Primary production at time series station DYFAMED

Phytoplankton carbon assimilation has been measured near monthly using the 14C method at DYFAMED France JGOFS time-series station from 1993 to 1999. Data were obtained using the "LET GO" technique, which allowed in situ injection of bicarbonate and incubation in enclosures at 10 depths. Incubation duration was 4 h around noon, from which daily production was estimated. The seasonal variation of the depth-integrated carbon assimilation exhibits a marked cycle. Maximum values reach 1.8 g C/m**2/d in March or April; constant lower values were observed from August to January, in the range 100-300 mg C/m**2/d. The annual primary production vary in the range 86-232 g C/m**2/yr, in the upper range of older estimations. Primary production normalized to chlorophyll a shows maximum values in the period of oligotrophy. This increase of carbon assimilation rate per unit of chlorophyll a appears as linked to the period of phosphorus-limited ecosystem, and vertical distribution of taxonomic pigments suggests a possible role of cyanobacteria. Potential export production has been estimated from primary production data and Fp ratio based on pigments concentrations. These estimates (which imply biological steady state conditions) vary in a wide range, from 19 to 71 g C/m**2/yr. There is a decoupling between years with high potential export production and years with high measured particulate fluxes, which highlights the question of balance by resupply of the limiting nutrients and the role of dissolved organic carbon. A possible shift of primary production towards a more regeneration-dominated system is suggested for recent years.

Oxygen concentration at time series station DYNAPROC

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 CO2, 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 O2 released during the two time series while the nitrate+nitrite concentrations as well as supplies were zero. After the wind event, the O2 : 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 to a 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.

Surface time series of nitrate, silicate and chlorophyll a (1999-2011) and CTD profiles (1999) at the PhytoCly station, Bay of Calvi, Corsica, Mediterranean Sea

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 unrecognized 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 <13.5°C). According to winter intensity, there were strong differences in both the duration and intensity of nutrient fertilization and phytoplankton blooms (chl a). The trophic character of the Bay of Calvi changed according to years, and ranged from very oligotrophic (i.e. subtropical regime, characterized by low seasonal variability) to mesotrophic (i.e. temperate regime, with a well-marked increase in nutrient concentrations and chl a during the winter-spring period) during mild and moderate winters, respectively. A third regime occurred during severe winters characterized by specific wind conditions (i.e. high frequency of northeasterly winds), when Mediterranean "high nutrient - low chlorophyll" conditions occurred as a result of enhanced crossshore exchanges and associated offshore export of the nutrient-rich water. There was no long-term trend (e.g. climatic) in either nutrient replenishment or the winter-spring phytoplankton bloom between 1979 and 2011, but both nutrients and chl a reflected interannual and decadal changes in winter intensity.

Anundance of phytoplankton at time series station DYNAPROC

A general study of biogeochemical processes (DYNAPROC cruise) was conducted in May 1995 at a time-series station in the open northwestern Mediterranean Sea where horizontal advection was weak. Short-term variations of the vertical distributions of pico- and nanophytoplankton were investigated over four 36-h cycles, along with parallel determinations of metabolic CO2 production rates and amino acid-containing colloid (AACC) concentrations at the chlorophyll maximum depth. The vertical (0-1000-m depth) distributions of (i) AACC, (ii) suspended particles and (iii) metabolic CO2 production rate were documented during the initial and final stages of these 36-h cycles. This study was concerned with diel vertical migration (DVM) of zooplankton, which provided periodic perturbations. Accordingly, the time scale of the experimental work varied from a few hours to a few days. Although all distributions exhibited a periodic behaviour, AACC distributions were generally not linked to diel vertical migrations. In the subsurface layer, Synechococcus made the most abundant population and large variations in concentration were observed both at day and at night. The corresponding integrated (over the upper 90 m) losses of Synechococcus during one night pointed to a potential source of exported organic matter amounting to 534 mg C/m**2. This study stresses the potential importance of organic matter export from the euphotic zone through the daily grazing activity of vertically migrating organisms, which would not be accounted for by measurements at longer time scales. The metabolic CO2 production exhibited a peak of activity below 500 m that was shifted downward, apparently in a recurrent way and independently of the vertical distributions of AACC or of suspended particulate material. To account for this phenomenon, a 'sustained wave train» hypothesis is proposed that combines the effect of the diel superficial faecal pellet production by swarming migrators and the repackaging activity of the nonmigrating midwater populations. Our results confirm the recent finding that the particulate compartment is not the major source of the observed instantaneous remineralisation rate and shed a new light on the fate of organic matter in the aphotic zone.

Land Surface Temperature continuous time series from SSM/I passive microwave radiometers, over northern latitudes (Latitudes > 45°N), during summer snow free period (2000-2011), with links to NetCDF files

Remote sensing instruments are key players to map land surface temperature (LST) at large temporal and spatial scales. In this paper, we present how we combine passive microwave and thermal infrared data to estimate LST during summer snow-free periods over northern high latitudes. The methodology is based on the SSM/I-SSMIS 37 GHz measurements at both vertical and horizontal polarizations on a 25 km × 25 km grid size. LST is retrieved from brightness temperatures introducing an empirical linear relationship between emissivities at both polarizations as described in Royer and Poirier (2010). This relationship is calibrated at pixel scale, using cloud-free independent LST data from MODIS instruments. The SSM/I-SSMIS and MODIS data are synchronized by fitting a diurnal cycle model built on skin temperature reanalysis provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The resulting temperature dataset is provided at 25 km scale and at an hourly time step during the ten-year analysis period (2000-2011). This new product was locally evaluated at five experimental sites of the EU-PAGE21 project against air temperature measurements and meteorological model reanalysis, and compared to the MODIS LST product at both local and circumpolar scale. The results giving a mean RMSE of the order of 2.2 K demonstrate the usefulness of the microwave product, which is unaffected by clouds as opposed to thermal infrared products and offers a better resolution compared to model reanalysis.

Mesozooplankton and phytoplankton time series of the Baltic Monitoring Program (BMP)

Within the monitoring programme of the Helsinki Commission (HELCOM) the mesozooplankton of the Bornholm Basin (ICES subdivision 25, station BMP-K2) was sampled by the WP-2 net (lOOfJm) 5-8 times a year in 1988-1992. Abundance, biomass, secondary production and productivity (P/B) were given for mesozooplankton groups and copepod species. Environmental factors recorded were temperature, chlorophyll a and primary production. Within copepods, the dominant species were Temora longicornis and Pseudocalanus minutus with yearly peak values of 40-50% of the monthly copepod numbers and biomasses. The annual production of Temora longicornis was highest (6.5g C/m**2/y). The biomass of all copepods was at its maximum in June (mean = 2.25g C/m**2), especially in 1992 (3.65g C/m**2). The differences between results from two methods used to calculate the production of copepods were greatest in June and July. The cladocerans were only important in summer and the appendicularians only in spring. The productivity (P/B) of the appendicularians was highest of all mesozooplankton groups. Numbers and the biomass of the meroplankton were one or two orders of magnitude below the holoplanktic groups.