146 results on '"Michael W. Lomas"'
Search Results
2. Seasonal Dynamics of Primary Production in the Southeastern Bering Sea Assessed Using Continuous Temporal and Vertical Dissolved Oxygen and Chlorophyll‐ a Measurements
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Jens M. Nielsen, Noel A. Pelland, Shaun W. Bell, Michael W. Lomas, Lisa B. Eisner, Phyllis Stabeno, Colleen Harpold, Scott Stalin, and Calvin W. Mordy
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Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,Oceanography - Published
- 2023
3. Ecophysiological basis of spatiotemporal patterns in picophytoplankton pigments in the global ocean
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Sornsiri Phongphattarawat, Heather A. Bouman, Michael W. Lomas, Shubha Sathyendranath, Glen A. Tarran, Osvaldo Ulloa, and Mikhail V. Zubkov
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Global and Planetary Change ,Ocean Engineering ,Aquatic Science ,Oceanography ,Water Science and Technology - Abstract
Information on the intracellular content and functional diversity of phytoplankton pigments can provide valuable insight on the ecophysiological state of primary producers and the flow of energy within aquatic ecosystems. Combined global datasets of analytical flow cytometry (AFC) cell counts and High-Performance Liquid Chromatography (HPLC) pigment concentrations were used to examine vertical and seasonal variability in the ratios of phytoplankton pigments in relation to indices of cellular photoacclimation. Across all open ocean datasets, the weight-to-weight ratio of photoprotective to photosynthetic pigments showed a strong depth dependence that tracked the vertical decline in the relative availability of light. The Bermuda Atlantic Time-series Study (BATS) dataset revealed a general increase in surface values of the relative concentrations of photoprotective carotenoids from the winter-spring phytoplankton communities dominated by low-light acclimated eukaryotic microalgae to the summer and early autumn communities dominated by high-light acclimated picocyanobacteria. In Prochlorococcus-dominated waters, the vertical decline in the relative contribution of photoprotective pigments to total pigment concentration could be attributed in large part to changes in the cellular content of photosynthetic pigments (PSP) rather than photoprotective pigments (PPP), as evidenced by a depth-dependent increase of the intracellular concentration of the divinyl chlorophyll-a (DVChl-a) whilst the intracellular concentration of the PPP zeaxanthin remained relatively uniform with depth. The ability of Prochlorococcus cells to adjust their DVChl-a cell-1 over a large gradient in light intensity was reflected in more highly variable estimates of carbon-to-Chl-a ratio compared to those reported for other phytoplankton groups. This cellular property is likely the combined result of photoacclimatory changes at the cellular level and a shift in dominant ecotypes. Developing a mechanistic understanding of sources of variability in pigmentation of picocyanobacteria is critical if the pigment markers and bio-optical properties of these cells are to be used to map their biogeography and serve as indicators of photoacclimatory state of subtropical phytoplankton communities more broadly. It would also allow better assessment of effects on, and adaptability of phytoplankton communities in the tropical/subtropical ocean due to climate change.
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- 2023
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4. Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN)
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Tatsuro Tanioka, Alyse A. Larkin, Allison R. Moreno, Melissa L. Brock, Adam J. Fagan, Catherine A. Garcia, Nathan S. Garcia, Skylar D. Gerace, Jenna A. Lee, Michael W. Lomas, and Adam C. Martiny
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Statistics and Probability ,Library and Information Sciences ,Statistics, Probability and Uncertainty ,Life Below Water ,Computer Science Applications ,Education ,Information Systems - Abstract
Concentrations and elemental stoichiometry of suspended particulate organic carbon, nitrogen, phosphorus, and oxygen demand for respiration (C:N:P:−O2) play a vital role in characterizing and quantifying marine elemental cycles. Here, we present Version 2 of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset. Version 1 is a previously published dataset of particulate organic matter from 70 different studies between 1971 and 2010, while Version 2 is comprised of data collected from recent cruises between 2011 and 2020. The combined GO-POPCORN dataset contains 2673 paired surface POC/N/P measurements from 70°S to 73°N across all major ocean basins at high spatial resolution. Version 2 also includes 965 measurements of oxygen demand for organic carbon respiration. This new dataset can help validate and calibrate the next generation of global ocean biogeochemical models with flexible elemental stoichiometry. We expect that incorporating variable C:N:P:-O2 into models will help improve our estimates of key ocean biogeochemical fluxes such as carbon export, nitrogen fixation, and organic matter remineralization.
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- 2022
5. Varying influence of phytoplankton biodiversity and stoichiometric plasticity on bulk particulate stoichiometry across ocean basins
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Céline Mouginot, Adam C. Martiny, Mark A. Altabet, Michael W. Lomas, Steven E. Baer, Kristina X. Terpis, and Debra A. Lomas
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0301 basic medicine ,geography ,Biogeochemical cycle ,QE1-996.5 ,geography.geographical_feature_category ,fungi ,030106 microbiology ,Biome ,Geology ,Plankton ,Particulates ,Carbon cycle ,Environmental sciences ,03 medical and health sciences ,030104 developmental biology ,Nutrient ,Oceanography ,Phytoplankton ,General Earth and Planetary Sciences ,Environmental science ,GE1-350 ,Oceanic basin ,General Environmental Science - Abstract
Concentrations and elemental ratios of suspended particulate organic matter influence many biogeochemical processes in the ocean, including patterns of phytoplankton nutrient limitation and links between carbon, nitrogen and phosphorus cycles. Here we present direct measurements of cellular nutrient content and stoichiometric ratios for discrete phytoplankton populations spanning broad environmental conditions across several ocean basins. Median cellular carbon-to-phosphorus and nitrogen-to-phosphorus ratios were positively correlated with vertical nitrate-to-phosphate flux for all phytoplankton groups and were consistently higher for cyanobacteria than eukaryotes. Light and temperature were inconsistent predictors of stoichiometric ratios. Across nutrient-rich and phosphorus-stressed biomes in the North Atlantic, but not in the nitrogen-stressed tropical North Pacific, we find that a combination of taxonomic composition and environmental acclimation best predict bulk particulate organic matter composition. Our findings demonstrate the central role of plankton biodiversity and plasticity in controlling linkages between ocean nutrient and carbon cycles in some regions. Phytoplankton biodiversity and cellular acclimation to vertical nutrient flux ratio control particulate stoichiometry in the North Atlantic, according to field observations of cellular elemental stoichiometry across taxonomic groups and ocean basins.
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- 2021
6. Phytoplankton and seston fatty acid dynamics in the northern Bering-Chukchi Sea region
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Jens M. Nielsen, Louise A. Copeman, Lisa B. Eisner, Kelia E. Axler, Calvin W. Mordy, and Michael W. Lomas
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Oceanography - Published
- 2023
7. Forecasting community reassembly using climate‐linked spatio‐temporal ecosystem models
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Alan C. Haynie, Elizabeth C. Siddon, Wei Cheng, Kirstin K. Holsman, Albert J. Hermann, Mayumi L. Arimitsu, Jon Richar, James T. Thorson, Lisa B. Eisner, Lewis A.K. Barnett, David G. Kimmel, and Michael W. Lomas
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business.industry ,Ecology ,Environmental resource management ,Distribution (economics) ,Environmental science ,Ecosystem ,business ,Ecology, Evolution, Behavior and Systematics - Published
- 2021
8. Whales in the carbon cycle: can recovery remove carbon dioxide?
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Heidi C. Pearson, Matthew S. Savoca, Daniel P. Costa, Michael W. Lomas, Renato Molina, Andrew J. Pershing, Craig R. Smith, Juan Carlos Villaseñor-Derbez, Stephen R. Wing, and Joe Roman
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Ecology, Evolution, Behavior and Systematics - Abstract
The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO
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- 2022
9. Marine phytoplankton resilience may moderate oligotrophic ecosystem responses and biogeochemical feedbacks to climate change
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Adam C. Martiny, George I. Hagstrom, Tim DeVries, Robert T. Letscher, Gregory L. Britten, Catherine A. Garcia, Eric Galbraith, David Karl, Simon A. Levin, Michael W. Lomas, Allison R. Moreno, David Talmy, Weilei Wang, and Katsumi Matsumoto
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Aquatic Science ,Oceanography - Published
- 2022
10. Impact of Growth Phase, Pigment Adaptation, and Climate Change Conditions on the Cellular Pigment and Carbon Content of Fifty-One Phytoplankton Isolates
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Aimee R. Neeley, Michael W. Lomas, Antonio Mannino, Crystal Thomas, and Ryan Vandermeulen
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Chlorophyll ,Diatoms ,Chlorophyll A ,Climate Change ,Phytoplankton ,Plant Science ,Biomass ,Aquatic Science ,Carbon Dioxide ,Ecosystem - Abstract
Owing to their importance in aquatic ecosystems, the demand for models that estimate phytoplankton biomass and community composition in the global ocean has increased over the last decade. Moreover, the impacts of climate change, including elevated carbon dioxide (COsub2/sub), increased stratification, and warmer sea surface temperatures, will likely shape phytoplankton community composition in the global ocean. Chemotaxonomic methods are useful for modeling phytoplankton community composition from marker pigments normalized to chlorophyll a (Chl a). However, photosynthetic pigments, particularly Chl a, are sensitive to nutrient and light conditions. Cellular carbon is less sensitive, so using carbon biomass instead may provide an alternative approach. To this end, cellular pigment and carbon concentrations were measured in 51 strains of globally relevant, cultured phytoplankton. Pigment-to-Chl a and pigment-to-carbon ratios were computed for each strain. For 25 strains, measurements were taken during two growth phases. While some differences between growth phases were observed, they did not exceed within-class differences. Multiple strains of Amphidinium carterae, Ditylum brightwellii and Heterosigma akashiwo were measured to determine whether time in culture influenced pigment and carbon composition. No appreciable trends in cellular pigment or carbon content were observed. Lastly, the potential impact of climate change conditions on the pigment ratios was assessed using a multistressor experiment that included increased mean light, temperature, and elevated pCOsub2/subon three species: Thalassiosira oceanica, Ostreococcus lucimarinus, and Synechococcus. The largest differences were observed in the pigment-to-carbon ratios, while the marker pigments largely covaried with Chl a. The implications of these observations to chemotaxonomic applications are discussed.
