Taxonomy of the Common Dolphins of the Eastern Pacific Ocean

Delphinus bairdii Dall is a species of dolphin distinct from D. delphis Linnaeus, with which it has usually been synonymized. D. bairdii has a longer rostrum relative to the zygomatic width of the skull; the ratio of these measurements falls at 1.55 or above for bairdii and 1.53 and below for delphis. In the eastern Pacific Ocean, D. bairdii is found in the Gulf of California and along the west coast of Baja California, Mexico; D. delphis is presently found in the waters off California. Until approximately the beginning of the present century, bairdii occurred farther north in the eastern Pacific Ocean, at least to the Monterey Bay area of California. Restriction of bairdii to more southerly waters, probably as an indirect result of a change in water temperature, may have permitted delphis to move into inshore Californian waters. The Pacific population of D. delphis has a somewhat shorter rostrum than the Atlantic population, and is perhaps subspecifically different. A thorough analysis of the entire genus Delphinus is needed before the relationship of all the populations can be understood and names properly applied.

A NEW SPECIES OF CATHOROPS (SILURIFORMES; ARIIDAE) FROM MESOAMERICA, WITH REDESCRIPTION OF FOUR SPECIES FROM THE EASTERN PACIFIC

The great similarities in the external morphologies and the lack of knowledge on ontogenetic and intersexual differences of species in the ariid genus Cathorops Jordan and Gilbert, 1882, has led to an abundance of misidentifications, causing great nomenclatural instability. Accordingly, the taxonomic statuses of the Cathorops species described from Eastern Pacific have remained controversial in the literature, even in recent studies. Here, we describe Cathorops raredonae, a new species from Mesoamerica (Mexico to El Salvador) and redescribe (in Cathorops) Tachysurus liropus Bristol, 1897, and Arius taylori Hildebrand, 1925, often listed as junior synonyms of Cathorops fuerthii (Steindachner, 1877) and Cathorops steindachneri (Gilbert and Starks, 1904), respectively, or treated as species inquirendae in Cathorops. We also redescribe and redefine the circumscriptions of C. fuerthii and C. steindachneri. Finally, we summarize current statuses of nominal species of Cathorops from the Eastern Pacific and provide an artificial key to identify the valid Pacific species.

Microplankton abundance and biomass in the Eastern Pacific

Particles of detritus were counted by size-groups and microplankton cells in samples stained with acid fuchsin and acridine orange. Data were obtained for eutrophic and oligotrophic waters. Seston in the eutrophic layer of eutrophic waters consists of 22-65% phytoplankton, 3-18% microzooplankton, and 32-65% detritus; in oligotrophic waters - of 3-7% phytoplankton, 1-5% microzooplankton, and 92-97% detritus. Amount of detritus in seston increases with depth up to 4.4 µg C/l (sigma = 1.48) at 500-4000 m. Microplankton biomass in deep water contains mostly olive-green cells and bacteria; no microzooplankton <200 µm long was found below 200 m. Aggregates 10-50 µm in diameter and fragments of organisms 50-200 µm long were dominant by weight among detrital particles. No discernible associations of microorganisms with detrital particles were observed.

Geochemistry of lavas and dikes from the upper oceanic crust of Hess Deep Rift, eastern Pacific Ocean

Strontium isotopes are useful tracers of fluid-rock interaction in marine hydrothermal systems and provide a potential way to quantify the amount of seawater that passes through these systems. We have determined the whole-rock Sr-isotopic compositions of a section of upper oceanic crust that formed at the fast-spreading East Pacific Rise, now exposed at Hess Deep. This dataset provides the first detailed comparison for the much-studied Ocean Drilling Program (ODP) drill core from Site 504B. Whole-rock and mineral Sr concentrations indicate that Sr-exchange between hydrothermal fluids and the oceanic crust is complex, being dependent on the mineralogical reactions occurring; in particular, epidote formation takes up Sr from the fluid increasing the 87Sr/86Sr of the bulk-rock. Calculating the fluid-flux required to shift the Sr-isotopic composition of the Hess Deep sheeted-dike complex, using the approach of Bickle and Teagle (1992, doi:10.1016/0012-821X(92)90221-G) gives a fluid-flux similar to that determined for ODP Hole 504B. This suggests that the level of isotopic exchange observed in these two regions is probably typical for modern oceanic crust. Unfortunately, uncertainties in the modeling approach do not allow us to determine a fluid-flux that is directly comparable to fluxes calculated by other methods.

Chemical composition of sediments and interstitial waters in the Gulf of California and Eastern Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.

Sulphur isotope composition in the Gulf of California and the Eastern Pacific

The book is devoted to study of diagenetic changes of organic matter and mineral part of sediments and interstitial waters of the Pacific Ocean due to physical-chemical and microbiological processes. Microbiological studies deal with different groups of bacteria. Regularities of quantitative distribution and the role of microorganisms in geochemical processes are under consideration. Geochemical studies highlight redox processes of the early stages of sediment diagenesis, alterations of interstitial waters, regularities of variations in chemical composition of iron-manganese nodules.