Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies

Global Trends in Marine Plankton Diversity across Kingdoms of Life

35 pages, 18 figures, 1 table, supplementary information https://doi.org/10.1016/j.cell.2019.10.008.-- Raw reads of Tara Oceans are deposited at the European Nucleotide Archive (ENA). In particular, newly released 18S rRNA gene metabarcoding reads are available under the number ENA: PRJEB9737. ENA references for the metagenomics reads corresponding to the size fraction < 0.22 μm (for prokaryotic viruses) analyzed in this study are included in Gregory et al. (2019); see their Table S3. ENA references for the metagenomics reads corresponding to the size fraction 0.22-1.6/3 μm (for prokaryotes and giruses) correspond to Salazar et al. (2019) (see https://zenodo.org/record/3473199). Imaging datasets from the nets are available through the collaborative web application and repository EcoTaxa (Picheral et al., 2017) under the address https://ecotaxa.obs-vlfr.fr/prj/412 for regent data, within the 3 projects https://ecotaxa.obs-vlfr.fr/prj/397, https://ecotaxa.obs-vlfr.fr/prj/398, https://ecotaxa.obs-vlfr.fr/prj/395 for bongo data, and within the 2 projects https://ecotaxa.obs-vlfr.fr/prj/377 and https://ecotaxa.obs-vlfr.fr/prj/378 for WP2 data. A table with Shannon values and multiple samples identifiers, plus a table with flow cytometry data split in six groups are available (https://doi.org/10.17632/p9r9wttjkm.1). Contextual data from the Tara Oceans expedition, including those that are newly released from the Arctic Ocean, are available at https://doi.org/10.1594/PANGAEA.875582The ocean is home to myriad small planktonic organisms that underpin the functioning of marine ecosystems. However, their spatial patterns of diversity and the underlying drivers remain poorly known, precluding projections of their responses to global changes. Here we investigate the latitudinal gradients and global predictors of plankton diversity across archaea, bacteria, eukaryotes, and major virus clades using both molecular and imaging data from Tara Oceans. We show a decline of diversity for most planktonic groups toward the poles, mainly driven by decreasing ocean temperatures. Projections into the future suggest that severe warming of the surface ocean by the end of the 21st century could lead to tropicalization of the diversity of most planktonic groups in temperate and polar regions. These changes may have multiple consequences for marine ecosystem functioning and services and are expected to be particularly significant in key areas for carbon sequestration, fisheries, and marine conservationTara Oceans (which includes both the Tara Oceans and Tara Oceans Polar Circle expeditions) would not exist without the leadership of the Tara Ocean Foundation and the continuous support of 23 institutes (https://oceans.taraexpeditions.org/). We further thank the commitment of the following sponsors: CNRS (in particular Groupement de Recherche GDR3280 and the Research Federation for the Study of Global Ocean Systems Ecology and Evolution FR2022/Tara Oceans-GOSEE), the European Molecular Biology Laboratory (EMBL), Genoscope/CEA, the French Ministry of Research, and the French Government “Investissements d’Avenir” programs OCEANOMICS (ANR-11-BTBR-0008), FRANCE GENOMIQUE (ANR-10-INBS-09-08), MEMO LIFE (ANR-10-LABX-54), the PSL∗ Research University (ANR-11-IDEX-0001-02), as well as EMBRC-France (ANR-10-INBS-02). Funding for the collection and processing of the Tara Oceans data set was provided by NASA Ocean Biology and Biogeochemistry Program under grants NNX11AQ14G, NNX09AU43G, NNX13AE58G, and NNX15AC08G (to the University of Maine); the Canada Excellence research chair on remote sensing of Canada’s new Arctic frontier; and the Canada Foundation for Innovation. We also thank agnès b. and Etienne Bourgois, the Prince Albert II de Monaco Foundation, the Veolia Foundation, Region Bretagne, Lorient Agglomeration, Serge Ferrari, Worldcourier, and KAUST for support and commitment. The global sampling effort was enabled by countless scientists and crew who sampled aboard the Tara from 2009–2013, and we thank MERCATOR-CORIOLIS and ACRI-ST for providing daily satellite data during the expeditions. We are also grateful to the countries who graciously granted sampling permission. We thank Stephanie Henson for providing ocean carbon export data and are also grateful to the other researchers who kindly made their data available. We thank Juan J. Pierella-Karlusich for advice regarding single-copy genes. C.d.V. and N.H. thank the Roscoff Bioinformatics platform ABiMS (http://abims.sb-roscoff.fr) for providing computational resources. C.B. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program (grant agreement 835067) as well as the Radcliffe Institute of Advanced Study at Harvard University for a scholar’s fellowship during the 2016-2017 academic year. M.B.S. thanks the Gordon and Betty Moore Foundation (award 3790) and the National Science Foundation (awards OCE#1536989 and OCE#1829831) as well as the Ohio Supercomputer for computational support. S.G.A. thanks the Spanish Ministry of Economy and Competitiveness (CTM2017-87736-R), and J.M.G. is grateful for project RT2018-101025-B-100. F.L. thanks the Institut Universitaire de France (IUF) as well as the EMBRC platform PIQv for image analysis. M.C.B., D.S., and J.R. received financial support from the French Facility for Global Environment (FFEM) as part of the “Ocean Plankton, Climate and Development” project. M.C.B. also received financial support from the Coordination for the Improvement of Higher Education Personnel of Brazil (CAPES 99999.000487/2016-03)Peer Reviewe

