Triple oxygen isotopes and oxygen/argon ratio measurements to enhance coastal and open ocean production/respiration comparisons

The accurate measurement of marine plankton production is required to constrain the global carbon balance. Traditional methods rely on bottle incubations, which are thought to underestimate plankton production. This study presents in situ measurements of gross oxygen production (G) derived from triple oxygen isotope analysis and of net community oxygen production (N) derived from O2/Ar ratios at station L4, which is part of the Western English Channel Observatory (WECO) and a latitudinal transect through the subtropical gyres in the Atlantic Ocean in October/November 2010. G and N were determined at weekly intervals between September 2009 and September 2010 at station L4. Annual N was positive (net autotrophic) at (0.88±0.24) mol m-2 a-1 O2. The triple oxygen isotope method overestimated G during winter months due to entrainment of waters from below the mixed layer. N of (3.8 ± 3.1) mmol m-2 a-1 O2 in the North Atlantic Gyre (NAG) and (2.9 ± 2.4) mmol m-2 a-1 O2 in the South Atlantic Gyre (SAG) show both gyres to be net autotrophic at the time of sampling. G values of (169±106) mmol m-2 a-1 O2 in the NAG and (250±130) mmol m-2 a-1 O2 in the SAG were higher than published results. Diapycnal mixing was found to contribute about 20% to apparent mixed layer N in both gyres and to G in the NAG. In order to achieve these results, a gas extraction line was built and tested. A method to halt biological activity in triple oxygen isotope and discrete O2/Ar samples was assessed. Benzalkonium chloride was found to be a less toxic alternative to mercuric chloride on short time scales of three days. Our results of N agree with previous in situ productivity measurements in these regions and highlight the importance of including physical effects in the estimates of G.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2012

Author dc:creator

• Gloel, Johanna

Language dc:language

en