Biogeochemical relationships between ultrafiltered dissolved organic matter and picoplankton activity in the Eastern Mediterranean Sea

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 57 (2010): 1460-1477, doi:10.1016/j.dsr2.2010.02.015.We targeted the warm, subsurface waters of the Eastern Mediterranean Sea (EMS) to investigate processes that are linked to the chemical composition and cycling of dissolved organic carbon (DOC) in seawater. The apparent respiration of semi-labile DOC accounted for 27 ± 18% of oxygen consumption in EMS mesopelagic and bathypelagic waters; this value is higher than that observed in the bathypelagic open ocean, so the chemical signals that accompany remineralization of DOC may thus be more pronounced in this region. Ultrafiltered dissolved organic matter (UDOM) collected from four deep basins at depths ranging from 2 to 4350 m exhibited bulk chemical (1H-NMR) and molecular level (amino acid and monosaccharide) abundances, composition, and spatial distribution that were similar to previous reports, except for a sample collected in the deep waters of the N. Aegean Sea that had been isolated for over a decade. The amino acid component of UDOM was tightly correlated with apparent oxygen utilization and prokaryotic activity, indicating its relationship with remineralization processes that occur over a large range of timescales. Principal component analyses of relative mole percentages of monomers revealed that oxygen consumption and prokaryotic activity were correlated with variability in amino acid distributions but not well correlated with monosaccharide distributions. Taken together, this study elucidates key relationships between the chemical composition of DOM and heterotrophic metabolism.TBM and AG acknowledge funding from the Hellenic GSRT/European Union (non-EU Grant No180) and SESAME Project (European Commission's Sixth Framework Program, EC Contract No GOCE-036949). TY was supported by the Japanese Society for the Promotion of Science (JSPS) Postdoctoral Fellowship for research abroad and DDC received a fellowship of the University of Groningen. Microbial laboratory work and molecular analyses were supported by a grant of the Earth and Life Science Division of the Dutch Science Foundation (ARCHIMEDES project, 835.20.023) to GJH. DJR and TBM were supported by grants from the Gordon and Betty Moore Foundation and from the C-MORE organization of NSF

Non-Redfield carbon and nitrogen cycling in the Arctic: Effects of ecosystem structure and dynamics

The C:N ratio is a critical parameter used in both global ocean carbon models and field studies to understand carbon and nutrient cycling as well as to estimate exported carbon from the euphotic zone. The so-called Redfield ratio (C:N = 6.6 by atoms) [Redfield et al., 1963] is widely used for such calculations. Here we present data from the NE Greenland continental shelf that show that most of the C:N ratios for particulate (autotrophic and heterotrophic) and dissolved pools and rates of transformation among them exceed Redfield proportions from June to August, owing to species composition, size, and biological interactions. The ecosystem components that likely comprised sinking particles and had relatively high C:N ratios (geometric means) included (1) the particulate organic matter (C:N = 8.9) dominated by nutrient-deficient diatoms, resulting from low initial nitrate concentrations (approximately 4 μM) in Arctic surface waters; (2) the dominant zooplankton, herbivorous copepods (C:N = 9.6), having lipid storage typical of Arctic copepods; and (3) copepod fecal pellets (C:N = 33.2). Relatively high dissolved organic carbon concentrations (median 105 μM) were approximately 25 to 45 μM higher than reported for other systems and may be broadly characteristic of Arctic waters. A carbon-rich dissolved organic carbon pool also was generated during summer. Since the magnitude of carbon and nitrogen uncoupling in the surface mixed layer appeared to be greater than in other regions and occurred throughout the productive season, the C:N ratio of particulate organic matter may be a better conversion factor than the Redfield ratio to estimate carbon export for broad application in northern high-latitude systems

Some environmental factors influencing phytoplankton in the Southern Ocean around South Georgia

