Hitchcock,G.L.,Lane,P.,Smith,S.,Luo,J.G.,Ortner,P.B.
Zooplankton spatial distributions in coastal waters of the northern Arabian Sea, August 1995 Journal Article
In: Deep-Sea Research Part II, vol. 49, no. 387, pp. 2403-2423, 2002.
Abstract | BibTeX | Tags: acoustic, Arabian Sea, displacement, Distribution, migration, Oman, surface temperature, temperature, trend, Upwelling, zooplankton
@article{,
title = {Zooplankton spatial distributions in coastal waters of the northern Arabian Sea, August 1995},
author = {Hitchcock,G.L.,Lane,P.,Smith,S.,Luo,J.G.,Ortner,P.B.},
year = {2002},
date = {2002-01-01},
journal = {Deep-Sea Research Part II},
volume = {49},
number = {387},
pages = {2403-2423},
abstract = {The spatial distribution of zooplankton biomass was surveyed in coastal waters of the northern Arabian Sea during the 1995 Southwest Monsoon (August) on cruise MB 95-06 of the NOAA Ship Malcolm Baldrige. Vertical patterns of displacement volumes from a limited set of paired day-night MOCNESS tows suggest there was little diel vertical migration in the coastal waters off the southern Arabian Peninsula. Zooplankton biomass varied from 5.2 to 15.1 9 dw m(-2) (178-517mM Cm-2) in the upper 200-300m of Omani coastal waters. Distributions of acoustic backscatter were mapped in eight daytime acoustic Doppler current profiler transects in coastal waters off Oman and Somalia. Several transects contained maxima in acoustic backscatter that coincided with cool, fresh surface features that were several tens of kilometers wide. Although there was considerable scatter in the relationship between acoustically determined biomass (ADB) of zooplankton and surface temperature, there was a trend of increased biomass in the cool surface temperatures of the Omani upwelling zone. Acoustic transects crossed two filaments that extended seaward from upwelling centers off Oman and Somalia. Estimated zooplankton ADB exported from the upwelling zones in the surface features was on the order of 300 kg dw s( -1 ). The physical and biological characteristics of filaments maintain zooplankton associated with upwelling areas, such as Calanoides carinatus, as they are advected offshore from coastal upwelling zones. (C) 2002 Published by Elsevier Science Ltd.},
keywords = {acoustic, Arabian Sea, displacement, Distribution, migration, Oman, surface temperature, temperature, trend, Upwelling, zooplankton},
pubstate = {published},
tppubtype = {article}
}
The spatial distribution of zooplankton biomass was surveyed in coastal waters of the northern Arabian Sea during the 1995 Southwest Monsoon (August) on cruise MB 95-06 of the NOAA Ship Malcolm Baldrige. Vertical patterns of displacement volumes from a limited set of paired day-night MOCNESS tows suggest there was little diel vertical migration in the coastal waters off the southern Arabian Peninsula. Zooplankton biomass varied from 5.2 to 15.1 9 dw m(-2) (178-517mM Cm-2) in the upper 200-300m of Omani coastal waters. Distributions of acoustic backscatter were mapped in eight daytime acoustic Doppler current profiler transects in coastal waters off Oman and Somalia. Several transects contained maxima in acoustic backscatter that coincided with cool, fresh surface features that were several tens of kilometers wide. Although there was considerable scatter in the relationship between acoustically determined biomass (ADB) of zooplankton and surface temperature, there was a trend of increased biomass in the cool surface temperatures of the Omani upwelling zone. Acoustic transects crossed two filaments that extended seaward from upwelling centers off Oman and Somalia. Estimated zooplankton ADB exported from the upwelling zones in the surface features was on the order of 300 kg dw s( -1 ). The physical and biological characteristics of filaments maintain zooplankton associated with upwelling areas, such as Calanoides carinatus, as they are advected offshore from coastal upwelling zones. (C) 2002 Published by Elsevier Science Ltd.
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.
Shalapyonok,A.,Olson,R.J.,Shalapyonok,L.S.
Arabian Sea phytoplankton during Southwest and Northeast Monsoons 1995: composition, size structure and biomass from individual cell properties measured by flow cytometry Journal Article
In: Deep-Sea Research Part II, vol. 48 , no. 221, pp. 1231-1261, 2001.
