Flux Of Particulate Organic Matter Research Articles

Vertical flux of particulate organic matter in a High Arctic fjord: Relative importance of terrestrial and marine sources

Vertical flux of particulate matter was recorded using a moored sediment trap during 2002-03 in the outer region of the 90 km long NE Greenland fjord Young Sound (74°18’N, 20°18’W). Sea ice covered the fjord for c. 9 months during the deployment. At 65 m depth total flux of material was 1420 g dry weight m-2 and annual fluxes of carbonate (g m-2), chlorophyll (mg m-2), particulate organic carbon (POC, g C m-2) and nitrogen (PON, g N m-2), were, 9, 53, 17 and 1.2 respectively. A steep increase in fluxes was observed during the summer thaw when sea ice broke up and water discharge from land began. Within the two months (July and August), >90% of the total annual vertical flux occurred.
 Isotopic (δ13C & δ15N) analysis of particulate organic material (POM) in the sediment trap, in phytoplankton and in the river material indicated that a maximum of c. 50% of the POM material originated from land. This is supported by the high C:N ratio (by atoms) of up to 22 found in the trapped organic material during the summer thaw as compared with 7–9 during winter and spring, when no discharge from land occurred. Seasonal measurements of the POC discharge from rivers to the outer region of the fjord corresponded to c. 40% of the vertical POC flux measured in the sediment trap, which further indicates a significant terrestrial contribution to the settling material in the outer fjord area.
 Besides POC, dissolved organic carbon (DOC) is discharged in an equal amount to the fjord from rivers, resulting in a total organic carbon (TOC) input from land to the outer region of Young Sound of 13 g C m-2 yr-1. This corresponds to c. 40% of the net TOC input from the Greenland Sea and to the outer part of the fjord during the ice-free productive period underlining the significant terrestrial contribution to sedimentation in the outer part of the fjord.
 Mean permanent accumulation rates based on the depth distributions of 210Pb, 137Cs and TOC in sediments at 60 m water depth in the outer fjord area revealed a burial of carbon within the sediment of 7.9 g C m-2 yr-1. In agreement with the sediment trap measurements, δ13C values within the sediment suggest that a substantial amount (c. 40%) of the POC in the sediment was of terrestrial origin. At the same sites, previous studies have reported an annual release of dissolved inorganic carbon (DIC) due to mineralization from the sediment of 12.6 g C m-2 yr-1. The sum of the annual DIC release and the burial within the sediment
 represents an expected total input to the sediment of 20.5 g C m-2 yr-1and compares well with the vertical flux measurement from the sediment trap of 17.0 g C m-2 yr-1 during the present study.

Exploring the connection between 210Po and organic matter in the northwestern Mediterranean

The disequilibrium between 210Po and its grandparent 210Pb has been proposed as a tracer of the vertical flux of sinking particulate organic matter in the ocean. The mechanism of association between 210Po and organic matter is, however, still unclear. To investigate this association we measured trace metals, minerals, organic carbon, nitrogen, and the natural radioisotopes 234Th, 228Th, 210Po, and 210Pb in sinking particles collected in sediment traps at 200 m in the northwestern Mediterranean. Pigments, fatty acids, and amino acids were used to identify the types and sources of particulate organic matter. Multivariate analyses were used to determine which components of sinking particulate matter are traced by 210Po and/or by the 210Po/ 210Pb ratio. Statistical analysis of the results indicates that the distribution of polonium in sinking marine particles is influenced by fresh phytoplankton-derived, nitrogen-rich organic matter as well as sulfur-containing amino acids. These findings are consistent with previous laboratory observations that the distribution of 210Po in biota parallels the distributions of both sulfur and protein, and indicate that these associations persist as material sinks through the water column. While this research generally supports the use of 210Po as a specific tracer of the flux of organic matter, the signals traced by 210Po/ 210Pb and 234Th/ 238U are not as distinct in the field as in laboratory experiments. Further work is needed to determine more precisely what 210Po/ 210Pb traces in order to increase the correspondence of 210Po/ 210Pb measurements to biogeochemically important rates and quantities.

