Annual patterns of nutrients and chlorophyll in a subtropical coastal lagoon under the upwelling influence (SW of Baja-California Peninsula)

10 páginas, 6 figuras, 1 tablaThe coastal lagoon of Bahía-Magdalena, located on the west coast of the Peninsula of Baja-California, is a subtropical ecosystem with an arid climate and very little freshwater input. During the 2005–2011 period the thermohaline properties varied between cold and warm half-yearly periods. They were influenced by the Transitional Water mass transported by the South California Current from February to July and by the Subtropical Surface Water from August to January. The nutrient concentrations increased (viz up to 16 μM of nitrate) from March to June, when the upwelling index was the highest. Similarly, the inter-annual variation of chlorophyll-a showed a six-monthly pattern with the highest average monthly concentrations being found in June (5 mg m−3in situ or 8 mg m−3 based on satellite information) and the lowest in December–January. A spatial zoning was also observed in the lagoon with a shallow inner zone that is warmer and richer in chlorophyll-a than the deeper closed mouth area. In the Bahía-Magdalena lagoon a spatial-temporal division into two zones and two seasons was repeated year after year with only minor differences. During the first semester in the outer zone, years 2006 and 2007 were colder and nutrient rich while 2010 was warmer, according to the upwelling conditions in the Southern California Region. Hence, among the coastal lagoons that present a prevailing marine influence, the coastal system of Bahía-Magdalena corresponds to an unusual type of subtropical coastal lagoon where the nutrient input is mainly due to upwelling phenomena.his article was supported by the SIP Mexican projects of the Instituto Politécnico Nacional from 2005 to 2011 in cooperation with the Spanish project CTM2011-28792-C02 financed by the ‘Ministerio de Economía y Competitividad’. We are very grateful to the Mexican COFAA (IPN) organism and EDI program for their grants and to the Mexican governmental agency CONACYT for financing the sabbatical (ref. 169030) of Dr. Rafael Cervantes-Duarte at the IIM (CSIC) of Spain during 2012.Peer reviewe

Cambios temporales en los componentes y los flujos de la materia en hundimiento en Cuenca Alfonso, Bahía de La Paz, durante el período 2002-2005

Para mejorar el conocimiento sobre la variación en magnitud y composición de los flujos sedimentarios y los procesos que la controlan – así como para documentar la existencia de ciclos estacionales y/o variaciones interanuales – se instaló una trampa de sedimentos de series de tiempo a 50 metros del fondo en Cuenca Alfonso, una depresión localizada al norte de Bahía de La Paz, con una profundidad máxima de 410 m. Los flujos de masa total (FMT), carbono orgánico (Corg) e inorgánico (CaCO3), ópalo (BSiO2) y por derivación, el flujo litogénico, fueron determinados a partir de 118 muestras, obtenidas en doce cruceros oceanográficos, y que constituyen cuatro años de recolección casi continua (85% de cobertura temporal). Estas muestras representan periodos independientes con una resolución de, generalmente, 7-8 días y excepcionalmente de 14-16 días. El FMT fue dominado -en el 75% de las muestras representó más de la mitad del mismo- por las partículas litogénicas (prom. 56± 10%). El análisis de los vientos sugiere que éstos son un factor importante en la regulación de la entrada de material terrígeno en esta zona semiárida y con escasa precipitación. Sin embargo, no se encontró una fuerte correlación entre la intensidad-dirección del viento con los flujos litogénicos lo que indica que otros factores, tales como la agregación biogénica de las grandes partículas que se hunden, pueden estar involucrados. Cuantitativamente, el CaCO3 fue el componente biogénico predominante (20%) seguido por el BSiO2 (14%) y el Corg (5.6%). Estos componentes mostraron variaciones importantes (> 1 D. Estd.) aún de una semana a otra. En general, la variabilidad de los flujos siguió un patrón semejante: valores por debajo del promedio se evidenciaron usualmente en primavera y verano, valores máximos en otoño con picos secundarios ocasionalmente en invierno. Existe variación considerable de los patrones de un año a otro, sin embargo, cuatro largas oscilaciones fueron observadas en 2002, mientras que, durante 2005, un fuerte decremento general particularmente de los componentes litogénico y de ópalo. Esto parece asociado a una disminución significativa del número de las rachas de vientos > 4.5 m s-1. El flujo de masa total (FMT) fluctuó entre 0.17 y 3.9 g m-2 d-1 y el promedio (0.76 g m-2d-1) equivale a un tasa de acumulación de sedimento de 0.4 mm a-1, similar a la reportada por estudios radiométricos sobre núcleos de sedimento. Esto indica que la trampa de sedimentos opera eficientemente en esta cuenca de sedimentación natural. Los huracanes son un caso especial. Los dos observados en 2003 inducen una sedimentación mucho más intensa del componente litogénico, el cual persiste por más de dos semanas. 46% del flujo litogénico promedio anual se recolectó en 29 días influenciados por los huracanes “Ignacio” y “Marty”. Los flujos del material marino, también se incrementaron lo que sugiere una intensificación de la productividad, particularmente de los cocolitofóridos. Comparando con otras cuencas marginales son claras las diferencias en magnitud, composición y estacionalidad: flujos dos y cuatro veces más altos de BSiO2 son registrados en Cuenca Guaymas y Santa Barbara, respectivamente, mientras que en Cuenca Alfonso el CaCO3 domina la sedimentación biogénica. ABSTRACT In order to improve our understanding of the variations in the magnitude and composition of the sedimentation fluxes and the processes that control them – as well as documenting seasonal cycles and interannual variations – a time-series sediment trap was installed 50 meters above the seafloor in Cuenca Alfonso, a 410 m deep depression in the northern part of Bahía de La Paz. Total mass fluxes (TMF), organic carbon (Corg) and inorganic carbon (CaCO3), biogenic silica (BSiO2) and, by difference, the lithogenic flux, were determined from 118 samples recovered during 12 oceanographic cruises. These represent 4 years of almost continuous collection (85% of the time span). The samples were generally of 7-8 day or, exceptionally, 14-16 day periods. The TMF was dominated by lithogenic particles – in 75% of the samples it amounted to more than half (average 56± 10%). Analysis of wind records suggest that this is an important factor regulating the input of terrigenous material in this semiarid zone with little precipitation. There is, however, no strong correlation between wind direction and intensity and the lithogenic flux, indicating that other factors, such as the biogenic aggregation of the large particles that sediment, which may be involved. Quantitatively, CaCO3 was the principal biogenic component (20%) followed by BSiO2 (14%) and Corg (5.6%). All of these components show important variations (>1 StDev) even from one week to the next. In general, the variability in the fluxes follows a similar pattern: below average values are usually encountered in spring and summer, with maximums in autumn and occasionally secondary peaks in winter. There is considerable variation in the patterns from year to year, however four broad oscillations are observed in 2002, while, during 2005, a strong general decrease in flux, particularly for the lithogenic and biogenic silica components. This appears to be associated with a large decrease in the number of wind gusts > 4.5 m s-1. The TMF fluctuated between 0.17 and 3.9 g m-2 d-1. The mean (0.76 g m-2d-1) is equivalent to a sediment accumulation rate of 0.4 mm y-1, similar to that reported from radiometric studies of the basin sediments. This indicates that the sediment trap operated efficiently in this natural sedimentation basin. Hurricanes were a special case. The two observed in 2003 induced much more intense sedimentation of the lithogenic component that persists for over two weeks. 46% of the average annual lithogenic fluxes sedimented during the 29 days influenced by the hurricanes “Ignacio” and “Marty”. Fluxes of marine components also increased, suggesting intensification of productivity, particularly that of coccolithophorids. There are clear differences in magnitude, composition and seasonality of fluxes in Cuenca Alfonso compared with other marginal basins. Fluxes 2 and 4 times greater for BSiO2 are reported from Guaymas and Santa Barbara Basins, respectively, while in Alfonso it is the CaCO3 that dominates the biogenic sedimentation

