Trap Deployment Research Articles

Sinking phytoplankton associated with carbon flux in the Atlantic Ocean

AbstractThe composition of sinking particles and the mechanisms leading to their transport ultimately control how much carbon is naturally sequestered in the deep ocean by the “biological pump.” While detrital particles often contain much of the sinking carbon, sinking of intact phytoplankton cells can also contribute to carbon export, which represents a direct flux of carbon from the atmosphere to the deep ocean by circumventing the surface ocean food web. Phytoplankton that contributed to carbon flux were identified in sinking material collected by short‐term sediment trap deployments conducted along a transect off the eastern shore of South America. Particulate organic carbon flux at 125 m depth did not change significantly along the transect. Instead, changes occurred in the composition and association of phytoplankton with detrital particles. The fluxes of diatoms, coccolithophores, dinoflagellates, and nano‐sized cells at 125 m were unrelated to the overlying surface population abundances, indicating that functional‐group specific transport mechanisms were variable across locations. The dominant export mechanism of phytoplankton at each station was putatively identified by principal component analysis and fell into one of three categories; (1) transport and sinking of individual, viable diatom cells, (2) transport by aggregates and fecal pellets, or (3) enhanced export of coccolithophores through direct settling and/or aggregation.

Tropical cyclones, derelict traps, and the future of the Florida Keys commercial spiny lobster fishery

Derelict commercial spiny lobster (Panulirus argus) traps may move hundreds of meters during high wind events, resulting in tissue abrasion, breakage, and often complete removal of critical habitat elements such as seagrass, sponge, and coral. Ghost traps continue to confine lobsters, often resulting in mortality. The legacy of trap debris in the Florida Keys (USA) combined with possible increased inputs of trap debris resulting from tropical cyclone intensification presents an immediate challenge for this fishery where social, economic, and ecological vulnerabilities to disturbance are intrinsically linked. Here, predictions of percent monthly trap loss in relation to maximum wind speed (km/h) under three scenarios of tropical cyclone intensification were evaluated across four levels of fishing effort (number of traps used). Across all tropical cyclone scenarios, Historical fishing effort (986,000 traps) produced the greatest number of lost traps, followed in decreasing order by Existing (479,000), Target (400,000), and Maximum Economic Yield (MEY; 180,000) efforts. Under a Business-as-Usual scenario of intensification, converting from Existing fishing effort to MEY reduced trap loss by over 62%. The scenarios suggest that were Existing fishing effort to be maintained in the coming decades, tropical cyclone-related trap loss could exceed 11 million over 60 years depending upon the rate of storm intensification. Existing programs for derelict trap removal cannot currently keep pace with accumulation; consequently, the proximal source of trap debris is increasing in the environment. The net increase in derelict traps and debris generated from their degradation will only be exacerbated under potential tropical cyclone intensification. This study underscores the need for using scenarios for future exploration of these issues, particularly incorporation of fisher responses to changes in climatic, economic, and management drivers (i.e., storms, market demand, gear reduction) that may affect trap deployment patterns.

Modeling the impact of floating oyster (Crassostrea virginica) aquaculture on sediment-water nutrient and oxygen fluxes

Bivalve aquaculture relies on naturally occurring phytoplankton, zooplankton, and detritus as food sources, thereby avoiding external nutrient inputs that are commonly associated with finfish aquaculture. High filtration rates and concentrated bivalve biomass within aquacul- ture operations, however, result in intense biodeposition of particulate organic matter (POM) on surrounding sediments, with potential adverse environmental impacts. Estimating the net deposi- tional flux is difficult in shallow waters due to methodological constraints and dynamic processes such as resuspension and advection. In this study, we combined sediment trap deployments with simulations from a mechanistic sediment flux model to estimate seasonal POM deposition, resus- pension, and processing within sediments in the vicinity of an eastern oyster Crassostrea virginica farm in the Choptank River, Maryland, USA. The model is the stand-alone version of a 2-layer sediment flux model currently implemented within larger models for understanding ecosystem responses to nutrient management. Modeled sedimentwater fluxes were compared to observed denitrification rates and nitrite + nitrate (NO2 � +NO3 � ), phosphate (PO4 3� ) and dissolved O2 fluxes. Model-derived estimates of POM deposition, which represent POM incorporated and processed within the sediment, comprised a small fraction of the material collected in sediment traps. These results highlight the roles of biodeposit resuspension and transport in effectively removing oyster biodeposits away from this particular farm, resulting in a highly diminished local environmental impact. This study highlights the value of sediment models as a practical tool for computing inte- grated measures of nitrogen cycling as a function of seasonal dynamics in the vicinity of aqua - culture operations.

