108 Hits in 1.1 sec

Relating phytoplankton photophysiological properties to community structure on large scales

Julia Uitz xUitz, Yannick Huot, Flavienne Bruyant, Marcel Babin, HervÉ Claustre
2008 Limnology and Oceanography  
Thus, we used coefficients derived from a global dataset and based on water-column integrated contents (Uitz et al. 2006) .  ...  ., Gieskes et al. 1988) , or size classes (Vidussi et al. 2001; Devred et al. 2006; Uitz et al. 2006) to estimate the community composition.  ... 
doi:10.4319/lo.2008.53.2.0614 fatcat:pxi77olrozfdxfhocrllyns2bi

Assessing Pigment-Based Phytoplankton Community Distributions in the Red Sea

Malika Kheireddine, Mustapha Ouhssain, Hervé Claustre, Julia Uitz, Bernard Gentili, Burton H. Jones
2017 Frontiers in Marine Science  
Previous studies (Claustre, 1994; Vidussi et al., 2001; Uitz et al., 2006 Uitz et al., , 2008 mentioned that these assumptions may sometimes lead to errors.  ...  The model requires the following inputs: (1) Uitz et al. (2008) .  ...  Copyright © 2017 Kheireddine, Ouhssain, Claustre, Uitz, Gentili and Jones. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).  ... 
doi:10.3389/fmars.2017.00132 fatcat:eoyiwhcqifhcnj5doocimi4qjq

A new look at ocean carbon remineralization for estimating deepwater sequestration

Lionel Guidi, Louis Legendre, Gabriel Reygondeau, Julia Uitz, Lars Stemmann, Stephanie A. Henson
2015 Global Biogeochemical Cycles  
In the present ocean F micro can vary between 0 and close to 1, whereas F pico could accounts for 75% of total Chl at most [Brewin et al., 2010; Kostadinov et al., 2010; Uitz et al., 2006 Uitz et al.,  ...  Our novel ocean-wide database of regionalized b values combined with recent availability of global satellite-derived phytoplankton size classes [Uitz et al., 2006] provided an opportunity to test this  ... 
doi:10.1002/2014gb005063 fatcat:xadzo5bjxzflvmwlz7z7am45n4

Vertical distribution of phytoplankton communities in open ocean: An assessment based on surface chlorophyll

Julia Uitz, Hervé Claustre, André Morel, Stanford B. Hooker
2006 Journal of Geophysical Research  
C08005 UITZ ET AL.: PIGMENT COMPOSITION FROM SURFACE CHLOROPHYLL thetic parameters typical of the different phytoplankton size classes can be selected.  ...  C08005 UITZ ET AL.: PIGMENT COMPOSITION FROM SURFACE CHLOROPHYLL ambiguities and the due reservation about the exact meaning of size class, this term (as well as the appellations pico, nano, micro) will  ... 
doi:10.1029/2005jc003207 fatcat:wunbqztusfcetgc6criqn2a4gm

The microbial carbon pump concept: Potential biogeochemical significance in the globally changing ocean

Louis Legendre, Richard B. Rivkin, Markus G. Weinbauer, Lionel Guidi, Julia Uitz
2015 Progress in Oceanography  
doi:10.1016/j.pocean.2015.01.008 fatcat:wr4heq5pwjgtnhk2ny4p2yqmu4

Hyperspectral Radiometry on Biogeochemical-Argo Floats: A Bright Perspective for Phytoplankton Diversity

Emanuele Organelli, National Research Council (CNR), Institute of Marine Sciences (ISMAR), Edouard Leymarie, Oliver Zielinski, Julia Uitz, Fabrizio D'Ortenzio, Hervé Claustre
2021 Oceanography  
Argo profiling floats across the globe, the Biogeochemical (BGC)-Argo program is the only network capable of providing detailed observations of the physics, chemistry, and biology of the top 2,000 m of our ocean up to every 10 days, even in remote regions and during unfavorable conditions for manual sampling. This rapidly expanding network will yield large amounts of data that will help us understand marine ecosystems and biogeochemistry, evaluate the impact of increasing human-derived
more » ... on Earth's climate, and develop science-based solutions for sustain-
doi:10.5670/oceanog.2021.supplement.02-33 fatcat:2frsxiut2bcijcenscyxiibyd4

Reconstructing Global Chlorophyll-a Variations Using a Non-linear Statistical Approach