Cambios temporales en los componentes y los flujos de la materia en hundimiento en Cuenca Alfonso, Bahía de La Paz, durante el período 2002-2005

impreso y PD

Relevance of new and regenerated nitrogen sources in the water column of magdalena bay (SW baja California Peninsula), Mexico

6 páginas, 3 figurasSix bimonthly surveys during 2007 were carried out in Magdalena Bay (Mexico) during spring tide conditions. Spatiotemporal variations of temperature, salinity, nitrite, nitrate, ammonium, phosphate and chlorophyll-a were analyzed in the Bay. During spring-early summer (April-June) seawaters were colder and richer in new nutrients and chlorophyll-a than autumn and winter (February and October-December). The coastal upwelling during spring-early summer contributes with new nutrients to the Bay, whereas bottom-recycled nutrients should be the main input during the autumn-winter period. Thus, nutrients availability, dissolved inorganic nitrogen and phosphate, promote a seasonal pattern of phytoplankton biomass in Magdalena Bay.El presente trabajo se realizó con el apoyo del Instituto Politécnico Nacional a través del proyecto SIP-20070265Peer reviewe

A multi-Species Microalgae Bloom in Bahia de La Paz, Gulf of California, México (June 2008)

Red tides Patches were observed in Bahía de La Paz in June 17 and 18 of 2008. According to temperature and wind data this bloom occurred under upwelling-like conditions. Examination of the red tide samples showed that the ciliate Myrionecta rubra and two naked dinoflagellates Gyrodinium instriatum and Katodinium glaucum as the main species responsible for this bloom Total density (microalgae and ciliate) at the sampling stations was similar on both days, varying from 4607 × 103 to cells L-1 to 4976 × 103 cells L-1 on the first day, and from 4172 × 103 cells L-1 to 5024 × 103 cells L-1 on the second day. Phytoplankton biomass (chlorophyll a) observed during the first day of the bloom was 1.5 mg m-3. Dinoflagellates and diatoms were the most numerically important phytoplankton groups. The phytoplankton community showed a high species richness, particularly heterotrophic dinoflagellates and ebridians. The ecological importance of the heterotrophic component of naked dinoflagellates and the ebriids for this bay is discussed

A multi-Species Microalgae Bloom in Bahia de La Paz, Gulf of California, México (June 2008)

Red tides Patches were observed in Bahía de La Paz in June 17 and 18 of 2008. According to temperature and wind data this bloom occurred under upwelling-like conditions. Examination of the red tide samples showed that the ciliate Myrionecta rubra and two naked dinoflagellates Gyrodinium instriatum and Katodinium glaucum as the main species responsible for this bloom Total density (microalgae and ciliate) at the sampling stations was similar on both days, varying from 4607 × 103 to cells L-1 to 4976 × 103 cells L-1 on the first day, and from 4172 × 103 cells L-1 to 5024 × 103 cells L-1 on the second day. Phytoplankton biomass (chlorophyll a) observed during the first day of the bloom was 1.5 mg m-3. Dinoflagellates and diatoms were the most numerically important phytoplankton groups. The phytoplankton community showed a high species richness, particularly heterotrophic dinoflagellates and ebridians. The ecological importance of the heterotrophic component of naked dinoflagellates and the ebriids for this bay is discussed