Potential controls of isoprene in the surface ocean

Abstract

Isoprene surface ocean concentrations and vertical distribution, atmospheric mixing ratios, and calculated sea-to-air fluxes spanning approximately 125°of latitude (80°N-45°S) over the Arctic and Atlantic Oceans are reported. Oceanic isoprene concentrations were associated with a number of concurrently monitored biological variables including chlorophyll a (Chl a), photoprotective pigments, integrated primary production (intPP), and cyanobacterial cell counts, with higher isoprene concentrations relative to all respective variables found at sea surface temperatures greater than 20°C. The correlation between isoprene and the sum of photoprotective carotenoids, which is reported here for the first time, was the most consistent across all cruises. Parameterizations based on linear regression analyses of these relationships perform well for Arctic and Atlantic data, producing a better fit to observations than an existing Chl a-based parameterization. Global extrapolation of isoprene surface water concentrations using satellite-derived Chl a and intPP reproduced general trends in the in situ data and absolute values within a factor of 2 between 60% and 85%, depending on the data set and algorithm used.

Marine isoprene production and consumption in the mixed layer of the surface ocean – a field study over two oceanic regions

“…Bonsang et al (1992), Milne et al (1995), andZindler et al (2014) did not find a significant correlation, whereas other studies could show a significant correlation and, therefore, attempted a linear regression to show a relationship between isoprene and chl a, as well as SST (Broadgate et al, 1997;Kurihara et al, 2010Kurihara et al, , 2012Ooki et al, 2015;Hackenberg et al, 2017). Comparing the different factors of each regression equation (Table 1), it can be seen that, even if the correlations for most of the datasets are significant, there is no globally unique regression factor to adequately describe the relationship between chl a (and SST) and isoprene.…”

“…As shown in Table 1, during ASTRA-OMZ there was no significant correlation between chl a and isoprene, whereas during SPACES and OA-SIS the correlation was significant but with low R 2 values (SPACES: R 2 = 0.30; OASIS: R 2 = 0.10) and different regression coefficients. Hackenberg et al (2017) split their data from three different cruises into two SST bins with SST values higher and lower than 20 • C, resulting in significant correlations with R 2 values from 0.37 to 0.82 depending on the cruise (Table 1). Ooki et al (2015) described a multiple linear relationship between isoprene, chl a, and SST when us- ing three different SST regimes (Table 1).…”

“…Ooki et al (2015) described a multiple linear relationship between isoprene, chl a, and SST when us- ing three different SST regimes (Table 1). Our correlations, using the approaches of Ooki et al (2015) and Hackenberg et al (2017), were significant, except for SST values higher than 27 • C, but the regression coefficients were also significantly different to those found by Ooki et al (2015) and Hackenberg et al (2017). These varying equations demonstrate that bulk chl a concentrations, or linear combinations of chl a concentration and SST, do not adequately predict the variability of isoprene in the global surface ocean, but they do point to these variables as among the main controls on isoprene concentration in the euphotic zone.…”

“…The concentrations generally range between < 1 and 200 pmol L −1 (Bonsang et al, 1992;Milne et al, 1995;Broadgate et al, 1997;Baker et al, 2000;Matsunaga et al, 2002;Broadgate et al, 2004;Kurihara et al, 2010;Zindler et al, 2014;Ooki et al, 2015;Hackenberg et al, 2017). Depending on region and season, concentrations of isoprene in surface waters can reach up to 395 and 541 pmol L −1 during phytoplankton blooms in the highly productive Southern Ocean and Arctic waters, respectively (Kameyama et al, 2014;Tran et al, 2013).…”

“…Studies have shown that the depth profile of isoprene mainly follows the chlorophyll a (chl a) profile, suggesting phytoplankton as an important source (Bonsang et al, 1992;Milne et al, 1995;Tran et al, 2013;Hackenberg et al, 2017); furthermore, Broadgate et al (1997) and Kurihara et al (2010) show a direct correlation between isoprene and chl a concentrations in surface waters and between 5 and 100 m depth, respectively. However, this link is not consistent enough on global scales to predict marine isoprene concentrations using chl a (Table 1).…”