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Abstract: Budgets of nitrate, dissolved oxygen, and particulate organic carbon (POC) were constructed from data collected on-board a Lagrangian, profiling float deployed between April 4 and May 25, 2008, as part of the North Atlantic Bloom Experiment. These measurements were used to estimate net community production (NCP) and apparent export of POC along the float trajectory. A storm resulting in deep mixing and temporary suspension of net production separated the bloom into early (April 23–27) and main (May 6–13) periods over which ∼264 and ∼805mmolCm−2 were produced, respectively. Subtraction of the total POC production from the NCP yielded maximum estimates of apparent POC export amounting to ∼92 and 574 mmolCm−2 during the early and main blooms, respectively. The bloom terminated the following day and ∼282 mmolCm−2 were lost due to net respiration (70%) and apparent export (30%). Thus, the majority of the apparent export of POC occurred continuously during the main bloom and a large respiration event occurred during bloom Termination. A comparison of the POC flux during the main bloom period with independent estimates at greater depth suggest a rapid rate of remineralization between 60 and 100m. We suggest the high rates of remineralization in the upper layers could explain the apparent lack of carbon overconsumption (C:N>6.6) in the North Atlantic during the spring bloom. [Copyright &y& Elsevier]

Abstract: Wetland processes are strongly influenced by hydrologic factors such as precipitation, surface runoff, and flooding dynamics. Anthropogenic disturbances to flooding regimes can thus substantially alter wetland habitat and biogeochemistry. The Kafue Flats, a large floodplain (∼6500km2) along the Kafue River in South-Central Zambia, is a wetland impacted by upstream and downstream hydropower dams. The main purpose of this study was to develop a water budget for the Kafue Flats under current conditions, quantify nutrient and organic carbon concentrations in the river, and use the combined information to estimate biogeochemical budgets. A water balance was developed for the Kafue Flats at a subcatchment scale for the years 2002–2009 using daily hydrological data. In addition, bi-monthly flow and chemical measurements were performed over 1year (May 2008–May 2009) at multiple stations. Evapotranspiration was an important process in the Flats, accounting for up to 49% of total hydrologic outputs in some subcatchments. Direct precipitation contributes substantial to water inputs to the flats: runoff from the upstream catchment accounted for 45% of water inputs to the Kafue Flats, while the remaining 55% came from direct precipitation to the Kafue Flats from its subcatchment. Estimates from the wet season suggest that ∼75% of the water flowing in the river’s main channel as it exits the Flats spent some time within the highly productive floodplain. This exchange between the floodplain and the river appeared to play an important role in nutrient and carbon export to the river’s main channel and out of the wetland. The floodplain was a net source of phosphate (220t/year), total nitrogen (1300tN/year, of which ∼90% was organic nitrogen) and total organic carbon (50,000tC/year) to downstream systems. Thus, when considering dam impacts and altered flooding dynamics in this system, potential changes to carbon and nutrient cycling also need to be taken in to consideration, which may have implications for nutrient availability within the Kafue Flats and nutrient export to downstream systems. [Copyright &y& Elsevier]

Abstract: The influence of environmental factors on size-fractionated phytoplankton production and biomass (chlorophyll a) and community composition was examined in the Hudson Bay system (Hudson Bay, Hudson Strait, and Foxe Basin; HBS) during August 2004 and September 2005 and 2006. Significant variability in the vertical structure of the water column and melt season length was observed between years and between regions of the HBS. Even though there was no year-to-year variability in the phytoplankton production and biomass, we observed significant differences in the phytoplankton size structure and taxonomic composition between mid and late summer. For all years, phytoplankton production and biomass were lower in Hudson Bay (51–1217mg C m−2 d−1; 11–57mg chl a m−2) than in Hudson Strait (675–2740mg C m−2 d−1; 28–97mg chl a m−2). Negative correlation between primary production and stratification strength of the upper water column suggested nutrient limited primary production in Hudson Bay and the south shore of Hudson Strait. Stratification and nitrate concentration also explained the variability in the physiological state (i.e., production:biomass ratio) and size structure of phytoplankton communities between mid and late summer. Daily estimated summer primary production averaged 0.32g C m−2 in Hudson Bay and 1.34g C m−2 in Hudson Strait. Phytoplankton production in the HBS was largely dominated by ultraphytoplankton. On average, only ca. 30% of total production was potentially exported from the euphotic zone. The dominance of flagellate-dominated community may explain the low export of matter and energy toward deeper waters and likely toward the upper trophic levels. [Copyright &y& Elsevier]

Abstract: The southern Yellow Sea (SYS), located to the north of the East China Sea (ECS), was considered part of the ECS when proposed the “continental shelf pump” (CSP) hypothesis. However, the original CSP carbon dioxide (CO2) uptake flux (2.9molCm−2 yr−1) appears to have been overestimated, primarily due to the differences between the SYS and the ECS in terms of their CO2 system. In this paper, we estimated air–sea CO2 fluxes in the SYS using the surface water partial pressure of CO2 (pCO2) measured in winter, spring, and summer, as well as that estimated in fall via the relationship of pCO2 with salinity, temperature, and chlorophyll a. The results indicate that overall, the entire investigated area was a net source of atmospheric CO2 during summer, winter, and fall, whereas it was a net sink during spring. Spatially, the nearshore area was almost a permanent CO2 source, while the central SYS shifted from being a CO2 sink in spring to a source in the other seasons of the year. Overall, the SYS is a net source of atmospheric CO2 on an annual scale, releasing ∼7.38TgC (1Tg=1012 g) to the atmosphere annually. Thus, the updated CO2 uptake flux in the combined SYS and ECS is reduced to ∼0.86molCm−2 yr−1. If this value is extrapolated globally following , the global continental shelf would be a sink of ∼0.29PgCyr−1, instead of 1PgCyr−1 (1Pg=1015 g). The SYS as a net annual source of atmospheric CO2 is in sharp contrast to most mid- and high-latitude continental shelves, which are CO2 sinks. We argue that unlike the ECS and the North Sea where carbon on the shelf could be exported to the open ocean, the SYS lacks the physical conditions required by the CSP to transport carbon off the shelf effectively. The global validity of the CSP theory is thus questionable. [Copyright &y& Elsevier]

