Substantial loss of isoprene in the surface ocean due to chemical and biological consumption

Abstract

Isoprene contributes to the formation of ozone and secondary organic aerosol in the atmosphere, and thus influences cloud albedo and climate. Isoprene is ubiquitous in the surface open ocean where it is produced by phytoplankton, however emissions from the global ocean are poorly constrained, in part due to a lack of knowledge of oceanic sink or degradation terms. Here, we present analyses of ship-based seawater incubation experiments with samples from the Mediterranean, Atlantic, tropical Pacific and circum-Antarctic and Subantarctic oceans to determine chemical and biological isoprene consumption in the surface ocean. We find the total isoprene loss to be comprised of a constant chemical loss rate of 0.05 ± 0.01 d−1 and a biological consumption rate that varied between 0 and 0.59 d−1 (median 0.03 d−1) and was correlated with chlorophyll-a concentration. We suggest that isoprene consumption rates in the surface ocean are of similar magnitude or greater than ventilation rates to the atmosphere, especially in chlorophyll-a rich waters.

Isoprene Production and Its Driving Factors in the Northwest Pacific Ocean

“…For constructing the isoprene budget in the mixed layer, a variable biological K loss (ranging between 0.01 and 0.1 day −1 ) was considered, which was used to reconcile observed in situ isoprene concentrations with the predicted production terms from phytoplankton incubation (Booge et al., 2018). Most recently, it has been reported that isoprene consumption rates in the surface ocean, including microbial consumption and chemical oxidation, are comparable or even greater than ventilation rates (Simó et al., 2022). This suggests that marine isoprene is actively involved in biogeochemical cycles within the ocean interior, potentially serving as a source of energy for microorganisms.…”

“…The results obtained in this study are generally at the high end or higher than the ranges presented in these previous reports. Furthermore, we computed the isoprene production rates according to the parameterizations and models proposed by Booge et al (2018), Conte et al (2020), Ooki et al (2015), Palmer and Shaw (2005), and Simó et al (2022), respectively. Those results are denoted using the format "Author's rate," like Palmer's rate.…”

Concentrations of dissolved dimethyl sulfide (DMS), methanethiol and other trace gases in context of microbial communities from the temperate Atlantic to the Arctic Ocean

“…Nevertheless, the concentrations in our study are overall much lower (about 1 order of magnitude) than reported by Tran et al (2013), indicating a high spatial variability of isoprene potentially re- lated to seasonally varying phytoplankton abundances. Simó et al (2022) recently highlighted the importance of biological consumption of isoprene in seawater, possibly matching the magnitude of isoprene ventilated to the atmosphere, advising to consider both the sources and sinks when discussing isoprene concentrations and variability. The correlations of Alcanivorax and Thalassolituus ASVs with both isoprene and Chl a support phytoplankton as the source of this trace gas.…”

“…Campen et al (2022) have recently emphasized the need to better link bacterial distribution with DMS and CO metabolism. In addition, the production and degradation of isoprene could be an important, yet understudied contribution to biogeochemical cycles (Carrión et al, 2020;Rodríguez-Ros et al, 2020;Simó et al, 2022).…”

Variability of dimethyl sulphide (DMS), methanethiol and other trace gases in context of microbial communities from the temperate Atlantic to the Arctic Ocean

“…Nevertheless, the concentrations are overall much lower (about one order of magnitude) than reported by Tran et al, (2013), indicating a high spatial variability of isoprene potentially related to seasonally varying phytoplankton abundances. Simó et al, (2022) recently highlighted the importance of biological consumption of isoprene in water, possibly matching the magnitude of isoprene ventilated to the atmosphere), advising to consider both the sources and sinks when discussing isoprene concentrations and variability. The correlations of Alcanivorax and Thalassolituus ASVs with both isoprene and Chl a support phytoplankton as source of this trace gas, and subsequent bacterial utilization (Alvarez et al, 2009).…”