Kumar,S.P.,Ramaiah,N.,Gauns,M.,Sarma,V.V.S.S.,Muraleedharan,P.M.,Raghukumar,S.,Kumar,M.D.,Madhupratap,M.
Physical forcing of biological productivity in the Northern Arabian Sea during the Northeast Monsoon Journal Article
In: Deep-Sea Research Part II, vol. 48 , no. 139, pp. 1115-1126, 2001.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, depth, feeding, lead, location, productivity, spatial scale, surface temperature, temperature
@article{,
title = {Physical forcing of biological productivity in the Northern Arabian Sea during the Northeast Monsoon},
author = {Kumar,S.P.,Ramaiah,N.,Gauns,M.,Sarma,V.V.S.S.,Muraleedharan,P.M.,Raghukumar,S.,Kumar,M.D.,Madhupratap,M.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48 },
number = {139},
pages = {1115-1126},
abstract = {Time-series observations at a nominally fixed location in the northern Arabian Sea (21§N, 64§E) during the Northeast Monsoon (winter, February) of l997 showed the prevalence of cold sea-surface temperatures (SST) and deep mixed layers resulting from winter cooling and convection. The covariation of nitrate concentrations in the surface layers and concentrations of chlorophyll a and primary production in the euphotic zone with mixed-layer depth (MLD) and wind suggests that carbon fixation was controlled primarily by physical forcing. Cooler waters during winter 1997 relative to winter 1995 were associated with deeper MLDs, higher nitrate concentrations, elevated primary productivity, and higher chlorophyll a concentrations, leading to the inference that even a 1§C decrease in SST could lead to significantly higher primary productivity. Satellite data on sea surface temperature (advanced very high-resolution radiometer; AVHRR) and TOPEX/POSEl- DON altimeter data suggest that this interannual variation is of basin-wide spatial scale. After the termination of winter cooling and subsequent warming during the Spring Intermonsoon, the Arabian Sea has low primary production. During the latter period, micro-organisms, i.e. heterotrophic bacteria and microzooplankton)-proliferate, a feeding mode through the microbial loop that appears to be inherent to mesozooplankton for sustaining their biomass throughout the year in this region.},
keywords = {Arabian Sea, chlorophyll, depth, feeding, lead, location, productivity, spatial scale, surface temperature, temperature},
pubstate = {published},
tppubtype = {article}
}
Time-series observations at a nominally fixed location in the northern Arabian Sea (21§N, 64§E) during the Northeast Monsoon (winter, February) of l997 showed the prevalence of cold sea-surface temperatures (SST) and deep mixed layers resulting from winter cooling and convection. The covariation of nitrate concentrations in the surface layers and concentrations of chlorophyll a and primary production in the euphotic zone with mixed-layer depth (MLD) and wind suggests that carbon fixation was controlled primarily by physical forcing. Cooler waters during winter 1997 relative to winter 1995 were associated with deeper MLDs, higher nitrate concentrations, elevated primary productivity, and higher chlorophyll a concentrations, leading to the inference that even a 1§C decrease in SST could lead to significantly higher primary productivity. Satellite data on sea surface temperature (advanced very high-resolution radiometer; AVHRR) and TOPEX/POSEl- DON altimeter data suggest that this interannual variation is of basin-wide spatial scale. After the termination of winter cooling and subsequent warming during the Spring Intermonsoon, the Arabian Sea has low primary production. During the latter period, micro-organisms, i.e. heterotrophic bacteria and microzooplankton)-proliferate, a feeding mode through the microbial loop that appears to be inherent to mesozooplankton for sustaining their biomass throughout the year in this region.
Banse,K.,English,D.C.
Geographical differences in seasonality of CZCS-derived phytoplankton pigment in the Arabian Sea for 1978-1986 Journal Article
In: Deep-Sea Research Part II, vol. 47, no. 322, pp. 1623-1677, 2000.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, depth, Gulf of Oman, lead, Oman, plankton, productivity, timing, trap, Upwelling
@article{,
title = {Geographical differences in seasonality of CZCS-derived phytoplankton pigment in the Arabian Sea for 1978-1986},
author = {Banse,K.,English,D.C.},
year = {2000},
date = {2000-01-01},
journal = {Deep-Sea Research Part II},
volume = {47},
number = {322},
pages = {1623-1677},
abstract = {In situ measurements of phytoplankton chlorophyll in the Arabian Sea were taken largely along temporally and spatially unevenly distributed sections, scarce especially prior to the operation of NASA's Coastal Zone Color Scanner (CZCS). Herein, the CZCS pigment observations between late 1978 and mid-1986 north of 10§N, including the outer Gulf of Oman, are depicted for 14 subregions beyond the continental shelves as daily means, often only five days apart. To eliminate bias from electronic overshoot, the data were reprocessed with a more conservative cloud screen than used for NASA's Global Data Set. The pattern, derived from the older in situ observations, of one period with elevated chlorophyll almost everywhere during the Southwest Monsoon (SWM) and one additional late-winter bloom in the north, is confirmed. The differing nitrate silicate ratios in freshly entrained water in the central and northern Arabian Sea seem to lead to different succession and perhaps to differing vertical fluxes, and during winter favor blooms only in the north. The spatial pigment pattern in the outer Gulf of Oman is not an extension of that of the northwestern Arabian Sea. The seasonal physical forcing explains much of the timing of pigment concentration changes, but not the levels maintained over long periods. From the CZCS observations it is unclear whether the period of high phytoplankton productivity expected during the SWM in the open Arabian Sea lasts for about two or four months. During this entire season, chlorophyll values in the upper layers rarely exceed 1-2 mg m-3 outside the zone influenced by the Arabian upwelling. Near 15§N, however, fluxes into sediment traps at 3 km depth indicate an onset of high primary production very soon after the arrival of the SWM and suggest a long period of high production in the open sea. The partial temporal disconnect during the SWM between pigment changes in the upper part of the euphotic zone and of fluxes into the traps is disconcerting. For future modeling of plankton production in the open Arabian Sea, the use of two size classes of phytoplankton is recommended. The utility of satellite-derived pigment concentrations (as opposed to temporal changes of pigment) for testing such models is questioned.},
