Gradient flux measurements of sea–air DMS transfer during the Surface Ocean Aerosol Production (SOAP) experiment

Abstract

Abstract. Direct measurements of marine dimethylsulfide (DMS) fluxes are sparse, particularly in the Southern Ocean. The Surface Ocean Aerosol Production (SOAP) voyage in February-March 2012 examined the distribution and flux of DMS in a biologically active frontal system in the southwest Pacific Ocean. Three distinct phytoplankton blooms were studied with oceanic DMS concentrations as high as 25 nmol L −1 . Measurements of DMS fluxes were made using two independent methods: the eddy covariance (EC) technique using atmospheric pressure chemical ionization-mass spectrometry (API-CIMS) and the gradient flux (GF) technique from an autonomous catamaran platform. Catamaran flux measurements are relatively unaffected by airflow distortion and are made close to the water surface, where gas gradients are largest. Flux measurements were complemented by near-surface hydrographic measurements to elucidate physical factors influencing DMS emission. Individual DMS fluxes derived by EC showed significant scatter and, at times, consistent departures from the Coupled Ocean-Atmosphere Response Experiment gas transfer algorithm (COAREG). A direct comparison between the two flux methods was carried out to separate instrumental effects from environmental effects and showed good agreement with a regression slope of 0.96 (r 2 = 0.89). A period of abnormal downward atmospheric heat flux enhanced near-surface ocean stratification and reduced turbulent exchange, during which GF and EC transfer velocities showed good agreement but modelled COAREG values were significantly higher. The transfer velocity derived from near-surface ocean turbulence measurements on a spar buoy compared well with the COAREG model in general but showed less variation. This first direct comparison between EC and GF fluxes of DMS provides confidence in compilation of flux estimates from both techniques, as well as in the stable periods when the observations are not well predicted by the COAREG model.

The sensitivity of Southern Ocean aerosols and cloud microphysics to sea spray and sulfate aerosol production in the HadGEM3-GA7.1 chemistry–climate model

“…How SSA should ultimately be represented in global models remains the subject of ongoing research. Along with Jaeglé et al (2011), other studies have found that SSA concentrations are correlated with sea surface temperature (Mårtensson et al, 2003;Sellegri et al, 2006;Sofiev et al, 2011;Grythe et al, 2014). More recently, Forestieri et al (2018) demonstrated that variability in seawater composition may have just as large an impact on SSA production as temperature.…”

Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the southwest Pacific Ocean

“…The following parameters were measured in surface waters (depths 2-10 m) in discrete samples from Niskin bottles on a conductivity-temperature-depth (CTD) rosette: nutrients according to methods described in Law et al (2011), particulate nitrogen concentration (Nodder et al, 2016), phytoplankton speciation, groups and numbers (optical microscopy of samples preserved in Lugol's solution) (Safi et al, 2007), and flow cytometry (Hall and Safi, 2001). In addition, the organic parameters measured included high-molecular-weight (HMW) reducing sugars (Somogyi, 1926(Somogyi, , 1952 for details see Burrell, 2015), DMSP (Walker et al, 2016) and CDOM measured using a liquid waveguide capillary cell (Gall et al, 2013). See Table S1 for measurement specifications and Law et al (2017) for further details and results for these parameters.…”

The sensitivity of Southern Ocean aerosols and cloud microphysics to sea spray and sulfate aerosol production in the HadGEM3-GA7.1 chemistry-climate model

“…In this study, we rely on observations from research voyages and the measurement stations at Amsterdam 1987(Sciare et al, 2001 and Cape Grim between 1989-1996 (Ayers and Gillett, 2000). Ship-borne measurements were obtained from the SOAP (Surface Ocean Aerosol Production) campaign, which sampled between 42-47 • S, 172-180 • E during February and March 2012 (Law et al, 2017;Bell et al, 2015;Smith et al, 2018), and SOIREE (the Southern Ocean Iron RElease Experiment), which sampled between 42-63 • S, 139-172 • E in February 1999 (Boyd and Law, 2001;Boyd et al, 2000). During SOIREE, DMS was measured in discrete water samples from vertical profiles and whilst underway in air and surface water (Turner et al, 2004).…”

“…During SOIREE, DMS was measured in discrete water samples from vertical profiles and whilst underway in air and surface water (Turner et al, 2004). During SOAP, surface water and surface microlayer DMS were measured (Walker et al, 2016) in addition to atmospheric DMS concentrations and emission fluxes (Bell et al, 2015;Smith et al, 2018).…”