Primary Production in the Sub-Antarctic and Polar Frontal Zones; SAZ-Sense Voyage, 2007
Entry ID:
ASAC_40_SAZ-Sense_Primary_Production
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Summary
Abstract:
The Sub-Antarctic Zone (SAZ) in the Southern Ocean provides a significant sink for atmospheric CO2 and quantification of this sink is therefore important in models of climate change. During the SAZ-Sense (Sub-Antarctic Sensitivity to Environmental Change) survey conducted during austral summer 2007, we examined CO2 sequestration through measurement of gross primary production rates using 14C. ... Sampling was conducted in the SAZ to the south-west and south-east of Tasmania, and in the Polar Frontal Zone (PFZ) directly south of Tasmania. Despite higher chlorophyll biomass off the south-east of Tasmania, production measurements were similar to the south-west with rates of 986.2 plus or minus 500.4 and 1304.3 plus or minus 300.1 mg C m-2 d-1, respectively. Assimilation numbers suggested the onset of cell senescence by the time of sampling in the south-east, with healthy phytoplankton populations to the south-west sampled three week earlier. Production in the PFZ (475.4 plus or minus 168.7 mg C m-2 d-1) was lower than the SAZ, though not significantly. The PFZ was characterised by a defined deep chlorophyll maximum near the euphotic depth (75 m) with low production due to significant light limitation. A healthy and less light-limited phytoplankton population occupied the mixed layer of the PFZ, allowing more notable production there despite lower chlorophyll. A hypothesis that iron availability would enhance gross primary production in the SAZ was not supported due to the seasonal effect that masked possible responses. However, highest production (2572.5 mg C m-2 d-1) was measured nearby in the Sub-Tropical Zone off south-east Tasmania in a region where iron was likely to be non-limiting (Bowie et al., 2009).
Table 1:Gross primary production at each CTD station and associated data; Mixed layer depth (Zm, m), incoming PAR (mol m-2 d-1), vertical light attenuation (Kd, m-1), euphotic depth (Zeu, m), differences between euphotic depth and mixed layer depth (Zeu-Zm, m), column-integrated chlorophyll a (0 to 150 m, mg m-2), column-integrated production (0 to 150 m, mg C m-2 d-1), production within the mixed layer (mg C m-2 d-1), production below the mixed layer (mg C m-2 d-1), production within the euphotic zone (1% PAR, mg C m-2 d-1), production below the euphotic zone (mg C m-2 d-1). Kd values that were calculated from chlorophyll a v PAR regressions are marked with an asterisk. At some stations there was a surface mixed layer as well as a secondary mixed layer and both depths are indicated.
Table 2:Photosynthetic attributes of phytoplankton with depth at each CTD station; Mixed layer depth (m), euphotic depth (Zeu, m), maximum photosynthetic rate [Pmax, mg C (mg chl a)-1 h-1], maximum photosynthetic rate corrected for photoinhibition [Pmaxb, mg C (mg chl a)-1 h-1], initial slope of the light-limited section of the P-I curve [alpha, mg C (mg chl a)-1 h-1 (micro-mol m-2 s-1)-1], rate of photoinhibition [beta, mg C (mg chl a)-1 h-1 (micro-mol m-2 s-1)-1], intercept of the P-I curve with the carbon uptake axis [c, mg C (mg chl a)-1 h-1], light intensity at which carbon-uptake became saturated (Ek, micro-mol m-2 s-1), and chlorophyll a measured using HPLC (mg m-3). 
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Geographic Coverage
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Spatial coordinates
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N: -43.5
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S: -54.1
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E: 153.3
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W: 140.6
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Data Set Citation
Dataset Release Date:
2011-08-15
Dataset DOI:
http://dx.doi.org/10.4225/15/515B76F4DBF24
Temporal Coverage
Start Date:
2007-01-19
Stop Date:
2007-02-19
Access Constraints
These data are publicly available from the provided URL.
Data Set Progress
COMPLETE
Distribution
Distribution Media:
Online
Fees:
No fees
Personnel
Role:
TECHNICAL CONTACT
Phone:
303-497-2941
City:
Boulder
Province or State:
CO
Postal Code:
80307
Country:
USA
Role:
SERF AUTHOR
Phone:
(301) 614-6898
Fax:
301-614-5268
Email:
Tyler.B.Stevens at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Global Change Master Directory
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Creation and Review Dates
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