Particle flux transformation in the mesopelagic water column: process analysis and global balance

Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km)

Statistical distributions of trace metal concentrations in the northwestern Mediterranean atmospheric aerosol

The concentrations of 11 crustal and anthropogenic trace metals (Li, Al, V, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) were measured from 2006 to 2008 in the atmospheric aerosol at a northwestern Mediterranean coast (station of Cap Ferrat, situated on the southeastern coast of France). Statistical models (lognormal, Weibull, and gamma) that best represented the trace metal distribution for this environment are described. The lognormal model was selected for the distributions of (in decreasing strength of the fit) Al, Co, Li, Zn, Mn, Cu, Pb, and Cd, i.e., metals that are introduced into the atmospheric aerosol by pulses inducing temporal variability in their concentrations. The gamma model was associated with Fe, i.e., metals that exhibit less inter-annual variability than the former trace metals. The third mode (Weibull) represented the distribution of the concentrations of V and Ni. The statistical approach presented in this study contributed to better define and constrain the distribution of the 11 trace metals of the atmospheric aerosol from the northwestern Mediterranean coast. In a close future, knowledge of these statistical distributions will allow using convolution models to separate their natural and anthropogenic contributions, therefore increasing our ability to study anthropogenic emissions of trace metals and their impact on the environmen

In situ imaging reveals the biomass of giant protists in the global ocean

International audiencePlanktonic organisms play crucial roles in oceanic food webs and global biogeochemical cycles1, 2. Most of our knowledge about the ecological impact of large zooplankton stems from research on abundant and robust crustaceans, and in particular copepods3, 4. A number of the other organisms that comprise planktonic communities are fragile, and therefore hard to sample and quantify, meaning that their abundances and effects on oceanic ecosystems are poorly understood. Here, using data from a worldwide in situ imaging survey of plankton larger than 600 μm, we show that a substantial part of the biomass of this size fraction consists of giant protists belonging to the Rhizaria, a super-group of mostly fragile unicellular marine organisms that includes the taxa Phaeodaria and Radiolaria (for example, orders Collodaria and Acantharia). Globally, we estimate that rhizarians in the top 200 m of world oceans represent a standing stock of 0.089 Pg carbon, equivalent to 5.2% of the total oceanic biota carbon reservoir5. In the vast oligotrophic intertropical open oceans, rhizarian biomass is estimated to be equivalent to that of all other mesozooplankton (plankton in the size range 0.2–20 mm). The photosymbiotic association of many rhizarians with microalgae may be an important factor in explaining their distribution. The previously overlooked importance of these giant protists across the widest ecosystem on the planet6 changes our understanding of marine planktonic ecosystems

Optical techniques for remote and in-situ characterization of particles pertinent to GEOTRACES

Field and laboratory characterization of marine particles is laborious and expensive. Proxies of particle properties have been developed that allow researchers to obtain high frequency distributions of such properties in space or time. We focus on optical techniques used to characterize marine particles in-situ, with a focus on GEOTRACES-relevant properties, such as bulk properties including particle mass, cross-sectional area, particle size distribution, particle shape information, and also single particle optical properties, such as individual particle type and size. We also address the use of optical properties of particles to infer particulate organic or inorganic carbon. In addition to optical sensors we review advances in imaging technology and its use to study marine particles in situ. This review addresses commercially available technology and techniques that can be used as a proxy for particle properties and the associated uncertainties with particular focus to open ocean environments, the focus of GEOTRACES

The wineglass effect shapes particle export to the deep ocean in mesoscale eddies

Mesoscale eddies in the ocean strongly impact the distribution of planktonic particles, mediating carbon fluxes over ~1/3 of the world ocean. However, mechanisms controlling particle transport through eddies are complex and challenging to measure in situ. Here we show the subsurface distribution of eddy particles funneled into a wineglass shape down to 1000 m, leading to a sevenfold increase of vertical carbon flux in the eddy center versus the eddy flanks, the “wineglass effect”. We show that the slope of the wineglass (R) is the ratio of particle sinking velocity to the radially inward velocity, such that R represents a tool to predict radial particle movement (here 0.05 m s−1). A simple model of eddy spindown predicts such an ageostrophic flow concentrating particles in the eddy center. We explore how size-specific particle flux toward the eddy center impacts eddies' biogeochemistry and export fluxes

Cross-shelf transport, oxygen depletion, and nitrate release within a forming mesoscale eddy in the eastern Indian Ocean

