruct patterns of upwelling to shelf edge coral reef systems on the GBR over the past 70 years. Data from the southern tip of the GBR shows that periodic upwelling corresponds to strong El Nino conditions, but the signal is complicated by large terrestrial runoff events on the adjacent mainland. In the central GBR, the shelf edge is much further from the mainland and here the upwelling signature is more clearly linked with ENSO cycles. We find no evidence that the supply of nutrients through upwelling to the central GBR has changed significantly since the 1930’s, this is at odds with suggestions that upwelling frequency may have increased as a result of a strengthening East Australia Current.
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