Abstract: Enrichment of the pelagic ecosystem associated with the proliferation of free-drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming. Lagrangian Sediment Traps (LST) were deployed autonomously beneath a large tabular, free-drifting iceberg (C-18a) in the NW Weddell Sea during March and April 2009 to collect sinking particles at a depth of 600m. Three LST deployments associated with C-18a, within a 30-km radius, collected sinking diatom frustules, dominated by Corethron pennatum and Fragilariopsis nana, euphausiid fragments, crustacean and fish fecal material, detrital aggregates and mineral grains. One LST deployment at a “control” site 74km away in open water devoid of icebergs collected diatom frustules, euphausiid molts, crustacean fecal material and detrital aggregates. Phytoplankton abundance, microbial abundance and biomass were significantly higher in the LST samples than in open-water collections at 500m depth. The mean mass flux and organic carbon flux associated with iceberg C-18a were twice as high, 124mgm−2 d−1 and 5.6mg Corg m−2 d−1, respectively, than at the control site. A similar trend was observed in Corg/234Th activity, being highest near C-18a and lowest at the control site. Extrapolation of the area of enrichment to 30km radius around C-18a, 2826km2, produces an estimated mass flux of 350tonsd−1 and carbon flux of 15.8tonsCorg d−1. Five similar sized icebergs to C-18a were identified in satellite images in a surrounding 47,636km2 area at the same time of sampling. Assuming a 30-km radius as the area of influence around each of these five icebergs, 46% of the total area would be enhanced with an export flux at 600m of 122.4tonsCorg d−1. The large numbers of smaller icebergs identified visually in this area would only increase this area of influence. Icebergs serve as areas of local enrichment and with increased proliferation, must be considered in the cycling of carbon in the Southern Ocean. [Copyright &y& Elsevier]

Abstract: The recent proliferation of icebergs in the Southern Ocean and the chemical and biological enrichment recently identified in the surrounding water raise the question of whether these icebergs are major contributors to drawdown of CO2 and the export of organic carbon to the deep ocean. The Lagrangian sediment trap (LST) was developed to measure the carbon export associated with these free-drifting icebergs. The core of the LST is a neutrally buoyant Sounding Oceanographic Lagrangian Observer (SOLO) float () that contains a variable-buoyancy engine, enabling it to sink to a set depth (600m for the iceberg study), drift at that depth, then resurface on preset time intervals. Four sediment-trap funnels and opening/closing sample cups mounted around each SOLO float collect sinking particulate matter. Additionally, an upward-looking acoustic system mounted on the float detects the presence of ice cover above. In March/April 2009, three LSTs were deployed in the NW Weddell Sea for a total of five successful missions. Four of these LST deployments were made near or under a large iceberg. The fifth deployment was made at a control site 74km from the nearest large iceberg. Sinking particulate matter was collected on each deployment. Despite the high-risk nature of the deployments, the LSTs successfully sampled particulate matter beneath drifting icebergs. [Copyright &y& Elsevier]

Abstract: Northeast Atlantic mode waters (NEAMW) are formed by subduction in a region which is a strong sink of atmospheric CO 2. The mechanisms underlying this sink were thoroughly examined in the frame of the POMME experiment, which covered the 2001 seasonal cycle with particular focus on meso to sub-mesoscales. The biological and physical data collected during POMME were used to initialize, constrain and evaluate a regional, 4.5km-resolution, bio-physical model simulation of the 2001 seasonal cycle in the region of NEAMW formation. We used this model to examine the contribution of sub-mesoscales on the annual budget of carbon export below the mixed-layer and on NEAMW biogeochemical characteristics. This is done by comparing a high-resolution (eddy) simulation at 4.5km resolution with a high-diffusivity (non-eddy) simulation where the only change is a stronger eddy diffusivity. We found that the model mixed-layer depth is more stratified and closer to reality in the eddy simulation. This result confirms with observational data the proposed mechanism of restratification of the upper ocean driven by sub-mesoscales. We found that the phytoplankton bloom and the subduction of NEAMW display strong contrasts at the sub-mesoscale. Nevertheless, the mean intensity of the bloom and of the subsequent biological pump are only marginally modified by sub-mesoscales (less than 5%), while the intensity of the physical pump (subduction of carbon) is moderately reduced (−10%) in the non-eddy experiment. Moreover, the biogeochemical and thermodynamical characteristics of NEAMW are substantially affected, with, in particular, a wider range of densities and biogeochemical characteristics biased toward winter conditions in the eddy simulation. These differences ensued essentially from lateral induction across sub-mesoscale filaments, which is found to contribute to subduction before seasonal stratification, i.e. before the effective subduction period. [Copyright &y& Elsevier]

Marquis, E., Niquil, N., Vézina, A. F., Petitgas, P., and Dupuy, C. 2011. Influence of planktonic foodweb structure on a system's capacity to support pelagic production: an inverse analysis approach. – ICES Journal of Marine Science, 68: 803–812.Coupled plankton/small pelagic (SP) fish systems were analysed to assess how foodweb structure influences the export of carbon to pelagic fish during the spring bloom in the Bay of Biscay. The investigation of carbon export flows through inverse analysis was supplemented by estimating the carrying capacity for pelagic fish production by applying linear programming. A planktonic foodweb dominated by microbial pathways had the highest trophic efficiency owing to the tight coupling between planktonic trophic levels and predation pressure on mesozooplankton by fish. Moreover, the magnitude of the gap between carrying capacity and estimated carbon export was related to the size structure of primary producers, with the picophytoplankton-based foodweb having the smallest gap and the microphytoplankton-based one the largest gap. Planktonic foodwebs dominated by small autotrophic cells channelled most of their available carbon to pelagic fish production, whereas foodwebs dominated by large phytoplankton were better suited to benthic communities with a large loss of carbon through sedimentation. Although the total carbon available to higher trophic levels does not vary with the size of the main primary producers, the potential export to SP fish depends on the structure of the planktonic foodweb. [ABSTRACT FROM PUBLISHER]

Abstract: We deployed autonomous particle-sensing SOLOPC floats more than eight times during five cruises, amassing almost 400 profiles of particle size () and abundance between the ocean surface and 100m. The profiles consistently had subsurface maxima in particle volume. The median (by volume) equivalent spherical diameter for the particle distribution was 0.4–0.8mm and increased with depth in a manner similar to that observed in coagulation simulations. There was a sharp cutoff at the bottom of the high particle concentration region. Estimation of particle fluxes made using the size distributions show an increasing downward movement through the particle field above the sharp particle cutoff. The increase of particle flux with depth through the euphotic zone implies a partial spatial separation of production and consumption. The sharp drop in particle volume and flux implies that the base of the particle-rich zone is a region of active particle consumption, possibly by zooplankton flux feeding. Our data show greater concentrations of zooplankton-type particles relative to marine snow-type particles below the particle maximum. Such behavior could explain why zooplankton are frequently observed at and immediately below the particle maximum rather than the productivity maximum and suggests an important role for flux feeding in carbon and nutrient cycling at the base of the particle maximum. This implies that zooplankton act as gatekeepers for the movement of organic matter to the mesopelagic. The ability of the SOLOPC to sample hourly with high resolution in the upper 100m of the ocean provides a powerful complement for the study of particles where it has been difficult to use sediment traps. [Copyright &y& Elsevier]

