Central Gulf Of California Research Articles

Seasonal and annual variability in particle fluxes in the Gulf of California: A response to climate forcing

A six-year time series of sediment trap samples is used to document seasonal and interannual changes in particle fluxes in Guaymas Basin, Gulf of California. Sedimentation in this region of the Gulf of California is dominated by two seasonally varying components: biogenic silica during the late fall–spring and lithogenic material during the summer. This variability in sediment fluxes is a direct response to the seasonally reversing monsoon climate in this region. In addition, this seasonal variability in particle flux to the seafloor combined with the lack of bioturbation results in the formation of sediment laminae or varves in Guaymas Basin. Observed interannual differences in the magnitude of sediment fluxes appear to be related to ENSO. These findings indicate that biogenic sediment fluxes, and hence primary productivity, are higher during non-ENSO years in the central Gulf of California. A decrease in the carbonate: opal flux ratio from 1991 to 1996 indicates that diatoms became an increasingly important component of the plankton during this period and further supports our findings that productivity in Guaymas Basin is higher during non-ENSO years.

Fishes of the Tropical Eastern Pacific

A comprehensive, color-illustrated guide to the marine fishes of the region extending from the central Gulf of California, southward to Ecuador. It covers 680 species, primarily species that inhabit inshore reefs and adjacent sand, rubble, and weed habitats. Pelagic fishes, including tunas, mackeral

Isolation and characterization of extremely thermophilic archaebacteria related to the genus Thermococcus from deep-sea hydrothermal guaymas basin

During the “Guaynaut” oceanographic cruise performed by IFREMER in November 1991, sediment cores were collected from high-temperature and petroleum-rich deposits in an active hydrothermal zone, at the Guaymas basin (Central gulf of California). Those samples were collected by the French deep-sea manned submersible “Nautile” at a depth of 2000 meters. Four sediment cores of 20–40-cm length were drilled at the bottom of a block assemblage of active smokers inside sediments whose temperatures were 3.5°C on the top to 105°C at 20 cm depth. They were subsampled in 22 slices of 5-cm thickness and used for isolation of heterotrophic hyperthermophilic microorganisms, after inoculation in sulfur-free SME liquid medium. From those enrichments 18 isolates were obtained, 2 growing at 95°C and 16 at 80°C, and their taxonomic characterization was undertaken. Lipid analysis indicated the presence of diethers and tetraethers in the cell walls and membranes, characteristic of Archaebacteria. Examinations by scanning electron microscopy showed that isolates were cocci of heterogeneous sizes (diameter from 0.1 to 0.5 micrometers) or thick, piled-up discs 0.5 μm thick and 1 μm in diameter. Both forms were embedded in a dense fiber network. Physiologically they were found to be anaerobic, heterotrophic, and hyperthermophilic (80°–95°C). Determination of the DNA base composition resulted in G + C mol % values ranging from 36 to 57. Qualitative hybridizations of the 18 isolate DNAs with hyperthermophilic Archaebacteria reference strain DNAs showed that hybridizations occurred neither with the two species of Pyrococcus nor with the two species of Desulfurococcus, nor with Staphylothermus marinus. On the other hand, all isolates hybridized with at least one of the three species of Thermococcus tested (T. celer, T. stetteri, T. litoralis). Restriction polymorphism on a PCR-amplified fragment of the rrn operon showed that 12 isolates had the same profile as T. celer and T. stetteri, 4 isolates had the same profile as T. litoralis, and 2 had new profiles, suggestive that they are new species.

