The Costa Rica Thermal Dome

Lead: Jorge Jimenez, MarViva Foundation


In the tropical East Pacific Ocean, off the coast of Central America, there is a phenomenon that is persistent enough from year to year to be considered as an oceanographic feature – it is referred to as the Costa Rica Thermal Dome (CRTD).  The feature, which can be up to 1,000 km in diameter, results from the interaction of swirling wind and ocean currents that cause the vertical conveyance of cold, nutrient-rich waters from the deep ocean towards the surface.  As this body of cold water bulges dome-like up into the water column, the warmer water above it is displaced laterally, resulting in a thinner layer of warm water above the upwelling than in surrounding areas.  Where nutrient-rich cold water meets warmer water close to the sunlit surface, planktonic algae thrive, sustaining a food chain of grazing zooplankton, filter-feeding forage fish, their predators such as tuna fish and diving birds, followed by sharks, dolphins, rays and whales.  The whole feature is an oasis of productivity and a biodiversity hotspot that attracts animals from far and wide, with many migratory animals using it as a staging post during their long journeys across the ocean.

The CRTD’s biological pulling power has not gone unnoticed by people in nearby countries of Central America.  Consistent concentrations of usually well-dispersed animals so close to their shores has led to the establishment of several industries and activities that exploit such a seemingly dependable resource, including commercial and recreational fishing, and wildlife-based tourism.  These industries are worth millions of dollars to the national economies and are prone to overexploitation.  A less obvious threat to the ecological integrity of the CRTD is the incessant marine traffic that traverses the feature following one of the busiest maritime trade routes in the world, form North Asia and America towards the Panama Canal, and vice versa.  Collisions with whales and pollution events from ships are likely to be far more numerous than presently recorded.

Whilst the existence of the CRTD has been known for some time, the realisation of its importance to both the ecosystem beyond its limits and to Central American society is only now starting to emerge.  Relatively little is known about the full assemblage of species that utilise the CRTD, and whether any of those species depend directly on the feature for their continued survival.  Even less is known about the fate of species should the feature’s persistence be compromised with the prospect of global climate change.  The detrimental effects of human activities, both land-based and at sea, on the biodiversity and ecosystem services that are supported by the CRTD are poorly understood, especially whether such effects are acute, chronic or reversible.  This work aims to catalogue all available information on the physical and biological characteristics of the CRTD, with the intention to fill the knowledge gaps identified.  In parallel, it intends to publicise the ecological and economic importance of the CRTD to Central American society, emphasising the trade-off in benefits between the two, and to devise a governance scheme that will rebalance that trade-off in favour of a sustainable future for both.


  • To describe the biodiversity, ecology and oceanography of the CRTD by production of a species distribution atlas.
  • To propose a model governance scheme for high seas around CRTD.


The actions involved in this work are:

  • Synthesis and publication of a spatial and temporal species distribution atlas for the CRTD.  Content to include visualisations of the feature’s oceanographic and ecological attributes, its value as a resource, and its biological and economic connectivity links to Central America.
  • Implementation of an extensive public outreach and media campaign to raise awareness of the value and relevance of biodiversity sustained by the CRTD, its linkages to human wellbeing, as well as the importance to conserve and manage marine areas beyond national jurisdiction.
  • Supporting the generation of a multisectoral recommendation on a potential macro-zonation plan for the CRTD via an international, high-level Marine Spatial Planning process, leading to the development of a potential governance model for the portion of the CRTD that lies in international waters.
  • Validate and promote the agreed recommendations and governance model amongst decision makers in Central America.


Raised public awareness of the importance and value of biodiversity, both as an environmental and an economic resource, is fundamental for the sustained coexistence of human society and wildlife, especially as biodiversity is vital for the continued functioning and provision of ecosystem services which, for the most part, humans take for granted.  Already, GOBI has contributed to the description of an EBSA (Upwelling system of Papagayo and adjacent areas) that recognises the wildlife corridor between Costa Rica’s coastline and the CRTD.  This work will build upon that recognition to reinforce the notion that biodiversity must be preserved, especially in areas beyond national jurisdiction where adequate protection and regulation are lacking.  It will also formulate a political mechanism so that actions can be taken at both national and regional scales to implement the preservation of biodiversity associated with the CRTD, and in doing all of this, contribute towards the fulfilment of GOBI’s objectives for the benefit of all.

Progress to date

Progress on this work has been achieved on several fronts.  Following extensive consultation with data specialists and experts, information on productivity, wind vectors, thermocline depth, purse seine fishing effort, the distribution of sharks, rays, blue whales and turtles, etc. has been compiled and mapped.  All of this information has contributed to the creation of an Atlas of the Costa Rica Thermal Dome (launched in August 2019) and an interactive geoportal accessible online.

In parallel, dedicated oceanographic surveys of the CRTD have been completed, yielding new information on environmental conditions – and pollutants – prevalent at the feature.  Such evidence has been put forward in support of the CRTDs case for becoming a World Heritage Site in the High Seas.  An analysis of possible governance schemes for the CRTD is under review, and once approved and published, the results will form the basis for negotiations with regional authorities to define an appropriate governance regime for the region.