Abstract: Dissolved organic carbon (DOC) data are presented from three meridional transects conducted in the North Atlantic as part of the US Climate Variability (CLIVAR) Repeat Hydrography program in 2003. The hydrographic sections covered a latitudinal range of 6°S to 63°N along longitudes 20°W (CLIVAR line A16), 52°W (A20) and 66°W (A22). Over 3700 individual measurements reveal unprecedented detail in the DOC distribution and systematic variations in the mesopelagic and bathypelagic zones of the North Atlantic basin. Latitudinal gradients in DOC concentrations combined with published estimates of ventilation rates for the main thermocline and North Atlantic Deep Water (NADW) indicate a net DOC export rate of 0.081PgCyr−1 from the epipelagic zone into the mesopelagic and bathypelagic zones. Model II regression and multiple linear regression models applied to pairwise measures of DOC and chlorofluorocarbon (CFC-12) ventilation age, retrieved from major water masses within the main thermocline and NADW, indicate decay rates for exported DOC ranging from 0.13 to 0.94μmolkg−1 yr−1, with higher DOC concentrations driving higher rates. The contribution of DOC oxidation to oxygen consumption ranged from 5 to 29% while mineralization of sinking biogenic particles drove the balance of the apparent oxygen utilization. [Copyright &y& Elsevier]

Fear of predation can have wide-ranging ecological effects. 1–4 This is especially true in the ocean's pelagic zone, the Earth's largest habitat, where vertical gradients in light and primary productivity force numerous taxa to migrate vertically each night to feed at the surface while minimizing risk from visual predators. 5–7 Despite its importance and the fact that it is driven by spatial differences in perceived risk, 8 diel vertical migration (DVM) is rarely considered within the "landscape of fear" 3,8,9 framework. 10 It is also far from the only such process in the pelagic zone. We used continuous, year-long records from an upward-looking echosounder and broadband hydrophone at a cabled observatory off Central California, USA, to observe avoidance reactions by several groups of pelagic animals to the presence of their predators. As expected, vertical migration was ubiquitous, but we also observed behaviors at shorter and longer timescales that were best explained by fear of predation. The presence of foraging odontocetes induced immediate diving behavior in mesopelagic sound-scattering layers, and schools of epipelagic fishes induced similar reaction in layers of zooplankton and mesopelagic micronekton. At longer timescales, the presence of fish schools significantly deepened vertical migration, rearranging life throughout the water column. We argue that behavioral reactions to predation risk are common in the pelagic zone at a range of spatiotemporal scales and that our understanding of food webs and biogeochemical cycling in this immense biome will be incomplete unless we account for fear. • High-resolution acoustic measurements continuously monitored pelagic animals • Zooplankton and micronekton move vertically at multiple timescales to avoid predators • These behaviors may have significant ecological and biogeochemical consequences • "Landscapes of fear," initially a terrestrial concept, are ubiquitous in the pelagic Fear of predation drives the largest animal migration on earth: a daily, worldwide commute between food at the ocean's surface and refuge in its dark interior. Using new acoustic data, Urmy et al. show that the "ecology of fear" drives a variety of dynamic vertical movements and is more important than widely recognized in the open ocean. [ABSTRACT FROM AUTHOR]

Abstract: We describe the first results obtained using a novel free-drifting neutrally buoyant sediment trap called PELAGRA (Particle Export measurement using a LAGRAngian trap). The trap uses an APEX float (Autonomous Profiling EXplorer) to maintain its location at a predetermined depth or density horizon and is designed to be deployed in the depth range 100–600m for periods of up to a week. PELAGRA was deployed into a well characterised region of the Northeast (NE) Atlantic over the Porcupine Abyssal Plain (PAP) during the summers of 2003, 2004, 2005 and 2006 in post-bloom conditions. In parallel, measurements were made of total and new primary production and estimates of particle export based on 234Th deficits in the upper water column. Samples of sinking material from PELAGRA were recovered almost uncontaminated by “swimmers”. The material collected differed from that obtained using water bottles and an in situ filtration system and this indicated selective export of centric diatoms. Fluxes of 234Th into the traps were less than that calculated from the deficit of this isotope in the upper water column. It is concluded that this reflects export events that had occurred prior to these deployments. Fluxes of organic carbon into the PELAGRA traps were similar to those expected from measurements of new production in the upper mixed layer. During 2006, simultaneous PELAGRA deployments at depths of 150 and 250m provided a direct measurement of the decrease in flux with depth. This decrease was substantially more than that predicted by the often-used “Martin equation” and yielded a “b value” of 1.7. Using this value in the NE Atlantic about 14% of the total production reaches a depth of 150m during the post-bloom period under nutrient limitation. [Copyright &y& Elsevier]

The article presents the study on the spectrophotometric properties of surface water dissolved in organic matter in peatland areas. The peatland areas in Great Britain, where the uplands have undergone afforestation, could suffer from runoffs, and enhanced dissolved organic matter (DOM) in rivers. The study provided reports on the DOM spectrophotometric properties of streamflow, with special attention to potential carbon sources in drainage ditches. Results suggested that ditches contain organic matter with different spectrophotometric character, which may be due to the exposure of bare peat faces adjacent to the ditches.

Abstract: Total 234Th and 238U vertical profiles in the water column were determined along a three-station transect perpendicular to the Eastern Weddell Sea ice shelf. The transect was sampled during pre-bloom (6–7 December 2003) and bloom (19–20 December 2003) conditions to follow changes occurring in the particulate organic carbon (POC) flux during an Antarctic phytoplankton ice-edge bloom. During the pre-bloom period, 234Th:238U ratios>1 (up to 1.3) were measured just above the thermocline at all stations, and throughout the entire mixed layer at the ice-edge. These water column data appear to be the first which support the hypothesis that sea-ice algae could represent an input of 234Th-rich material in polar waters due to cellular uptake of the radionuclide and/or its adsorption onto the extracellular polymeric substances (EPS) produced by these organisms. A simple conceptual model is proposed to link observed 234Th:238U ratios to the input of 234Th-enriched sea-ice algae caused by ice-melting. The extensive, deep-water 234Th deficit observed during the second transect likely results from the combination of vertical particle export and water-seafloor exchange processes. POC steady-state (SS) fluxes out of the photic layer were negative or ∼nil (−11 to 2 mmol m−2 d−1) under pre-bloom conditions, probably due to ice-algae input at the ice-edge and remineralization elsewhere, whereas POC non-steady-state (NSS) fluxes were generally higher (7 to 33 mmol m−2 d−1) when the bloom was developing. We have estimated that these flux values could change by as much as 75% if a sea-ice algae 234Th input term were included in the simple one-box model used. This suggests that failure to consider the sea-ice algae compartment, when using 234Th as a proxy to assess carbon export in seasonally ice-covered regions, could at times lead to significant biases in the interpretation of 234Th-based particle flux estimates. [Copyright &y& Elsevier]