Diatoms in the Gulf of California: Seasonal flux patterns and the sediment record for the last 15,000 years

Flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central Gulf of California over a 2‐year period. Fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the Guaymas Basin and the western side of the Carmen Basin, indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year. The annual maximum in diatom flux occurred during the winter season of both years, either as a sustained event over many weeks (1990) or as a series of short blooms (1991–1992). Of the most abundant taxa, only hyalochaete Chaetoceros species showed a clear seasonal cycle, with a flux maximum in the spring of both years. Factor analysis defines five assemblages representing (1) summer and fall conditions of surface stratification and nutrient limitation, (2) winter bloom triggered by onset of strong northwesterly winds, (3) late spring to summer production probably related to sporadic events during periods of weak southeasterly winds, (4) spring 1991 inferred to reflect the distal edge of a coastal upwelling phase, (5) lateral advection of resuspended sediments from the continental shelf, possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991–1992 El Niño‐Southern Oscillation (ENSO). The diatom data support the inference that subtropical Pacific water penetrates deeper into the gulf during ENSO events. In order to compare the sediment trap record to a sediment core, a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa, which showed little downcore variation. This produces five factors representing (1) summer‐fall low production, (2) early winter bloom, (3) late winter‐spring upwelling, (4) ENSO conditions and (5) a late spring‐summer assemblage of uncertain significance. Variation of species characterisic of each factor was examined in piston core Atlantis II 125‐8 56JPC taken from the oxygen minimum zone in Guaymas Basin. Correlation to nearby Deep Sea Drilling Project Hole 480 indicates that the core penetrates to about 15 ka, with laminated sediments in the Holocene (0–10 ka) and late deglacial (11–13 ka) and massive (nonlaminated) sediments around Younger Dryas time (10–11 ka) and before 13 ka. Downcore variations in the diatom assemblage do not correspond directly to presence of laminations, implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production. Presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages (ENSO and winter bloom indicators) and not with occurrence of laminations, suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production. Prior to 12 ka, production was lower than at present during all seasons, implying weaker winds throughout the year; subtropical waters extended to the midgulf as they do today during ENSO events. Between 11 and 12 ka, conditions were similar to those of the present, with relatively high winter and spring production resulting from northwesterly winds. ENSO events were still common, although less so than during the preceding period. Younger Dryas time was one of transition with intermediate conditions: a slackening of winter‐spring northwesterly winds and reduction of total annual production, and increased occurrence of ENSO conditions. In the early to middle Holocene winter, northwesterlies increased to a maximum, resulting in very high production, but apparently did not persist into spring; subtropical waters mostly disappeared from the gulf. In the late Holocene, northwesterly winds have supported high production during both winter and spring seasons.

Phytoplankton productivity and biomass by size classes, in the central Gulf of California during spring 1985

An oceanographic cruise was performed in the central region of the Gulf of California from March 31 to April 9, 1985. Nineteen hydrographic casts to 0, 25, 50, 75 and 100 m were made in four transects to estimate the size-fractionated biomass of the phytoplankton (chlorophyll a). Five size-fractionated 14C assimilation experiments were also done. A thermal front was recorded during the cruise period, with similar characteristics to those previously reported for this area. The contribution of nannoplankton to the biomass was higher at most stations, although maximum values of chlorophyll a and primary productivity were found near the coast, where the abundance of microphytoplankton was higher. The higher values of the assimilation ratios corresponded to the stations with the higher nannoplankton percentage, indicating higher efficiency in their production rates. The assimilation ratios and primary productivity rates were lower than those reported in March of 1983 and 1984, when Gulf waters were under the influence of the El Niño event, but of the same order of magnitude as during normal years.

Varve formation in the Gulf of California: Insights from time series sediment trap sampling and remote sensing

The varved sediments that accumulate in the central Gulf of California (Guaymas and Carmen Basins) provide a record that allows for the resolution of annual to decadal-scale climate variability in this region. Time-series sediment trapping, combined with remotely sensed observations of sea surface temperature (AVHRR) and color (CZCS), have been used to examine the mechanism of varve formation in the central Gulf. SST and surface pigment concentration records for both the mainland and Baja sides of the Gulf display similar seasonal trends. High temperatures and low pigment concentrations occur synchronously on both sides of the central Gulf from June through to October. In association with the 1991/92 El Niño, warm temperatures persist in the central Gulf until December. Low SSTs typically occur from December through May, with high pigment concentrations marking the period from November through April. The summer-early fall (June–October) is a time of high terrigenous and biogenic sediment fluxes. During this time of year, the total flux is dominated by eolian-transported lithogenic material and dark laminae are deposited during this period. During El Niño years, high terrigenous fluxes may extend into winter. Light laminae represent deposition from November through May, during which time biogenic material dominates the total sediment flux. High opal fluxes beginning in November are attributed to seasonal cooling of surface water and upward mixing of nutrients. True upwelling conditions do not develop in the Gulf until late winter-spring. During this time, the total flux is still dominated by opal but the magnitude of the flux is reduced. This may be an artifact of phytoplankton grazing and not lower production rates.

