Dickson,M-L.,Orchardo,J.,Barber,R.T.,Marra,J.,McCarthy,J.J.,Sambrotto,R.N.
Production and respiration rates in the Arabian Sea during the 1995 Northeast and Southwest Monsoons Journal Article
In: Deep-Sea Research Part II, vol. 48, no. 89, pp. 1199-1230, 2001.
Abstract | BibTeX | Tags: Arabian Sea, Distribution, ecosystem, location, nearshore, respiration
@article{,
title = {Production and respiration rates in the Arabian Sea during the 1995 Northeast and Southwest Monsoons},
author = {Dickson,M-L.,Orchardo,J.,Barber,R.T.,Marra,J.,McCarthy,J.J.,Sambrotto,R.N.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48},
number = {89},
pages = {1199-1230},
abstract = {In this paper we examine the relationships among oxygen, carbon and nitrogen production and respiration rate measurements made in the Arabian Sea during the 1995 Northeast (NEM) and Southwest (SWM) Monsoons. Increased biological production characterized the SWM, with rates 12-53% higher than the NEM. Inmost cases, we found remarkable similarity in production rates during the two monsoons and an absence of strong spatial gradients in production between nearshore and offshore waters, especially during the SWM. Daily 14C and total 15Nproduction underestimated gross C production, and at the majority of stations 14C and total 15N production were either the same as net C production or between gross and net C production. Moreover, new production (15NO3), scaled to carbon, was substantially less than net C production. Approximately 50% of the PO14C was metabolized during the photoperiod, with smaller losses (7-11%) overnight. The simplest explanation for the discrepancy between gross and total 15N production and between net C and new production was the loss of 15N-labeled particulate matter as dissolved organic matter. Partitioning of metabolized gross C production into respiratory and dissolved pools showed distinct onshore-offshore distributions that appeared to be related to the composition of the phytoplankton assemblage and probably reflected the trophodynamics of the ecosystem. The percentage of gross C production released as dissolved organic carbon (DOC) was highest in the nearshore waters where diatoms dominated the phytoplankton assemblage, while community respiration was a more important fate for production further offshore where picoplankton prevailed. In general, stations that retained more gross C production as net production (i.e., high net C/gross C ratios) had higher rates of DOC production relative to community respiration. Locations where community respiration exceeded DOC production were characterized by low rates of net C production and had low net C/gross C ratios. In those ecosystems, less net C production was retained because higher metabolic losses reduced gross C production to a greater extent than at the more productive sites. },
keywords = {Arabian Sea, Distribution, ecosystem, location, nearshore, respiration},
pubstate = {published},
tppubtype = {article}
}
In this paper we examine the relationships among oxygen, carbon and nitrogen production and respiration rate measurements made in the Arabian Sea during the 1995 Northeast (NEM) and Southwest (SWM) Monsoons. Increased biological production characterized the SWM, with rates 12-53% higher than the NEM. Inmost cases, we found remarkable similarity in production rates during the two monsoons and an absence of strong spatial gradients in production between nearshore and offshore waters, especially during the SWM. Daily 14C and total 15Nproduction underestimated gross C production, and at the majority of stations 14C and total 15N production were either the same as net C production or between gross and net C production. Moreover, new production (15NO3), scaled to carbon, was substantially less than net C production. Approximately 50% of the PO14C was metabolized during the photoperiod, with smaller losses (7-11%) overnight. The simplest explanation for the discrepancy between gross and total 15N production and between net C and new production was the loss of 15N-labeled particulate matter as dissolved organic matter. Partitioning of metabolized gross C production into respiratory and dissolved pools showed distinct onshore-offshore distributions that appeared to be related to the composition of the phytoplankton assemblage and probably reflected the trophodynamics of the ecosystem. The percentage of gross C production released as dissolved organic carbon (DOC) was highest in the nearshore waters where diatoms dominated the phytoplankton assemblage, while community respiration was a more important fate for production further offshore where picoplankton prevailed. In general, stations that retained more gross C production as net production (i.e., high net C/gross C ratios) had higher rates of DOC production relative to community respiration. Locations where community respiration exceeded DOC production were characterized by low rates of net C production and had low net C/gross C ratios. In those ecosystems, less net C production was retained because higher metabolic losses reduced gross C production to a greater extent than at the more productive sites.