Study design and body mass influence RAIs from camera trap studies: evidence from the Felidae

AbstractCamera trapping is a widespread tool used to study mammals and to derive abundance and density estimates of wild populations. For the majority of Felidae species, individuals are identifiable from camera trap images because of their unique coat patterns; therefore, camera trapping is used extensively for felids to build individual capture histories. For those species not individually identifiable, one can be tempted to use trap success rate as a relative abundance index (RAI) to inform conservation and management decisions, although robust scientific approach can be used for this scenario. Indeed, recent studies have shown that RAIs can be biased by species‐specific behaviour, camera trap deployment and by the body size of the species. Here, we investigate how camera trap rates (henceforth RAIs) vary between species within the Felidae and whether these RAIs are related to body mass or camera‐trapping approach (whether the species is targeted or not) accounting for likely confounding factors such as trapping effort, inter‐trap distance and number of deployed cameras. We explored all the literature available from primary scientific databases dealing with camera trap studies in Felidae. The literature search resulted in 179 studies from which 513 records for 30 felid species from 53 countries were obtained. Across species, the number of detections (accounting for trapping effort) was positively related to species log‐body mass and to the targeting of species in the survey. Hence, comparing RAIs across species of different body size and within species with different camera‐trapping approaches might be misleading. Accounting for variability in species body mass is of primary importance when designing multi‐species camera trap survey, and in the subsequent analysis of data, in addition to conducting trials to test for species‐specific camera‐trapping responses.

Export fluxes in a naturally iron-fertilized area of the Southern Ocean – Part 1: Seasonal dynamics of particulate organic carbon export from a moored sediment trap

Abstract. A sediment trap moored in the naturally iron-fertilized Kerguelen Plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth, current speeds were typically low (~ 10 cm s−1) and primarily tidal-driven (M2 tidal component). Although advection was weak, the sediment trap may have been subject to hydrodynamical and biological (swimmer feeding on trap funnel) biases. Particulate organic carbon (POC) flux was generally low (< 0.5 mmol m−2 d−1), although two episodic export events (< 14 days) of 1.5 mmol m−2 d−1 were recorded. These increases in flux occurred with a 1-month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 ± 4.4 mmol m−2 yr−1 was low considering the shallow deployment depth but comparable to independent estimates made at similar depths (~ 300 m) over the plateau, and to deep-ocean (> 2 km) fluxes measured from similarly productive iron-fertilized blooms. Although undertrapping cannot be excluded in shallow moored sediment trap deployment, we hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for the low POC flux beneath the base of the winter mixed layer. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

The relative importance of phytoplankton aggregates and zooplankton fecal pellets to carbon export: insights from free-drifting sediment trap deployments in naturally iron-fertilised waters near the Kerguelen Plateau

Abstract. The first KErguelen Ocean and Plateau compared Study (KEOPS1), conducted in the naturally iron-fertilised Kerguelen bloom, demonstrated that fecal material was the main pathway for exporting carbon to the deep ocean during summer (January–February 2005), suggesting a limited role of direct export via phytodetrital aggregates. The KEOPS2 project reinvestigated this issue during the spring bloom initiation (October–November 2011), when zooplankton communities may exert limited grazing pressure, and further explored the link between carbon flux, export efficiency and dominant sinking particles depending upon surface plankton community structure. Sinking particles were collected in polyacrylamide gel-filled and standard free-drifting sediment traps (PPS3/3), deployed at six stations between 100 and 400 m, to examine flux composition, particle origin and their size distributions. Results revealed an important contribution of phytodetrital aggregates (49 ± 10 and 45 ± 22% of the total number and volume of particles respectively, all stations and depths averaged). This high contribution dropped when converted to carbon content (30 ± 16% of total carbon, all stations and depths averaged), with cylindrical fecal pellets then representing the dominant fraction (56 ± 19%). At 100 and 200 m depth, iron- and biomass-enriched sites exhibited the highest carbon fluxes (maxima of 180 and 84 ± 27 mg C m-2 d-1, based on gel and PPS3/3 trap collection respectively), especially where large fecal pellets dominated over phytodetrital aggregates. Below these depths, carbon fluxes decreased (48 ± 21% decrease on average between 200 and 400 m), and mixed aggregates composed of phytodetritus and fecal matter dominated, suggesting an important role played by physical aggregation in deep carbon export. Export efficiencies determined from gels, PPS3/3 traps and 234Th disequilibria (200 m carbon flux/net primary productivity) were negatively correlated to net primary productivity with observed decreases from ~ 0.2 at low-iron sites to ~ 0.02 at high-iron sites. Varying phytoplankton communities and grazing pressure appear to explain this negative relationship. Our work emphasises the need to consider detailed plankton communities to accurately identify the controls on carbon export efficiency, which appear to include small spatio-temporal variations in ecosystem structure.

