Climate Fact: North Atlantic Sea Level Cycles
Global sea level is rising at a rate of about 1.2 inches per decade due to an influx of glacial melt water and thermal expansion of the oceans. The relative sea level rise that each coastal location experiences, however, differs from this global average due to local factors such as land subsidence and land uplift (which typically happens as glaciers melt), as well as cyclical variability in ocean currents. Sea levels off America’s east coast fluctuate by around two inches over a period of 20-30 years. This fluctuation is linked to variability in the strength of the Atlantic Meridional Overturning Circulation (AMOC), which occurs in the North Atlantic around Greenland and is considered to be the “engine” behind Earth’s thermohaline circulation. This thermohaline circulation moves heat from the ocean surface to the depths and nutrients from the depths to the surface. Strengthening of the AMOC leads to strengthening of the currents that move heat from the tropical Atlantic to the northern portions of the Atlantic basin. When North Atlantic temperatures are at their warmest point in the cycle, sea levels off Europe’s coast peak. This crest in sea level then propagates westward, and about eight to ten years after sea levels off Europe’s coast reach their peak, sea levels off America’s east coast peak. This cycle is currently causing a relative decline in east coast sea levels.
Seasons: Winter, Spring, Summer, Fall
Source: Frankcombe, LM and Dijkstra, HA. “Coherent multidecadal variability in North Atlantic sea level.” Geophysical Research Letters 36 (2009): L15604.