Sambrotto,R.N.
Nitrogen production in the northern Arabian Sea during the Spring Intermonsoon and Southwest Monsoon seasons Journal Article
In: Deep-Sea Research Part II, vol. 48, no. 470, pp. 1173-1198, 2001.
Abstract | BibTeX | Tags: Arabian Sea, budget, impact, population, populations, productivity, respiration, Upwelling
@article{,
title = {Nitrogen production in the northern Arabian Sea during the Spring Intermonsoon and Southwest Monsoon seasons},
author = {Sambrotto,R.N.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48},
number = {470},
pages = {1173-1198},
abstract = {Planktonic nitrogen productivity and regeneration were measured with 15NO3, 15NH4 and 15N-urea tracers during the Spring Intermonsoon (SI) and Southwest Monsoon (SWM) seasons in the northern Arabian Sea from the Omani coast southeast to 10§N. On an areal basis, new (nitrate) productivity and the nitrogen f-ratio varied from 0.1 to 13 mmol m-2 d-1 and 0.03 to 0.4, respectively. Including urea in total nitrogen uptake lowered the f-ratio by 29% on average for individual samples, and during the SI was most important in offshore regions. The lowest nitrate productivity rates also were measured in offshore regions during the SI, where low, but detectable, nitrate levels limited uptake. The onset of the SWM was associated with an order of magnitude increase in nitrate uptake seaward of the Findlater Jet as compared to the SI. Apparently, the positive effect of the increased availability of nitrate and the Ekman transport of established phytoplankton populations to the region more than offset the degraded light conditions caused by the deep (>80 m) mixed layers. Despite the increases in offshore nitrate uptake, both a budget of surface particulate material and 234Th POC flux estimates indicated that the mid- SWM reduced the efficiency of material export from surface waters and disrupted the linkage between new production and export that was evident in the SI. In the mid-SWM, new production mainly accumulated in deeply mixed surface waters offshore, and may be responsible for the well documented lag between the onset of the SWM and export. In the coastal upwelling region, new production rates were significantly greater during the SWM only near filaments of coastal water advected offshore. Ammonium regeneration rates and concentrations increased significantly in coastal regions during the SWM, and nitrification likely was a significant sink for some of the ammonium produced there. The transport of some of the remainder of this reduced nitrogen offshore would fuel nitrogen production without having an impact on local respiration. This is one of several factors that may confound the comparison of new and net production in coastal regions during the early SWM. },
keywords = {Arabian Sea, budget, impact, population, populations, productivity, respiration, Upwelling},
pubstate = {published},
tppubtype = {article}
}
Planktonic nitrogen productivity and regeneration were measured with 15NO3, 15NH4 and 15N-urea tracers during the Spring Intermonsoon (SI) and Southwest Monsoon (SWM) seasons in the northern Arabian Sea from the Omani coast southeast to 10§N. On an areal basis, new (nitrate) productivity and the nitrogen f-ratio varied from 0.1 to 13 mmol m-2 d-1 and 0.03 to 0.4, respectively. Including urea in total nitrogen uptake lowered the f-ratio by 29% on average for individual samples, and during the SI was most important in offshore regions. The lowest nitrate productivity rates also were measured in offshore regions during the SI, where low, but detectable, nitrate levels limited uptake. The onset of the SWM was associated with an order of magnitude increase in nitrate uptake seaward of the Findlater Jet as compared to the SI. Apparently, the positive effect of the increased availability of nitrate and the Ekman transport of established phytoplankton populations to the region more than offset the degraded light conditions caused by the deep (>80 m) mixed layers. Despite the increases in offshore nitrate uptake, both a budget of surface particulate material and 234Th POC flux estimates indicated that the mid- SWM reduced the efficiency of material export from surface waters and disrupted the linkage between new production and export that was evident in the SI. In the mid-SWM, new production mainly accumulated in deeply mixed surface waters offshore, and may be responsible for the well documented lag between the onset of the SWM and export. In the coastal upwelling region, new production rates were significantly greater during the SWM only near filaments of coastal water advected offshore. Ammonium regeneration rates and concentrations increased significantly in coastal regions during the SWM, and nitrification likely was a significant sink for some of the ammonium produced there. The transport of some of the remainder of this reduced nitrogen offshore would fuel nitrogen production without having an impact on local respiration. This is one of several factors that may confound the comparison of new and net production in coastal regions during the early SWM.
