Linking Southern Ocean mixed‐layer dynamics to net community production on various timescales

2021 ◽  
Author(s):  
Zuchuan Li ◽  
M. Susan Lozier ◽  
Nicolas Cassar
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Ocean Mixed Layer ◽  
Net Community Production ◽  
Community Production

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 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 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 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.

Estimating net community production in the Southern Ocean based on atmospheric potential oxygen and satellite ocean color data

2012 ◽  
Vol 26 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
C. D. Nevison ◽  
R. F. Keeling ◽  
M. Kahru ◽  
M. Manizza ◽  
B. G. Mitchell ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Color ◽  
Net Community Production ◽  
Color Data ◽  
Satellite Ocean Color ◽  
Potential Oxygen ◽  
Community Production

scholarly journals High-resolution view of the spring bloom initiation and net community production in the Subantarctic Southern Ocean using glider data

2015 ◽  
Vol 72 (6) ◽  
pp. 1999-2020 ◽  
Author(s):  
Sandy J. Thomalla ◽  
Marie-Fanny Racault ◽  
Sebastiaan Swart ◽  
Pedro M. S. Monteiro
Keyword(s):  
Climate Change ◽  
High Resolution ◽  
Southern Ocean ◽  
High Growth ◽  
Biomass Accumulation ◽  
Horizontal Resolution ◽  
Early Summer ◽  
Detection Methods ◽  
Net Community Production ◽  
Community Production

Abstract In the Southern Ocean, there is increasing evidence that seasonal to subseasonal temporal scales, and meso- to submesoscales play an important role in understanding the sensitivity of ocean primary productivity to climate change. This drives the need for a high-resolution approach to resolving biogeochemical processes. In this study, 5.5 months of continuous, high-resolution (3 h, 2 km horizontal resolution) glider data from spring to summer in the Atlantic Subantarctic Zone is used to investigate: (i) the mechanisms that drive bloom initiation and high growth rates in the region and (ii) the seasonal evolution of water column production and respiration. Bloom initiation dates were analysed in the context of upper ocean boundary layer physics highlighting sensitivities of different bloom detection methods to different environmental processes. Model results show that in early spring (September to mid-November) increased rates of net community production (NCP) are strongly affected by meso- to submesoscale features. In late spring/early summer (late-November to mid-December) seasonal shoaling of the mixed layer drives a more spatially homogenous bloom with maximum rates of NCP and chlorophyll biomass. A comparison of biomass accumulation rates with a study in the North Atlantic highlights the sensitivity of phytoplankton growth to fine-scale dynamics and emphasizes the need to sample the ocean at high resolution to accurately resolve phytoplankton phenology and improve our ability to estimate the sensitivity of the biological carbon pump to climate change.

scholarly journals Assessment of Southern Ocean mixed-layer depths in CMIP5 models: Historical bias and forcing response

2013 ◽  
Vol 118 (4) ◽  
pp. 1845-1862 ◽  
Author(s):  
J.-B. Sallée ◽  
E. Shuckburgh ◽  
N. Bruneau ◽  
A. J. S. Meijers ◽  
T. J. Bracegirdle ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Cmip5 Models ◽  
Ocean Mixed Layer
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