14. Recent Sea Level Changes

difference between eustatic and isostatic sea level changes

• Eustatic: Global sea level changes due to volume/temperature of ocean water.

• Isostatic: Local/regional changes caused by land rising or sinking.

What causes eustatic sea level changes

• Glacier growth/melting (fast)

• Thermal expansion of water (medium)

• Tectonic changes in ocean basins (very slow

Over what timescales do eustatic changes occur

• Fast (thousands of years): glacial melt

• Medium (decades to centuries): thermal expansion

• Slow (millions of years): tectonic plate movement

Causes isostatic sea level changes

• Post-glacial rebound

• Tectonic uplift/subsidence

• Volcanic weight changes

• Sediment loading and compaction (e.g., deltas)

Over what timescales do isostatic changes occur

thousands to tens of thousands of years, but some (e.g., earthquakes, sedimentation) can occur much faster.

What is causing sea level change in Grand Isle, Louisiana

Isostatic subsidence from sediment compaction in the Mississippi Delta

What is causing sea level change in Yakutat, Alaska

Isostatic rebound from melting of the Cordilleran/Laurentide Ice Sheets

Causing sea level change near Norfolk, VA (Chesapeake Bay)

• Isostatic subsidence from collapse away from former ice sheet.

• Slowed Gulf Stream increases local sea level via water piling up (steric effect).

Causing sea level change in Lima, Peru

Tectonic subsidence near a convergent subduction zone.

How fast is modern global sea level rising

Around 3.1 mm/year

Modern sea level rise compared to Meltwater Pulse 1A

• Today: ~3.1 mm/year
  

• Meltwater Pulse 1A: ~56 mm/year (28 m in 500 years)