NUEVOS REGISTROS Y ALGUNAS NOTAS PARA LA FLORA ALGAL MARINA DE LA COSTA OCCIDENTAL DEL ESTADO DE BAJA CALIFORNIA, MÉXICO

Based on samples collected on the westerncoast of Baja California during 1990, 1996 and1997. Prasinocladus ascus Proskauer,Feldmannia hemispherica (Saunders)Hollenberg, Spongonema tomentosum(Hudson) Kutzing, Prasinocladus ascusProskauer and Prasinocladus marinus(Cyenkowski) Waern, are reported for the firsttime for the Mexican Pacific coast. Themorphology, reproductive stage, habitat andgeographic distribution are presented for eachspecies.Con base en el material recolectado en lacosta occidental del estado de Baja California,durante 1990, 1996 y 1997. Se citan por primeravez a Feldmannia hemispherica (Saunders)Hollenberg, Spongonema tomentosum(Hudson) Kutzing, Prasinocladus ascusProskauer y Prasinocladus marinus(Cyenkowski) Waern, para la costa del Pacíficode México. Cada especie se presenta condatos relativos a su morfología, estadioreproductivo, hábitat y distribucióngeográfica

Productividad primaria marina dominada por diatomeas en el Pacífico nororiental mexicano durante el último milenio

Las diatomeas, el principal grupo del plancton silíceo, contribuyen con más del 40% de la producción primaria marina y dominan las comunidades del plancton en el Océano del Sur, Pacífico Norte y regiones de surgencias del Pacífico tropical y ecuatorial. La razón Si (OH)4/NO3- >1.0 en aguas subsuperficiales del margen suroccidental de Baja California (MSO-BC), sugiere que las diatomeas crecen en condiciones óptimas de nutrientes y alcanzan valor Si (OH)4/NO3 <3 en condiciones cercanas al límite por deficiencia de Fe o P. Estos valores son más altos que la razón Si:N <1 para muchos de los océanos. Por lo tanto, si la productividad primaria es dominada por diatomeas en el último milenio, la razón Si:N deberá ser <3. Para dar respuesta a esta pregunta, se colectó un multinúcleo a 700 m de profundidad en el MSO-BC. Las muestras seccionadas cada centímetro fueron liofilizadas y homogenizadas para cuantificar el contenido de ópalo biogénico (OB) y nitrógeno total (NT), a partir de los cuales se calculó la razón Si:N y el fósforo orgánico. El contenido de OB y NT se incrementó de manera constante y la razón Si:N tuvo un promedio y desviación estándar de 2.8±0.1, mientras que el Porg 1.1±0.9 mg kg-1. Los resultados sugieren que en el último milenio, la productividad primaria ha estado dominada por diatomeas producto del ácido silícico exportado del Golfo de California hacia el margen de Magdalena, hipótesis que tiene que ser validada, bajo un océano limitado por Fe, y no por nitratos y ortofosfatos

Variability of marine biological productivity in the northeastern Pacific over the past millennium

In this study we present new data of biogenic opal (BO), organic carbon (OC), and calcium carbonate (CaCO3) in a highresolution record from the western coast of Baja California Sur, Mexico. The variability of marine biological productivity in this area is dominated by El Niño and La Niña events on different time scales. The BO and OC contents showed a decrease between AD 1100 and 1400. From AD 1400 to the present, BO and OC showed a significant increase, indicating permanent upwelling conditions. The CaCO3 content showed an inverse correlation with OC, which suggests that the exported OC fluxes are a significant factor controlling CaCO3 dissolution in the sediment. The increase in BO and OC was synchronic with a decline in the number of El Niño events (6 ± 4 every 100 years) over the last 600 years of the millennium.

Coupled response of rainfall and denitrification to solar forcing during the Holocene in Alfonso Basin.