Optimization and sensitivity study of a biogeochemistry ocean model using an implicit solver and in situ phosphate data

A new implicit method for obtaining equilibrium solutions and their sensitivity to changes in parameters is described and applied to an OCMIP‐2 type ocean‐biogeochemistry model. The method is used to optimize model parameters by minimizing the difference between the observed and simulated PO4 distribution. The optimized parameters include (1) the exponent α in the power law vertical profile for particulate organic matter (POM) fluxes, (2) the fraction σ of biological production allocated to dissolved organic matter (DOM) and (3) the rate constant κ for the remineralization of DOM. Global PO4 observations constrain σ and κ but not independently because their sensitivity patterns are highly correlated. In contrast, the sensitivity pattern for α is uncorrelated to those of the other parameters, allowing it to be independently constrained. We show that export production from POC is well constrained by the distribution of PO4 in an OCMIP‐2 type model, but that new production and export production from DOC are not well constrained. With the optimal parameter set (α = −1.0, σ = 0.74, and κ = 1.0 yrs−1) the fraction of the spatial PO4 variance captured by our model increases from 60% with the reference OCMIP‐2 parameters to 70%. Combined changes in σ and κ account for most of the improvements by reducing but not completely eliminating the nutrient trapping effect in the Eastern Equatorial Pacific and northern Indian Ocean that causes the model to over‐predict PO4 concentrations. Important remaining model‐data misfits in the deep North Atlantic where PO4 is over predicted and in the North Pacific where the model does not produce the observed sharp nutricline are likely attributable to deficiencies in ocean transport. The fact that the fraction of unexplained variance is large at the optimal parameter values highlights the importance of properly simulating physical transport for ocean biogeochemical modeling.

Downward fluxes of particulate organic matter in coastal and oceanic areas off Chile: The role of the OMZ and functional groups of the plankton

Flujos verticales de particulas han sido estimados durante la ultima decada en sistemas costeros y oceanicos frente a Chile centro-sur. Trampas cilindricas derivando con la corriente han sido usadas bajo la capa de mezcla de sistemas costeros, mientras que trampas automaticas conicas han sido ancladas en sistemas oceanicos profundos. Los flujos hacia 2300 m de profundidad frente a Coquimbo estuvieron dominados por carbonado de calcio (~70 mg m-2 d-1) mas que carbono organico particulado (POC ~7 mg m-2 d-1), donde foraminiferos (Neogloboquadrina pachyderma) y pellet fecales de Euphausia mucronata y Oikopleura spp, juegan un papel muy importante como vehiculos de carbonato y carbono, respectivamente. En sistemas de surgencia costera (i.e., Concepcion), el flujo vertical dominante fue POC, principalmente gobernado por pellets fecales de eufausidos y diatomeas de los generos Thalassiosira, Chaetoceros y Skeletonema. La degradacion bacteriana de material organico exportado hacia zonas mas profundas del oceano no aparece significativamente afectada por los niveles caracteristicos de concentracion de oxigeno disuelto oxicos versus hipoxicos en las diferentes masas de agua.

Metazoan meiofauna abundance in relation to environmental variables in the northern Gulf of Mexico deep sea

In order to more fully understand the distribution of meiofauna and how they respond to topographic, geochemical and physical forcing in the northern Gulf of Mexico, meiofauna abundance and environmental variables were analyzed in a hypothesis-based univariate and multivariate design. Meiofauna abundance was significantly related to water depth, but also exhibited significant longitudinal differences resulting from proximity to Mississippi River outflow. Canyon features in proximity of Mississippi River outflow were found to greatly enhance meiofauna abundance. The Florida Escarpment interacts with Mississippi River outflow and the Loop Current to enhance meiofauna abundance at stations lying directly above and below the escarpment. Multivariate comparisons of meiofauna abundance with environmental variables revealed a strong Mississippi River influence. River outflow alters local sediment characteristics, and interacts with loop current eddies and dynamic slope topography to increase particulate organic matter flux in the northeastern region, thus creating areas of higher than normal meiofauna abundance.

