196 research outputs found
9. Las diversas facetas de El Niño y sus efectos en la costa del PerĂș
El fenĂłmeno El Niño es el modo dominante de la variabilidad interanual en el OcĂ©ano PacĂfico, resultando de un proceso de interacciĂłn entre el ocĂ©ano y la atmĂłsfera en el PacĂfico Tropical, Las Ășltimas Investigaciones demuestran que existen varias facetas de este fenĂłmeno que varĂan segĂșn las modalidades de interacciĂłn entre el ocĂ©ano y la atmosfera asĂ como sus ubicaciones. Existen por lo menos dos tipos de El Niño, con expresiones diferentes sobre la Temperatura Superficial del Mar en el Pacifico Tropical y en la costa de PerĂș: uno que se desarrolla en el Pacifico Central (tiende a estar asociado a condiciones oceĂĄnicas mĂĄs frĂas que favorecen el estado ĂĄrido de la costa peruana y condiciones oceĂĄnicas hypĂłxicas), y otro que se desarrolla en el Pacifico Este (que transforma la costa peruana en una âtĂpicaâ zona tropical, caracterizada por aguas costeras calientes y oxigenadas, y una lluvia intensa). Hoy en dĂa, los esfuerzos de investigaciĂłn para entender los mecanismos involucrados en los diferentes tipos de El Niño han sido reforzados, dado que, en las Ășltimas dĂ©cadas, se ha incrementado la frecuencia de ocurrencia de estos eventos en el Pacifico Central, sugiriĂ©ndose que podrĂa ser una consecuencia del cambio climĂĄtico. El perfeccionamiento de los modelos regionales acoplados tanto ocĂ©ano - atmosfera como ocĂ©ano - biogeoquĂmlco, tiene como objetivo mejorar la comprensiĂłn de la vulnerabilidad de la biosfera peruana al cambio climĂĄtico y proponer un paradigma que represente la bimodalidad de la variabilidad interanual en el Pacifico Tropical.El Niño est le mode dominant de la variabilitĂ© interannuelle dans lâocĂ©an Pacifique, rĂ©sultant dâun processus dâinteraction entre lâocĂ©an et lâatmosphĂ©re dans le Pacifique tropical. Les recherches rĂ©centes montrent quâil existe plusieurs facettes de ce phĂ©nomĂšne qui varient selon les modalitĂ©s dâinteraction entre lâocĂ©an et lâatmosphĂ©re et leurs emplacements. Il y a au moins deux types de El Niño, avec des expressions diffĂ©rentes sur la TempĂ©rature de surface dans le Pacifique tropical et le long de la cote du PĂ©rou: un qui se dĂ©roule dans le Pacifique central (associĂ© ĂĄ des conditions ocĂ©aniques froides qui favorisent lâĂ©tat aride de la cote pĂ©ruvienne et des conditions ocĂ©aniques dâhypoxie), et un autre qui a lieu dans le Pacifique oriental (qui transforme la cote pĂ©ruvienne en une zone tropicale «typique», caractĂ©risĂ© par des eaux cĂłtiĂ©res chaudes et oxygĂ©nĂ©es, et de fortes pluies). Aujourdâhui, les efforts de recherche pour comprendre les mĂ©canismes impliquĂ©s dans les diffĂ©rents types de El Niño ont Ă©tĂ© renforcĂ©s, en raison de lâaccroissement de la frĂ©quence dâoccurrence de ces Ă©vĂ©nements dans le Pacifique central au cours des derniĂšres dĂ©cennies a accru, suggĂ©rant quâll pourrait sâagir dâune consĂ©quence du changement dimatique. Lâoptimisation des modeles rĂ©gionaux couplĂ©s ocĂ©an - atmosphĂ©re et ocĂ©an - blogĂ©ochimiques, vise Ă amĂ©liorer la comprĂ©hension de la vulnĂ©rabilitĂ© de la biosphĂ©re pĂ©ruvienne au changement dimatique et de proposer un paradigme qui reprĂ©sente la bimodalitĂ© de la variabilitĂ© Interannuelle dans le Pacifique tropical.The El Niño phenomenon is the dominant mode of inter-annual variability in the Pacific Ocean, which results from the ÂĄnteraction between the ocean and atmosphere in the tropical Pacific. Recent research shows that there are several facets of this phenomenon, which vary according to the modalities of ÂĄnteraction between the ocean and atmosphere, as well as their locations. There are at least two types of El Niño with different expresslons on the sea surface temperature in the tropical Pacific and on the coast of Peru: one that takes place in the Central Pacific (which tends to be associated with colder oceanic conditions who favoring the aridity of the Peruvian coast and the ocean conditions hypoxic), and another that takes place in the Eastern Pacific (which transforms the Peruvian coast in a âtypicalâ tropical zone, with warm and oxygenated Coastal waters, and heavy rain). Nowadays, research efforts to understand the mechanisms involved in the different types of El Niño have been strengthened, since in recent decades has increased the frequency of these events in the Central Pacific, suggesting that ÂĄt might be a result of climate change. The ÂĄmprovement of both regional models coupled ocean - atmosphere and ocean - biogeochemical aims to Improve the understanding of the vulnerability of the Peruvian biosphere to climate change, and propose a paradigm that represents the bimodality of the Inter-annual variability in the tropical Pacific
Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific
Background: In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings: A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance: For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems
Large scale patterns in vertical distribution and behavior of mesopelagic scattering layers
Recent studies suggest that previous estimates of mesopelagic biomasses are severely biased, with
the new, higher estimates underlining the need to unveil behaviourally mediated coupling between shallow and deep ocean habitats. We analysed vertical distribution and diel vertical migration (DVM)
of mesopelagic acoustic scattering layers (SLs) recorded at 38 kHz across oceanographic regimes encountered during the circumglobal Malaspina expedition. Mesopelagic SLs were observed in all areas covered, but vertical distributions and DVM patterns varied markedly. The distribution of mesopelagic backscatter was deepest in the southern Indian Ocean (weighted mean daytime depth: WMD 590 m) and shallowest at the oxygen minimum zone in the eastern Pacific (WMD 350 m). DVM was evident in all areas covered, on average ~50% of mesopelagic backscatter made daily excursions from mesopelagic depths to shallow waters. There were marked differences in migrating proportions between the regions, ranging from ~20% in the Indian Ocean to ~90% in the Eastern Pacific. Overall the data suggest strong spatial gradients in mesopelagic DVM patterns, with implied ecological and biogeochemical consequences. Our results suggest that parts of this spatial variability can be explained by horizontal patterns in physical-chemical properties of water masses, such as oxygen, temperature and turbidity.En prensa2,927
Phytoplankton composition and abundance assessment in the Nador lagoon (Mediterranean coast of Morocco)
We evaluated phytoplankton abundance, composition and trophic state of the Nador lagoon (Morocco) on the basis of data taken in the period November 2007 to August 2008. Sampling was performed at 11 stations (bottle samples at 0.5 m depth and horizontal plankton net tows with mesh size of 20 mm). Among seven identified phytoplankton classes, diatoms and dinoflagellates dominated with 133 and 169 species, respectively. Frequent phytoplankton blooms were contributed by one to three species in the lagoon. Abundance and seasonality of phytoplankton characterized the Nador lagoon as a highly eutrophicated environment
Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean
Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earthâoceanâatmosphere dynamic exchange of elements. The ratiosâ dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from âŒ4.40 to 6.40 mmol:mol and âŒ6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (âŒ4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (âŒ7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratiosâ variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect
High-resolution imaging of human atherosclerotic carotid plaques with micro18F-FDG PET scanning exploring plaque vulnerability
FDG-PET can be used to identify vulnerable plaques in atherosclerotic disease. Clinical FDG-PET camera systems are restricted in terms of resolution for the visualization of detailed inflammation patterns in smaller vascular structures. The aim of the study is to evaluate the possible added value of a high-resolution microPET system in excised carotid plaques using FDG. In this study, 17 patients with planned carotid endarterectomy were included. Excised plaques were incubated in FDG and subsequently imaged with microPET. Macrophage presence in plaques was evaluated semi-quantitatively by immunohistochemistry. Plaque calcification was assessed additionally with CT and correlated to FDG uptake. Finally, FDG uptake and macrophage infiltration were compared with patient symptomatology. Heterogeneous distributions and variable intensities of FDG uptake were found within the plaques. A positive correlation between the distribution of macrophages and the FDG uptake (r = 0.68, P <.01) was found. A negative correlation was found between areas of calcifications and FDG uptake (r = -0.84, P <.001). Ratio FDG(max) values as well as degree of CD68 accumulation were significantly higher in CVA patients compared with TIA or amaurosis fugax patients (P <.05) and CVA patients compared with asymptomatic patients (P <.05). This ex vivo study demonstrates that excised carotid plaques can be visualized in detail using FDG microPET. Enhancement of clinical PET/CT resolution for similar imaging results in patients is needed
Reexamination of the species assignment of Diacavolinia pteropods using DNA barcoding
© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 8 (2013): e53889, doi:10.1371/journal.pone.0053889.Thecosome pteropods (Mollusca, Gastropoda) are an ecologically important, diverse, and ubiquitous group of holoplanktonic animals that are the focus of intense research interest due to their external aragonite shell and vulnerability to ocean acidification. Characterizing the response of these animals to low pH and other environmental stressors has been hampered by continued uncertainty in their taxonomic identification. An example of this confusion in species assignment is found in the genus Diacavolinia. All members of this genus were originally indentified as a single species, Cavolinia longirostris, but over the past fifty years the taxonomy has been revisited multiple times; currently the genus comprises 22 different species. This study examines five species of Diacavolinia, including four sampled in the Northeast Atlantic (78 individuals) and one from the Eastern tropical North Pacific (15 individuals). Diacavolina were identified to species based on morphological characteristics according to the current taxonomy, photographed, and then used to determine the sequence of the âDNA barcodingâ region of the cytochrome c oxidase subunit I (COI). Specimens from the Atlantic, despite distinct differences in shell morphology, showed polyphyly and a genetic divergence of <3% (K2P distance) whereas the Pacific and Atlantic samples were more distant (~19%). Comparisons of Diacavolinia spp. with other Cavolinia spp. reveal larger distances (~24%). These results indicate that specimens from the Atlantic comprise a single monophyletic species and suggest possible species-level divergence between Atlantic and Pacific populations. The findings support the maintenance of Diacavolinia as a separate genus, yet emphasize the inadequacy of our current taxonomic understanding of pteropods. They highlight the need for accurate species identifications to support estimates of biodiversity, range extent and natural exposure of these planktonic calcifiers to environmental variability; furthermore, the apparent variation of the pteropods shell may have implications for our understanding of the speciesâ sensitivity to ocean acidification.This material is based upon work supported by the National Science Foundation under Grant Number OCE-0928801. AEM was funded through the WHOI Postdoctoral Scholarship. Support to LBB was provided by the College of Liberal Arts & Sciences, University of Connecticut; and by the Census of Marine Life/Alfred P. Sloan Foundation
Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea
Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20â23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles
Coastal Upwelling Supplies Oxygen-Depleted Water to the Columbia River Estuary
Low dissolved oxygen (DO) is a common feature of many estuarine and shallow-water
environments, and is often attributed to anthropogenic nutrient enrichment from
terrestrial-fluvial pathways. However, recent events in the U.S. Pacific
Northwest have highlighted that wind-forced upwelling can cause naturally
occurring low DO water to move onto the continental shelf, leading to
mortalities of benthic fish and invertebrates. Coastal estuaries in the Pacific
Northwest are strongly linked to ocean forcings, and here we report observations
on the spatial and temporal patterns of oxygen concentration in the Columbia
River estuary. Hydrographic measurements were made from transect (spatial
survey) or anchor station (temporal survey) deployments over a variety of wind
stresses and tidal states during the upwelling seasons of 2006 through 2008.
During this period, biologically stressful levels of dissolved oxygen were
observed to enter the Columbia River estuary from oceanic sources, with minimum
values close to the hypoxic threshold of 2.0 mg Lâ1. Riverine
water was consistently normoxic. Upwelling wind stress controlled the timing and
magnitude of low DO events, while tidal-modulated estuarine circulation patterns
influenced the spatial extent and duration of exposure to low DO water. Strong
upwelling during neap tides produced the largest impact on the estuary. The
observed oxygen concentrations likely had deleterious behavioral and
physiological consequences for migrating juvenile salmon and benthic crabs.
Based on a wind-forced supply mechanism, low DO events are probably common to
the Columbia River and other regional estuaries and if conditions on the shelf
deteriorate further, as observations and models predict, Pacific Northwest
estuarine habitats could experience a decrease in environmental quality
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