Brown,S.L.,Landry,M.R.,Christensen,S.,Garrison,D.,Gowing,M.M.,Bidigare,R.R.,Campbell,L.
Microbial community dynamics and taxon-specific phytoplankton production in the Arabian Sea during the 1995 monsoon seasons Journal Article
In: Deep-Sea Research Part II, vol. 49, no. 57, pp. 2345-2376, 2002.
Abstract | BibTeX | Tags: Arabian Sea, assessment, growth, population, prey, Upwelling
@article{,
title = {Microbial community dynamics and taxon-specific phytoplankton production in the Arabian Sea during the 1995 monsoon seasons},
author = {Brown,S.L.,Landry,M.R.,Christensen,S.,Garrison,D.,Gowing,M.M.,Bidigare,R.R.,Campbell,L.},
year = {2002},
date = {2002-01-01},
journal = {Deep-Sea Research Part II},
volume = {49},
number = {57},
pages = {2345-2376},
abstract = {As part of the US JGOFS Arabian Sea Process Study in 1995, we investigated temporal and spatial patterns in microbial dynamics and production during the late Southwest (SW) Monsoon (August-September 1995) and the early Northeast (NE) Monsoon (November-December 1995) seasons using the seawater-dilution technique. Experiments were coupled with population assessments from high-performance liquid chromatography, flow cytometry, and microscopy to estimate further taxon-specific phytoplankton growth, grazing and production. Dilution estimates of total primary production varied substantially, from 7 to 423 mg Cl-1 d-1, and were generally in good agreement with rate estimates from 14C-uptake incubations. Both primary production and secondary bacterial production were, on average, 2.5xhigher during the SW Monsoon than the NE Monsoon. Relative to the total community, photosynthetic prokaryotes contributed 23% and 53% of production during the SW and NE Monsoons, respectively. Prochlorococcus spp. production was well balanced by grazing losses, while >50% of Synechococcus spp. production during the SW Monsoon appeared to escape grazing by protists. Diatoms comprised >30% of primary production at a high biomass station during the SW Monsoon but <30% at all stations during the NE Monsoon. Growth rates of Synechococcus spp. and diatoms appeared to be limited by inorganic nitrogen concentrations, while Prochlorococcus spp., dinoflagellates and Phaeocystis spp. were not. Losses to protistan grazing were strongly correlated with phytoplankton biomass and production. Despite sufficient prey levels, protistan biomass was modest and constant across the region during both seasons. Of the larger taxa, diatoms were grazed the least effectively with only 50% of daily production accounted for by protistan grazing. Combined estimates of protistan and mesozooplankton grazing at upwelling stations during the SW Monsoon leave ~10% of primary production unaccounted for and available for sinking and/or lateral advection. Similarly high rates of net production at northern coastal stations during the NE Monsoon suggest that this area also may contribute to regional export flux},
keywords = {Arabian Sea, assessment, growth, population, prey, Upwelling},
pubstate = {published},
tppubtype = {article}
}
As part of the US JGOFS Arabian Sea Process Study in 1995, we investigated temporal and spatial patterns in microbial dynamics and production during the late Southwest (SW) Monsoon (August-September 1995) and the early Northeast (NE) Monsoon (November-December 1995) seasons using the seawater-dilution technique. Experiments were coupled with population assessments from high-performance liquid chromatography, flow cytometry, and microscopy to estimate further taxon-specific phytoplankton growth, grazing and production. Dilution estimates of total primary production varied substantially, from 7 to 423 mg Cl-1 d-1, and were generally in good agreement with rate estimates from 14C-uptake incubations. Both primary production and secondary bacterial production were, on average, 2.5xhigher during the SW Monsoon than the NE Monsoon. Relative to the total community, photosynthetic prokaryotes contributed 23% and 53% of production during the SW and NE Monsoons, respectively. Prochlorococcus spp. production was well balanced by grazing losses, while >50% of Synechococcus spp. production during the SW Monsoon appeared to escape grazing by protists. Diatoms comprised >30% of primary production at a high biomass station during the SW Monsoon but <30% at all stations during the NE Monsoon. Growth rates of Synechococcus spp. and diatoms appeared to be limited by inorganic nitrogen concentrations, while Prochlorococcus spp., dinoflagellates and Phaeocystis spp. were not. Losses to protistan grazing were strongly correlated with phytoplankton biomass and production. Despite sufficient prey levels, protistan biomass was modest and constant across the region during both seasons. Of the larger taxa, diatoms were grazed the least effectively with only 50% of daily production accounted for by protistan grazing. Combined estimates of protistan and mesozooplankton grazing at upwelling stations during the SW Monsoon leave ~10% of primary production unaccounted for and available for sinking and/or lateral advection. Similarly high rates of net production at northern coastal stations during the NE Monsoon suggest that this area also may contribute to regional export flux
Sherry,N.D.,Wood,A.M.
Phycoerythrin-containing picocyanobacteria in the Arabian Sea in February 1995: diel patterns, spatial variability, and growth rates Journal Article
In: Deep-Sea Research Part II, vol. 48 , no. 225, pp. 1263-1283, 2001.
