Towards a merged satellite and in situ fluorescence ocean chlorophyll product

Understanding the ocean carbon cycle requires a precise assessment of phytoplankton biomass in the oceans. In terms of numbers of observations, satellite data represent the largest available data set. However, as they are limited to surface waters, they have to be merged with in situ observations. Amongst the in situ data, fluorescence profiles constitute the greatest data set available, because fluorometers have operated routinely on oceanographic cruises since the 1970s. Nevertheless, fluorescence is only a proxy of the total chlorophyll <i>a</i> concentration and a data calibration is required. Calibration issues are, however, sources of uncertainty, and they have prevented a systematic and wide range exploitation of the fluorescence data set. In particular, very few attempts to standardize the fluorescence databases have been made. Consequently, merged estimations with other data sources (e.g. satellite) are lacking. <br><br> We propose a merging method to fill this gap. It consists firstly in adjusting the fluorescence profile to impose a zero chlorophyll <i>a</i> concentration at depth. Secondly, each point of the fluorescence profile is then multiplied by a correction coefficient, which forces the chlorophyll <i>a</i> integrated content measured on the fluorescence profile to be consistent with the concomitant ocean colour observation. The method is close to the approach proposed by Boss et al. (2008) to correct fluorescence data of a profiling float, although important differences do exist. To develop and test our approach, in situ data from three open ocean stations (BATS, HOT and DYFAMED) were used. Comparison of the so-called "satellite-corrected" fluorescence profiles with concomitant bottle-derived estimations of chlorophyll <i>a</i> concentration was performed to evaluate the final error (estimated at 31%). Comparison with the Boss et al. (2008) method, using a subset of the DYFAMED data set, demonstrated that the methods have similar accuracy. The method was applied to two different data sets to demonstrate its utility. Using fluorescence profiles at BATS, we show that the integration of "satellite-corrected" fluorescence profiles in chlorophyll <i>a</i> climatologies could improve both the statistical relevance of chlorophyll <i>a</i> averages and the vertical structure of the chlorophyll <i>a</i> field. We also show that our method could be efficiently used to process, within near-real time, profiles obtained by a fluorometer deployed on autonomous platforms, in our case a bio-optical profiling float. The application of the proposed method should provide a first step towards the generation of a merged satellite/fluorescence chlorophyll <i>a</i> product, as the "satellite-corrected" profiles should then be consistent with satellite observations. Improved climatologies with more consistent satellite and in situ data are likely to enhance the performance of present biogeochemical models

Recent changes in avalanche activity in the French Alps and their links with climatic drivers: an overview

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGEInternational audienceThis paper synthetizes our ongoing work on relations between natural avalanche activity and climate change in the French Alps and subregions. Firm results mainly concern occurrences, runout altitudes and high return period avalanches on long time scales (averages over “full” winters and winter-spring sub-seasons) since ~1950. Work in progress concerns extrapolation under future climate, shorter time scales (avalanche cycles), and more generally risk assessment under unstationarity. The strength and interest of the approach rely on the exceptional quality/quantity of avalanche records and snow and weather covariates available/used and on the development of specific statistical treatment methods

Consorciação das culturas de erva-mate (Ilex paraguariensis A. St Hilaire) e feijão (Phaseolus vulgaris L.).

Este trabalho foi executado com o objetivo de medir-se o rendimento do sistema agroflorestal erva-mate/feijao (Ilex paraguariensis / Phaseolus vulgaris), comparando-se três densidades da cultura agrícola (quatro, cinco e seis linhas) e dois tipos de mudas de erva-mate (normais e pseudo-estacas), plantadas a 3x1 m. Após um ano de consórcio, com duas colheitas de feijão (safra das águas e da seca), obteve-se maior sobrevivência no campo utilizando-se pseudo-estacas (89% contra 75% das mudas normais) recomendando-se esta técnica de plantação para a espécie estudada. A produção de feijão não foi significativamente diferenciada pelas densidades populacionais, recomendando-se o uso de quatro linhas de cultura, em função da influência dos espaçamentos mais densos sobre a sobrevivência da ervamate. A altura das plantas não foi afetada pelas alternativas de consórcio empregadas. O sistema possibilitou rendas adicionais com a exploração da cultura agrícola, quase cobrindo os custos variáveis de implantação da cultura de erva-mate

The potential use of geostationary MTG/FCI to retrieve chlorophyll-<i>a</i> concentration at high temporal resolution for the open oceans