Abstract | BibTeX | Tags: abundance, Arabian Sea, diel, Distribution, location, surface temperature, temperature, Upwelling
@article{,
title = {Arabian Sea phytoplankton during Southwest and Northeast Monsoons 1995: composition, size structure and biomass from individual cell properties measured by flow cytometry},
author = {Shalapyonok,A.,Olson,R.J.,Shalapyonok,L.S.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48 },
number = {221},
pages = {1231-1261},
abstract = {As part of the US JGOFS Arabian Sea Process Study, we determined the abundance, size distributions and carbon biomass of autotrophic phytoplankton in the Arabian Sea during summer Southwest and fall Northeast Monsoon seasons of 1995 (R/V Thomas G. Thompson cruises TN 049 and TN 053). Flowcytometry of 60-ml samples was used to enumerate and determine scattering and fluorescence properties of Prochlorococcus sp., Synechococcus sp., and eukaryotic phytoplankton with cell equivalent spherical diameter up to 40 æm. Cellular forward light scattering was calibrated against Coulter size using 22 phytoplankton cultures spanning the size range 0.8-40 æm, grown exponentially in natural sunlight. The phytoplankton community structure was strongly linked to water-mass characteristics, and was affected by both intense monsoon-related environmental forcing and widespread and dynamic mesoscale structures; the magnitude of spatial variability was similar to that between seasons for all three phytoplankton groups. Prochlorococcus was numerically dominant in the more oligotrophic, stratified areas with surface nitrate concentrations below 0.1 æM and surface temperatures above 27§C. Its abundance was significantly greater during the NE Monsoon and was inversely correlated with the abundance of the two other groups. Synechococcus and eukaryotic phytoplankton cell concentrations covaried at most locations, were highest in areas of intense, monsoon-related mixing, and changed less between seasons than Prochlorococcus. The bulk of biomass of all three groups was located within the mixed layer. Only eukaryotes formed notable subsurface maxima at several offshore locations where Prochlorococcus dominated the mixed layer. Dramatically elevated eukaryotic phytoplankton concentrations in the nutrient-rich upwelling areas were due to the blooming of smaller (<3 æm) cells. Surprisingly, stratified, offshore, nutrient-depleted areas had concentrations of 10-40 æm phytoplankton cells similar to or even higher than upwelling areas. Thus, the mean eukaryotic cell size and the relative contribution of large nanoeukaryotes to the phytoplankton biomass were highest in offshore waters. Eukaryotes accounted for most of the phytoplankton carbon biomass - from about 50 to 80% on average during both seasons. Both Prochlorococcus and large (10 æm) nanoeukaryotes reached their greatest biomass contributions - up to 40% each - in the offshore oligotrophic locations. For the SW and NE Monsoon cruises, flow cytometrically-measured phytoplankton was estimated at 1.1 and 2.2 gCm-2 on average and comprised 33 and 38% of POC, respectively. Diel variability in cellular carbon content accounted for 52% of the observed variability in cellular carbon content for Prochlorococcus, 26% for Synechococcus, and 14% for eukaryotic phytoplankton cells at the surface.},
keywords = {abundance, Arabian Sea, diel, Distribution, location, surface temperature, temperature, Upwelling},
pubstate = {published},
tppubtype = {article}
}
As part of the US JGOFS Arabian Sea Process Study, we determined the abundance, size distributions and carbon biomass of autotrophic phytoplankton in the Arabian Sea during summer Southwest and fall Northeast Monsoon seasons of 1995 (R/V Thomas G. Thompson cruises TN 049 and TN 053). Flowcytometry of 60-ml samples was used to enumerate and determine scattering and fluorescence properties of Prochlorococcus sp., Synechococcus sp., and eukaryotic phytoplankton with cell equivalent spherical diameter up to 40 æm. Cellular forward light scattering was calibrated against Coulter size using 22 phytoplankton cultures spanning the size range 0.8-40 æm, grown exponentially in natural sunlight. The phytoplankton community structure was strongly linked to water-mass characteristics, and was affected by both intense monsoon-related environmental forcing and widespread and dynamic mesoscale structures; the magnitude of spatial variability was similar to that between seasons for all three phytoplankton groups. Prochlorococcus was numerically dominant in the more oligotrophic, stratified areas with surface nitrate concentrations below 0.1 æM and surface temperatures above 27§C. Its abundance was significantly greater during the NE Monsoon and was inversely correlated with the abundance of the two other groups. Synechococcus and eukaryotic phytoplankton cell concentrations covaried at most locations, were highest in areas of intense, monsoon-related mixing, and changed less between seasons than Prochlorococcus. The bulk of biomass of all three groups was located within the mixed layer. Only eukaryotes formed notable