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- Title
Nutrient dynamics and biological consumption in a large continental shelf system under the influence of both a river plume and coastal upwelling.
- Authors
Aiqin Han; Minhan Dai; Shuh-Ji Kao; Jianping Gan; Qing Li; Lifang Wang; Weidong Zhai; Lei Wang
- Abstract
We examined the dynamics of dissolved inorganic nitrogen (DIN, nitrate + nitrite), dissolved inorganic phosphorus (DIP), and silicate (Si(OH)4) in the northern shelf of the South China Sea in summer, which is under a complex hydrodynamic scheme largely shaped by river plume and coastal upwelling, along with the enhanced biological consumption of nutrients therein. The Pearl River plume, with high nutrient concentrations (⇔ 0.1-14.2 µmol L-1 for DIN, ⇔ 0.02-0.10 µmol L-1 for DIP, and ⇔ 0.2-18.9 µmol L-1 for Si(OH)4), occupied a large area of the middle shelf (salinity < 33.5). The nearshore area had high nutrient concentrations apparently sourced from subsurface nutrient-replete waters through wind-driven coastal upwelling. These nutrient levels were significantly elevated relative to those on the oligotrophic outer shelf where DIN, DIP, and Si(OH)4 concentrations dropped to < 0.1 µmol L-1, ⇔ 0.02-0.03 µmol L-1, and ⇔ 2.0 µmol L-1, respectively. A three end-member mixing model was constructed based on potential temperature and salinity conservation to assess biological consumption of inorganic nutrients, which was denoted by Δ and defined by the deviation from conservative mixing. In the coastal upwelling zone and deep chlorophyll maximum layer, the nutrient uptake ratio ΔDIN : ΔDIP was 16.7, which is the classic Redfield ratio. In contrast, in the river plume the uptake ratio was 61.3 ± 8.7. We believed that an alternative non-DIP source likely contributed to this higher DIN : DIP consumption ratio in the river plume regime. Meanwhile, Si(OH)4 showed predominant consumption in the river plume and a combination of regeneration and consumption along the path of the coastal upwelling current.
- Subjects
NITROGEN; PHOSPHORUS; SILICATES; HYDRODYNAMICS; TEMPERATURE; CHLOROPHYLL
- Publication
Limnology & Oceanography, 2012, Vol 57, Issue 2, p9
- ISSN
0024-3590
- Publication type
Article
- DOI
10.4319/lo.2012.57.2.0486