Alkenone producers during late Oligocene-early Miocene revisited

This study investigates ancient alkenone producers among the late Oligocene–early Miocene coccolithophores recorded at Deep Sea Drilling Project (DSDP) Site 516. Contrary to common assumptions, Reticulofenestra was not the most important alkenone producer throughout the studied time interval. The comparison between coccolith species-specific absolute abundances and alkenone contents in the same sedimentary samples shows that Cyclicargolithus abundances explain 40% of the total variance of alkenone concentration and that the species Cyclicargolithus floridanus was a major alkenone producer, although other related taxa may have also contributed to the alkenone production at DSDP Site 516. The distribution of the different alkenone isomers (MeC37:2, EtC38:2, and MeC38:2) remained unchanged across distinct changes in species composition, suggesting similar diunsaturated alkenone compositions within the Noelaerhabdaceae family during the late Oligocene–early Miocene. However, the overall larger cell size of Cyclicargolithus may have implications for the alkenone-based reconstruction of past partial pressure of CO2. Our results underscore the importance of a careful evaluation of the most likely alkenone producers for periods (>1.85 Ma) predating the first occurrence of contemporary alkenone producers (i.e., Emiliania huxleyi and Gephyrocapsa oceanica)

Increased pCO2 changes the lipid production in important aquacultural feedstock algae Isochrysis galbana, but not in Tetraselmis suecica

Increased anthropogenic CO2 emissions are leading to an increase in CO2 uptake by the world's oceans and seas, resulting in ocean acidification with a decrease in global ocean water pH by as much as 0.3–0.4 units by the year 2100. The direct effects of changing pCO2 on important microalgal feedstocks are not as well understood. Few studies have focused on lipid composition changes in specific algal species in response to ocean acidification and yet microalgae are an indispensable food source for various marine species, including juvenile shellfish. Isochrysis galbana and Tetraselmis suecica are widely used in aquaculture as feeds for mussels and other shellfish. The total lipid contents and concentrations of I. galbana and T. suecica were investigated when grown under present day (400 ppm) and ocean acidification conditions (1000 ppm) to elucidate the impact of increasing pCO2 on an important algae feedstock. Total lipids, long-chain alkenones (LCAs) and alkenoates decreased at 1000 ppm in I. galbana. I. galbana produces higher lipids than T. suecica, and is perhaps as a result more impacted by the change in carbon available for lipid production under higher pCO2. I. galbana is an important feedstock, more easily assimilated for growth in juvenile shellfish and reductions in lipid composition may prove problematic for the growth of future shellfish aquaculture. Our findings suggest that higher pCO2 impacts on algal lipid growth are species specific and warrant further study. It is therefore vital to examine the impact of high CO2 on algal lipid production, especially those commercial shellfish feed varieties to predict future impacts on commercial aquaculture

Assessing environmental controls on the distribution of long-chain alkenones in the Canadian Prairies

Long-chain alkenones (LCAs) have been used for decades to reconstruct quantitative sea-surface temperature records, but they also have a great potential for paleotemperature reconstructions in lacustrine settings. Here, we investigated how the presence and abundance of LCAs in surface sediments from 106 lakes varied with environmental conditions in lakes of the northern Great Plains (Canadian Prairies) in southern Saskatchewan, Canada. Consistent with preliminary research, we found LCAs in 55% of surveyed lakes, with mean concentrations of 143 μg/g dry sediment, but very high concentrations (up to 2.3 mg/g dry sediment) in 7% of lakes. Statistical analyses indicate that salinity and stratification play key roles in determining LCA presence and abundance supporting previous research in Spain and the northern Great Plains, USA. Overall, the alkenone unsaturation index (U37K) was not correlated significantly with average summer water temperature, probably because the timing of maximum LCA production occurs during the spring season. We conclude that improved seasonal sampling is required within the study lakes to better identify the timing and habitat of haptophyte production, and allow development of environmental temperature reconstruction tools

Genomic identification of the long-chain alkenone producer in freshwater Lake Toyoni, Japan: implications for temperature reconstructions

