Thierry Moutin

Aix-Marseille Université | AMU · Institut OSU Pythéas

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (A T ), total dissolved inorganic carbon (C T ), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbona...

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (A T), total dissolved inorganic carbon (C T), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbonate...

The Mediterranean region has been shown to be particularly exposed to climate change, with observed trends that are more pronounced than the global tendency. In forecast studies based on a RCP 8.5 scenario, there seems to be a consensus that, along with an increase in temperature and salinity over the next century, a reduction in the intensity of d...

Using biogeochemical-Argo float measurements, we propose, for the first time, an optical proxy for particulate organic nitrogen concentration (PON) in the Western Tropical South Pacific, an area influenced by dinitrogen (N2) fixation. Our results show a significant relationship between the backscattering coefficient at 700 nm (bbp) and PON, especia...

In recent studies, the Mediterranean region is once again identified as a region particularily sensitive to climate change, with recorded temperature and sea level rises during the last decades exceeding the mean variations recorded at global scale. Moreover, according to climate scenarios, there seems to be some consensus regarding the impact on c...

The Mediterranean Sea (MS) is a semi-enclosed sea characterized by a zonal west-east gradient of oligotrophy, where microbial growth is controlled by phosphate availability in most situations. External inputs of nutrients including Gibraltar inputs, river inputs and atmospheric deposition are therefore of major importance for the biogeochemistry of...

Plain Language Summary In the poor and nutrient‐depleted waters of the tropical Pacific, islands act as sources of nutrients fertilizing nearby waters. These nutrients are consumed by microscopic photosynthesizing algae, the phytoplankton. The resulting phytoplankton enrichments (blooms) in turn support productive ecosystems. This phenomenon, terme...

The Mediterranean Sea (MS) is a semi-enclosed sea characterized by a zonal west-east gradient of oligotrophy, where microbial growth is controlled by phosphate availability in most situations. External inputs of nutrients including Gibraltar inputs, river inputs and atmospheric deposition are therefore of major importance for the biogeochemistry of...

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...

Microstructure measurements were performed along the OUTPACE longitudinal transect in the tropical Pacific (Moutin and Bonnet, 2015). Small-scale dynamics and turbulence in the first 800 m surface layer were characterized based on hydrographic and current measurements at fine vertical scale and turbulence measurements at centimeter scale using a ve...

The Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise took place in the western tropical South Pacific (WTSP) during the austral summer (March–April 2015). The aim of the OUTPACE project was to investigate a longitudinal gradient of biological and biogeochemical features in the WTSP, and especially the role of N2 fixation in the...

The western tropical South Pacific was sampled along a longitudinal 4000 km transect (OUTPACE cruise, 18 February, 3 April 2015) for the measurement of carbonate parameters (total alkalinity and total inorganic carbon) between the Melanesian Archipelago (MA) and the western part of the South Pacific gyre (WGY). This paper reports this new dataset a...

In the Western Tropical South Pacific, patches of high chlorophyll concentrations linked to the occurrence of N2-fixing organisms are found in the vicinity of volcanic islands. The survival of these organisms relies on a high bioavailable iron supply whose origin and fluxes remain unknown. Here, we measured high dissolved iron (DFe) concentrations...

Surface waters (0–200 m) of the western tropical South Pacific (WTSP) were sampled along a longitudinal 4000 km transect (OUTPACE cruise, DOI: 10.17600/15000900) during the austral summer (stratified) period (18 February to 3 April 2015) between the Melanesian Archipelago (MA) and the western part of the SP gyre (WGY). Two distinct areas were consi...

Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31 to 50 mg C m−2 d−1 within the western su...

Constraining the rates and spatial distribution of dinitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution...

We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February–March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) st...

Microstructure measurements were performed along the OUTPACE longitudinal transect in the tropical Pacific (Moutin and Bonnet, 2015). Small-scale dynamics and three-dimensional turbulence in the first 800 m surface layer were characterized based on hydrographic and current measurements at fine scale and turbulence measurements at cm scale using a v...

The western tropical South Pacific was sampled along a longitudinal 4000 km transect (OUTPACE cruise, 18 Feb., 3 Apr. 2015) for measurement of carbonates parameters (total alkalinity and total inorganic carbon) between the Melanesian Archipelago (MA) and the western part of the South Pacific gyre (WGY). This manuscript reports this new dataset and...

The Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise took place in the Western Tropical South Pacific (WTSP) during the austral summer (March–April 2015). The aim of the OUTPACE project is to investigate a longitudinal gradient of biological and biogeochemical features in the WTSP, and especially the role of N2 fixation on the C...

