Size-fractionated primary production studies in the vicinity of the Subtropical Front and an adjacent warm-core eddy south of Africa in austral winter

• Published in: Journal of Plankton Research
• Main Authors: Froneman, P.W., McQuaid, C.D., Laubscher, R.K.
• Format: Text
• Language: English
• Published: Oxford University Press 1999
• Subjects: ORIGINAL ARTICLES; Antarctic; Austral; Antarc*
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/21/11/2019; https://doi.org/10.1093/plankt/21.11.2019

Results are presented of size-fractionated primary production studies conducted in the vicinity of the Subtropical Front (STF), an adjacent warm-core eddy, and in Sub-antarctic waters during the third South African Antarctic Marine Ecosystem Study (SAAMES III) in austral winter (June/July) 1993. Throughout the investigation, total chlorophyll (Chl a ) biomass and production were dominated by small nano- and picophytoplankton. No distinct patterns in total Chl a were evident. At stations ( n = 7) occupied in the vicinity of the STF, total integrated biomass values ranged from 31 to 53 mg Chl a m–2. In the vicinity of the eddy, integrated biomass at the eddy edge ( n = 3) ranged from 24 to 54 mg Chl a m–2 and from 32 to 43 mg Chl a m–2 in the eddy ( n = 2). At the station occupied in the Sub-antarctic waters, total integrated biomass was 43 mg Chl a m–2. Total daily integrated production was highest at stations occupied in the vicinity of the STF and at the eddy edge. Here, total integrated production ranged from 150 to 423 mg C m–2 day–1 and from 244 to 326mg C m–2 day–1, respectively. In the eddy centre, total integrated production varied between 134 and 156 mg C m–2 day–1. At the station occupied in the Sub-antarctic waters, the lowest integrated production (141 mg C m–2 day–1) during the entire survey was recorded. Availability of macronutrients did not appear to limit total production. However, the low silicate concentrations during the survey may account for the predominance of small nano- and picophytoplankton. Differences in production rates between the eddy edge and eddy core were related to water column stability. In contrast, at stations occupied in the vicinity of the STF, the control of phytoplankton production appears to be related to several processes, including water column stability and, possibly, iron availability.