scholarly journals Spring net community production and its coupling with the CO<sub>2</sub> dynamics in the surface water of the northern Gulf of Mexico

2019 ◽  
Author(s):  
Zong-Pei Jiang ◽  
Wei-Jun Cai ◽  
John Lehrter ◽  
Baoshan Chen ◽  
Zhangxian Ouyang ◽  
...  
Keyword(s):  
Surface Water ◽  
Gulf Of Mexico ◽  
Co2 Fluxes ◽  
Spring Season ◽  
Biological Production ◽  
Net Community Production ◽  
Northern Gulf Of Mexico ◽  
Co2 Sink ◽  
Community Production

Abstract. Net community production (NCP) in the surface mixed layer of the northern Gulf of Mexico (nGOM) and its coupling with the CO2 system were examined during the productive spring season. NCP was estimated using multiple approaches: (1) underway O2 and Ar ratio, (2) light/dark bottle oxygen incubations, and (3) non-conservative changes in dissolved inorganic carbon and nutrients; in order to assess uncertainties and compare the temporal-spatial scales associated with the different approaches. NCP estimates derived from various methods showed similar pattern along the river-ocean mixing gradient. The NCPO2Ar estimated from the high resolution O2 and Ar underway measurement is characterized by negative rates (−25.4 mmol C m−2 d−1) at the high nutrient and high turbidity river end (salinity  31) oligotrophic offshore waters due to nutrient limitation. Air-sea CO2 fluxes generally showed corresponding changes from being a strong CO2 source in the river channel to a CO2 sink in the plume. CO2 fluxes were near zero in offshore waters indicating balanced autotrophy and heterotrophy at these sites. Overall, the surface water in the nGOM (93–89.25° W, 28.5–29.5° N) was strongly autotrophic during the spring season in spring 2017 with mean NCP rate of 21.2 mmol C m−2 d−1 and as a CO2 sink of −6.7 mmol C m−2 d−1. By using a 1-D model, we demonstrated that a temporal mismatch between in situ biological production and gas exchange of O2 and CO2 could result in decoupling between NCP and CO2 flux (e.g., autotropic water as a CO2 source outside the Mississippi river mouth and heterotopic water as a CO2 sink near the Atchafalaya Delta). This decoupling was a result of in situ biological production superimposed on the lingering background pCO2 from the source water because of the slow air-sea CO2 exchange rate and buffering effect of the carbonate system.

scholarly journals Spring net community production and its coupling with the CO<sub>2</sub> dynamics in the surface water of the northern Gulf of Mexico

2019 ◽  
Vol 16 (18) ◽  
pp. 3507-3525
Author(s):  
Zong-Pei Jiang ◽  
Wei-Jun Cai ◽  
John Lehrter ◽  
Baoshan Chen ◽  
Zhangxian Ouyang ◽  
...  
Keyword(s):  
Surface Water ◽  
Gulf Of Mexico ◽  
Mississippi River ◽  
Phytoplankton Production ◽  
Biological Production ◽  
Net Community Production ◽  
Northern Gulf Of Mexico ◽  
Co2 Sink ◽  
Community Production

Abstract. Net community production (NCP) in the surface water of the northern Gulf of Mexico (nGOM) and its coupling with the CO2 system were examined during the productive spring season. NCP was estimated using multiple approaches: (1) underway O2 and Ar ratio, (2) oxygen changes during light/dark bottle oxygen incubations, and (3) non-conservative changes in dissolved inorganic carbon or nutrients. These methods all showed high spatial variability of NCP and displayed similar patterns along the river–ocean mixing gradient, showing high production rates in plume regions. NCPO2Ar estimated from high-resolution O2 and Ar underway measurement indicated heterotrophic conditions at the high-nutrient and high-turbidity Mississippi River end (-51.3±11.9 mmol C m−2 d−1 when salinity < 2) resulting from the influence of terrestrial carbon input and light limitation on photosynthesis. High NCPO2Ar rates (105.0±59.2 mmol C m−2 d−1, up to 235.4 mmol C m−2 d−1) were observed in the Mississippi and Atchafalaya plumes at intermediate salinities between 15 and 30 where light and nutrients were both favorable for phytoplankton production. NCPO2Ar rates observed in the high-salinity, oligotrophic offshore waters (salinity > 35.5) were close to zero due to nutrient limitation. Air–sea CO2 fluxes generally showed corresponding changes, from being a strong CO2 source in the river channel (55.5±7.6 mmol C m−2 d−1), to a CO2 sink in the plume (-13.4±5.5 mmol C m−2 d−1), and to being nearly in equilibrium with the atmosphere in offshore waters. Overall, the surface water of the nGOM was net autotrophic during spring 2017, with an area-weighted mean NCPO2Ar of 21.2 mmol C m−2 d−1, and was a CO2 sink of −6.7 mmol C m−2 d−1. A temporal mismatch between in situ biological production and gas exchange of O2 and CO2 was shown through a box model to result in decoupling between NCPO2Ar and CO2 flux (e.g., autotrophic water as a CO2 source outside the Mississippi River mouth and heterotopic water as a CO2 sink in the Atchafalaya coastal water). This decoupling was a result of in situ biological production superimposed on the lingering background pCO2 from the source water because of the slow air–sea CO2 exchange rate and the buffering effect of the carbonate system.