Research cruises to quantify biogeochemical fluxes in the ocean require taking measurements at stations lasting at least several days. A popular experimental design is the quasi-Lagrangian drifter, often mounted with in situ incubations or sediment traps that follow the flow of water over time. After initial drifter deployment, the ship tracks the...

As part of the Oligotrophy to UlTra-oligotrophy PACific Experiment cruise, which took place in the Western Tropical South Pacific during the austral summer (March–April 2015), we present data on nitrate, phosphate and on particulate and dissolved organic matter. The stoichiometric nitrogen-to-phosphorus ratios of the inorganic and organic material an...

Constraining the rates and spatial distribution of di-nitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution...

Heterotrophic prokaryotic production (BP) was studied in the Western Tropical South Pacific using the leucine technique. Integrated over the euphotic zone, BP ranged from 58–120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31–50 mg C m−2 within the subtropical gyre. Nitrogen was often one of the main factor controlling BP on short time...

Surface waters (0–200 m) of the western tropical South Pacific (WTSP) were sampled along a longitudinal 4000 km transect (OUTPACE cruise, 18 Feb., 3 Apr. 2015) during the stratified period between the Melanesian Archipelago (MA) and the western part of the SP gyre (WGY). Two distinct areas were considered for the MA, the western MA (WMA) and the ea...

We performed N budgets at three stations in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (Feb. Mar. 2015) and quantified all major N fluxes both entering the system (N2 fixation, nitrate eddy diffusion, atmospheric deposition) and leaving the system (PN export). Thanks to a Lagrangian strategy, we sampled the sam...

Research cruises to quantify biogeochemical fluxes in the ocean require taking measurements at stations lasting at least several days. A popular experimental design is the quasi-Lagrangian drifter, with in situ incubations that follow the flow of water over time. The ship then tracks the drifter because subsequent measurements are supposed to remai...

The temporal evolution of a surface chlorophyll a bloom sampled in the western tropical South Pacific during the 2015 Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise is examined. This region is usually characterized by largely oligotrophic conditions, i.e. low concentrations of inorganic nutrients at the surface and deep chloro...

The overall goal of OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) was to obtain a successful representation of the interactions between planktonic organisms and the cycle of biogenic elements in the western tropical South Pacific Ocean across trophic and N2 fixation gradients. Within the context of climate change, it is necessary to...

The temporal evolution of a surface chlorophyll-a bloom sampled in the Western Tropical South Pacific during the 2015 Oligotrophy to UlTra-oligotrophy PACific Experiment cruise is examined. This region is usually characterized by largely oligotrophic conditions, ie low concentrations of inorganic nutrients at the surface and deep chlorophyll-a maxi...

The overall goal of OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) was to obtain a successful representation of the interactions between planktonic organisms and the cycle of biogenic elements in the western tropical South Pacific Ocean across trophic and N2 fixation gradients. Within the context of climate change, it is necessary to...

The VAHINE mesocosm experiment in the oligotrophic waters of the Nouméa lagoon (New Caledonia), where high N2 fixation rates and abundant diazotroph organisms were observed, aimed to assess the role of the nitrogen input through N2 fixation in carbon production and export and to study the fate of diazotroph-derived nitrogen (DDN) throughout the pla...

In a coastal lagoon with a shallow, 25 m water column off the southwest coast of New Caledonia, large-volume ( ∼ 50 m3) mesocosm experiments were undertaken to track the fate of newly fixed nitrogen (N). The mesocosms were intentionally fertilized with 0.8 µM dissolved inorganic phosphorus to stimulate diazotrophy. N isotopic evidence indicates tha...

In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph-derived nit...

Studies investigating the fate of diazotrophs through the microbial food web are lacking, although N2 fixation can fuel up to 50 % of new production in some oligotrophic oceans. In particular, the role played by heterotrophic prokaryotes in this transfer is largely unknown. In the frame of the VAHINE (VAriability of vertical and tropHIc transfer of...

On the global scale, N2 fixation provides the major external source of reactive nitrogen to the surface ocean, surpassing atmospheric and riverine inputs, and sustains ∼ 50 % of new primary production in oligotrophic environments. The main goal of the VAriability of vertical and tropHIc transfer of diazotroph derived N in the south wEst Pacific (VA...

At the global scale, N2 fixations provides the major external source of reactive nitrogen to the surface ocean, before atmospheric and riverine inputs, and sustains ~50 % of new primary production in oligotrophic environments. The main goal of the VAHINE project was to study the fate of nitrogen newly fixed by diazotrophs (or diazotroph-derived nit...

