Consulta: creatorFacets:"Whitby, Hannah"
Registros recuperados: 6
Data/hora: 13/06/2024 14:42:39

A call for refining the role of humic-like substances in the oceanic iron cycle
Provedor de dados: 5
Autores: Whitby, Hannah; Planquette, Helene; Cassar, Nicolas; Bucciarelli, Eva; Osburn, Christopher L.; Janssen, David J.; Cullen, Jay T.; González, Aridane G.; Völker, Christoph; Sarthou, Geraldine.
Primary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the...
Tipo: Text
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00622/73388/72598.pdf

Effects of copper on the dinoflagellate Alexandrium minutum and its allelochemical potency
Provedor de dados: 5
Autores: Long, Marc; Holland, Aleicia; Planquette, Helene; Gonzalez Santana, David; Whitby, Hannah; Soudant, Philippe; Sarthou, Geraldine; Hégaret, Helene; Jolley, Dianne F.
The dinoflagellate Alexandrium minutum produces toxic compounds, including paralytic shellfish toxins, but also some unknown extracellular toxins. Although copper (Cu) is an essential element, it can impair microalgal physiology and increase their toxic potency. This study investigated the effect of different concentrations of dissolved Cu (7 nM, 79 nM and 164 nM) on A. minutum allelochemical potency, here defined as negative effects of a protist on competing protists through the release of chemicals. This was studied in relation to its physiology. The effects of Cu were assessed on A. minutum growth, reactive oxygen species level, photosynthesis proxies, lipid metabolism, exudation of dissolved organic compounds, allelochemical potency and on the...
Tipo: Text
Palavras-chave: Alexandrium; Copper; Toxicity; Allelopathy; Physiology; Exudate.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00484/59612/62629.pdf

Contribution of electroactive humic substances to the iron-binding ligands released during microbial remineralisation of sinking particles
Provedor de dados: 5
Autores: Whitby, Hannah; Bressac, Matthieu; Sarthou, Geraldine; Ellwood, Michael J.; Guieu, Cécile; Boyd, Philip W.
Iron is a key micronutrient in seawater, but concentrations would be negligible without the presence of organic ligands. The processes influencing the ligand pool composition are poorly constrained, limiting our understanding of the controls on dissolved iron distributions. To address this, the release of iron and iron‐binding ligands during the microbial remineralisation of sinking particles was investigated by deploying in situ particle interceptor/incubator devices at subsurface sites in the Mediterranean Sea and Subantarctic. Analyses revealed the pool of released ligands was largely dominated by electroactive humic substances (74 ± 28%). The release of ligands during remineralisation ensured that concurrently released iron remained in solution, which...
Tipo: Text
Palavras-chave: Iron; Ligand; Humic; Remineralisation; Particle; Degradation.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00618/72981/72055.pdf

Chemical Speciation of Copper in a Salt Marsh Estuary and Bioavailability to Thaumarchaeota
Provedor de dados: 5
Autores: Whitby, Hannah; Hollibaugh, James T.; Van Den Berg, Constant M. G.
The concentrations of dissolved copper (Cu-d), copper-binding ligands, thiourea-type thiols, and humic substances (HScu) were measured in estuarine waters adjacent to Sapelo Island, Georgia, USA, on a monthly basis from April to December 2014. Here we present the seasonal cycle of copper speciation within the estuary and compare it to the development of an annually occurring bloom of Ammonia Oxidizing Archaea (AOA), which require copper for many enzymes. Two types of complexing ligands (L-1 and L-2) were found to dominate with mean complex stabilities (log K'(cuL)) of 14.5 and 12.8. Strong complexation resulted in lowering the concentration of free cupric ion (Cu2+) to femtomolar (fM) levels throughout the study and to sub-fM levels during the summer...
Tipo: Text
Palavras-chave: Copper speciation; Cathodic stripping voltammetry; Humic substances; Thiols; Thiourea; Organic ligands; Thaumarchaeota; Ammonia-oxidizing archaea.
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00616/72834/72735.pdf

Processes Driving Iron and Manganese Dispersal From the TAG Hydrothermal Plume (Mid-Atlantic Ridge): Results From a GEOTRACES Process Study
Provedor de dados: 5
Autores: González-santana, David; Planquette, Helene; Cheize, Marie; Whitby, Hannah; Gourain, Arthur; Holmes, Thomas; Guyader, Vivien; Cathalot, Cecile; Pelleter, Ewan; Fouquet, Yves; Sarthou, Geraldine.
Hydrothermal vents are a recognized source of trace elements to the ocean inventory. Nevertheless, the contribution of slow-spreading ridges remains poorly resolved. To address this, high-resolution dissolved (&lt;0.45 μm) iron (dFe) and manganese (dMn) samples were collected during the GEOTRACES HERMINE GApr07 process study at the Mid Atlantic Ridge. Samples were collected at nine stations, from the TAG vent site to 75 km south-southwest following the neutrally buoyant plume. Concentrations of dMn and dFe ranged from 71 ± 6 and 51 ± 2 nmol kg–1 right above the vent site to 0.43 ± 0.01 and 1.56 ± 0.02 nmol kg–1 at the most distal station, respectively. Using a 5-box model coupled with our data, we show that as the plume traveled away from the vent,...
Tipo: Text
Palavras-chave: Iron; Manganese; Hydrothermal; TAG; Mid Atlantic Ridge; GEOTRACES.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00643/75530/76431.pdf

Investigating the microbial ecology of coastal hotspots of marine nitrogen fixation in the western North Atlantic
Provedor de dados: 5
Autores: Wang, Seaver; Tang, Weiyi; Delage, Erwan; Gifford, Scott; Whitby, Hannah; González, Aridane G.; Eveillard, Damien; Planquette, Helene; Cassar, Nicolas.
Variation in the microbial cycling of nutrients and carbon in the ocean is an emergent property of complex planktonic communities. While recent findings have considerably expanded our understanding of the diversity and distribution of nitrogen (N2) fixing marine diazotrophs, knowledge gaps remain regarding ecological interactions between diazotrophs and other community members. Using quantitative 16S and 18S V4 rDNA amplicon sequencing, we surveyed eukaryotic and prokaryotic microbial communities from samples collected in August 2016 and 2017 across the Western North Atlantic. Leveraging and significantly expanding an earlier published 2015 molecular dataset, we examined microbial community structure and ecological co-occurrence relationships associated...
Tipo: Text
Palavras-chave: Element cycles; Marine biology.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00685/79677/82454.pdf