Beschreibung: The relationship between the vertical flux of microplankton and its standing stock in the upper ocean was determined in the subtropical (33°N, 21°W) and tropical (18°N, 30°W) northeast Atlantic in spring 1989 as part of the North Atlantic Bloom Experiment. In the subtropical area specific sedimentation rates at all depths were low (0.1% of standing stock) and 10-20% of settled particulate organic carbon (POC) was viable diatoms. The high contribution of viable diatoms, their empty frustules and tintinnid loricae to settled material characterized a system in transition between a diatom bloom sedimentation event and an oligotrophic summer situation. In the tropical area specific sedimentation rates were similar, but absolute rates (3 mg C m?2 day?1) were only about a third of those in the subtropical area. Microplankton carbon contributed only 2-6% to POC. Hard parts of heterotrophs found embedded in amorphous detrital matter suggest that particles had passed through a complex food web prior to sedimentation. Coccolithophorids, not diatoms dominated the autotrophic fraction in traps, and a shift in the composition of autotrophs may indicate a perturbation of the oligotrophic system.

Beschreibung: Here we present concentrations of chlorophyll a, phaeopigments, particulate organic carbon and nitrogen from water samples collected at discrete depths with a CTD-rosette during the European Iron Fertilization Experiment (EIFEX). The experiment was carried out from February 11 to March 20, 2004 in the 60-km diameter, rotating core of an eddy, formed by a meander of the Antarctic Polar Front (centred at around 49°10' S and 2°10' E). Samples were taken within the eddy inside and outside the fertilized patch, and in a few cases outside the eddy.Chlorophyll concentrations were determined by fluorometry using a Turner Design Model 10-AU digital fluorometer. Sampling, measurements and calibration of the fluorometer was carried out following the JGOFS protocol procedure (Knap et al, 1996). Results of the fluorometer calibration diverged by 5% between beginning and end of the cruise. Chlorophyll a content was calculated using average parameter values from the two calibrations. Measurement uncertainty was estimated from triplicate water samples taken from depths ranging between 10 and 100 m depth and averaged 5% of measured values. Samples for particulate organic carbon and nitrogen (POC and PON) were filtered onto precombusted Whatman GF/F filters and processed following recommendations by Lorrain et al. (2003). Samples were measured independently on three different analysers: a CN2500 CHN Analyser (Thermo Finnigan MAT) coupled to a Delta+ mass spectrometer (Thermo Finnigan MAT) via Conflo II interface (Thermo Finnigan MAT), a Carlo-Erba NA-1500 Series II elemental analyzer coupled to a Finnegan Delta+ mass spectrometer and a Euro EA Elemental Analyser. Differences due to methods were within the range of measurement variability (below 2%). The particulate organic phosphorus (POP) content was determined colorimetrically using the method from Hansen and Koroleff (1999; measurement variability 4%). Biogenic silica (BSi) was measured following the wet alkaline digestion method according to Müller and Schneider (1993; measurement variability 2%).

Beschreibung: Optical particle measurements are emerging as an important technique for understanding the ocean carbon cycle, including contributions to estimates of their downward flux, which sequesters carbon dioxide (CO2) in the deep sea. Optical instruments can be used from ships or installed on autonomous platforms, delivering much greater spatial and temporal coverage of particles in the mesopelagic zone of the ocean than traditional techniques, such as sediment traps. Technologies to image particles have advanced greatly over the last two decades, but the quantitative translation of these immense datasets into biogeochemical properties remains a challenge. In particular, advances are needed to enable the optimal translation of imaged objects into carbon content and sinking velocities. In addition, different devices often measure different optical properties, leading to difficulties in comparing results. Here we provide a practical overview of the challenges and potential of using these instruments, as a step toward improvement and expansion of their applications.

