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Dissolved O2/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean


Hamme, RC and Cassar, N and Lance, VP and Vaillancourt, RD and Bender, ML and Strutton, PG and Moore, TS and DeGrandpre, MD and Sabine, CL and Ho, DT and Hargreaves, BR, Dissolved O2/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean, Journal of Geophysical Research: Oceans, 117, (1) Article C00F12. ISSN 0148-0227 (2012) [Refereed Article]

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Copyright Statement

Copyright 2012 by the American Geophysical Union.

DOI: doi:10.1029/2011JC007046


We use continuous and discrete measurements of the dissolved O2/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O2/Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O2/Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on-deck 24 h 14C incubations and gross carbon production values from photosynthesis-irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5-4.2 times higher but with uncertainties in that ratio near r+-2. These comparisons show that the photosynthesis-irradiance experiments based on 1-2 h 14C incubations underestimated gross carbon production.

Item Details

Item Type:Refereed Article
Keywords:southern ocean, productivity measures
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Biological oceanography
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Strutton, PG (Professor Peter Strutton)
ID Code:80215
Year Published:2012
Web of Science® Times Cited:65
Deposited By:IMAS Research and Education Centre
Deposited On:2012-10-24
Last Modified:2022-08-29

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