Binding of thorium(IV) to carboxylate, phosphate and sulfate functional groups from marine exopolymeric substances (EPS)

Th(IV) isotopes are important proxies in oceanographic investigations, and are used as tracers of particle dynamics and particulate organic matter (POC) fluxes out of the euphotic zone through the use of 234Th/POC ratios. These approaches rely on empirically determined and variable POC to 234Th ratios, which might be controlled, in parts, by the abundance of exopolymeric substances (EPS). EPS contain acidic polysaccharides (APS) and are excreted by both phytoplankton and bacteria. To this end, radiotracer experiments with EPS from microbial cultures were conducted to determine the binding environment of 234Th(IV)-binding ligands in colloids and suspended particles in marine systems. In these experiments, the 234Th distribution during isoelectric focusing (IEF) and polyacrylamide gel electrophoresis (PAGE) was related to the functional group composition of EPS and of colloidal organic matter (COM) isolated from the Gulf of Mexico (GOM) using cross-flow ultrafiltration. EPS was extracted from phytoplankton ( Emiliania huxleyi and Synechococcus elongatus) and bacteria ( Sagittula stellata and Roseobacter gallaeciensis) cultures by repeated alcohol precipitation. Phosphate and sulfate concentrations were determined using ion chromatography (IC). IEF profiles indicated that 49% to 65% of the 234Th-labeled EPS from plankton and bacteria as well as COM samples from the GOM was found concentrated below pH of 4, near an isoelectric point, pH IEP, of about 2. The carboxylic acid maxima for extracted EPS and COM samples appeared close to the pH IEF of 234Th(IV). The phosphate maximum appeared at the same pH IEF as 234Th(IV) for EPS from R. gallaeciensis and S. elongatus. The sulfate maximum was found at the same pH IEF as 234Th(IV) for EPS from S. elongatus and COM. The molecular weight (MW) of the strongly Th(IV)-binding ligand varied from 1 to 14 kDa, depending on the species, but was about 10 kDa in COM. Thus, depending on the species of plankton or bacteria, the MW and specific functional group composition of the strongly 234Th(IV)-binding amphiphilic biomolecule can vary. Therefore, different acidic functional groups can, at times, contribute to the binding of Th(IV) to the EPS chelating ligand, which can also have different MWs. This implies that the binding environment for Th(IV), which is present at total concentrations at least a million times lower than the acid functional groups, consists of strong polydentate chelate complexes in clustered structures of carboxylate, sulfates and/or phosphates. The combination of strongly chelating groups and amphiphilicity gives this biomolecule the unique properties of a “sticky” ligand.

Seasonal fluctuations in the flux of particulate organic matter discharged from net pens for fish farming

Fish farming using net pens consumes large amounts of food for the reared fish, resulting in organic enrichment of the sediment below the fish farm from organic discharge in the forms of fish feces and food residues. Sediment traps were set at a net pen within and outside a fish farm, and organic flux on the sea floor was compared. The year-mean organic flux to the sea floor caused by fish farming from September 2003 to September 2004 was estimated at 2.11 gC/m2/day in total organic carbon (TOC) and 0.26 gN/m2/day in total nitrogen (TN), which were 2.5 times (TOC flux) and 2.2 times (TN flux) larger than that for natural organic flux outside the fish farm. The seasonal fluctuation patterns of organic flux to the sea floor below the fish farm did not necessarily coincide with those for the amount of food spent for the fish farming. The largest organic flux to the sea floor occurred in the autumn, when the vertical mixing of the water had just started. Therefore, organic enrichment of the sediment on the sea floor of a fish farm proceeded during this season.

Upland Forest Linkages to Seasonal Wetlands: Litter Flux, Processing, and Food Quality

The flux of materials across ecosystem boundaries has significant effects on recipient systems. Because of edge effects, seasonal wetlands in upland forest are good systems to explore these linkages. The purpose of this study was to examine flux of coarse particulate organic matter as litter fall into seasonal wetlands in Minnesota, and the relationship of this flux to development of mosquitoes (Aedes aegypti). We hypothesized that litter flux into seasonal wetlands was dominated by upland plant litter that was lower quality and slower to breakdown than wetland litter, and that development rate of mosquitoes reared on upland litter was less than those reared on wetland litter. Of total litter fall into the wetlands, 71% originated in upland forest. Carbon to nitrogen ratios differed between upland litter (mostly sugar maple (Acer saccharum) and trembling aspen (Populus tremuloides) leaves) and wetland litter (mostly black ash (Fraxinus nirgra) leaves), averaging 63.9 and 47.7, respectively over two years. Breakdown rate of black ash leaves was faster than upland leaves (k (day−1) = 0.00329 and 0.00156, respectively), based on the average between wetland margins and centers. Development of mosquito larvae fed black ash leaves was faster than larvae fed upland leaves. Our results demonstrate linkages between upland forests and seasonal wetlands through litter fall. The abundance of upland litter in the wetlands may influence litter breakdown and carbon assimilation by invertebrates. Wetlands receiving high amounts of upland versus wetland litter may be lower quality habitats for invertebrates that depend on detrital pools for their development.

