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A recent paradigm explains that the downward pumping of biogenic carbon in the ocean is performed by the combined action of six different biological carbon pumps (BCPs): the biological gravitational pump, the physically driven pumps (Mixed Layer Pump, Eddy Subduction Pump and Large-scale Subduction Pump), and the animal-driven pumps (diurnal and seasonal vertical migrations of zooplankton and larger animals). Here, we propose a research community approach to implement the new paradigm through the integrated study of these BCPs in the World Ocean. The framework to investigate the BCPs combines measurements from different observational platforms, i.e., oceanographic ships, satellites, moorings, and robots (gliders, floats, and robotic surface vehicles such as wavegliders and saildrones). We describe the following aspects of the proposed research framework: variables and processes to be measured in both the euphotic and twilight zones for the different BCPs; spatial and temporal scales of occurrence of the various BCPs; selection of key regions for integrated studies of the BCPs; multi-platform observational strategies; and upscaling of results from regional observations to the global ocean using deterministic models combined with data assimilation and machine learning to make the most of the wealth of unique measurements. The proposed approach has the potential not only to bring together a large multidisciplinary community of researchers, but also to usher the community toward a new era of discoveries in ocean sciences.

In this Food for Thought, I use my experience of writing scientific publications to stress some aspects of the process that were especially significant for me, and from which I try to derive some general suggestions. These aspects include strong interactions (co-evolution) between paper writing and some of my research directions; the pleasure of writing with co-authors; writing as a tool of scientific creativity; long scientific quests through several publications; the importance of writing books, if possible starting early in the career; being published, reaching readers, and contributing to the advancement of knowledge; and giving in to the pleasure of writing. I explain that I often seized unexpected opportunities that led me to develop ideas and write publications that influenced the course of my career, but I do not necessarily suggest that anyone proceed as I did. My motivation was the enjoyment of exploring new topics, and I wholeheartedly recommend that everyone give in to the pleasure of writing.

