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Taillandier Vincent - One of the best experts on this subject based on the ideXlab platform.

  • Deep maxima of phytoplankton biomass, primary production and bacterial production in the Mediterranean Sea
    'Copernicus GmbH', 2021
    Co-Authors: Marañón Sainz Emilio, Uitz Julia, Boss, Emmanuel S, Perez-lorenzo Maria, Dinasquet Julie, Haentjens Nils, Dimier Céline, Engel Anja, Van Wambeke France, Taillandier Vincent
    Abstract:

    The deep chlorophyll maximum (DCM) is a ubiquitous feature of phytoplankton vertical distribution in stratified waters that is relevant to our understanding of the mechanisms that underpin the variability in photoautotroph ecophysiology across environmental gradients and has implications for remote sensing of Aquatic Productivity. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we obtained 23 concurrent vertical profiles of phytoplankton chlorophyll a, carbon biomass and primary production, as well as heterotrophic prokaryotic production, in the western and central Mediterranean basins. Our main aims were to quantify the relative role of photoacclimation and enhanced growth as underlying mechanisms of the DCM and to assess the trophic coupling between phytoplankton and heterotrophic prokaryotic production. We found that the DCM coincided with a maximum in both the biomass and primary production but not in the growth rate of phytoplankton, which averaged 0.3 d−1 and was relatively constant across the euphotic layer. Photoacclimation explained most of the increased chlorophyll a at the DCM, as the ratio of carbon to chlorophyll a (C:Chl a) decreased from ca. 90–100 (g:g) at the surface to 20–30 at the base of the euphotic layer, while phytoplankton carbon biomass increased from ca. 6 mg C m−3 at the surface to 10–15 mg C m−3 at the DCM. As a result of photoacclimation, there was an uncoupling between chlorophyll a-specific and carbon-specific Productivity across the euphotic layer. The ratio of fucoxanthin to total chlorophyll a increased markedly with depth, suggesting an increased contribution of diatoms at the DCM. The increased biomass and carbon fixation at the base of the euphotic zone was associated with enhanced rates of heterotrophic prokaryotic activity, which also showed a surface peak linked with warmer temperatures. Considering the phytoplankton biomass and turnover rates measured at the DCM, nutrient diffusive fluxes across the nutricline were able to supply only a minor fraction of the photoautotroph nitrogen and phosphorus requirements. Thus the deep maxima in biomass and primary production were not fuelled by new nutrients but likely resulted from cell sinking from the upper layers in combination with the high photosynthetic efficiency of a diatom-rich, low-light acclimated community largely sustained by regenerated nutrients. Further studies with increased temporal and spatial resolution will be required to ascertain if the peaks of deep primary production associated with the DCM persist across the western and central Mediterranean Sea throughout the stratification season.Ministerio de Ciencia, Innovación y Universidades | Ref. PGC2018-094553B-I00European Commission, H2020 | Ref. n. 81757

  • Deep maxima of phytoplankton biomass, primary production and bacterial production in the Mediterranean Sea
    'Copernicus GmbH', 2021
    Co-Authors: Maranon Emilio, Van Vambeke France, Uitz Julia, Boss, Emmanuel S, Perez-lorenzo Maria, Dinasquet Julie, Haentjens Nils, Dimier Céline, Engel Anja, Taillandier Vincent
    Abstract:

    The deep chlorophyll maximum (DCM) is a ubiquitous feature of phytoplankton vertical distribution in stratified waters that is relevant to our understanding of the mechanisms that underpin the variability in photoautotroph ecophysiology across environmental gradients and has implications for remote sensing of Aquatic Productivity. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we obtained 23 concurrent vertical profiles of phytoplankton chlorophyll a, carbon biomass and primary production, as well as heterotrophic prokaryotic production, in the western and central Mediterranean basins. Our main aims were to quantify the relative role of photoacclimation and enhanced growth as underlying mechanisms of the DCM and to assess the trophic coupling between phytoplankton and heterotrophic prokaryotic production. We found that the DCM coincided with a maximum in both the biomass and primary production but not in the growth rate of phytoplankton, which averaged 0.3 d−1 and was relatively constant across the euphotic layer. Photoacclimation explained most of the increased chlorophyll a at the DCM, as the ratio of carbon to chlorophyll a (C:Chl a) decreased from ca. 90–100 (g:g) at the surface to 20–30 at the base of the euphotic layer, while phytoplankton carbon biomass increased from ca. 6 mg C m−3 at the surface to 10–15 mg C m−3 at the DCM. As a result of photoacclimation, there was an uncoupling between chlorophyll a-specific and carbon-specific Productivity across the euphotic layer. The ratio of fucoxanthin to total chlorophyll a increased markedly with depth, suggesting an increased contribution of diatoms at the DCM. The increased biomass and carbon fixation at the base of the euphotic zone was associated with enhanced rates of heterotrophic prokaryotic activity, which also showed a surface peak linked with warmer temperatures. Considering the phytoplankton biomass and turnover rates measured at the DCM, nutrient diffusive fluxes across the nutricline were able to supply only a minor fraction of the photoautotroph nitrogen and phosphorus requirements. Thus the deep maxima in biomass and primary production were not fuelled by new nutrients but likely resulted from cell sinking from the upper layers in combination with the high photosynthetic efficiency of a diatom-rich, low-light acclimated community largely sustained by regenerated nutrients. Further studies with increased temporal and spatial resolution will be required to ascertain if the peaks of deep primary production associated with the DCM persist across the western and central Mediterranean Sea throughout the stratification season