Abstract: Particle export from the upper waters of the oligotrophic ocean may play a crucial role in the global carbon cycle. Mesoscale eddies have been hypothesized to inject new nutrients into oligotrophic surface waters, thereby increasing new production and particle export in otherwise nutrient deficient regimes. The E-Flux Program was a large multidisciplinary project designed to investigate the physical, biological and biogeochemical characteristics of cold-core cyclonic eddies that form in the lee of the Hawaiian Islands. There, we investigated particle dynamics using 210Pb–210Po disequilibrium. Seawater samples for 210Pb and 210Po were collected both within (IN) and outside (OUT) of two cyclones, Noah and Opal, at different stages of their evolution as well as from the eddy generation region. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO2) export fluxes were determined using water-column PC, PN, and bSiO2 inventories and the residence times of 210Po. PC and PN fluxes at 150m ranged from 1.58±0.10 to 1.71±0.16mmolCm−2 d−1 and 0.22±0.02 to 0.30±0.02mmolNm−2 d−1 within Cyclones Opal and Noah. PC and PN fluxes at OUT stations sampled during both cruises were of similar magnitudes, 1.69±0.16 to 1.67±0.16mmolCm−2 d−1 and 0.30±0.03 to 0.26±0.03mmolNm−2 d−1. The bSiO2 fluxes within Cyclone Opal were 0.157±0.010mmolSim−2 d−1 versus 0.025±0.002mmolSim−2 d−1 at OUT stations. These results of minimal PC and PN export, but significant eddy-induced bSiO2 fluxes, agree very well with other studies that used a variety of direct and indirect methods. Thus, our results suggest that using elemental inventories and residence times of 210Po is another independent and robust method for determining particle export and should be investigated more fully. [Copyright &y& Elsevier]

Abstract: Mesoscale eddies may enhance primary production (PP) in the open ocean by bringing nutrient-rich deep waters into the euphotic zone, potentially leading to increased transport of particles to depth. This hypothesis remains controversial, however, due to a paucity of direct particle export measurements. In this study, we investigated particle dynamics using 234Th–238U disequilibria within a mesoscale cold-core eddy, Cyclone Opal, which formed in the lee of the Hawaiian Islands. 234Th samples were collected along two transects across Cyclone Opal as well as during a time-series within the eddy core during a decaying diatom bloom. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO2) fluxes at 150m varied spatially and temporally within the eddy and strongly depended on the 234Th model formulation used (e.g., steady state versus non-steady state, inclusion of upwelling, etc.). Particle fluxes estimated from a steady state model assuming an upwelling rate of 2mday−1 yielded the best fit to sediment-trap data. These 234Th-derived particle fluxes ranged from 332±14 to 1719±53μmolCm−2 day−1, 27±3 to 114±12μmolNm−2 day−1, and 33±20 to 309±73μmolSim−2 day−1. Although PP rates within Cyclone Opal were elevated by a factor of 2–3, PC and PN fluxes were the same, within error, inside and outside of Cyclone Opal. The ratio of PC export to PP remained surprisingly low at <0.03 and similar to those measured in surrounding waters. In contrast, bSiO2 fluxes within the eddy core were three times higher. Detailed analyses of 234Th depth profiles consistently showed excess 234Th at 100–175m, associated with the remineralization and possible accumulation of suspended and dissolved organic matter from the surface. We suggest that strong microzooplankton grazing facilitated particulate organic matter recycling and resulted in the export of empty diatom frustules. Thus, while eddies may increase PP, they do not necessarily increase PC and PN export to deep waters. This may be a general characteristic of wind-driven cyclonic eddies of the North Pacific Subtropical Gyre and suggests that eddies may preferentially act as a silica pump, thereby playing an important role in promoting silicic-acid limitation in the region. [Copyright &y& Elsevier]

Abstract: The phytoplankton bloom that develops over the Kerguelen plateau following natural input of iron is analysed on a regional and seasonal scale. The relation between chlorophyll, bathymetry, and surface advection fields is not as obvious as it first appears from large-scale annual mean field. The high chlorophyll biomass does not always correspond with the shallowest water, and there are portions of the plateau, which persistently exhibit low chlorophyll. Despite this complex dynamic, a one-dimensional model calibrated for HNLC (high-nutrient low-chlorophyll) region is able to capture the observed increase in chlorophyll by increasing the deep iron concentration. The elemental budget shows similarity in terms of carbon, nitrogen, and silicon but differences in terms of iron with the budget calculated during the mission. This discrepancy either has its origin in the structure of the iron cycling in the model or in the temporal scarcity of data that could only be collected during the summer months. In the model, flexibility of the Fe/C ratio associated with high Fe export and input fluxes prevents high carbon sequestration efficiency. This first insight with remote sensing data and the model allows the validation of some of the key mechanisms of natural iron fertilization and exposes problems that will need to be solved to have a complete biogeochemical diagnostic of this natural iron fertilization. [Copyright &y& Elsevier]

Abstract: The sinking of particles that make up the biological pump is not vertical but nearly horizontal. This means that the locations where the particles are formed may be distant from their collection in a sediment trap. This has led to the development of the concept of the statistical funnel to describe the spatial–temporal sampling characteristics of a sediment trap. Statistical funnels can be used to quantify the source region in the upper ocean where collected particles were created (source funnels) or the location of the collected particles during that deployment (collection funnels). Here, we characterize statistical funnels for neutrally buoyant, surface-tethered and deep-ocean moored trap deployments conducted just north of Hawaii in the Pacific Ocean. Three-dimensional realizations of the synoptic velocity field, created using satellite altimeter and shipboard acoustic Doppler current profiler data, are used to advect sinking particles back to their source for sinking velocities of 50–200m per day. Estimated source- and collection-funnel characteristics for the 5-day collections made by neutrally buoyant and surface-tethered traps are similar with typical scales of several km to several 10s of km. Deep-moored traps have daily source-funnel locations that can be many 100s of km distant from the trap and have long-term containment radii that range from 140 to 340km depending upon sinking rate. We assess the importance of particle source regions using satellite estimates of chlorophyll concentration as a surrogate for the spatial distribution of particle export. Our analysis points to the need to diagnose water-parcel trajectories and particle sinking rates in the interpretation of sinking-particle fluxes from moored or freely drifting sediment traps, especially for regions where there are significant horizontal gradients in the export flux. But whence come the little siliceous and calcareous shells…[brought up] from the depth of over miles? Did they live in the surface waters immediately above? Or is their habitat in some remote part of the sea, whence, at their death, the currents were set forth as pallbearers, with the command to deposit the dead corpses where the plummet found them? (Maury, 1858). [Copyright &y& Elsevier]

Abstract: It has long been recognised that some oceanic regions have persistently low-chlorophyll levels, even though there are abundant inorganic nutrients. Studies have shown that these high-nutrient low-chlorophyll (HNLC) areas are depleted in iron, an essential micronutrient. In these regions biological production can be enhanced with artificial mesoscale iron fertilisation. However, the ability of iron-induced blooms to efficiently sequester carbon to mesopelagic depths is still an open question. It is hypothesised that sub-Antarctic islands in the HNLC Southern Ocean are also a source of iron and thus fuel the natural phytoplankton blooms observed in their proximity, thereby enhancing levels of particulate organic carbon (POC) export. To test the third part of this hypothesis, POC export was measured in the Southern Ocean region of the Crozet Islands (52°E, 46°S) during the austral summer of 2004/2005 as part of the CROZEX project. Based on satellite imagery, a high-chlorophyll region (maximum concentration=4μgl−1) north and downstream of the islands was distinguished from a low-chlorophyll region (typical concentration=0.3μgl−1) south and upstream of the islands. POC export estimates were obtained by using the naturally occurring particle-reactive radionuclide tracer 234Th. POC export was initially 15mmolCm−2 d−1 in the high-chlorophyll bloom region, compared with 5mmolCm−2 d−1 in the low-chlorophyll, non-bloom region. After a moderately small bloom at the southern control stations (max concentration=0.7μgl−1) the spatial variability in POC export was lost, resulting in equally high levels of POC export (ca. 20mmolCm−2 d−1) throughout the study region. Comparison of 234Th-derived POC export with estimates of new production, calculated from nitrate budgets, revealed evidence for a decoupling of new and export production, with this effect most apparent within the northern bloom area. In addition to methodological issues this apparent decoupling of new and export production could be due to a buildup of dissolved organic nitrogen within the bloom region, thus reducing the amount of POC available for export to mesopelagic depths. [Copyright &y& Elsevier]