A widely used method is found to overestimate organic pollution in natural waters, and an alternative method is proposed., Microbial degradation of dissolved organic carbon (DOC) in aquatic environments can cause oxygen depletion, water acidification, and CO2 emissions. These problems are caused by labile DOC (LDOC) and not refractory DOC (RDOC) that resists degradation and is thus a carbon sink. For nearly a century, chemical oxygen demand (COD) has been widely used for assessment of organic pollution in aquatic systems. Here, we show through a multicountry survey and experimental studies that COD is not an appropriate proxy of microbial degradability of organic matter because it oxidizes both LDOC and RDOC, and the latter contributes up to 90% of DOC in high-latitude forested areas. Hence, COD measurements do not provide appropriate scientific information on organic pollution in natural waters and can mislead environmental policies. We propose the replacement of the COD method with an optode-based biological oxygen demand method to accurately and efficiently assess organic pollution in natural aquatic environments.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter considers the Earth’s overall habitability, that is, the proportion of the surface of the planet that is habitable. It examines variations in the extent of the Earth’s habitable environments over a wide range of periods: diurnal, annual, within centuries, and from tens of thousands to hundreds of millions of years. These variations include the recurrence of large and very large volcanic eruptions, the Ice Age of the Quaternary period (last 2.6 million years), the three snowball Earth episodes, long periods of high and low temperature during the last half billion years, and the alternation of greenhouse and icehouse Earth since 4.5 billion years. The chapter also examines the five mass extinctions documented by the fossil record of the last 540 million years, which are witnesses of major crashes in habitability. Biological innovations have also caused major changes in overall habitability. These innovations include oxygen-producing photosynthesis, calcification, silicification, methanogenesis, oxygen respiration, and multicellularity. The overall habitability of Earth is affected by astronomical and environmental factors that include the Earth’s rotation and orbit around the Sun, the Milankovich orbital cycles, changes in the positions of continents, the impacts of large meteoroids, large volcanic eruptions, and climate changes. In addition, it is presently affected by anthropogenic changes of atmospheric gases. The chapter ends with a summary of key points concerning the interactions between the Solar System, Earth, its overall habitability, and organisms.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This takeover, which is unique in the Solar System, is explained by the existence of interactions between a small number of key environmental and biological mechanisms. Throughout the book, hidden relationships are identified among the suite of nested systems made of the ecosystems, the Earth System, the Solar System, and the Universe. This chapter considers successively five aspects of the Earth System in the context of the Solar System: the organisms, which are subject to biological evolution, and their key features; the Solar System, populated by billions of objects, which is the homeland of Earth in the Universe; Earth together with its sister planets and their moons; a brief history of the 13.7 billion-year Universe; and a brief history of 4.6 billion-year Earth. Several astronomical characteristics have hidden connections with organisms, such as: formation of key chemical elements in dying stars; long-term changes in Earth’s orbit (Milankovitch cycles) responsible for the succession of glacial and interglacial episodes since 2.6 million years; supply of water by asteroids and/or comets; characteristics of the Earth-Moon system favouring the long-term presence of liquid water. The chapter ends with a summary of key points concerning connections between organisms, Earth, the Solar System, and the whole Universe. The co-evolution of Earth and its organisms and ecosystems created the whole Earth system, called here the Living Earth. The latter was achieved 2.5 billion years before present, after two phases called Mineral Earth and Cradle Earth.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter examines both the conditions that make the Earth’s temperature generally suitable for organisms, which determines the thermal habitability of the planet, and the effects of ecosystems on temperature. The chapter considers successively: the thermal limits for growth and survival, and the temperatures on Earth, Venus, Mars and the Moon; the sources of energy at the surface of Earth; the solar radiation flux that reaches Earth; the fate of the solar radiation absorbed by the Earth System; the effects of the absorbed solar radiation on the climate system; how the atmosphere and Earth’s distance from the Sun contribute to set the range of temperatures that occur on Earth; and the long-term controls on Earth’s temperature. It examines the latitudinal, diurnal and seasonal variations in the solar radiation flux and their effects on organisms. The presence of the Moon likely favoured the general occurrence on Earth of climatic conditions suitable for organisms since their establishment on the planet about 4 billion years ago. The chapter also describes the atmospheric and oceanic circulations, and their combined effects on the redistribution of heat on the planet. It considers the faint young Sun paradox and the long-term control of the concentration of atmospheric carbon dioxide. The chapter ends with a summary of key points concerning the interactions between the Solar System, Earth, its temperature, and its ecosystems.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. In this Chapter 10, elements from Chapters 1– 9 are reorganized into a broad picture of the development of the Earth System over billions of years, called The Legend of the Eons. The latter considers successively: the major external and internal abiotic processes that affect the Earth System; the Earth’s acquisition of its physical properties, and their effects on the evolution of the planet; the main steps of biological evolution; the evolution of free oxygen in the Earth’s environment; and the emergence of negative feedback loops in the Earth System. These aspects are combined to describe the evolution of the Earth System, including the effects of human societies. The chapter then focuses on the Anthropocene, which is the period during which human societies had significant impacts on the Earth System, and examines distant events at the onset of the Anthropocene, followed by the growth of human population and its effects on the environment. The Chapter concludes on examples that explain how, during the second part of the twentieth century, countries acted in concert to reduce or eliminate the causes of large-scale or global environmental disturbances. These examples show that governments took action when scientific evidence and public pressure convinced them to do so. However, many other developing global environmental problems were not addressed in the twentieth century despite mounting evidence that they were building up. The consequences are addressed in Chapter 11.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter explores the original nature of the Earth’s atmosphere in the Solar System and some of its connections with organisms, and considers the main atmospheric gases and their interactions with ecosystems. It also examines: the atmosphere of Earth and the other planets in the Solar System, and that of exoplanets, that is, planets outside the Solar System; astronomical and planetary effects on the Earth’s atmosphere; and the connections between atmosphere and climate. The atmospheres of some the numerous moons of planets Jupiter, Saturn and Neptune, and of dwarf planet Pluto are also included. The main atmospheric gases considered in this chapter are: water vapour, nitrogen, oxygen, ozone, carbon dioxide, and methane. The consideration of exoplanets leads to the notion of habitability and the Goldilocks principle, which refers to the children’s story “The Three Bears”. It is explained that two conditions that allow planet Earth to retain its atmosphere are its relatively large mass and safe distance from the Sun. Comparing the different atmospheres of Earth and Venus shows that the natural greenhouse effect can hinder or favour organisms and ecosystems. Different environmental conditions on the two planets led Earth to lose most of its atmospheric carbon, whereas Venus retained an atmosphere with a very high concentration of carbon dioxide (CO2). The chapter ends with a summary of key points concerning the interactions between the Solar System, Earth, its atmosphere, and its ecosystems.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter considers feedbacks and feedback loops that deeply affected the Earth System at some crucial steps of its long history, and continue to affect it today. It explains the different effects of positive and negative feedback loops on the Earth System, which cause runaway effects or promote a settling to equilibrium or self-regulation, respectively. Two negative feedback loops, which involve the oceanic carbonate system and the chemical alteration of silicate rocks, respectively, have generally prevented the occurrence of runaway cooling or warming of the planet. The Chapter examines in detail three major characteristics of the Earth System—the greenhouse effect, the ocean’s nitrogen-to-phosphorus ratio (whose actual value in the ocean is known as the Redfield ratio), and the level of atmospheric oxygen—and describes how major negative feedback loops contribute to regulate these characteristics at various timescales ranging from hundreds of years to tens of millions of years. For example, the history of free oxygen (O2) on Earth began with the emergence of O2-photosynthetic organisms, and largely determined the course of the Earth System over more than 2.4 billion years. The chapter further considers interactions between different types of components of the Earth System, and especially interactions between the feedback loops that regulate environmental O2 and solid oceanic carbonate, and environmental O2 and the oceanic nitrogen-to-phosphorus ratio. It also examines the responses of large-scale processes of the Earth System to geological, biological, and anthropogenic forcing factors, the climate and biological evolution.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. Concluding Chapter 11 focuses on the Anthropocene, which is the period during which human societies had significant impacts on the Earth System, and considers key events that are happening in the twenty-first century and might happen afterwards. The chapter examines four main global anthropogenic perturbations of the Earth System – climate change, ocean acidification, the loss of biodiversity, and water and food insecurity – in terms of: their general mechanisms; the main human activities that contribute to these perturbations; and their feedbacks into the environment and human activities. It also explains the responses provided by adaptation and mitigation approaches to the ongoing global anthropogenic perturbations of the Earth System. The purpose of adaptation is to manage the unavoidable, and that of mitigation to avoid the unmanageable. Adaptation and mitigation are illustrated using sea level rise as example. The text then looks at possible states of the Earth System beyond the twenty-first century, which are: a long interglacial; a very long interglacial; shifting from the present icehouse conditions to those of a greenhouse; and crossing planetary thresholds, caused by runaway warming. The chapter concludes with considerations of what planet Earth would be without some of the key biological innovations that shaped the Earth System. This leads to the idea that humans should become the stewards of their unique planet without delay, taking into account the imperative need to preserve both its habitability and biodiversity.