- Published
- 2021
11. Drawdown of Atmospheric pCO 2 Via Variable Particle Flux Stoichiometry in the Ocean Twilight Zone
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Katsumi Matsumoto, Tatsuro Tanioka, and Michael W. Lomas
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Total organic carbon ,Remineralisation ,chemistry.chemical_element ,Biological pump ,Photosynthesis ,Atmospheric sciences ,Carbon cycle ,Geophysics ,chemistry ,Drawdown (hydrology) ,General Earth and Planetary Sciences ,Environmental science ,Carbon ,Stoichiometry - Abstract
The strength of the biological soft tissue pump in the ocean critically depends on how much organic carbon is produced via photosynthesis and how efficiently the carbon is transferred to the ocean ...
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- 2021
12. Exploring long-term trends in marine ecosystems: machine-learning approaches to global change biology
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Michael W. Lomas, Domenico D'Alelio, Nadia Sanseverino, Luca Russo, Luigi Maria Cusano, and Salvatore Rampone
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business.industry ,Computer science ,Global change ,Variance (accounting) ,15. Life on land ,Missing data ,Machine learning ,computer.software_genre ,Term (time) ,13. Climate action ,Hindcast ,Marine ecosystem ,Ecosystem ,14. Life underwater ,Artificial intelligence ,business ,Construct (philosophy) ,computer - Abstract
The observation of marine systems and the acquisition of physical, chemical, biological, and ecological data have increasingly grown in the last century. Marine systems are undergoing multiple and overlapping impacts that menace ecological communities, but global change impacts on the ecosystem functioning are not easily assessable, for several reasons. For instance, because time-series datasets can include a sizeable amount of sparse and missing values, and the physical-biological interrelationships establishing within marine ecosystems can determine ample fluctuations, incoherent peaks and, overall, a high variance in the variables under study. Herein, we propose coupling linear statistics and different categories of Machine Learning techniques as a good compromise to construct and test suitable mechanistic models for hindcasting and forecasting the dynamics of key ecological processes, such as primary productivity in the open ocean.
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- 2021
13. Adaptive carbon export response to warming in the Sargasso Sea
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Michael W. Lomas, Nicholas R. Bates, Rodney J. Johnson, Deborah K. Steinberg, and Tatsuro Tanioka
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Multidisciplinary ,Oceans and Seas ,fungi ,Phytoplankton ,General Physics and Astronomy ,Phosphorus ,Seawater ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology ,Carbon ,Ecosystem ,Carbon Cycle - Abstract
Ocean ecosystem models predict that warming and increased surface ocean stratification will trigger a series of ecosystem events, reducing the biological export of particulate carbon to the ocean interior. We present a nearly three-decade time series from the open ocean that documents a biological response to ocean warming and nutrient reductions wherein particulate carbon export is maintained, counter to expectations. Carbon export is maintained through a combination of phytoplankton community change to favor cyanobacteria with high cellular carbon-to-phosphorus ratios and enhanced shallow phosphorus recycling leading to increased nutrient use efficiency. These results suggest that surface ocean ecosystems may be more responsive and adapt more rapidly to changes in the hydrographic system than is currently envisioned in earth ecosystem models, with positive consequences for ocean carbon uptake.
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- 2021
14. Drawdown of Atmospheric pCO2 via Dynamic Particle Export Stoichiometry in the Ocean Twilight Zone
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Tatsuro Tanioka, Katsumi Matsumoto, and Michael W. Lomas
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Total organic carbon ,chemistry ,Drawdown (hydrology) ,Environmental science ,Particle ,chemistry.chemical_element ,Photosynthesis ,Atmospheric sciences ,Carbon ,pCO2 ,Stoichiometry - Abstract
The strength of the biological soft tissue pump in the ocean critically depends on how much organic carbon is produced via photosynthesis and how efficiently the carbon is transferred to the ocean ...
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- 2021
15. A nutrient limitation mosaic in the eastern tropical Indian Ocean
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Adam C. Martiny, Olga Antipova, Michael W. Lomas, Benjamin S. Twining, Steven E. Baer, and Sara Rauschenberg
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0106 biological sciences ,geography ,Biogeochemical cycle ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Oceanography ,01 natural sciences ,chemistry.chemical_compound ,Indian Ocean Gyre ,Nitrate ,chemistry ,Phytoplankton ,Environmental science ,Trace metal ,Oceanic basin ,Transect ,Bay ,0105 earth and related environmental sciences - Abstract
The Indian Ocean accounts for about one fifth of global ocean net primary production but remains undersampled relative to other major ocean basins. The eastern tropical Indian Ocean is characterized by extremely low concentrations of both macronutrients and the micronutrient iron. We measured concentrations of dissolved and particulate trace metals (Fe, Mn, Zn, Pb) in the upper ocean along the GO-SHIP IO9N transect (28˚S to 17˚N, mostly along the 95˚E meridian) during a cruise in April 2016. Cellular quotas (metal/C) of Fe, Mn, Co, Ni, Cu, and Zn were measured in small eukaryotic flagellates (2–7 μm). Deckboard bottle incubation experiments were conducted at one station in each of three putative biogeochemical regions: southern Indian Ocean gyre (SIO, 28-10˚S); equatorial Indian Ocean (EqIO, 10˚S - 5˚N); Bay of Bengal (BoB, 5-17˚N). Nitrate and phosphate were below detection limits in surface waters across the transect. Dissolved and particulate Fe were
- Published
- 2019
16. Carbon and nitrogen productivity during spring in the oligotrophic Indian Ocean along the GO-SHIP IO9N transect
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Adam C. Martiny, Catherine A. Garcia, Benjamin S. Twining, Steven E. Baer, Nathan S. Garcia, Sara Rauschenberg, and Michael W. Lomas
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0106 biological sciences ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,biology ,010604 marine biology & hydrobiology ,Oceanography ,biology.organism_classification ,01 natural sciences ,Latitude ,Productivity (ecology) ,Phytoplankton ,Environmental science ,Autotroph ,Prochlorococcus ,Transect ,Hydrography ,0105 earth and related environmental sciences - Abstract
There is limited biogeochemical rate data from the oligotrophic central Indian Ocean, but it is known that there are geographical gradients in the physical and chemical conditions that may lead to unique biogeochemical regimes. As participants on a GO-SHIP repeat hydrography cruise, a transect was completed in spring of 2016 from 28 °S to 18 °N in the Indian Ocean, roughly along the 95 °E meridion. Cell count samples (phytoplankton and heterotrophic bacteria) analyzed by flow cytometry, and samples for carbon and nitrogen productivity incubations, assessed by stable isotopic tracers, were obtained from 20 m at approximately every other degree of latitude. Microbial cell counts by flow cytometry indicate that Prochlorococcus was the principal autotroph, but with increasing contributions of Synechococcus around the equator. Large eukaryotes (> 20 μm), imaged using FlowCAM, were generally absent or in very low abundance (
- Published
- 2019
17. Nutrient supply controls particulate elemental concentrations and ratios in the low latitude eastern Indian Ocean
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Benjamin S. Twining, Steven E. Baer, Catherine A. Garcia, Adam C. Martiny, Nathan S. Garcia, Sara Rauschenberg, and Michael W. Lomas
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0106 biological sciences ,010504 meteorology & atmospheric sciences ,Nitrogen ,Iron ,Science ,General Physics and Astronomy ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Phosphorus metabolism ,Nutrient ,Ocean gyre ,Nitrogen Fixation ,Phytoplankton ,MD Multidisciplinary ,Water Movements ,Seawater ,14. Life underwater ,lcsh:Science ,Nitrogen cycle ,Indian Ocean ,0105 earth and related environmental sciences ,Prochlorococcus ,geography ,Multidisciplinary ,geography.geographical_feature_category ,biology ,010604 marine biology & hydrobiology ,fungi ,Phosphorus ,General Chemistry ,Biodiversity ,Nutrients ,Particulates ,biology.organism_classification ,Carbon ,Oceanography ,13. Climate action ,Environmental science ,lcsh:Q ,Bay - Abstract
Variation in ocean C:N:P of particulate organic matter (POM) has led to competing hypotheses for the underlying drivers. Each hypothesis predicts C:N:P equally well due to regional co-variance in environmental conditions and biodiversity. The Indian Ocean offers a unique positive temperature and nutrient supply relationship to test these hypotheses. Here we show how elemental concentrations and ratios vary over daily and regional scales. POM concentrations were lowest in the southern gyre, elevated across the equator, and peaked in the Bay of Bengal. Elemental ratios were highest in the gyre, but approached Redfield proportions northwards. As Prochlorococcus dominated the phytoplankton community, biodiversity changes could not explain the elemental variation. Instead, our data supports the nutrient supply hypothesis. Finally, gyre dissolved iron concentrations suggest extensive iron stress, leading to depressed ratios compared to other gyres. We propose a model whereby differences in iron supply and N2-fixation influence C:N:P levels across ocean gyres., The Indian Ocean provides a unique environmental gradient to test underlying drivers of the elemental composition of particulate organic matter. Here the authors show that nutrient supply, over temperature and biodiversity changes, controls regional variation of elemental ratios in the tropical Indian Ocean.