Data on phytoplankton and zooplankton biomass, and physical and chemical variables, are combined with a published multivariate description of diatom species composition to interpret variation within an area around South Georgia surveyed during an austral summer. Large-scale species distributions could be equated to the different water masses which reflected the interaction of the Antarctic Circumpolar Current with the island and the Scotia Ridge. Small-scale factors were found to act at an interstation scale and imposed local variation on the biogeographic pattern. Nutrient depletion could be related to phytoplankton biomass but no single inorganic nutrient of those measured (NO 3 −N, PO 4 −P and silica) could be identified as important. The ratio Si:P appeared to be more important as an ecological factor. The impact of grazing by krill and other zooplankton could only be resolved as differences in phytoplankton biomass and phaeopigment content. Diatom species composition showed a relation to local krill abundance very different from that suggested by published studies, but could be explained as the effect of earlier grazing outside the study area. The effects of vertical mixing could not account for interstation differences as pycnocline depth was uniformly greater than euphotic depth, and vertical stability very low. Some comparison was made with data collected in 1926–31 by the Discovery Investigations. Significant differences in the distribution of certain taxa such as Chaetoceros criophilum and C. socialis were traced to major differences in hydrology.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46983/1/300_2004_Article_BF00443379.pd

Elements majeurs des particules en suspension de la Mediterranee occidentale

Chemical analyses of major elements (C, N, P, Si, Al, Fe, Ca, Mg) were performed on more than 500 samples of suspended matter from the western Mediterranean Sea. Four samples collected with a free-floating sediment trap were also analysed. The vertical distribution of particulate organic carbon, POC, reported herein is characteristic of oligotrophic mid-latitude regions. In open waters, the concentration of particulate aluminium is nearly constant. A fraction of particulate silicon Si sub(p) is of terrigenous origin, the rest is biogenic. The biogenic fraction of particulate iron and magnesium is noticeable only in the surface layer, where Fe sub(bio)/POC and Mg sub(bio)/POC ratios are about 10 super(-3). It is not possible to estimate the terrigenous and biogenic fractions of particulate calcium

Consumption and production on scales of a few days of inorganic carbon, nitrate and oxygen by the planktonic community: results of continuous measurements at the Dyfamed Station in the northwestern Mediterranean Sea (May 1995)

Continuous measurements between 0 and 200 m depth were performed every 2 h over two separate periods of four days at a station in the open northwestern Mediterranean Sea (Dyfamed Station) during the Dynaproc cruise in May 1995, Estimates of the daily variations in profiles of temperature, partial pressure of CO,, oxygen, chlorophyll a and nutrients were obtained. The distributions of the various physical and chemical properties were clearly different during the two time series, which were separated by a period of 11 days during which a wind event occurred. The mean daily utilization or production due to biological processes of dissolved inorganic carbon (DIC), nitrate + nitrite and oxygen were calculated along isopycnals using a vertical diffusion model. Between the surface and about 20 m depth, DIC was consumed and 0, released during the two time series while the nitrate + nitrite concentrations as well as supplies were zero, After the wind event, the O-2:C:N ratios of consumption (or production) were, on average, near the Redfield ratios, but during the first time series, the C :N utilization ratio between 20 and 35 m was two to three times that of Redfield stoichiometry and the oxygen release was low. The integrated net community production (NCP) in terms of carbon was equivalent during the two time series, whereas the chlorophyll a biomass was twice as high, on average, during the first time series but did decrease, These results imply that the production systems were different during the two periods. The first time series corresponds toa period at the end of production, due to the nutrient depletion in the euphotic layer. The formation of degradation products of the living material in dissolved organic form is probably important as indicated by the high C:N utilization ratios. The second time series corresponds to a reactivation of the primary production due to the upward shift of nutrients after the wind event. (C) 2000 Elsevier Science Ltd. All rights reserved

Distributions of carbonate properties and oxygen along the water column (0-2000m) in the central part of the NW Mediterranean Sea (Dyfamed site): influence of winter vertical mixing on air-sea CO2 and O-2 exchanges

