Conversely, toluene concentrations were not always highest in the top 75 m, and their profile shape and mean concentrations did not always follow the distribution of Chl a. Yet, higher toluene concentrations near the surface were commonly observed in casts with high Chl a. The absence of a clear pattern with depth is probably due to toluene origin not only in phytoplankton but also in bacteria which are not related to Chl a, as well as toluene's short lifetime that prevents accumulation. These depth profiles support distinct biological sources of benzene and toluene in seawater.