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

2013 ◽  
Vol 10 (10) ◽  
pp. 16923-16972 ◽  
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 1–2 weeks, and 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 non-parametric 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, Patagonian Shelf, 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, 14 mmol C m–2 d–1, falls within the range of 8.3–24 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 Decoupling of ΔO<sub>2</sub>∕Ar and particulate organic carbon dynamics in nearshore surface ocean waters

2020 ◽  
Vol 17 (12) ◽  
pp. 3277-3298
Author(s):  
Sarah Z. Rosengard ◽  
Robert W. Izett ◽  
William J. Burt ◽  
Nina Schuback ◽  
Philippe D. Tortell
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Mixed Layer ◽  
Vertical Mixing ◽  
Optical Measurements ◽  
Community Respiration ◽  
Carbon Export ◽  
Net Community Production ◽  
High Productivity ◽  
Lower Productivity

Abstract. We report results from two Lagrangian drifter surveys off the Oregon coast, using continuous shipboard sensors to estimate mixed-layer gross primary productivity (GPP), community respiration (CR), and net community production (NCP) from variations in biological oxygen saturation (ΔO2∕Ar) and optically derived particulate organic carbon (POC). At the first drifter survey, conducted in a nearshore upwelling zone during the development of a microplankton bloom, net changes in ΔO2∕Ar and [POC] were significantly decoupled. Differences in GPP and NCP derived from ΔO2∕Ar (NCPO2/Ar) and POC (NCPPOC) time series suggest the presence of large POC losses from the mixed layer. At this site, we utilized the discrepancy between NCPO2/Ar and NCPPOC, and additional constraints derived from surface water excess nitrous oxide (N2O), to evaluate POC loss through particle export, DOC production, and vertical mixing fluxes. At the second drifter survey, conducted in lower-productivity, density-stratified offshore waters, we also observed offsets between ΔO2∕Ar and POC-derived GPP and CR rates. At this site, however, net [POC] and ΔO2∕Ar changes yielded closer agreement in NCP estimates, suggesting a tighter relationship between production and community respiration, as well as lower POC loss rates. These results provide insight into the possibilities and limitations of estimating productivity from continuous underway POC and ΔO2∕Ar data in contrasting oceanic waters. Our observations support the use of diel POC measurements to estimate NCP in lower-productivity waters with limited vertical carbon export and the potential utility of coupled O2 and optical measurements to estimate the fate of POC in high-productivity regions with significant POC export.

scholarly journals The relation of mixed-layer net community production to phytoplankton community composition in the Southern Ocean

2015 ◽  
Vol 29 (4) ◽  
pp. 446-462 ◽  
Author(s):  
Nicolas Cassar ◽  
Simon W. Wright ◽  
Paul G. Thomson ◽  
Thomas W. Trull ◽  
Karen J. Westwood ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Community Composition ◽  
Mixed Layer ◽  
Phytoplankton Community ◽  
Net Community Production ◽  
Phytoplankton Community Composition ◽  
Community Production

scholarly journals Evaluating Southern Ocean biological production in two ocean biogeochemical models on daily to seasonal timescales using satellite chlorophyll and O<sub>2</sub> / Ar observations

2015 ◽  
Vol 12 (3) ◽  
pp. 681-695
Author(s):  
B. F. Jonsson ◽  
S. Doney ◽  
J. Dunne ◽  
M. L. Bender
Keyword(s):  
New Zealand ◽  
Southern Ocean ◽  
Drake Passage ◽  
Ecosystem Dynamics ◽  
Net Community Production ◽  
Biogeochemical Models ◽  
In Situ Observations ◽  
Satellite Chlorophyll ◽  
Community Production

Abstract. We assess the ability of ocean biogeochemical models to represent seasonal structures in biomass and net community production (NCP) in the Southern Ocean. Two models are compared to observations on daily to seasonal timescales in four different sections of the region. We use daily satellite fields of chlorophyll (Chl) as a proxy for biomass and in situ observations of O2 and Ar supersaturation (ΔO2 / Ar) to estimate NCP. ΔO2 / Ar is converted to the flux of biologically generated O2 from sea to air (O2 bioflux). All data are aggregated to a climatological year with a daily resolution. To account for potential regional differences within the Southern Ocean, we conduct separate analyses of sections south of South Africa, around the Drake Passage, south of Australia, and south of New Zealand. We find that the models simulate the upper range of Chl concentrations well, underestimate spring levels significantly, and show differences in skill between early and late parts of the growing season. While there is a great deal of scatter in the bioflux observations in general, the four sectors each have distinct patterns that the models pick up. Neither model exhibits a significant distinction between the Australian and New Zealand sectors and between the Drake Passage and African sectors. South of 60° S, the models fail to predict the observed extent of biological O2 undersaturation. We suggest that this shortcoming may be due either to problems with the ecosystem dynamics or problems with the vertical transport of oxygen.

scholarly journals The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

2011 ◽  
Vol 8 (2) ◽  
pp. 227-237 ◽  
Author(s):  
N. Cassar ◽  
P. J. DiFiore ◽  
B. A. Barnett ◽  
M. L. Bender ◽  
A. R. Bowie ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Light Availability ◽  
Austral Summer ◽  
Ocean Mixed Layer ◽  
Carbon Export ◽  
Net Community Production ◽  
Independent Evidence ◽  
Frontal Zones ◽  
Mixed Layers ◽  
Community Production

