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Anilkumar, N.
- Is Primary Productivity in the Indian Ocean Sector of Southern Ocean Affected by Pigment Packaging Effect
Abstract Views :212 |
PDF Views:91
Authors
S. C. Tripathy
1,
S. Pavithran
1,
P. Sabu
1,
R. K. Naik
1,
S. B. Noronha
1,
P. V. Bhaskar
1,
N. Anilkumar
1
Affiliations
1 National Centre for Antarctic and Ocean Research, Ministry of Earth Sciences, Headland Sada, Vasco-da-Gama, Goa 403 804, IN
1 National Centre for Antarctic and Ocean Research, Ministry of Earth Sciences, Headland Sada, Vasco-da-Gama, Goa 403 804, IN
Source
Current Science, Vol 107, No 6 (2014), Pagination: 1019-1026Abstract
The probable cause for photoinhibition of primary productivity (PP) in the surface layers of the Indian Ocean sector of the Southern Ocean (SO) was studied during the austral summer (February) 2010. Chlorophyll a (Chl a) and PP values were higher for polar stations compared to offshore stations and showed surface maxima; however, subsurface Chl a maxima was observed in two of the offshore stations. Biomass explained 36% of variance in PP and was not the sole controlling factor for PP variability. Euphotic zone integrated PP showed increasing trend from offshore to polar stations and varied from 159.56 to 1083.57 mg C m-2 d-1. The relationship between Chl a-specific PP (PB) and the corresponding photosynthetically active radiation in the water column was linear for offshore and curvilinear for polar stations, indicating the occurrence of 'photoinhibition' in the surface waters of polar stations. This could be ascribed to the onset of pigment packaging (the 'package effect') as larger phytoplankton (diatoms) dominated the polar stations, where macronutrients ratio was ideal (N : P ∼ 16 and N : Si ∼ 1) for growth of diatoms. Despite high Chl a in the polar waters, the corresponding PP was proportionally not high compared to the offshore stations. We suggest that larger phytoplankton are susceptible to pigment packaging, which in turn decreases their light-absorption/photosynthetic efficiency, resulting in lower PP, which is otherwise expected to be higher in the presence of elevated biomass.Keywords
Light Absorption, Package Effect, Primary Productivity, Phytoplankton Community.Full Text
- Observational Evidence of the Southward Transport of Water Masses in the Indian Sector of the Southern Ocean
Abstract Views :188 |
PDF Views:93
Authors
Affiliations
1 National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-gama, Goa 403 804, IN
1 National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-gama, Goa 403 804, IN
Source
Current Science, Vol 107, No 9 (2014), Pagination: 1573-1581Abstract
The southward transport of water masses in the Indian sector of the Southern Ocean (SO) is compared using the hydrographic data collected during the austral summer of 2010 and 2011. It has been found that subtropical surface water (STSW) underwent maximum southward displacement during the study period. The southward extent of STSW was at 45°S during 2011, but was restricted to 427°S during 2010. During 2011, three eddies were identified along the cruise track, whereas during 2010 eddies were absent. Satellite sea-level anomaly showed that these eddies were associated with the highly unstable Agulhas Return Current (ARC). The present study shows that STSW is transported along the peripheries of these eddies during 2011. There are indications of transport of mode water as well, but this is not resolved in the present study. Analysis of eddy kinetic energy shows a positive linear decadal trend; also, peak eddy lagged the southern annular mode by a year. This indicates that though the eddies may act locally, they are linked to the large-scale variability in the southern hemisphere.Keywords
Eddy Kinetic Energy, Oceanic Fronts, Subtropical Surface Water, Water Masses.Full Text
- Seasonal Surface Chlorophyll a Variability in the Seychelles–Chagos Thermocline Ridge
Abstract Views :214 |
PDF Views:80
Authors
Affiliations
1 National Institute of Ocean Technology, Chennai 600 100, IN
2 National Centre for Antarctic and Ocean Research, Goa 403 804, IN
1 National Institute of Ocean Technology, Chennai 600 100, IN
2 National Centre for Antarctic and Ocean Research, Goa 403 804, IN
Source
Current Science, Vol 114, No 04 (2018), Pagination: 868-878Abstract
Seychelles–Chagos Thermocline Ridge (SCTR, 5°–10°S, 50°–75°E) in the southwestern tropical Indian Ocean is a unique area that experiences year-round upwelling. This is a response to the upward Ekman pumping prevalent in the region. Satellite data, model data and objectively analysed Argo temperature/salinity data have been used to study the seasonal surface chlorophyll a (chl a) variability in SCTR. Variability of surface chl a concentration in SCTR showed a weak semiannual signature. The western part of SCTR (WSCTR, 50°–62°E) is characterized by higher chl a concentration than the eastern part (ESCTR, 63°–75°E). Average chl a concentration in WSCTR/ESCTR showed a primary peak in July– August (~0.26/~0.16 mg/m3) and a secondary peak in January (~0.14/~0.12 mg/m3). Minimum chl a concentration (~0.12/~0.1 mg/m3) was observed during March– April and December–January. The high amplitude of chl a variability observed during July–August is associated with weak stratification and deep mixed layer depth (MLD). Deep MLD reaching to nutrient-rich thermocline entrains nutrients to the surface and thereby increases the surface chl a concentration. However, the low surface chl a concentration is a result of shallow MLD in the region. The deep MLD (30–40 m) observed during June–October is dominated by wind mixing and supported by buoyancy mixing. Shallow MLD (<30 m) observed during rest of the year is due to weak wind mixing and high surface buoyancy. The high surface buoyancy is a manifestation of ocean surface warming and presence of low saline surface waters in the SCTR region.Keywords
Buoyancy Flux, Chlorophyll a, Climatology, Wind Mixing.Full Text
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