Abstract: Annual phytoplankton blooms are observed around most sub-Antarctic islands during austral spring and summer, but are absent in the surrounding high-nutrient low-chlorophyll (HNLC) ocean. The CROZEX study (2004/2005) tested the hypothesis that annual blooms occurring immediately north of the Crozet islands in the Polar Frontal Zone (PFZ) develop because of natural iron fertilisation, while to their south in HNLC waters, there is insufficient iron (Fe) to promote blooms. Size-fractionated nitrogen uptake (ρN) experiments using 15N-NO3 −, NH4 + and urea addressed three major goals. Firstly, measurements of NO3 − uptake (ρNO3 −) aimed to establish whether ρNO3 − responds to natural Fe fertilisation. Secondly, we compared regional ρNO3 − rates, hypothesising that in Fe-fertilised regions, ρNO3 − should exceed that in HNLC regions. Thirdly, by using satellite imagery, we extrapolated ρNO3 − measurements made during a declining bloom to reconstruct seasonal ρNO3 − by the spring bloom. Finally, we estimated the ‘new’ Fe demand required to support ρNO3 −, comparing this with estimated Fe fluxes. Diatoms and colonial Phaeocystis dominated phytoplankton communities north of the islands, while to the south, Phaeocystis was absent. Total ρN was elevated north of the islands (∼400μmolm−2 d−1) relative to south of the islands (∼250μmolm−2 d−1). Nitrate uptake showed a clear response to Fe fertilisation, exhibiting a strong north (∼198μmolm−2 d−1) to south (∼74μmolm−2 d−1) gradient, while neither ρNH4 + nor ρurea showed such significant latitudinal gradients. The N–S integrated f-ratio gradient was 0.47–0.28 while specific N uptake ( d−1) rates were significantly higher in the Fe-fertilised region relative to those in the southern HNLC region. The potential for NH4 + inhibition of ρNO3 − did not appear to be significant. High PON:chl-a ratios combined with relatively low 14C:15N uptake ratios suggested that most phytoplankton were relatively chlorotic and carbon stressed, with the exception of those growing actively within a cyclonic eddy where neither Fe nor light appeared to be limiting. Size-fractionated ρNO3 − and f-ratios exhibited a complex response to NH4 + and Fe availability, with f-ratios in the >20-μm fraction being low (∼0.3) in the HNLC region, but significantly higher (∼0.7) in a localised diatom-dominated bloom in the northern Fe-fertilised region. In contrast, f-ratios in the <2-μm size class were similar everywhere (∼0.44), indicative of Fe-limitation for large-celled diatoms in the southern HNLC region. As a result of Fe-regulated ρNO3 −, new production showed a N–S gradient of ∼24 to ∼15mmolCm−2 d−1, very similar to carbon export determined from NO3 − ‘draw-down’ and from 234Th measurements. The estimated DFe demand required to support seasonal ρNO3 − in the northern region, based on conservative cellular Fe:N quotas, required surface (to 100m) pre spring-bloom DFe concentrations of ∼0.75nmoll−1. Our results support the hypothesis that phytoplankton blooms north of the islands are stimulated by natural Fe fertilisation, with a direct impact on ρNO3 −, particularly for larger cells, resulting in higher new production rates relative to those from the Fe-limited HNLC region south of the Crozet islands. [Copyright &y& Elsevier]

Abstract: 234Th/238U disequilibrium was studied in the water column during three cruises (March–April 1997) carried out in the framework of the HFF experiment in the Gulf of Lions. The purposes were to investigate short temporal (15–20 days) and spatial (20–50 Km) variations in the water column and to determine export fluxes from the euphotic zone, in relation to environmental features of the study area. Sampling stations were identified in order to evaluate along and across slope transports. Activity-depth profiles show that both temporal and spatial variations occurred at the scale of the experiment. 234Th deficiencies, with respect to 238U and indicating removal from surface waters, can be observed at all stations, with higher values measured at the shelf break. Particulate thorium activities do not correlate directly with suspended matter concentration. Dissolved 234Th values higher than 238U activities were observed three times in surface waters. They are probably due to desorption processes favoured by vertical mixing and/or lateral transport by the Northern Current and the Rhône river. Fluxes and residence times were obtained using both steady-state (SS) and non-steady-state formalisms (NSS). Lateral transport was calculated to define intra-station influences. Results showed a complex spatial setting with generally higher export at the shelf break (due to enhanced vertical exchange and stronger continental influence), and agreed with the general circulation pattern, characterized by large anti-cyclonic meanders flowing from the Northern Current core area to coastal zones that produce an intense mesoscale activity. Export fluxes from the euphotic zone of particulate organic carbon (PPOC) and suspended particulate matter (PSPM) were calculated from C/234Thp and SPM/234Thp ratios at 165 m depth and thorium fluxes. Under SS conditions, estimates ranged from 11 to 52 mgC m−2d−1 and between 162 and 1244 mg m−2d−1, for PPOC and PSPM, respectively, and a general agreement was observed with HFF sediment trap results. Export ratios (ThE) varied from typical oceanic settings to early bloom conditions, and decreased after the onset of water column early summer stratification. [Copyright &y& Elsevier]

Loads and yields of dissolved and particulate organic and inorganic carbon (DOC, POC, DIC, PIC) were measured and modeled at three locations on the Yukon River (YR) and on the Tanana and Porcupine rivers (TR, PR) in Alaska during 2001-2005. Total YR carbon export averaged 7.8 Tg C yr−1, 30% as OC and 70% as IC. Total C yields (0.39-1.03 mol C m−2 yr−1) were proportional to water yields (139-356 mm yr−1; r2 = 0.84) at all locations. Summer DOC had an aged component (fraction modern (FM) = 0.94-0.97), except in the permafrost wetland-dominated PR, where DOC was modern. POC had FM = 0.63-0.70. DOC had high concentration, high aromaticity, and high hydrophobic content in spring and low concentration, low aromaticity, and high hydrophilic content in winter. About half of annual DOC export occurred during spring. DIC concentration and isotopic composition were strongly affected by dissolution of suspended carbonates in glacial meltwater during summer. [ABSTRACT FROM AUTHOR]