Abstract | BibTeX | Tags: abundance, Arabian Sea, depth, diel, growth, length, population, survey
@article{,
title = {Phycoerythrin-containing picocyanobacteria in the Arabian Sea in February 1995: diel patterns, spatial variability, and growth rates},
author = {Sherry,N.D.,Wood,A.M.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48 },
number = {225},
pages = {1263-1283},
abstract = {The abundance of phycoerythrin-containing picocyanobacteria in the surface mixed layer was measured both along-shore and offshore between 8 and 23 February 1995 in the Northwestern Arabian Sea. Water samples from 3m depth were taken at 2-h intervals and picocyanobacterial abundance and frequency of dividing cells were determined by epifluorescence microscopy. Cell counts showed an average diel change from a mid-day minimum of ~50'103 cells ml-1 to an evening maximum of ~180'103 cells ml-1. The diel change was greater than the differences observed between physically and spatially discrete water masses. By counting the frequency of dividing cells (FDC) and using a novel approach to estimating the length of time required to complete cell division, growth and loss rates were both estimated to be ~2.9 d-1 with daily turnover being 140% of the mean standing stock. If differences in the intrinsic population growth rate (æ) and the net rate of change in cell number (r) are assumed to be due to grazing, then grazing occurred throughout the day at a relatively constant rate (reflecting phytoplankton loss rates of ~0.12 h-1). Cell division rates peaked in the late afternoon and early evening. FDC decreased throughout the night, suggesting that dark-inhibition of cell division is weak or nonexistent in the picocyanobacteria we studied. While all cell types included in this study would be identified as Synechococcus by flow cytometry because they were small unicells with bright phycoerythrin fluorescence, morphological variability suggests that the community was actually taxonomically diverse and included cells other than Synechococcus, including Synechocystis. Despite this diversity, the strong diel patterns we observed persisted throughout the study region, suggesting that great care should be taken when interpreting picocyanobacterial survey data and experimental results that do not account for the e!ects of time-of-day.},
keywords = {abundance, Arabian Sea, depth, diel, growth, length, population, survey},
pubstate = {published},
tppubtype = {article}
}
The abundance of phycoerythrin-containing picocyanobacteria in the surface mixed layer was measured both along-shore and offshore between 8 and 23 February 1995 in the Northwestern Arabian Sea. Water samples from 3m depth were taken at 2-h intervals and picocyanobacterial abundance and frequency of dividing cells were determined by epifluorescence microscopy. Cell counts showed an average diel change from a mid-day minimum of ~50'103 cells ml-1 to an evening maximum of ~180'103 cells ml-1. The diel change was greater than the differences observed between physically and spatially discrete water masses. By counting the frequency of dividing cells (FDC) and using a novel approach to estimating the length of time required to complete cell division, growth and loss rates were both estimated to be ~2.9 d-1 with daily turnover being 140% of the mean standing stock. If differences in the intrinsic population growth rate (æ) and the net rate of change in cell number (r) are assumed to be due to grazing, then grazing occurred throughout the day at a relatively constant rate (reflecting phytoplankton loss rates of ~0.12 h-1). Cell division rates peaked in the late afternoon and early evening. FDC decreased throughout the night, suggesting that dark-inhibition of cell division is weak or nonexistent in the picocyanobacteria we studied. While all cell types included in this study would be identified as Synechococcus by flow cytometry because they were small unicells with bright phycoerythrin fluorescence, morphological variability suggests that the community was actually taxonomically diverse and included cells other than Synechococcus, including Synechocystis. Despite this diversity, the strong diel patterns we observed persisted throughout the study region, suggesting that great care should be taken when interpreting picocyanobacterial survey data and experimental results that do not account for the e!ects of time-of-day.
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.
Brown,S.L.,Landry,M.R.,Barber,R.T.,Campbell,L.,Garrison,D.L.,Gowing,M.M.