This book investigates the billion-year takeover of planet Earth by its organisms and ecosystems. This chapter examines the effects of the Earth’s magnetic field on the long-term atmosphere and the resulting consequences for organisms. The chapter focuses in turn on: the succession of phases of the atmosphere, and the corresponding Earth System conditions; the use of the magnetic field by wildlife and humans; the magnetic fields of Earth and other astronomical bodies in the Solar System; the contribution of the magnetic field to the takeover of Earth by organisms in aquatic environments and on continents; and the use by researchers of magnetic fields fossilized in rocks to explore ancient Earth. The chapter considers the mechanisms by which the Earth’s magnetic field is generated, and how the interactions between the magnetic fields of Earth and the Sun contributed to protect both the atmosphere and the water of the planet. The magnetic field protects the Earth’s atmosphere, and the latter shields the liquid water from loss to space. The presence of the liquid ocean was a key factor in the development of ecosystems and the build-up of large biomasses. In addition, organisms on continents are largely protected from direct hits of cosmic rays by the magnetic field which both shields the atmosphere from most cosmic rays and protects the atmosphere whose thickness absorbs most of the cosmic radiation that passes the shield. The chapter ends with a summary of key points concerning the interactions between the Solar System, Earth, the long-term atmosphere, and organisms.

This study analyzes the pH of surface-sediment porewater (i.e. 2-3 cm below the water-sediment interface), and concentrations of CaCO3 and organic carbon (OC) in 1192 sediment cores from the northern South China Sea, in water depths ranging from 137 to 3702 m. This is the first study in the literature to analyze the large-scale spatial variability of deep-water surface-sediment pH over a large ocean basin. The data showed strong spatial variations in pH. The lowest pH values (= 7.5, and up to 8.3) were located in a fourth area, which corresponded to the western branch of the KIC where sediments have been intensively eroded by bottom currents. The pH of surface sediment porewater was significantly linearly related to water depth, bottom-water temperature, and CaCO3 concentration (p < 0.05 for the whole sampling area). This study shows that the pH of surface sediment porewater can be sensitive to characteristics of the overlying water column, and suggests that it will respond to global warming as changes in surface-ocean temperature and pH progressively reach deeper waters. (C) 2016 Elsevier Ltd. All rights reserved.

Despite widespread climate-driven reductions of coral cover on tropical reefs, little attention has been paid to the possibility that changes in the geographic distribution of coral recruitment could facilitate beneficial responses to the changing climate through latitudinal range shifts. To address this possibility, we compiled a global database of normalized densities of coral recruits on settlement tiles (corals m^) deployed from 1974 to 2012, and used the data therein to test for latitudinal range shifts in the distribution of coral recruits. In total, 92 studies provided 1253 records of coral recruitment, with 77% originating from settlement tiles immersed for 3-24 mo, herein defined as long-immersion tiles (LITs); the limited temporal and geographic coverage of data from short-immersion tiles (SITs; deployed for 20° latitude). These trends indicate that a global decline in coral recruitment has occurred since 1974, and the persistent reduction in the densities of recruits in equatorial latitudes, coupled with increased densities in sub-tropical latitudes, suggests that coral recruitment may be shifting poleward., 論文

Carbon is a keystone element in global biogeochemical cycles. It plays a fundamental role in biotic and abiotic processes in the ocean, which intertwine to mediate the chemistry and redox status of carbon in the ocean and the atmosphere. The interactions between abiotic and biogenic carbon (e.g. CO2, CaCO3, organic matter) in the ocean are complex, and there is a half-century-old enigma about the existence of a huge reservoir of recalcitrant dissolved organic carbon (RDOC) that equates to the magnitude of the pool of atmospheric CO2. The concepts of the biological carbon pump (BCP) and the microbial loop (ML) shaped our understanding of the marine carbon cycle. The more recent concept of the microbial carbon pump (MCP), which is closely connected to those of the BCP and the ML, explicitly considers the significance of the ocean's RDOC reservoir and provides a mechanistic framework for the exploration of its formation and persistence. Understanding of the MCP has benefited from advanced ‘omics’ and novel research in biological oceanography and microbial biogeochemistry. The need to predict the ocean's response to climate change makes an integrative understanding of the BCP, ML and MCP a high priority. In this review, we summarize and discuss progress since the proposal of the MCP in 2010 and formulate research questions for the future.

