scholarly journals Spatial and temporal variability of the phytoplankton carbon to chlorophyll ratio in the equatorial Pacific: A basin-scale modeling study

2009 ◽  
Vol 114 (C7) ◽  
Author(s):  
Xiujun Wang ◽  
Robert Le Borgne ◽  
Raghu Murtugudde ◽  
Antonio J. Busalacchi ◽  
Michael Behrenfeld
Keyword(s):  
Temporal Variability ◽  
Equatorial Pacific ◽  
Spatial And Temporal Variability ◽  
Scale Modeling ◽  
Basin Scale ◽  
Modeling Study

scholarly journals Nitrogen uptake and regeneration pathways in the equatorial Pacific: a basin scale modeling study

2009 ◽  
Vol 6 (4) ◽  
pp. 8247-8278
Author(s):  
X. Wang ◽  
R. Murtugudde ◽  
R. Le Borgne
Keyword(s):  
Inorganic Nitrogen ◽  
Euphotic Zone ◽  
Equatorial Pacific ◽  
Ammonium Uptake ◽  
Regeneration Rate ◽  
Scale Modeling ◽  
Basin Scale ◽  
Zooplankton Excretion ◽  
Over The Top ◽  
Modeling Study

Abstract. It is well known that most primary production is fueled by regenerated nitrogen in the open ocean. Therefore, studying the nitrogen cycle by focusing on uptake and regeneration pathways would advance our understanding of nitrogen dynamics in the marine ecosystem. Here, we carry out a basin-scale modeling study, by assessing model simulations of nitrate and ammonium, and rates of nitrate uptake, ammonium uptake and regeneration in the equatorial Pacific. Model-data comparisons show that the model is able to reproduce many observed features of nitrate, ammonium, such as the deep ammonium maximum (DAM). The model also reproduces the observed de-coupling of ammonium uptake and regeneration, i.e. regeneration rate greater than uptake rate in the lower euphotic zone. The de-coupling largely explains the observed DAM in the equatorial Pacific Ocean. Our study indicates that zooplankton excretion and remineralization of organic nitrogen play a different role in nitrogen regeneration. Rates of zooplankton excretion vary from &lt0.01 mmol m−3 d−1 to 0.1 mmol m−3 d−1 in the upper euphotic zone while rates of remineralization fall within a narrow range (0.015–0.025 mmol m−3 d−1). Zooplankton excretion contributes up to 70% of total ammonium regeneration in the euphotic zone, and is largely responsible for the spatial variability of nitrogen regeneration. However, remineralization provides a steady supply of ammonium in the upper ocean, and is a major source of inorganic nitrogen for the oligotrophic regions. Overall, ammonium generation and removal are approximately balanced over the top 150 m in the equatorial Pacific.

scholarly journals Nitrogen uptake and regeneration pathways in the equatorial Pacific: a basin scale modeling study

2009 ◽  
Vol 6 (11) ◽  
pp. 2647-2660 ◽  
Author(s):  
X. J. Wang ◽  
R. Murtugudde ◽  
R. Le Borgne
Keyword(s):  
Inorganic Nitrogen ◽  
Euphotic Zone ◽  
Equatorial Pacific ◽  
Ammonium Uptake ◽  
Regeneration Rate ◽  
Scale Modeling ◽  
Basin Scale ◽  
Zooplankton Excretion ◽  
Over The Top ◽  
Modeling Study

Abstract. It is well known that most primary production is fueled by regenerated nitrogen in the open ocean. Therefore, studying the nitrogen cycle by focusing on uptake and regeneration pathways would advance our understanding of nitrogen dynamics in the marine ecosystem. Here, we carry out a basin-scale modeling study, by assessing model simulations of nitrate and ammonium, and rates of nitrate uptake, ammonium uptake and regeneration in the equatorial Pacific. Model-data comparisons show that the model is able to reproduce many observed features of nitrate, ammonium, such as the deep ammonium maximum (DAM). The model also reproduces the observed de-coupling of ammonium uptake and regeneration, i.e., regeneration rate greater than uptake rate in the lower euphotic zone. The de-coupling largely explains the observed DAM in the equatorial Pacific Ocean. Our study indicates that zooplankton excretion and remineralization of organic nitrogen play a different role in nitrogen regeneration. Rates of zooplankton excretion vary from <0.01 mmol m−3 d−1 to 0.1 mmol m−3 d−1 in the upper euphotic zone while rates of remineralization fall within a narrow range (0.015–0.025 mmol m−3 d−1 . Zooplankton excretion contributes up to 70% of total ammonium regeneration in the euphotic zone, and is largely responsible for the spatial variability of nitrogen regeneration. However, remineralization provides a steady supply of ammonium in the upper ocean, and is a major source of inorganic nitrogen for the oligotrophic regions. Overall, ammonium generation and removal are approximately balanced over the top 150 m in the equatorial Pacific.