Picophytoplankton dynamics and production in the Arabian Sea during the 1995 Southwest Monsoon Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 56, pp. 1745-1768, 1999.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, growth, impact, Oceanic, population, populations, productivity, Upwelling
@article{,
title = {Picophytoplankton dynamics and production in the Arabian Sea during the 1995 Southwest Monsoon},
author = {Brown,S.L.,Landry,M.R.,Barber,R.T.,Campbell,L.,Garrison,D.L.,Gowing,M.M.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {56},
pages = {1745-1768},
abstract = {Phytoplankton community structure is expected to shift to larger cells (e.g., diatoms) with monsoonal forcing in the Arabian Sea, but recent studies suggest that small primary producers remain active and important, even in areas strongly influenced by coastal upwelling. To better understand the role of smaller phytoplankton in such systems, we investigated growth and grazing rates of picophytoplankton populations and their contributions to phytoplankton community biomass and primary productivity during the 1995 Southwest Monsoon (August-September). Environmental conditions at six study stations varied broadly from openocean oligotrophic to coastal eutrophic, with mixed-layer nitrate and chlorophyll concentrations ranging from 0.01 to 11.5 æM NO3 and 0.16 to 1.5 æg Chl a. Picophytoplankton comprised up to 92% of phytoplankton carbon at the oceanic stations, 35% in the diatom dominated coastal zone, and 26% in a declining Phaeocystis bloom. Concurrent in situ dilution and 14C-uptake experiments gave comparable ranges of community growth rates (0.53-1.05 d-1 and 0.44-1.17 d-1, to the 1% light level), but uncertainties in C:Chl a confounded agreement at individual stations. Microzooplankton grazing utilized 81% of community phytoplankton growth at the oligotrophic stations and 54% at high-nutrient coastal stations. Prochlorococcus (PRO) was present at two oligotrophic stations, where its maximum growth approached 1.4 d-1 (two doublings per day) and depth-integrated growth varied from 0.2 to 0.8 d-1. Synechococcus (SYN) growth ranged from 0.5 to 1.1 d-1 at offshore stations and 0.6 to 0.7 d-1 at coastal sites. Except for the most oligotrophic stations, growth rates of picoeukaryotic algae (PEUK) exceeded PRO and SYN, reaching 1.3 d-1 offshore and decreasing to 0.8 d-1 at the most coastal station. Microzooplankton grazing impact averaged 90, 70, and 86% of growth for PRO, SYN, and PEUK, respectively. Picoplankton as a group accounted for 64% of estimated gross carbon production for all stations, and 50% at highnutrient, upwelling stations. Prokaryotes (PRO and SYN) contributed disproportionately to production relative to biomass at the most oligotrophic station, while PEUK were more important at the coastal stations. Even during intense monsoonal forcing in the Arabian Sea, picoeukaryotic algae appear to account for a large portion of primary production in the coastal upwelling regions, supporting an active community of protistan grazers and a high rate of carbon cycling in these areas. },
keywords = {Arabian Sea, chlorophyll, growth, impact, Oceanic, population, populations, productivity, Upwelling},
pubstate = {published},
tppubtype = {article}
}
Phytoplankton community structure is expected to shift to larger cells (e.g., diatoms) with monsoonal forcing in the Arabian Sea, but recent studies suggest that small primary producers remain active and important, even in areas strongly influenced by coastal upwelling. To better understand the role of smaller phytoplankton in such systems, we investigated growth and grazing rates of picophytoplankton populations and their contributions to phytoplankton community biomass and primary productivity during the 1995 Southwest Monsoon (August-September). Environmental conditions at six study stations varied broadly from openocean oligotrophic to coastal eutrophic, with mixed-layer nitrate and chlorophyll concentrations ranging from 0.01 to 11.5 æM NO3 and 0.16 to 1.5 æg Chl a. Picophytoplankton comprised up to 92% of phytoplankton carbon at the oceanic stations, 35% in the diatom dominated coastal zone, and 26% in a declining Phaeocystis bloom. Concurrent in situ dilution and 14C-uptake experiments gave comparable ranges of community growth rates (0.53-1.05 d-1 and 0.44-1.17 d-1, to the 1% light level), but uncertainties in C:Chl a confounded agreement at individual stations. Microzooplankton grazing utilized 81% of community phytoplankton growth at the oligotrophic stations and 54% at high-nutrient coastal stations. Prochlorococcus (PRO) was present at two oligotrophic stations, where its maximum growth approached 1.4 d-1 (two doublings per day) and depth-integrated growth varied from 0.2 to 0.8 d-1. Synechococcus (SYN) growth ranged from 0.5 to 1.1 d-1 at offshore stations and 0.6 to 0.7 d-1 at coastal sites. Except for the most oligotrophic stations, growth rates of picoeukaryotic algae (PEUK) exceeded PRO and SYN, reaching 1.3 d-1 offshore and decreasing to 0.8 d-1 at the most coastal station. Microzooplankton grazing impact averaged 90, 70, and 86% of growth for PRO, SYN, and PEUK, respectively. Picoplankton as a group accounted for 64% of estimated gross carbon production for all stations, and 50% at highnutrient, upwelling stations. Prokaryotes (PRO and SYN) contributed disproportionately to production relative to biomass at the most oligotrophic station, while PEUK were more important at the coastal stations. Even during intense monsoonal forcing in the Arabian Sea, picoeukaryotic algae appear to account for a large portion of primary production in the coastal upwelling regions, supporting an active community of protistan grazers and a high rate of carbon cycling in these areas.
Caron,D.A.,Dennett,M.R.