In a few years, the Flexible Combined Imager (FCI) on-board Meteosat Third Generation will provide images of European Seas, the Atlantic Ocean, and the Mediterranean Sea every 2.5 min (regions above 30° N) or 10 min (full disk). Although dedicated to meteorological applications, this sensor has blue, green, and red spectral bands allowing to consider the adaptation of a band-ratio algorithm to retrieve chlorophyll-a concentration (chl-a). However, the radiometric specification of the FCI sensor is far from the minimum requirement recommended for ocean colour sensors and the validity of FCI data for oceanic applications is not clear. This present article aims to determine if, and under which conditions, chl-a could be estimated from FCI data. From the National Aeronautics and Space Administration bio-Optical Marine Algorithm data set in situ data set, a blue green band-ratio algorithm adapted to FCI spectral characteristics is proposed. Then, the impact of FCI radiometric noise on chl-a estimations is investigated in detail. Results show that noise-induced chl-a error increases with chl-a and solar zenith angle. For a chl-a estimation based on a unique pixel, this error ranges between 20% and 100% which prevents any direct utilisation and suggests that it is necessary to degrade the spatio-temporal resolution to obtain an acceptable noise-related uncertainty on chl-a. With a spatial (9 pixels) and temporal (1 h) averaging process, chl-a can be estimated with a noise-induced error less than 10% for chl-a up to 5 mg m−3 and solar zenith angle lower than 60°. Our analysis also showed that the noise-related error associated to the atmospheric correction process can be neglected compared to the radiometric noise of the visible bands themselves if it is assumed that aerosol type is uniform over large areas (9 km × 9 km boxes)

The 2006 July 17 Java (Indonesia) tsunami from satellite imagery and numerical modelling: A single or complex source?

The Mw 7.8 2006 July 17 earthquake off the southern coast of Java, Indonesia, has been responsible for a very large tsunami causing more than 700 casualties. The tsunami has been observed on at least 200 km of coastline in the region of Pangandaran (Wes

Autonomic pain responses during sleep: a study of heart rate variability

The autonomic nervous system (ANS) reacts to nociceptive stimulation during sleep, but whether this reaction is contingent to cortical arousal, and whether one of the autonomic arms (sympathetic/parasympathetic) predominates over the other remains unknown. We assessed ANS reactivity to nociceptive stimulation during all sleep stages through heart rate variability, and correlated the results with the presence of cortical arousal measured in concomitant 32-channel EEG. Fourteen healthy volunteers underwent whole-night polysomnography during which nociceptive laser stimuli were applied over the hand. RR intervals (RR) and spectral analysis by wavelet transform were performed to assess parasympathetic (HF(WV)) and sympathetic (LF(WV) and LF(WV)/HF(WV) ratio) reactivity. During all sleep stages, RR significantly decreased in reaction to nociceptive stimulations, reaching a level similar to that of wakefulness, at the 3rd beat post-stimulus and returning to baseline after seven beats. This RR decrease was associated with an increase in sympathetic LF(WV) and LF(WV)/HF(WV) ratio without any parasympathetic HF(WV) change. Albeit RR decrease existed even in the absence of arousals, it was significantly higher when an arousal followed the noxious stimulus. These results suggest that the sympathetic-dependent cardiac activation induced by nociceptive stimuli is modulated by a sleep dependent phenomenon related to cortical activation and not by sleep itself, since it reaches a same intensity whatever the state of vigilance

Quantifying bamboo coral growth rate nonlinearity with the radiocarbon bomb spike : a new model for paleoceanographic chronology development

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 125 (2017): 26-39, doi:10.1016/j.dsr.2017.04.006.Bamboo corals, long-lived cold water gorgonin octocorals, offer unique paleoceanographic archives of the intermediate ocean. These Isididae corals are characterized by alternating gorgonin nodes and high Mg-calcite internodes, which synchronously extend radially. Bamboo coral calcite internodes have been utilized to obtain geochemical proxy data, however, growth rate uncertainty has made it difficult to construct precise chronologies for these corals. Previous studies have relied upon a tie point from records of the anthropogenic Δ14C bomb spike preserved in the gorgonin nodes of live-collected corals to calculate a mean radial extension rate for the outer ~50 years of skeletal growth. Bamboo coral chronologies are typically constructed by applying this mean extension rate to the entire coral record, assuming constant radial extension with coral age. In this study, we aim to test this underlying assumption by analyzing the organic nodes of six California margin bamboo corals at high enough resolution (<0.5 mm) to identify the Δ14C bomb spike, including two tie points at 1957 and 1970, plus coral collection date (2007.5) for four samples. Radial extension rates between tie points ranged from 10 to 204 μm/year, with a decrease in growth rate evident between the 1957-1970 and 1970- 2007.5 periods for all four corals. A negative correlation between growth rate and coral radius (r = -0.7; p = 0.03) was determined for multiple bamboo coral taxa and individuals from the California margin, demonstrating a decline in radial extension rate with specimen age and size. To provide a mechanistic basis for these observations, a simple mathematical model was developed based on the assumption of a constant increase in circular cross sectional area with time to quantify this decline in radial extension rate with coral size between chronological tie points. Applying the area-based model to our Δ14C bomb spike time series from individual corals improves chronology accuracy for all live-collected corals with complete Δ14C bomb spikes. Hence, this study provides paleoceanographers utilizing bamboo corals with a method for reducing age model uncertainty within the anthropogenic bomb spike era (~1957-present). Chronological uncertainty is larger for the earliest portion of coral growth, particularly for skeleton precipitated prior to bomb spike tie points, meaning age estimations for samples living before 1957 remain uncertain. Combining this technique with additional chronological markers could improve age models for an entire bamboo coral. Finally, the relative consistency in growth rate in similarly-aged corals of the same depth and location supports the hypothesis that skeletal growth may be limited by local environmental conditions.This research was made possible by National Science Foundation Award #1420984 to M. LaVigne and a Clare Boothe Luce Fellowship to M. Frenkel