Physical Agents of Land Loss: Relative Sea Level
There is a tendency to think of sea level as a uniform surface around the world that is used as a datum from which land elevations and ocean depths are measured. Actually sea level is not the same everywhere and it also moves up and down with time. Ocean levels in the Pacific are slightly higher than in the Atlantic and ocean levels near the equator are higher than those at the poles. The factors that spatially influence ocean levels include oceanographic conditions (currents), meteorological conditions (atmospheric pressure, wind), terrestrial conditions (river discharge), and geophysical conditions (geoid anomalies). The factors that influence temporal sea level fluctuations range from high frequency (daily, seasonal) astronomical tides to low frequency changes in global climate. Major climatic (atmospheric temperature) fluctuations over periods of thousands of years cause global sea level to fall and then rise as continental ice sheets form and subsequently melt.
The accurate term for a tide gauge record is relative sea level change because it includes the combined movement of both water and land. Even if sea level was constant there could be changes in relative sea level. For example, a rising land surface would produce a relative fall in sea level, whereas a sinking land surface would produce a relative rise in sea level.