Final answer:
Surface seawater with a pH of about 8.0 is considered slightly basic or alkaline. The pH scale indicates that anything above 7 is basic, while a shift in pH represents a significant change in acidity or basicity.
Step-by-step explanation:
The pH of surface seawater usually has a value of around 8.0. This indicates that seawater is slightly basic (or alkaline). The pH scale, which ranges from 0 to 14, classifies solutions with a pH less than 7 as acidic, and those with a pH greater than 7 as basic. Water is neutral, with a pH of 7. Since seawater's pH is closer to the neutral point than the extremes of the scale, it provides an environment conducive to marine life. For substances, a pH shift indicates a ten-fold change in hydrogen ion concentration (H+), hence a change from pH 7 to pH 8 means the seawater is ten times less acidic than neutral water.