Effects of Temperature and Light on Methane Production of Widespread Marine Phytoplankton

Abstract

Abstract Methane (CH 4 ) production in the ocean surface mixed layer is a widespread but still largely unexplained phenomenon. In this context marine algae have recently been described as a possible source of CH 4 in surface waters. In the present study we investigated the effects of temperature and light intensity (including daylength) on CH 4 formation from three widespread marine algal species Emiliania huxleyi , Phaeocystis globosa , and Chrysochromulina sp. Rates of E. huxleyi increased by 210% when temperature increased in a range from 10°C to 21.5°C, while a further increase in temperature (up to 23.8°C) showed reduction of CH 4 production rates. Our results clearly showed that CH 4 formation of E. huxleyi is controlled by light: When light intensity increased from 30 to 2,670 μmol m −2 s −1 , CH 4 emission rates increased continuously by almost 1 order of magnitude and was more than 1 order of magnitude higher when the daylength (light period) was extended from 6/18 hr light‐dark cycle to continuous light. Furthermore, light intensity is also an important factor controlling CH 4 emissions of Chrysochromulina sp. and P. globosa and could therefore be a species‐independent regulator of phytoplankton CH 4 production. Based on our results, we might conclude that extensive blooms of E. huxleyi could act as a main regional source of CH 4 in surface water, since blooming of E. huxleyi is related to the seasonal increase in both light and temperature, which also stimulate CH 4 production. Under typical global change scenarios, E. huxleyi will increase its CH 4 production in the future.