Abstract: Subtropical ocean gyres are believed to be characterized by low carbon export from the surface into the deep ocean. However, due to their large areas, even relatively small average export could be of significance for the global carbon cycle. To better constrain carbon export from the surface ocean in such regions, radioactive disequilibria between the particle-reactive, short-lived radionuclide 234Th (half-life 24.1d) and its parent 238U were used to estimate fluxes of 234Th and particulate organic carbon (POC) from surface waters of the North and South Atlantic subtropical gyres and their fringes. Samples were collected between ∼50°S and ∼50°N as part of the Atlantic Meridional Transect (AMT) programme during April/May 2004 (AMT14). Application of a steady-state model to the 234Th data revealed particle export from the surface (234Th deficit) and, in one instance, some evidence for shallow particle remineralisation at depth (234Th excess). Export fluxes of POC were calculated from water column 234Th /238U disequilibria and the POC to 234Th ratios on large rapidly sinking particles (>50μm). Based on latitudinal distributions of selected hydrographic and biological parameters within the topmost 300m of the water column, the transect was divided into six regions: ‘temperate’ (35°–50°N and 35°–50°S), ‘oligotrophic’ (20°–35°N and 5°–35°S), ‘equatorial’ (5°S–5°N), and ‘upwelling’ (5°–20°N). The lowest 234Th-derived POC export fluxes were found in the oligotrophic gyres and ranged from 0 in the northern to 6mmolCm−2 d−1 in the southern oligotrophic, indicating a tightly coupled food web. Enhanced POC export was associated with the equatorial region (25mmolCm−2 d−1) and the upwelling region north of the equator (15mmolCm−2 d−1). POC export in the temperate regions ranged from 7mmolCm−2 d−1 to a maximum of 41mmolCm−2 d−1. High fluxes at the poleward edges of the oligotrophic gyres probably result from episodic nutrient-loading processes associated with submesoscale features. Estimates of instantaneous primary production (PP) were compared with 234Th-derived POC export, the latter bearing information from the past few weeks. Most export efficiencies that were calculated based on this comparison were high (10s%), suggesting uncoupling of PP and export estimates due to the different time scales of the approaches. Moreover, this uncoupling points to the occurrence of pulsed high-export events that could be easily missed by instantaneous sampling but traced by temporally quasi-integrating tracers such as 234Th. Results from this study suggest that although carbon export in the oligotrophic centres of the gyres may be low, carbon sequestration in the temperate fringes of the gyres as well as in the equatorial and upwelling regions can be substantial, and that spatio–temporal variability in these areas of the world''s oceans needs to be considered more fully in the context of global oceanic carbon sequestration. [Copyright &y& Elsevier]

Apparent oxygen utilisation is potentially biased by abiotic, physical processes. Using a coupled 3-D circulation-oxygen model, this potential is quantitatively estimated for a region in the eastern subtropical North Atlantic, called the Beta Triangle, where an inconsistency exists between observational estimates of high carbon export from the euphotic zone, based on oxygen utilisation rates in the thermocline (Jenkins 1982). and those of low nutrient supply to the euphotic zone (Lewis et al. 1986, 2004). Our results indicate that in the upper ocean, the Jenkins (1982) estimate is indeed biased high by approximately 10% due to abiotic processes feigning respiration, thus contributing to the apparent inconsistency. Vertical integration, however, yields an abiotic fraction of less than 3%, so the apparent observational discrepancy can not be resolved. [ABSTRACT FROM AUTHOR]

Abstract: We present water column profiles of excess particulate Ba (Baxs, an estimate of biogenic Ba from total particulate Ba after small corrections for lithogenic Ba) along a transect in the Australian sector of the Southern Ocean from the Subantarctic Zone (SAZ) to the Sea Ice Zone during spring (October–December 2001). Surface water Baxs contents appear related to phytoplankton derived particles. Below, in the twilight zone, mesopelagic Baxs records the changes in plankton biomass from the mixed layer over a time scale of a few weeks and confirms its usefulness as an indicator of the carbon remineralisation process. In comparison to the SAZ, the mesopelagic Baxs accumulation is larger and begins at shallower depths south of the Polar Front Zone (PFZ), in the Antarctic Zone (AZ), where diatoms are the dominant component of the phytoplankton community. Summer results from 1998, when mesopelagic Baxs accumulations were larger, also show this latitudinal trend. In contrast, as observed also for deep particulate organic carbon fluxes, the flux of Baxs to moored deep sea sediment traps was larger in the nano-phytoplankton dominated SAZ than the diatom dominated PFZ. Overall, the results suggest relatively high particulate carbon export to the deep sea in the absence of strong remineralisation in the SAZ, and relatively low export to the deep sea in the presence of strong remineralisation further south. Mesopelagic carbon remineralisation is higher in summer than in spring as also observed on deep sediment traps carbon fluxes. Our findings are supported by 234Th and N-uptake proxies from the same transect. This study expands the utility of Ba as an indicator of biogeochemical processes in the twilight zone and supports its usability as a paleoceanographic proxy for deep C export. [Copyright &y& Elsevier]

The modern Sea of Okhotsk and the high-latitude glacial ocean share similar radiolarian faunas suggesting they also share environmental similarities. This sea favors deep- (>200 m) over shallow-living species as evidenced by collections of sediment traps set at 258 and 1061 m in the central part of the Sea. Of the twelve dominant polycystine radiolarian species, four live above and eight below 258 m. The shallow-living species’ productivity maxima coincide with spring and fall phytoplankton blooms while deep-living species’ annual production, nearly twice that of the shallow-living species, is concentrated in fall. Previous workers have shown that summer plankton tows collect higher concentrations of polycystine Radiolaria below than above 200 m and that Radiolaria, fish and zooplankton have unusual concentration maxima between 200 and 500 m. The paucity of Radiolaria and other consumers above 200 m coincides with an upper (0–150 m) cold (−1.5°C to 1.5°C), low salinity layer while higher concentrations below 200 m occur within warmer saltier water. This unusual biological structure must produce a lower ratio of shallow (<200 m) to deep carbon remineralization than elsewhere in the world ocean.Deep-living radiolarian species, similar to those of the modern Sea of Okhotsk, dominate glacial high-latitude deep-sea sediments. If the hydrographic and biological structures that produced these glacial faunas were like those of the modern Sea of Okhotsk, then glacial high-latitude oceans would have differed from today''s in at least two respects. Surface waters were less saline and more stable enhancing the spread of winter sea ice. This stability, combined with a deepening of nutrient regeneration would have reduced surface water nutrients contributing to a reduction of atmospheric carbon dioxide. [Copyright &y& Elsevier]