Flexible responses to predators in a marine fish

The effect of predators on the behavior of signal blennies, Emblemaria hypacanthus (Pisces Chaenopsidae), was examined by comparing populations from two sites in the central Gulf of California that differed significantly in the abundance of predatory fishes. At the low-risk site the sexes differed in habitat use with males and females spending most of their time in shelters and in the open, respectively. At the high-risk site both sexes spent most of their time in shelters and also moved less and retreated into shelters more frequently than they did at the low-risk site. Both sexes fed at similar rates at the two sites, but their feeding efficiency was not measured. Males at the high-risk site courted females less vigorously and exhibited less intense courtship coloration than did males at the low-risk site. Although this difference in coloration was evident in the field over 3 consecutive years, males from both sites exhibited full courtship coloration in aquaria lacking predators. This implies that the ...

Samuraia tabularasa gen. nov., sp. nov. (Cnidaria, Hydrozoa, Hydrocorynidae), an intertidal hydroid from the Gulf of California, Mexico

Samuraia tabularasa, the samurai hydroid, a previously unreported genus and species of athecate hydrozoan, family Hydrocorynidae, is described, based upon field and laboratory observations. Colonies live attached to rocky substrates in the middle of the intertidal zone in the northern and central Gulf of California, Mexico. The principal characters that allow this species to be referred to a new genus are associated with its mode of sexual reproduction by eumedusoids that can remain attached to the colony, or be released as ephemeral, rudimentary structures. This is in contrast to the feeding, free medusae produced by the two species of the other genus, Hydrocoryne, in the family Hydrocorynidae.

Numerical simulations of hydrothermal circulation resulting from basalt intrusions in a buried spreading center

A two-dimensional, one by two-kilometer section through the seafloor was simulated with a numerical model to investigate coupled fluid and heat flow resulting from basalt intrusions in a buried spreading center. Boundary and initial conditions and physical properties of both sediments and basalt were constrained by field surveys and drilling in the Guaymas Basin, central Gulf of California. Parametric variations in these studies included sediment and basalt permeability, anisotropy in sediment permeability, and the size of heat sources. Faults were introduced through new intrusions both before and after cooling. Background heat input caused fluid convection at velocities ≤ 3 cm a −1 through shallow sediments. Eighty to ninety percent of the heat introduced at the base of the simulations exited through the upper, horizontal surface, even when the vertical boundaries were made permeable to fluid flow. The simulated injection of a 25–50 m thick basalt intrusion at a depth of 250 m resulted in about 10 yr of pore-fluid expulsion through the sea-floor in all cases, leaving the sediments above the intrusions strongly underpressured. A longer period of fluid recharge followed, sometimes accompanied by reductions in total seafloor heat output of 10% in comparison to pre-intrusion values. Additional discharge-recharge events were dispersed chaotically through the duration of the cooling period. These cycles in heat and fluid flow resulted from the response of the simulated system to a thermodynamic shock, the sudden emplacement of a large heat source, and not from mechanical displacement of sediments and pore fluids, which was not simulated. Water/rock mass ratios calculated from numerical simulations are in good agreement with geochemical estimates from materials recovered from the Guaymas Basin, assuming a bulk basalt permeability value of at least 10 −17 m 2/(10 −2 mD). The addition of faults through intrusions and sediments in these simulations did not facilitate continuous, rapid venting. Increased heat input at the base of the faults resulted in temporarily greater fluid discharge, but the flow could not be sustained because the modeled system could not recharge cold fluid quickly enough to remove sufficient heat through the vents.

