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Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters
| Content Provider | Semantic Scholar |
|---|---|
| Author | Thomalla, Sandy J. Waldron, Hn Lucas, Mike Read, Jane F. Ansorge, Isabelle Jane Pakhomov, Evgeny A. |
| Copyright Year | 2010 |
| Abstract | During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the South- west Indian and Madagascar Ridge, between the Prince Ed- ward Islands and 31 S. The sections crossed a number of major fronts and smaller mesoscale features and cov- ered a wide productivity spectrum from subtropical to sub- antarctic waters. Associated with the physical survey were measurements of size fractionated chlorophyll, nu- trients and nitrogen (NO3, NH4 and urea) uptake rates. Subtropical waters were characterised by low chlorophyll concentrations (max = 0.27.3 mg m 3 ) dominated by pico- phytoplankton cells (> 81%) and very low f-ratios (< 0.1), indicative of productivity based almost entirely on recy- cled ammonium and urea. Micro-phytoplankton growth was limited by the availability of NO3 (< 0.5 mmol m 3 ) and Si(OH)4 (< 1.5 mmol m 3 ) through strong vertical strat- ification preventing the upward flux of nutrients into the euphotic zone. Biomass accumulation of small cells was likely controlled by micro-zooplankton grazing. In sub- antarctic waters, total chlorophyll concentrations increased (max = 0.74 mg m 3 ) relative to the subtropical waters and larger cells became more prevalent, however smaller phy- toplankton cells and low f-ratios (< 0.14) still dominated, despite sufficient NO 3 availability. The results from this study favour Si(OH)4 limitation, light-limited deep mixing and likely Fe deficiency as the dominant mechanisms con- trolling significant new production by micro-phytoplankton. The percentage of micro-phytoplankton cells and rates of new production did however increase at oceanic frontal re- gions (58.6% and 11.22%, respectively), and in the region of the Prince Edward archipelago (61.4% and 14.16%, re- spectively). Here, water column stabilization and local Fe- enrichment are thought to stimulate phytoplankton growth rates. Open ocean regions such as these provide important areas for local but significant particulate organic carbon ex- port and biological CO2 draw-down in an overall high nutri- ent low chlorophyll Southern Ocean. |
| Starting Page | 113 |
| Ending Page | 127 |
| Page Count | 15 |
| File Format | PDF HTM / HTML |
| DOI | 10.5194/os-7-113-2011 |
| Volume Number | 7 |
| Alternate Webpage(s) | http://researchspace.csir.co.za/dspace/bitstream/handle/10204/7069/Thomalla_2013.pdf;jsessionid=D503967D892B7D7547025FCE54F937E2?sequence=1 |
| Alternate Webpage(s) | https://www.ocean-sci.net/7/113/2011/os-7-113-2011.pdf |
| Alternate Webpage(s) | https://open.uct.ac.za/bitstream/handle/11427/6451/thesis_sci_2001_thomalla_sj.pdf?isAllowed=y&sequence=1 |
| Alternate Webpage(s) | https://doi.org/10.5194/os-7-113-2011 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