Phytoplankton growth and mortality during the 1995 Northeast Monsoon and Spring Intermonsoon in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 63, pp. 1665-1690, 1999.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, growth, mortality, Oceanic, trend, Trends
@article{,
title = {Phytoplankton growth and mortality during the 1995 Northeast Monsoon and Spring Intermonsoon in the Arabian Sea},
author = {Caron,D.A.,Dennett,M.R.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {63},
pages = {1665-1690},
abstract = {Phytoplankton growth rates and mortality rates were experimentally examined at eight stations in the Arabian Sea along the U.S. JGOFS cruise track during the 1995 Northeast Monsoon (January) and Spring Intermonsoon (March-April). Instantaneous growth rates averaged over an entire cruise were approximately twice as high during the NE Monsoon than during the Spring Intermonsoon period (overall averages of 0.84 ñ 0.29 (s.d.) versus 0.44 ñ 0.19 d-1). Average herbivore grazing (mortality) rates, however, were quite similar for the two seasons (overall averages of 0.35 ñ 0.18 and 0.30 ñ 0.17 d-1 for the NE Monsoon and Spring Intermonsoon, respectively). The absolute amounts of phytoplankton biomass consumed during each season also were similar (29 and 25% of standing stock consumed d-1 for the January and March-April cruises, respectively), as were the geographical trends of this removal. These seasonal trends in growth and removal rates resulted in net phytoplankton growth rates that were considerably higher during the January cruise (0.48 d-1) than during the March-April cruise (0.14 d-1). That is, phytoplankton production was more closely balanced during the Spring Intermonsoon season (87% of daily primary production consumed) relative to the NE Monsoon season (49% of daily primary production consumed). Station-to-station variability was high for rate measurements during either cruise. Nevertheless, there was a clear onshore-offshore trend in the absolute rate of removal of phytoplankton biomass (æg chlorophyll consumed l-1 d-1) during both cruises. Coastal stations had removal rates that were typically 2-4 times higher than removal rates at oceanic stations.},
keywords = {Arabian Sea, chlorophyll, growth, mortality, Oceanic, trend, Trends},
pubstate = {published},
tppubtype = {article}
}
Phytoplankton growth rates and mortality rates were experimentally examined at eight stations in the Arabian Sea along the U.S. JGOFS cruise track during the 1995 Northeast Monsoon (January) and Spring Intermonsoon (March-April). Instantaneous growth rates averaged over an entire cruise were approximately twice as high during the NE Monsoon than during the Spring Intermonsoon period (overall averages of 0.84 ñ 0.29 (s.d.) versus 0.44 ñ 0.19 d-1). Average herbivore grazing (mortality) rates, however, were quite similar for the two seasons (overall averages of 0.35 ñ 0.18 and 0.30 ñ 0.17 d-1 for the NE Monsoon and Spring Intermonsoon, respectively). The absolute amounts of phytoplankton biomass consumed during each season also were similar (29 and 25% of standing stock consumed d-1 for the January and March-April cruises, respectively), as were the geographical trends of this removal. These seasonal trends in growth and removal rates resulted in net phytoplankton growth rates that were considerably higher during the January cruise (0.48 d-1) than during the March-April cruise (0.14 d-1). That is, phytoplankton production was more closely balanced during the Spring Intermonsoon season (87% of daily primary production consumed) relative to the NE Monsoon season (49% of daily primary production consumed). Station-to-station variability was high for rate measurements during either cruise. Nevertheless, there was a clear onshore-offshore trend in the absolute rate of removal of phytoplankton biomass (æg chlorophyll consumed l-1 d-1) during both cruises. Coastal stations had removal rates that were typically 2-4 times higher than removal rates at oceanic stations.
Johnson,Z.,Landry,M.L.,Bidigare,R.R.,Brown,S.L.,Campbell,L.,Gunderson,J.,Marra,J.,Trees,C.
Energetics and growth kinetics of a deep Prochlorococcus spp. population in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 129, pp. 1719-1743, 1999.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, growth, marine, performance, population, populations
@article{,
title = {Energetics and growth kinetics of a deep Prochlorococcus spp. population in the Arabian Sea},
author = {Johnson,Z.,Landry,M.L.,Bidigare,R.R.,Brown,S.L.,Campbell,L.,Gunderson,J.,Marra,J.,Trees,C.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {129},
pages = {1719-1743},
abstract = {During the US JGOFS process studies in the Arabian Sea (1995), secondary fluorescence maxima (SFM) were observed frequently at the oxic-anoxic interface at the extreme base of the euphotic zone. These secondary peaks were most prominent during the early NE monsoon in the central oligotrophic portion of the Arabian Sea, although they were spatially and temporally variable. Based on high performance liquid chromatography (HPLC) and flow cytometry analyses, SFM were determined to be populated almost exclusively by the marine cyanobacterium Prochlorococcus spp. While SFM were about half the magnitude of primary fluorescence peaks, chlorophyll a biomass was typically an order of magnitude less than at the primary maxima (although total chlorophyll (a + b) differed only by a factor of two). Photosynthesis versus irradiance response curves revealed an efficient population adapted to extremely low light (~0.02-0.05% surface irradiance) largely through increased light absorption capabilities. A theoretical spectral irradiance absorption effciency model based on available spectral irradiance, individual cell properties, and bulk particulate spectral absorption also supports a well-adapted low-light population. Deck-incubated C-14 uptake as well as dilution growth experiments revealed instantaneous growth rates on the order of æ = 0.01 d-1. However, additional in situ observations suggest SFM populations may be more dynamic than the growth rates estimates from shipboard bottle incubations predict. We advance four hypotheses for the regulation of SFM populations including: (1) reduced loss rates, (2) discontinuous environmental conditions, (3) enhanced sub-oxic growth, and (4) physical mechanisms.},
keywords = {Arabian Sea, chlorophyll, growth, marine, performance, population, populations},
pubstate = {published},
tppubtype = {article}
}
During the US JGOFS process studies in the Arabian Sea (1995), secondary fluorescence maxima (SFM) were observed frequently at the oxic-anoxic interface at the extreme base of the euphotic zone. These secondary peaks were most prominent during the early NE monsoon in the central oligotrophic portion of the Arabian Sea, although they were spatially and temporally variable. Based on high performance liquid chromatography (HPLC) and flow cytometry analyses, SFM were determined to be populated almost exclusively by the marine cyanobacterium Prochlorococcus spp. While SFM were about half the magnitude of primary fluorescence peaks, chlorophyll a biomass was typically an order of magnitude less than at the primary maxima (although total chlorophyll (a + b) differed only by a factor of two). Photosynthesis versus irradiance response curves revealed an efficient population adapted to extremely low light (~0.02-0.05% surface irradiance) largely through increased light absorption capabilities. A theoretical spectral irradiance absorption effciency model based on available spectral irradiance, individual cell properties, and bulk particulate spectral absorption also supports a well-adapted low-light population. Deck-incubated C-14 uptake as well as dilution growth experiments revealed instantaneous growth rates on the order of æ = 0.01 d-1. However, additional in situ observations suggest SFM populations may be more dynamic than the growth rates estimates from shipboard bottle incubations predict. We advance four hypotheses for the regulation of SFM populations including: (1) reduced loss rates, (2) discontinuous environmental conditions, (3) enhanced sub-oxic growth, and (4) physical mechanisms.