Sediment flux and recent paleoclimate in JordanBasin, Gulf of Maine

We report planktonic foraminiferal fluxes (accumulation rates) and oxygen isotopes (δ18O) from a nine-month sediment trap deployment, and δ18O from three sediment cores in Jordan Basin, Gulf of Maine. The sediment trap was deployed at 150m, about halfway to the basin floor, and samples were collected every three weeks between August 2010 and May 2011. The planktonic foraminiferal fauna in the trap is dominated by Neogloboquadrina incompta that reached a maximum flux in the second half of October. Oxygen isotope ratios on that species indicate that on average during the collecting period it lived in the surface mixed layer, when compared to predicted values based on data from a nearby hydrographic buoy from the same period. New large diameter piston cores from Jordan Basin are 25 and 28m long. Marine hemipelagic sediments are 25m thick, and the sharp contact with underlying red deglacial sediments is bracketed by two radiocarbon dates on bivalves that indicate ice-free conditions began 16,900 calibrated years ago. Radiocarbon dating of foraminifera indicates that the basin floor sediments (270–290m) accumulated at >3m/kyr during the Holocene, whereas rates were about one tenth that on the basin slope (230m). In principle, Jordan Basin sediments have the potential to provide time series with interannual resolution. Our results indicate the Holocene is marked by ~2°C variability in SST, and the coldest events of the 20th century, during the mid 1960s and mid 1920s, appear to be recorded in the uppermost 50cm of the seafloor.

What did we learn about ocean particle dynamics in the GEOSECS–JGOFS era?

Particles determine the residence time of many dissolved elements in seawater. Although a substantial number of field studies were conducted in the framework of major oceanographic programs as GEOSECS and JGOFS, knowledge about particle dynamics is still scarce. Moreover, the particulate trace metal behavior remains largely unknown. The GEOSECS sampling strategy during the 1970s focused on large sections across oceanic basins, where particles were collected by membrane filtration after Niskin bottle sampling, biasing the sampling toward the small particle pool. Late in this period, the first in situ pumps allowing large volume sampling were also developed. During the 1990s, JGOFS focused on the quantification of the “exported carbon flux” and its seasonal variability in representative biogeochemical provinces of the ocean, mostly using sediment trap deployments. Although scarce and discrete in time and space, these pioneering studies allowed an understanding of the basic fate of marine particles. This understanding improved considerably, especially when the analysis of oceanic tracers such as natural radionuclides allowed the first quantification of processes such as dissolved-particle exchange and particle settling velocities. Because the GEOTRACES program emphasizes the importance of collecting, characterizing and analyzing marine particles, this paper reflects our present understanding of the sources, fate and sinks of oceanic particles at the early stages of the program.

Variation in Baiting Intensity Among CO2-Baited Traps Used to Collect Hematophagous Arthropods.

Hematophagous arthropods transmit the etiological agents of numerous diseases and as a result are frequently the targets of sampling to characterize vector and pathogen populations. Arguably, the most commonly used sampling approach involves traps baited with carbon dioxide. We report results of a laboratory study in which the performance of carbon dioxide-baited traps was evaluated using measures of baiting intensity, the amount of carbon dioxide released per unit time during trap deployment. We evaluated the effects of trap design, carbon dioxide source, and wind speed on baiting intensity and documented significant effects of these factors on the length of sampling (time to baiting intensity = 0), maximum baiting intensity, and variation in baiting intensity during experimental trials. Among the three dry ice-baited trap types evaluated, traps utilizing insulated beverage coolers as dry ice containers sampled for the longest period of time, had the lowest maximum but most consistent baiting intensity within trials and were least sensitive to effects of wind speed and dry ice form (block vs. pellet) on baiting intensity. Results of trials involving traps baited with carbon dioxide released from pressurized cylinders suggested that this trap type had performance comparable to dry ice-baited insulated cooler traps but at considerably higher cost.