The bulk sedimentary δ15N record of Alfonso Basin displayed changes both from a regional source possibly associated with changes in the isotopic signal of NO3– dissolved in Subsurface Subtropical Water and from a climate source governed by solar forcing (total solar irradiance) over the strength of the North American monsoon (i.e., rainfall), causing intermediate water suboxia and promoting denitrification in the basin. High values of bulk sedimentary δ15N (maximum of 14.5‰) agree with increases in land-derived organic matter (from –14.8% to 49.2%) and with a decrease in terrigenous percentage (from 84.8% to 61.6%) during the Middle and Late Holocene, suggesting that increased rainfall and freshwater input promotes increased stratification of the water column, which inhibits vertical mixing and produces a reduction in oxygen content in an already oxygen-poor zone.

Sediment variations and littoral transport at La Victoria Beach, Cádiz, Spain

The evolution of La Victoria Beach, located in the province of Cádiz (Spain), was evaluated from February to October 2004 by comparing the lithology and slope of two beach sections: the northern or Final Victoria (FV) section and the southern or Hotel Victoria (HV) section. Textural parameters and CaCO3 content of 24 sediment samples were obtained, and littoral transport was determined by fluorescent tracers. Topographic profiles were measured every 15 days using a total station during low spring tides. The sediment samples were analyzed by the method of moments and their textural paramete (mean, asymmetry, sorting, and kurtosis) calculated. The textural analysis showed that the sediment in section FV during the study period was moderately well classified and extremely leptokurtic, whereas section HV had two sediment groups: fine sands near the breaker zone and very fine pebbles at the berm; however, the winter period was evident in both sections. The CaCO3 content varied between 3% and 9%, indicating beach instability. The direction of the littoral transport, in agreement with the region’s behavior, was NW–SE, and showed a displacement of 130 m at 0.29 m s–1.

Macroalgas submareales de la bahía de Todos Santos, Baja California, México Submareal macroalgae of the Todos Santos Bay, Baja California, Mexico

Con el fin de identificar y caracterizar la composición de especies de la zona submareal de la bahía de Todos Santos, Baja California, México; se realizaron muestreos de macroalgas marinas bentónicas en 7 sitios durante 1995-2000. Como resultado de 25 buceos Scuba entre 3 y 33 m de profundidad se encontraron 150 especies de macroalgas para el área de estudio; 10 son Chlorophyta, 26 Phaeophyta y 114 Rhodophyta. Del total, 47 son registros nuevos para el área de estudio y 2 de éstos, Faucheocolax attenuata Setchell y Minium parvum R.L. Moe, son nuevos para la flora marina del Pacífico de México. Se incluye una revisión de las investigaciones en las que se han considerado las macroalgas presentes en la bahía de Todos Santos y una discusión sobre la composición de las especies encontradas, su distribución vertical y reproducción, así como sobre las especies epífitas y parásitas del área.<br>In order to identify and characterize the species composition of the subtidal zone of the Todos Santos Bay, Baja California, Mexico, benthic marine macroalgae were sampled at 7 sites from 1995 to 2000. As a result of 25 scuba at derds for the study area, of which Faucheocolax attenuata Setchell and R.L Moe Minium parvum are new to the marine flora of Pacific Mexico. We include a research that consider the macroalpths between 3 and 33 m we found a total of 150 species of macroalgae for the study area, of which 10 are Chlorophyta, 26 Phaeophyta and 114 Rhodophyta; 47 species represent new recogae in the Todos Santos Bay and a discussion on the composition of species found, its vertical distribution and reproduction, particularly the species epiphytes and parasites present in the study area

Reply to the comment by Muñoz-Pérez and Gómez-Pina on “Sediment variations and litoral transport at La Victoria Beach, Spain"

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Acumulación de carbono orgánico total y carbonato de calcio en la zona de oxígeno mínimo del Pacífico nororiental mexicano

