CO2 emission will continue exaggerating, as fossil fuels will most likely remain the major source of energy in next couple decades. The increased carbon in the atmosphere moves into marine ecosystems, making the world’s oceans more acidic. The rate of ocean acidification (OA) today is faster than any time in the past 300 million years. In addition, pumping CO2 into the deep ocean has been proposed as a viable way to decrease emissions (carbon sequestration), but the environmental consequences of this remain essentially unknown, while such an activity will likely make OA more intense at the pumping locations. Ocean acidification affects life histories of organisms and ocean biogeochemical nutrient cycling. It is critical to understand the interplay between OA and marine biochemical and physiological processes before Earth's seas become inhospitable to life as it is known today. It remains unclear how marine microorganisms will adapt to OA and to what extent their activities will be affected. In order to advance our understanding on these fundamental scientific questions and be able to predict the consequences of OA to marine ecosystems, we propose to characterize the adaptive responses of microbial communities to multiple stressors associated with OA particularly on (1) pH and temperature changes at shallow water depth and (2) high CO2 concentration at deep water conditions using advanced high-pressure chambers available in the Dai Lab.