Internal tide—shelf topography interactions as a forcing factor governing the large-scale distribution and burial fluxes of particulate organic matter (POM) in the Benguela upwelling system

This study investigates the role of internal tides in driving the sedimentation and re-suspension of biogenic POM on the Namibian shelf and give rise to stable 500–800 km long shore alternating bands of high and low POM concentrations. Temperature time series data (September 2000–March 2001) from the benthic boundary layer at three sites are used to hypothesise that the dominant forcing mechanism are internal tides and their interaction with the shelf break zones. Vertical displacements of the temperature structure by 100–150 m at the outer shelf break (depth 450 m) are shown to occur through out the 6-month time series. In contrast at non-shelf break sites the vertical displacements of temperature are negligible. The shear–stresses predicted landward of the shelf break zone from 100–150 m vertical displacements of the temperature structure are significantly higher (>0.1 Pa) than the critical shear–stresses which govern the re-suspension of biogenic particles and fine sediments (0.05–0.1 Pa). Short-term ADCP data was used to show that critical shear–stress distribution at the different POM areas is consistent with the predicted net accumulation and net erosional zones of POM across the Namibian shelf. This study hypothesises that the barotropic–baroclinic tidal coupling governs vertical particle flux dynamics whereas Ekman and inertial flows are thought to govern the horizontal advection scales that result in the observed POM distribution. The importance of this improved dynamical understanding has implications for both carbon burial efficiency as well as the variability in the suitability of benthic fisheries habitats.

Internal carbon and nutrient cycling in Lake Baikal: sedimentation, upwelling, and early diagenesis

The internal cycles of carbon, silica, nitrogen, and phosphorus in the South and North Basins of Lake Baikal were quantified in the frame of a multidisciplinary collaboration. Fluxes of particulate organic matter from the epilimnion to the deep water were quantified with integrating sediment traps deployed at 200- to 250-m water depth and compared with fluxes measured in near-bottom traps to reveal mineralization in the water column. Sedimentation rates were determined with dated sediment cores to calculate mass accumulation rates of elements in the sediment. Advective and turbulent transport of dissolved nutrients in the water column was based on a set of monitoring data, which included temperature and current data, as well as hydrochemical data of the water column. Diffusive fluxes from the sediment to the overlying water column were determined by applying different porewater sampling techniques. The combination of these data resulted in consistent internal budgets for carbon, nitrogen, and phosphorus in Lake Baikal: the new production in the South Basin was 1730 mmol C m −2 year −1 and the mass accumulation rate in the sediment 220 mmol C m −2 year −1, whereas in the more secluded North Basin, new production was only 1220 mmol C m −2 year −1 and mass accumulation rate 125 mmol C m −2 year −1. Fluxes of particle-bound nitrogen, phosphorus, and biogenic silica were by about 30% smaller in the North Basin than in the South Basin. Export fluxes of nitrogen from the surface zone to the deep water were 150 mmol N and 100 mmol N m −2 year −1. Denitrification rates in the sediment were estimated from mass-loss calculation to 38 and 53 mmol N m −2 year −1 for the South and North Basin, respectively, corresponding to 25% and 52% of the total nitrogen input to the hypolimnion. Nitrogen (19 and 13 mmol m −2 year −1) was finally buried in the sediments of the South and North Basins; 10.1 and 3.5 mmol P m −2 year −1, and 1830 and 1400 mmol Si m −2 year −1 were transferred to the deep water in the South and North Basin where 28% and 70% P, and 64% and 54% Si were retained in the sediments. A diatom bloom occurred during our sampling period of 2 years, which usually occurs only every 3 to 5 years. Accordingly, Si flux data from sediment traps were increased by an estimated 50% compared with the long-term average illustrating the necessity of several years of field measurements to compensate for the natural dynamics of Lake Baikal.