Assessing trap and lure effectiveness for the monitoring of Sirex noctilio

Abstract Lure‐baited traps are an important tool for monitoring the spread and establishment of the Sirex woodwasp Sirex noctilio. The utility of these traps, however, is limited in areas with low wasp populations as a result of the reliance on a plant volatile (kairomone) lure in the absence of an identified pheromone. Knowledge of the optimal trap type and deployment strategy is also lacking. We tested the effectiveness of a putative pheromone in baited traps, by means of a series of field trials in South Africa, over a 3‐year period. We also examined the influence of lure type, trap type and trap height on capture success. The pheromone was found to be ineffective as an attractant under South African field conditions for both male and female wasps. Lure type, trap type and trap height were found to have little to no effect on female wasp catch. Given the moderately strong responses to the blend under wind tunnel and laboratory conditions, we suggest possible aspects of the biology and life history of S. noctilio that may influence lure effectiveness. The traditional black intercept panel traps with kairomone lure remains the best trap for S. noctilio, at least where populations are high.

Present-day fluxes of coccolithophores and diatoms in the pelagic Ionian Sea

Biogenic fluxes from two sediment traps in the Ionian sea (35°13′N, 21°30′E) at 500 and 2800m water depth are discussed in relation with the main oceanographic and external forcing and compared with previous data from a nearby location. This study is part of a multi-year sediment trap deployment, aimed at assessing seasonality and interannual variability of biogenic and abiogenic fluxes. Here, we focus on fluxes related to two main phytoplankton groups: coccolithophores and diatoms.At our mooring site, high-coccolithophore and low-diatom fluxes confirm the oligotrophic character of the pelagic eastern Mediterranean year-round. Coccolithophore assemblages are dominated by the cosmopolitan species Emiliania huxleyi, followed by the deep-dwelling Florisphaera profunda and by several minor species. Diatom assemblages are dominated by Thalassionema bacillare and Nitzschia interruptestriata, with ~100 common and minor species. Overall, the combined flux pattern of coccolithophores and diatoms shows a clear seasonality throughout the study period, which can be related to changing oceanographic conditions and a different depth of production within the photic zone. Worth to note is the extremely high abundance, with respect to previous pelagic records, of species indicative of an intense deep chlorophyll maximum (DCM), which could indicate a shoaling of the nutricline. This feature can be related to the variability that affects surface hydrography and the deep water masses.Additionally, the occurrence of neritic, benthic and brackish to fresh-water diatom species, mainly in the deeper trap, could be linked to either lateral transport within the water column or the atmospheric input of Saharan dust, which is known to be common over the eastern Mediterranean especially during spring time.Finally, correlation of the flux pattern at different depths allowed sinking speeds for total and biogenic particles to be calculated, which ranged from 70 to >200mday−1. Three possible mechanisms can explain such high sinking rates and the coincidence of biogenic and total particle fluxes in the traps: a) the ballast effect of coccoliths; b) the packaging effect of fecal pellets related to the grazing activity of zooplankton; and c) the ballast effect of dust particles.

Can Mass Trapping Reduce Thrips Damage and Is It Economically Viable? Management of the Western Flower Thrips in Strawberry

The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a cosmopolitan, polyphagous insect pest that causes bronzing to fruit of strawberry (Fragaria x ananassa). The main aim of this study was to test whether mass trapping could reduce damage and to predict whether this approach would be economically viable. In semi-protected strawberry crops, mass trapping of F. occidentalis using blue sticky roller traps reduced adult thrips numbers per flower by 61% and fruit bronzing by 55%. The addition of the F. occidentalis aggregation pheromone, neryl (S)-2-methylbutanoate, to the traps doubled the trap catch, reduced adult thrips numbers per flower by 73% and fruit bronzing by 68%. The factors affecting trapping efficiency through the season are discussed. Damage that would result in downgrading of fruit to a cheaper price occurred when bronzing affected about 10% of the red fruit surface. Cost-benefit analysis using this threshold showed that mass trapping of thrips using blue sticky roller traps can be cost-effective in high-value crops. The addition of blue sticky roller traps to an integrated pest management programme maintained thrips numbers below the damage threshold and increased grower returns by a conservative estimate of £2.2k per hectare. Further work is required to develop the F. occidentalis aggregation pheromone for mass trapping and to determine the best timing for trap deployment. Mass trapping of thrips is likely to be cost-effective in other countries and other high-value crops affected by F. occidentalis damage, such as cucumber and cut flowers.

