Segmented flow coil equilibrator for continuous measurement of volatile organic compounds in seawater of the polar oceans

Volatile organic compounds (VOCs) are a group of molecules that influence aspects of atmospheric chemistry such as oxidation chemistry and particle formation. Most VOCs are produced from a variety of anthropogenic and natural sources; with emissions from the oceans least well known/ quantified. In this thesis I focus on methanol, acetone, acetaldehyde, DMS and isoprene. Uncertainty persists as to the factors influencing their variability in seawater concentrations. The polar oceans are particularly undersampled regions with few to no measurements of these compounds, which is partially due to a lack of suitable instrumentation. To increase available instrumentation, this thesis describes the development of a Segmented Flow Coil Equilibrator coupled to a commercially available Proton Transfer Reaction-Mass Spectrometer for measurements of VOCs in seawater. Its main advantage lies in its ability to measure underway and discrete samples. The method is used to make depth profile and underway measurements in the Canadian Arctic Archipelago during sea ice melt season. Highest VOC concentrations are generally observed at the surface, apart from DMS and isoprene which sometimes display a subsurface maximum. Generally, highest surface concentrations of VOCs are observed in partial ice cover. Concentrations of acetone and acetaldehyde were about 30 – 50 % higher in partial ice cover compared to ice-free waters. This thesis also presents ambient air, underway and depth profile measurements from a transect in the subpolar Southern Ocean, used to calculate surface saturations and air – sea fluxes. Correlations with other biogeochemical data allowed me to elucidate factors controlling seawater concentrations of these VOCs. This dataset contains the first evidence of a statistically significant, but small diel change (on the order of 8 – 26 %) in seawater isoprene, acetone and acetaldehyde concentrations in the open ocean. The measurements presented in this thesis will be useful to constrain ocean source/sink strength. The analysis points towards factors controlling the global variability of these compounds in the ocean

Segmented flow coil equilibrator coupled to a proton-transfer-reaction mass spectrometer for measurements of a broad range of volatile organic compounds in seawater

We present a technique that utilises a segmented flow coil equilibrator coupled to a proton-transferreaction mass spectrometer to measure a broad range of dissolved volatile organic compounds. Thanks to its relatively large surface area for gas exchange, small internal volume, and smooth headspace-water separation, the equilibrator is highly efficient for gas exchange and has a fast response time (under 1 min). The system allows for both continuous and discrete measurements of volatile organic compounds in seawater due to its low sample water flow (100 cm3 min-1) and the ease of changing sample intake. The equilibrator setup is both relatively inexpensive and compact. Hence, it can be easily reproduced and installed on a variety of oceanic platforms, particularly where space is limited. The internal area of the equilibrator is smooth and unreactive. Thus, the segmented flow coil equilibrator is expected to be less sensitive to biofouling and easier to clean than membrane-based equilibration systems. The equilibrator described here fully equilibrates for gases that are similarly soluble or more soluble than toluene and can easily be modified to fully equilibrate for even less soluble gases. The method has been successfully deployed in the Canadian Arctic. Some example data from underway surface water and Niskin bottle measurements in the sea ice zone are presented to illustrate the efficacy of this measurement system

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

Dimethyl sulfide and volatile organic compounds (VOCs) are important for atmospheric chemistry. The emissions of biogenically derived organic gases, including dimethyl sulfide and especially isoprene, are not well constrained in the Southern Ocean. Due to a paucity of measurements, the role of the ocean in the atmospheric 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 ĝˆ1/4 11 000 km long transect at approximately 60ĝˆ S in February-April 2019. Concentrations, oceanic saturations, and estimated fluxes of five simultaneously sampled gases (dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde) 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-3 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 dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde were 0.17 (±0.09), 0.053 (±0.034), 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 production. Campaign mean (±1σ) fluxes of 4.3 (±7.4) μmol m-2 d-1 DMS and 0.028 (±0.021) μmol m-2 d-1 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-2 d-1, but it also had a few occasional episodes of outgassing. This section of the Southern Ocean was found to be a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean net flux of -0.55 (±1.14) μmol m-2 d-1 for acetone and -0.28 (±1.22) μmol m-2 d-1 for acetaldehyde. The data collected here will be important for constraining the air-sea exchange, cycling, and atmospheric impact of these gases, especially over the Southern Ocean