The Labrador Sea is a major sink of anthropogenic CO2 due to deep-water formation in winter. To investigate the relative importance of different forms of export flux, we used a physical-biogeochemical model to simulate the vertical fluxes of particulate and dissolved biogenic carbon as a function of winter convection, food web dynamics and zooplankton vertical migration. The C:N ratio of these export fluxes was simulated based on trophic dynamics and bacterial activity. The model was run using winter convection and seasonal mixed layer evolution extracted from multi-year physical data collected in the central Labrador Sea. Comparisons between model output and data from the Labrador Sea and other systems indicate that the model provides a realistic picture of carbon and nitrogen pools and fluxes. Our results suggest that on an annual basis, dissolved organic carbon (DOC) export by deep, vertical convection is greater than that of the sinking flux of POC. Furthermore, the C:N ratio of exported dissolved organic matter (DOM) is higher than that of the particle sinking flux, resulting in 23% more carbon exported than would be estimated if predictions were made from the Redfield ratio (e.g., 11.4 vs. 7.0 for DOM and particulate organic matter, respectively, at the bottom of the euphotic zone and 17.2 vs. 9.3 at 1000 m depth). The active export of carbon by the respiration and mortality of migrating zooplankton amounts to 19% of sinking flux annually, but only 6% of total carbon export because of the high rates of DOC export in deep-water formation regions. Our model simulations indicate that non-Redfield ratio DOC export characterizes the function of the biological pump in deep-water formation regions. [Copyright &y& Elsevier]

The modern Sea of Okhotsk and the high-latitude glacial ocean share similar radiolarian faunas suggesting they also share environmental similarities. This sea favors deep- (>200 m) over shallow-living species as evidenced by collections of sediment traps set at 258 and 1061 m in the central part of the Sea. Of the twelve dominant polycystine radiolarian species, four live above and eight below 258 m. The shallow-living species’ productivity maxima coincide with spring and fall phytoplankton blooms while deep-living species’ annual production, nearly twice that of the shallow-living species, is concentrated in fall. Previous workers have shown that summer plankton tows collect higher concentrations of polycystine Radiolaria below than above 200 m and that Radiolaria, fish and zooplankton have unusual concentration maxima between 200 and 500 m. The paucity of Radiolaria and other consumers above 200 m coincides with an upper (0–150 m) cold (−1.5°C to 1.5°C), low salinity layer while higher concentrations below 200 m occur within warmer saltier water. This unusual biological structure must produce a lower ratio of shallow (<200 m) to deep carbon remineralization than elsewhere in the world ocean.Deep-living radiolarian species, similar to those of the modern Sea of Okhotsk, dominate glacial high-latitude deep-sea sediments. If the hydrographic and biological structures that produced these glacial faunas were like those of the modern Sea of Okhotsk, then glacial high-latitude oceans would have differed from today''s in at least two respects. Surface waters were less saline and more stable enhancing the spread of winter sea ice. This stability, combined with a deepening of nutrient regeneration, reduced surface water nutrients contributing to a reduction of atmospheric carbon dioxide. [Copyright &y& Elsevier]

We studied the effect of nutrient inputs on the carbon (C) budget of rocky shore communities using a set of eight large experimental mesocosms. The mesocosms received a range of inorganic nitrogen (N) and phosphorus (P) additions, at an N:P ratio of 16. These additions were designed to elevate the background concentration, relative to that in eutrophic Oslofjord (Norway) waters, by 1, 2, 4, 8, 16, 32 μmol dissolved inorganic nitrogen (DIN)l-1 (and the corresponding P increase). Two unamended mesocosms were used as controls. The nutrients were added continuously for 27 months before gross primary production (GPP), respiration (R), net community production (NCP), and dissolved organic carbon (DOC) production were assessed for the dominant algal species (Fucus serratus) and for the whole experimental ecosystem. Inputs and outputs of DOC and particulate organic carbon (POC) from the mesocosms were also quantified. The F. serratus communities were generally autotrophic (average P/R ratio = 1.33 ± 0.12), with the GPP independent of the nutrient inputs to the mesocosms, and maintained a high net DOC production during both day (0.026 ± 0.008 g C m-2 h-1) and night (0.015 ± 0.004 g C m-2 h-1). All the experimental rocky shore ecosystems were autotrophic (P/R ratio = 2.04 ± 0.28), and neither macroalgal biomass nor production varied significantly with increasing nutrient inputs. Most of the excess production from these autotrophic ecosystems was exported from the systems as DOC, which accounted for 69% and 58% of the NCP of the dominant community and the experimental ecosystem, respectively, the rest being lost as POC. High DOC release and subsequent export from the highly energetic environments occupied by rocky shore communities may prevent the development of eutrophication symptoms and render these communities resistant to eutrophication. Corresponding author; e-mail: ieacbe@clust.uib.es --> [ABSTRACT FROM AUTHOR]

The structure and variability of the plankton community and the distribution and composition of suspended particulate matter, were investigated in the polynya of Terra Nova Bay (western Ross Sea) during the austral summer 1997/1998, with the ultimate objective of understanding the trophic control of carbon export from the upper water column. Sampling was conducted along a transect parallel to the shore, near the retreating ice edge at the beginning of December, closer to the coast at the beginning of February, and more offshore in late February. Hydrological casts and water sampling were performed at several depths to measure total particulate matter (TPM), particulate organic carbon (POC), biogenic silica (BSi), chlorophyll a (Chl a) and phaeopigment (Phaeo) concentrations. Subsamples were taken for counting autotrophic and heterotrophic pico- and nanoplankton and to assess the abundance and composition of microphyto- and microzooplankton. Statistical analysis identified two major groups of samples: the first included the most coastal surface samples of early December, characterized by the prevalence of autotrophic nanoplankton biomass; the second included all the remaining samples and was dominated by microphytoplankton. With regard to the relation of the plankton community composition to the biogenic suspended and sinking material, we identified the succession of three distinct periods. In early December Phaeocystis dominated the plankton assemblage in the well-mixed water column, while at the retreating ice-edge a bloom of small diatoms (ND) was developing in the lens of superficial diluted water. Concentrations of biogenic particulates were generally low and confined to the uppermost layer. The very low downward fluxes, the near absence of faecal pellets and the high Chl a/Phaeo ratios suggested that the herbivorous food web was not established yet or, at least, was not working efficiently. In early February the superficial pycnocline and the increased water column stability favoured the development of the most intense bloom of the season, essentially sustained by micro-sized diatoms (MD). The shift of the autotrophic community toward this size component produced major changes in the composition of particulate matter and determined its export to depth. The particulate organic carbon (POC)/chlorophyll a (Chl a) and Chl a/Phaeo ratios more than halved, biogenic silica (BSi)/POC and BSi/Chl a strongly increased. Downward fluxes were greatly enhanced (reaching the yearly maximum) and essentially occurred via faecal pellets, underscoring the high efficiency of the herbivorous food web. In late February the deepening of the pycnocline, together with the decrease in light intensity, contributed to halting the diatom bloom. The biomass of small heterotrophs (HNF and MCZ) significantly increased relative to the previous period, favouring the shift toward a mistivorous food web (sensu [Ophelia 41 (1995) 153]) and resulting in the retention of biogenic matter in the superficial layer. Only in early February, with the increase in the size of primary producers (essentially represented by micro-sized diatoms), did the grazing food web become efficient [S. Afr. J. Mar. Sci. 12 (1992) 477], fuelling the long-lived carbon pool and enhancing export to depth (and hence carbon sequestration) via the sinking of large diatoms and high amounts of faecal pellets. The conditions predominating in the Terra Nova Bay polynya in mid-summer probably increased the efficiency of the CO2 pump, possibly causing the Bay to act as a carbon sink. [Copyright &y& Elsevier]