Kinkade,C.S.,Marra,J.,Dickey,T.D.,Langdon,C.,Sigurdson,D.E.,Weller,R.
Diel bio-optical variability observed from moored sensors in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 136, pp. 1813-1831, 1999.
Abstract | BibTeX | Tags: Arabian Sea, diel, growth, thermocline
@article{,
title = {Diel bio-optical variability observed from moored sensors in the Arabian Sea},
author = {Kinkade,C.S.,Marra,J.,Dickey,T.D.,Langdon,C.,Sigurdson,D.E.,Weller,R.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {136},
pages = {1813-1831},
abstract = {As part of the Forced Upper Ocean Dynamics Program, which ran concurrently with the US JGOFS Arabian Sea Expedition, five moorings were deployed in the historical axis of the Findlater Jet. In addition to other variables, moored sensors collected photosynthetically active radiation (PAR), particulate beam attenuation (Cp), stimulated fluorescence (FLU), and dissolved oxygen (O2) data from October 1994 to October 1995. Diel bio-optical signals were recorded during two periods between the Northeast and Southwest Monsoons at 10, 35, and 65 m. Spectral analysis shows significant diel cycles of Cp, FLU, and O2, but the strength of these cycles was not constant over time. Daily periodicity was lowest for all bio-optical signals just after a strong storm during the 1994 Fall Intermonsoon period. During a phytoplankton bloom associated with a cool advective feature, the FLU and O2 diel signals were most pronounced. Although these signals are biological responses to the daily cycle of irradiance, they are mediated by hydrographic conditions; strongest when phytoplankton are confined within the mixed layer or thermocline, and thus exposed to light intensities long enough to display these responses to PAR. Fluorescence quenching at 10 m due to high irradiance (~1000 æEinstein m-2 s-1) forced the ratio of fluorescence to particulate attenuation into a diel periodicity at 10 m, but not at 35 m (noontime irradiance ~200 æEinstein m-2 s-1), where the FLU and Cp increases were almost in phase. Diel changes in Cp, when scaled to particulate organic carbon, suggest a net production of ~20 mg C m-3 d-1 at 10 and 35 m. We estimate a specific growth rate from a calculated particle production rate balanced by a constant grazing over 24 h to be 0.77 d-1, and using a C*c of 424 mg C m-2, estimate a carbon : chl a ratio between 85 and 115 for a 10-d window during the 1994 Fall Intermonsoon period },
keywords = {Arabian Sea, diel, growth, thermocline},
pubstate = {published},
tppubtype = {article}
}
As part of the Forced Upper Ocean Dynamics Program, which ran concurrently with the US JGOFS Arabian Sea Expedition, five moorings were deployed in the historical axis of the Findlater Jet. In addition to other variables, moored sensors collected photosynthetically active radiation (PAR), particulate beam attenuation (Cp), stimulated fluorescence (FLU), and dissolved oxygen (O2) data from October 1994 to October 1995. Diel bio-optical signals were recorded during two periods between the Northeast and Southwest Monsoons at 10, 35, and 65 m. Spectral analysis shows significant diel cycles of Cp, FLU, and O2, but the strength of these cycles was not constant over time. Daily periodicity was lowest for all bio-optical signals just after a strong storm during the 1994 Fall Intermonsoon period. During a phytoplankton bloom associated with a cool advective feature, the FLU and O2 diel signals were most pronounced. Although these signals are biological responses to the daily cycle of irradiance, they are mediated by hydrographic conditions; strongest when phytoplankton are confined within the mixed layer or thermocline, and thus exposed to light intensities long enough to display these responses to PAR. Fluorescence quenching at 10 m due to high irradiance (~1000 æEinstein m-2 s-1) forced the ratio of fluorescence to particulate attenuation into a diel periodicity at 10 m, but not at 35 m (noontime irradiance ~200 æEinstein m-2 s-1), where the FLU and Cp increases were almost in phase. Diel changes in Cp, when scaled to particulate organic carbon, suggest a net production of ~20 mg C m-3 d-1 at 10 and 35 m. We estimate a specific growth rate from a calculated particle production rate balanced by a constant grazing over 24 h to be 0.77 d-1, and using a C*c of 424 mg C m-2, estimate a carbon : chl a ratio between 85 and 115 for a 10-d window during the 1994 Fall Intermonsoon period
McCarthy,J.J.,Garside,C.,Nevins,J.L.
