Underway seawater and atmospheric measurements of volatile organic compounds in the Southern Ocean

Abstract

<p><strong>Abstract.</strong> Dimethyl sulfide and volatile organic compounds and are important for atmospheric chemistry. The oceanic emissions of biogenically derived gases, including dimethyl sulfide and especially isoprene, are not well constrained. The role of the ocean in the global budgets of atmospheric methanol, acetone and acetaldehyde is even more poorly known. In order to quantify the air-sea fluxes of these gases we measured their seawater concentrations and air mixing ratios in the Atlantic sector of the Southern Ocean, along a ~ 11 000 km long transect at approximately 60° S in Feb–Apr 2019. Concentrations, oceanic saturations and estimated fluxes of several simultaneously sampled volatile organic compounds (methanol, acetone, acetaldehyde, dimethyl sulfide and isoprene) are presented here. Campaign mean (± 1σ) surface water concentrations of dimethyl sulfide, isoprene, methanol, acetone and acetaldehyde were 2.60 (± 3.94), 0.0133 (± 0.0063), 67 (± 35), 5.5 (± 2.5) and 2.6 (± 2.7) nmol dm<sup>−3</sup> respectively. In this dataset, seawater isoprene and methanol concentrations correlated positively. Furthermore, seawater acetone, methanol and isoprene concentrations were found to correlate negatively with the fugacity of carbon dioxide, possibly due to a common biological origin. Campaign mean (± 1σ) air mixing ratios of methanol, acetone and acetaldehyde were relatively low at 0.17 (± 0.08), 0.081 (± 0.031) and 0.049 (± 0.040) ppbv. We observed diel changes in averaged acetaldehyde concentrations in seawater and ambient air (and to a lesser degree also for acetone and isoprene), which suggest light-driven productions. Campaign mean (± 1σ) fluxes of 4.3 (± 7.4) µmol m<sup>−2</sup> d<sup>−1</sup> DMS and 0.028 (± 0.021) µmol m<sup>−2</sup> d<sup>−1</sup> isoprene are determined where a positive flux indicates from the ocean to the atmosphere. Methanol was largely undersaturated in the surface ocean with a mean (± 1σ) net flux of −2.4 (± 4.7) µmol m<sup>−2</sup> d<sup>−1</sup>, but also had a few occasional episodes of outgassing This section of the Southern Ocean was found to be both a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean flux of −0.55 (± 1.15) µmol m<sup>−2</sup> d<sup>−1</sup> for acetone and −0.28 (± 1.22) µmol m<sup>−2</sup> d<sup>−1</sup> for acetaldehyde. The data collected here will be important for constraining the oceanic source/sink of these gases and potentially help to elucidate the presence of common sources/sinks for these compounds.</p>

Remote Sensing Retrieval of Isoprene Concentrations in the Southern Ocean

“…A band of higher isoprene concentrations and air sea fluxes is observed around the Subantarctic front (approximately between 40°S and 50°S), as already depicted by Ooki et al (2015) and Wohl et al (2020). However, the air sea fluxes show a more spread distribution than concentrations, with weaker gradients toward continental shelves and islands.…”

“…For model development and validation, we also compiled surface (0-10 m depth) isoprene, CHL and temperature data from four other research cruises conducted entirely or partly in the SO (>40°S), namely: KH-09-5-2010 (Ooki et al, 2015), AMT23-2013 and AMT22-2012 (Hackenberg et al, 2017), and ANDREXII-2019 (Wohl et al, 2020) (Table S1 in the supporting information and Figure 1). Description of measurement procedures can be found in the corresponding publications.…”

High-resolution distribution and emission of dimethyl sulfide and its relationship with pCO2 in the Northwest Pacific Ocean

“…The KOCR region had the lowest mean wind speed (mean: 5 ± 2 m s -1 ), which was accompanied by a relatively low DMS mixing ratio, despite the DMS concentration being relatively high in this region (Table 1). The concentrations of sea surface DMS did not correlate with atmospheric DMS mixing ratios (r = -0.017, P > 0.05) (Table S1), likely because, the transport of air mass was much faster than that of seawater, leading a decoupling between atmospheric and seawater DMS concentrations (Aranami and Tsunogai, 2004;Wohl et al, 2020). The surface seawater DMS concentrations were roughly uniform and generally low in the NECR, but the atmospheric DMS mixing ratios were high (mean: 74 ± 30 pptv), due to the high DMS sea-air flux caused by the high wind speeds (mean: ~12 m/s).…”

“…Kim et al (2017) used a membrane inlet mass spectrometer (MIMS) to analyze the horizontal distribution of DMS in the Amundsen Sea Polynya region. Wohl et al (2020); Wohl et al (2022) used a segmented flow coil equilibrator coupled to a proton transfer reaction mass spectrometer (EI-PTR-MS) to measure dissolved gases (e.g., DMS and isoprene) in the Southern Ocean and the Canadian Arctic. However, there were few studies on the DMS of seawater and atmosphere in the Northwest Pacific Ocean at present, and DMS data were relatively discrete (Figure S1) (DMS data of Northwest Pacific surface seawater was obtained from NOAA-PMEL DMS database, https://saga.pmel.noaa.gov/dms/).…”

Remote sensing retrieval of isoprene concentrations in the Southern Ocean

“…For model development and validation, we also compiled surface (0-10 m depth) isoprene, CHL and temperature data from four other research cruises conducted entirely or partly in the SO (>40°S), namely: KH-09-5-2010 (Ooki et al, 2015), AMT23-2013and AMT22-2012(Hackenberg et al, 2017, and ANDREXII-2019 (Wohl et al, 2020) (Table S1 in the supporting information and Figure 1). Description of measurement procedures can be found in the corresponding publications.…”