International audience; Dissolved oxygen (O2) is a relevant tracer to interpret variations of both water mass properties in the open ocean and biological production in the surface layer of both coastal and open waters. Deep-water formation is very active in the northwestern Mediterranean Sea, where it influences intermediate and deep waters properties, nutrients replenishment and biological production. This study analyses, for the first time, the 20-year time series of monthly O2 concentrations at the DYFAMED long-term sampling site in the Ligurian Sea. Until the winters of 2005 and 2006, a thick and strong oxygen minimum layer was present between 200 and 1300 m because dense water formation was then local, episodic and of low intensity. In 2005-2006, intense and rapid deep convection injected 24 mol O2 m-2 between 350 and 2000 m from December 2005 to March 2006. Since this event, the deep layer has been mostly ventilated during winter time by newly formed deep water spreading from the Gulf of Lion 250 km to the west and by some local deep mixing in early 2010, 2012 and 2013. In the context of climate change, it is predicted that the intensity of deep convection will become weaker in the Mediterranean, which could potentially lead to hypoxia in intermediate and deep layers with substantial impact on marine ecosystems. With the exception of winters 2005 and 2006, the O2 changes in surface waters followed a seasonal trend that reflected the balance between air-sea O2 exchanges, changes in the depth of the mixed layer and phytoplankton net photosynthesis. We used the 20-year O2 time series to estimate monthly and annual net community production. The latter was 7.1 mol C m-2 yr-1, consistent with C-14 primary production determinations and sediment-trap carbon export fluxes at DYFAMED.

The “biological carbon pump” causes carbon sequestration in deep waters by downward transfer of organic matter, mostly as particles. This mechanism depends to a great extent on the uptake of CO2 by marine plankton in surface waters and subsequent sinking of particulate organic carbon (POC) through the water column. Most of the sinking POC is remineralized during its downward transit, and modest changes in remineralization have substantial feedback on atmospheric CO2 concentrations, but little is known about global variability in remineralization. Here we assess this variability based on modern underwater particle imaging combined with field POC flux data and discuss the potential sources of variations. We show a significant relationship between remineralization and the size structure of the phytoplankton assemblage. We obtain the first regionalized estimates of remineralization in biogeochemical provinces, where these estimates range between −50 and +100% of the commonly used globally uniform remineralization value. We apply the regionalized values to satellite-derived estimates of upper ocean POC export to calculate regionalized and ocean-wide deep carbon fluxes and sequestration. The resulting value of global organic carbon sequestration at 2000 m is 0.33 Pg C yr−1, and 0.72 Pg C yr−1 at the depth of the top of the permanent pycnocline, which is up to 3 times higher than the value resulting from the commonly used approach based on uniform remineralization and constant sequestration depth. These results stress that variable remineralization and sequestration depth should be used to model ocean carbon sequestration and feedback on the atmosphere.

International audience; Nitrogen and iron largely determine phytoplankton production in the ocean, yet there are few direct incubation studies on nutrient limitation of phytoplankton in the western tropical North Pacific Ocean. Here, we assessed the effects of N and Fe amendments on both photosynthesis and biomass of phytoplankton (including final chlorophyll a biomass and taxonomic composition) in that region. Overall, the carrying capacity of phytoplankton biomass was primarily constrained by N, and Fe was a limiting resource only near the equator where phytoplankton was co-limited by N and Fe. Positive growth responses in nutrient-receiving treatments were predominantly caused by diatoms, sometimes together with Synechococcus. The often strong stimulation of large phytoplankton in these treatments substantially modified the phytoplankton assemblage from picoplankton-to diatom-dominated, which was often accompanied by a significant increase in photosynthetic competence. This is the first report showing that phytoplankton in the tropical western North Pacific are primarily limited by N, and co-limited by Fe in some areas. We combined our results with those from comparable studies in the tropical and subtropical Pacific Ocean to propose a general typology that describes and predicts the long-term effects of rate-limiting N and Fe on phytoplankton final biomass and changes in community structure.