  • Deep maxima of phytoplankton biomass, primary production and bacterial production in the Mediterranean Sea during late spring
    'Copernicus GmbH', 2020
    Co-Authors: Maranon Emilio, Van Vambeke France, Uitz Julia, Boss, Emmanuel S, Perez-lorenzo Maria, Dinasquet Julie, Haentjens Nils, Dimier Céline, Taillandier Vincent
    Abstract:

    The deep chlorophyll maximum (DCM) is a ubiquitous feature of phytoplankton vertical distribution in stratified waters that is relevant for our understanding of the mechanisms that underpin the variability in photoautotroph ecophysiology across environmental gradients and has implications for remote sensing of Aquatic Productivity. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we obtained 23 concurrent vertical profiles of phytoplankton chlorophyll a, carbon biomass and primary production, as well as heterotrophic prokaryotic production, in the western and central Mediterranean basins. Our main aims were to quantify the relative role of photoacclimation and enhanced growth as underlying mechanisms of the DCM and to assess the trophic coupling between phytoplankton and heterotrophic prokaryotic production. We found that the DCM coincided with a maximum in both biomass and primary production but not in growth rate of phytoplankton, which averaged 0.3 d−1 and was relatively constant across the euphotic layer. Photoacclimation explained most of the increased chlorophyll a at the DCM, as the carbon to chlorophyll a ratio (C:Chl a) decreased from ca. 90–100 (g:g) at the surface to 20–30 at the base of the euphotic layer, while phytoplankton carbon biomass increased from ca. 6 mgC m−3 at the surface to 10–15 mgC m−3 at the DCM. As a result of photoacclimation, there was an uncoupling between chlorophyll a-specific and carbon-specific Productivity across the euphotic layer. The fucoxanthin to total chlorophyll a ratio increased markedly with depth, as did the biomass contribution of large cells, suggesting a dominance of diatoms at the DCM. The increased biomass and carbon fixation at the base of the euphotic zone was associated with enhanced rates of heterotrophic prokaryotic activity, which also showed a surface peak linked with warmer temperatures. Considering the phytoplankton biomass and turnover rates measured at the DCM, nutrient diffusive fluxes across the nutricline were able to supply only a minor fraction of the photoautotroph nitrogen and phosphorus requirements. Thus the deep maxima in biomass and primary production were not fueled by new nutrients, but likely resulted from cell sinking from the upper layers in combination with the high photosynthetic efficiency of a diatom-rich, low-light acclimated community largely sustained by regenerated nutrients. Further studies with increased temporal and spatial resolution will be required to ascertain if the deep primary production peaks associated with the DCM persist across the western and central Mediterranean Sea throughout the stratification season

Meixun Zhao - One of the best experts on this subject based on the ideXlab platform.

  • pre aged soil organic carbon as a major component of the yellow river suspended load regional significance and global relevance
    Earth and Planetary Science Letters, 2015
    Co-Authors: Timothy I Eglinton, Daniel B Montlucon, Cameron Mcintyre, Meixun Zhao
    Abstract:

    Abstract Large rivers connect the continents and the oceans, and corresponding material fluxes have a global impact on marine biogeochemistry. The Yellow River transports vast quantities of suspended sediments to the ocean, yet the nature of the particulate organic carbon (POC) carried by this system is not well known. The focus of this study is to characterize the sources, composition and age of suspended POC collected near the terminus of this river system, focusing on the abundance and carbon isotopic composition (13C and 14C) of specific biomarkers. The concentrations of vascular plant wax lipids (long-chain (≥C24) n-alkanes, n-fatty acids) and POC co-varied with total suspended solid (TSS) concentrations, indicating that both were controlled by the overall terrestrial sediment flux. POC exhibited relatively uniform δ13C values (−23.8 to −24.2‰), and old radiocarbon ages (4000–4640 yr). However, different biomarkers exhibited a wide range of 14C ages. Short-chain (C16, C18) fatty acid 14C ages were variable but generally the youngest organic components (from 502 yr to modern), suggesting they reflect recently biosynthesized material. Lignin phenol 14C ages were also variable and relatively young (1070 yr to modern), suggesting rapid export of carbon from terrestrial primary production. In contrast, long-chain plant wax lipids display relatively uniform and significantly older 14C ages (1500–1800 yr), likely reflecting inputs of pre-aged, mineral-associated soil OC from the Yellow River drainage basin. Even-carbon-numbered n-alkanes yielded the oldest 14C ages (up to 26 000 yr), revealing the presence of fossil (petrogenic) OC. Two isotopic mass balance approaches were explored to quantitively apportion different OC sources in Yellow River suspended sediments. Results indicate that the dominant component of POC (53–57%) is substantially pre-aged (1510–1770 yr), and likely sourced from the extensive loess-paleosol deposits outcropping within the drainage basin. Of the remaining POC, between 10 and 31% is fossil in origin (>26 000 yr), resulting from the physical erosion of ancient sedimentary rock and input of fossil fuel residues from anthropogenic activity, and 16–33% is modern carbon derived from terrestrial and Aquatic Productivity. These findings have implications both regarding the provenance and vintage of organic matter signatures emanating from the Yellow River basin and similar catchments containing extensive paleosol sequences, as well as for the reactivity and fate of this POC upon supply to adjacent marginal seas.

Dan Hammarlund - One of the best experts on this subject based on the ideXlab platform.

  • multi component stable isotope records from late weichselian and early holocene lake sediments at imiolki poland palaeoclimatic and methodological implications
    Journal of Quaternary Science, 2009
    Co-Authors: Karina Apolinarska, Dan Hammarlund
    Abstract:

    Late Weichselian and early Holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of Lake Lednica, western Poland. Along with sediment and pollen stratigraphic data, a wide range of carbonate components occurring in the sediments was analysed for delta C-13 and delta O-18, including shells of several gastropod species and the bivalve genus Pisidium, carapaces of the ostracod subfamily Candoninae and oogonia of the Aquatic macrophyte genus Chara. The development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the Late Weichselian are clearly reflected by rising carbonate content, distinct isotopic shifts in bulk carbonates and decreasing delta C-13 values of bulk organic matter in the sediments. The GI-1/GS-1 (the Bolling-Allerod Interstadial complex/Younger Dryas Stadial) and the GS-1/Preboreal transitions are marked by significant shifts in delta O-18 values of 2-3 parts per thousand, as well as by distinct changes in carbonate content, indicative of a decrease and a subsequent increase in mean annual temperature. Corresponding delta C-13 records reflect primarily changes in Aquatic Productivity, with favourable conditions for phytoplankton and macrophytes during GI-1 and the Preboreal resulting in persistent C-13 enrichment. The Younger Dryas Stadial is characterised by depletions in C-13 and O-18, with indications of a climatic tripartition. Consistent offsets in delta C-13 and delta O-18 between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate-precipitating biota. Largely parallel first-order variations in delta C-13 and delta O-18 of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information, although more detailed reconstructions can be obtained from multi-component analysis. Copyright (C) 2009 John Wiley & Sons, Ltd.

  • climate and environment during the younger dryas gs 1 as reflected by composite stable isotope records of lacustrine carbonates at torreberga southern sweden
    Journal of Quaternary Science, 1999
    Co-Authors: Dan Hammarlund, Thomas W D Edwards, Svante Bjorck, Bjorn Buchardt, Barbara Wohlfarth
    Abstract:

    Climatic and environmental changes during the Younger Dryas stadial (GS-1) and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient Lake Torreberga, southern Sweden. Event GS-1 is represented in the sediment sequence by 3.5 m of clay containing lacustrine carbonates of various origins. Comparison of isotopic records obtained on mollusc shells, ostracod valves, and Chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures. Variations in soil erosion rates can also be estimated from a simple isotope-mass-balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments. The well-known, rapid climatic shifts characterising the Last Termination in the North Atlantic region are clearly reflected in the isotopic data, as well as longer-term changes within GS-1. Following maximum cooling shortly after the Allerod-Younger Dryas (GI-1-GS-1) transition, a progressive warming and a slight increase in Aquatic Productivity is indicated. At the Younger Dryas- Preboreal (GS-1-PB) transition mean annual air temperature rapidly increased by more than 5°C and summer lake-water temperature increased by ca. 12°C. The subsequent Preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature. These results are in harmony with recent findings about large-scale climate dynamics during the Last Termination. Copyright © 1999 John Wiley & Sons, Ltd.

David J S Montagnes - One of the best experts on this subject based on the ideXlab platform.