Liquid hydrocarbon-bearing inclusions in modern hydrothermal chimmeys and mounds from the southern trough of Guaymas Basin, Gulf of California

Liquid hydrocarbon-bearing inclusions of variable shape (e.g. spherical, bowling pin, rod, and highly irregular) occur in hydothermal minerals of chimneys and mounds in the southern trough of Guaymas Basin, central Gulf of California. The inclusions are preferentially trapped in amorphous silica which occurs as spherules and 0.01 mm-thick encrustations on sulfides, sulfates and carbonates. The inclusions are primary and pseudosecondary and were trapped during, not after, mineral growth. The inclusions are both two-phase (liquid hydrocarbon and vapor/gas) and three-phase (liquid hydrocarbon, aqueous fluid and vapor), and range from 2 to 50 μm in diameter. The large range in liquid hydrocarbon and acqueous fluid contents indicates that the hydrothermall fluid and liquid hydrocarbon were never a homogeneous solution, but that hydrocarbons were transported as immiscible and, possibly, solvated forms. The liquid hydrocarbon varies in color from deep to pale orange-brown and fluoresces a yellow color during excitation by u.v. light, indicating a condesate (mainly C 1 to ∼C 10 hydrocarbons) composition. Measurable quantities of hydrocarbons from the inclusions could not be isolated by mineral dissolution, by pyrolsis and decrepitation analyses suggest that the more volatile components predominate. Two-phase hydrocarbon inclusions homogenized with the liquid at temperatures ranging from 75 to 190°C (excluding one high measurement). To obtain true trapping temperatures, an unknown pressure correction is required; however, the trapping temperature of these hydrocarbon inclusions was estimated by measuring trapping temperatures for adjacent aqueous inclusions which range from 116 to 226°C. Geochemical modelling using these trapping temperatures indicates that the amorphous silica precipitated from the hydrothermal fluid due to conductive cooling in addition to mixing with ambient sea water. The temperatures required for the formation of petroleum and its transport to the seafloor in the Guaymas Basin coincide with those necessary for the precipitation of amorphous silica in the Guaymas Basin hydrothermal system.

Seasonal variability of temperature, salinity, velocity, vorticity and sea level in the central Gulf of California, as inferred from historical data

Seasonal variability of temperature, salinity, velocity, vorticity and sea level in the central Gulf of California, as inferred from historical data

Seasonal variability of temperature, salinity, velocity, vorticity and sea level in the central Gulf of California, as inferred from historical data

AbstractHistorical data from 17 cruises into the Guaymas basin, central part of the Gulf of California, are globally analysed. Temperature, across‐gulf integrated velocity, sea level, and salinity have a significant seasonal cycle. The last variable has an important semi‐annual component, presenting four extremes per year. The others are mainly annual, reaching their maximum values in summer and their minima in winter.By interaction with the atmosphere, the central gulf is gaining heat and losing fresh water during the whole year, on a monthly‐mean time scale (the only exception is an unimportant gain of fresh water in August). This implies net heat and salinity fluxes into the open ocean, through the gulf's mouth.Temperature and salinity vertical gradients at the surface are well correlated with atmospheric forcing, through turbulent diffusion of heat and salt. Average velocity correlates with the along‐gulf wind stress with zero lag, as if frictionally dragged in a surface layer, with a short relaxation time. Seasonal sea‐level changes are mainly caused by the thermal expansion of the water column.Horizontal processes (advection and diffusion) are as important as, or more important than, vertical diffusion for both heat and salt balances in the upper layers.Vorticity, the across‐gulf derivative of the velocity field, does not show a seasonal cycle. Its contribution to the instantaneous geostrophic velocity and surface elevation near each coast is larger than that due to the across‐gulf average velocity.