International audience; Atmospheric input of anthropogenic lead increased globally over the last centuries. The present study shows that the concentrations of lead in sediment cores from low-productivity Hudson Bay, northern Canada, remained relatively constant over the last centuries. The lack of imprint of the increased anthropogenic lead input in this marine environment is not consistent with the increased lead concentrations in nearby lakes over the same period. In addition, the observed trend in lead isotopic composition in our cores suggests an apparent progressive overprint of anthropogenic lead during the 1900's. In other words, isotopes clearly registered the increasingly anthropogenic nature of lead in the sedimentary record, but total lead concentrations remained constant, indicating that some process limited the export of lead to the sediment. These observations point to a long-term limitation of the downward export of particles in Hudson Bay. Given that the source of lead was the same for both Hudson Bay and neighboring highproductivity lakes, we hypothesize that the very low primary productivity of Hudson Bay waters was responsible for the low vertical export of lead to marine sediments. We further propose that primary productivity is the most important factor that generally drives the vertical export of particulate matter, and thus hydrophobic contaminants, in near-oligotrophic marine environments.

Large macroalgal blooms (i.e. green tides of Ulva prolifera) occurred in the southern Yellow Sea, China, yearly from 2007 to 2016. They were among the largest of such outbreaks around the world, and these blooms likely originated along the coast of the Jiangsu Province, China. Understanding the roles of nutrients in the onset of these macroalgal blooms is needed to identify their origin. This study analyzes the spatiotemporal variations in dissolved inorganic nitrogen and phosphorus (DIN and PO4-P) and the N/P ratio along the Jiangsu coast from 1996 to 2014 during late-March to April, the months which corresponds to the pre-bloom period of green tides since 2007. A zone of high DIN and PO4-P concentrations has developed along the Jiangsu coast, between the cities of Sheyang and Nantong, since 1996. There was an 18-year trend of increasing DIN concentrations during the pre-bloom period as well as a positive correlation between the U. prolifera biomass and DIN concentrations. Nutrient inputs from rivers and mariculture in the Jiangsu Province may have provided nitrogen that contributed the magnitude of macroalgal blooms that subsequently spread into the southern Yellow Sea. (C) 2017 Elsevier B.V. All rights reserved.

International audience; Transparent Exopolymer Particles (TEP) have received considerable attention since they were first described in the ocean more than 20 years ago. This is because of their carbon-rich composition, their high concentrations in ocean’s surface waters, and especially because of their ability to promote aggregation due to their high stickiness (i.e. biological glue). As large aggregates contribute significantly to vertical carbon flux, TEP are commonly seen as a key factor that drives the downward flux of particulate organic carbon (POC). However, the density of TEP is lower than that of seawater, which causes them to remain in surface waters and even move upwards if not ballasted by other particles, which often leads to their accumulation in the sea surface microlayer. Hence we question here the generally accepted view that TEP always increase the downward flux of POC via gravitational settling. In the present reassessment of the role of TEP, we examine how the presence of a pool of non-sinking carbon-rich particulate organic matter in surface waters influences the cycling of organic carbon in the upper ocean at daily to decadal time scales. In particular, we focus on the role of TEP in the retention of organic carbon in surface waters versus downward export, and discuss the potential consequences of climate change on this process and on the efficiency of the biological carbon pump. We show that TEP sink only when ballasted with enough high-density particles to compensate their low density, and hence that their role in vertical POC export is not solely linked to their ability to promote aggregation, but also to their contribution to the buoyancy of POC. It follows that the TEP fraction of POC determines the degree of retention and remineralization of POC in surface waters versus its downward export. A high TEP concentration may temporally decouple primary production and downward export. We identify two main parameters that affect the contribution of TEP to POC cycling; TEP stickiness, and the balance between TEP production and degradation rates. Because stickiness, production and degradation of TEP vary with environmental conditions, the role of TEP in controlling the balance between retention versus export, and hence the drawdown of atmospheric CO2 by the biological carbon pump, can be highly variable, and is likely to be affected by climate change.

International audience; Large amounts of soot are continuously deposited on the global ocean. Even though significant concentrations of soot particles are found in marine waters, the effects of these aerosols on ocean ecosystems are currently unknown. Using a combination of in situ and experimental data, and results from an atmospheric transport model, we show that the deposition of soot particles from an oil-fired power plant impacted biogeochemical properties and the functioning of the pelagic ecosystem in tropical oligotrophic oceanic waters off New Caledonia. Deposition was followed by a major increase in the volume concentration of suspended particles, a change in the particle size spectra that resulted from a stimulation of aggregation processes, a 5% decrease in the concentration of dissolved organic carbon (DOC), a decreases of 33 and 23% in viral and free bacterial abundances, respectively, and a factor~2 increase in the activity of particle-attached bacteria suggesting that soot introduced in the system favored bacterial growth. These patterns were confirmed by experiments with natural seawater conducted with both soot aerosols collected in the study area and standard diesel soot. The data suggest a strong impact of soot deposition on ocean surface particles, DOC, and microbial processes, at least near emission hot spots.