Monitoring the Status and Trends of Tropical Forest Terrestrial Vertebrate Communities from Camera Trap Data: A Tool for Conservation

Reducing the loss of biodiversity is key to ensure the future well being of the planet. Indicators to measure the state of biodiversity should come from primary data that are collected using consistent field methods across several sites, longitudinal, and derived using sound statistical methods that correct for observation/detection bias. In this paper we analyze camera trap data collected between 2008 and 2012 at a site in Costa Rica (Volcan Barva transect) as part of an ongoing tropical forest global monitoring network (Tropical Ecology Assessment and Monitoring Network). We estimated occupancy dynamics for 13 species of mammals, using a hierarchical modeling approach. We calculated detection-corrected species richness and the Wildlife Picture Index, a promising new indicator derived from camera trap data that measures changes in biodiversity from the occupancy estimates of individual species. Our results show that 3 out of 13 species showed significant declines in occupancy over 5 years (lowland paca, Central American agouti, nine-banded armadillo). We hypothesize that hunting, competition and/or increased predation for paca and agouti might explain these patterns. Species richness and the Wildlife Picture Index are relatively stable at the site, but small herbivores that are hunted showed a decline in diversity of about 25%. We demonstrate the usefulness of longitudinal camera trap deployments coupled with modern statistical methods and advocate for the use of this approach in monitoring and developing global and national indicators for biodiversity change.

Particle sinking dynamics and POC fluxes in the Eastern Tropical South Pacific based on 234Th budgets and sediment trap deployments

Assuming steady-state over seasonal to annual timescales, and limited horizontal export of dissolved nutrients, the vertical fluxes of limiting nutrients into the euphotic zone should be balanced by particle export. Sediment traps and 234Th budgets have both been used extensively throughout the oceans as a means to measure this particulate flux from the upper ocean. One main goal of these efforts has been to determine the amount of CO2 fixed by primary producers in the surface ocean that is exported as particulate organic carbon (POC) and conversely, the decrease of particle flux with depth has been used to estimate remineralization rates of nutrients. Although disagreement between trap-derived and 234Th-derived fluxes has often been noted, the possible reasons for the imbalance are numerous, and thus often it is difficult to assign causes. Here, we examine many commonly implicated contributors to the disagreement, allowing us to assess data from a recent 2-year study in the ETSP that shows systematic disagreement between the two methods. Averaging results from both years, sediment traps collected 0.2–1.5mmolCm−2d−1 (mean: 0.74mmolCm−2d−1) of POC, while the thorium-based method estimated an average POC flux of 1.5–14mmolCm−d−1 (mean: 6.2mmolCm−2d−1). The study area spans regions of differing ecological structure, as inferred from trap mineralogy, and the flux disagreement coincides with this ecological range. We interpret the difference as undercollection of poorly ballasted, slowly sinking particles by the sediment traps. Using both methods simultaneously offers insight into ecosystem structure and resulting particle flux dynamics. The thorium deficit-based flux is 5–10% of previously published estimates of primary productivity based on 14C incubations (Pennington et al., 2006), and 8–20% of concurrent estimates based on 14C incubations and oxygen supersaturation (Capone et al., personal communication; Prokopenko et al., personal communication).

δ15N values of settling biogenic particles in the eastern Bransfield Basin (west Antarctic) and their records for the surface-water condition