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- 2018
18. Insights into the controls on metabolite distributions along a latitudinal transect of the western Atlantic Ocean
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Elizabeth B. Kujawinski, Kido Soule Mc, Krista Longnecker, Steven J. Hallam, Michael W. Lomas, Maya P. Bhatia, and Johnson Wm
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chemistry.chemical_classification ,education.field_of_study ,Metabolite ,Population ,Particulates ,Deep sea ,chemistry.chemical_compound ,chemistry ,Osmolyte ,Environmental chemistry ,Photic zone ,Organic matter ,Seawater ,education - Abstract
Metabolites, or the small organic molecules that are synthesized by cells during metabolism, comprise a complex and dynamic pool of carbon in the ocean. They are an essential form of information, linking genotype to phenotype at the individual, population and community levels of biological organization. Characterizing metabolite distributions inside microbial cells and dissolved in seawater is essential to understanding the controls on their production and fate, as well as their roles in shaping marine microbial food webs. Here, we apply a targeted metabolomics method to quantify particulate and dissolved distributions of a suite of biologically relevant metabolites including vitamins, amino acids, nucleic acids, osmolytes, and intermediates in biosynthetic pathways along a latitudinal transect in the western Atlantic Ocean. We find that, in the euphotic zone, most particulate or intracellular metabolites positively co-vary with the most abundant microbial taxa. In contrast, dissolved metabolites exhibited greater variability with differences in distribution between ocean regions. Although fewer particulate metabolites were detected below the euphotic zone, molecules identified in the deep ocean may be linked to preservation of organic matter or adaptive physiological strategies of deep-sea microbes. Based on the identified metabolite distributions, we propose relationships between certain metabolites and microbial populations, and find that dissolved metabolite distributions are not directly related to their particulate abundances.
- Published
- 2021
19. Large-scale genome sequencing reveals the driving forces of viruses in microalgal evolution
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Khaled M. Hazzouri, Joan Blanchette, Sarah Daakour, Ashish Jaiswal, David R. Nobles, David R. Nelson, Amphun Chaiboonchoe, Bushra Saeed Dohai, Khaled M. A. Amiri, Julie Sexton, Alexandra Mystikou, Mark Hurd, Amnah Alzahmi, Kyle J. Lauersen, Michael Preston, Kourosh Salehi-Ashtiani, Weiqi Fu, and Michael W. Lomas
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food.ingredient ,Coccolithovirus ,Genomics ,Biology ,Microbiology ,Genome ,DNA sequencing ,03 medical and health sciences ,Viral Proteins ,0302 clinical medicine ,food ,Chlorovirus ,Virology ,Microalgae ,14. Life underwater ,Ecosystem ,030304 developmental biology ,0303 health sciences ,Pandoravirus ,Whole Genome Sequencing ,Phylum ,Marseillevirus ,High-Throughput Nucleotide Sequencing ,biology.organism_classification ,Evolutionary biology ,Viruses ,Parasitology ,030217 neurology & neurosurgery - Abstract
Summary Being integral primary producers in diverse ecosystems, microalgal genomes could be mined for ecological insights, but representative genome sequences are lacking for many phyla. We cultured and sequenced 107 microalgae species from 11 different phyla indigenous to varied geographies and climates. This collection was used to resolve genomic differences between saltwater and freshwater microalgae. Freshwater species showed domain-centric ontology enrichment for nuclear and nuclear membrane functions, while saltwater species were enriched in organellar and cellular membrane functions. Further, marine species contained significantly more viral families in their genomes (p = 8e–4). Sequences from Chlorovirus, Coccolithovirus, Pandoravirus, Marseillevirus, Tupanvirus, and other viruses were found integrated into the genomes of algal from marine environments. These viral-origin sequences were found to be expressed and code for a wide variety of functions. Together, this study comprehensively defines the expanse of protein-coding and viral elements in microalgal genomes and posits a unified adaptive strategy for algal halotolerance.
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- 2020
20. Linking regional shifts in microbial genome adaptation with surface ocean biogeochemistry
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Adam C. Martiny, George I. Hagstrom, Catherine A. Garcia, Michael W. Lomas, Lucas J. Ustick, Alyse A. Larkin, and Simon A. Levin
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Biogeochemical cycle ,Surface ocean ,Ecology (disciplines) ,Adaptation, Biological ,Medical and Health Sciences ,General Biochemistry, Genetics and Molecular Biology ,Microbial ,elemental stoichiometry ,Genetics ,Seawater ,Adaptation ,Life Below Water ,Atlantic Ocean ,Indian Ocean ,metagenomics ,Evolutionary Biology ,Genome ,Pacific Ocean ,Ecology ,Microbiota ,Human Genome ,Biogeochemistry ,Articles ,Biological Sciences ,Biological ,Genome, Microbial ,Microbial population biology ,Metagenomics ,Environmental science ,Metagenome ,Microbial genome ,General Agricultural and Biological Sciences - Abstract
Linking ‘omics measurements with biogeochemical cycles is a widespread challenge in microbial community ecology. Here, we propose applying genomic adaptation as ‘biosensors’ for microbial investments to overcome nutrient stress. We then integrate this genomic information with a trait-based model to predict regional shifts in the elemental composition of marine plankton communities. We evaluated this approach using metagenomic and particulate organic matter samples from the Atlantic, Indian and Pacific Oceans. We find that our genome-based trait model significantly improves our prediction of particulate C : P (carbon : phosphorus) across ocean regions. Furthermore, we detect previously unrecognized ocean areas of iron, nitrogen and phosphorus stress. In many ecosystems, it can be very challenging to quantify microbial stress. Thus, a carefully calibrated genomic approach could become a widespread tool for understanding microbial responses to environmental changes and the biogeochemical outcomes. This article is part of the theme issue ‘Conceptual challenges in microbial community ecology’.
- Published
- 2020
21. Understanding Diatoms’ Past and Future Biogeochemical Role in High‐Latitude Seas
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Michael W. Lomas and Jeffrey W. Krause
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Thesaurus (information retrieval) ,Biogeochemical cycle ,Geophysics ,Oceanography ,High latitude ,General Earth and Planetary Sciences ,Climate change ,Environmental science - Published
- 2020
22. Reply to: Sources of C30 steroid biomarkers in Neoproterozoic–Cambrian rocks and oils
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Michael W. Lomas, Ilya Bobrovskiy, Christian Hallmann, Samuel S. Bowser, Patrick De Deckker, Fabrice Not, Jochen J. Brocks, Benjamin J. Nettersheim, Eva C. M. Nowack, Jan Pawlowski, Arne Schwelm, Janet M. Hope, Christiane Schmidt, Marleen Stuhr, Michal Kucera, Karin A F Zonneveld, and Ralf Schiebel
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Ecology ,biology ,medicine.medical_treatment ,medicine ,Rhizaria ,Computational biology ,biology.organism_classification ,Ecology, Evolution, Behavior and Systematics ,Steroid - Published
- 2020
23. Ambient nitrate switches the ammonium consumption pathway in the euphotic ocean
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Yifan Zhu, Dalin Shi, Minhan Dai, Thomas W. Trull, Yao Zhang, Hua-Xia Sheng, Xianhui Sean Wan, Shuh-Ji Kao, and Michael W. Lomas
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0106 biological sciences ,010504 meteorology & atmospheric sciences ,Science ,General Physics and Astronomy ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,chemistry.chemical_compound ,Nitrate ,Phytoplankton ,Ammonium ,Photic zone ,lcsh:Science ,Nitrogen cycle ,0105 earth and related environmental sciences ,Multidisciplinary ,010604 marine biology & hydrobiology ,fungi ,Assimilation (biology) ,General Chemistry ,New production ,chemistry ,Environmental chemistry ,Environmental science ,Nitrification ,lcsh:Q - Abstract
Phytoplankton assimilation and microbial oxidation of ammonium are two critical conversion pathways in the marine nitrogen cycle. The underlying regulatory mechanisms of these two competing processes remain unclear. Here we show that ambient nitrate acts as a key variable to bifurcate ammonium flow through assimilation or oxidation, and the depth of the nitracline represents a robust spatial boundary between ammonium assimilators and oxidizers in the stratified ocean. Profiles of ammonium utilization show that phytoplankton assemblages in nitrate-depleted regimes have higher ammonium affinity than nitrifiers. In nitrate replete conditions, by contrast, phytoplankton reduce their ammonium reliance and thus enhance the success of nitrifiers. This finding helps to explain existing discrepancies in the understanding of light inhibition of surface nitrification in the global ocean, and provides further insights into the spatial linkages between oceanic nitrification and new production., The underlying regulatory mechanisms of phytoplankton assimilation and microbial oxidation of ammonium in the surface ocean are unclear. Here, using isotope labeling experiments, the authors show that ambient nitrate is a key variable bifurcating ammonium flow through assimilation or oxidation.
- Published
- 2018
24. Diatom growth, biogenic silica production, and grazing losses to microzooplankton during spring in the northern Bering and Chukchi Seas
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Seth L. Danielson, Jeffrey W. Krause, and Michael W. Lomas
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Biomass (ecology) ,Oceanography ,Water column ,Diatom ,Productivity (ecology) ,biology ,Phytoplankton ,Environmental science ,Biogenic silica ,biology.organism_classification ,Bloom ,Food web - Abstract
It is unclear how warming polar marine systems will alter the magnitude of diatom productivity and its fate within the food web. We examined diatom productivity and size-fractionated phytoplankton grazing losses to protozoan grazers in the northern Bering and Chukchi seas during June 2017. Sea ice was nearly absent and water temperatures were unseasonably warm; such conditions may be considered normal in future decades. Among 28 experiments conducted, five were in bloom conditions. Diatom biomass and production rates were similar to previous studies, suggesting the early ice retreat did not lead to appreciably reduced diatom growth. Statistical analyses showed that 77% of the variance in diatom growth rate could be explained by a combination of nutrients, light, and their interaction, but the interactive effect was most important (explaining 66% of the variance). Protozoan grazing intensity on phytoplankton was largely affected by size, specifically, grazing on larger phytoplankton (e.g. diatoms) was highly variable among stations, with many stations having unquantifiable rates. Protozoan grazers consumed an average of 23 ± 35% of growth at bloom stations and 55 ± 102% among non-bloom stations. For smaller phytoplankton, grazing was persistent and less variable spatially, consuming 64 ± 38% of growth at bloom stations and 79 ± 63% at non-bloom stations. Although previous studies (that did not size-fractionate samples) inferred that protozoan grazers control diatom biomass during blooms, our results suggest that diatom productivity largely escaped protozoan grazing losses, especially in bloom conditions, likely due to temporal lag between phytoplankton and protist biomass accumulation. Thus, during bloom conditions, it was estimated that 20–50 times more diatom organic matter was available for higher trophic levels and/or export (as opposed to water column remineralization) than under non-bloom conditions, despite only a 12-fold increase in gross diatom production in the bloom.
