Why Atlantic and Pacific Sea Levels Differ

It's Not a Single Level

Mean sea level differs between ocean basins due to:

1. Basin Geometry – Atlantic's narrow, meridional shape vs. Pacific's broad, zonal expanse alters circulation and steric height.
2. Earth's Rotation (Coriolis) – Deflects flows, creating western boundary currents (Gulf Stream, Kuroshio) that pile water against western margins.
3. Temperature/Salinity (Density) – Atlantic is saltier and cooler → denser water → lower steric height *locally*, but large-scale circulation redistributes mass.
4. Land Barriers – Americas block direct Pacific-Atlantic exchange (except Drake Passage, Indonesian Throughflow).
5. Climate Change – Non-uniform thermal expansion, ice-melt fingerprints, circulation shifts cause regional sea-level trends to diverge.

Current Difference

Pacific mean sea level is ~20–40 cm *higher* than Atlantic at the Panama Canal—a key reason the canal needs locks.

Takeaway

Sea level is a dynamic, spatially variable field—not a universal constant.