Oceans are the planet's largest carbon sink, and when carbon dioxide (CO2) reacts with seawater it forms carbonic acid and subsequently H+ and bicarbonate. The increased seawater acidity has direct impacts on coastal industry, communities, and ecosystems. Reversal of ocean acidification is a primary co-benefit of implementing marine carbon dioxide removal (mCDR) strategies for decarbonization. mCDR interventions alter the ocean's CO2-bicarbonate-carbonate equilibrium in favor of lowering ocean acidity. mCDR is a topic of growing interest both with DOE (FECM, WPTO etc.) and private sector (Climate Works, Ocean Visions etc.), and based on current state-of-technology and its anticipated benefits, bipolar membrane electrodialysis (BPMED) and related electrochemical methods for ocean alkalinity enhancement have received significant interest and investment as promising mCDR technology interventions. Generally, the electrochemical systems produce an acid and base stream from seawater and electricity. While the base is used for ocean alkalization (which allows more CO2 capture by seawater), the acid is a waste stream. Management of the waste stream is a current Go/No-Go challenge for these systems (including the pilot system approved for installation at PNNL). In fact, the acid waste management renders the process net CO2 positive (acid storage, neutralization, and transport are carbon intensive). Here we report a novel approach that utilizes the waste acid on-site to double the overall CO2 capture of the process and makes the process net carbon negative (i.e. effective decarbonization strategy). We show for the first time the benefits of using the acid to increase marine photosynthetic CO2 capture rates by 3.5x to increase overall CO2 capture by 2x. This is the first example of coupling electrochemical and biological mCDR strategies.