- Published
- 2021
25. Spatiotemporal variability of the nitrogen deficit in bottom waters on the eastern Bering Sea shelf
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Michael W. Lomas, David G. Kimmel, Kelly A. Kearney, Patrick H. Ressler, Lisa B. Eisner, Eric Wisegarver, Phyllis J. Stabeno, Peter Proctor, Kathy Mier, and Calvin W. Mordy
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0106 biological sciences ,geography ,geography.geographical_feature_category ,Denitrification ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,fungi ,Geology ,Aquatic Science ,Oceanography ,01 natural sciences ,Sink (geography) ,Bottom water ,Dissolved organic carbon ,Sea ice ,Environmental science ,Spatial variability ,Hydrography ,Nitrogen cycle ,0105 earth and related environmental sciences - Abstract
As water flows from the North Pacific Ocean to the Arctic Ocean, it passes through the shallow eastern shelf of the Bering Sea which serves as a major sink of inorganic nitrogen. This study explores the physical and biological factors that influence the spatiotemporal variability of this sink. A regional relationship of dissolved inorganic nitrogen to inorganic phosphorus (DIN:P) was established for waters entering the shelf. Residuals from this relationship (termed N∗∗) are a measure of the nitrogen deficit and were determined for bottom waters on the shelf using nutrient data collected on 52 hydrographic cruises spanning 2003 – 2018. Spatial variability in N∗∗ was related to advection, cross-shelf and vertical mixing, and residence time (using simulated ages of bottom water over the middle shelf). On average, this deficit accounted for approximately one-third of the inorganic nitrogen that enters the shelf, and the highest deficits (>8 μM DIN) were observed on the middle shelf between 60°N and St. Lawrence Island (63°N). Temporal variability in N∗∗ was examined over the middle shelf, and higher nitrogen deficits that occurred in colder years were hypothesized to result from weaker flow and increased export of organic matter in the presence of sea ice. On the southern middle shelf, the volume integrated (40 m to bottom) seasonal change in N∗∗ was equivalent to a denitrification rate of 0.7 ± 0.3 mmol N m-2 d-1. Rates of nitrogen loss were also estimated by combining N∗∗ with the simulated residence time of water on the shelf and found to be 0.20 ± 0.02 mmol N m-2 d-1. These rates were comparable to prior measurements of denitrification/anammox reported on the shelf. The nitrogen deficit could not be wholly ascribed to denitrification/anammox as the N:P stoichiometric ratio in particulate matter is known to be lower at higher latitudes, and a lower ratio was observed when dissolved organic matter was measured in a small number of samples. It remains unclear how future reductions in sea ice might impact the extent of nitrogen loss in the Bering Sea.
- Published
- 2021
26. Stoichiometry of Prochlorococcus, Synechococcus , and small eukaryotic populations in the western North Atlantic Ocean
- Author
-
Céline Mouginot, Kristina X. Terpis, Steven E. Baer, Michael W. Lomas, and Adam C. Martiny
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,biology ,Ecology ,010604 marine biology & hydrobiology ,Phosphorus ,chemistry.chemical_element ,Synechococcus ,biology.organism_classification ,01 natural sciences ,Microbiology ,Phosphorus metabolism ,Nutrient ,chemistry ,Photic zone ,Prochlorococcus ,Nitrogen cycle ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Redfield ratio - Abstract
In the North Atlantic Ocean, we found that natural populations of Prochlorococcus adhered to Redfield ratio dimensions when comparing cell quotas of carbon to nitrogen, but had flexible composition under nutrient and light stress, allowing for a broad range of cellular carbon- and nitrogen-to-phosphorus ratios. Synechococcus populations also exhibited a wide range of elemental stoichiometry, including carbon-to-nitrogen ratios and increased their carbon-to-phosphorus ratios in response to low dissolved phosphorus availability. Small eukaryotic populations tended to have lower carbon-to-phosphorus ratios than single cell cyanobacterial groups, with the exception of one group of samples, which highlights the importance of community composition when determining how biological diversity influences bulk particle stoichiometry. The ratio of dissolved nitrogen:phosphorus fluxes into the euphotic zone was not correlated to nitrogen:phosphorus cellular quotas. The lack of a homeostatic relationship implies that other mechanisms, such as species-specific adaptation to oligotrophic phosphorus concentrations, control elemental particle ratios.
- Published
- 2017
27. Nutrient and phytoplankton dynamics on the inner shelf of the eastern <scp>B</scp> ering <scp>S</scp> ea
- Author
-
Carol Ladd, Michael W. Lomas, David H. Shull, Eric Wisegarver, Phyllis J. Stabeno, Nancy Kachel, Raymond N. Sambrotto, Peter Proctor, Lisa B. Eisner, Calvin W. Mordy, and Allan H. Devol
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,fungi ,Front (oceanography) ,New production ,Oceanography ,01 natural sciences ,stomatognathic diseases ,Geophysics ,Nutrient ,Hydrographic survey ,stomatognathic system ,Space and Planetary Science ,Geochemistry and Petrology ,Benthic zone ,Phytoplankton ,Earth and Planetary Sciences (miscellaneous) ,Sedimentary rock ,sense organs ,Nitrogen cycle ,Geology ,0105 earth and related environmental sciences - Abstract
The nitrogen cycle on the inner shelf of the southeastern Bering Sea is complicated due to limited nutrient replenishment across this broad shelf, and substantial nitrogen loss through sedimentary processes. While diffusion at the inner front may periodically support new production, the shelf is generally hypothesized to be a regenerative system. This study uses a combination of hydrographic surveys, and measurements of nitrogen assimilation and benthic fluxes to examine nitrogen cycling on the inner shelf, and connectivity between the middle and inner shelves of the southern and central Bering Sea. Results establish the inner shelf as primarily a regenerative system even in spring, although new production can occur at the inner front. Results also identify key processes that influence nutrient supply to the inner shelf, and reveal coupling between the middle shelf nutrient pool and production on the inner shelf. This article is protected by copyright. All rights reserved.
- Published
- 2017
28. Mesozooplankton grazing during spring sea-ice conditions in the eastern Bering Sea
- Author
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Celia Gelfman, Robert G. Campbell, Michael W. Lomas, Philip Alatalo, Carin J. Ashjian, Evelyn B. Sherr, Celia Ross, Barry F. Sherr, and Donna Van Keuren
- Subjects
0106 biological sciences ,Biomass (ecology) ,010504 meteorology & atmospheric sciences ,Ecology ,010604 marine biology & hydrobiology ,Biology ,Spring bloom ,Oceanography ,biology.organism_classification ,01 natural sciences ,Zooplankton ,Grazing ,Phytoplankton ,Calanus ,Bloom ,Trophic cascade ,0105 earth and related environmental sciences - Abstract
Mesozooplankton (copepods and euphausiids) grazing rates and prey preferences were determined during a series of three research cruises to the eastern Bering Sea in spring 2008, 2009, and 2010. Chlorophyll was dominated by large cells (>5 µm), especially at bloom locations where they usually comprised greater than 90% of the total chlorophyll biomass. The relative importance of microzooplankton to the prey field biomass decreased with increasing chlorophyll concentration, and was less than 10% of the total prey biomass in ice-edge bloom regions. Overall, microzooplankton was the preferred prey of the mesozooplankton, although phytoplankton/ice algae were the dominant component of the diet because of their much greater biomass, especially during blooms. There were differences between mesozooplankton species in their prey preferences: Metridia pacifica, Pseudocalanus spp. and Calanus spp. had the strongest preference for microzooplankton prey, while euphausiids (Thysanoessa spp.) and Neocalanus flemingeri/plumchrus appeared to feed non-selectively on all prey items. Mesozooplankton exhibited a saturating feeding response to chlorophyll concentration (Holling׳s type II) that could be modeled by Michaelis–Menten equations. Taxa-specific maximum ingestion rates generally followed allometric theory, with smaller zooplankton having higher feeding rates than larger zooplankton, and ranged from about 4–30% body carbon day−1. Trophic cascades during grazing experiments could result in a substantial underestimate of chlorophyll ingestion rates, especially for those taxa that had a strong preference for microzooplankton. Grazing impacts by mesozooplankton on the integrated chlorophyll biomass and primary production were 2.7±4.4 and 26±48% day−1, respectively. Impacts increased significantly with increasing mesozooplankton biomass, which increased from early to late spring. However, grazing impacts were extremely low in ice-edge bloom regions. Our findings suggest that even when grazing by microzooplankton is included in our grazing impact estimates, about 50% of the primary production in phytoplankton blooms during spring on the eastern Bering Sea shelf is not grazed and is available for direct export to the benthic community.