A Note On Non-Seasonal Variability In The Central Gulf Of California

A Note On Non-Seasonal Variability In The Central Gulf Of California

Geostrophic flow in the guaymas basin, central gulf of California

Hydrographic data taken during 17 cruises through the Guaymas Basin, central Gulf of California, between 1939 and 1983, are used to calculate the along-gulf geostrophic transport. In addition to the traditional assumption of a deep level of no-motion for the geostrophic calculations, absolute velocities are estimated using constraints of mass conservation or minimum kinetic energy in the whole section. The three methods give similar results in the upper hundred meters. A seasonal cycle is observed for the total transport in the upper hundred meters, varying from a maximum of 0.4 × 10 6 m 3 s −1 (corresponding to an average speed of 5 cm s −1) in May–June to a minimum of −0.7 × 10 6m 3s −1 in January–February. Data from the October cruises show large variability around the seasonal hindcast. The across-gulf variation of the surface flow and the deep circulation do not show any seasonal signal.

Female choice and male reproductive success in the angel blenny, Coralliozetus angelica (Teleostei: Chaenopsidae)

Correlates of reproductive success of male Coralliozetus angelica were studied in field populations in the central Gulf of California by collecting males with their shelters (vacant barnacle tests) and counting the number of eggs defended. Male body size was positively correlated with the number of eggs defended. This apparently resulted from female preference for large males since females preferred to mate with the larger of two males in laboratory choice experiments. Condition of males, as assessed by their relative head width, was also positively correlated with the number of eggs defended. Fit of males in their shelter entrance, male colour intensity, and male size relative to immediately surrounding males were not correlated with reproductive success. The quality of shelters was an important determinant of male reproductive success since females apparently avoided mating with males in heavily fouled shelters. Large shelters tended to be more heavily fouled than small shelters and male size and shelter size were positively correlated. The resulting negative correlation of male size and shelter quality apparently constrained female preference for large males and may be an important factor limiting the degree of polygyny in this species.

Seasonal and interannual thermohaline variability in the Guaymas Basin of the Gulf of California

Temperature and salinity data for the years 1939–1983 are used to investigate seasonal and interannual scales of the hydrographic variability across the Guaymas Basin, which is located between 27° and 28°N in the Central Gulf of California. Winter conditions extend from December to April and summer conditions from June to October, with transition periods in May and November. Sea surface temperature increases from about 16°C in February–March to 31°C in August. No clear seasonal cycle in surface salinity was found. Typical values are above 35.1‰ even in winter, and up to 35.5‰ in November. Relatively cold and low salinity near-surface waters observed in June 1957 and in June 1982, suggest advection of California Current Water to the Guaymas Basin. Subtropical Subsurface Water may occur around the year, but is obscured by vertical mixing with Gulf Water mainly during winter, when vertical stratification is weaker. The Intermediate and Deep Pacific Water masses successively fill the Guaymas Basin to the bottom (2000 m), showing very stable T-S characteristics. Positive sea level anomalies at Guaymas increases during El Nin˜o years, and anomalous low salinity and high temperature at the surface indicate the presence in the Guaymas Basin of water from the south. Observed differences reached 0.4‰ in surface salinity and 3°–5°C in surface temperature. There is evidence that the observed low salinities could not be due to abundant precipitation. An additional effect is a deepening of the winter pycnocline down about 200 m, compared to the usual depth of <100 m. In summer, this effect is not as clear as in winter, due to the strong stratification. The effects of the very strong 1982–1983 and 1957–1958 ENSO episodes may have lasted for one and two years, respectively. It is argued that during an ENSO event the Transition Water of the California Current meet and mix near the Gulf entrance with the Tropical Surface Water of the Costa Rica Coastal Current. This mixed water could have been carried north into the Gulf by local surface circulation. In 1983 it was found at the surface in the Guaymas Basin above the southeastward flow of the colder and saltier Gulf Water.