subsurface maxima at several offshore locations where Prochlorococcus dominated the mixed layer. Dramatically elevated eukaryotic phytoplankton concentrations in the nutrient-rich upwelling areas were due to the blooming of smaller (<3 æm) cells. Surprisingly, stratified, offshore, nutrient-depleted areas had concentrations of 10-40 æm phytoplankton cells similar to or even higher than upwelling areas. Thus, the mean eukaryotic cell size and the relative contribution of large nanoeukaryotes to the phytoplankton biomass were highest in offshore waters. Eukaryotes accounted for most of the phytoplankton carbon biomass - from about 50 to 80% on average during both seasons. Both Prochlorococcus and large (10 æm) nanoeukaryotes reached their greatest biomass contributions - up to 40% each - in the offshore oligotrophic locations. For the SW and NE Monsoon cruises, flow cytometrically-measured phytoplankton was estimated at 1.1 and 2.2 gCm-2 on average and comprised 33 and 38% of POC, respectively. Diel variability in cellular carbon content accounted for 52% of the observed variability in cellular carbon content for Prochlorococcus, 26% for Synechococcus, and 14% for eukaryotic phytoplankton cells at the surface.
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.
Tudhope,A.W.,Lea,D.W.,Shimmield,G.B.,Chilcott,C.P.,Head,S.
Monsoon climate and Arabian Sea coastal upwelling recorded in massive corals from southern Oman Journal Article
In: Palaios, vol. 11, no. 486, pp. 347-361, 1996.
Abstract | BibTeX | Tags: Arabian Sea, coral, India, Oman, surface temperature, temperature, Upwelling
@article{,
title = {Monsoon climate and Arabian Sea coastal upwelling recorded in massive corals from southern Oman},
author = {Tudhope,A.W.,Lea,D.W.,Shimmield,G.B.,Chilcott,C.P.,Head,S.},
year = {1996},
date = {1996-01-01},
journal = {Palaios},
volume = {11},
number = {486},
pages = {347-361},
abstract = {Corals living in the coastal waters of southern Oman experience the influence of the seasonally reversing Asian monsoon system. The objective of the research reported here is to assess the potential for using the skeletal chemistry of these corals to investigate past variability in the monsoon climate. To this end, 20-year long, monthly resolution geochemical records are presented for cores from two massive Porites corals, located 20 km apart near Marbat on the Arabian Sea coast of southern Oman. We consider four aspects of skeletal chemistry: oxygen and carbon isotopic composition, barium content and the nature and occurence of annual fluorescent bands within the coral skeletons. Coral skeletal ë18O documents variations in sea surface temperature which have regional and basin-wide significance. In particular, the ë18O of coral skeleton precipitated during the period of the NE monsoon is strongly correlated with annual rainfall anomalies in India, whilst that precipitated during the period of the SW monsoon appears to provide information on variability in the strength of coastal upwelling. The stable carbon isotope composition and barium content of these particular corals display strong annual cycles, but do not appear to directly record interannual climatic/oceanographic variability. It is concluded that corals on the coast of southern Oman have great potential to provide high-resolution, century-long records of oceanographic and climatic variability associated with the operation of the monsoon climate system.},
keywords = {Arabian Sea, coral, India, Oman, surface temperature, temperature, Upwelling},
pubstate = {published},
tppubtype = {article}
}
Corals living in the coastal waters of southern Oman experience the influence of the seasonally reversing Asian monsoon system. The objective of the research reported here is to assess the potential for using the skeletal chemistry of these corals to investigate past variability in the monsoon climate. To this end, 20-year long, monthly resolution geochemical records are presented for cores from two massive Porites corals, located 20 km apart near Marbat on the Arabian Sea coast of southern Oman. We consider four aspects of skeletal chemistry: oxygen and carbon isotopic composition, barium content and the nature and occurence of annual fluorescent bands within the coral skeletons. Coral skeletal ë18O documents variations in sea surface temperature which have regional and basin-wide significance. In particular, the ë18O of coral skeleton precipitated during the period of the NE monsoon is strongly correlated with annual rainfall anomalies in India, whilst that precipitated during the period of the SW monsoon appears to provide information on variability in the strength of coastal upwelling. The stable carbon isotope composition and barium content of these particular corals display strong annual cycles, but do not appear to directly record interannual climatic/oceanographic variability. It is concluded that corals on the coast of southern Oman have great potential to provide high-resolution, century-long records of oceanographic and climatic variability associated with the operation of the monsoon climate system.