Elodie Martinez, Thomas Gorgues, Matthieu Lengaigne, Clement Fontana, Raphaëlle Sauzède, Christophe Menkes, Julia Uitz, Emanuele Di Lorenzo, Ronan Fablet
2020 Frontiers in Marine Science  
Monitoring the spatio-temporal variations of surface chlorophyll-a concentration (Chl, a proxy of phytoplankton biomass) greatly benefited from the availability of continuous and global ocean color satellite measurements from 1997 onward. These two decades of satellite observations are however still too short to provide a comprehensive description of Chl variations at decadal to multi-decadal timescales. This paper investigates the ability of a machine learning approach (a non-linear
more » ... approach based on Support Vector Regression, hereafter SVR) to reconstruct global spatio-temporal Chl variations from selected surface oceanic and atmospheric physical parameters. With a limited training period (13 years), we first demonstrate that Chl variability from a 32-years global physical-biogeochemical simulation can generally be skillfully reproduced with a SVR using the model surface variables as input parameters. We then apply the SVR to reconstruct satellite Chl observations using the physical predictors from the above numerical model and show that the Chl reconstructed by this SVR more accurately reproduces some aspects of observed Chl variability and trends compared to the model simulation. This SVR is able to reproduce the main modes of interannual Chl variations depicted by satellite observations in most regions, including El Niño signature in the tropical Pacific and Indian Oceans. In stark contrast with the trends simulated by the biogeochemical model, it also accurately captures spatial patterns of Chl trends estimated by satellite data, with a Chl increase in most extratropical regions and a Chl decrease in the center of the subtropical gyres, although the amplitude of these trends are underestimated by half. Results from our SVR reconstruction over the entire period (1979–2010) also suggest that the Interdecadal Pacific Oscillation drives a significant part of decadal Chl variations in both the tropical Pacific and Indian Oceans. Overall, this study demonstrates that non-linear statistical reconstructions can be complementary tools to in situ and satellite observations as well as conventional physical-biogeochemical numerical simulations to reconstruct and investigate Chl decadal variability.
doi:10.3389/fmars.2020.00464 fatcat:lymfho3fwrdvja2ixyjgdo25f4

Multivariate approach for the retrieval of phytoplankton size structure from measured light absorption spectra in the Mediterranean Sea (BOUSSOLE site)

Emanuele Organelli, Annick Bricaud, David Antoine, Julia Uitz
2013 Applied Optics  
The numerical coefficients used to compute the contribution of the three size classes to the taxonomic structure of the algal community were calculated by multiple regression on a global data set by Uitz  ... 
doi:10.1364/ao.52.002257 pmid:23670753 fatcat:42w6d7nksbgdjlx333ns5gncyq

Assessing phytoplankton community composition from hyperspectral measurements of phytoplankton absorption coefficient and remote-sensing reflectance in open-ocean environments

Julia Uitz, Dariusz Stramski, Rick A. Reynolds, Jean Dubranna
2015 Remote Sensing of Environment  
Some limitations of this approach have been recognized; for example, certain pigments may be found in more than one size class (Vidussi et al., 2001; Uitz et al., 2006) .  ...  ., Bouman, Platt, Sathyendranath, & Stuart, 2005; Cermeño, Estévez-Blanco, Marañon, & Fernandez, 2005; Uitz, Huot, Bruyant, Babin, & Claustre, 2008) , the transfer of primary production to higher trophic  ... 
doi:10.1016/j.rse.2015.09.027 fatcat:cpphqtmgx5hbhefk3phkzxnvn4

DMS dynamics in the most oligotrophic subtropical zones of the global ocean

Sauveur Belviso, Italo Masotti, Alessandro Tagliabue, Laurent Bopp, P. Brockmann, Cédric Fichot, Guy Caniaux, Louis Prieur, Joséphine Ras, Julia Uitz, Hubert Loisel, David Dessailly (+3 others)
2011 Biogeochemistry  
Specific pigments and classes are described in Uitz et al. (2006) , see their Table 2 .  ...  Here, we used the pigment grouping method recently improved by Uitz et al. (2006) . Seven pigments are used as biomarkers of several phytoplankton taxa.  ... 
doi:10.1007/s10533-011-9648-1 fatcat:j3nhnpolpzcdfgznnpiwx3arey

Estimates of phytoplankton class-specific and total primary production in the Mediterranean Sea from satellite ocean color observations

Julia Uitz, Dariusz Stramski, Bernard Gentili, Fabrizio D'Ortenzio, Hervé Claustre
2012 Global Biogeochemical Cycles  
[2005] as input to the parameterization of Uitz et al. [2006] .  ...  Specifically, a novel approach was proposed for quantifying the chlorophyll a biomass [Uitz et al., 2006] and primary production [Uitz et al., 2008] associated with three phytoplankton classes, i.e  ... 
doi:10.1029/2011gb004055 fatcat:gqrvna2mezfyrjquu4z3mdvtku

