The ocean's alkalinity varies over time, most significantly over geologic timescales (millennia). Changes in the balance between terrestrial weathering and sedimentation of carbonate minerals (for example, as a function of ocean acidification) are the primary long-term drivers of alkalinity in the ocean. Over human timescales, mean ocean alkalinity is relatively stable. Seasonal and annual variability of mean ocean alkalinity is very low.
Alkalinity varies by location depending on evaporation/precipitation, advection of water, biological processes, and geochemical processes.
River dominated mixing also occurs close to the shore; it is strongest close to the mouth of a large river. Here, the rivers can act as either a source or a sink of alkalinity.  A follows the outflow of the river and has a linear relationship with salinity. 
Oceanic alkalinity also follows general trends based on latitude and depth. It has been shown that A is often inversely proportional to sea surface temperature (SST). Therefore, it generally increases with high latitudes and depths. As a result, upwelling areas (where water from the deep ocean is pushed to the surface) also have higher alkalinity values.
There are many programs to measure, record, and study oceanic alkalinity, together with many of the other characteristics of seawater, like temperature and salinity. These include: GEOSECS (Geochemical Ocean Sections Study), TTO/NAS (Transient Tracers in the Ocean/North Atlantic Study), JGOFS (Joint Global Ocean Flux Study), WOCE (World Ocean Circulation Experiment), CARINA (Carbon dioxide in the Atlantic Ocean).