Description: 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%).

Description: 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.

Description: 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.