OS32A-01
The R/V EL PUMA and JUSTO SIERRA impact on the development of oceanography in Mexico
The acquisition of the two research vessels (R/V EL PUMA AND R/V JUSTO SIERRA) of the Universidad Nacional Autónoma de México represented a milestone for the development of oceanography and capacity building in Mexico. These boats were designed to conduct multi and interdisciplinary research in the Economic Exclusive Zone of Mexico in the main areas of oceanography (Physics, Geology, Chemistry and Biology). Its use, by different institutions, resulted in a substantial advancement of the knowledge of Marine ecosystems of Mexico. About 460 oceanographic campaigns, with more than 8700 participants, have been conducted since the boats arrived. These covered a wide array of topics of the marine ecosystem from the inner shelf to deep sea. Extensive research was done on current patterns, primary productivity and pollution monitoring of the Mexican Pacific, Sea of Cortez, Gulf of Mexico and Caribbean sea. Marine biodiversity studies were also carried which discovered more than 180 new species in Mexican seas. Ecological characterization and paleo-oceanographic research from continental shelf to deep sea also registered a substantial advance. The vessels are now renewed with hi-tech equipment for sea bottom, water column and navigation that increased their research capacity, representing again a new milestone in the history of oceanography in Mexico. This improved capacity is very promising and opens new and sound opportunities for carrying modern oceanographic in order to improve knowledge of the Mexican Economic Exclusive Zone.
OS32A-02
Hydrography of Bahia Todos Santos, Baja California: Results of more than twenty five years of investigations.
The first study of Bahia Todos Santos (BTS) was reported by Walton in 1955. We conducted oceanographic studies in BTS since 1979. The BTS has a connection with a coastal lagoon named Estero de Punta Banda (EPB), two islands at the western portion and the Port of Ensenada. The general hydrographic characteristics are: In winter the water became homogeneous, less saline (<33.4) and with low stability. During spring and summer a hydrographic structure of three layers is noticed. The deepest layer is composed of the southern California water mass with a relatively high salinity (>33.6) low temperature (13°C), low oxygen (~3mL L-1) and rich in nutrient concentration. The isothermal top layer has relatively high temperature (>17°C) and oxygen concentration (>6mL L-1). The intermediate transition layer (seasonal thermocline) has minimum salinity, maximum oxygen and high stability. During fall there is distribution of heat from the surface layer to the entire water column. The thermic waves propagate with decrease amplitude in ~3 months, from surface to bottom water. The California Current flow generally southward off the western United States and northern Mexico and is one of the major coastal upwelling of the word oceans. The upwelling events in BTS appear regularly at the SW portion and were typically characterized by an increase in pCO2, decrease of O2, increase of nutrients and a lower temperature. Upwelling activity increases surface nutrient availability causing rise in the primary productivity and hence increased zooplankton biomass. The annual upwelling event which had a maximum strength on May, the seasonal warming and cooling, and the water advection were the dominant modifying processes for the variability of seawater characteristics. Higher salinities are located close to the coastline and lower off the bay. The levels of oxygen, alkalinity, pH and chlorophyll indicate that the maximum concentration of phytoplankton is located at the center of the bay. The nitrification support the primary productivity and the NO3 levels were below detection limits; the N/P ratio in 2005 was from 10 to 25; and for 2006 was below 5. There is a net enrichment of anthropogenic nutrients at BTS. The heavy metals and pesticides studies started since the early 80's with problems still to solve for Tl, Cd. There is a net Pb enrichment and higher Cr concentrations at the NE of the bay. The EPB is a wetland ~7 Km. long located at the SE part of the BTS. The EPB is a net source of DIP (deltaDIP = +0.13 mmol m-2 day-1), that brings agricultural runoff to the BTS. It is typically a hypersaline system during summer and a net heterotrophic (p-r = -14 mmol m-2 day-1), and a net denitrifying (nfix-denit = -2.1 mmol m-2 day-1) system. Some anomalies were in 2005 the presence of a huge red tide observed inside BTS (about 50% of the bay) that last for more than six months, this HAB's has killed many fishes (anoxia) and marine mammals. The hydrographic conditions during the red tide were, temperature anomalies higher than 2°C above normal; high nutrient concentration above the normal. In 2006 the values were normal again. The Port of Ensenada, increased in size and activities (tourism, transportation, coastguards for national security, cement industry, research) these developments generate some management problems, like the beach and coastline modification. The aground of the APL Panama, activates the management agencies to prevent and control pollution.