Natural variability in air–sea gas transfer efficiency of CO2

The flux of CO2 between the atmosphere and the ocean is often estimated as the air–sea gas concentration difference multiplied by the gas transfer velocity (K660). The first order driver for K660 over the ocean is wind through its influence on near surface hydrodynamics. However, field observations have shown substantial variability in the wind speed dependencies of K660. In this study we measured K660 with the eddy covariance technique during a ~ 11,000 km long Southern Ocean transect. In parallel, we made a novel measurement of the gas transfer efficiency (GTE) based on partial equilibration of CO2 using a Segmented Flow Coil Equilibrator system. GTE varied by 20% during the transect, was distinct in different water masses, and related to K660. At a moderate wind speed of 7 m s−1, K660 associated with high GTE exceeded K660 with low GTE by 30% in the mean. The sensitivity of K660 towards GTE was stronger at lower wind speeds and weaker at higher wind speeds. Naturally-occurring organics in seawater, some of which are surface active, may be the cause of the variability in GTE and in K660. Neglecting these variations could result in biases in the computed air–sea CO2 fluxes

La vida marina de los polos emite a la atmósfera gases inesperados con efectos climáticos

Es la principal conclusión de un nuevo estudio del Institut de Ciències del Mar (ICM-CSIC), el Instituto de Química Física Rocasolano (IQFR-CSIC) y el Plymouth Marine Laboratory (PML). El trabajo revela que el plancton marino emite a la atmósfera trazas de gases atmosféricos que se creían de origen exclusivamente antropogénico y que tienen potenciales efectos climáticosPeer reviewe

Volatile Organic Compounds Released by <i>Oxyrrhis marina</i> Grazing on <i>Isochrysis galbana</i>

A range of volatile organic compounds (VOCs) have been found to be released during zooplankton grazing on microalgae cultivated for commercial purposes. However, production of grazing-derived VOCs from environmentally relevant species and their potential contribution to oceanic emissions to the atmosphere remains largely unexplored. Here, we aimed to qualitatively explore the suite of VOCs produced due to grazing using laboratory cultures of the marine microalga Isochrysis galbana and the herbivorous heterotrophic dinoflagellate Oxyrrhis marina with and without antibiotic treatment. The VOCs were measured using a Vocus proton-transfer-reaction time-of-flight mass spectrometer, coupled to a segmented flow coil equilibrator. We found alternative increases of dimethyl sulfide by up to 0.2 nmol dm−3 and methanethiol by up to 10 pmol dm−3 depending on the presence or absence of bacteria regulated by antibiotic treatment. Additionally, toluene and xylene increased by about 30 pmol dm−3 and 10 pmol dm−3, respectively during grazing only, supporting a biological source for these compounds. Overall, our results highlight that VOCs beyond dimethyl sulfide are released due to grazing, and prompt further quantification of this source in budgets and process-based understanding of VOC cycling in the surface ocean

Suppression of air-sea CO2 transfer by surfactants – direct evidence from the Southern Ocean

Uncertainty in the CO2 gas transfer velocity (K660) severely limits the accuracy of air-sea CO2 flux calculations and hence hinders our ability to produce realistic climate projections. Recent field observations have suggested substantial variability in K660, especially at low and high wind speeds. Laboratory experiments have shown that naturally occurring surface active organic materials, or surfactants, can suppress gas transfer. Here we provide direct open ocean evidence of gas transfer suppression due to surfactants from a ~11,000 km long research expedition by making measurements of the gas transfer efficiency (GTE) along with direct observation of K660. GTE varied by 20% during the Southern Ocean transect and was distinct in different watermasses. Furthermore GTE correlated with and can explain about 9% of the scatter in K660, suggesting that surfactants exert a measurable influence on air-sea CO2 flux. Relative gas transfer suppression due to surfactants was ~30% at a global mean wind speed of 7 m s-1 and was more important at lower wind speeds. Neglecting surfactant suppression may result in substantial spatial and temporal biases in the computed air-sea CO2 fluxes

