Rising atmospheric CO₂ is driving concurrent ocean acidification (OA) and ocean warming (OW), fundamentally altering marine biogeochemical processes. Coccolithophores, a major group of calcifying phytoplankton, play a dual role in the carbon cycle by producing both particulate organic carbon (POC) through photosynthesis and particulate inorganic carbon (PIC) through calcification. However, their integrated response to OA and OW, and the implications for carbon cycling in marginal seas, remain undetermined. Here, we synthesize results from 136 published studies to quantify the effects of OA and OW on coccolithophore growth, POC quota, and PIC quota. We then couple these physiological responses with observational datasets of coccolithophore cell abundance in marginal seas to assess potential changes in their contribution to carbon cycling. Our analysis shows that OA significantly reduces growth rates and PIC quota while enhancing POC quota, resulting in a marked decline in the PIC: POC ratio. In contrast, OW increases growth rates but exerts no consistent effect on PIC: POC. By integrating these responses with cell abundance data across oceans, we find that future ocean changes may enhance coccolithophore-driven organic carbon production but simultaneously weaken the ballast effect associated with PIC, potentially reducing the efficiency of carbon export to the deep ocean. This synthesis will be further extended to examine coccolithophore-driven changes in carbon cycling across distinct depth layers, including the surface, deep chlorophyll maximum, and the base of the euphotic zone. Hence, given the prominent role of coccolithophores in marginal seas, these physiological and stoichiometric shifts are likely to modify carbon cycling by decoupling organic carbon production from mineral ballast-driven export. Our findings highlight that future changes in ocean carbonate chemistry and temperature may restructure the balance between carbon production and export in coastal and marginal systems, with important implications for regional carbon sequestration.