OS32A-03
Particulate Matter Fluxes in Cuenca Alfonso During 2002-2005
Time-series sediment trap data were collected between 2002 and 2005 from Cuenca Alfonso, a 400m-deep basin in Bahía de La Paz, a large embayment on the southwestern coast of the Gulf of California. Despite the lack of significant land drainage in this semi-dessert environment, terrigenous material, probably wind-born, dominates the sinking particulate matter. Peak lithogenic fluxes appear to be associated with higher frequencies of wind gusts stronger than 5 ms-1. Total mass flux fluctuated from week to week, and between years, averaging 277 gm-2y-1, essentially the same as radiometrically-determined accumulation rates of about 0.4 mmy-1 in cores of the underlying sediment. In 2003, the passage of 2 hurricanes induced high winds and flash flooding and the total mass flux offshore remained very high for two weeks following each event. This unusual sedimentation was equivalent to that of a full year without hurricanes and such events may account for some of the laminations found in cores. During most of 2005, on the other hand, sedimentation rates were lower than average. Although fluxes of all components tended to be highest during late fall and early winter, biogenic fluxes displayed peaks during all seasons of the year in Cuenca Alfonso. This is in contrast to the strong seasonal alternation between terrigenous sedimentation and diatom blooms observed in Guaymas Basin in the central Gulf. Furthermore, calcium carbonate dominated over biogenic silica within the marine component. Average annual fluxes of CaCO3, biogenic silica and POC were 52.5, 32.5 and 13.9 gm-2y-1, respectively.
OS32A-04
Silicoflagellate Fluxes in Cuenca Alfonso, Mexico During the 2002-2003 El Niño Event
Changes in the circulation and water mass patterns in the Gulf of California are closely associated with changes in atmospheric circulation. At the interannual scale, such changes are associated with events like El Niño, which in the Gulf are characterized by greater penetration of tropical-equatorial water. Subsamples of sediment trap material, collected between January 2002 and February 2004 were examined with the aim of inferring average oceanographic conditions in Cuenca Alfonso, Bahia de La Paz and those during the relatively mild 2002- 03 El Niño. Analysis of the silicoflagellate data series reveals seasonal and interannual relationships between the silicoflagellate fluxes and the dynamics of the water column. Comparison of silicoflagellate fluxes with those of the diatom group indicate that the former represent 0-52% of their combined flux. Both silicate groups generally co-vary but show differences in intensity. Thirteen taxa made up the silicoflagellate species composition. The simultaneous occurrence of Dictyocha epiodon and Distephanus speculum with Dictyocha calida and Dictyocha californica during August 2002 to May 2003, indicated the presence of both California Current Water and Equatorial Surface Water in the area close to Cuenca Alfonso. This favored the increase, mainly in November-December, in the flux of the dominant species, Octactis pulchra (as high as 7 x 106 skeletons m-2 day-1). Spring, on the other hand, was notable for a drop in the total silicoflagellate flux, probably due to the influence of the El Niño event. The subsequent increase in species typical of warm water and the replacement of the dominant species (O. pulchra) by Dictyocha messanensis var messanensis, suggest that the effects of El Niño extended to the fall of 2003.
OS32A-05
Coccolithophore Dynamics In Alfonso Basin: Seasonal Variation And Species Composition
The production of organic and inorganic carbon by coccolithophores is considered to play a significant role in the global carbon cycle. Therefore, detailed knowledge of their vertical flux is needed. Here we present a time-series record of coccolithophore standing stock and vertical coccolith flux from Alfonso Basin, southwest coast of the Gulf of California. This location is of particular interest as it is very sensitive to changes in environmental conditions and these may be preserved in laminated underlying sediments. Coccolithophore standing stock and assemblage composition were obtained from plankton samples taken at 3- month intervals during 2002-2003. Furthermore, coccolith flux and species composition were determined in samples from a time-series sediment trap (sampling intervals 7-14 days) deployed at 350 m depth from January 2002 to October 2003. The coccolithophore standing stock and coccolith flux varied considerably between sampling periods but, in general, a seasonal pattern was apparent, with low fluxes in spring-summer and maximal values in autumn- winter. During 2002, fluxes ranged from 0.02x108 coccoliths m-2 d-1 in summer to 64.7x108 coccoliths m-2 d-1 in autumn. Values increased considerably during 2003: registering 52.4 x108 coccoliths m-2 d-1 in spring to the highest (128.8x108 coccoliths m-2 d-1) in late summer/autumn. The latter are related to hurricanes that occurred during the sampling period. In total 47 taxa were identified but only three species, Gephyrocapsa oceanica (43.6%), Emiliania huxleyi (28%) and Florisphera profunda (15.7%), constituted 88 percent of the total coccolith flux. This corresponds to the species composition observed in the water column. G. oceanica was always present and its flux pattern followed that of the total flux. The flux of E. huxleyi remained almost constant during the observed time period whereas F. profunda showed peak fluxes in autumn. Although the cosmopolitan species E. huxleyi has been considered the most important coccolithophore species on a global scale, G. oceanica is the most abundant species in Alfonso Basin and perhaps other marginal seas.