scholarly journals Neural network-based estimates of Southern Ocean net community production from in situ O<sub>2</sub> / Ar and satellite observation: a methodological study

2014 ◽  
Vol 11 (12) ◽  
pp. 3279-3297 ◽  
Author(s):  
C.-H. Chang ◽  
N. C. Johnson ◽  
N. Cassar
Keyword(s):  
Neural Network ◽  
Organic Carbon ◽  
Southern Ocean ◽  
Mixed Layer ◽  
Sea Surface ◽  
Carbon Export ◽  
Net Community Production ◽  
Basin Scale ◽  
Community Production

Abstract. Southern Ocean organic carbon export plays an important role in the global carbon cycle, yet its basin-scale climatology and variability are uncertain due to limited coverage of in situ observations. In this study, a neural network approach based on the self-organizing map (SOM) is adopted to construct weekly gridded (1° × 1°) maps of organic carbon export for the Southern Ocean from 1998 to 2009. The SOM is trained with in situ measurements of O2 / Ar-derived net community production (NCP) that are tightly linked to the carbon export in the mixed layer on timescales of one to two weeks and with six potential NCP predictors: photosynthetically available radiation (PAR), particulate organic carbon (POC), chlorophyll (Chl), sea surface temperature (SST), sea surface height (SSH), and mixed layer depth (MLD). This nonparametric approach is based entirely on the observed statistical relationships between NCP and the predictors and, therefore, is strongly constrained by observations. A thorough cross-validation yields three retained NCP predictors, Chl, PAR, and MLD. Our constructed NCP is further validated by good agreement with previously published, independent in situ derived NCP of weekly or longer temporal resolution through real-time and climatological comparisons at various sampling sites. The resulting November–March NCP climatology reveals a pronounced zonal band of high NCP roughly following the Subtropical Front in the Atlantic, Indian, and western Pacific sectors, and turns southeastward shortly after the dateline. Other regions of elevated NCP include the upwelling zones off Chile and Namibia, the Patagonian Shelf, the Antarctic coast, and areas surrounding the Islands of Kerguelen, South Georgia, and Crozet. This basin-scale NCP climatology closely resembles that of the satellite POC field and observed air–sea CO2 flux. The long-term mean area-integrated NCP south of 50° S from our dataset, 17.9 mmol C m−2 d−1, falls within the range of 8.3 to 24 mmol C m−2 d−1 from other model estimates. A broad agreement is found in the basin-wide NCP climatology among various models but with significant spatial variations, particularly in the Patagonian Shelf. Our approach provides a comprehensive view of the Southern Ocean NCP climatology and a potential opportunity to further investigate interannual and intraseasonal variability.

scholarly journals Net community production of oxygen derived from in vitro and in situ 1-D modeling techniques in a cyclonic mesoscale eddy in the Sargasso Sea

2009 ◽  
Vol 6 (8) ◽  
pp. 1799-1810 ◽  
Author(s):  
B. Mouriño-Carballido ◽  
L. A. Anderson
Keyword(s):  
Mesoscale Eddy ◽  
Sampling Period ◽  
Sargasso Sea ◽  
Net Community Production ◽  
Mesoscale Dynamics ◽  
In Vitro Incubation ◽  
Net Heterotrophy ◽  
Community Production

Abstract. It has been proposed that the disagreement traditionally reported between in vitro incubation and in situ estimates of oxygen net community production (NCP) could be explained, at least partially, by undersampling episodic pulses of net autotrophy associated with mesoscale dynamics. In this study we compare in vitro incubation estimates of net community production with in situ estimates, derived from oxygen profiles and a 1-D model, within a cyclonic eddy investigated in the Sargasso Sea in summer 2004. The in vitro NCP rates measured at the center of the eddy showed a shift from net autotrophy (7±3 mmol O2 m−2 d−1) to net heterotrophy (−25±5 mmol O2 m−2 d−1) from late June to early August. The model-derived NCP rates also showed a temporal decline (19±6 to −3±7 and 11±8 mmol O2 m−2 d−1), but they were systematically higher than the in vitro estimates and reported net autotrophy or balance for the sampling period. In this comparison episodic pulses in photosynthesis or respiration driven by mesoscale eddies can not explain the discrepancy between the in vitro and in situ estimates of NCP. This points to methodological artefacts or temporal or submesoscale variability as the mechanisms responsible for the disagreement between the techniques, at least in this dataset.

In situ hydrocarbon concentrations from pressurized cores in surface sediments, Northern Gulf of Mexico

2007 ◽  
Vol 107 (4) ◽  
pp. 498-515 ◽  
Author(s):  
Katja U. Heeschen ◽  
Hans Jürgen Hohnberg ◽  
Matthias Haeckel ◽  
Friedrich Abegg ◽  
Manuela Drews ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Surface Sediments ◽  
Northern Gulf Of Mexico
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