Nitrogen dynamics during the Arabian Sea Northeast Monsoon Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 151, pp. 1623-1664, 1999.
Abstract | BibTeX | Tags: Arabian Sea, depth, development, diel, growth, productivity
@article{,
title = {Nitrogen dynamics during the Arabian Sea Northeast Monsoon},
author = {McCarthy,J.J.,Garside,C.,Nevins,J.L.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {151},
pages = {1623-1664},
abstract = {This investigation focused on the weaker and less well understood of the two Arabian Sea monsoonal wind phases, the NE Monsoon, which persists for 3-4 months in the October to February period. Historically, this period has been characterized as a time of very low nutrient availability and low biological production. As part of the US JGOFS Arabian Sea Process Study, 17 stations were sampled on a cruise in January 1995 (late NE Monsoon) and, 15 stations were sampled on a cruise in November 1995 (early NE Monsoon). Only the southern most stations (10§ and 12§N) and one shallow coastal station were as nutrient-depleted as had been expected from the few relevant prior studies in this region. Experiments were conducted to ascertain the relative importance of different nitrogenous nutrients and the sufficiency of local regeneration processes in supplying nitrogenous nutrients utilized in primary production. Except for the southern oligotrophic stations, the euphotic zone concentrations of NO3- were typically 5-10-fold greater than those of NO2- and NH4+. There was considerable variation (20-40-fold) in nutrient concentration both within and between the two sections on each cruise. All nitrogenous nutrients were more abundant (2-4-fold) later in the NE Monsoon. Strong vertical gradients in euphotic zone NH4- concentration, with higher concentrations at depth, were common. This was in contrast to the nearly uniform euphotic zone concentrations for both NO3- and NO2-. Half-saturation constants for uptake were higher for NO3- (1.7 æmol kg-1 (s.d.=0.88, n=8)) than for NH4+ (0.47 æmol kg-1 (s.d.=0.33, n=5)). Evidence for the suppressing effect of NH4+ on NO3- uptake was widespread, although not as severe as has been noted for some other regions. Both the degree of sensitivity of NO3- uptake to NH4+ concentration and the half-saturation constant for NO3+ uptake were correlated with ambient NO3- concentration. The combined e!ect of high affnity for low concentrations of NH4+ and the effect of NH4+ concentration on NO3- uptake resulted in similarly low f-ratios, 0.15 (s.d.=0.07, n=15) and 0.13 (s.d.=0.08, n=17), for early and late observations in the NE Monsoon, respectively. Stations with high f-ratios had the lowest euphotic zone NH4+ concentrations, and these stations were either very near shore or far from shore in the most oligotrophic waters. At several stations, particularly early in the NE Monsoon, the utilization rates for NO2- were equal to or greater than 50% the utilization rates for NO3- . When converted with a Redfield C : N value of 6.7, the total N uptake rates measured in this study were commensurate with measurements of C productivity. While nutrient concentrations at some stations approached levels low enough to limit phytoplankton growth, light was shown to be very important in regulating N uptake at all stations in this study. Diel periodicity was observed for uptake of all nitrogenous nutrients at all stations. The amplitude of this periodicity was positively correlated with nutrient concentration. The strongest of these relationships occurred with NO3- . Ammonium concentration strongly influenced the vertical profiles for NO3- uptake as well as for NH4+ uptake. Both NO2- and NH4+ were regenerated within the euphotic zone at rates comparable to rates of uptake of these nutrients, and thus maintenance of mixed layer concentrations did not require diffusive or advective fluxes from other sources. Observed turnover times for NH4+ were typically less than one day. Rapid turnover and the strong light regulation of NH4+ uptake allowed the development and maintenance of vertical structure in NH4+ concentration within the euphotic zone. In spite of the strong positive effect of light on NO2- uptake and its strong negative effect on NO2- production, the combined effects of much longer turnover times for this nutrient and mixed layer dynamics resulted in nearly uniform NO2- concentrations within the euphotic zone. Responses of the NE Monsoon planktonic community to light and nutrients, in conjunction with mixed layer dynamics, allowed for effcient recycling of N within the mixed layer. As the NE Monsoon evolved and the mixed layer deepened convectively, NO2- and NO3- concentrations increased correspondingly with the entrainment of deeper water. Planktonic N productivity increased 2-fold, but without a significant change the new vs. recycled N proportionality. Consequently, NO3- turnover time increased from about 1 month to greater than 3 months. This reflected the overriding importance of recycling processes in supplying nitrogenous nutrients for primary production throughout the duration of the NE Monsoon. As a result, NO3- supplied to the euphotic zone during the NE Monsoon is, for the most part, conserved for utilization during the subsequent intermonsoon period. },