Large-scale regional marine ecosystems can be compared for various processes that include their structure and biodiversity, functioning, services, and effects on biogeochemical processes. The comparisons can proceed from data up, or from conceptual models down, or from a combination of models and data. This study proposes a typology of methods and approaches that are currently used, or could possibly be used for making large-scale ecosystem comparisons. The various methods and approaches are illustrated with examples drawn from the literature. © 2011 Elsevier B.V.

The marine macrophyte Ulva prolifera is the dominant green-tide-forming seaweed in the southern Yellow Sea, China. Here we assessed, in the laboratory, the growth rate and nutrient uptake responses of U. prolifera to different nutrient treatments. The growth rates were enhanced in incubations with added organic and inorganic nitrogen [i.e. nitrate (NO3−), ammonium (NH4+), urea and glycine] and phosphorus [i.e. phosphate (PO43−), adenosine triphosphate (ATP) and glucose 6-phosphate (G-6-P)], relative to the control. The relative growth rates of U. prolifera were higher when enriched with dissolved organic nitrogen (urea and glycine) and phosphorus (ATP and G-6-P) than inorganic nitrogen (NO3− and NH4+) and phosphorus (PO43−). In contrast, the affinity was higher for inorganic than organic nutrients. Field data in the southern Yellow Sea showed significant inverse correlations between macroalgal biomass and dissolved organic nutrients. Our laboratory and field results indicated that organic nutrients such as urea, glycine and ATP, may contribute to the development of macroalgal blooms in the southern Yellow Sea.

Le Quére, Corinne ... et al.-- 23 pages, 13 figures, 4 tables, supplement https://dx.doi.org/10.5194/bg-13-4111-2016-supplement, Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs): six types of phytoplankton, three types of zooplankton, and heterotrophic procaryotes. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing macrozooplankton (e.g. krill), and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean high-nutrient lowchlorophyll (HNLC) region during summer. When model simulations do not include macrozooplankton grazing explicitly, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there is no iron deposition from dust. When model simulations include a slow-growing macrozooplankton and trophic cascades among three zooplankton types, the high-chlorophyll summer bias in the Southern Ocean HNLC region largely disappears. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton community growth rates. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean, C. Le Quéré and E. T. Buitenhuis were funded by UK-NERC projects NE/C516079/1 and NE/K001302/1, and European Commission project EMBRACE 282672. R. Moriarty was funded by EU FAASIS project MEST/CT/2004/514159. M. Vogt was funded by the Marie Curie Research and Training Network GREENCYCLES project MC-RTN-512464 and EUR-OCEANS project 282672

We have investigated the relationships between covariations in environmental variables and variations in distributions of marine copepod diversity over an extensive latitudinal range from 86.5 degrees N to 46.5 degrees S. For this purpose, 7 data sets (representing 13,713 samples) of copepod species composition data and 11 environmental data sets were assembled. Principal components analysis was applied to investigate the relationships among the mean and seasonal variations in environmental descriptors (ocean temperature, chlorophyll a [ Chl a], net primary production, and other physical and chemical properties of the ocean) and their relationships with spatial variations in copepod diversity. High copepod diversity corresponded to a combination of high ocean temperature and salinity and low Chl a and nutrient concentrations (nitrate, silicate, phosphate). To a lesser extent, high-diversity regions were also correlated to low seasonal variability in oxygen, ocean temperature, and mixed-layer depth. Regression on principal components provided a robust prediction of global copepod diversity (R-2 = 0.45, p < 0.001) as our subset of environmental data was representative of the full range of environmental variability that occurs globally.

Most artificial lighting systems operate with a 100-120 Hz flickering, an undesirable condition for studies on photosynthesis, requiring a fluctuating (flashing light effect) as well as a constant light flux. The amplitude of this flickering depends on the type of lamps and on the power supply. Selected lamps and related power supplies providing a flickering-free light source are critically reviewed. A new system is proposed, that combines a high intensity discharge lamp (simulating natural sunlight) with a high-frequency (>40kHz) ballast. This power supply provides a flickering-free light flux, and offers such advantages as the use of lamps with high energy output and long life expectancy.

International audience; Three vertical ocean carbon pumps have been known for almost three decades to sequester atmospheric carbon in the deep-water and sediment reservoirs, i.e. the solubility pump, the carbonate pump, and the soft-tissue (also known as organic, or biological) carbon pump (BCP). These three pumps maintain the vertical gradient in total dissolved inorganic carbon between the surface and deep waters. The more recently proposed microbial carbon pump (MCP) would maintain a gradient between short- and long-lived dissolved organic carbon (DOC; average lifetimes of 100 years, respectively). Long-lived DOC is an additional proposed reservoir of sequestered carbon in the ocean. This review: examines critically aspects of the vertical ocean carbon pumps and the MCP, in particular their physical dimensions and their potential roles in carbon sequestration; normalises the dimensions of the MCP to allow direct comparisons with the three vertical ocean carbon pumps; compares the MCP and vertical ocean carbon pumps; organises in a coherent framework the information available in the literature on refractory DOC; explores the potential effects of the globally changing ocean on the MCP; and identifies the assumptions that generally underlie the MCP studies, as bases for future research. The study: proposes definitions of terms, expressions and concepts related to the four ocean carbon pumps (i.e. three vertical pumps and MCP); defines the magnitude for the MCP as the rate of production of DOC with an average lifetime of >100 years and provides its first estimate for the World Ocean, i.e. 0.2 Pg C year−1; and introduces an operational “first-time-sequestration” criterion that prevents organic carbon fluxes from being assigned to both the BCP and the MCP. In our review of the potential effects of predicted climate-related changes in the ocean environment on the MCP, we found that three of the seven predicted changes could potentially enhance carbon sequestration by the MCP, and three could diminish it.