Identifying the lacustrine haptophyte species that produce long-chain alkenones (LCAs) is essential prior to down-core temperature reconstructions. Here, we investigated the identity of LCA-producing species from Lake Toyoni, Japan using 18S ribosomal DNA (rDNA) and organic geochemical analyses. The rDNA analyses identified eighteen operational taxonomic units (OTUs) of which only one fell within the haptophyte phylotype. This haptophyte belongs to the Group I phylotype, as supported by the LCA distribution found in surface and down-core sediments, and is closely related to a haptophyte found in Lake BrayaSø (Greenland). The inferred temperature using the Greenland calibration is very close to the Lake Toyoni surface temperature recorded during the spring/early summer season, when the LCA-producing haptophyte is likely to bloom. We therefore suggest that the temperature calibration from the Lake BrayaSø, Greenland is a suitable calibration for down-core temperature reconstructions at Lake Toyoni

Novel alkenone-producing strains of genus Isochrysis (Haptophyta) isolated from Canadian saline lakes show temperature sensitivity of alkenones and alkenoates

Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5–40 g/L) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., UK37 and UK'37) are temperature-dependent in culture experiments, and that alkenoate indices (e.g., UA37, UA38, RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 10 °C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies

Novel alkenone-producing strains of genus Isochrysis (Haptophyta) isolated from Canadian saline lakes show temperature sensitivity of alkenones and alkenoates

Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5–40 g/L) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., UK37 and UK'37) are temperature-dependent in culture experiments, and that alkenoate indices (e.g., UA37, UA38, RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 10 °C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies

Identification des producteurs d’alcénones dans le registre sédimentaire du Cénozoïque : implications pour l’utilisation des proxys de paléo-température (UK’ 37) et de paléo-pCO2 (ɛp37 : 2)

Alkenones have been widely used as proxies for the reconstruction of sea surface temperatures and of partial pressure of CO2 (pCO2) in ancient periods. In modern oceans, these long-chain ketones are mainly produced by the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. However, there is a huge gap between the first record of alkenonesin the Cretaceous (~120 Ma) and the first occurrence of the modern alkenone producers (< 2Ma). Thus, it seems crucial to identify ancient alkenone producers to ensure the applicability of environmental proxies based on these biomarkers in pre-Quaternary sediments. In this PhD thesis, three case studies are considered corresponding to key periods in the evolution history of the Noelaerhabdaceae family, which includes the Cenozoic ancestors of modern alkenone producers. The comparison between alkenone contents (distribution and concentrations) andNoelaerhabdaceae species-specific relative and absolute abundances in marine sedimentsdating back to the Eocene-Oligocene (35-31 Ma), the Oligocene-Miocene (25-16 Ma) and thelate Pliocene (3.6-2.6 Ma) shows that, contrary to common assumptions, Reticulofenestra was not the only genus responsible for alkenone production during the Cenozoic. Results also underscore the importance of a careful identification of alkenone producers and of their cellsize for pCO2 reconstructions for pre-Quaternary periods. On the contrary, the identificationof producers does not seem essential to obtain consistent paleo-temperature estimates.Les alcénones sont largement utilisées comme proxys pour estimer des températures d’eaux de surface océanique ou des pressions partielles de CO2 (pCO2) dans des périodes anciennes. Dans les océans actuels, ces cétones à longues chaînes carbonées sont essentiellement produites par les coccolithophoridés Emiliania huxleyi et Gephyrocapsa oceanica. Il existe toutefois un écart temporel important entre le premier enregistrement sédimentaire des alcénones au Crétacé (~120 Ma) et la première apparition des producteurs actuels (< 2 Ma). Il apparaît donc essentiel d’identifier les producteurs anciens d’alcénones afin d’assurer la fiabilité des proxys environnementaux basés sur ces biomarqueurs pour les périodes préquaternaires. Cette thèse présente trois cas d’étude correspondant à des périodes clés de l’évolution de la famille des Noëlaerhabdaceae, qui comprend les ancêtres cénozoïques des producteurs actuels d’alcénones. La comparaison entre le contenu en alcénones (distribution et concentrations) et les abondances relatives et absolues des différentes espèces de Noëlaerhabdaceae dans des sédiments marins datant de l’Eocène-Oligocène (35-31 Ma), del’Oligocène-Miocène (25-16 Ma) et du Pliocène supérieur (3,6-2,6 Ma) montre que,contrairement aux hypothèses précédentes, Reticulofenestra n’était pas le seul genre responsable de la production d’alcénones au Cénozoïque. Les résultats démontrent également qu’il est essentiel d’identifier avec précision les producteurs et la taille de leur cellule pour les estimations de pCO2. Au contraire, l’identification formelle des producteurs ne semble pas indispensable pour obtenir des estimations de températures cohérentes