- Published
- 2016
29. An introduction and overview of the Bering Sea Project: Volume IV
- Author
-
Carin J. Ashjian, Michael F. Sigler, Phyllis J. Stabeno, Jeffrey M. Napp, H. Rodger Harvey, Michael W. Lomas, and Thomas I. Van Pelt
- Subjects
0106 biological sciences ,Oceanography ,010504 meteorology & atmospheric sciences ,13. Climate action ,010604 marine biology & hydrobiology ,Environmental science ,14. Life underwater ,01 natural sciences ,0105 earth and related environmental sciences ,Volume (compression) - Published
- 2016
30. Variation in annual production of copepods, euphausiids, and juvenile walleye pollock in the southeastern Bering Sea
- Author
-
Phyllis J. Stabeno, Ronald A. Heintz, Michael F. Sigler, Michael W. Lomas, George L. Hunt, and Jeffrey M. Napp
- Subjects
0106 biological sciences ,Thysanoessa ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,biology ,010604 marine biology & hydrobiology ,Spring bloom ,Oceanography ,biology.organism_classification ,01 natural sciences ,Zooplankton ,Match/mismatch ,Pollock ,Fishery ,Sea ice ,Calanus ,Copepod ,0105 earth and related environmental sciences - Abstract
We synthesize recent research on variation in annual production of copepods (Calanus spp.), euphausiids (Thysanoessa spp.), and juvenile walleye pollock (Gadus chalcogrammus) in the southeastern Bering Sea. We reach five conclusions: 1) the timing of the spring bloom is more important than the amount of annual primary production for the transfer of primary to secondary production (i.e., timing matters); 2) summer and fall, not just spring, matter: organisms must maximize energy intake devoted to somatic growth and storage of lipids and minimize energy expenditures during each season; 3) stored lipids are important for the overwinter survival of both zooplankton and age-0 walleye pollock; 4) variation in ice extent and timing of ice retreat affect the spatial distributions of phytoplankton, zooplankton, and age-0 walleye pollock; when these spatial distributions match in late-ice-retreat years, the annual production of copepods, euphausiids, and juvenile walleye pollock often increases (i.e., location matters); 5) if years with late ice retreat, which favor copepod, euphausiid, and juvenile walleye pollock production, occur in succession, top–down control increases. These conclusions help to explain annual variation in production of copepods, euphausiids and juvenile walleye pollock. Copepods and euphausiids often are more abundant in cold years with late ice retreat than in warm years with early ice retreat due to bloom timing and the availability of ice algae during years with late ice retreat. As a consequence, age-0 walleye pollock consume lipid-enriched prey in cold years, better preparing them for their first winter and their overwinter survival is greater. In addition, there is a spatial match of primary production, zooplankton, and age-0 walleye pollock in cold years and a mismatch in warm years.
- Published
- 2016
31. Seasonal and long-term changes in elemental concentrations and ratios of marine particulate organic matter
- Author
-
Adam C. Martiny, Yann Bozec, Nicolas Savoye, Michael W. Lomas, Agathe Talarmin, Helene Frigstad, and David M. Karl
- Subjects
0106 biological sciences ,Atmospheric Science ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Phosphorus ,chemistry.chemical_element ,Pelagic zone ,Estuary ,Particulates ,01 natural sciences ,Nutrient ,Oceanography ,chemistry ,Ecological stoichiometry ,Environmental Chemistry ,Environmental science ,Ecosystem ,0105 earth and related environmental sciences ,General Environmental Science ,Redfield ratio - Abstract
What is the temporal variability of the elemental stoichiometry of marine microbial communities across ocean regions? To answer this question, we present an analysis of environmental conditions, particulate organic carbon, nitrogen, and phosphorus concentrations and their ratios across 20 time series (3–25 years duration) representing estuarine, coastal, and open ocean environments. The majority of stations showed significant seasonal oscillations in particulate organic elemental concentrations and ratios. However, shorter-term changes contributed most to overall variance in particulate organic matter concentrations and ratios. We found a correlation between the seasonal oscillations of environmental conditions and elemental ratios at many coastal but not open ocean and estuarine stations. C:N peaked near the seasonal temperature minimum and nutrient maximum, but some stations showed other seasonal links. C:N ratios declined with time over the respective observation periods at all open ocean and estuarine stations as well as at five coastal station but increased at the nine other coastal stations. C:P (but not N:P) declined slightly at Bermuda Atlantic Time-series Study but showed large significant increases at Hawaii Ocean Time-series and Arendal stations. The relationships between long-term changes in environmental conditions and particulate organic matter concentrations or ratios were ambiguous, but interactions between changes in temperature and nutrient availability were important. Overall, our analysis demonstrates significant changes in elemental ratios at long-term and seasonal time scales across regions, but the underlying mechanisms are currently unclear. Thus, we need to better understand the detailed mechanisms driving the elemental composition of marine microbial ecosystems in order to predict how oceans will respond to environmental changes.
- Published
- 2016
32. Machine learning identifies a strong association between warming and reduced primary productivity in an oligotrophic ocean gyre
- Author
-
Valerio Morfino, Michael W. Lomas, Luca Russo, Salvatore Rampone, Nadia Sanseverino, Luigi Maria Cusano, Domenico D'Alelio, and James E. Cloern
- Subjects
0301 basic medicine ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,lcsh:Medicine ,Machine learning ,computer.software_genre ,Photosynthesis ,01 natural sciences ,Article ,Microbial ecology ,03 medical and health sciences ,Nutrient ,Ocean gyre ,Phytoplankton ,14. Life underwater ,lcsh:Science ,0105 earth and related environmental sciences ,Marine biology ,geography ,Multidisciplinary ,geography.geographical_feature_category ,business.industry ,Global warming ,lcsh:R ,Primary production ,15. Life on land ,Applied mathematics ,030104 developmental biology ,Productivity (ecology) ,13. Climate action ,Environmental science ,lcsh:Q ,Artificial intelligence ,business ,computer - Abstract
Phytoplankton play key roles in the oceans by regulating global biogeochemical cycles and production in marine food webs. Global warming is thought to affect phytoplankton production both directly, by impacting their photosynthetic metabolism, and indirectly by modifying the physical environment in which they grow. In this respect, the Bermuda Atlantic Time-series Study (BATS) in the Sargasso Sea (North Atlantic gyre) provides a unique opportunity to explore effects of warming on phytoplankton production across the vast oligotrophic ocean regions because it is one of the few multidecadal records of measured net primary productivity (NPP). We analysed the time series of phytoplankton primary productivity at BATS site using machine learning techniques (ML) to show that increased water temperature over a 27-year period (1990–2016), and the consequent weakening of vertical mixing in the upper ocean, induced a negative feedback on phytoplankton productivity by reducing the availability of essential resources, nitrogen and light. The unbalanced availability of these resources with warming, coupled with ecological changes at the community level, is expected to intensify the oligotrophic state of open-ocean regions that are far from land-based nutrient sources.
- Published
- 2019
33. Biogeochemical controls of surface ocean phosphate
- Author
-
E. Malcolm S. Woodward, Thierry Moutin, David M. Karl, J. Keith Moore, Taketoshi Kodama, Adam C. Martiny, Fuminori Hashihama, Michael W. Lomas, Jian Ma, Philip W. Boyd, Jota Kanda, Weiwei Fu, Gregory A. Cutter, Ken Furuya, Michael J. Ellwood, Qian P. Li, Yuh-ling Lee Chen, DEPARTMENT OF EARTH SYSTEM SCIENCES UNIVERSITY OF CALIFORNIA IRVINE CA USA, Partenaires IRSTEA, Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Department of Ecology and Evolutionary Biology, University of California, University of California [Irvine] (UCI), University of California-University of California, Bermuda Institute of Ocean Sciences (BIOS), Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, Department of Oceanography, National Sun Yat-sen University, Kaohsiung 80424, Taiwan, National Sun Yat-Sen University (NSYSU), Department of Ocean, Earth and Atmospheric Sciences [Norfolk], Old Dominion University [Norfolk] (ODU), Research School of Earth Sciences, Australian National University, Graduate School of Agricultural and Life Sciences [UTokyo] (GSALS), The University of Tokyo (UTokyo), University of Hawai'i [Honolulu] (UH), National Research Institute for Fisheries Science,Japan Fisheries Research and Education Agency, Université Paris Diderot - Paris 7 (UPD7), Key Laboratory of Orogenic Belts and Crustal Evolution - Ministry of Education, Peking University [Beijing], Agricultural Information Institute (AII), Chinese Academy of Agricultural Sciences (CAAS), Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Plymouth Marine Laboratory, University of California [Irvine] (UC Irvine), and University of California (UC)-University of California (UC)
- Subjects
0106 biological sciences ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,Earth, Planet ,Climate ,Iron ,Oceans and Seas ,chemistry.chemical_element ,Atmospheric sciences ,01 natural sciences ,Phosphates ,chemistry.chemical_compound ,Nutrient ,Nitrogen Fixation ,Ecosystem ,Seawater ,14. Life underwater ,Biomass ,Research Articles ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Biomass (ecology) ,Multidisciplinary ,010604 marine biology & hydrobiology ,Phosphorus ,fungi ,Biogeochemistry ,SciAdv r-articles ,Phosphate ,Geochemistry ,chemistry ,13. Climate action ,Phytoplankton ,Environmental science ,geographic locations ,Research Article - Abstract
High-sensitivity measurements reveal variation in surface ocean phosphate, leading to a new model for ocean nutrient cycles., Surface ocean phosphate is commonly below the standard analytical detection limits, leading to an incomplete picture of the global variation and biogeochemical role of phosphate. A global compilation of phosphate measured using high-sensitivity methods revealed several previously unrecognized low-phosphate areas and clear regional differences. Both observational climatologies and Earth system models (ESMs) systematically overestimated surface phosphate. Furthermore, ESMs misrepresented the relationships between phosphate, phytoplankton biomass, and primary productivity. Atmospheric iron input and nitrogen fixation are known important controls on surface phosphate, but model simulations showed that differences in the iron-to-macronutrient ratio in the vertical nutrient supply and surface lateral transport are additional drivers of phosphate concentrations. Our study demonstrates the importance of accurately quantifying nutrients for understanding the regulation of ocean ecosystems and biogeochemistry now and under future climate conditions.
