The uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere has resulted in a decrease in seawater aragonite saturation state (Ω_arag), which affects the health of carbonate-bearing organisms and the marine ecosystem. A substantial short-term variability of surface water Ω_arag, with an increase of up to 0.32, was observed in the central Mid-Atlantic Bight off the Delaware and the Chesapeake Bays over a short period of 10 days in summer 2015. High-frequency underway measurements for temperature, salinity, percentage saturation of dissolved oxygen, oxygen to argon ratio, pH, fCO₂, and measurements based on discrete samples for pH, dissolved inorganic carbon, and total alkalinity are used to investigate how physical and biogeochemical processes contribute to the changes of Ω_arag. Quantitative analyses show that physical advection and mixing processes are the dominant forces for higher Ω_arag in slope waters while biological carbon removal and CO₂ degassing contribute to increased Ω_arag in shelf waters.