The SOLAS air-sea gas exchange experiment (SAGE) 2004

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 58 (2011): 753-763, doi:10.1016/j.dsr2.2010.10.015.The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive Subpolar Zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study quantifying key biological and physical drivers influencing the air-sea gas exchange processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air-sea tracer exchange at the 10’s of km’s scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describes air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties, and wind speed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 tonne Fe2+, this was a very modest response compared to the other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co- limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAX’s to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO2 was small and masked by a general increase in pCO2 due to mixing with higher pCO2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.SAGE was jointly funded through the New Zealand Foundation for Research, Science and Technology (FRST) programs (C01X0204) "Drivers and Mitigation of Global Change" and (C01X0223) "Ocean Ecosystems: Their Contribution to NZ Marine Productivity." Funding was also provided for specific collaborations by the US National Science Foundation from grants OCE-0326814 (Ward), OCE-0327779 (Ho), and OCE 0327188 OCE-0326814 (Minnett) and the UK Natural Environment Research Council NER/B/S/2003/00282 (Archer). The New Zealand International Science and Technology (ISAT) linkages fund provided additional funding (Archer and Ziolkowski), and the many collaborator institutions also provided valuable support

Shipboard measurements of dimethyl sulfide and SO 2 southwest of Tasmania during the First Aerosol Characterization Experiment (ACE 1)

Measurements of seawater dimethylsulfide (DMS), atmospheric dimethylsulfide, and sulfur dioxide (SO2) were made on board the R/VDiscoverer in the Southern Ocean, southeast of Australia, as part of the First Aerosol Characterization Experiment (ACE 1). The measurements covered a latitude range of 40°S–55°S during November-December 1995. Seawater DMS concentrations ranged from 0.4 to 6.8 nM, with a mean of 1.7±1.1 nM (1σ). The highest DMS concentrations were found in subtropical convergence zone waters north of 44°S, and the lowest were found in polar waters south of 49°S. In general, seawater DMS concentrations increased during the course of the study, presumably due to the onset of austral spring warming. Atmospheric DMS concentrations ranged from 24 to 350 parts per trillion by volume (pptv), with a mean of 112±61 pptv (1σ). Atmospheric SO2 was predominantly of marine origin with occasional anthropogenic input, as evidenced by correlation with elevated 222Rn and air mass trajectories. Concentrations ranged from 3 to 1000 pptv with a mean of 48.8± 49 pptv (1σ) and a median 15.8 pptv. The mean SO2 concentration observed in undisturbed marine air was 11.9±7.6 pptv (1σ), and the mean DMS to SO2 ratio in these conditions was 13±9 (1σ). Diurnal variations in SO2 were observed, with a daytime maximum and early morning minimum in agreement with model simulations of DMS oxidation in the marine boundary layer. Steady state calculations and photochemical box model simulations suggest that the DMS to SO2 conversion efficiency in this region is 30–50%. Comparison of these results with results from warmer regions suggests that the DMS to SO2 conversion efficiency has a positive temperature dependence

Shipboard measurements of dimethyl sulfide and SO 2 southwest of Tasmania during the First Aerosol Characterization Experiment (ACE 1)

Measurements of seawater dimethylsulfide (DMS), atmospheric dimethylsulfide, and sulfur dioxide (SO2) were made on board the R/VDiscoverer in the Southern Ocean, southeast of Australia, as part of the First Aerosol Characterization Experiment (ACE 1). The measurements covered a latitude range of 40°S–55°S during November-December 1995. Seawater DMS concentrations ranged from 0.4 to 6.8 nM, with a mean of 1.7±1.1 nM (1σ). The highest DMS concentrations were found in subtropical convergence zone waters north of 44°S, and the lowest were found in polar waters south of 49°S. In general, seawater DMS concentrations increased during the course of the study, presumably due to the onset of austral spring warming. Atmospheric DMS concentrations ranged from 24 to 350 parts per trillion by volume (pptv), with a mean of 112±61 pptv (1σ). Atmospheric SO2 was predominantly of marine origin with occasional anthropogenic input, as evidenced by correlation with elevated 222Rn and air mass trajectories. Concentrations ranged from 3 to 1000 pptv with a mean of 48.8± 49 pptv (1σ) and a median 15.8 pptv. The mean SO2 concentration observed in undisturbed marine air was 11.9±7.6 pptv (1σ), and the mean DMS to SO2 ratio in these conditions was 13±9 (1σ). Diurnal variations in SO2 were observed, with a daytime maximum and early morning minimum in agreement with model simulations of DMS oxidation in the marine boundary layer. Steady state calculations and photochemical box model simulations suggest that the DMS to SO2 conversion efficiency in this region is 30–50%. Comparison of these results with results from warmer regions suggests that the DMS to SO2 conversion efficiency has a positive temperature dependence

Inorganic Bromine in the Marine Boundary Layer: a Critical Review.

Abstract not availableJRC.H-Institute for environment and sustainability (Ispra