Correction of pathlength amplification in the filter-pad technique for measurements of particulate absorption coefficient in the visible spectral region

Dariusz Stramski, Rick A. Reynolds, Sławomir Kaczmarek, Julia Uitz, Guangming Zheng
2015 Applied Optics  
Spectrophotometric measurement of particulate matter retained on filters is the most common and practical method for routine determination of the spectral light absorption coefficient of aquatic particles, a p λ, at high spectral resolution over a broad spectral range. The use of differing geometrical measurement configurations and large variations in the reported correction for pathlength amplification induced by the particle/filter matrix have hindered adoption of an established measurement
more » ... otocol. We describe results of dedicated laboratory experiments with a diversity of particulate sample types to examine variation in the pathlength amplification factor for three filter measurement geometries; the filter in the transmittance configuration (T), the filter in the transmittance-reflectance configuration (T-R), and the filter placed inside an integrating sphere (IS). Relationships between optical density measured on suspensions (OD s ) and filters (OD f ) within the visible portion of the spectrum were evaluated for the formulation of pathlength amplification correction, with power functions providing the best functional representation of the relationship for all three geometries. Whereas the largest uncertainties occur in the T method, the IS method provided the least sample-to-sample variability and the smallest uncertainties in the relationship between OD s and OD f . For six different samples measured with 1 nm resolution within the light wavelength range from 400 to 700 nm, a median error of 7.1% is observed for predicted values of OD s using the IS method. The relationships established for the three filter-pad methods are applicable to historical and ongoing measurements; for future work, the use of the IS method is recommended whenever feasible.
doi:10.1364/ao.54.006763 pmid:26368092 fatcat:3szh2valp5fr5fvfz6faucqjbu

Deep maxima of phytoplankton biomass, primary production and bacterial production in the Mediterranean Sea

Emilio Marañón, France Van Wambeke, Julia Uitz, Emmanuel S. Boss, Céline Dimier, Julie Dinasquet, Anja Engel, Nils Haëntjens, María Pérez-Lorenzo, Vincent Taillandier, Birthe Zäncker
2021 Biogeosciences  
et al., 2010 (Uitz et al., , 2012 Robinson et al., 2018) .  ...  The factors used were 1.41 (Uitz et al., 2006) , 1.6 (Di Cicco et al., 2017) and 1.74 (Di Cicco, 2014) .  ... 
doi:10.5194/bg-18-1749-2021 fatcat:tofbojcjqbeb7n5lfqnwjgeptm

Variations in the optical properties of a particle suspension associated with viral infection of marine bacteria

Julia Uitz, Dariusz Stramski, Anne-Claire Baudoux, Rick A. Reynolds, Vanessa M. Wright, Jean Dubranna, Farooq Azam
2010 Limnology and Oceanography  
A laboratory experiment was conducted to examine the temporal dynamics of the particle size distribution (PSD) and associated optical variability caused by viral infection of marine heterotrophic bacteria. The PSD covering a broad range of particle size from < 50 nm to 200 mm was measured in parallel with the spectral particulate absorption and beam attenuation coefficients, from which the particulate scattering coefficient, b p (l), was determined. Within 12 h following infection, the host
more » ... erial population collapsed, viral abundance increased, and submicron particles were produced as bacteria were disrupted and cell debris released, resulting in a large decrease in b p (l) seen as an almost complete clearing of the particle suspension. Throughout the remainder of the experiment, significant changes in the PSD occurred primarily within the size range of relatively large particles (. 4 mm), likely as a result of the aggregation of smaller-sized particles originating from the host lysis. The PSD data were used as input for Mie scattering calculations to evaluate the effects of these particle dynamics in terms of relative contributions of different particle size classes to the scattering and backscattering coefficients. This analysis showed a significant increase in the effect of particle aggregation on light scattering during the second and third days after infection. Viral lysis of bacteria and subsequent particle dynamics produce large variations in the PSD over a broad size range on timescales from hours to a few days, and such processes lead to correspondingly large changes in the suspension optical properties.
doi:10.4319/lo.2010.55.6.2317 fatcat:wdfftiipubhc5kt2av4w26j66m

On the discrimination of multiple phytoplankton groups from light absorption spectra of assemblages with mixed taxonomic composition and variable light conditions

Emanuele Organelli, Caterina Nuccio, Luigi Lazzara, Julia Uitz, Annick Bricaud, Luca Massi
2017 Applied Optics  
The contribution of each phytoplankton size class in the simulated mixed algal assemblages, calculated according to Uitz et al.  ... 
doi:10.1364/ao.56.003952 pmid:29047522 fatcat:h6l6i5vy6fef5bhdxa7wl7awmq
« Previous Showing results 1 — 15 out of 108 results