International audienceMesoscale eddies may drive a significant component of cross-shelf transport important in the ecology of shelf ecosystems and adjacent boundary currents. The Leeuwin Current in the eastern Indian Ocean becomes unstable in the austral autumn triggering the formation of eddies. We hypothesized that eddy formation represented the major driver of cross-shelf transport during the autumn. Acoustic Doppler Current Profiler profiles confirmed periodic offshore movement of 2 Sv of shelf waters into the forming eddy from the shelf, carrying a load of organic particles (>0.06 mm). The gap between inflow and outflow then closed, such that the eddy became isolated from further direct input of shelf waters. Drifter tracks supported an anticyclonic surface flow peaking at the eddy perimeter and decreasing in velocity at the eddy center. Oxygen and nutrient profiles suggested rapid remineralization of nitrate mid-depth in the isolated water mass as it rotated, with a total drawdown of oxygen of 3.6 mol m 22 to 350 m. Depletion of oxygen, and release of nitrate, occurred on the timescale of 1 week. We suggest that N supply and N turnover are rapid in this system, such that nitrate is acting primarily as a regenerated nutrient rather than as a source of new nitrogen. We hypothesize that sources of eddy particulate C and N could include particles sourced from coastal primary producers within 500 km such as macrophytes and sea-grasses known to produce copious detritus, which is prone to resuspension and offshore transport

Light color acclimation is a key process in the global ocean distribution of Synechococcus cyanobacteria

Understanding the functional diversity of specific microbial groups at the global scale is critical yet poorly developed. By combining the considerable knowledge accumulated through recent years on the molecular bases of photosynthetic pigment diversity in marine Synechococcus, a major phytoplanktonic organism, with the wealth of metagenomic data provided by the Tara Oceans expedition, we have been able to reliably quantify all known pigment types along its transect and provide a global distribution map. Unexpectedly, cells able to dynamically change their pigment content to match the ambient light color were ubiquitous and predominated in many environments. Altogether, our results unveiled the role of adaptation to light quality on niche partitioning in a key primary producer

The wineglass effect shapes particle export to the deep ocean in mesoscale eddies

Mesoscale eddies in the ocean strongly impact the distribution of planktonic particles, mediating carbon fluxes over ~1/3 of the world ocean. However, mechanisms controlling particle transport through eddies are complex and challenging to measure in situ. Here we show the subsurface distribution of eddy particles funneled into a wineglass shape down to 1000 m, leading to a sevenfold increase of vertical carbon flux in the eddy center versus the eddy flanks, the “wineglass effect”. We show that the slope of the wineglass (R) is the ratio of particle sinking velocity to the radially inward velocity, such that R represents a tool to predict radial particle movement (here 0.05ms�1). A simple model of eddy spindown predicts such an ageostrophic flow concentrating particles in the eddy center. We explore how size-specific particle flux toward the eddy center impacts eddies' biogeochemistry and export fluxes

Eukaryotic virus composition can predict the efficiency of carbon export in the global ocean

海洋ウイルスの種組成と炭素の鉛直輸送の相関を確認 --ウイルスによる地球環境の制御を示唆. 京都大学プレスリリース. 2021-01-15.The biological carbon pump, in which carbon fixed by photosynthesis is exported to the deep ocean through sinking, is a major process in Earth's carbon cycle. The proportion of primary production that is exported is termed the carbon export efficiency (CEE). Based on in-lab or regional scale observations, viruses were previously suggested to affect the CEE (i.e., viral “shunt” and “shuttle”). In this study, we tested associations between viral community composition and CEE measured at a global scale. A regression model based on relative abundance of viral marker genes explained 67% of the variation in CEE. Viruses with high importance in the model were predicted to infect ecologically important hosts. These results are consistent with the view that the viral shunt and shuttle functions at a large scale and further imply that viruses likely act in this process in a way dependent on their hosts and ecosystem dynamics

Effect of type and concentration of ballasting particles on sinking rate of marine snow produced by the Appendicularian Oikopleura dioica

Ballast material (organic, opal, calcite, lithogenic) is suggested to affect sinking speed of aggregates in the ocean. Here, we tested this hypothesis by incubating appendicularians in suspensions of different algae or Saharan dust, and observing the sinking speed of the marine snow formed by their discarded houses. We show that calcite increases the sinking speeds of aggregates by ~100% and lithogenic material by ~150% while opal only has a minor effect. Furthermore the effect of ballast particle concentration was causing a 33 m d(-1) increase in sinking speed for a 5×10(5) µm(3) ml(-1) increase in particle concentration, near independent on ballast type. We finally compare our observations to the literature and stress the need to generate aggregates similar to those in nature in order to get realistic estimates of the impact of ballast particles on sinking speeds