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RESEARCH ARTICLE
Contents Vol 60(10)

Sources of nutrients driving production in the Gulf of Carpentaria, Australia: a shallow tropical shelf system

Michele A. Burford A D , Peter C. Rothlisberg B and Andrew T. Revill C
+ Author Affiliations
- Author Affiliations

A Australian Rivers Institute, Griffith University, Nathan, Qld 4111, Australia.

B CSIRO Marine and Atmospheric Research, PO Box 120, Cleveland, Qld 4163, Australia.

C CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tas. 7001, Australia.

D Corresponding author. Email: m.burford@griffith.edu.au

Marine and Freshwater Research 60(10) 1044-1053 https://doi.org/10.1071/MF08291
Submitted: 14 October 2008  Accepted: 3 March 2009   Published: 20 October 2009

Abstract

The tropical Gulf of Carpentaria, Australia, has recently been identified as one of the world’s least impacted marine areas, presenting a unique opportunity to understand the nutrient drivers of productivity. The present study examined the nitrogen (N) sources and transformations in this pristine area and the role of N in fuelling primary productivity, principally based on summer data. The N budget estimates on a whole-of-Gulf basis suggest that river N inputs are unlikely to be major contributors to primary productivity. In the deeper waters of the Gulf, beyond the coastal boundary current, the main source of N is estimated to be N fixation by cyanobacteria, principally the abundant genus Trichodesmium. The present study measured high N fixation rates and depleted δ15N–N ratios in the particulate matter in the water column during a summer bloom. During summer, bottom N concentrations increased and δ15N–N ratios were depleted, suggesting that benthic mineralisation is occurring. It is therefore likely that detrital material from N-rich Trichodesmium is an important contributor to benthic processes. During winter, wind-driven mixing results in N from the bottom waters reaching the euphotic zone, and fuelling primary productivity. Therefore, Trichodesmium has an important direct and indirect role in contributing to primary productivity in this pristine tropical ecosystem.

Additional keywords: nitrogen budget, nitrogen fixation, Trichodesmium.


Acknowledgements

We acknowledge the help of the captain and crew of the RV Southern Surveyor and FV Flinders Pearl, Robert Pendrey, Frank Coman, Andrew Cook and Catherine Leigh in undertaking field sampling, Neale Johnson undertook the nutrient analyses, Jason Kerr measured ethylene production, Scott Condie and Eric Wolanski provided data on physical processes in the Gulf, Andrew Brooks provided river flow rate data, Wayne Rochester provided data and data management expertise, Catherine Leigh provided a figure, Miles Furnas provided nutrient data from Torres Strait, and Scott Condie and one anonymous reviewer provided comments on the manuscript.


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