keywords = {Arabian Sea, depth, development, diel, growth, productivity},
pubstate = {published},
tppubtype = {article}
}
This investigation focused on the weaker and less well understood of the two Arabian Sea monsoonal wind phases, the NE Monsoon, which persists for 3-4 months in the October to February period. Historically, this period has been characterized as a time of very low nutrient availability and low biological production. As part of the US JGOFS Arabian Sea Process Study, 17 stations were sampled on a cruise in January 1995 (late NE Monsoon) and, 15 stations were sampled on a cruise in November 1995 (early NE Monsoon). Only the southern most stations (10§ and 12§N) and one shallow coastal station were as nutrient-depleted as had been expected from the few relevant prior studies in this region. Experiments were conducted to ascertain the relative importance of different nitrogenous nutrients and the sufficiency of local regeneration processes in supplying nitrogenous nutrients utilized in primary production. Except for the southern oligotrophic stations, the euphotic zone concentrations of NO3- were typically 5-10-fold greater than those of NO2- and NH4+. There was considerable variation (20-40-fold) in nutrient concentration both within and between the two sections on each cruise. All nitrogenous nutrients were more abundant (2-4-fold) later in the NE Monsoon. Strong vertical gradients in euphotic zone NH4- concentration, with higher concentrations at depth, were common. This was in contrast to the nearly uniform euphotic zone concentrations for both NO3- and NO2-. Half-saturation constants for uptake were higher for NO3- (1.7 æmol kg-1 (s.d.=0.88, n=8)) than for NH4+ (0.47 æmol kg-1 (s.d.=0.33, n=5)). Evidence for the suppressing effect of NH4+ on NO3- uptake was widespread, although not as severe as has been noted for some other regions. Both the degree of sensitivity of NO3- uptake to NH4+ concentration and the half-saturation constant for NO3+ uptake were correlated with ambient NO3- concentration. The combined e!ect of high affnity for low concentrations of NH4+ and the effect of NH4+ concentration on NO3- uptake resulted in similarly low f-ratios, 0.15 (s.d.=0.07, n=15) and 0.13 (s.d.=0.08, n=17), for early and late observations in the NE Monsoon, respectively. Stations with high f-ratios had the lowest euphotic zone NH4+ concentrations, and these stations were either very near shore or far from shore in the most oligotrophic waters. At several stations, particularly early in the NE Monsoon, the utilization rates for NO2- were equal to or greater than 50% the utilization rates for NO3- . When converted with a Redfield C : N value of 6.7, the total N uptake rates measured in this study were commensurate with measurements of C productivity. While nutrient concentrations at some stations approached levels low enough to limit phytoplankton growth, light was shown to be very important in regulating N uptake at all stations in this study. Diel periodicity was observed for uptake of all nitrogenous nutrients at all stations. The amplitude of this periodicity was positively correlated with nutrient concentration. The strongest of these relationships occurred with NO3- . Ammonium concentration strongly influenced the vertical profiles for NO3- uptake as well as for NH4+ uptake. Both NO2- and NH4+ were regenerated within the euphotic zone at rates comparable to rates of uptake of these nutrients, and thus maintenance of mixed layer concentrations did not require diffusive or advective fluxes from other sources. Observed turnover times for NH4+ were typically less than one day. Rapid turnover and the strong light regulation of NH4+ uptake allowed the development and maintenance of vertical structure in NH4+ concentration within the euphotic zone. In spite of the strong positive effect of light on NO2- uptake and its strong negative effect on NO2- production, the combined effects of much longer turnover times for this nutrient and mixed layer dynamics resulted in nearly uniform NO2- concentrations within the euphotic zone. Responses of the NE Monsoon planktonic community to light and nutrients, in conjunction with mixed layer dynamics, allowed for effcient recycling of N within the mixed layer. As the NE Monsoon evolved and the mixed layer deepened convectively, NO2- and NO3- concentrations increased correspondingly with the entrainment of deeper water. Planktonic N productivity increased 2-fold, but without a significant change the new vs. recycled N proportionality. Consequently, NO3- turnover time increased from about 1 month to greater than 3 months. This reflected the overriding importance of recycling processes in supplying nitrogenous nutrients for primary production throughout the duration of the NE Monsoon. As a result, NO3- supplied to the euphotic zone during the NE Monsoon is, for the most part, conserved for utilization during the subsequent intermonsoon period.
Al-Jabri,M.
Marine epilithic algal communities on artificial and natural substrates Technical Report
no. 5, 1996.