Monthly measurements of pH, alkalinity and oxygen over two years (February 1998-February 2000) at the Dyfamed site in the central zone of the Ligurian-Provencal Basin of the Mediterranean made it possible to assess the vertical distributions (5-2000 m) and the seasonal variations of these properties. Alkalinity varies linearly with salinity between surface water and the Levantine Intermediate Water (marked by a maximum of temperature and salinity). In deep water, total alkalinity is also correlated linearly to salinity, but the slope of the regression line is 15% less. In surface water, the pH at 25degreesC varies between 7.91 and 8.06 on the total proton scale depending upon the season. The lowest values are observed in winter, the highest in spring and in summer. These variations are primarily due to biological production. The pH goes through a minimum around 150-200m and a small maximum below the intermediate water. The total dissolved inorganic carbon content (deduced from pH and alkalinity) is variable in surface water (2205-2310 mumol kg(-1)) and has a maximum in intermediate water, which is related to the salinity maximum. Normalized total inorganic carbon at a constant salinity is strongly negatively correlated with pH at 25degreesC. The fugacity of CO2, (fCO(2)) varies between 320 and 430 muatm in surface water, according to the season. Below the seasonal thermocline, the maximum fCO(2) (about 410 muatm) is located around 150-200 m. The presence of a minimum of oxygen in the intermediate water of this area has been observed for several years, but our measurements made it possible to specify the relationship between oxygen and salinity in deep water. Data from the intense vertical mixing during the winters of 1999 and 2000 were used to calculate the oxygen quantity exchanged with the atmosphere during these periods. The estimated quantity of oxygen entering the Mediterranean Sea exceeds that deduced from exchange coefficients calculated with the formula of Wanninkhof and McGillis. During the vertical mixing in the 1999 winter, fCO(2) in surface water was on average below equilibrium with atmospheric fCO(2), thus implying that CO2 was entering the sea. However, on this time scale, even with high exchange coefficients, the estimated CO2 uptake had no significant influence on the inorganic carbon content in the water column. (C) 2002 Elsevier Science Ltd. All rights reserved

Processes controlling annual variations in the partial pressure of CO2 in surface waters of the central northwestern Mediterranean Sea (Dyfamed site)

Measurements of the partial pressure of CO, (pCO(2)) in surface waters, and other water properties were performed monthly during a 2-year period from February 1998 through February 2000, at a station in the open northwestern Mediterranean Sea (Dyfamed Station). On seasonal timescale, the pCO(2) minimum of 300 muatm in winter was followed by an increase of 120 muatm (pCO(2) reaching 420 muatm) related to warming of surface waters in summer. Estimates of the underlying processes (mixing, biological activity and air-sea gas exchange) governing the monthly variations of the upper layer PC02 were obtained from observed variations in total inorganic carbon content (TCO2) in the surface, and from the vertical distribution of physical parameters and TCO2, Monthly variations in TCO2 due to gas exchange were determined from wind speed and from the air-sea PC02 gradient. The impact of biological activity was estimated from the difference between the observed variations in TCO2 and the evaluations of air-sea exchange and carbon supply by physical processes. Mixing at the base of the mixed layer counteracts the late winter to summer TCO2 drawdown (about 80 mmol m(-3)) due to a net organic production of about 100 mmol m(-3). The carbon consumption continues until early summer despite the absence of nutrients in the upper layer from April or May. The net carbon production in the mixed layer during the warming period exceeds by a factor of 1.6 the carbon production deduced from nitrate fluxes and using the usual Redfield C:N ratio of 6.6:1. The TCO2 increase during the autumn is primarily associated with convective vertical mixing induced by upper layer cooling and deepening. On the other hand, the contribution of air-sea gas exchange to TCO2 variations remains relatively small aside from summer months, when the CO2 oversaturation is high and the mixed layer is only 15-20 m depth. (C) 2002 Elsevier Science Ltd. All rights reserved

Contribution à l'étude du système des carbonates en méditerranée (distribution et variation spatio-temporelle de la pression partielle de CO2 dans les eaux superficielles du bassin liguro-provençal)

PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocVILLEFRANCHE/MER-Observ.Océano (061592201) / SudocSudocFranceF

Phosphorus and nitrogen in the Mediterranean Sea: Specificities and forecasting

The Mediterranean Sea constitutes a small-scale model of a real ocean for studying the fate of trace elements. Peculiarities in the phosphorus and nitrogen cycles permit a better knowledge of the Mediterranean ecosystem and a forecast of their temporal evolutions. The apparent deficit of the Mediterranean nitrogen budget and the abnormally high N/P ratio (compared with the value for the Atlantic) can be explained by a high biological fixation of atmospheric nitrogen, probably due to certain kinds of plankton and bacteria and the presence of Posidonia oceanica and its epiphytes