The interplay between short-term, mild physicochemical forcing and plankton dynamics in a coastal area

Two intensive surveys were conducted in the coastal waters of Barcelona (northwest Mediterranean) to assess short-term variations of biological parameters in relation to environmental conditions. Surveys lasted 1 week, with three to four samplings per day, and were carried out in autumn and spring. Rather than exploring extreme events, we aimed to study the effects of regular low or moderate perturbations, such as meteorological fronts, on the dynamics of the system. We focused on two attributes: wave height, as a proxy for mechanical energy entering the system, and nutrient inputs, whose variability in total load and relative composition is a central characteristic of coastal areas. The effects of the temporal coupling or uncoupling of both factors were examined. Sudden nutrient fluxes uncoupled from water motion tended to favor bacteria and heterotrophic nanoflagellates, while their concurrence with some water column mixing shaped a favorable scenario for large autotrophs. Ultimately, these two distinct biological responses pointed toward two main disturbance scenarios: episodes of nutrient enrichment uncoupled from mixing, mostly related to episodic water spills from the nearby city that contributed to high relative loads of ammonium and organic compounds; and episodes of increased wind caused by passing weather fronts that promoted some water column mixing and the entrainment of nutrients from bottom sediments or from adjacent water masses

On some relationships between storms and plankton dynamics

6 pages, 4 figuresThe physico-chemical fields of the pelagic environment are constantly fluctuating at different spatial and temporal scales. Storms are extreme events of such fluctuations that cascade down to small scales to alter nutrient availability to microscopic algae or swimming and mating behaviour of motile plankton. Mediterranean storms sometimes are also responsible for the transport of micro and macronutrients from Saharan origin, albeit the significance for marine production is still under question. In coastal ecosystems, storms represent dissolved nutrient injections via run-off and resuspension that trigger planktonic succession events. Storms may also have a role in the development and mitigation of harmful algal blooms, events with economic and health consequences that are of growing societal concern. Based on laboratory experiments on the effects of turbulence on swimming behaviour and population growth of dinoflagellates, a conceptual sequence of events is proposed for bloom initiation. Overall, storms affect, directly or indirectly, the dynamics of plankton and hence ecosystem production and cannot be considered catastrophic or hazardous in this context. The full potential of such relationships will be evidenced once biological time series match the resolution and spatial coverage of meteorological and oceanic data. As the frequency and intensity of storms is subject to global change, future oceanic ecosystem production should be affected as wellThe project “Aproximación multiescalar al estudio de la variabilidad de la producción marina” (CSIC 200830I101) has made the writing of this paper possiblePeer Reviewe

Análisis de episodios de viento en un área costera: una herramienta para la estimación de la variabilidad en la turbulencia en estudios con plancton

[EN] Turbulence at different scales, from generation to dissipation, influences planktonic communities. Many experimental studies have recently been done to determine the effects of small-scale turbulence on plankton, but it is difficult to state the relevance of the findings since there is little unbiased information on turbulence variability in the sea. In this study, we use wind velocity data series from several meteorological stations located along the Catalan coast to estimate the spatial and temporal variability of small-scale turbulence in the upper ocean. Using a peaks-over-threshold approach, we develop a statistical model to assess the frequency of wind events as a function of their persistence and intensity. Finally, the wind speed data series are converted into turbulent energy dissipation rate estimates at 1 m depth to determine the general distribution of turbulence on the Catalan coast. Geographical variability is larger than seasonal variability in frequency and persistence of wind events, owing to differences in local relief. These statistical models developed for wind events combined with empirical relationships between wind and turbulence, are tools for estimating the occurrence and persistence of turbulent events at a given location and season. They serve to put into context the past, present and future studies of the effects of turbulence on coastal planktonic organisms and processes[ES] La turbulencia a diferentes escalas, desde su generación a su disipación, afecta a la comunidad planctónica. Recientemente el interés por los efectos de la turbulencia de escala pequeña se ha desarrollado mucho, pero es difícil establecer la importancia de tales estudios, puesto que no hay información completa de la variabilidad de la turbulencia en el mar. En el presente trabajo, usamos series de datos de viento provenientes de diversas estaciones meteorológicas situadas a lo largo del litoral catalán para estudiar la variabilidad espacio-temporal de la turbulencia de escala pequeña. Mediante una aproximación POT ("peaks-over-threshold"), desarrollamos un modelo estadístico para estimar la frecuencia de episodios de viento, en función de su persistencia e intensidad. Los datos de velocidad de viento son utilizados para estimar las tasas de disipación de la energía turbulenta a 1 metro de profundidad, con el fin de determinar la distribución general de la turbulencia en la costa catalana. Debido al relieve local, la variabilidad geográfica es mayor que la estacional en la frecuencia y persistencia de episodios de viento. El modelo estadístico desarrollado, junto con relaciones empíricas entre viento y turbulencia, pueden ser usados para estimar la ocurrencia y frecuencia de episodios en una localidad y estación dadas. Sirven para poner en contexto estudios pasados, presentes y futuros sobre los efectos de la turbulencia en el planctonO.G. had a Spanish CSIC-I3P fellowship sponsored by INNOVA oceanografía litoral, S.L. This study was supported by the EU project NTAP (EVK3-CT-2000-00022) and Spanish projects TURFI (REN2002-01591/MAR) and VARITEC (REN2003-08071-C02-01/MAR). This is ELOISE contribution 519/40Peer reviewe

Saharan dust deposition may affect phytoplankton growth in the mediterranean sea at ecological time scales

The surface waters of the Mediterranean Sea are extremely poor in the nutrients necessary for plankton growth. At the same time, the Mediterranean Sea borders with the largest and most active desert areas in the world and the atmosphere over the basin is subject to frequent injections of mineral dust particles. We describe statistical correlations between dust deposition over the Mediterranean Sea and surface chlorophyll concentrations at ecological time scales. Aerosol deposition of Saharan origin may explain 1 to 10% (average 5%) of seasonally detrended chlorophyll variability in the low nutrient-low chlorophyll Mediterranean. Most of the statistically significant correlations are positive with main effects in spring over the Eastern and Central Mediterranean, conforming to a view of dust events fueling needed nutrients to the planktonic community. Some areas show negative effects of dust deposition on chlorophyll, coinciding with regions under a large influence of aerosols from European origin. The influence of dust deposition on chlorophyll dynamics may become larger in future scenarios of increased aridity and shallowing of the mixed layerPostprint (published version