Spatial and seasonal distribution patterns of suspended particulate matter, particulate organic carbon (POC), particulate nitrogen, chlorophyll a and phytoplankton abundance and biomass were analysed along two transects in the southern Adriatic and northern Ionian Seas. Moreover, 2 years of samples collected by sediment traps at one selected station for each transect are used to assess the variability of fluxes of biogenic (organic carbon, total nitrogen, carbonates, biogenic silica) and lithogenic constituents.According to the low suspended matter concentration, the two study areas can be considered as representative of oligotrophic systems. The availability of diverse nutrient forms (inorganic or organic), due to the different water column structure and circulation dynamics, affected the structure of phytoplankton communities. Along the Adriatic transect, the influence of waters coming from the northern Adriatic was evident at the surface of the western stations. The phytoplankton community was mainly represented by diatoms and nanoflagellates. In the northern Ionian, particulate matter concentration decreases with respect to the Adriatic stations (st. A1) and the community was dominated by nanoflagellates (54% in cell number), and coccolithophorids (26%).In the southern Adriatic, the vertical mixing convection related to the climatic variability, supplying inorganic nutrients in the upper layers from the deep, represents the dominant process, increasing primary production and downward fluxes of particulate matter in early spring. Higher mass fluxes measured at the bottom are likely due to horizontal and advective contributions of material originated in the shelf area and transported into the basin by mesoscale circulation.Vertical fluxes in the Ionian mainly depend on production processes occurring in the photic layer, such as spring and autumn blooms, controlled by the seasonal mixing and dynamics of the water column. Fluxes are characterised by discontinuous and short-time events correlated with the end phase of micro-phytoplankton blooms.At both stations, the low carbon export (less than 4% of primary productivity) indicates high carbon utilisation and/or high degradation efficiencies of particulate organic matter, i.e. fast recycling in the upper water column. [Copyright &y& Elsevier]

The distribution of primary production (PP), particulate carbon export from the photic zone to deeper layer, and nutrient concentrations are investigated in the Mediterranean Sea (MS) during May–June 1996. A decrease in integrated primary production, particulate carbon export and nutrient availability towards the eastern part of the Mediterranean sea was observed while integrated chlorophyll a remains rather constant. This pattern may be explained both by the adaptation of phytoplanktonic organisms to low light conditions and by a more efficient nutrient diffusion from the deeper layer in the east related to the position of the nutricline and density gradient. Integrated primary production ranging from 350 to 450 mgC m−2 day−1 in the west decreases toward the east to a value of about 150 mgC m−2 day−1. The latter value may appear as a limit for primary production rates under strong oligotrophic conditions. Particulate carbon export represents 4.0+2.9% of integrated primary production. Up to 90–95% of primary production is then sustained by internal recycling of organic matter. Evidence of a limitation of production by phosphate was obtained from differences between depth of nitracline and phosphacline and by enrichment experiments. The wide range of oligotrophic conditions in the Mediterranean Sea provides a case study for links between C, N and P-cycles. [Copyright &y& Elsevier]

Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality. [ABSTRACT FROM AUTHOR]

Organic matter (OM) plays a significant role in the formation of oxygen minimum zones (OMZs) and associated biogeochemical cycling. OM supply processes to the OMZ include physical transport, particle formation, and sinking as well as active transport by migrating zooplankton and nekton. In addition to the availability of oxygen and other electron acceptors, the remineralization rate of OM is controlled by its biochemical quality. Enhanced microbial respiration of OM can induce anoxic microzones in an otherwise oxygenated water column. Reduced OM degradation under low-oxygen conditions, on the other hand, may increase the CO 2 storage time in the ocean. Understanding the interdependencies between OM and oxygen cycling is of high relevance for an ocean facing deoxygenation as a consequence of global warming. In this review, we describe OM fluxes into and cycling within two large OMZs associated with eastern boundary upwelling systems that differ greatly in the extent of oxygen loss: the highly oxygen-depleted OMZ in the tropical South Pacific and the moderately hypoxic OMZ in the tropical North Atlantic. We summarize new findings from a large German collaborative research project, Collaborative Research Center 754 (SFB 754), and identify knowledge gaps and future research priorities.

An important pathway for CO 2 sinking in the ocean is via the "biological pump", driven by the production of particulate organic carbon (POC) in the surface ocean and its subsequent export to the deeper ocean via vertical settling. Here we examine the vertical fluxes of POC in the continental slope of the northern Gulf of Mexico by utilizing the short-lived radionuclide pair 210Po - 210Pb. The total activities of 210Po and 210Pb ranged from 2.5 ± 0.35 to 16.52 ± 1.98 dpm 100 L-1 and from 3.47 ± 0.45 to 24.49 ± 3.42 dpm 100 L-1 respectively with the exception of higher activities of 210Po (87.36 ± 11.38 dpm 100 L-1) and 210Pb (32.25 ± 4.35 dpm 100 L-1) from the near bottom water in the hypersaline anoxic Orca basin. In the upper 150 m of the water column, the inventories of 210Pb were consistently greater than those of 210Po while the total overall water column inventories of 210Po and 210Pb were found to be near equilibrium. The 210Po fluxes varied between 9.8 ± 6.34 dpm m-2 d-1 and 30.7 ± 12.06 dpm m-2 d-1 with corresponding POC fluxes between 8.6 mg C m-2 d-1 and 37.65 mg C m-2 d-1. The fluxes showed a general decreasing trend further offshore, closely following a similar trend in net primary productivity across the slope. The export efficiency ratios "e-ratios" of the biological pump over this slope region was found to vary between 0.027 and 0.11 averaging at 0.05 ± 0.01, which is low. The 210Po based and the model-based e-ratio estimates were different but within the range of previous estimates. • 210Po has an average residence time of 2.18 ± 0.47 year in the continental shelf. • 210Po based POC fluxes varied between 8.59 and 37.65 mg C m-2 d-1 across the shelf. • The e-ratio varied between 0.027 and 0.11 (mean = 0.05 ± 0.01) for this region is found to be low. • Highest reported activities of 210Po and 210Pb for open ocean observed in the hypersaline Orca basin. [ABSTRACT FROM AUTHOR]

The sink demand was increased on a source maize leaf (Zea mays L. cv. F7F2) by darkening all the leaves except the fourth, which was maintained under the prevailing irradiance conditions. The parameters of carbon metabolism were measured precisely during the first hours, and then daily during one week. The ambient photosynthetic activity and the maximum photosynthetic capacity were not altered by the treatment but the soluble carbohydrate and starch contents diminished, while ADP-glucose pyrophosphorylase (EC 2.7.7.27) activity increased. The carbon export rate, evaluated by the rate of disappearance of radioactivity after a 1-min 14CO2 pulse, was faster than in control leaves. A compartmental analysis of the time course of 14C export further indicated that the sucrose pool providing the export flux was largely increased by the dark treatment. The darkened leaf 5, taken as an example of the darkened sources, was completely depleted of its carbohydrate content after one day in the dark and remained devoid of carbohydrates during the following week. [ABSTRACT FROM AUTHOR]