Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system

Eastern boundary upwelling systems (EBUS) are regions of high primary production often associated with oxygen minimum zones (OMZs). They represent key regions for the oceanic nitrogen (N) cycle. By exporting organic matter (OM) and nutrients produced in the coastal region to the open ocean, EBUS can play an important role in sustaining primary production in subtropical gyres. However, losses of fixed inorganic N through denitrification and anammox processes take place in oxygen depleted environments such as EBUS, and can potentially mitigate the role of these regions as a source of N to the open ocean. EBUS can also represent a considerable source of nitrous oxide (N2O) to the atmosphere, affecting the atmospheric budget of N2O. In this paper a 3-D coupled physical/biogeochemical model (ROMS/BioEBUS) is used to investigate the N budget in the Namibian upwelling system. The main processes linked to EBUS and associated OMZs are taken into account. The study focuses on the northern part of the Benguela upwelling system (BUS), especially the Walvis Bay area (between 22° S and 24° S) where the OMZ is well developed. Fluxes of N off the Walvis Bay area are estimated in order to understand and quantify (1) the total N offshore export from the upwelling area, representing a possible N source that sustains primary production in the South Atlantic subtropical gyre; (2) export production and subsequent losses of fixed N via denitrification and anammox under suboxic conditions (O2 < 25 mmol O2 m−3); and (3) the N2O emission to the atmosphere in the upwelling area. In the mixed layer, the total N offshore export is estimated as 8.5 ± 3.9 × 1010 mol N yr−1 at 10° E off the Walvis Bay area, with a mesoscale contribution of 20%. Extrapolated to the whole BUS, the coastal N source for the subtropical gyre corresponds to 0.1 ± 0.04 mol N m−2 yr−1. This N flux represents a major source of N for the gyre compared with other N sources, and contributes 28% of the new primary production estimated for the South Atlantic subtropical gyre. Export production (16.9 ± 1.3 × 1010 mol N yr−1) helps to maintain an OMZ off Namibia in which coupled nitrification, denitrification and anammox processes lead to losses of fixed N and N2O production. However, neither N losses (0.04 ± 0.025 × 1010 mol N yr−1) nor N2O emissions (0.03 ± 0.002 × 1010 mol N yr−1) significantly impact the main N exports of the Walvis Bay area. The studied area does not significantly contribute to N2O emissions (0.5 to 2.7%) compared to the global coastal upwelling emissions. Locally produced N2O is mostly advected southward by the poleward undercurrent

Giant Hydrogen Sulfide Plume in the Oxygen Minimum Zone off Peru Supports Chemolithoautotrophy

In Eastern Boundary Upwelling Systems nutrient-rich waters are transported to the ocean surface, fuelling high photoautotrophic primary production. Subsequent heterotrophic decomposition of the produced biomass increases the oxygen-depletion at intermediate water depths, which can result in the formation of oxygen minimum zones (OMZ). OMZs can sporadically accumulate hydrogen sulfide (H2S), which is toxic to most multicellular organisms and has been implicated in massive fish kills. During a cruise to the OMZ off Peru in January 2009 we found a sulfidic plume in continental shelf waters, covering an area >5500 km2, which contained ~2.2×104 tons of H2S. This was the first time that H2S was measured in the Peruvian OMZ and with ~440 km3 the largest plume ever reported for oceanic waters. We assessed the phylogenetic and functional diversity of the inhabiting microbial community by high-throughput sequencing of DNA and RNA, while its metabolic activity was determined with rate measurements of carbon fixation and nitrogen transformation processes. The waters were dominated by several distinct γ-, δ- and ε-proteobacterial taxa associated with either sulfur oxidation or sulfate reduction. Our results suggest that these chemolithoautotrophic bacteria utilized several oxidants (oxygen, nitrate, nitrite, nitric oxide and nitrous oxide) to detoxify the sulfidic waters well below the oxic surface. The chemolithoautotrophic activity at our sampling site led to high rates of dark carbon fixation. Assuming that these chemolithoautotrophic rates were maintained throughout the sulfidic waters, they could be representing as much as ~30% of the photoautotrophic carbon fixation. Postulated changes such as eutrophication and global warming, which lead to an expansion and intensification of OMZs, might also increase the frequency of sulfidic waters. We suggest that the chemolithoautotrophically fixed carbon may be involved in a negative feedback loop that could fuel further sulfate reduction and potentially stabilize the sulfidic OMZ water

Sequential Isotopic Signature Along Gladius Highlights Contrasted Individual Foraging Strategies of Jumbo Squid (Dosidicus gigas)

