Measurements of isoprene and six monoterpenes (alpha- and beta-pinene, myrcene, delta3-carene, ocimene and limonene) were made during research cruises in the Atlantic Ocean and Arctic (80 degrees N - 50 degrees S). The trace gas species were quantified in the surface ocean, in depth profiles and in the marine boundary layer (MBL).
Atmospheric mixing ratios of the analytes were typically below the detection limit (DL) to a few pptv over the Atlantic and mostly <DL (sub-pptv) in the Arctic, after careful quality control to exclude influence from contaminated air. Isoprene mixing ratios were similar to published observations in oligotrophic regions, but monoterpene levels much lower than previously reported. It is unclear whether this discrepancy is caused by sampling over lower-productivity waters, or by analytical differences including potential contamination.
Isoprene concentrations in the surface ocean varied from ca. 1 to 70 pmol L^(-1), similar to the majority of previous studies, and correlated reasonably with several supporting biological parameters available for the cruises. Chlorophyll-a, various pigments including photoprotective carotenoids and Fucoxanthin, cyanobacterial cell counts and primary production yielded significant linear regressions (with R^2 = 0.4 - 0.6), which improved when separated into two temperature regimes with a threshold at 20 degrees C.
Monoterpene concentrations in seawater are reported for the first time, varying from <DL (sub-pmol L^(-1)) to up to several pmol L^(-1) with no clear trends or relationships with biological data. The monoterpene generally showing the highest levels in water and air was limonene; however this was attributed mostly to contamination.
The impacts of emissions derived from this new data on global atmospheric chemistry and secondary organic aerosol formation in the MBL were estimated to be small in light of recent literature and previously published marine terpene data; however they may play a role in nucleation processes as recently suggested, even at low concentrations.