scholarly journals Spatial and temporal variability in nutrients and carbon uptake during 2004 and 2005 in the eastern equatorial Pacific Ocean

2012 ◽  
Vol 9 (11) ◽  
pp. 4369-4383 ◽  
Author(s):  
A. P. Palacz ◽  
F. Chai
Keyword(s):  
Temporal Variability ◽  
Remote Sensing Data ◽  
Zooplankton Biomass ◽  
Equatorial Pacific ◽  
Ocean Modeling ◽  
Spatial And Temporal Variability ◽  
Equatorial Pacific Ocean ◽  
Regional Ocean Modeling System ◽  
Eastern Equatorial Pacific ◽  
Physical Interactions

Abstract. The eastern equatorial Pacific plays a~great role in the global carbon budget due to its enhanced biological productivity linked to the equatorial upwelling. However, as confirmed by the Equatorial Biocomplexity cruises in 2004 and 2005, nutrient upwelling supply varies strongly, partly due to the tropical instability waves (TIWs). The aim of this study was to examine patterns of spatial and temporal variability in the biological uptake of NO3, Si(OH)4 and carbon in this region, and to evaluate the role of biological and physical interactions controlling this variability over seasonal and intraseasonal time scales. Here, high resolution Pacific ROMS–CoSiNE (Regional Ocean Modeling System–Carbon, Silicon, Nitrogen Ecosystem) model results were evaluated with in situ and remote sensing data. The results of model–data comparison revealed a good agreement in domain-average hydrographic and biological rate estimates, and patterns of spatio-temporal variability in primary productivity. We confirmed that TIWs have the potential to enhance phytoplankton biomass through an increased supply of nutrients and elevated local and instantaneous phytoplankton nutrient uptake as opposed to only advecting biomass. Furthermore, we concluded that initial biological conditions (e.g., zooplankton biomass) may play an important additional constraint on biological responses, in particular of large phytoplankton such as diatoms, to TIW-induced perturbations in the physical and biogeochemical fields and fluxes. In order to fully resolve the complexity of biological and physical interactions in the eastern equatorial Pacific, we recommended improving CoSiNE and other models by introducing more phytoplankton groups, variable Redfield and carbon to chlorophyll ratios, as well as resolving the Fe–Si co-limitation of phytoplankton growth.

scholarly journals Spatial and temporal variability in nutrients and carbon uptake during 2004 and 2005 in the eastern equatorial Pacific Ocean

2012 ◽  
Vol 9 (1) ◽  
pp. 701-744
Author(s):  
A. P. Palacz ◽  
F. Chai
Keyword(s):  
Temporal Variability ◽  
Remote Sensing Data ◽  
Equatorial Pacific ◽  
Carbon Uptake ◽  
Spatial And Temporal Variability ◽  
Equatorial Pacific Ocean ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Eastern Equatorial Pacific ◽  
Physical Interactions

Abstract. The Eastern Equatorial Pacific plays a great role in the global carbon budget due to its enhanced biological productivity linked to the equatorial upwelling. However, as confirmed by the Equatorial Biocomplexity cruises in 2004 and 2005, nutrient upwelling supply varies strongly, also due to the Tropical Instability Waves. The aim of this study is to examine patterns of spatial and temporal variability in the biological uptake of NO3, Si(OH)4 and carbon in this region, and to evaluate the role of biological and physical interactions controlling these processes over seasonal and intra-seasonal time scales. Here, high resolution Pacific ROMS-CoSiNE model results are combined with in situ and remote sensing data. The results of model-data comparison reveal an excellent agreement in domain-average hydrographic and biological rate estimates, and patterns of spatio-temporal variability in primary productivity. We demonstrate for the first time that Tropical Instability Waves can be directly linked to increased NO3 and Si(OH)4 upwelling supply and enhanced nutrient and carbon uptake, in particular by large phytoplankton such as diatoms. In order to fully resolve the complexity of biological and physical interactions in the Eastern Equatorial Pacific, we recommend improving the CoSiNE model by introducing more phytoplankton groups and a variable Redfield ratio.

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