International audienceBackground: Cephalopods play a major role in marine ecosystems, but knowledge of their feeding ecology is limited. In particular, intra- and inter-individual variations in their use of resources has not been adequatly explored, although there is growing evidence that individual organisms can vary considerably in the way they use their habitats and resources. Methodology/Principal Findings: Using d13C and d15N values of serially sampled gladius (an archival tissue), we examined high resolution variations in the trophic niche of five large (.60 cm mantle length) jumbo squids (Dosidicus gigas) that were collected off the coast of Peru. We report the first evidence of large inter-individual differences in jumbo squid foraging strategies with no systematic increase of trophic level with size. Overall, gladius d13C values indicated one or several migrations through the squid's lifetime (,8-9 months), during which d15N values also fluctuated (range: 1 to 5%). One individual showed an unexpected terminal 4.6% d15N decrease (more than one trophic level), thus indicating a shift from higher- to lower-trophic level prey at that time. The data illustrate the high diversity of prey types and foraging histories of this species at the individual level. Conclusions/Significance: The isotopic signature of gladii proved to be a powerful tool to depict high resolution and ontogenic variations in individual foraging strategies of squids, thus complementing traditional information offered by stomach content analysis and stable isotopes on metabolically active tissues. The observed differences in life history strategies highlight the high degree of plasticity of the jumbo squid and its high potential to adapt to environmental changes

9. Las diversas facetas de El Niño y sus efectos en la costa del Perú

El fenómeno El Niño es el modo dominante de la variabilidad interanual en el Océano Pacífico, resultando de un proceso de interacción entre el océano y la atmósfera en el Pacífico Tropical, Las últimas Investigaciones demuestran que existen varias facetas de este fenómeno que varían según las modalidades de interacción entre el océano y la atmosfera así 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 Perú: uno que se desarrolla en el Pacifico Central (tiende a estar asociado a condiciones oceánicas más frías que favorecen el estado árido de la costa peruana y condiciones oceánicas hypóxicas), y otro que se desarrolla en el Pacifico Este (que transforma la costa peruana en una “típica” zona tropical, caracterizada por aguas costeras calientes y oxigenadas, y una lluvia intensa). Hoy en día, los esfuerzos de investigación para entender los mecanismos involucrados en los diferentes tipos de El Niño han sido reforzados, dado que, en las últimas décadas, se ha incrementado la frecuencia de ocurrencia de estos eventos en el Pacifico Central, sugiriéndose que podría ser una consecuencia del cambio climático. El perfeccionamiento de los modelos regionales acoplados tanto océano - atmosfera como océano - biogeoquímlco, tiene como objetivo mejorar la comprensión de la vulnerabilidad de la biosfera peruana al cambio climático y proponer un paradigma que represente la bimodalidad de la variabilidad interanual en el Pacifico Tropical.El Niño est le mode dominant de la variabilité interannuelle dans l’océan Pacifique, résultant d’un processus d’interaction entre l’océan et l’atmosphére dans le Pacifique tropical. Les recherches récentes montrent qu’il existe plusieurs facettes de ce phénomène qui varient selon les modalités d’interaction entre l’océan et l’atmosphére et leurs emplacements. Il y a au moins deux types de El Niño, avec des expressions différentes sur la Température de surface dans le Pacifique tropical et le long de la cote du Pérou: un qui se déroule dans le Pacifique central (associé á des conditions océaniques froides qui favorisent l’état aride de la cote péruvienne et des conditions océaniques d’hypoxie), et un autre qui a lieu dans le Pacifique oriental (qui transforme la cote péruvienne en une zone tropicale «typique», caractérisé par des eaux cótiéres chaudes et oxygénées, et de fortes pluies). Aujourd’hui, les efforts de recherche pour comprendre les mécanismes impliqués dans les différents types de El Niño ont été renforcés, en raison de l’accroissement de la fréquence d’occurrence de ces événements dans le Pacifique central au cours des dernières décennies a accru, suggérant qu’ll pourrait s’agir d’une conséquence du changement dimatique. L’optimisation des modeles régionaux couplés océan - atmosphére et océan - blogéochimiques, vise à améliorer la compréhension de la vulnérabilité de la biosphére péruvienne au changement dimatique et de proposer un paradigme qui représente la bimodalité de la variabilité 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 ¡nteraction 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 ¡nteraction 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 “typical” 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 ¡t might be a result of climate change. The ¡mprovement 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

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

Utility of Atherosclerosis Imaging in the Evaluation of High-Density Lipoprotein–Raising Therapies

Decreased level of high density-lipoprotein cholesterol (HDL-C) is a rigorous predictor for future cardiovascular events. Much effort is being made to develop HDL-C–raising pharmacotherapies in the attempt to avert the pandemic of atherosclerotic disease. Important properties by which HDL-C–raising compounds are effective involve improvement of cholesterol uptake from macrophages in plaque for transport back to the liver, improvement of endothelial function, and anti-inflammatory effects. Vascular imaging can aid in the determination which HDL-C–raising compounds are effective. Ultrasound and MRI have proved suitable for assessment of structural changes of the vessel wall. Ultrasound can also be used or assessment of endothelial function. 18F-fluordeoxyglucose positron emission tomography has opened up the possibility to assess vessel wall inflammation. In this article we discuss these various imaging techniques and how they can assess efficacy as well as provide pathophysiologic information on the mechanism of action of novel HDL-C–raising drugs

Nitrous oxide as a function of oxygen and archaeal gene abundance in the North Pacific

Natural Environment Research Council (NERC) (NE/E01559X/1)

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

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

Copernicus Marine Service Ocean State Report

This is the final version. Available from Taylor & Francis via the DOI in this record