The VAHINE mesocosm experiment in the oligotrophic waters of the Noumea lagoon (New Caledonia) aimed to assess the role of the nitrogen input through N2 fixation on carbon production and export, and to study the fate of diazotroph-derived nitrogen (DDN) throughout the planktonic food web. A 1D-vertical biogeochemical mechanistic model was used in a...

In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph derived nit...

In a shallow, coastal lagoon off the southwest coast of New Caledonia, large-volume (~ 50 m3) mesocosm experiments were undertaken to track the fate of newly fixed nitrogen (N). The mesocosms were intentionally fertilized with 0.8 μM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. N isotopic evidence indicates that the dominant sourc...

N2 fixation fuels ~ 50 % of new primary production in the oligotrophic South Pacific Ocean. The VAHINE mesocosm experiment designed to track the fate of diazotroph derived nitrogen (DDN) in the New Caledonia lagoon. Here, we examined the temporal dynamics of heterotrophic bacterial production during this experiment. Three replicate large-volume (~...

In a shallow, coastal lagoon off the southwest coast of New Caledonia, large-volume (~ 50 m3) mesocosm experiments were undertaken to track the fate of newly fixed nitrogen (N). The mesocosms were intentionally fertilized with 0.8 μM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. N isotopic evidence indicates that the dominant sourc...

The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities, resulting in a potential major role of dissolved organic carbon (DOC) export in the biological pump. Strong DOC accumulation in surface waters is already well documented, though measurement...

The dinitrogen (N2) fixed by diazotrophs and released as dissolved nitrogen (DN) has been compared in batch cultures of four marine diazotrophic cyanobacteria: the colony forming Trichodesmium IMS101 and the unicellular strains Cyanothece ATCC51142, Crocosphaera watsonii WH8501 and WH0003. Two approaches were conducted for this purpose. The first a...

In the oligotrophic ocean characterized by nitrate (NO3−) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. In this study, we deployed large in situ mesocosms in New Caledonia in order to investigate (1) the contribution of N2 fixation and DON...

In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to pr...

The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities. This has direct implications on the stock of dissolved organic carbon (DOC), whose high variability has already been well-documented even if measurements are still sparse and are associated...

Microbial transformations are key processes in marine phosphorus cycling. In this study, we investigated the contribution of phototrophic and heterotrophic groups to phosphate (Pi) uptake fluxes in the euphotic zone of the low- Pi Mediterranean Sea and estimated Pi uptake kinetic char- acteristics. Surface soluble reactive phosphorus (SRP) con- cen...

Radiolabeled orthophosphate (Pi) incubations coupled with cell sorting were conducted in the Mediterranean Sea to assess the contribution of picoplanktonic groups to total Pi uptake and to potentially explain their spatial distribution. Under natural Pi concentrations (P-deficient and stratified conditions during the survey), total Pi uptake was do...

We examined rates of N2 fixation from the surface to 2000 m depth in the Eastern Tropical South Pacific (ETSP) during El Niño (2010) and La Niña (2011). Replicated vertical profiles performed under oxygen-free conditions show that N2 fixation takes place both in euphotic and aphotic waters, with rates reaching 155 to 509 µmol N m(-2) d(-1) in 2010...

Biological N2 fixation rates were quantified in the Eastern Tropical South Pacific (ETSP) during both El Niño (February 2010) and La Niña (March–April 2011) conditions, and from Low-Nutrient, Low-Chlorophyll (20°S) to High-Nutrient, Low-Chlorophyll (HNLC) (10°S) conditions. N2 fixation was detected at all stations with rates ranging from 0.01 to 0....

Biological N-2 fixation rates were quantified in the Eastern Tropical South Pacific (ETSP) during both El Nino (February 2010) and La Nina (March-April 2011) conditions, and from Low-Nutrient, Low-Chlorophyll (20 degrees S) to High-Nutrient, Low-Chlorophyll (HNLC) (10 degrees S) conditions. N-2 fixation was detected at all stations with rates rangi...

The analysis of a compilation of deep CTD casts conducted in the western Mediterranean from 1998 to 2011 has documented the role that dense water formation, and particularly deep dense shelf water cascading off the Gulf of Lions, plays in transporting suspended particulate matter from the coastal regions down to the basin. Deep CTD casts reveal tha...

We studied a longitudinal transect in the Mediterranean Sea (MS) and along this transect, the influence of anticyclonic eddies at three long duration (LD) stations. The deep chlorophyll maximum depth, the euphotic layer depth and the top of the nitracline depth are clearly correlated outside of the eddies, and deepen from the oligotrophic western t...