  • predicting temperature impacts on Aquatic Productivity questioning the metabolic theory of ecology s canonical activation energies
    Limnology and Oceanography, 2019
    Co-Authors: Qing Wang, Zhao Lyu, Said Omar, Stephen J Cornell, Zhou Yang, David J S Montagnes
    Abstract:

    Microalgae contribute ~ 50% to global primary production, most of which is consumed by protozoa. Determining the thermal‐sensitivity of this trophic interaction is, therefore, fundamental to predicting impacts of climate change. Here, we question the application of current predictive approaches. Thermal responses are commonly described by the Arrhenius function: urn:x-wiley:00243590:media:lno11105:lno11105-math-0002, where r is a rate (e.g., growth), A is a scaling factor, Ea is the activation energy, k is the Boltzmann‐constant, and T is absolute temperature. The influential metabolic theory of ecology (MTE) proposes that estimates of Ea for heterotrophs and autotrophs are 0.65 eV and 0.32 eV, respectively; when applied to specific growth rate of algae and protozoa, this difference has significant predictive consequences. Through literature review and statistical evaluation, we show that the MTE predictions do not apply to taxon‐specific responses of protozoa (n = 103) or algae (n = 183), with mean Ea of 0.71 eV (95% confidence interval [CI]: 0.69–0.74) and 0.61 eV (95% CI: 0.58–0.63), respectively. To obtain these, we fitted a series of models where Ea was constant within a defined group (e.g., protozoa), and the amplitude A depended on the individual responses within the group. Then, by applying the MTE and our predictions to a generic protozoan‐algal, predator‐prey model we show that: (1) the “canonical” MTE values lead to misrepresenting Productivity by several fold; (2) a general response encompassing both groups (0.69 eV) should suffice for such models; and (3) applying our new responses has substantial effects on algal‐protozoan population dynamics over temperature shifts of ~ 5°C.

  • do temperature food interactions matter responses of production and its components in the model heterotrophic flagellate oxyrrhis marina
    Aquatic Microbial Ecology, 2006
    Co-Authors: Susan A Kimmance, David Atkinson, David J S Montagnes
    Abstract:

    The consequence of interactions between temperature and food concentration for pro- tistan population dynamics and estimates of Aquatic Productivity are relatively unknown, primarily because we lack adequate parameters for models. Here, using the heterotrophic flagellate Oxyrrhis marina Dujardin, we demonstrate the importance of considering temperature and food concentration in combination, to determine the responses of grazing rate, specific growth rate, cell volume, specific production and yield. Specific growth rate and cell volume responded in different ways to tempera- ture-food concentrations: prey concentration had greatest positive effects on specific growth rate with increasing temperature, and prey concentration had greatest positive effects on cell volume with decreasing temperature. The effect of these contrasting interactions on specific production (=specific growth rate × cell carbon) was a greater response to prey concentration at intermediate temperatures. We also observed that the threshold food concentration for growth increased with increasing temper- ature, but yield showed no clear thermal response. By applying iterative curve-fitting to data obtained from multiple temperature-food concentration combinations, we produced phenomenolog- ical models of grazing rate, specific growth rate, and cell volume. We then compared predictions from a simple predator-prey simulation model that applied either our derived equations or a single expo- nential (Q10) relationship to the specific growth and ingestion responses at 20°C. Considerable differ- ences in predator and prey abundance were obtained between the 2 models. Our results demonstrate the potentially complex effects of food and temperature in combination on production parameters, and we argue that these should be considered in Aquatic ecosystem simulation models.

Yuhong Wang - One of the best experts on this subject based on the ideXlab platform.

  • a multi proxy sediment record of late holocene and recent climate change from a lake near ny alesund svalbard
    Boreas, 2011
    Co-Authors: Shan Jiang, Xiaodong Liu, Jing Sun, Linxi Yuan, Liguang Sun, Yuhong Wang
    Abstract:

    The Arctic constitutes a unique and important environment with a significant role in the dynamics and evolution of the earth system. Arctic lake sediments, which accumulate slowly over time, contain abundant information about the biological communities that lived within the water body, as well as in the surrounding catchment. In this study, we collected a sediment core from Ny-Alesund, Svalbard, performed multi-proxy analyses on sediment pigments, mineral magnetic susceptibility, various sediment quality (i. e. organic matter content, CaCO3 content, carbon and nitrogen isotope), and diatom composition, and reconstructed the history of ecosystem responses to environmental variations, especially regarding Aquatic Productivity and lake catchment surface processes. Ny-Alesund has undergone distinct ecological and climatic changes. During the Little Ice Age, the cold climate was unfavourable for the growth of lake algae, and therefore the lake primary Productivity declined. After about AD 1890 and during the 20th century, the warming climate and reduced ice cover led to rapid lithological change and growth of lake algae, enhanced lake pri- mary Productivity, and increased input of nutrients derived from increased chemical weathering into the lake. The lake ecosystem on Ny-Alesund has had rapid responses to climatic and environmental changes in the Arctic.