1. Development of an oceanographic observatory in the Mexican Pacific Ocean to understand the pelagic ecosystem response to the climate variability and climate change Gilberto Gaxiola-Castro 1, Bertha Lavaniegos 1, Reginaldo Durazo 2, José Rubén Lara-Lara 1, Raúl Aguirre- Gómez 3, José Gómez-Valdés 1, José Carriquiry 4, Alejandro Parés-Sierra 1 In the northeastern Pacific Ocean we are developing a long-term ecological research program (IMECOCAL) to understand the pelagic ecosystem response to the climate variability and climate change. The IMECOCAL program began in October 1997, and we are expecting to continue until at least 2008 year, with the CONACYT (Mexican Council of Science and Technology) and CICESE supports. The IMECOCAL program is quarterly visiting an oceanographic area of the southern California Current region off Baja California, with approximately 80 hydrographic stations. Also, we are planning two continuous sampling sites, one in northern Baja California y another in the south of the Peninsula. One of our main goals is understand the interannual variability of the physical-biological interactions in the pelagic ecosystem, with the study of ocean heat transport together with temporal changes of temperature and salinity in the water column, and their relationships with plankton fluctuations. Also, we are searching the long-term signature of the climate change over the ocean, with sediments analysis collected at San Lazaro Basin, one of the few anoxic basins of the eastern Pacific Ocean. The new project is modeling the effects of climate variability on the structure of the pelagic ecosystem, selecting some plankton key species and the primary production variability. IMECOCAL survey locations over an AVHRR-NOAA image which show the spatial SST variability during summer (July, 1998). SubArtic cool surface temperature water is entering from the north, and warm subtropical water is coming from the south. Upper-ocean geostrophic flow estimated from the 0/500 dbar dynamic height anomaly for the CalCOFI-California and IMECOCAL- Baja California areas for October 2000, and January 2001. In situ water column integrated primary production on cruises realized from July 1998 to October 2002. The samples were collected offshore the Baja California peninsula with the IMECOCAL program in some of the locations in the figures showed before,. Hovmuller diagram of AVHRR-SST from January 1998 to December 2002 for the first 100-km offshore, showing the El Niño 1997-98 and La Niña 1999-2000 effects. SST contours are each 2  C. Seasonal variability of zooplankton biomass (displacement volume) from October 1997 to February 2003, as sampled by the IMECOCAL program. Averaged zooplankton biomass are related with the long-term zooplankton variability (1951-1984) obtained by the CalCOFI program off Baja California. Note the relative increase of biomass during the El Niño 1997-98, with mean and lower values (August and October) in La Niña. Monthly 10-m temperature differences from September-October 1997 to July 2005, in relation to the long-term mean (1950- 1978) off Baja California. It is notorious the influence of El Niño 1997-98, and La Niña 1999. After the year 2003 a moderate warming event is dominating the region off Baja California. Climatology of the zooplankton volume (Log-mean ml/1000 m 3 ) for the IMECOCAL area (top figure, 1997-2005). In the middle figure are presented the 1951-1984 zooplankton volume mean obtained from the CalCOFI cruises off Baja California. In the bottom figures are the differences (percentages) between the 1951-1984 and the 1997-2005 zooplankton data. January and April show the higher differences in zooplankton volumes, mainly at the southern region of the IMECOCAL area. The minima differences are for the October season. The El Niño (1997-98) and La Niña (1999-2000) affected the plankton interannual variability of the pelagic ecosystem off Baja California. Recently, the most important perturbation off Baja California has been the subarctic water intrusion. Integrated chlorophyll dropped in 2003 and remained in low level through 2005. However, the variability in zooplankton biomass and abundance follow an inverse tendency to the chlorophyll since 2003. The zooplankton biomass follow a more seasonal pattern in the northern region, and the relative abundance of some groups (euphausiids, tunicates and main predators) was lower than central region. In the central region, most of the functional zooplankton groups maintain high abundance. Long-term oceanographic studies off Baja California are very useful to understand the plankton variability in the pelagic ecosystem. The exceptional CalCOFI program surveyed off Baja California until 1984, and has been continued by the Mexican IMECOCAL program. The main goal of this program is to understand how physical processes regulate the changes in the pelagic ecosystem of the southern region of the California Current. For that objective we are developing a long-term monitoring project to study the climatic and oceanographic variability effect in this region, maintaining core oceanographic measurements during the surveys, and collecting high frequency data on buoys, islands and land stations. Also, we are conducting modeling studies to explore plankton and small pelagic fish response to regional and global physical forcing as well as to local anthropogenic perturbations on the coastal areas. In addition, we are looking to develop a new generation of research oceanographers for the program, with fellowships for graduate and undergraduate students. The IMECOCAL program was initiated with a 3-year grant fro the Inter-American Institute of Global Change Research (IAI), follow with a four-year grant from the National Council of Science and Technology (CONACYT- Mexico), which was extended to six more year, covering the oceanographic surveys until 2006. Also, some funds came from the National Science Foundation (NSF-USA), under a joint grant with the Scripps Institution of Oceanography at La Jolla (SIO-UCSD). Actually, we are asking for funds to the CONACYT to continue for at least three more years of monitoring. Time series of the first three EOF modes of sea surface temperature (SST in relative units) from January 1997 to May 2002 Time series of the first three EOF modes of SeaWIFS Chlorophyll concentrations (relative units) from January 1997 to May 2002. 1 CICESE, México. 2 FCM-UABC, México. 3 IG-UNAM, México. 4 IIO-UABC, México