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

Microrheology reveals microscale viscosity gradients in planktonic systems

Microbial activity in planktonic systems creates a dynamic and heterogeneous microscale seascape that harbors a diverse community of microorganisms and ecological interactions of global significance. In recent decades great effort has been put into understanding this complex system, particularly focusing on the role of chemical patchiness, while overlooking a physical parameter that governs microbial life and is affected by biological activity: viscosity. Here we reveal spatial heterogeneity of viscosity in planktonic systems by using microrheological techniques that allow measurement of viscosity at length scales relevant to microorganisms. We show the viscous nature and the spatial extent of the phycosphere, the region surrounding phytoplankton. In ~45% of the phytoplankton cells analyzed we detected increases in viscosity that extended up to 30 μm away from the cell with up to 40 times the viscosity of seawater. We show also how these gradients of viscosity can be amplified around a lysing phytoplankton cell as its viscous contents leak away. Finally, we report conservative estimates of viscosity inside marine aggregates, hotspots of microbial activity, more than an order of magnitude higher than in seawater. Since the diffusivities of dissolved molecules, particles and microorganisms are inversely related to viscosity, microheterogeneity in viscosity alters the microscale distribution of microorganisms and their resources, with pervasive implications for the functioning of the planktonic ecosystem. Increasing viscosities impacts ecological interactions and processes, such as nutrient uptake, chemotaxis and particle encounter, that occur at the microscale but influence carbon and nutrient cycles at a global scale

Microrheology reveals microscale viscosity gradients in planktonic systems

Microbial activity in planktonic systems creates a dynamic and heterogeneous microscale seascape that harbours a diverse community of microorganisms and ecological interactions of global significance. In recent decades a great effort has been put into understanding this complex system, particularly focusing on the role of chemical patchiness, while overlooking a physical parameter that governs microbial life and is affected by biological activity: viscosity. Here we use microrheological techniques to measure viscosity at length scales relevant to microorganisms. Our results reveal the viscous nature and the spatial extent of the phycosphere, the microenvironment surrounding phytoplankton cells, and show heterogeneity in viscosity at the microscale. Such heterogeneity affects the distribution of chemicals and microorganisms, with pervasive and profound implications for the functioning of the planktonic ecosystem

Responses of coastal osmotrophic planktonic communities to simulated events of turbulence and nutrient load throughout a year

A year-long series of monthly experiments with laboratory enclosures were conducted with water from Blanes Bay (NW Mediterranean) to analyse the change in the short-time response of the osmotrophic planktonic community to simulated turbulence and nutrient input events. Both experimental factors triggered a relative increase of biomass in the enclosures, in terms of chlorophyll a, bacteria and particulate organic matter. Ratios of particulate organic nitrogen to phosphorus became lower in the water than in the sediment, although turbulence partially smoothed out this difference. Initial physico-chemical conditions significantly influenced the short-time responses to experimental forcing. The response to turbulence, in terms of chlorophyll a, was maximum in spring. The response to nutrient enrichment was found to be seasonal, and was correlated with photoperiod and temperature, and also in situ nitrate and silicate concentrations and Secchi depth, which are proxies of recent inputs of nutrients resulting from episodes of resuspension and river discharge. This study shows robust qualitative regularities in the response of the osmotrophic planktonic community to episodes of turbulence and nutrient enrichment, with quantitative variability throughout the year, depending mostly on the recent record of hydrodynamic forcing

A novel μCT analysis reveals different responses of bioerosion and secondary accretion to environmental variability

Corals build reefs through accretion of calcium carbonate (CaCO3) skeletons, but net reef growth also depends on bioerosion by grazers and borers and on secondary calcification by crustose coralline algae and other calcifying invertebrates. However, traditional field methods for quantifying secondary accretion and bioerosion confound both processes, do not measure them on the same time-scale, or are restricted to 2D methods. In a prior study, we compared multiple environmental drivers of net erosion using pre- and post-deployment micro-computed tomography scans (μCT; calculated as the % change in volume of experimental CaCO3 blocks) and found a shift from net accretion to net erosion with increasing ocean acidity. Here, we present a novel μCT method and detail a procedure that aligns and digitally subtracts pre- and post-deployment μCT scans and measures the simultaneous response of secondary accretion and bioerosion on blocks exposed to the same environmental variation over the same time-scale. We tested our method on a dataset from a prior study and show that it can be used to uncover information previously unattainable using traditional methods. We demonstrated that secondary accretion and bioerosion are driven by different environmental parameters, bioerosion is more sensitive to ocean acidity than secondary accretion, and net erosion is driven more by changes in bioerosion than secondary accretion

Influència de la variabilitat de la turbulència en la dinàmica del plàncton osmotròfic en una zona costanera

Memoria de tesis doctoral presentada por Òscar Guadayol Roig para optar al grado de Doctor por la Universitat Politècnica de Catalunya (UPC), realizada bajo la dirección de la Dra. Celia Marrasé Peña y del Dr. Francesc Peters del Institut de Ciències del Mar (ICM-CSIC).-- 146 pages[EN] Why is turbulence so important for plankton? Plankton is at the base of the marine trophic web. It can be defined from a hydrodynamic point of view, as the collection of organisms that live suspended in a body of water with a limited ability to regulate its position. Therefore plankton drifts with currents, tides and other water motions, which become environmental properties inherent to planktonic life. Planktonic organisms range several orders of magnitude in size, from tenths of microns to meters, although most are microscopic. They can feed on other particles (phagotrophs) or acquire dissolved substances (osmotrophs), incorporating them into particulate form. Osmotrophic plankton dominates the flux of carbon within the pelagic ecosystem, through CO2 fixation (primary production) and re-mineralization (respiration). In fact, the majority of primary production in aquatic systems, which accounts for roughly half of the global primary production (Field et al. 1998), is performed by osmotrophic plankton through photosynthesis. Parallely, bacterioplankton is responsible for the majority of organic carbon respired in the ocean (e.g. Rivkin and Legendre 2001). […][CAT] Per què la turbulència és tan important per al plàncton? El plàncton es troba a la base de la xarxa tròfica marina. Des d’un punt de vista hidrodinàmic es pot definir com el conjunt d’organismes que viuen en suspensió en una massa d’aigua amb una capacitat limitada per regular la seva posició. Per tant, el plàncton es desplaça seguint tot tipus de moviments de l’aigua, com ara les corrents o les marees, que esdevenen propietats ambientals inherents a la vida planctònica. La mida d’aquests organismes abasta varis ordres de magnitud, des d’unes dècimes de micròmetres fins a metres, encara que la majoria són microscòpics. Poden alimentar-se d’altres organismes, i llavors parlem de fagòtrofs, o prendre substàncies dissoltes del medi, i llavors ho fem d’osmòtrofs. El plàncton osmotròfic domina el flux de carboni a l’ecosistema pelàgic, a través de la fixació de CO2 (la producció primària) i la remineralització de matèria orgànica (respiració). De fet, la majoria de la producció primària en els sistemes aquàtics, que representa aproximadament la meitat de la producció primària global (Field et al. 1998), és duta a terme pel plàncton osmòtrofic a través de la fotosíntesi. […]This thesis has been mainly supported by the EU project NTAP (EVK3-CT-2000-00022) and by the Spanish projects VARITEC (REN2003-08071-C02-01/MAR) and TURFI (REN2002-01591/MAR). Òscar Guadayol had a Spanish I3P fellowship from the CSICPeer Reviewe

oscar-guadayol/chemotaxisIBM: Release for Zenodo

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