- Published
- 2019
34. Genomic adaptation of marine phytoplankton populations regulates phosphate uptake
- Author
-
Catherine A. Garcia, Lucas J. Ustick, Adam C. Martiny, and Michael W. Lomas
- Subjects
chemistry.chemical_compound ,chemistry ,Ecology ,Phytoplankton ,Aquatic Science ,Adaptation ,Biology ,Oceanography ,Phosphate - Published
- 2019
35. Subtle biogeochemical regimes in the Indian Ocean revealed by spatial and diel frequency of Prochlorococcus haplotypes
- Author
-
Alyse A. Larkin, Nathan S. Garcia, Steven E. Baer, Michael W. Lomas, Benjamin S. Twining, Kimberly A. Ingoglia, Adam C. Martiny, and Catherine A. Garcia
- Subjects
Indian ocean ,Biogeochemical cycle ,Oceanography ,biology ,Haplotype ,Prochlorococcus ,Aquatic Science ,biology.organism_classification ,Diel vertical migration - Published
- 2019
36. Putative sponge biomarkers in unicellular Rhizaria question an early rise of animals
- Author
-
Eva C. M. Nowack, Arne Schwelm, Ralf Schiebel, Michael W. Lomas, Samuel S. Bowser, Fabrice Not, Marleen Stuhr, Michal Kucera, Karin A F Zonneveld, Janet M. Hope, Christiane Schmidt, Benjamin J. Nettersheim, Ilya Bobrovskiy, Jochen J. Brocks, Christian Hallmann, Patrick De Deckker, and Jan Pawlowski
- Subjects
Zoology ,010502 geochemistry & geophysics ,01 natural sciences ,03 medical and health sciences ,Sponge spicule ,Algae ,Kimberella ,Animals ,Life Science ,Ecology, Evolution, Behavior and Systematics ,Phylogeny ,030304 developmental biology ,0105 earth and related environmental sciences ,Trophic level ,0303 health sciences ,Ecology ,biology ,Rhizaria ,biology.organism_classification ,Porifera ,Sponge ,Sterols ,Paleoecology ,Dickinsonia ,Biomarkers - Abstract
The dawn of animals remains one of the most mysterious milestones in the evolution of life. The fossil lipids 24-isopropylcholestane and 26-methylstigmastane are considered diagnostic for demosponges—arguably the oldest group of living animals. The widespread occurrence and high relative abundance of these biomarkers in Ediacaran sediments from 635–541 million years (Myr) ago have been viewed as evidence for the rise of animals to ecological importance approximately 100 Myr before their rapid Cambrian radiation. Here we show that the biosynthesis of 24-isopropylcholestane and 26-methylstigmastane precursors is common among early-branching unicellular Rhizaria—heterotrophic protists that play an important role in trophic cycling and carbon export in the modern ocean. Negating these hydrocarbons as sponge biomarkers, our study places the oldest evidence for animals closer to the Cambrian Explosion. Cambrian silica hexactine spicules that are approximately 535 Myr old now represent the oldest diagnostic sponge remains, whereas approximately 558-Myr-old Dickinsonia and Kimberella (Ediacara biota) provide the most reliable evidence for the emergence of animals. The proliferation of predatory protists may have been responsible for much of the ecological changes during the late Neoproterozoic, including the rise of algae, the establishment of complex trophic relationships and the oxygenation of shallow-water habitats required for the subsequent ascent of macroscopic animals. Fossil lipid biomarkers previously thought to be diagnostic of sponges (and thus indicative of animal life) are found to be preserved in unicellular Rhizarian protists, questioning a pre-Cambrian origin of sponges.
- Published
- 2019
37. Seasonal changes in water quality and Sargassum biomass in southwest Australia
- Author
-
Michael W. Lomas, Ravi Fotedar, Shovonlal Roy, Michael O'Leary, Anthony J. Cole, and Tin C. Hoang
- Subjects
0106 biological sciences ,Canopy ,010504 meteorology & atmospheric sciences ,Population ,Aquatic Science ,01 natural sciences ,medicine ,Southwest Australia ,education ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,education.field_of_study ,Biomass (ecology) ,geography ,geography.geographical_feature_category ,Ecology ,biology ,010604 marine biology & hydrobiology ,Coral reef ,Seasonality ,medicine.disease ,biology.organism_classification ,Oceanography ,Sargassum ,Water quality - Abstract
Sargassum C. Agardh is one of the most diverse genera of marine macro-algae and commonly inhabits shallow tropical and sub-tropical waters. This study aimed to investigate the effect of seasonality and the associated water quality changes on the distribution, canopy cover, mean thallus length and the biomass of Sargassum beds around Point Peron, Shoalwater Islands Marine Park, Southwest Australia. Samples of Sargassum and seawater were collected every three months from summer 2012 to summer 2014 from four different reef zones. A combination of in situ observations and WorldView-2 satellite remote-sensing images were used to map the spatial distribution of Sargassum beds and other associated benthic habitats. The results demonstrated a strong seasonal variation in the environmental parameters, canopy cover, mean thallus length, and biomass of Sargassum, which were significantly (P < 0.05) influenced by the nutrient concentration (PO43-, NO3-, NH4+) and rainfall. However, no variation in any studied parameter was observed among the four reef zones. The highest Sargassum biomass peaks occurred between late spring and early summer (from September to January). The results provide essential information to guide effective conservation and management, as well as sustainable utilisation of this coastal marine renewable resource.
- Published
- 2016
38. Mesoscale and sub-mesoscale variability in phytoplankton community composition in the Sargasso Sea
- Author
-
Michael W. Lomas, Stacey R. Goldberg, Emily A. Goldman, Douglas W. Bell, Eric M. Lachenmyer, Tammi L. Richardson, and Bridget E. Cotti-Rausch
- Subjects
0301 basic medicine ,Biomass (ecology) ,010504 meteorology & atmospheric sciences ,Mesoscale meteorology ,Aquatic Science ,Plankton ,Biology ,Oceanography ,biology.organism_classification ,01 natural sciences ,03 medical and health sciences ,030104 developmental biology ,Water column ,Downwelling ,Phytoplankton ,Upwelling ,Prochlorococcus ,0105 earth and related environmental sciences - Abstract
The Sargasso Sea is a dynamic physical environment in which strong seasonal variability combines with forcing by mesoscale (~100 km) eddies. These drivers determine nutrient, light, and temperature regimes and, ultimately, the composition and productivity of the phytoplankton community. On four cruises (2011 and 2012; one eddy per cruise), we investigated links between water column structure and phytoplankton community composition in the Sargasso at a range of time and space scales. On all cruises, cyanobacteria ( Prochlorococcus and Synechococcus ) dominated the phytoplankton numerically, while haptophytes were the dominant eukaryotes (up to 60% of total chl- a ). There were substantial effects of mesoscale and sub-mesoscale forcing on phytoplankton community composition in both spring and summer. Downwelling (in anticyclones) resulted in Prochlorococcus abundances that were 22−66% higher than at ‘outside’ stations. Upwelling (in cyclones) was associated with significantly higher abundances and POC biomass of nanoeukaryotes. In general, however, each eddy had its own unique characteristics. The center of anticyclone AC1 (spring 2011) had the lowest phytoplankton biomass (chl- a ) of any eddy we studied and had lower nitrate+nitrite (N+N −2 ) and eukaryote chl- a biomass as compared to its edge and to the Bermuda Atlantic Time-Series station (BATS). At the center of cyclone C1 (summer 2011), we observed uplift of the 26.5 kg m −3 isopycnal and high nutrient inventories (N+N=74±46 mmol m −2 ). We also observed significantly higher haptophyte chl- a (non-coccolithophores) and lower cyanobacterial chl- a at the center and edge of C1 as compared to outside the eddy at BATS. Cyclone C2 (spring 2012) exhibited a deep mixed layer, yet had relatively low nutrient concentrations. We observed a shift in the taxonomic composition of haptophytes between a coccolithophore-dominated community in C2 (98% of total haptophyte chl- a ) and a non-coccolithophore community at BATS. In summer 2012, downwelling associated with anticyclone AC2 occurred at the edge of the eddy (not at the center), where AC2 interacted with a nearby cyclone. At the edge, we found significantly lower Synechococcus abundances and higher eukaryote chl- a compared to the center of AC2 and BATS. These along-transect nuances demonstrate the significance of small-scale perturbations that substantially alter phytoplankton community structure. Therefore, while seasonality in the North Atlantic is the primary driver of broad-scale trends in phytoplankton community composition, the effects of transient events must be considered when studying planktonic food webs and biogeochemical cycling in the Sargasso Sea.