Abstract. The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January–February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O2 m−2 d−1. NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. The strong correlation between NCP and dissolved Fe may be difficult to interpret because of the correlation of dissolved Fe to MLD and because the concentration of iron may not be a good indicator of its availability. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer.

scholarly journals The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

2010 ◽  
Vol 7 (4) ◽  
pp. 5649-5674 ◽  
Author(s):  
N. Cassar ◽  
P. J. DiFiore ◽  
B. A. Barnett ◽  
M. L. Bender ◽  
A. R. Bowie ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Primary Productivity ◽  
Light Availability ◽  
Austral Summer ◽  
Carbon Export ◽  
Net Community Production ◽  
Independent Evidence ◽  
Frontal Zones ◽  
Mixed Layers ◽  
Community Production

Abstract. The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January–February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O2 m−2 d−1. Both gross primary productivity (estimated from the oxygen triple isotope anomaly) and NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer.

scholarly journals Decoupling of net community production and particulate organic carbon dynamics in near shore surface ocean waters

2019 ◽  
Author(s):  
Sarah Z. Rosengard ◽  
Robert W. Izett ◽  
William J. Burt ◽  
Nina Schuback ◽  
Philippe D. Tortell
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Mixed Layer ◽  
Vertical Mixing ◽  
Optical Measurements ◽  
Net Community Production ◽  
Diel Cycles ◽  
Lower Productivity ◽  
Doc Production ◽  
Community Production

Abstract. We report results from two Lagrangian surveys off the coast of Oregon, using continuous ship-board sensors to estimate mixed layer net community production (NCP) from diel cycles in biological oxygen saturation (∆O2 / Ar) and optically-derived estimates of particulate organic carbon (POC) and phytoplankton carbon (Cph). The first drifter survey, conducted in a nearshore upwelling zone during the development of a microplankton bloom, exhibited significant differences in NCP derived from ∆O2 / Ar and POC diel cycles, suggesting the presence of large POC losses from the mixed layer. At this site, we utilized the discrepancy between NCPO2 / Ar and NCPPOC, along with additional constraints derived from mixed layer nutrient inventories and surface water excess nitrous oxide (N2O), to estimate particle export, vertical mixing fluxes and DOC production. We estimate that export, vertical mixing and DOC production account for 13–45 %, 24–38 % and 25–49 % of the daily NCP discrepancy, respectively. In contrast, the second drifter survey occurred in more oligotrophic offshore waters, where NCP derived from ∆O2 / Ar and POC measurements were more closely coupled, suggesting a tighter relationship between production and community respiration. These results support the use of diel POC measurements to accurately estimate NCP in lower productivity waters with limited vertical carbon export. Although diel POC measurements may underestimate NCP in higher productivity waters, our results highlight the potential utility of coupled O2 and optical measurements to estimate the fate of POC in such regions.

scholarly journals An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export

2016 ◽  
Vol 116 ◽  
pp. 49-76 ◽  
Author(s):  
William Z. Haskell ◽  
Maria G. Prokopenko ◽  
Douglas E. Hammond ◽  
Rachel H.R. Stanley ◽  
William M. Berelson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Southern California ◽  
Carbon Budget ◽  
Nutrient Flux ◽  
Net Community Production ◽  
Community Production

scholarly journals High-Resolution Sea Surface Temperature and Salinity in the Global Ocean from Raw Satellite Data

2019 ◽  
Vol 11 (19) ◽  
pp. 2191 ◽  
Author(s):  
Encarni Medina-Lopez ◽  
Leonardo Ureña-Fuentes
Keyword(s):  
Neural Network ◽  
High Resolution ◽  
Satellite Data ◽  
Google Earth ◽  
Sea Surface ◽  
Global Ocean ◽  
The Neural Network ◽  
Wide Range ◽  
Sentinel 2

The aim of this work is to obtain high-resolution values of sea surface salinity (SSS) and temperature (SST) in the global ocean by using raw satellite data (i.e., without any band data pre-processing or atmospheric correction). Sentinel-2 Level 1-C Top of Atmosphere (TOA) reflectance data is used to obtain accurate SSS and SST information. A deep neural network is built to link the band information with in situ data from different buoys, vessels, drifters, and other platforms around the world. The neural network used in this paper includes shortcuts, providing an improved performance compared with the equivalent feed-forward architecture. The in situ information used as input for the network has been obtained from the Copernicus Marine In situ Service. Sentinel-2 platform-centred band data has been processed using Google Earth Engine in areas of 100 m × 100 m. Accurate salinity values are estimated for the first time independently of temperature. Salinity results rely only on direct satellite observations, although it presented a clear dependency on temperature ranges. Results show the neural network has good interpolation and extrapolation capabilities. Test results present correlation coefficients of 82 % and 84 % for salinity and temperature, respectively. The most common error for both SST and SSS is 0.4 ∘ C and 0 . 4 PSU. The sensitivity analysis shows that outliers are present in areas where the number of observations is very low. The network is finally applied over a complete Sentinel-2 tile, presenting sensible patterns for river-sea interaction, as well as seasonal variations. The methodology presented here is relevant for detailed coastal and oceanographic applications, reducing the time for data pre-processing, and it is applicable to a wide range of satellites, as the information is directly obtained from TOA data.

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