Local meteorological conditions, bathymetry, and tidal and oceanic currents affect local current patterns. These conditions can result in upwelling of deep, cooler water to the surface. Complementary factors such as longshore or offshore winds, tropical storms, eddies behind reefs, or shelving seafloors also may act as mixing agents.
Below are some resources and suggestions to assist in identifying areas of potential cooling:
At the broadest scale (1,000s of kilometers), consult NOAA’s global temperature maps that provide the histories of sea surface temperature (SST), including global hotspots of high temperature. Regions that now regularly receive SSTs approaching average hot season maximums are particularly vulnerable to coral bleaching.
Note: Use the highest resolution available. Currently, 50km resolution SST maps are freely available, and 4km resolution maps are now available through the National Oceanographic Data Center’s Pathfinder SST Program.
At the regional scale (100s of kilometers), look for reefs that are close to local currents, and deep water and whose corals may benefit from cooler water temperatures. Identify major obstructions in the path of currents (e.g., sheer reefs, islands and seamounts rising from great depths, ridges across currents, and promontories that extend underwater) where cool waters are unlikely to extend, as opposed to high flow areas that are more likely to be cooled by deeper waters. Also identify constrictions, such as channels and narrow passages between landmasses, that funnel and intensify the flow and mixing of oceanic and major regional and tidal currents.
At the local scale (10s of kilometers), the same features of bathymetry, current flows and eddies, constrictions, and obstructions to current flows apply, but at a much finer scale. Look for areas that have not bleached because they might be ones in which cooling occurs.
Cooling Factor (0:50)
David Obura discusses how cooling played a role in reducing the effects of bleaching in the 1998 bleaching event that devastated the Western Indian Ocean.
Cooling and Deeper Water (0:28)
Jamie Oliver discusses how deeper cooler water may protect corals from bleaching.