Sediment trap deployments in the eastern Brans-field Basin (west Antarctic) show seasonal and inter-annual variability in particle fluxes, with most of total annual flux at mid-depth occurring during a short period. High seasonality in particle flux may be associated with biological processes (the timing of phytoplankton blooms) and physical factor (sea-ice cover). Inter-annual variability of particle flux may also reflect inter-annual variation of sea-ice cover related to the biological processes. Most notable is that year-round high particle flux is observed in sediment traps moored near the seabed, which is not unexpected, emphasizing the contribution of supplementary transport of lithogenic particles particularly during the unproductive season. In this case, particles in relatively rapid vertical transit, such as aggregates and fecal pellets, are presumably mixed with laterally-transported particles. The relationship between δ15N values and biogenic particle flux highlights the contribution of particles in lateral transit to the vertical setting particles downward to the near-bottom sediment trap. Mid-depth sediment trap shows clear seasonal δ15N variability, whereas the near-bottom sediment trap shows no distinct seasonal trend, indicating the contamination of low δ15N, fresh organic material by high δ15N, regenerated and more refractory material resuspended from shallow continental margin. However, judging from the flux-weight δ15N values between the mid-depth and near-bottom sediment traps, biogeochemical components contained in the horizontally delivered particles are not critical to prevent the surface-water condition preserved in those of downward sinking particles. Our results provide the convincing implications from the recovery of paleoclimatic information using sediment cores from the eastern Bransfield Basin (west Antarctic).

The role of Synechococcus in vertical flux in the Costa Rica upwelling dome

Despite evidence that picophytoplankton contribute to export from marine pelagic ecosystems to some extent, few field studies have experimentally evaluated the quantitative importance of that flux or specifically assessed the relative strengths of alternate ecological pathways in transporting picophytoplankton carbon to depth. In experimental studies in the Costa Rica Dome (CRD), we used a combination of methods – flow cytometry (FCM), microscopy, pigments, dilution assays, mesozooplanton gut contents and sediment traps – to follow production, grazing and export fates of the dominant picophytoplankter, Synechococcus spp. (Syn), relative to the total phytoplankton community. Syn accounted for an average of 25% (range 9–50%) of total phytoplankton production during four 4-day drifter experiments at CRD sites. During the same experiments, sediment trap deployments at the base of the euphotic zone measured total organic carbon export ranging from 50 to 72mgCm−2d−1. Flow cytometry measurements of the trap samples showed that only 0.11% of this carbon was recognizable as ungrazed sinking Syn. Phycoerythrin (PE) measurements on the same samples, which we attributed mostly to transport of intact cells in mesozooplankton fecal pellets, gave export contributions of unassimilated Syn eight-times higher than ungrazed sinking cells, though still <1% of total carbon. Grazing of mesozooplankton on Syn was confirmed by PE measurements of mesozooplankton guts and the visual presence of Syn cells in fecal pellets. Microzooplankton grazing estimates from dilution experiments, combined with degradation rates of mesozooplankton fecal material in the water column, allowed us to estimate indirectly the additional flux of carbon transferred through protozoan grazers before being exported as mesozooplankton fecal pellets. Assuming one to three protozoan trophic steps, this Syn pathway contributed on average an additional 0.5–5.7% of organic carbon flux. A similar budget for total phytoplankton, based on chlorophyll a and phaeopigments was consistent with fecal pellets as the dominant mechanism of sinking carbon. Therefore, while Syn sinking as ungrazed cells or aggregates were minor components of export, the indirect trophic pathway involving mesozooplankton predation on protozoan consumers of Syn comprised the major mode of bulk carbon export for Syn-generated primary production.

Isotope fractionation during nitrogen remineralization (ammonification): Implications for nitrogen isotope biogeochemistry

The 15N/14N isotopic ratio of marine particulate organic matter usually increases as a consequence of preferential 14N-remineralization (ammonification) during decay in the oxic water-column and at the oxic seafloor. However, a fractionation factor 15ε of sediment ammonification in natural environments has not been determined yet. Here, the 15ε of sedimentary ammonification is calculated in a set of seven sapropel containing sediment cores, two subrecent sediment cores and four sediment trap deployments from the Eastern Mediterranean Sea. Data clearly reveal Rayleigh type isotope fractionation and a fractionation factor 15ε between −1.43‰ and −2.3‰. Hence, sediments – and probably sinking particulate organic matter as well – can be important sources of isotopically depleted reactive nitrogen. The knowledge of 15ε further enables to reconstruct paleo export fluxes from sediment cores if original and actual δ15N as well as N accumulation rates are known.

