The cellular respiration process consists of a very complex series of chemical reactions, but the short summary of it is that it ultimately converts food energy (from carbohydrates, fats, and proteins) into ATP energy. (shapesense.com)
Warmer conditions reduce the solubility of oxygen from the atmosphere and increase oxygen consumption because the biological respiration processes are boosted. (sciencedaily.com)
When in balance, primary production and respiration processes result in large diel variability (Table 2), but are essentially CO2 - neutral; however, over longer timescales, spatial and / or temporal decoupling of these processes can change pH drastically (Borges and Gypens 2010; Provoost et al. 2010; Cai et al. 2011). (link.springer.com)