Importance of canopy herbivores to dissolved and particulate organic matter fluxes to the forest floor

Few studies deal with the origin and contribution of organic matter (OM) fluxes from forest canopies to the variability of DOM and nutrient dynamics in the forest floor. Recent studies indicate a microbial and phytophages origin of OM in the throughfall of temperate forest ecosystems and reported inputs of dissolved (<0.45 μm) organic carbon (DOC) with throughfall range between 40 and 160 kg C ha −1 year −1. Data on particulate organic matter (0.45 μm<POM<2 mm) associated with throughfall fluxes are rare and not often considered in terrestrial ecosystem element budgets. Using field and laboratory experiments, we investigated the direct effects of canopy infestation by two functional groups of herbivores (sap and leaf feeders) on dissolved and particulate organic matter fluxes in throughfall and their impact on forest floor processes. Throughfall fluxes of particulate amino-nitrogen beneath infested spruce were about 60% and those of hexose-carbon beneath infested hardwood trees up to 70% higher compared to uninfested control trees. Corresponding fluxes to filtered samples showed no statistically significant differences. In column irrigation experiments, different levels of aphid infestation (uninfested, moderately, heavy infested) were simulated by adding honeydew to the irrigation solution. Forest floor solution chemistry from forest floor showed a significant reduction in NH 4–N and NO 3–N fluxes, slightly reduced DON fluxes and significantly increased CO 2 effluxes following honeydew application. We suggest that the amount of POM compounds transported with throughfall solution and its subsequent effects on forest floor processes depend on the herbivore functional group and on the level of infestation. From both a quantitative and qualitative point of view, our data indicate that herbivory-mediated organic matter in particulate and dissolved forms contribute considerably to the overall throughfall input of organic substances into the forest floor.

Use of Keeling plots to determine sources of dissolved organic carbon in nearshore and open ocean systems

We apply a Keeling mixing model commonly used in atmospheric sciences to oceanic dissolved organic carbon (DOC) 14C and concentrations to demonstrate that DOC distribution across spatial transects or depth profiles can be modeled as two‐component mixtures; one component consists of an old refractory pool to which a newly synthesized component pool is added. We then use the Keeling approach to determine the Δ14C signature of excess DOC added to background concentrations in nearshore and open ocean systems. Our analysis indicates enrichment in 14C of excess DOC in coastal waters relative to offshore waters, particularly in spring when river discharge increases. These findings are consistent with the export of 14C‐enriched terrestrial DOC to the ocean and inconsistent with the idea of selective degradation of young terrestrial DOC in estuaries, resulting in export of old refractory component to the ocean. In the middle Atlantic Bight region, during the spring, excess DOC has a 14C signature similar to that of DOC in the major rivers, whereas during the peak primary productivity of the summer season, excess DOC has a signature more similar to that of dissolved inorganic carbon. Variability in the Δ14C of excess DOC in the open ocean was lower than that of the coastal ocean. Minima in Δ14C values of excess DOC in the open ocean were measured during periods of high particulate organic matter (POC) flux, indicating that POC can interact with DOC and selectively remove 14C‐enriched components from the surface ocean. The Keeling plot provides a powerful approach for determining the isotopic composition of excess DOC from an entire DOC profile or transect.

