文档介绍：ARTICLE IN PRESS
Deep-Sea Research II 54 (2007) 925–942
Variability in nitrogen uptake and fixation in the oligotrophic
waters off the south west coast of Australia
. Twomey, . WaiteÃ, V. Pez, . Pattiaratchi
School of Environmental Systems Engineering, The University of Western Australia, 35 Stirling Hwy, Crawley,
Western Australia 6009, Australia
Received 5 December 2005; received in revised form 17 October 2006; accepted 18 October 2006
Available online 6 June 2007
Abstract
The results presented in this study provide the first broad-scale regional characterisation of the phytoplankton-nitrogen
dynamics across the continental shelf between the Abrolhos Islands and Cape Leeuwin, Western Australia. We
demonstrate key features of N-uptake, including nitrate and ammonium uptake and N fixation, across the dominant
current systems of the west coast of Australia during a 2-week period in spring–summer. The surface waters of the region
were N impoverished with low phytoplankton biomass. Nitrate and ammonium uptake rates were among the lowest on
record, and f-ratios were high compared to other oligotrophic systems (f-ratio throughout), indicating an equal
preference for nitrate and ammonium uptake. Areas of high phytoplankton biomass were most likely fuelled by nitrate
transported into the euphotic zone during temporally short bursts of upwelling on weekly, rather than monthly time
scales. When upwelling had relaxed, phytoplankton productivity was largely maintained by microbial regeneration in the
euphotic zone. A large proportion (20–60%) of the phytoplankton biomass was comprised of picoplankton and
nanoplankton cyano