Characterization of turbulence from a fine-scale parameterization and microstructure measurements in the Mediterranean Sea during the BOUM experiment

International audienceOne of the main purposes of the BOUM experiment was to find evidence of the possible impact of submesoscale dynamics on biogeochemical cycles. To this aim physical as well as biogeochemical data were collected along a zonal transect through the western and eastern basins of the Mediterranean Sea. Along this transect 3-day fixed point stations were performed within anticyclonic eddies during which microstructure measurements of the temperature gradient were collected over the top 100 m of the water column. We focus here on the characterization of turbulent mixing. The analysis of microstructure measurements revealed a high level of turbulent kinetic energy (TKE) dissipation rate in the seasonal pycnocline and a moderate level below with mean values of the order of 10−6 W kg−1 and 10−8 W kg−1, respectively. The Gregg Henyey (Gregg, 1989) fine-scale parameterization of TKE dissipation rate produced by internal wave breaking, and adapted here following Polzin et al. (1995) to take into account the strain to shear ratio, was first compared to these direct measurements with favorable results. The parameterization was then applied to the whole data set. Within the eddies, a significant increase of dissipation at the top and base of eddies associated with strong near-inertial waves is observed. Vertical turbulent diffusivity is increased both in these regions and in the weakly stratified eddy core. The stations collected along the East–West transect provide an overview of parameterized TKE dissipation rates and vertical turbulent diffusivity over a latitudinal section of the Mediterranean Sea. Strong TKE dissipation rates are found within the first 500 m and up to 1500 m above the bottom. Close to the bottom where the stratification is weak, the inferred vertical turbulent diffusivity can reach Kz≃10−3 m2 s−1 and may therefore have a strong impact on the upward diffusive transport of deep waters masses

Characterization of turbulence and validation of fine-scale parametrization in the Mediterranean Sea during BOUM experiment

International audienceOne main purpose of BOUM experiment was to give evidence of the possible impact of submesoscale dynamics on biogeochemical cycles. To this aim physical as well as biogeochemical data were collected along a zonal transect through the western and eastern basins. Along this transect 3 day fixed point stations were performed within anticyclonic eddies during which microstructure measurements were collected over the first 100 m. We focus here on the characterization of turbulent mixing induced by internal wave breaking. The analysis of microstructure measurements revealed a high level of turbulence in the seasonal pycnocline and a moderate level below with energy dissipation mean values of the order of 10-6 W kg-1 and 10-8 W kg-1, respectively. Fine-scale parameterizations developed to mimic energy dissipation produced by internal wavebreaking were then tested against these direct measurements. Once validated a parameterization has been applied to infer energy dissipation and mixing over the whole data set, thus providing an overview over a latitudinal section of the Mediterranean sea. The results evidence a significant increase of dissipation at the top and base of eddies associated with strong near inertial waves. Vertical turbulent diffusivity is increased both in these regions and in the weakly stratified eddy core

Circulation and water mass transports on the East Antarctic shelf in the Mertz Glacier region

International audienceThe East Antarctic shelf off Adélie-George V Land is known to be an important region for Dense Shelf Water (DSW) formation as a result of intense sea ice production in the Mertz Glacier Polynya during the winter season. It is also a region where the warm modified Circumpolar Deep Water (mCDW) penetrates onto the shelf during the summer. Using hydrographic observations from a summer survey in 2008 we implement a box inverse model to propose a comprehensive view of the steady state circulation on this shelf in summer. Additional information from mooring observations collected on the depression slope is used to provide context to the retrieved circulation scheme. Over the depression slope, the summer baroclinic structure of the currents is found to contrast with the almost barotropic structure in winter. The summer circulation is strongly constrained by the DSW distribution and forms a clockwise circulation primarily transporting the fresh surface waters and the warm mCDW around the dome of DSW. Over the upper flank of the Mertz Bank, the inflow branch transports the mCDW towards the Mertz Glacier, while, over the lower part of the slope, the outflow branch returns to the sill a diluted mode of the same water mass. A total of 0.19 Sv of mCDW inflows at the sill and two-third reach the Mertz Glacier and recirculate in front of it, allowing the mCDW to penetrate into the deeper part of the depression. Possible scenarios of interaction between the mCDW and the DSW with the glacier are examined. It is shown that, despite the water mass pathways and transports suggest possible ice-ocean interaction, both lateral and basal melting were likely small in summer 2008. Finally, our results suggest that, in addition to bathymetric features, the distribution of the residual DSW which is left from the preceding winter sets up regional pressure gradients which provide a seasonal control on the shelf circulation. In particular, the spring collapse of the convective patch would contribute to setting up a deep pycnocline which strongly impacts the shelf circulation in the following summer, with possible feedback of the mCDW transports on the polynya activity and water mass formation

Impact of environmental factors on in situ determination of iron in seawater by flow injection analysis