International audience; Using a previous model based on the microbial hub (HUB; consists of heterotrophic bacteria and microzooplankton, the latter being heterotrophic protists), we investigated the effects of competition for inorganic and organic resources in planktonic food webs by proposing and developing the concept of `competition switches'. A competition switch controls the flow of carbon toward either the HUB or other food web compartments. The 3 switches are PB: competition for inorganic nutrients between bacteria and phytoplankton; MB: competition for detritus between bacteria and mesozooplankton; and M mu: competition for large-sized phytoplankton production between microzooplankton and mesozooplankton. Here, we explored the novel hypothesis that competition for resources between the HUB and other food web compartments plays a crucial role in controlling the flows of biogenic carbon in the euphotic zone. We ran a numerical model to determine the potential effects of the 3 competition switches and found that the most important switch is MB, followed by PB and M mu. Comparison of our model results with field data indicated that the strong effects of HUB competition for resources with phytoplankton and mesozooplankton exist both in our model as well as in the world ocean. Finally, comparison of our model results with carbon flows estimated by the linear inverse approach showed that the competition switches can determine large changes in the flows of carbon in marine pelagic food webs. The focus of our study was the propagation of competition effects that occur at the core of the food web.

This work is based on a long time series of data collected in the well-preserved Bay of Calvi (Corsica island, Ligurian Sea, NW Mediterranean) between 1979 and 2011, which include physical characteristics (31 years), chlorophyll a (chl a, 15 years), and inorganic nutrients (13 years). Because samples were collected at relatively high frequencies, which ranged from daily to biweekly during the winter-spring period, it was possible to (1) evidence the key role of two interacting physical variables, i.e. water temperature and wind intensity, on nutrient replenishment and phytoplankton dynamics during the winter-spring period, (2) determine critical values of physical factors that explained interannual variability in the replenishment of surface nutrients and the winter-spring phytoplankton bloom, and (3) identify previously unrecognised characteristics of the planktonic ecosystem. Over the >30 year observation period, the main driver of nutrient replenishment and phytoplankton (chl a) development was the number of wind events (mean daily wind speed >5 m s(-1)) during the cold-water period (subsurface water

Arrieta et al . (Reports, 17 April 2015, p. 331) propose that low concentrations of labile dissolved organic carbon (DOC) preclude prokaryotic consumption of a substantial fraction of DOC in the deep ocean and that this dilution acts as an alternative mechanism to recalcitrance for long-term DOC storage. Here, we show that the authors’ data do not support their claims.

The carbon to nitrogen (C:N) stoichiometry of phytoplankton production varied significantly during the spring–summer bloom in the North Water Polynya (NOW), from April through July 1998. The molar ratio of particulate organic carbon (POC) to nitrogen (PON) production by phytoplankton (ΔPOC:ΔPON) increased from 5.8 during April through early June to 8.9 in late June and July. The molar dissolved inorganic carbon (DIC) to nitrate+nitrite (NO 3 ) drawdown ratio (ΔDIC: ΔNO 3 ) increased from 6.7 in April and May, to 11.9 in June (no estimate for July because of ice melting). The discrepancy between ΔPOC:ΔPON and ΔDIC:ΔNO 3 was likely due to dissolved organic carbon (DOC) production. Increased ΔPOC:ΔPON of phytoplankton and surface water ΔDIC:ΔNO 3 throughout the phytoplankton blooms resulted from changes in physical properties of the upper water column, such as reduced thickness of the surface mixed layer that exposed phytoplankton to increased photosynthetically available radiation (PAR), accompanied by NO 3 depletion. This is expected to have significant effects on the cycling of carbon (C) and nitrogen (N) in pelagic ecosystems, as the increased C:N ratio of organic matter decreases its quality as substrate for grazers and microbial communities. Based on ΔPOC:ΔPON, the ratio of POC to chlorophyll a (Chl) production (ΔPOC:ΔChl) and the relationship between Chl yields and NO 3 depletion, we estimate that 71±17% and 46±20% of the depleted NO 3 went to PON production in the euphotic zone over the polynya from April to early June, and late June to July, respectively. The remaining NO 3 was likely channelled to dissolved organic nitrogen (DON) and heterotrophic bacteria, which were not returned to the dissolved inorganic nitrogen (DIN) pool through recycling during the course of the study. Hence, the autotrophic production of organic N and its recycling by the microbial food web were not coupled temporally.

