Oceanic properties are being altered at an unprecedented rate by global climate change. Our seas are warming, becoming more acidic, and there is evidence of oxygen depletion at depth and of less plant nutrients (such as phosphate) being supplied to surface waters. How will the biogeochemical cycles of key elements such as C, N and P, which underpin much of the oceans' productivity, be altered by such ocean global change? How will the role of oceanic microbes be modified by such a changing ocean, and how will it feedback on the alteration of ocean properties? In this presentation, I will provide illustrative examples using the oceans' Nitrogen cycle (role of unicellular and colonial N fixers) and C cycle (the oceans biological pump, that sequesters carbon into the deep ocean for centuries) to explore how biogeochemical cycles will be altered in the coming decades, and whether the concurrent responses of microbes may be critical to rebalancing ocean productivity and biogeochemistry.