Changing concentrations of CO, CH ₄ , C ₅ H ₈ , CH ₃ Br, CH ₃ I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments

Abstract

Oceanic iron (Fe) fertilization experiments have advanced the understanding of how Fe regulates biological productivity and air-sea carbon dioxide (CO2) exchange. However, little is known about the production and consumption of halocarbons and other gases as a result of Fe addition. Besides metabolizing inorganic carbon, marine microorganisms produce and consume many other trace gases. Several of these gases, which individually impact global climate, stratospheric ozone concentration, or local photochemistry, have not been previously quantified during an Feenrichment experiment. We describe results for selected dissolved trace gases including methane (CH4), isoprene (C5H8), methyl bromide (CH 3Br), dimethyl sulfide, and oxygen (O2), which increased subsequent to Fe fertilization, and the associated decreases in concentrations of carbon monoxide (CO), methyl iodide (CH 3I), and CO 2 observed during the Southern Ocean Iron Enrichment Experiments. P revious iron (Fe) fertilization experiments have been conducted in the North (1) and equatorial Pacific (2, 3) and in the Southern Ocean (4, 5). The Southern Ocean, the largest of the high-nutrient low-chlorophyll regions, represents 6% of the global ocean and has the potential to enhance carbon sequestration by Fe fertilization (6-9), which could slow carbon dioxide (CO 2 ) accumulation in the atmosphere and potentially help alleviate global warming. Experimental MethodsThe experimental design and other results of the Southern Ocean Iron Enrichment Experiment (SOFeX) are presented in an overview paper (8). Of the two regions fertilized with Fe during SOFeX, we focus here on the region north of the Antarctic Polar Front. An area Ϸ15 ϫ 15 km at 56.2°S, 172.0°W (southeast of New Zealand in the southwest Pacific sector of the Southern Ocean) was fertilized with a solution of acidified iron sulfate (FeSO 4 ) over 48 h to a concentration of Ϸ1.2 ϫ 10 Ϫ9 mol⅐liter Ϫ1 (1.2 nM) beginning on January 12, 2002. The background Fe concentration ([Fe]) was Ϸ0.1 nM. A second (36 h) application of FeSO 4 (Ϸ1.2 nM) ended on January 17. These Fe additions were intended to simulate glacial era concentrations of iron in the Southern Ocean (8, 10). The region, or patch, was allowed time to bloom and then was surveyed over a 50-h period, between February 8 and 10, 4 weeks after the first Fe application. By this time the patch had reached a surface area that was a factor of 10 larger than during the initial Fe addition with iron concentrations in the patch of Ϸ0.3 nM (8). During this survey we approached the patch from the South working our way northeast, while crisscrossing the patch. After the shape and orientation of the patch became apparent [elongated and stretching from the southwest to the northeast (11)], more intensive sampling began along the patch. Observations of fluorescence, the partial pressure of CO 2 in seawater (pCO 2 ) (Fig. 1A), dissolved O 2 (Fig. 1B), chlorophyll, and primary productivity indicated a pronounced change in biological activity in the mixed layer (upper 40-5...

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…All the phytoplankton investigated emitted isoprene, with the highest production rates (per unit chlorophyll a) occurring in the cyanobacteria (Trichodesmium and Synechococcus) and the lowest in the chlorophyte Dunaliella tertiolecta. Isoprene production was also shown to be elevated in waters fertilized with iron during the SOFeX experiment (Wingenter et al, 2004). Mean (± SD) isoprene concentration was 560 ± 13 pptv in the fertilized patch, compared with 139 ± 6 pptv outside the patch in unfertilized water (Wingenter et al, 2004).…”

“…DMS production was associated with high in situ phytoplankton productivity during the Southern Ocean Iron enrichment Experiment (SOFeX). In a patch of water in which productivity was stimulated by the addition of the limiting nutrient iron, the mean (± SD) DMS concentration was 7600 ± 480 pptv, compared with 1560 ± 90 pptv outside the fertilized patch (Wingenter et al, 2004).…”

Ocean Iron Fertilization Experiments: Past–Present–Future with Introduction to Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) Project

“…Dimethylsulfide (DMS), hypothesized to be a precursor of sulfate aerosols that cause cloud formation and so climate cooling, was measured during all OIF experiments (Lawrence, 2002). Significant increases in DMS production were found in some of the OIF experiments (i.e., IronEx-2, SOIREE, EisenEx, and SOFeX-N) (Turner et al, 1996;Turner et al, 2004;Wingenter et al, 2004;Liss et al, 2005). In particular, DMS production increased 6.5-fold after iron addition during 25 SOIREE (Turner et al, 2004).…”

“…During SOFeX-N experimentation, iron addition results for HVOC were complicated: CH 3 Cl concentrations remained unchanged; CH 3 Br concentrations increased by ~14 %; and while generally CH 3 I concentrations decreased by ~23 % (Wingenter et al, 2004). CH 3 I concentrations increased 2-fold in EisenEx (Liss et al, 2005).…”

“…Halogenated volatile organic compounds (HVOCs, such as CH 3 Cl, CH 3 Br, and CH 3 I), well known for their ability to 30 destroy ozone in the lower stratospheric ozone and marine boundary layer (Solomon et al, 1994), were also measured during the OIF experiments (Wingenter et al, 2004;Liss et al, 2005). During SOFeX-N experimentation, iron addition results for HVOC were complicated: CH 3 Cl concentrations remained unchanged; CH 3 Br concentrations increased by ~14 %; and while generally CH 3 I concentrations decreased by ~23 % (Wingenter et al, 2004).…”