OS32A-06
Paleoceanographic Research in Mexico: Holocene Marine Sedimentary Record of the Gulf of California
An overview of Holocene paleoceanographic studies the Gulf of California is presented, with emphasis on contributions from Mexican institutions. The Gulf of California is our best modern example of a young oceanic basin in the early stages of rifting. The Gulf stretches south to north for more than 1200 km, from the ocean- continent boundary at the mouth of the Gulf to a sediment-filled continental rift at its northern limit. Recent studies in the Gulf have produced some new ideas and models about its circulation patterns and the controls on interannual to decadal timescales, which demand attention for the importance on the tropical and equatorial Pacific as the main region of forcing. The paleoceanographic community has been interested in the very unique records covering the seafloor of the Gulf. The Gulf sedimentary records show extremely high fidelity of annual to decadal oceanic and climatic past variability. Community of earth scientists in Mexico and abroad has been drawn to these sediments for its possibilities as a rich repository of detailed oceanographic and climatic information. In particular, they have studied sedimentary records from the Gulf to understand oceanographic and climatic changes that shaped its circulation and sediment production patterns, to develop ocean and climate scenarios in different space-time scales during Holocene and to interpret the nature and origin of these records. Several proxy data have been used to infer climatic and oceanographic changes. Major efforts have concentrated on five sites that share two important oceanographic features. All of them are under oxygen deficient waters and accumulate the remains of rich high biological productivity waters above: Guaymas, Carmen, Pescadero, La Paz, and Alfonso basins. Several cores of various lengths have been collected at each of the five sites, which are being studied at different institutions and universities in the country to gain information about the climatic and oceanographic changes of the tropical ocean and its deeper waters of remote origin in this valuable natural laboratory of the Gulf of California.
OS32A-07
Holocene Rainfall and Productivity Variation in the Gulf of California
Recent data reveals significant Holocene climate and oceanography changes in the Gulf of California (GC). Much of the published data is based on sediment cores from Guaymas basin in the mid GC region. We report on laminated sediment cores data from slope basins in the lower GC. Our history covers about 7700 YBP (cal yrs) in Alfonso basin (west side) and 9500 YBP in eastern Pescadero basin (east side) and is based on an analysis of sediment microfabric, organic carbon, biogenic and lithogenic components and stable isotopes. The broad picture of ocean-climate change in the lower GC is similar to Guaymas basin, with interesting differences. Prior to about 7000 YBP, the mass-accumulation rates (MAR) of terrigenous and biogenic silica on the mainland side are high but variable and suggests high primary productivity (PP) and runoff. Monsoon conditions were established by at least 6000 YBP with higher accumulation of biogenic silica on the east and carbonate on the west, reflective of the strong gradient in PP across the GC. In the early Holocene, biogenic and lithogenic components vary at ca. 900 yr cycles but are out of phase. Between 7000 and 4200 YBP, a general decline in biogenic silica flux rates and an increase in benthic δ13C of intermediate waters suggest a period of declining PP. Beginning at about 4200 YBP, the sediment and biogenic records signal a significant change in the lower GC. A major pulse of biogenic sedimentation occurs between 4000 and 3400 YBP across the GC, followed by a cyclic pattern of biogenic silica accumulation and carbonate dissolution with periodicities at 350 and 900 yrs. There are strong peaks of variability in the laminations, biogenic silica and coccolith record at about 150, 200 and 350 yrs, suggestive of solar forcing. The variability in all of the sediment records increases after about 2 ka. Rates of terrigenous accumulation fall in step-like fashion at 3000, 2000 and 1500 YBP and reverse only during the Little Ice Age (LIA). The data suggest sharp contrasts in climate with declining rainfall and intensified winds. After 2000 YBP the west-east gradient in PP appears to intensify. During the last 400 yrs there has been an intensification of these trends, especially since the end of the LIA (130 YBP)
OS32A-08
Features observed in the Southern Gulf of Mexico
The southern Gulf of Mexico has been studied at different scale. The analysis of dynamic topography shows a cyclonic eddy that dominates mesoscale circulation, its formation and westwards shift have been simulated by a numerical model as a result of the variation of the intensity of the Yucatan Current and the topography of the Bay of Campeche . There are hydrographic features of smaller scale such as topographical effect at the western margin of the Yucatan shelf which induce an uplift of cool water, and internal waves at the shelf edge. Over the Campeche canyon a subsurface anticyclonic-cyclonic eddy pair appears as well as an associated thermal front. On the other hand, the southern gulf coastal waters are influenced by river runoff, such as from the Grijalva- Usumacinta Rivers system, this runoff induces haline fronts and some times thermal and haline gradients occur with surface temperature and salinity increasing offshore, where low temperature and salinity values produce an inverse effect on water density.