Remote Sensing Retrieval of Isoprene Concentrations in the Southern Ocean

Isoprene produced by marine phytoplankton acts as a precursor of secondary organic aerosol and thereby affects cloud formation and brightness over the remote oceans. Yet the marine isoprene emission is poorly constrained, with discrepancies among estimates that reach 2 orders of magnitude. Here we present ISOREMS, the first satellite‐only based algorithm for the retrieval of isoprene concentration in the Southern Ocean. Sea surface concentrations from six cruises were matched with remotely sensed variables from MODIS Aqua, and isoprene was best predicted by multiple linear regression with chlorophyll a and sea surface temperature. Climatological (2002–2018) isoprene distributions computed with ISOREMS revealed high concentrations in coastal and near‐island waters, and within the 40–50°S latitudinal band. Isoprene seasonality paralleled phytoplankton productivity, with annual maxima in summer. The annual Southern Ocean emission of isoprene was estimated at 63 Gg C yr−1. The algorithm can provide spatially and temporally realistic inputs to atmospheric and climate models

Marine biogenic emissions of benzene and toluene and their contribution to secondary organic aerosols over the polar oceans

Natural processes in the polar oceans lead to emission of a variety of reactive gases contributing to atmospheric chemistry and aerosol formation. The identity and air–sea fluxes of most of these gases are poorly characterized, bringing uncertainty to the assessment of pre-industrial aerosol sources. Here we present seawater and atmospheric measurements of benzene and toluene in the open Southern Ocean and the Arctic marginal ice zone. Our data suggest a marine biogenic source for these two compounds, which have typically been associated with anthropogenic pollution. Calculated average emission fluxes were 0.024 and 0.037 μmol m-2 d-1 for benzene and toluene, respectively. Including the observed emissions in a chemistry–climate model increased secondary organic aerosol mass concentrations only by 0.1–1.2 % over the Arctic but by 7.7–77.3 % over the Southern Ocean far from continental sources. Climate models must consider the hitherto overlooked emissions of biogenic benzene and toluene from pristine oceanic regions

Marine biogenic emissions of benzene and toluene and their contribution to secondary organic aerosols over the polar oceans

11 pages, 5 figures, 1 table, supplementary materials https://www.science.org/doi/10.1126/sciadv.add9031.-- Data and materials availability: All data needed to evaluate the conclusions of the paper are present in the paper and/or the Supplementary Materials. The measurements and fluxes from the Southern Ocean can be accessed through the following DOI: https://doi.org/10.5281/zenodo.6523780 (last access 23 November 2022). The measurements and fluxes from the Arctic can be accessed through the following DOI: https://doi.org/10.21963/13271 (last access 23 November 2022). The CAM-Chem (public version) code is available at www2.acom.ucar.edu/gcm/cam-chem (last access 23 November 2022). Some of the data presented here were collected by the Canadian research icebreaker CCGS Amundsen and made available by the Amundsen Science program, which is supported by the Canada Foundation for Innovation Major Science Initiatives Fund. The views expressed in this publication do not necessarily represent the views of Amundsen Science or that of its partnersReactive trace gas emissions from the polar oceans are poorly characterized, even though their effects on atmospheric chemistry and aerosol formation are crucial for assessing current and preindustrial aerosol forcing on climate. Here, we present seawater and atmospheric measurements of benzene and toluene, two gases typically associated with pollution, in the remote Southern Ocean and the Arctic marginal ice zone. Their distribution suggests a marine biogenic source. Calculated emission fluxes were 0.023 ± 0.030 (benzene) and 0.039 ± 0.036 (toluene) and 0.023 ± 0.028 (benzene) and 0.034 ± 0.041 (toluene) μmol m−2 day−1 for the Southern Ocean and the Arctic, respectively. Including these average emissions in a chemistry-climate model increased secondary organic aerosol mass concentrations only by 0.1% over the Arctic but by 7.7% over the Southern Ocean, with transient episodes of up to 77.3%. Climate models should consider the hitherto overlooked emissions of benzene and toluene from the polar oceansThis work was supported by the European Union Horizon 2020 grant SUMMIT ERC-2018-AdG 834162 (to R.S.), the Spanish National Research Council grant PEGASO CTM2012-37615 (to R.S.), the “Severo Ochoa Centre of Excellence” accreditation grant CEX2019-000928-S (to ICM), the European Union Horizon 2020 grant CLIMAHAL ERC-2016-COG 726349 (to A.S.-L.), the UK Research and Innovation grant ORCHESTRA NE/N018095/1, and the NSF grant CESMPeer reviewe