- Published
- 2016
39. Decadal variability in the oxygen inventory of North Atlantic subtropical underwater captured by sustained, long‐term oceanographic time series observations
- Author
-
Enrique Montes, Frank E. Muller-Karger, Sennai Habtes, Michael W. Lomas, Andrés Cianca, and Laura Lorenzoni
- Subjects
0106 biological sciences ,Atmospheric Science ,Global and Planetary Change ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,North Atlantic Deep Water ,Climate change ,Subtropics ,01 natural sciences ,Term (time) ,Oceanography ,Atlantic Equatorial mode ,North Atlantic oscillation ,Climatology ,Atlantic multidecadal oscillation ,Environmental Chemistry ,Environmental science ,Underwater ,0105 earth and related environmental sciences ,General Environmental Science - Published
- 2016
40. Spring plankton dynamics in the Eastern Bering Sea, 1971–2050: Mechanisms of interannual variability diagnosed with a numerical model
- Author
-
Diane K. Stoecker, Barry F. Sherr, Evelyn J. Lessard, Carin J. Ashjian, Michael W. Lomas, Raymond N. Sambrotto, Evelyn B. Sherr, Jinlun Zhang, Neil S. Banas, and Robert G. Campbell
- Subjects
0106 biological sciences ,Biomass (ecology) ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Forcing (mathematics) ,Spring bloom ,Plankton ,Oceanography ,01 natural sciences ,Geophysics ,QA273 ,Space and Planetary Science ,Geochemistry and Petrology ,Ecosystem model ,Phytoplankton ,Earth and Planetary Sciences (miscellaneous) ,Hindcast ,Environmental science ,Ecosystem ,0105 earth and related environmental sciences - Abstract
A new planktonic ecosystem model was constructed for the Eastern Bering Sea based on observations from the 2007-2010 BEST/BSIERP (Bering Ecosystem Study/Bering Sea Integrated Ecosystem Research Program) field program. When run with forcing from a data-assimilative ice-ocean hindcast of 1971-2012, the model performs well against observations of spring bloom time evolution (phytoplankton and microzooplankton biomass, growth and grazing rates, and ratios among new, regenerated, and export production). On the southern middle shelf (57°N, station M2), the model replicates the generally inverse relationship between ice-retreat timing and spring bloom timing known from observations, and the simpler direct relationship between the two that has been observed on the northern middle shelf (62°N, station M8). The relationship between simulated mean primary production and mean temperature in spring (15 February to 15 July) is generally positive, although this was found to be an indirect relationship which does not continue to apply across a future projection of temperature and ice cover in the 2040s. At M2, the leading direct controls on total spring primary production are found to be advective and turbulent nutrient supply, suggesting that mesoscale, wind-driven processes - A dvective transport and storminess - may be crucial to long-term trends in spring primary production in the southeastern Bering Sea, with temperature and ice cover playing only indirect roles. Sensitivity experiments suggest that direct dependence of planktonic growth and metabolic rates on temperature is less significant overall than the other drivers correlated with temperature described above.
- Published
- 2016
41. Satellite-derived estimates of primary production during the Sargasso Sea winter/spring bloom: Integration of in-situ time-series data and ocean color remote sensing observations
- Author
-
Joji Ishizaka, Hoang C. Tin, and Michael W. Lomas
- Subjects
0106 biological sciences ,In situ ,010504 meteorology & atmospheric sciences ,Ecology ,010604 marine biology & hydrobiology ,Aquatic Science ,Seasonality ,Spring bloom ,medicine.disease ,01 natural sciences ,Ocean color ,Climatology ,Ocean color remote sensing ,medicine ,Environmental science ,Sargasso sea ,Animal Science and Zoology ,Photic zone ,Time series ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences - Abstract
Accurate estimates of primary production from satellite-derived data on both regional and global scales are one of the most important goals of international ocean color remote-sensing programs. This manuscript presents surface concentrations and vertical distributions of chlorophyll-a (Chl-a) data as a proxy for phytoplankton biomass, and calculated photosynthesis–irradiance (P–E) curve parameters, which were used to estimate integrated monthly primary production in the Sargasso Sea euphotic zone from 2004 to 2009. The measured surface Chl-a in the Sargasso Sea was low but exhibited strong seasonal variation, and correlated well with satellite estimates of Chl-a. Underwater light transmission was modeled using a shifted Gaussian model from 69 vertical Chl-a profiles, which were collected in the Sargasso Sea. The P–E curve parameters were experimentally derived; the maximum photosynthetic rate, P m B ranged from 1.51 to 3.05 (mgC(mgChl-a) −1 h −1 ) and the maximum light utilization coefficient, α B , ranged from 0.017 to 0.806 (mgC(mgChl−a) −1 (Wm −2 ) −1 h −1 ). These data and previously published P–E curve parameter estimates were used in a spectrally varying model to estimate integrated primary production in the Sargasso Sea euphotic zone. Output from two of the four primary production models agreed well with in-situ measurements (±20%) and captured the strong seasonal variation.
- Published
- 2016
42. Radiometric approach for the detection of picophytoplankton assemblages across oceanic fronts
- Author
-
Zachary K. Erickson, Mikhail V. Zubkov, Heather A. Bouman, P. Jeremy Werdell, Priscila Kienteca Lange, Susanne E. Craig, Wayne H. Slade, Astrid Bracher, Nicole J. Poulton, Ivona Cetinić, Giorgio Dall'Olmo, Michael W. Lomas, Glen A. Tarran, and Robert J. W. Brewin
- Subjects
02 engineering and technology ,Convergence zone ,01 natural sciences ,010309 optics ,Optics ,Ocean gyre ,0103 physical sciences ,Phytoplankton ,14. Life underwater ,geography ,geography.geographical_feature_category ,biology ,business.industry ,Atmospheric correction ,Hyperspectral imaging ,021001 nanoscience & nanotechnology ,Synechococcus ,biology.organism_classification ,Atomic and Molecular Physics, and Optics ,Oceanography ,13. Climate action ,Ocean color ,Environmental science ,Prochlorococcus ,0210 nano-technology ,business - Abstract
Cell abundances of Prochlorococcus, Synechococcus, and autotrophic picoeukaryotes were estimated in surface waters using principal component analysis (PCA) of hyperspectral and multispectral remote-sensing reflectance data. This involved the development of models that employed multilinear correlations between cell abundances across the Atlantic Ocean and a combination of PCA scores and sea surface temperatures. The models retrieve high Prochlorococcus abundances in the Equatorial Convergence Zone and show their numerical dominance in oceanic gyres, with decreases in Prochlorococcus abundances towards temperate waters where Synechococcus flourishes, and an emergence of picoeukaryotes in temperate waters. Fine-scale in-situ sampling across ocean fronts provided a large dynamic range of measurements for the training dataset, which resulted in the successful detection of fine-scale Synechococcus patches. Satellite implementation of the models showed good performance (R2 > 0.50) when validated against in-situ data from six Atlantic Meridional Transect cruises. The improved relative performance of the hyperspectral models highlights the importance of future high spectral resolution satellite instruments, such as the NASA PACE mission’s Ocean Color Instrument, to extend our spatiotemporal knowledge about ecologically relevant phytoplankton assemblages.
- Published
- 2020
43. Size-fractionated biomass and primary productivity of Sargasso Sea phytoplankton
- Author
-
Michael W. Lomas, Emily G. Baumann, Tammi L. Richardson, Bridget E. Cotti-Rausch, and Eric M. Lachenmyer
- Subjects
Biomass (ecology) ,Biogeochemical cycle ,Oceanography ,Abundance (ecology) ,Phytoplankton ,Environmental science ,Pelagic zone ,Aquatic Science ,Deep sea ,Food web ,Trophic level - Abstract
The size structure of phytoplankton communities greatly influences the function of pelagic food webs and, ultimately, the flux of material from the surface ocean to the deep sea. While the biomass and taxonomic composition of organisms in a specific size class are important characteristics of a food web, the activity of that size fraction is more directly relevant to trophic dynamics and biogeochemical cycling. Even if a size class dominates cell abundance or biomass, does it necessarily contribute the most to total primary productivity (PP)? We asked this question for phytoplankton communities from the Sargasso Sea. The picophytoplankton (0.7–2 μm) accounted for 53–85% of the total integrated chl-a and 46–99% or more of the total integrated PP. The microphytoplankton (20–200 μm) were responsible for up to 38% of the total PP, but accounted for no more than 22% of total chl-a. Variations in the picophytoplankton size-class explained 84% of the variance in total integrated chl-a and 87% of the variance in total PP. Size-dependent relative contributions to chl-a versus PP varied with depth, with differences generally driven by vertical variations in C:chl-a ratios and chl-specific rates of PP. Use of the relative contributions of picophytoplankton to biomass as a predictor of their contributions to total primary productivity resulted in an average underestimate of ~7%.
- Published
- 2020
44. Parallel phylogeography of Prochlorococcus and Synechococcus
- Author
-
Alyssa G. Kent, Steven E. Baer, Alyse A. Larkin, Céline Mouginot, Michael W. Lomas, Jeremy S. Huang, and Adam C. Martiny
- Subjects
Technology ,Biology ,Microbiology ,Article ,03 medical and health sciences ,Phylogenetics ,Seawater ,Clade ,Atlantic Ocean ,Ecology, Evolution, Behavior and Systematics ,Phylogeny ,030304 developmental biology ,Prochlorococcus ,Ecotype ,Synechococcus ,0303 health sciences ,Genetic diversity ,Pacific Ocean ,Phylogenetic tree ,030306 microbiology ,Biological Sciences ,biology.organism_classification ,Biological Evolution ,Phylogeography ,Evolutionary biology ,Water Microbiology ,Environmental Sciences - Abstract
The globally abundant marine Cyanobacteria Prochlorococcus and Synechococcus share many physiological traits but presumably have different evolutionary histories and associated phylogeography. In Prochlorococcus, there is a clear phylogenetic hierarchy of ecotypes, whereas multiple Synechococcus clades have overlapping physiologies and environmental distributions. However, microbial traits are associated with different phylogenetic depths. Using this principle, we reclassified diversity at different phylogenetic levels and compared the phylogeography. We sequenced the genetic diversity of Prochlorococcus and Synechococcus from 339 samples across the tropical Pacific Ocean and North Atlantic Ocean using a highly variable phylogenetic marker gene (rpoC1). We observed clear parallel niche distributions of ecotypes leading to high Pianka's Index values driven by distinct shifts at two transition points. The first transition point at 6°N distinguished ecotypes adapted to warm waters but separated by macronutrient content. At 39°N, ecotypes adapted to warm, low macronutrient vs. colder, high macronutrient waters shifted. Finally, we detected parallel vertical and regional single-nucleotide polymorphism microdiversity within clades from both Prochlorococcus and Synechococcus, suggesting uniquely adapted populations at very specific depths, as well as between the Atlantic and Pacific Oceans. Overall, this study demonstrates that Prochlorococcus and Synechococcus have shared phylogenetic organization of traits and associated phylogeography.