A Comparison of Simulated Particle Fluxes Using NEMURO and Other Ecosystem Models in the Western North Pacific

JGOFS has revealed the importance of marine biological activity to the global carbon cycle. Ecological models are valuable tools for improving our understanding of biogeochemical cycles. Through a series of workshops, the North Pacific Marine Science Organization (PICES) developed NEMURO (North Pacific Ecosystem Model Understanding Regional Oceanography) a model, specifically designed to simulate the lower trophic ecosystem in the North Pacific Ocean. Its ability to simulate vertical fluxes generated by biological activities has not yet been validated. Here compare NEMURO with several other lower trophic level models of the northern North Pacific. The different ecosystem models are each embedded in a common three-dimensional physical model, and the simulated vertical flux of POM and the biomass of phytoplankton are compared. The models compared are: (1) NEMURO, (2) the Kishi and Nakata Model (Kishi et al., 1981), (3) KKYS (Kawamiya et al., 1995, 2000a, 2000b), and (4) the Denman model (Denman and Pena, 2002). With simple NPZD models, it is difficult to describe the production of POM (Particulate Organic Matter) and hence the simulations of vertical flux are poor. However, if the parameters are properly defined, the primary production can be well reproduced, even though none of models we used here includes iron limitation effects. On the whole, NEMURO gave a satisfactory simulation of the vertical flux of POM in the northern North Pacific.

BUDGET AND FLUXES OF PARTICULATE ORGANIC CARBON AND NITROGEN ACCORDING TO THE DATA ON THEIR VERTICAL DISTRIBUTION IN THE DEEP PART OF THE BLACK SEA

On the basis of the analysis of the many-year data on the vertical distributions of particulate organic carbon and nitrogen, we compute their annual average amounts for three typical layers of water in the deep part of the Black Sea: for a layer located above the oxycline and characterized by the formation of new portions of particulate organic matter in the course of photosynthesis, inside the oxycline, where the major part of oxygen is consumed and the major part of the flux of particulate organic matter is oxidized, and for the upper part of the anoxic zone characterized by the most active microbiological processes of oxidation of the organic substances and production of sulfides. The available literature data on sedimentation traps are used to study the downward annual average fluxes of particulate organic matter from the euphotic zone into the oxycline and into the anaerobic zone. The seasonal variability of the amounts and fluxes of particulate carbon and nitrogen is revealed.

Biogeochemical processes and labile composition of settling particulate organic matter in the south-west Pacific Ocean

Settling particles collected by sediment traps deployed for approximately 1 year in the Coral Sea and Tasman Sea were analysed to understand the biogeochemical processes controlling the cycling and flux of particulate organic matter (POM) in the south-west Pacific. Samples were analysed for 20 amino acids (AA) and two hexosamines (HA) and the data were interpreted together with already published data on opal (biogenic silica), organic carbon and total nitrogen contents. Mean fluxes of labile carbon and nitrogen at one site were significantly different (P &lt; 0.04, t-test; n = 14–18) from those at other sites. The southernmost trap recorded the highest concentrations of AA, HA and organic carbon normalized AA. At a site in the south, POM was more degraded in the deep trap than in the shallow trap. Occasionally, higher fluxes were also recorded at the deep trap relative to the shallow trap. The C/Natomic ratio coupled with AA- and HA-based parameters clearly suggested contribution of POM through resuspension as well as lateral advection at the more southern site, whereas a strong influence of zooplankton on total mass flux was revealed at the northern site during the period August–September 1995. It is evident from the data that higher flux of particles having higher labile contents (AA and HA) is more prevalent in the Tasman Sea than in the Coral Sea.

Vertical and latitudinal variations in amino acid fluxes and compositions of settling particles along 175°E in the North Pacific Ocean

Settling particles collected by sediment traps deployed for about one year (1993–94) at four sites along 175°E longitude in the central North Pacific have been analyzed for amino acids (AA) and amino sugars (or hexosamines, HA). These compounds account for about 12.5–27.9% of particulate organic carbon flux to the deep ocean. Biogeochemical indicator parameters varied in the range comparable with similar studies conducted in other oceanic sites. Correlations between non-protein AA (β-alanine and γ-aminobutyric acid) and flux parameters indicate repackaging of settling particulate organic matter (POM) around intermediate water depth (below 1500 m) at all trap sites. Mean values of indicator parameters in the shallow trap differ significantly (Student’s t-test; p < 0.03) from those in deep traps at the same site. Latitudinal trends in POM flux and its labile composition suggest that relatively fresh POM is being deposited at a higher rate in the subarctic area of the Pacific. However, this trend is not so clear in deep traps, probably due to the influence of bioactive transport and deposition of laterally advected particles in these traps. Total and particulate organic carbon fluxes normalized to primary productivity estimates show a sharp rise in efficiency of the biological pump towards the subarctic area, which is responsible for enhanced fluxes of particles with a high labile content to the deep ocean in this part of the Pacific.