A new time series of particle export from neutrally buoyant sediments traps at the Bermuda Atlantic Time-series Study site

Neutrally buoyant sediment traps (NBSTs) were deployed concurrently with particle interceptor traps (PITs) on monthly cruises of the Bermuda Atlantic Time-series Study (BATS) from June 2007 to July 2010. In most months, particulate organic carbon flux measured by the two sediment trap systems agreed within the range of variability for two separate NBSTs. In three periods of this study however, the PITs collected more than three times the amount of particulate organic carbon (POC) than the NBSTs. One of these periods coincided with two instances when the mixed layer was deeper than the trap deployment depth, which may lead to biased collection. One of the anomalous periods occurred during summer months, for which we were unable to find existing evidence of biogeochemical changes that would lead to such increases in POC flux. The third anomalous period occurred when the POC flux measured by the NBSTs was near zero. We hypothesize that the PITs may have a positive bias at low fluxes relative to the NBSTs. Zooplankton swimmers accounted for 49±20% of the total measured carbon flux over the three year period and swimmer removal by screening of samples through a 350μm mesh was established as an effective method for this site. Process blank corrections based on sample-identical blanks were important for determining mass and carbon flux from both the NBSTs and the PITs. This new record of particle export from NBSTs suggests that the observed carbon imbalance in this region of the ocean (Michaels et al., 1994) is not due to undersampling by the PITs and that export ratios may be even lower than previously thought.

Spatial and temporal variability of Alexandrium cyst fluxes in the Gulf of Maine: Relationship to seasonal particle export and resuspension

Quantification of Alexandrium cyst fluxes through the Gulf of Maine water column is central to understanding the linkage between the source and fate of annual Alexandrium blooms in the offshore waters. These blooms often lead to paralytic shellfish poisoning (PSP) and extensive closures of shellfish beds. We report here on time-series sediment trap deployments completed at four offshore locations in the gulf between 2005 and 2010 as components of two ECOHAB–GOM field programs. Data presented documents the substantial spatial and temporal fluctuations in Alexandrium fundyense cyst fluxes in the gulf. Cyst delivery out of the euphotic zone peaked primarily between July and August following annual spring–summer Alexandrium blooms and was greatest in the western gulf. At all sites, cyst flux maxima to the subsurface waters were rarely coincident with seasonal peaks in the total mass export of particulate material indicating that cyst delivery was primarily via individually sinking cysts. Where persistent benthic nepheloid layers (BNLs) exist, significant sediment resuspension input of cysts to the near-bottom water column was evidenced by deep cyst fluxes that were up to several orders of magnitude greater than that measured above the BNL. The largest cyst fluxes in the BNL were observed in the eastern gulf, suggesting greater resuspension energy and BNL cyst inventories in this region. Temporal similarities between peak cyst export out of the upper ocean and peak cyst fluxes in the BNL were observed and document the contribution of seasonal, newly formed cysts to the BNL. The data however also suggest that many Alexandrium cells comprising the massive, short-lived blooms do not transition into cysts. Time-series flow measurements and a simple 1D model demonstrate that the BNL cyst fluxes reflect the combined effects of tidal energy-maintained resuspension, deposition, and input of cysts from the overlying water column.

Impact of a warm anomaly on export fluxes of biogenic matter in the eastern Fram Strait

As part of the HAUSGARTEN long-term observatory, sediment trap deployments were carried out before, during, and after the anomalously warm Atlantic Water inflow observed from 2005 to 2007 in the eastern Fram Strait. Downward export of particulate organic carbon (POC), zooplankton fecal pellet carbon (FPC), and biogenic particulate silica (bPSi) were measured from August 2002 to June 2003 and from July 2004 to July 2008 to indirectly assess the impact of the warm anomaly on phytoplankton and zooplankton communities in the region. Lower and less frequent bPSi fluxes were observed during most of the warm anomaly period, reflecting a shift in phytoplankton community composition towards dominance of small-sized phytoplankton under warmer conditions. Lower FPC fluxes observed concurrently with the lower bPSi fluxes may indicate a decrease in fecal pellet production due to changing feeding conditions. In addition, the export of smaller fecal pellets in fall 2005 and spring 2006 suggests a dominance of smaller zooplankton during the warm anomaly. Nonetheless, bPSi and FPC export always increased in the presence of ice cover in the area above the sediment trap, even during the warm anomaly period, suggesting that sea ice is a key factor influencing the frequency of export events in the eastern Fram Strait. The scarcity of ice over the sampling area in 2005 and 2006 may partly be due to the warm anomaly, although solar radiation and ice drift due to wind stress also govern ice cover extent in the region. Overall, the warm anomaly resulted in a shift in the composition of the export fluxes when associated with an absence of ice cover in the eastern Fram Strait.