Laws,E.A.,Landry,M.R.,Barber,R.T.,Campbell,L.,Dickson,M-L.,Marra,J.
Carbon cycling in primary production bottle incubations: inferences from grazing experiments and photosynthetic studies using 14C and 18O in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 47, no. 142, pp. 1339-1352, 2000.
Abstract | BibTeX | Tags: Arabian Sea, respiration
@article{,
title = {Carbon cycling in primary production bottle incubations: inferences from grazing experiments and photosynthetic studies using 14C and 18O in the Arabian Sea},
author = {Laws,E.A.,Landry,M.R.,Barber,R.T.,Campbell,L.,Dickson,M-L.,Marra,J.},
year = {2000},
date = {2000-01-01},
journal = {Deep-Sea Research Part II},
volume = {47},
number = {142},
pages = {1339-1352},
abstract = {Estimates of photosynthesis based on the incorporation of 14C-labeled inorganic carbon into particulate carbon were compared to estimates of gross photosynthesis based on net O2 production and the production of 18O2 from H218O during the US Joint Global Ocean Flux Study (US JGOFS) Arabian Sea process cruises. For samples incubated below the surface and at optical depths <3, the 14C uptake : gross photosynthesis ratio averaged 0.45 ñ 0.1. This result is in accord with theoretical considerations of the combined effects of the Mehler reaction, photorespiration, dark respiration, excretion, and grazing e!ects on the two estimates of photosynthesis. The 14C uptake : gross photosynthesis ratio was distinctly higher (0.62) for samples incubated at the surface. This result is likely due to UV light e!ects, since the O2 and 14C incubations were done in quartz and polysulfone bottles, respectively. The 14C uptake : gross photosynthesis ratio was lower (0.31) for bottles incubated at optical depths >3. This result probably reflects an increase in the ratio of dark respiration to net photosynthesis in the vicinity of the compensation light level },
keywords = {Arabian Sea, respiration},
pubstate = {published},
tppubtype = {article}
}
Estimates of photosynthesis based on the incorporation of 14C-labeled inorganic carbon into particulate carbon were compared to estimates of gross photosynthesis based on net O2 production and the production of 18O2 from H218O during the US Joint Global Ocean Flux Study (US JGOFS) Arabian Sea process cruises. For samples incubated below the surface and at optical depths <3, the 14C uptake : gross photosynthesis ratio averaged 0.45 ñ 0.1. This result is in accord with theoretical considerations of the combined effects of the Mehler reaction, photorespiration, dark respiration, excretion, and grazing e!ects on the two estimates of photosynthesis. The 14C uptake : gross photosynthesis ratio was distinctly higher (0.62) for samples incubated at the surface. This result is likely due to UV light e!ects, since the O2 and 14C incubations were done in quartz and polysulfone bottles, respectively. The 14C uptake : gross photosynthesis ratio was lower (0.31) for bottles incubated at optical depths >3. This result probably reflects an increase in the ratio of dark respiration to net photosynthesis in the vicinity of the compensation light level