Upper ocean carbon fluxes in the Atlantic Ocean: The importance of the POC:PIC ratio

The mean depth distribution of the POC:PIC ratio of sinking particles, measured with particle interceptor traps deployed in the Atlantic Ocean, is fitted by an exponential function (POC:PIC = 64.3Z−0.56; r2 = 0.69) The function is successfully evaluated by comparison with (a) estimates of the POC:PIC ratio of export production, computed from seasonal changes of nitrate and alkalinity and (b) estimates of the POC:PIC ratio of remineralization on shallow isopycnals. The basin mean POC:PIC ratio of export production is 4.2–4.37. The POC:PIC‐depth function is combined with empirical relationships between the flux of particulate organic matter, primary production and depth, satellite derived primary production data sets, and the regional distribution of ψ (the ratio of released CO2:precipitated carbonate during CaCO3 formation) in order to estimate the effective carbon flux (Jeff) in the Atlantic Ocean. Remineralization of organic carbon above the winter mixed layer (11–17%) and CaCO3 sequestration from the winter mixed layer (13–16%), which is the balance between CaCO3 production and shallow dissolution, are the two main processes which control the difference between export production (0.9 and 2.9 GT C yr−1) and Jeff (0.64 and 2.2 GT C yr−1) on the basin scale (65°N to 65°S). CaCO3 sequestration is the dominant process modulating effective carbon export in the tropics, while shallow POC remineralization dominates in temperate and polar waters. Observed regional patterns like polarward increases of the POC:PIC export ratio and of ψ counteract each other largely when Jeff is computed.

DISTURBANCE MODERATES BIODIVERSITY–ECOSYSTEM FUNCTION RELATIONSHIPS: EXPERIMENTAL EVIDENCE FROM CADDISFLIES IN STREAM MESOCOSMS

We present empirical evidence that the direct and indirect effects of species richness on ecological processes depend on a system's disturbance regime. We manipulated the number of species of freshwater suspension feeders (net-spinning caddisflies) in lab- oratory stream mesocosms where communities were either subject to a periodic mortality or were left undisturbed. We hypothesized that disturbance would alter the direct effect of suspension-feeder species richness on the flux of their resource, particulate organic matter (POM), and alter the indirect effects of suspension-feeder species richness on algal pro- ductivity and biofilm respiration (via nutrient recycling). The direct effect of suspension- feeder species richness on POM flux did indeed change with disturbance regime. The flux of POM from the water column to stream bed was not influenced by species richness in the absence of disturbance, but increased as species richness was increased in disturbed streams. This apparently occurred because a high taxonomic evenness in disturbed streams minimized current ''shading'' (i.e., the blocking of flow from upstream to downstream neighbors) that, in turn, allowed diverse assemblages to capture a greater fraction of sus- pended resources. Disturbance also altered the indirect effect of suspension feeder species richness on algal productivity. In the absence of disturbance, increasing species richness led to dominance by a competitively superior suspension feeding taxon that had particularly low rates of nutrient excretion. Reduced nutrient availability, in turn, caused algal pro- ductivity to decline as a function of species richness. Periodic disturbances, however, pre- vented taxonomic dominance and eliminated this indirect effect of suspension feeder species richness on stream productivity. Our results suggest that disturbance can moderate rela- tionships between biodiversity and ecosystem functioning by (1) increasing the chance that diversity generates unique system properties (i.e., ''emergent'' properties), or (2) suppress- ing the probability of ecological processes being controlled by a single taxon (i.e., the ''selection-probability'' effect).