International audienceA sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (C p = 2.8 Â 10 À 5 P + 3.4 Â 10 À 2 s nmol À 1 , R 2 = 0.997, for H = 13 8C) and an exponential relation as a function of temperature (C H = 0.009e 0.103H , R 2 = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 Â [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 Am), acidified and stored at pH 1.8) corresponded to 29 F 4% of Fe a (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fe a (71 F 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8)

Sea-ice detection for autonomous underwater vehicles and oceanographic lagrangian platforms by continuous-wave laser polarimetry

International audienceThe use of Lagrangian platforms and of Autonomous Underwater Vehicles (AUVs) in oceanography has increasedrapidly over the last decade along with the development of improved biological and chemical sensors. These vehicles provide new spatial and temporal scales for observational studies of the ocean. They offer a broad range of deployment and recovery capabilities that reduce the need of large research vessels. This is especially true for ice-covered Arctic ocean where surface navigation is only possible during the summer period. Moreover, safe underwater navigation in icy waters requires the capability of detecting sea ice on the surface (ice sheets). AUVs navigating in such conditions risk collisions, RF communication shadowing, and being trapped by ice keels. In this paper, an underwater sea-ice detection apparatus is described. The source is a polarized continuous wave (CW) diode-pumped solid-state laser (DPSS) module operating at 532 nm. The detector is composed of a polarizing beam splitter, which separates light of S and P polarization states and two photodetectors, one foreach polarized component. Since sea-ice is a strong depolarizer, the ratio P/S is an indicator of the presence or absence of sea-ice. The system is capable of detecting sea-ice at a distance of 12m. This apparatus is designed to be used by free drifting profiling floats (e.g., Argo floats), buoyancy driven vehicles (e.g., sea gliders) and propeller-driven robots (e.g., Hugin class AUV)

Sea-ice detection for autonomous underwater vehicles and oceanographic lagrangian platforms by continuous-wave laser polarimetry

International audienceThe use of Lagrangian platforms and of Autonomous Underwater Vehicles (AUVs) in oceanography has increasedrapidly over the last decade along with the development of improved biological and chemical sensors. These vehicles provide new spatial and temporal scales for observational studies of the ocean. They offer a broad range of deployment and recovery capabilities that reduce the need of large research vessels. This is especially true for ice-covered Arctic ocean where surface navigation is only possible during the summer period. Moreover, safe underwater navigation in icy waters requires the capability of detecting sea ice on the surface (ice sheets). AUVs navigating in such conditions risk collisions, RF communication shadowing, and being trapped by ice keels. In this paper, an underwater sea-ice detection apparatus is described. The source is a polarized continuous wave (CW) diode-pumped solid-state laser (DPSS) module operating at 532 nm. The detector is composed of a polarizing beam splitter, which separates light of S and P polarization states and two photodetectors, one foreach polarized component. Since sea-ice is a strong depolarizer, the ratio P/S is an indicator of the presence or absence of sea-ice. The system is capable of detecting sea-ice at a distance of 12m. This apparatus is designed to be used by free drifting profiling floats (e.g., Argo floats), buoyancy driven vehicles (e.g., sea gliders) and propeller-driven robots (e.g., Hugin class AUV)

Arctic mid-winter phytoplankton growth revealed by autonomous profilers

International audienc

The evolution of light and vertical mixing across a phytoplankton ice-edge bloom

During summer, phytoplankton can bloom in the Arctic Ocean, both in open water and under ice, often strongly linked to the retreating ice edge. There, the surface ocean responds to steep lateral gradients in ice melt, mixing, and light input, shaping the Arctic ecosystem in unique ways not found in other regions of the world ocean. In 2016, we sampled a high-resolution grid of 135 hydrographic stations in Baffin Bay as part of the Green Edge project to study the ice-edge bloom, including turbulent vertical mixing, the under-ice light field, concentrations of inorganic nutrients, and phytoplankton biomass. We found pronounced differences between an Atlantic sector dominated by the warm West Greenland Current and an Arctic sector with surface waters originating from the Canadian archipelago. Winter overturning and thus nutrient replenishment was hampered by strong haline stratification in the Arctic domain, whereas close to the West Greenland shelf, weak stratification permitted winter mixing with high-nitrate Atlantic-derived waters. Using a space-for-time approach, we linked upper ocean dynamics to the phytoplankton bloom trailing the retreating ice edge. In a band of 60 km (or 15 days) around the ice edge, the upper ocean was especially affected by a freshened surface layer. Light climate, as evidenced by deep 0.415 mol m–2 d–1 isolumes, and vertical mixing, as quantified by shallow mixing layer depths, should have permitted significant net phytoplankton growth more than 100 km into the pack ice at ice concentrations close to 100%. Yet, under-ice biomass was relatively low at 20 mg chlorophyll-a m–2 and depth-integrated total chlorophyll-a (0–80 m) peaked at an average value of 75 mg chlorophyll-a m–2 only around 10 days after ice retreat. This phenological peak may hence have been the delayed result of much earlier bloom initiation and demonstrates the importance of temporal dynamics for constraints of Arctic marine primary production