The overall goal of the BOUM (Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean) experiment was to obtain a better representation of the interactions between planktonic organisms and the cycle of biogenic elements in the Mediterranean Sea (MS), in the context of global climate change and, more particularly, on the role of...

Intact polar membrane lipids compose a significant fraction of cellular material in plankton and their synthesis imposes a substantial constraint on planktonic nutrient requirements. As a part of the Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean (BOUM) cruise we examined the distribution of several classes of intact p...

The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coe...

The variability of inherent optical properties is investigated in the ultra-oligotrophic waters of the Mediterranean Sea sampled during the BOUM experiment performed during early summer 2008. Bio-optical relationships found for ultra-oligotrophic waters of the three anticyclonic gyres sampled significantly depart from the mean standard relationship...

The variability of inherent optical properties is investigated in the ultra-oligotrophic waters of the Mediterranean Sea sampled during the BOUM experiment performed during early summer 2008. Bio-optical relationships found for ultra-oligotrophic waters of the three anticyclonic gyres sampled significantly depart from the mean standard relationship...

The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coe...

Microorganisms play a major role in the marine phosphate biogeochemical cycle but the relative contribution of picoplanktonic groups is not well understood. Previous studies have shown that combining uptake measurements of radiolabeled dissolved inorganic phosphate (P-i) substrate with cell sorting by flow cytometry is a powerful tool for the asses...

The semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is t...

This study provides extensive data on planktonic N2 fixation rates across the whole Mediterranean Sea. They show that N2 fixation occurs in Mediterranean waters during the stratification period, with a clear decreasing trend from the oligotrophic western basin (10-76 mumol m-2 d-1) to the ultra oligotrophic eastern basin (0-0.4 mumol m-2 d-1). High...

The overall goal of the BOUM (Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean) experiment was to obtain a better representation of the interactions between planktonic organisms and the cycle of biogenic elements in the Mediterranean Sea (MS), in the context of global climate change and, more particularly, on the role of...

Intact polar membrane lipids compose a significant fraction of cellular material in plankton and their synthesis imposes a substantial constraint on planktonic nutrient requirements. As a part of the Biogeochemistry from the Oligotrophic to the Ultraoligtrophic Mediterranean (BOUM) cruise we examined the distribution of several classes of intact po...

The abundance and activity of the major members of the heterotrophic microbial community – from viruses to ciliates – were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediter-ranean Sea is characterized by a west to east gradient of deep-ening of DCM (deep chlorophyll maximum) and increasing oligotr...

We characterized alkaline phosphatase (AP) activity (APA) and report AP kinetic parameters in the North and South Pacific Subtropical Gyres (NPSG and SPSG, respectively) to evaluate the relative importance of APA in dissolved organic P (DOP) remineralization. APA potential hydrolysis rates were low but measurable (0.10 +/- 0.06 nmol L(-1) h(-1), n...

The biogeochemistry of carbon and nutrients (N,P) in the surface layer of the ocean strongly depends on the complex interactions between primary producers (phytoplankton) and remineralizers (heterotrophic bacteria). To understand how these interactions impact the overall DOC dynamics in the surface layer of the Mediterranean Sea, we implemented, us...

The silicon biogeochemical cycle has been studied in the Mediterranean Sea during late summer/early autumn 1999 and summer 2008. The distribution of nutrients, particulate carbon and silicon, fucoxanthin (Fuco), and total chlorophyll-a (TChl-a) were investigated along an eastward gradient of oligotrophy during two cruises (PROSOPE and BOUM) encompa...

This study provides extensive data on planktonic N2 fixation fluxes across the whole Mediterranean Sea, representing a variety of trophic conditions. They show that N2 fixation occurs in Mediterranean waters during the stratification period, with a clear decreasing trend from the western basin (10–76 μmol m−2 d−1) to the eastern basin (0–0.4 μmol m...

The silicon biogeochemical cycle has been studied in the Mediterranean Sea during late summer/early autumn 1999 and summer 2008. The distribution of nutrients, particulate carbon and silicon, fucoxanthin (Fuco), and total chlorophyll- a (TChl- a ) were investigated along an eastward gradient of oligotrophy during two cruises (PROSOPE and BOUM) enco...

The abundance and activity of the major members of the heterotrophic microbial community – from viruses to ciliates – were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to the east gradient of deepening of DCM (deep chlorophyll maximum) and increasing oligo...

The abundance and activity of the major members of the heterotrophic microbial community – from viruses to ciliates – were studied along a longitudinal transect across the Mediterranean Sea in the summer of 2008. The Mediterranean Sea is characterized by a west to the east gradient of deepening of DCM (deep chlorophyll maximum) 5 and increasing oli...