It is reported that there is an ongoing decrease in the pH value of ocean water because of global warming. It happens due to :

Ocean acidification is primarily driven by the ocean's absorption of atmospheric carbon dioxide (CO2). As anthropogenic activities increase CO2 levels in the atmosphere, the ocean acts as a reservoir, absorbing approximately one-third of these emissions [1]. When CO2 dissolves in seawater, it reacts with water molecules to form carbonic acid (H2CO3) [5]. This acid subsequently dissociates, releasing hydrogen ions (H+) into the water [2]. The increase in hydrogen ion concentration directly leads to a decrease in the pH value, making the water more acidic [3]. While global warming itself can slightly reduce the solubility of CO2 in warmer surface waters, the net ongoing decrease in pH is fundamentally caused by the larger cumulative uptake of CO2 from the atmosphere as concentrations rise. Nitrogen uptake is not the driver of this acidification process.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 18: Ocean Acidification > 18.I. OCEAN ACIDIFICATION > p. 263
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 18: Ocean Acidification > How it reacts? > p. 264
3. [5] https://iucn.org/our-work/topic/oceans-and-climate-change/ocean-acidification
4. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 20: Impact of Climate Change > 20.4" ECOSYSTEMS AND BIO.DIVERSITY > p. 277