Sizing Up the Great Atlantic Sargassum Belt

• In June 2026, the Great Atlantic Sargassum Belt reached its annual peak, marking the second-highest abundance recorded by satellites, just behind 2025.
• The Caribbean Sea and the Gulf of Mexico experienced record-high concentrations of the floating brown algae.
• NASA's PACE satellite, using the Ocean Color Instrument (OCI), now provides high-sensitivity, hyperspectral monitoring to track the algae's expansion.

2026 Trends and Distribution

• The Sargassum belt stretches from West Africa to the Gulf of Mexico.
• Regional records were set in June 2026:
  • Western Caribbean: 3.6 million metric tons.
  • Eastern Caribbean: 9 million metric tons.
  • Gulf of Mexico: 5 million metric tons, nearly double the previous record set in 2025.
• While ocean currents largely spared Florida's west coast, significant amounts were delivered to the Florida Keys and the state’s east coast.

Ecological and Economic Impact

• In moderate, open-ocean quantities, Sargassum is beneficial, providing habitat and oxygenating water through photosynthesis.
• Near-shore impacts are often negative:
  • Marine life: Mats can tangle, suffocate, or smother corals and seagrasses upon sinking.
  • Human impact: Decomposing seaweed on beaches releases hydrogen sulfide, a toxic gas with a potent odor that affects both tourism and coastal ecosystems.

Scientific Monitoring

• Since 2011, total Sargassum in the Atlantic has increased significantly, doubling roughly every five years.
• Drivers for the proliferation are still under investigation but likely involve ocean warming, increased nutrient sources, and biological interactions that support sustained growth.
• The PACE satellite provides superior data for the Sargassum Watch System:
  • Hyperspectral capability allows for the distinction of Sargassum from other algae, such as Trichodesmium.
  • Increased sensitivity improves monitoring during winter months and provides higher-resolution data for daily tracking.