Smitha, B R; Dr. Sajeev, R(Cochin University of Science and Technology, November , 2010)
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Abstract:
Upwelling regions occupies only a small portion of the global ocean
surface. However it accounts for a large fraction of the oceanic primary
production as well as fishery. Therefore understanding and quantifying
the upwelling is of great importance for the marine resources
management. Most of the coastal upwelling zones in the Arabian Sea are
wind driven uniform systems. Mesoscale studies along the southwest
coast of India have shown high spatial and temporal variability in the
forcing mechanism and intensity of upwelling. There exists an
equatorward component of wind stress as similar to the most upwelling
zones along the eastern oceanic boundaries. Therefore an offshore
component of surface Ekman transport is expected throughout the year.
But several studies supported with in situ evidences have revealed that
the process is purely recurring on seasonal basis. The explanation
merely based on local wind forcing alone is not sufficient to support the
observations. So, it is assumed that upwelling along the South Eastern
Arabian Sea is an effect of basin wide wind forcing rather than local
wind forcing. In the present study an integrated approach has been made to understand the process of upwelling of the South Eastern Arabian Sea.
The latitudinal and seasonal variations (based on Sea Surface
Temperature, wind forcing, Chlorophyll a and primary production),
forcing mechanisms (local wind and remote forcing) and the factors
influencing the system (Arabian Sea High Saline Water, Bay of Bengal
water, runoff, coastal geomorphology) are addressed herewith.
Description:
Department of
Physical Oceanography,Cochin
University of Science and Technology
Bijoy, Nandan S; Lathika, Cicily Thomas; Padmakumar, K B; Smitha, B R; Asha Devi, C R; Sanjeevan, V N(Polish Academy of Sciences, Institute of Oceanology, 2013)
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Abstract:
The phytoplankton standing crop was assessed in detail along the South Eastern
Arabian Sea (SEAS) during the different phases of coastal upwelling in 2009.During phase 1 intense upwelling was observed along the southern transects
(8◦N and 8.5◦N). The maximum chlorophyll a concentration (22.7 mg m −3) was
observed in the coastal waters off Thiruvananthapuram (8.5◦N). Further north
there was no signature of upwelling, with extensive Trichodesmium erythraeum
blooms. Diatoms dominated in these upwelling regions with the centric diatom
Chaetoceros curvisetus being the dominant species along the 8◦N transect. Along
the 8.5◦N transect pennate diatoms like Nitzschia seriata and Pseudo-nitzschia sp.
dominated. During phase 2, upwelling of varying intensity was observed throughout
the study area with maximum chlorophyll a concentrations along the 9◦N transect
(25 mg m−3) with Chaetoceros curvisetus as the dominant phytoplankton. Along
the 8.5◦N transect pennate diatoms during phase 1 were replaced by centric diatoms
like Chaetoceros sp. The presence of solitary pennate diatoms Amphora sp. and
Navicula sp. were significant in the waters off Kochi. Upwelling was waning during
phase 3 and was confined to the coastal waters of the southern transects with
the highest chlorophyll a concentration of 11.2 mg m−3. Along with diatoms,
dinoflagellate cell densities increased in phases 2 and 3. In the northern transects
(9◦N and 10◦N) the proportion of dinoflagellates was comparatively higher and was
represented mainly by Protoperidinium spp., Ceratium spp. and Dinophysis spp.