Identification of alkenone producers in the Cenozoic sedimentary record : implications for the use of paleo-temperature (UK’ 37) and paleo-pCO2 (ɛp37 : 2) proxies

Les alcénones sont largement utilisées comme proxys pour estimer des températures d’eaux de surface océanique ou des pressions partielles de CO2 (pCO2) dans des périodes anciennes. Dans les océans actuels, ces cétones à longues chaînes carbonées sont essentiellement produites par les coccolithophoridés Emiliania huxleyi et Gephyrocapsa oceanica. Il existe toutefois un écart temporel important entre le premier enregistrement sédimentaire des alcénones au Crétacé (~120 Ma) et la première apparition des producteurs actuels (< 2 Ma). Il apparaît donc essentiel d’identifier les producteurs anciens d’alcénones afin d’assurer la fiabilité des proxys environnementaux basés sur ces biomarqueurs pour les périodes préquaternaires. Cette thèse présente trois cas d’étude correspondant à des périodes clés de l’évolution de la famille des Noëlaerhabdaceae, qui comprend les ancêtres cénozoïques des producteurs actuels d’alcénones. La comparaison entre le contenu en alcénones (distribution et concentrations) et les abondances relatives et absolues des différentes espèces de Noëlaerhabdaceae dans des sédiments marins datant de l’Eocène-Oligocène (35-31 Ma), del’Oligocène-Miocène (25-16 Ma) et du Pliocène supérieur (3,6-2,6 Ma) montre que,contrairement aux hypothèses précédentes, Reticulofenestra n’était pas le seul genre responsable de la production d’alcénones au Cénozoïque. Les résultats démontrent également qu’il est essentiel d’identifier avec précision les producteurs et la taille de leur cellule pour les estimations de pCO2. Au contraire, l’identification formelle des producteurs ne semble pas indispensable pour obtenir des estimations de températures cohérentes.Alkenones have been widely used as proxies for the reconstruction of sea surface temperatures and of partial pressure of CO2 (pCO2) in ancient periods. In modern oceans, these long-chain ketones are mainly produced by the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. However, there is a huge gap between the first record of alkenonesin the Cretaceous (~120 Ma) and the first occurrence of the modern alkenone producers (< 2Ma). Thus, it seems crucial to identify ancient alkenone producers to ensure the applicability of environmental proxies based on these biomarkers in pre-Quaternary sediments. In this PhD thesis, three case studies are considered corresponding to key periods in the evolution history of the Noelaerhabdaceae family, which includes the Cenozoic ancestors of modern alkenone producers. The comparison between alkenone contents (distribution and concentrations) andNoelaerhabdaceae species-specific relative and absolute abundances in marine sedimentsdating back to the Eocene-Oligocene (35-31 Ma), the Oligocene-Miocene (25-16 Ma) and thelate Pliocene (3.6-2.6 Ma) shows that, contrary to common assumptions, Reticulofenestra was not the only genus responsible for alkenone production during the Cenozoic. Results also underscore the importance of a careful identification of alkenone producers and of their cellsize for pCO2 reconstructions for pre-Quaternary periods. On the contrary, the identificationof producers does not seem essential to obtain consistent paleo-temperature estimates

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