In order to understand the mechanisms responsible for the high productivity and bio- geochemical cycling of carbon in the North Water Polynya (NOW), we determined physical proper- ties and nutrient concentrations of the upper water column, and phytoplankton production, during spring/summer (April to July) 1998. Phytoplankton production of total organic carbon (PTOC) was par- titioned into production of dissolved and particulate organic carbon (PDOC and PPOC, respectively), the latter being further partitioned into production of large and small phytoplankton (PL and PS, respectively) using 5 µm as threshold. The highest PTOC was 6 g C m -2 d -1 at peak bloom. The fraction of PDOC in PTOC was lower in periods of high PTOC than those of low PTOC. Averaged over the whole polynya for the sampling period, PDOC and PPOC accounted for 34 and 66% of the fixed carbon, respec- tively, and 81 and 19% of PPOC were in the PL and PS fractions, respectively. Variations in the inte- grated assimilation numbers of large and small phytoplankton were mostly explained by nutrients and irradiance. Even though PPOC was dominated by large phytoplankton, the sinking rates of the phytoplankton cells were relatively low (0 to 0.7 m d -1 ), hence low export of PPOC to depth (17%), and relatively high potential transfer to large pelagic organisms through the herbivorous food web. This explains why the NOW is a major feeding and spawning area for fish, mammals and birds.

The growth and dynamics of plankton in the ocean vary with natural cycles, global climate change and the long-term evolution of ecosystems. The ocean is a large reservoir for CO2 and the food webs in the upper ocean play critical roles in regulating the global carbon cycle, changes in atmospheric CO2 and associated global warming. Microheterotrophs are a key component of the upper ocean food webs. Here, we report on the results of an analysis of the distribution of bacteria and related properties in the World Ocean. We found that, for the data set as a whole, there is a significant latitudinal gradient in all field-measured and computed bacterial properties, except growth rate. Gradients were, for the most part, driven by an equator-ward increase in the Southern Hemisphere. The biomass, rates of production and respiration and dissolved organic carbon concentrations were significantly higher in the Northern than the Southern hemispheres. In contrast, growth rates were the same in the two hemispheres. We conclude that the lower biomass and production in the Southern Hemisphere reflects greater top-down control by microbial grazers, which would be due to a lower abundance or activity of omnivorous zooplankton in the Southern than Northern Hemispheres. These large spatial differences in dynamics, structure and activity of the bacterial community and the microbial food web will be reflected in different patterns of carbon cycling, export and air–sea exchange of CO2 and the potential ability of the ocean to sequester carbon.

Changes in both the environment and environmental research have led to the development of new protocols and approaches. These new approaches consider both the effects of changes in the global environment on living organisms (i.e. the responses of ecosystems to environmental processes) and the feedback responses of these organisms and ecosystems (i.e. the effects of living organisms on the environment). The present paper focuses on pelagic food webs in aquatic ecosystems. We examine three major effects of global environmental changes on aquatic organisms: (i) the release of pollutants and biological agents in lakes and nearshore marine waters; (ii) the loss of biodiversity and the collapse of commercially exploited resources that were heretofore renewable. We develop detailed examples of the effects of human activities on marine organisms (i.e. the effects of nutrient supply on the structure of pelagic food webs in marine systems. Finally, we examine (iii) the food-web-controlled exchanges of CO2 between the atmosphere and the ocean, as a feedback effect of pelagic ecosystems on the global environment with respect to the ongoing climate change.

Ice algae, phytoplankton, zooplankton and the vertical fluxes of chloropigments andparticulate organic carbon (POC) were monitored from May to June/July of 1992, 1994 and 1995under the ice of Barrow Strait (Canadian Arctic Archipelago). Large interannual differences in thetiming, magnitude and nature of vertical fluxes were driven by meteorological events that controlledsnow cover and by differences in zooplankton assemblages. In 1992, ice algae released from the icematrix were intensely recycled by the exceptionally abundant calanoid Pseudocalanus acuspes . Thepersistent snow cover delayed the phytoplankton bloom until after the ice break-up in July. Ice algaewere abruptly released and sank rapidly to depth following early rain in late May 1994 and a heat-wave in early June 1995. In both years, the early removal of snow triggered an under-ice phyto-plankton bloom and strong downward fluxes of POC and chloropigments (13.7 gC m –2 , 381 mgchloropigments m –2 in 1994). In the absence of nutrient limitation, under-ice fluxes represented anet addition to the annual flux of POC. The analysis of local climate from 1950 to 1995 suggests thatstrong and early under-ice fluxes of biogenic carbon in spring may become more frequent under theclimatic conditions anticipated by general circulation models.KEY WORDS: Sea ice · Carbon flux · Climate forcing · Copepod grazing · Arctic