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Characterisation of water masses and phytoplankton nutrient limitation in the East Australian Current separation zone during spring 2008

Citation

Hassler, CS and Djajadikarta, JR and Doblin, MA and Everett, JD and Thompson, P, Characterisation of water masses and phytoplankton nutrient limitation in the East Australian Current separation zone during spring 2008, Deep-Sea Research. Part 2: Topical Studies in Oceanography, 58, (5) pp. 664-677. ISSN 0967-0645 (2011) [Refereed Article]

Copyright Statement

Copyright 2010 Elsevier Ltd. All rights reserved.

DOI: doi:10.1016/j.dsr2.2010.06.008

Abstract

This study focuses on the comparison of oceanic and coastal cold-core eddies with inner-shelf and East Australian Current (EAC) waters at the time of the spring bloom (October 2008). The surface water was biologically characterised by the phytoplankton biomass, composition, photo-physiology, carbon fixation and by nutrient-enrichment experiments. Marked differences in phytoplankton biomass and composition were observed. Contrasted biomarker composition suggests that biomarkers could be used to track water masses in this area. Divinyl chlorophyll a, a biomarker for tropical Prochlorophytes, was found only in the EAC. Zeaxanthin a biomarker for Cyanophytes, was found only within the oceanic eddy and in the EAC, whereas chlorophyll b (Chlorophytes) was only present in the coastal eddy and at the front between the inner-shelf and EAC waters. This study showed that cold-core eddies can affect phytoplankton, biomass, biodiversity and productivity. Inside the oceanic eddy, greater phytoplankton biomass and a more complex phytoplankton community were observed relative to adjacent water masses (including the EAC). In fact, phytoplankton communities inside the oceanic eddy more closely resembled the community observed in the inner-shelf waters. At a light level close to half-saturation, phytoplankton carbon fixation (gCd-1) in the oceanic eddy was 13-times greater than at the frontal zone between the eddy and the EAC and 3-times greater than in the inner-shelf water. Nutrient-enrichment experiments demonstrated that nitrogen was the major macronutrient limiting phytoplankton growth in water masses associated with the oceanic eddy. Although the effective quantum yield values demonstrate healthy phytoplankton communities, the phytoplankton community bloomed and shifted in response to nitrogen enrichments inside the oceanic eddy and in the frontal zone between this eddy and the EAC. An effect of Si enrichment was only observed at the frontal zone between the eddy and the EAC. No response to nutrient enrichment was observed in the inner-shelf water where ambient NOx, Si and PO4 concentrations were up to 14, 4 and 3-times greater than in the EAC and oceanic eddy. Although results from the nutrient-enrichment experiments suggest that nutrients can affect biomass and the composition of the phytoplankton community, the comparison of all sites sampled showed no direct relationship between phytoplankton biomass, nutrients and the depth of the mixed layer. This is probably due to the different timeframe between the rapidly changing physical and chemical oceanography in the separation zone of the EAC.

Item Details

Item Type:Refereed Article
Keywords:East Australian Current, eddy, nutrient limitation, phytoplankton
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical Oceanography
Objective Division:Environment
Objective Group:Flora, Fauna and Biodiversity
Objective Field:Flora, Fauna and Biodiversity of environments not elsewhere classified
Author:Thompson, P (Dr Peter Thompson)
ID Code:119908
Year Published:2011
Web of Science® Times Cited:16
Deposited By:Centre for Ecology and Biodiversity
Deposited On:2017-08-07
Last Modified:2017-10-05
Downloads:0

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