Impact of ENSO variability on the flux and composition of sinking POM in the western equatorial Pacific Ocean: Amino acids and hexosamines

Abstract Sediment trap moorings deployed along the equator at three distinct oceanographic zones within the western Pacific Ocean during 1991–93, 1994–95, and 1999 provided data on total mass and amino acid fluxes and composition of particulate organic matter (POM) sinking in this part of the Pacific. An intercomparison of annual averages of various parameters revealed discrete patterns in flux and composition of POM under the El Nino (1991–93, 1994–95) and La Nina (1999) conditions that prevailed over the equatorial Pacific during the sampling periods. In the hemipelagic zone of the far western equatorial Pacific, where terrestrial deposition of particles larger than 5 μm accounts for >25% of the total sediment, average total mass and amino acid fluxes were relatively higher during El Nino than during La Nina. However, at the oligotrophic warm pool and upwelling sites, total mass and amino acid fluxes were higher during La Nina. Influence of ENSO-related changes in the sinking particle flux was much clearer in the hemipelagic zone compared to that in the warm pool. Average values of biogeochemical parameters such as glucosamine/galactosamine and amino acids/hexosamines, and bulk parameters like amino acid carbon and nitrogen contents relative to organic carbon and total nitrogen (THAA-C% and THAA-N%, respectively), and organic carbon normalised amino acid concentrations indicated that sinking POM was more labile during La Nina at all the sites. The ratios Aspartic acid/β-alanine, Glutamic acid/γ-aminobutyric acid, and relative concentration of non-protein amino acids (β-alanine+γ-aminobutyric acid) suggested that POM degradation was more intense during La Nina than during El Nino conditions at all sites. >

Effects of hypoxia and organic enrichment on the coastal marine environment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 238:249-279 (2002) - doi:10.3354/meps238249 Effects of hypoxia and organic enrichment on the coastal marine environment John S. Gray*, Rudolf Shiu-sun Wu, Ying Ying Or Department of Biology and Chemistry, City University, Tat Chee Avenue, Kowloon, Hong Kong *Present address: Department of Biology, University of Oslo, Pb 1064 Blindern, 0316 Oslo, Norway. E-mail: j.s.gray@bio.uio.no ABSTRACT: Eutrophication is one of the most severe and widespread forms of disturbance affecting coastal marine systems. Whilst there are general models of effects on benthos, such as the Pearson-Rosenberg (P-R) model, the models are descriptive rather than predictive. Here we first review the process of increased organic matter production and the ensuing sedimentation to the seafloor. It is shown that there is no simple relationship between nutrient inputs and the vertical flux of particulate organic matter (POM). In particular, episodic hydrographic events are thought to be the key factor leading to high rates of sedimentation and accompanying hypoxia. We extend an earlier review of effects of hypoxia to include organisms living in the water column. In general, fishes are more sensitive to hypoxia than crustaceans and echinoderms, which in turn are more sensitive than annelids, whilst molluscs are the least sensitive. Growth is affected at oxygen concentrations between 6.0 and 4.5 mgO2 l-1, other aspects of metabolism are affected at between 4 and 2 mgO2 l-1 and mortality occurs where concentrations are below 2.0 to 0.5 mgO2 l-1. Field studies, however, show that complex behavioural changes also occur as hypoxia increases, and these are described herein. The areas where hypoxia occurs are frequently areas that are stagnant or with poor water exchange. Thus again, hydrographic factors are key processes determining whether or not hypoxia and eutrophication occur. Tolerance to ammonia and hydrogen sulphide is also reviewed, as these substances are found at near zero concentrations of oxygen and are highly toxic to most organisms. However, the effects of interactions between oxygen, ammonia and hydrogen sulphide only occur below oxygen concentrations of ca. 0.5 mgO2 l-1, since only below this concentration are hydrogen sulphide and oxygen released into the water. Models of eutrophication and the generation of hypoxia are discussed, and in particular the P-R model is analysed. Although agreement with the model is widely reported the actual predictions of the model have rarely been tested. Our review suggests that the major effects on benthic fauna result from hypoxia rather than organic enrichment per se and suggests that the P-R model is descriptive rather than predictive. Finally, a managerial tool is proposed, based on the stages of effects of hypoxia and organic enrichment suggested by the P-R model and on an earlier study. The proposed strategy involves rapid assessment tools and indicates where more detailed surveys are needed. Managers are advised that remedial action will not produce rapid results and that recovery from eutrophication will probably take decades. Thus it is essential to detect potential hypoxia and eutrophication effects at early stages of development. KEY WORDS: Eutrophication · Hypoxia · Hydrogen sulphide · Ammonia · Effects on fauna Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 238. Online publication date: August 08, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.