Abstract
Marine-derived volatile organic compounds (VOCs) influence global carbon cycling, atmospheric reactions, and climate. Yet, the biogenic production (sources) and consumption (sink) rates of marine VOCs are not well-constrained and are currently excluded from global chemical transport models. We directly measured the net biogenic production rates of seven VOCs (acetaldehyde, acetone, acetonitrile, dimethylsulfide, isoprene, methanethiol, and methanol) in surface seawater during four field campaigns in the North Atlantic Ocean that targeted different stages of the phytoplankton annual cycle. All of the VOCs exhibited strong seasonal trends, with generally positive rates during May (peak spring bloom) and lower, sometimes negative rates (net consumption), during November and/or March (the winter bloom minimum transition). Strong latitudinal gradients were identified for most VOCs during May and September, with greater production observed in the northern regions compared to the southern regions. These gradients reflect the interplay between high phytoplankton and bacterial productivity. During the bloom transition stages (March and September), acetaldehyde and acetone exhibited net production rates that bracketed zero, suggesting that biogenic production was either very low or indicative of a tightly coupled system with more complex underlying microbial VOC cycling. Our data provides the first direct evidence for widespread biogenic acetonitrile production and consumption in the surface ocean and the first net biogenic production rates for methanethiol in natural seawater.
Highlights
Volatile organic compounds (VOCs), such as isoprene and acetaldehyde, have high vapor pressures (US EPA, 2017) that expedite their transfer from aqueous systems into the atmosphere
Serial dilutions were performed with synthetic air that had passed through a dynamic stripping chamber filled with 100 mL of ASW media
We explore the coupled state of volatile organic compounds (VOCs) production in the North Atlantic Ocean and environmental factors that influence the balance between the biological VOC production and consumption terms
Summary
Volatile organic compounds (VOCs), such as isoprene and acetaldehyde, have high vapor pressures (US EPA, 2017) that expedite their transfer from aqueous systems into the atmosphere. Numerous studies have revealed the capacity of marine phytoplankton cultures to produce a variety of VOCs (Moore et al, 1994; Shaw et al, 2003), measurements of biogenic production and consumption in the natural marine environment are currently lacking. Abiotic controls (0.22 μm gravity filtered natural seawater) were used to account for the physical removal (“stripping”) of VOCs from the seawater due to the bubbling process (Figure 2). VOC concentrations in abiotic controls were calculated for each measurement using the regression models listed in Supplementary Table S3. Additional details on the temperature-dependence and computation of abiotic control concentrations is available in Supplementary Section 1 and Supplementary Table S3. Note that isoprene was very quickly stripped from the seawater (
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