COSTA RICA THER­MAL DOME

Scuba Diving - - GEAR BAG -

The large-scale ecol­ogy of this re­gion is driven by the in­ter­play of two vast, rich ecosys­tems: the Costa Rica Ther­mal Dome north of the equa­tor and the Hum­boldt-gala­pa­gos sys­tem that reaches from South Amer­ica and spreads along the equa­tor. These sys­tems are two of only three ar­eas on Earth — the other be­ing in the north­west In­dian Ocean — where ex­ten­sive cold-wa­ter up­wellings bring an abun­dance of marine life to the open oceans of the trop­ics. Trop­i­cal seas in gen­eral are vir­tual deserts, but where these cool-wa­ter sys­tems ap­proach the sur­face, plank­ton erupts, and mil­lions of ocean giants feed on tril­lions of prey an­i­mals over sev­eral thou­sand square miles. As the sun moves north and south with the sea­sons, these two gi­ant sys­tems — par­tic­u­larly the CRTD to the north — shift, ex­pand, and con­tract with the ebb and flow of the sea­sons.

The CRTD is a bulge of deep, cold, nutrient-rich wa­ter be­tween 100 and 200 miles across, de­pend­ing on time of year, pulled up from the depths to just a few yards be­low the sur­face. When it rises, it brings an ex­plo­sion of life. Co­cos Is­land — about 5 miles long by a lit­tle over 2 miles wide, 340 miles off Costa Rica — is at the south­ern edge of the CRTD through the mid­dle of the year.

Un­like other is­lands of the east­ern trop­i­cal Pa­cific, Co­cos is lush and green. Ham­mer­head num­bers at Co­cos may be the high­est in the world. From May through Septem­ber, ham­mer­heads, whale sharks and man­tas reach their high­est num­bers around the is­land.

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