Beschreibung: Vertical phytoplankton distribution, temperol fluctuations and sedimentation rates were studied in the central Baltic Sea during the "Baltic Sea Patchiness Experiment 1986" (PEX'86). Vertical particle flux was measured with free sediment traps deployed at 30 and 60m depth for ten April/May 1986 within the PEX grid (20 x 40 nautical drifting days in miles). In the vicinity of one drifting trap water samples were collected in 10-12 depths down to 70m and vertical profiles of temperature, salinity, beam attenuation and light intensity were measured at three hour intervals. Water samples were analyzed for Chl.a, POC and PON content, dry weight and nutrients. Particulate parameters including the activity of 137 Cs were measured in trap samples. Suspended and sedimented particulates were counted under an inverted microscope. Precision and accuracy of the microscopical counts are discussed and confidence limits are calculated for different spec1es and applied counting schemes. Errors in all cases were smaller than the observed in situ variability. A general description of spring blooms in the central Baltic is given and the particular situation of spring 1986 is summarized. Within the station grid of PEX'86 an anticyclonic eddy was observed in which this study was conducted. Here the phytoplankton had reached peak concentrations and mass sedimentation of diatoms was about to start. The bloom was dominated by Thalassiosira levanderi and Chaetoceros spp. (lOµm size). Achnantes taeniata, Mesodinium rubrum, Gonyaulax catenata and an autotrophic Gymnodinium species (26-30µm) were also abundant. Horizontal patchiness and advection caused greater variability in the distribution of phytoplankton biomass blooms as well as temperature and attenuation during the first days than during the latter half of the investigation period. In four different areas within the PEX grid different developed independently. On still smaller time and space scales, the phytoplankton species composition also changed. The degree of patchiness was different for different species. General concepts explaining vertical distribution patterns of phytoplankton by physical and biological mechanisms are discussed. The species-specific distribution of selected diatoms, dinoflagellates and of the funktionally autotrophic ciliate M.rubrum are described. None of the species were homogeneously distributed although no vertical density stratification was observed. Whereas the diatoms and M.rubrum were present within the whole trophogenic layer, the dinoflagellates were only found in the upper 30m. The vertical distribution was different for concentrations were encountered each at species and different maximum depths respectively. Mechanisms affecting species-specific distribution of mobile and non-mobile phytoplankters in isopycnal layers are discussed in light of the particular situation of this study. Diurnal vertical migration is shown for two dinoflagellates and the phytociliate and triggering factors are discussed. All three species migrated upwards during the day and downwards at night. In its detail, however, the migratory behaviour differed between species and also within single populations. Different strategies of adaptation of phytoplankton to changing environmental conditions are suggested: Wheras diatoms adapt to fluctuations of the light climate by physiological adaptations, mobile organisms have the possibility to stay in an isolume layer. The significance of turbulence, of chainformation and of resting stages in the life cycles of phytoplankton is also evaluated. Trap deployments reveiled that only T.levanderi and Chaetoceros spp. sedimented. Their daily relative sedimentation rates (losses as % of standing stocks) increased over time and were species-specific (for T.levanderi max. 50%). Since part of the T.levanderi population was actively dividing (20% of the standing stock was found as paired cells) their suspended concentration decreased slower than that of Chaetoceros spp., although the daily sedimentation of the latter species was only about 30% of the standing stock. T.levanderi occured in chains in the water column but only single cells were found in sedimented material and paired cells were never found in the trap samples. Chaetoceros spores were rare in the water column and only sporadically collected by the sediment traps. The relative sedimentation rate of all other species was less than 5% per day. The settling velocity of the cells was estimated in different independent ways to be about 40-60m/d. This high sinking speed was attributed to aggregate formation. The results indicate that aggregate formation is not only species-specific but also differs between life-stages within one species. Variability of sedimentation rates on a timescale of hours was high, suggesting a diurnal pattern. Sedimentation did not change the vertical distribution patterns, indicating that cells were sinking with similar rates from all depths. The advantages of a Lagrangian sampling strategy (time series measurements 1n the vicinity of a free drifting buoy) for investigating phytoplankton development in time are evaluated and compared to a sampling at a moored station (Eulerian approach). In an environment that exhibits an intense patchiness even at spatial scales of lOOm, as encountered in this study, the influence of advection and patchiness on a time-series with a resolution of hours to days can not be neglected even if the Lagrangian approach is followed. Furthermore, in this study the variability of var1ous parameters measured in an Eulerian mode was not generally higher than that following the Lagrangian one, as one would have expected.

Beschreibung: The sinking of particulate matter from the upper ocean dominates the export and sequestration of organic carbon by the biological pump, a critical component of the Earth's carbon cycle. Controls on carbon export are thought to be driven by ecological processes that produce and repackage sinking biogenic particles. Here, we present observations during the demise of the Northeast Atlantic Ocean spring bloom illustrating the importance of storm-induced turbulence on the dynamics of sinking particles. A sequence of four large storms caused upper layer mean turbulence levels to vary by more than three orders of magnitude. Large particle (>0.1 to 10 mm) abundance and size changed accordingly: increasing via shear coagulation when turbulence was moderate and decreasing rapidly when turbulence was intense due to shear disaggregation. Particle export was also tied to storm forcing as large particles were mixed to depth during mixed layer deepening. After the mixed layer shoaled, these particles, now isolated from intense surface mixing, grew larger and subsequently sank. This sequence of events matched the timing of sinking particle flux observations. Particle export was influenced by increases in aggregate abundance and porosity, which appeared to be enhanced by the repeated creation and destruction of aggregates. Last, particle transit efficiency through the mesopelagic zone was reduced by presumably biotic processes that created small particles (〈0.5 mm) from larger ones. Our results demonstrate that ocean turbulence significantly impacts the nature and dynamics of sinking particles, strongly influencing particle export and the efficiency of the biological pump.