Is the Caribbean Sea Saltwater? Salinity, Sources & Variations

Yes, the Caribbean Sea Is Saltwater

It's a marginal sea of the Atlantic Ocean with average salinity ~36 PSU (practical salinity units)—i.e., 36 g dissolved salts per kg seawater.

Salinity Context

• Open ocean average: 35 PSU.
• Caribbean: 35.5–36.5 PSU (slightly saltier due to high evaporation, limited freshwater input).
• Major salts: NaCl (~85%), MgCl₂, MgSO₄, CaSO₄, K⁺, Br⁻.

What Drives Variations?

Why It Matters

• Marine life: Coral reefs need 32–40 PSU; hypersaline lagoons stress them.
• Circulation: Salinity gradients drive thermohaline flow.
• Desalination: Higher salinity = more energy for reverse osmosis.
• Climate indicator: Salinity trends track water cycle intensification.

Not Uniform

Coastal lagoons (e.g., Laguna Madre) can hit 50+ PSU; river mouths drop to <20 PSU. But the open Caribbean Sea is consistently saline.