Geophysical description: The Pacific Ocean covers a great expanse, nearly one-third of the earth's surface. At the equator the Pacific spans over 17,000 km (11,000 mi). The "Upwelling Zones" Tropical Pacific study area encompasses a subset of the Pacific – the area 15 degrees north and south of the equator from 90°W (about the same longitude as New Orleans) to the International Date Line (i.e., 180°, about the same longitude as eastern New Zealand). Even with the many topographic features found on the sea floor, such as plateaus, ridges, trenches, and seamounts, the entire Pacific has an average depth of 4,000 m (13,000 ft). The depth of the Tropical Pacific study area ranges from about 2,000m to 6,000 m (about 6,500 ft to 20,000 ft).

Ocean-atmosphere environment: Normally, trade winds blow steadily towards the west across the Tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 0.5 meters (20 inches) higher at Indonesia than at Ecuador. The sea surface temperature is warmer in the western Tropical Pacific, with cool temperatures off South America due to upwelling of cold water from depth. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry.

Marine life: Although levels of primary production can be high within the Tropical Pacific Ocean upwelling system, the area's great depth inhibits the formation of the complex marine food webs seen in shallower waters. Grounds for migratory fish such as tuna, not much is known about the Tropical Pacific's food web thanks to its remote location. However some researchers believe that largest proportion of the Pacific tuna catch originates from warm waters, even though these are regions with low phytoplankton populations. Field based research on tuna migration is key in resolving the apparent discrepancy between low primary productivity and high tuna production.

Important events: "El Niño" and "La Niña" – disruptions of the ocean-atmosphere system that have important consequences for weather around the globe – originate in the Tropical Pacific Ocean, often with significant impacts to the marine food web. To learn more, we provide a link to the abstract of a published article (.pdf format): "Unusual large-scale phytoplankton blooms in the equatorial Pacific" (Ryan et al, 2002). We also invite educators to email the lead author of this publication, Dr. John Ryan of the Monterey Bay Aquarium Research Institute (MBARI) for a reprint of the full article or other research-related questions.

• Unusual large-scale phytoplankton blooms in the equatorial Pacific: Abstract (Ryan et al, 2002)
• Satellite Data Capture a Big Climate Effect on Tiny Ocean Life (NASA Press Release, 2005)
• El Nino Theme Page (National Oceanic and Atmospheric Administration)
• Information on El Niño (US Geological Survey)
• 'Phytopia: Discovery of the Marine Ecosystem' CD-ROM (Bigelow Laboratory for Ocean Sciences)
• Research-related questions or comments should be directed to Dr. John Ryan
• Education-related questions or comments should be directed to Annette deCharon

Click here to access the Upwelling Zones data & analysis tools

• Lehodey, P., 2001,The pelagic ecosystem of the tropical Pacific Ocean: Dynamic spatial modelling and spatial consequences of ENSO. Progress in Oceanography, v. 49 p. 439-468.
• Ryan, J.P., P.S. Polito, P.G. Strutton, and F.P. Chavez, 2002, Progress in Oceanography, v. 55, p. 263 - 285.

Click here to access the Upwelling Zones data & analysis tools