- Published
- 2018
45. High Variability in Cellular Stoichiometry of Carbon, Nitrogen, and Phosphorus Within Classes of Marine Eukaryotic Phytoplankton Under Sufficient Nutrient Conditions
- Author
-
Nathan S. Garcia, Julie Sexton, Tracey Riggins, Jeff Brown, Michael W. Lomas, and Adam C. Martiny
- Subjects
0106 biological sciences ,Microbiology (medical) ,010504 meteorology & atmospheric sciences ,growth ,lcsh:QR1-502 ,chemistry.chemical_element ,dinoflagellate ,01 natural sciences ,Microbiology ,lcsh:Microbiology ,chemistry.chemical_compound ,Nutrient ,Nitrate ,eukaryote ,Phytoplankton ,Growth rate ,Original Research ,0105 earth and related environmental sciences ,biology ,010604 marine biology & hydrobiology ,Phosphorus ,Dinoflagellate ,temperature ,15. Life on land ,biology.organism_classification ,Nitrogen ,diatom ,cell size ,Diatom ,chemistry ,Environmental chemistry ,prymnesiophyte ,protist - Abstract
Current hypotheses suggest that cellular elemental stoichiometry of marine eukaryotic phytoplankton such as the ratios of cellular carbon:nitrogen:phosphorus (C:N:P) vary between phylogenetic groups. To investigate how phylogenetic structure, cell volume, growth rate, and temperature interact to affect the cellular elemental stoichiometry of marine eukaryotic phytoplankton, we examined the C:N:P composition in 30 isolates across 7 classes of marine phytoplankton that were grown with a sufficient supply of nutrients and nitrate as the nitrogen source. The isolates covered a wide range in cell volume (5 orders of magnitude), growth rate (
- Published
- 2018
46. List of Contributors
- Author
-
Zouher Amzil, Jean-Marie Bard, Michael A. Borowitzka, Nathalie Bourgougnon, Intan C. Dewi, Amandine M.N. Caruana, Yusuf Chisti, Laurence Coiffard, Céline Couteau, Aurélie Couzinet-Mossion, Justine Dumay, Charlotte Falaise, Joël Fleurence, Joe M. Fox, Taejun Han, Claire Hellio, Matthew L. Julius, Jang K. Kim, Ira A. Levine, Michael W. Lomas, Virginie Mimouni, Michèle Morançais, Jean-Luc Mouget, Hassan Nazih, Jihae Park, P.D. Rajakumar, Julianne P. Sexton, Lionel Ulmann, Gaëtane Wielgosz-Collin, Charles Yarish, and Paul V. Zimba
- Published
- 2018
47. Clade and strain specific contributions of Synechococcus and Prochlorococcus to carbon export in the Sargasso Sea
- Author
-
Susanne Neuer, Demetra Hamill, Michael W. Lomas, Francesca De Martini, and Julie Robidart
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,biology ,Strain (chemistry) ,010604 marine biology & hydrobiology ,chemistry.chemical_element ,Aquatic Science ,Oceanography ,biology.organism_classification ,Synechococcus ,01 natural sciences ,chemistry ,Botany ,Environmental science ,Sargasso sea ,Prochlorococcus ,Clade ,Carbon ,0105 earth and related environmental sciences - Published
- 2017
48. Vertical decoupling of nitrate assimilation and nitrification in the Sargasso Sea
- Author
-
Michael W. Lomas, Daniel M. Sigman, Bess B. Ward, and Sarah E. Fawcett
- Subjects
Carbon dioxide in Earth's atmosphere ,Nitrogen assimilation ,chemistry.chemical_element ,Aquatic Science ,Oceanography ,Deep sea ,Nitrogen ,chemistry.chemical_compound ,Nitrate ,chemistry ,Phytoplankton ,Environmental science ,Photic zone ,Nitrification - Abstract
The fraction of phytoplankton growth that leads to the rain of organic carbon out of the sunlit surface ocean (“export production”) is central to the ocean׳s sequestration of atmospheric carbon dioxide. Nitrate assimilation has long been taken as a measure of export production; however, this has recently been questioned by suggestions that much of the nitrate in the sunlit layer (the “euphotic zone”) originates from biological nitrogen (N) already in surface waters. This view has been supported by recent observations of euphotic zone nitrate elevated in δ 18 O relative to its δ 15 N, taken as indicative of nitrification (the oxidation of recycled ammonium to nitrite and then nitrate). To evaluate the potential importance of nitrification in the Sargasso Sea euphotic zone, we measured the δ 15 N and δ 18 O of seawater nitrate for samples with ≥0.2 µM nitrate collected on 18 cruises in the Sargasso Sea, and here we present the first large data set to correct for the low but often measurable concentrations of nitrite. Regardless of season, nitrate (i.e., nitrate-only rather than nitrate+nitrite as is commonly reported) δ 15 N and δ 18 O increase in unison from below the base of the euphotic zone toward the surface. This pattern derives from nitrate assimilation by phytoplankton, implying that nitrification is much slower than the upward transport of nitrate into the lower Sargasso Sea euphotic zone. In the twilight zone below the euphotic zone, we observe a rise in nitrate δ 18 O (relative to deeper waters) that is not accompanied by a rise in δ 15 N, suggesting nitrification co-occurring with nitrate assimilation. Nitrification, therefore, does not appear to occur in euphotic zone waters overlapping with nitrate assimilation only in the ~150 m-thick twilight zone layer below it. In net, the data argue for a simpler N cycle for the Sargasso Sea euphotic zone than has recently been suggested, with the rate of euphotic zone nitrate assimilation approximating that of organic carbon export to the deep ocean.
- Published
- 2015
49. Decoupling of net community and export production on submesoscales in the Sargasso Sea
- Author
-
Michael W. Lomas, Rachel H. R. Stanley, Ken O. Buesseler, Norman B. Nelson, David A. Siegel, and Margaret L. Estapa
- Subjects
Atmospheric Science ,Global and Planetary Change ,Ocean observations ,Biogeochemical cycle ,Sampling (statistics) ,Decoupling (cosmology) ,Oceanography ,Environmental Chemistry ,Sargasso sea ,Environmental science ,Spatial variability ,Transect ,General Environmental Science ,Trophic level - Abstract
Determinations of the net community production (NCP) in the upper ocean and the particle export production (EP) should balance over long time and large spatial scales. However, recent modeling studies suggest that a horizontal decoupling of flux-regulating processes on submesoscales (≤10 km) could lead to imbalances between individual determinations of NCP and EP. Here we sampled mixed-layer biogeochemical parameters and proxies for NCP and EP during 10, high-spatial resolution (~2 km) surface transects across strong physical gradients in the Sargasso Sea. We observed strong biogeochemical and carbon flux variability in nearly all transects. Spatial coherence among measured biogeochemical parameters within transects was common but rarely did the same parameters covary consistently across transects. Spatial variability was greater in parameters associated with higher trophic levels, such as chlorophyll in >5.0 µm particles, and variability in EP exceeded that of NCP in nearly all cases. Within sampling transects, coincident EP and NCP determinations were uncorrelated. However, when averaged over each transect (30 to 40 km in length), we found NCP and EP to be significantly and positively correlated (R = 0.72, p = 0.04). Transect-averaged EP determinations were slightly smaller than similar NCP values (Type-II regression slope of 0.93, standard deviation = 0.32) but not significantly different from a 1:1 relationship. The results show the importance of appropriate sampling scales when deriving carbon flux budgets from upper ocean observations.
- Published
- 2015
50. Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific
- Author
-
B. L. Mackinson, R. P. Kelly, Gillian Stewart, S.B. Moran, and Michael W. Lomas
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,lcsh:Life ,Biology ,01 natural sciences ,Ocean gyre ,lcsh:QH540-549.5 ,Phytoplankton ,14. Life underwater ,Picoplankton ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Total organic carbon ,geography ,geography.geographical_feature_category ,010604 marine biology & hydrobiology ,lcsh:QE1-996.5 ,fungi ,Biological pump ,Plankton ,Particulates ,lcsh:Geology ,lcsh:QH501-531 ,Oceanography ,Sediment trap ,lcsh:Ecology ,sense organs - Abstract
The contributions of micro-, nano-, and picoplankton to particle export were estimated from measurements of size-fractionated particulate 234Th, organic carbon, and phytoplankton indicator pigments obtained during five cruises between 2010 and 2012 along Line P in the subarctic northeast Pacific Ocean. Sinking fluxes of particulate organic carbon (POC) and indicator pigments were calculated from 234Th–238U disequilibria and, during two cruises, measured by a sediment trap at Ocean Station Papa. POC fluxes at 100 m ranged from 0.65 to 7.95 mmol m−2 d−1, similar in magnitude to previous results at Line P. Microplankton pigments dominate indicator pigment fluxes (averaging 69 ± 19% of total pigment flux), while nanoplankton pigments comprised the majority of pigment standing stocks (averaging 64 ± 23% of total pigment standing stocks). Indicator pigment loss rates (the ratio of pigment export flux to pigment standing stocks) point to preferential export of larger microplankton relative to smaller nano- and picoplankton. However, indicator pigments do not quantitatively trace particle export resulting from zooplankton grazing, which may be an important pathway for the export of small phytoplankton. These results have important implications for understanding the magnitude and mechanisms controlling the biological pump at Line P in particular, and more generally in oligotrophic gyres and high-nutrient, low-chlorophyll (HNLC) regions where small phytoplankton represent a major component of the autotrophic community.
- Published
- 2015
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