Hydrothermal petroleum from diatomites in the Gulf of California

Summary The plate boundary zone within Guaymas Basin, Central Gulf of California, is a set of spreading axes offset by a central transform fault and covered by a thick sedimentary sequence. The high heat flow and concurrent hydrothermal circulation cause extensive thermal alteration and leaching of the organic and mineral matter covering the rift graben. The rapid vertical migration of the leach and subsequent quenching by colder seawater results in the precipitation of hydrothermal deposits rich in sulphides and organic pyrolysates at the sediment surface. Deposits from the northeastern half of the Basin’s Southern Trough have been sampled using the D.S.R.V. Alvin , to examine the organic condensate character and regional patterns, from which fractionation processes during hydrothermal fluid migration may be inferred. With the characterization of the bitumen, three major patterns are resolved: (1) Hydrocarbons with n -alkane predominance and no carbon number preference are the most common pattern; (2) branched and/or unsaturated hydrocarbon predominance relative to n -alkanes mainly within the kerosene-diesel range; (3) biodegraded material, dominated by a naphthenic hump, with a minor contribution of resolved compounds. Samples with predominant n -alkanes are further defined by their molecular weight range into distinct subgroups. Waxy condensates versus kerosene-range n -alkanes are found at different localities and may reflect regional differences in hydrothermal fluid exit temperatures. It is postulated that variable pyrolytic temperatures and selective fractionation of pyrolysates during migration, with differential condensation and precipitation under varied thermal regimes, induce the observed general patterns. In addition, post-depositional processes such as biodegradation and removal of low molecular weight components by water solubilization can affect the bitumen character.

Geodetic measurements of plate motions across the central Gulf of California, 1982‐1986

A trilateration network was set up in early 1982 by a team of French and Mexican institutions across the central part of the Gulf of California in order to study the plate boundary related movements in this transition area between the San Andreas fault system and the East Pacific Rise. The reobservation of this network in March 1986 provides a first set of data on the present day deformations in this area. Both surveys used AGA8 Laser geodimeter measurements between 11 stations located on elevated points of Baja California and Sonora and on the islands between the peninsula and mainland coasts. Deformation patterns during the 1982‐1986 interval, obtained through three different methods indicate mainly a right lateral shear movement in the Gulf axis direction N46°W. Between Baja California Peninsula and Angel de la Guarda Island 17 ± 4 cm of dextral slip occurred. Between the coast of Sonora and the central islands of the Gulf the mean displacement amount to about 23 ± 12 cm. In the southwestern part of the network, weaker movements seem to have occurred, and are smaller than estimated errors. This may indicate either that the boundary is locked in this part or is deflected towards the ESE. These results, which give an estimation of the relative plate velocity of 8 ± 3 cm/a, are consistent with the generally accepted relative movement between North American and Pacific plates (about 6 cm/a).

Sources and hydrothermal alteration of organic matter in Quaternary sediments: A synthesis of studies from the Central Gulf of California

Deep sea drilling in the Central Gulf of California, a young and active spreading centre, shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter, especially near sills and above magma chambers where hydrothermal activity is concentrated. Even on the nearby passive margin, where there are no sills, heat flow is moderately high and hydrocarbon generation has begun in immature sequences. Migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated. Thermogenic methane is more widespread, though not in the passive margin bordering the spreading centre. Despite the incidence of hydrocarbon generation and migration, the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum. The organic matter in these sediments is mostly marine because the Gulf of California generally has low runoff from land and highly productive surface waters. Turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the Guaymas Basin. The highest concentrations of organic matter are found in laminated diatomites deposited on the Guaymas passive margin within the oxygen minimum zone.

A 20-year varve record of siliceous phytoplankton variability in the central Gulf of California

Year-to-year variability in the structure of the preserved siliceous phytoplankton assemblage is reconstructed from a box core retrieved from the varved sediments along the Guaymas slope of the Gulf of California. A 20-year record from 1953 through 1972 is obtained from interpretation of the varve stratigraphy supported by 210Pb and 228Th dating. Ecological time series derived from microfossil analysis show a strong coherence with interannual sea-level anomalies indicating a response to large-scale climatic variability associated with the El Niño/Southern Oscillation phenomenon. El Niño periods are generally marked by increases in preserved abundances of the total siliceous assemblage and in particular by greater numbers of individuals within species whose distribution is limited to tropical and subtropical waters.