keywords = {Arabian Sea, chlorophyll, depth, Gulf of Oman, lead, Oman, plankton, productivity, timing, trap, Upwelling},
pubstate = {published},
tppubtype = {article}
}
In situ measurements of phytoplankton chlorophyll in the Arabian Sea were taken largely along temporally and spatially unevenly distributed sections, scarce especially prior to the operation of NASA's Coastal Zone Color Scanner (CZCS). Herein, the CZCS pigment observations between late 1978 and mid-1986 north of 10§N, including the outer Gulf of Oman, are depicted for 14 subregions beyond the continental shelves as daily means, often only five days apart. To eliminate bias from electronic overshoot, the data were reprocessed with a more conservative cloud screen than used for NASA's Global Data Set. The pattern, derived from the older in situ observations, of one period with elevated chlorophyll almost everywhere during the Southwest Monsoon (SWM) and one additional late-winter bloom in the north, is confirmed. The differing nitrate silicate ratios in freshly entrained water in the central and northern Arabian Sea seem to lead to different succession and perhaps to differing vertical fluxes, and during winter favor blooms only in the north. The spatial pigment pattern in the outer Gulf of Oman is not an extension of that of the northwestern Arabian Sea. The seasonal physical forcing explains much of the timing of pigment concentration changes, but not the levels maintained over long periods. From the CZCS observations it is unclear whether the period of high phytoplankton productivity expected during the SWM in the open Arabian Sea lasts for about two or four months. During this entire season, chlorophyll values in the upper layers rarely exceed 1-2 mg m-3 outside the zone influenced by the Arabian upwelling. Near 15§N, however, fluxes into sediment traps at 3 km depth indicate an onset of high primary production very soon after the arrival of the SWM and suggest a long period of high production in the open sea. The partial temporal disconnect during the SWM between pigment changes in the upper part of the euphotic zone and of fluxes into the traps is disconcerting. For future modeling of plankton production in the open Arabian Sea, the use of two size classes of phytoplankton is recommended. The utility of satellite-derived pigment concentrations (as opposed to temporal changes of pigment) for testing such models is questioned.
Wiggert,J.D.,Jones,B.H.,Dickey,T.D.,Brink,K.H.,Weller,R.A.,Marra,J.,Codispoti,L.A.
The Northeast Monsoon's impact on mixing, phytoplankton biomass and nutrient cycling in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 47, no. 254, pp. 1353-1385, 2000.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, depth, growth, impact, lead, productivity, surface temperature, temperature, zooplankton
@article{,
title = {The Northeast Monsoon's impact on mixing, phytoplankton biomass and nutrient cycling in the Arabian Sea},
author = {Wiggert,J.D.,Jones,B.H.,Dickey,T.D.,Brink,K.H.,Weller,R.A.,Marra,J.,Codispoti,L.A.},
year = {2000},
date = {2000-01-01},
journal = {Deep-Sea Research Part II},
volume = {47},
number = {254},
pages = {1353-1385},
abstract = {In the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing. Due to the proximity of the permanent pycnocline to the sea surface, this mixing does not penetrate below 125 m. However, a strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to nitrate concentrations over the upper 100 m that exceed 4 æM toward the end of the monsoon. During the 1994/1995 US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined to be 1.35 gC/m2/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained. An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity. This model consisted of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by a rate constant determined by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface buoy that was part of the ONR Arabian Sea Experiment's central mooring. Our numerical experiments show that elevated surface evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration. We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface chlorophyll a concentration that have been previously observed in this region.},
keywords = {Arabian Sea, chlorophyll, depth, growth, impact, lead, productivity, surface temperature, temperature, zooplankton},
pubstate = {published},
tppubtype = {article}
}
In the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing. Due to the proximity of the permanent pycnocline to the sea surface, this mixing does not penetrate below 125 m. However, a strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to nitrate concentrations over the upper 100 m that exceed 4 æM toward the end of the monsoon. During the 1994/1995 US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined to be 1.35 gC/m2/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained. An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity. This model consisted of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by a rate constant determined by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface buoy that was part of the ONR Arabian Sea Experiment's central mooring. Our numerical experiments show that elevated surface evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration. We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface chlorophyll a concentration that have been previously observed in this region.