Elliott,A.J.,Savidge,G.
Some features of the upwelling off Oman Journal Article
In: Journal of Marine Research, vol. 48, no. 365, pp. 319-333, 1990.
Abstract | BibTeX | Tags: Gulf of Oman, oceanography, Oman, plankton, surface temperature, temperature, Upwelling
@article{,
title = {Some features of the upwelling off Oman},
author = {Elliott,A.J.,Savidge,G.},
year = {1990},
date = {1990-01-01},
journal = {Journal of Marine Research},
volume = {48},
number = {365},
pages = {319-333},
abstract = {Hydrographic and ADCP data were collected in the coastal waters of Oman during the 1987 summer monsoon. the minimum surface temperatures, up to 5§C below ambient offshore values, were found close to the coast and in the vicinity of the Kuria Muria Islands. Strong surface gradients were observed near Ras al Hadd at the entrance to the Gulf of Oman where the geostrophic surface flow exceeded 1.0m/s. The alongshore flux in the top 300m of a region extending 100km from the coast was estimated to be 10 x 106 m3/s. Evidence for an offshore filament of cool water was found in both current and temperature data.},
keywords = {Gulf of Oman, oceanography, Oman, plankton, surface temperature, temperature, Upwelling},
pubstate = {published},
tppubtype = {article}
}
Hydrographic and ADCP data were collected in the coastal waters of Oman during the 1987 summer monsoon. the minimum surface temperatures, up to 5§C below ambient offshore values, were found close to the coast and in the vicinity of the Kuria Muria Islands. Strong surface gradients were observed near Ras al Hadd at the entrance to the Gulf of Oman where the geostrophic surface flow exceeded 1.0m/s. The alongshore flux in the top 300m of a region extending 100km from the coast was estimated to be 10 x 106 m3/s. Evidence for an offshore filament of cool water was found in both current and temperature data.
Bruce,J.G.
Some details of upwelling off the Somali and Arabian coasts Journal Article
In: Journal of Marine Research, vol. 32, no. 58, pp. 419-423, 1974.
Abstract | BibTeX | Tags: Arabian Sea, oceanography, salinity, surface temperature, temperature, Upwelling
@article{,
title = {Some details of upwelling off the Somali and Arabian coasts},
author = {Bruce,J.G.},
year = {1974},
date = {1974-01-01},
journal = {Journal of Marine Research},
volume = {32},
number = {58},
pages = {419-423},
abstract = {Surface temperature and salinity maps from measurements during the period of maximum coastal upwelling in the Arabian Sea are given. The region of coldest, temperature <14 §C and freshest, salinity ,35.15 % surface water of Ras Mabber (9§ N Somali coast) shifted northeastward during a 10 day period. Off the Arabian coast the upwelled water was not as cold (minimum 18§C) or fresh (minimum 35.7%) and was found between 16§N and 20§N.},
keywords = {Arabian Sea, oceanography, salinity, surface temperature, temperature, Upwelling},
pubstate = {published},
tppubtype = {article}
}
Surface temperature and salinity maps from measurements during the period of maximum coastal upwelling in the Arabian Sea are given. The region of coldest, temperature <14 §C and freshest, salinity ,35.15 % surface water of Ras Mabber (9§ N Somali coast) shifted northeastward during a 10 day period. Off the Arabian coast the upwelled water was not as cold (minimum 18§C) or fresh (minimum 35.7%) and was found between 16§N and 20§N.