The distribution and preservation of the total organic carbon (TOC) and CaCO3 in marine sediments is important because its connection to the carbon cycle and the regulation of atmospheric CO2. Studies of the sinking, accumulation and carbon burial are limited and therefore it is necessary to know, identify and quantify the content of this element in marginal sediments. In the present work was determined the distribution and accumulation of TOC and CaCO3 in surface sediments with different conditions of oxygenation of the water column in the southwestern margin of the Peninsula of Baja California. The highest accumulation of TOC occurred over a wide oxygen minimum zone (OMZ), TOC gradually decreases towards the coastline. The deposition and accumulation of CaCO3 was preferentially higher in the region where the OMZ is narrow and deep. The 2 to 8% of TOC generated in the photic zone is preserved and buried in the sediment, being consistent with values calculated by models of the ocean biological pump. The TOC and CaCO3 accumulation suggest that this region is important and key in the global carbon cycle of the ocean, and contributed significantly in regulating the climate changes in the past.La distribución y preservación del carbono orgánico total (COT) y CaCO3 en sedimentos marinos es importante porque están vinculados al ciclo del carbono y a la regulación del CO2 atmosférico. Los estudios sobre el hundimiento, acumulación y enterramiento de carbono son limitados por lo que es necesario conocer, determinar y cuantificar el contenido de este elemento en sedimentos marginales. En el presente trabajo fue determinada la distribución y la acumulación del COT y CaCO3 en sedimentos superficiales con diferentes condiciones de oxigenación de la columna de agua en el margen suroccidental de la Península de Baja California. La mayor acumulación de COT ocurrió sobre una amplia zona de oxígeno mínimo (ZOM), el COT disminuye gradualmente hacia la línea de costa. La depositación y acumulación de CaCO3 fue preferentemente mayor en la región donde la ZOM es estrecha y profunda. El 2 a 8% del COT generado en la zona fótica es preservado y enterrado en el sedimento, siendo concordantes con valores calculados por modelos de la bomba biológica del océano. La acumulación de COT y CaCO3 sugiere que esta región es un componente importante y clave en el ciclo global del carbono en el océano, y contribuyó significativamente en la regulación de los cambios climáticos en el pasado

Slip History and the Role of the Agua Blanca Fault in the Tectonics of the North American–Pacific Plate Boundary of Southern California, USA and Baja California, Mexico

The Agua Blanca fault (ABF) is a west-northwest–trending oblique dextral-normal fault that defines the southern boundary of the Big Bend domain (BBD) of the Pacific–North American plate margin and the northern limit to the rigid Baja California microplate. Our geologic and geodetic studies demonstrate that finite slip on the ABF reaches a maximum of ∼11 km of nearly pure dextral strike slip in central portions of the fault, whereas the magnitude of displacement decreases and the proportion of extension increases in the sections to both the east and west. To the east, the ABF appears to die out before crossing into the San Pedro Mártir fault, with slip transferred onto a series of more northerly-trending, dip-slip faults. To the west, the ABF bifurcates to form the Santo Tomás fault (STF) in the Valle Santo Tomás section, where we measure ∼5 km of dextral offset for the ABF and ∼3 km estimated offset on the STF. And we report a measurement of ∼7 km of dextral offset on the ABF in the Punta Banda section. Small offset faults proximal to the ABF likely accommodate additional dextral shear in the western sections of the fault. The STF in the Valle Santo Tomás section and the ABF in the Punta Banda section exhibit 0.58 and 0.65 km of extensional heave, or ∼7% and 10% of the total displacement in each section, respectively. Block modeling based on geodetic data agrees well with geologic determinations of slip direction and reveals near perfect alignment of the central ABF with the relative block motion vectors and increased proportions of fault-perpendicular extension to both the east (3%–10%) and west (5%–13%). Based on our new estimates of the total offsets combined with existing slip rates, the ABF likely initiated between 3.3 and 1.5 Ma. This age range overlaps with those reported for other faults within the area of the BBD southwest of the San Andreas fault. The ABF has a more westerly orientation than the transpressional restraining-bend segment of the San Andreas, yet it accommodates transtensional shearing. This requires a reevaluation of the processes that control transpression and transtension within the BBD