Abstract | BibTeX | Tags: Arabian Gulf, Arabian Sea, coral, developing, Green turtles, growth, Gulf of Oman, habitat, marine, monitoring, Oman, pollution, productivity, salinity, temperature, turtles
@techreport{,
title = {Marine epilithic algal communities on artificial and natural substrates },
author = {Al-Jabri,M.},
year = {1996},
date = {1996-01-01},
volume = {FSC 1580-91 },
number = {5},
pages = {1-15},
abstract = {INTRODUCTION The Epilithic Algal Community (EAC) of coral reefs are diverse assemblages of small filamentous green, red, blue-green algae ('turf species') and crustose coralline red algal. These have low biomass but show rapid growth rate (Klumpp and Mckinnon, 1989) and this algal community colonizes the reefs and serves as the primary food source for herbivores. The diversity and richness of reef fauna can also be attributed largely to the high productivity of EAC (Klumpp and Mckinnon, 1989); thus the EAC is the major source of food for herbivores such as damselfish, echinoids, surgeonfish (sohal and yellow tail), parrotfish and green turtles. The main algal functional form group (Littler et a¡.,1983) is the filamentous group. In the Arabian Sea, however, there is a diverse algal community of filamentous, sheet-group, coarsely branched group and thick leathery group due to upwelling, (Mardela, 1975, Jupp et al, 1996). The Gulf of Oman does not experience upwelling due to the summer S.W. monsoon, so in this part of Oman, because of the physical conditions prevailing, there are high salinities and temperatures in summer as well as wide temperature variation and, combined with largely sand substrates here, coral reefs are not as widely distributed as in many tropical seas and their growth and diversity is not as great. In spite of this, they still contribute a highly complex community (Sheppard and Salm, 1988). During the past three decades, many of the natural marine habitats in the world and Arabian Gulf in particular are being destroyed, degraded or are actually disappearing as a result of oil pollution, coastal infilling and other activities associated with industrial development. Because the EAC is very important for grazers, many studies on natural reefs and artificial reefs structures including oil platforms, piers, jetties and other coastal installations have been carried out (Seaman and Sprague, 1991). Artificial habitat enhancement has been practiced primarily to attract fishes in various parts of the world, however in Oman there are no studies yet that have been made to understand the mechanisms of attractive effect of artificial structures. In addition, few studies on reef coral community and no detailed study of EAC have been carried out in Oman with studies along the Gulf of Oman just mentioning few macroalgae and green filamentous algae, e.g. Entromorpha (Sheppard and Salm, 1988). On the Gulf of Oman coasts, only sparse clumps of larger macroalgae (>10cm) of sheet-group, coarsely branched and thick leathery groups are found (Mardela, 1975) with, for example, only scattered plants such as Padina and Halymenia (Cordero, 1992). In view of the importance of EAC on natural and artificial reefs this preliminary study will provide valuable baseline biological data about the growth of algae as well as the faunal assemblages that accumulate around artificial substrates. Data from this study would be useful to assist researchers in the future in monitoring herbivorous fish resources as well as the succession of communities developing on artificial reefs.},
keywords = {Arabian Gulf, Arabian Sea, coral, developing, Green turtles, growth, Gulf of Oman, habitat, marine, monitoring, Oman, pollution, productivity, salinity, temperature, turtles},
pubstate = {published},
tppubtype = {techreport}
}
INTRODUCTION The Epilithic Algal Community (EAC) of coral reefs are diverse assemblages of small filamentous green, red, blue-green algae ('turf species') and crustose coralline red algal. These have low biomass but show rapid growth rate (Klumpp and Mckinnon, 1989) and this algal community colonizes the reefs and serves as the primary food source for herbivores. The diversity and richness of reef fauna can also be attributed largely to the high productivity of EAC (Klumpp and Mckinnon, 1989); thus the EAC is the major source of food for herbivores such as damselfish, echinoids, surgeonfish (sohal and yellow tail), parrotfish and green turtles. The main algal functional form group (Littler et a¡.,1983) is the filamentous group. In the Arabian Sea, however, there is a diverse algal community of filamentous, sheet-group, coarsely branched group and thick leathery group due to upwelling, (Mardela, 1975, Jupp et al, 1996). The Gulf of Oman does not experience upwelling due to the summer S.W. monsoon, so in this part of Oman, because of the physical conditions prevailing, there are high salinities and temperatures in summer as well as wide temperature variation and, combined with largely sand substrates here, coral reefs are not as widely distributed as in many tropical seas and their growth and diversity is not as great. In spite of this, they still contribute a highly complex community (Sheppard and Salm, 1988). During the past three decades, many of the natural marine habitats in the world and Arabian Gulf in particular are being destroyed, degraded or are actually disappearing as a result of oil pollution, coastal infilling and other activities associated with industrial development. Because the EAC is very important for grazers, many studies on natural reefs and artificial reefs structures including oil platforms, piers, jetties and other coastal installations have been carried out (Seaman and Sprague, 1991). Artificial habitat enhancement has been practiced primarily to attract fishes in various parts of the world, however in Oman there are no studies yet that have been made to understand the mechanisms of attractive effect of artificial structures. In addition, few studies on reef coral community and no detailed study of EAC have been carried out in Oman with studies along the Gulf of Oman just mentioning few macroalgae and green filamentous algae, e.g. Entromorpha (Sheppard and Salm, 1988). On the Gulf of Oman coasts, only sparse clumps of larger macroalgae (>10cm) of sheet-group, coarsely branched and thick leathery groups are found (Mardela, 1975) with, for example, only scattered plants such as Padina and Halymenia (Cordero, 1992). In view of the importance of EAC on natural and artificial reefs this preliminary study will provide valuable baseline biological data about the growth of algae as well as the faunal assemblages that accumulate around artificial substrates. Data from this study would be useful to assist researchers in the future in monitoring herbivorous fish resources as well as the succession of communities developing on artificial reefs.