Net community production and carbon export during the late summer in the Ross Sea, Antarctica

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.

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Distribution of CO2species, estimates of net community production, and air-sea CO2exchange in the Ross Sea polynya

Journal of Geophysical Research Atmospheres ◽

10.1029/97jc02473 ◽

1998 ◽

Vol 103 (C2) ◽

pp. 2883-2896 ◽

Cited By ~ 110

Author(s):

Nicholas R. Bates ◽

Dennis A. Hansell ◽

Craig A. Carlson ◽

Louis I. Gordon

Keyword(s):

Ross Sea ◽

Net Community Production ◽

Community Production

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Concurrent estimates of carbon export reveal physical biases in ΔO2/Ar-based net community production estimates in the Southern California Bight

Journal of Marine Systems ◽

10.1016/j.jmarsys.2018.03.008 ◽

2018 ◽

Vol 183 ◽

pp. 23-31 ◽

Cited By ~ 3

Author(s):

William Z. Haskell ◽

John C. Fleming

Keyword(s):

Southern California ◽

Southern California Bight ◽

Carbon Export ◽

Net Community Production ◽

Community Production

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Interannual variations in nutrients, net community production, and biogeochemical cycles in the Ross Sea

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2006.02.014 ◽

2006 ◽

Vol 53 (8-10) ◽

pp. 815-833 ◽

Cited By ~ 51

Author(s):

Walker O. Smith ◽

Amy R. Shields ◽

Jill A. Peloquin ◽

Giulio Catalano ◽

Sasha Tozzi ◽

...

Keyword(s):

Ross Sea ◽

Biogeochemical Cycles ◽

Interannual Variations ◽

Net Community Production ◽

Community Production

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Variations in the abundance and distribution of aggregates in the Ross Sea, Antarctica

Elem Sci Anth ◽

10.1525/elementa.355 ◽

2019 ◽

Vol 7 ◽

Author(s):

Vernon L. Asper ◽

Walker O. Smith

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Ross Sea ◽

Late Summer ◽

Early Summer ◽

Particulate Carbon ◽

Carbon Export ◽

Phaeocystis Antarctica ◽

Abundance And Distribution ◽

The Vertical Distribution

The vertical distribution and temporal changes in aggregate abundance and sizes were measured in the Ross Sea, Antarctica between 2002 and 2005 to acquire a more complete understanding of the mechanisms and rates of carbon export from the euphotic layer. Aggregate abundance was determined by photographic techniques, and water column parameters (temperature, salinity, fluorescence, transmissometry) were assessed from CTD profiles. During the first three years the numbers of aggregates increased seasonally, being much more abundant within the upper 200 m in late summer than in early summer from 50 to 100 m (12.5 L–1 in early summer vs. 42.9 L–1 in late summer). In Year 4 aggregate numbers were substantially greater than in other years, and average aggregate abundance was maximal in early rather than late summer (177 vs. 84.5 L–1), which we attributed to the maximum biomass and aggregate formation being reached earlier than in other years. The contribution of aggregate particulate organic carbon to the total particulate carbon pool was estimated to be 20%. Ghost colonies, collapsed colonies of the haptophyte Phaeocystis antarctica, were observed during late summer in Year 4, with maximum numbers in the upper 100 m of ca. 40 L–1. Aggregate abundance, particulate organic carbon and ghost colonies all decreased exponentially with depth, and the rate of ghost colony disappearance suggested that their contribution to sedimentary input was small at the time of sampling. Bottom nepheloid layers were commonly observed in late summer in both transmissometer and aggregate data. Late summer nepheloid layers had fluorescent material within them, suggesting that the particles were likely generated during the same growing season. Longer studies encompassing the entire production season would be useful in further elucidating the role of these aggregates in the carbon cycle of these regions.

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Late summer net community production in the central Arctic Ocean using multiple approaches

Global Biogeochemical Cycles ◽

10.1002/2014gb004833 ◽

2014 ◽

Vol 28 (10) ◽

pp. 1129-1148 ◽

Cited By ~ 23

Author(s):

Adam Ulfsbo ◽

Nicolas Cassar ◽

Meri Korhonen ◽

Steven Heuven ◽

Mario Hoppema ◽

...

Keyword(s):

Arctic Ocean ◽

Late Summer ◽

Net Community Production ◽

Central Arctic Ocean ◽

Community Production

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Vertical structure, seasonal drawdown, and net community production in the Ross Sea, Antarctica

Journal of Geophysical Research Atmospheres ◽

10.1029/2009jc005954 ◽

2011 ◽

Vol 116 (C10) ◽

Cited By ~ 23

Author(s):

Matthew C. Long ◽

Robert B. Dunbar ◽

Philippe D. Tortell ◽

Walker O. Smith ◽

David A. Mucciarone ◽

...

Keyword(s):

Vertical Structure ◽

Ross Sea ◽

Net Community Production ◽

Community Production

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Dissolved oxygen dynamics during a phytoplankton bloom in the Ross Sea polynya

Antarctic Science ◽

10.1017/s0954102014000881 ◽

2015 ◽

Vol 27 (4) ◽

pp. 362-372 ◽

Cited By ~ 7

Author(s):

Bastien Y. Queste ◽

Karen J. Heywood ◽

Walker O. Smith ◽

Daniel E. Kaufman ◽

Timothy D. Jickells ◽

...

Keyword(s):

Dissolved Oxygen ◽

Primary Productivity ◽

Ross Sea ◽

Phytoplankton Bloom ◽

Net Primary Production ◽

Biological Processes ◽

Carbon Export ◽

Net Community Production ◽

Spatio Temporal ◽

The Difference

AbstractThe Ross Sea polynya is one of the most productive regions in the Southern Ocean. However, limited access and high spatio-temporal variability of physical and biological processes limit the use of conventional oceanographic methods to measure early season primary productivity. High-resolution observations from two Seagliders provide insights into the timing of a bloom in the southern Ross Sea polynya in December 2010. Changes in chlorophyll and oxygen concentrations are used to assess bloom dynamics. Using a ratio of dissolved oxygen to carbon, net primary production is estimated over the duration of the bloom showing a sensitive balance between net autotrophy and heterotrophy. The two gliders, observing spatially distinct regions during the same period, found net community production rates of -0.9±0.7 and 0.7±0.4 g C m-2 d-1. The difference highlights the spatial variability of biological processes and is probably caused by observing different stages of the bloom. The challenge of obtaining accurate primary productivity estimates highlights the need for increased observational efforts, particularly focusing on subsurface processes not resolved using surface or remote observations. Without an increased observational effort and the involvement of emerging technologies, it will not be possible to determine the seasonal trophic balance of the Ross Sea polynya and quantify the shelf’s importance in carbon export.

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

Biogeosciences Discussions ◽

10.5194/bgd-10-16923-2013 ◽

2013 ◽

Vol 10 (10) ◽

pp. 16923-16972 ◽

Cited By ~ 1

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.

Download Full-text