Varying Biological Activity and Wind Stress Affect the DMS Response during the SAGE Iron Enrichment Experiment

Graham Jones,Darren Fortescue,Simon Wright,Damien T Maher,Stacey King,Mike Harvey,Hilton Swan,Anke Schneider

doi:10.3390/jmse8040268

Abstract

Surface dissolved dimethylsulfide (DMS) and depth-integrated dimethylsulfoniopropionate (DMSP) measurements were made from March to April 2004 during the SOLAS Air–Sea Gas Exchange Experiment (SAGE), a multiple iron enrichment experiment in subantarctic waters SE of New Zealand. During the first two iron enrichments, chl a and DMS production were constrained, but during the third enrichment, large pulses of DMS occurred in the fertilised IN patch, compared with the unfertilised OUT patch. During the third and fourth iron infusions, total chl a concentrations doubled from 0.52 to 1.02 µg/L. Hapto8s and prasinophytes accounted for 50%, and 20%, respectively, of total chl a. The large pulses of DMS during the third iron enrichment occurred during high dissolved DMSP concentrations and wind strength; changes in dinoflagellate, haptophyte, and cyanobacteria biomass; and increased microzooplankton grazing that exerted a top down control on phytoplankton production. A further fourth iron enrichment did cause surface waters to increase in DMS, but the effect was not as great as that recorded in the third enrichment. Differences in the biological response between SAGE and several other iron enrichment experiments were concluded to reflect microzooplankton grazing activities and the microbial loop dominance, resulting from mixing of the MLD during storm activity and high winds during iron enrichment.

Highlights

Carbon dioxide levels continue to rise in the atmosphere, with predictions of a 1.5–2 ◦C increase in temperature by the end of the century [1], causing increased drought, bush fires, flooding, and sea level rise
We report the first continuous underway measurements of dissolved DMS concentrations, together with its precursor DMSP, in subantarctic waters SE of New Zealand sampled during the SOLAS Air–Sea Gas Exchange Experiment (SAGE), where four iron infusions were added to these waters over 15 days in 2004
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Summary

Introduction

Carbon dioxide levels continue to rise in the atmosphere, with predictions of a 1.5–2 ◦C increase in temperature by the end of the century [1], causing increased drought, bush fires, flooding, and sea level rise. There are many reasons for this, but a major one is that it is not easy to stimulate the growth of large-cell diatoms, which seem to be needed to fix large amounts of CO2 and transport it to the deep sea. Another reason is that fertilization of the ocean with iron can increase microzooplankton grazing, so that as soon as the CO2 is fixed by phytoplankton, it is released to the atmosphere again during the grazing of the phytoplankton

Methods

Results

Discussion

Conclusion