Vertical Flux Of Organic Matter Research Articles

Particulate organic carbon export fluxes estimates by 234Th[sbnd]238U disequilibrium in the oxygen minimum zone off the Peruvian coast

The Peruvian upwelling zone is one of the most productive marine ecosystems in the world with a spectacular, pronounced oxygen minimum zone (OMZ). Globally OMZs are increasing in size and intensity with far-reaching consequences for the marine biological carbon pump and carbon export; thus, these zones need to be carefully monitored to be able to understand future climate change impacts. The current study was carried out in 2013 and 2017 to quantify the vertical flux of organic matter exported out of the productive surface layer by measuring 234Th238U disequilibria in the water column. Samples were collected in January 2013 and May 2017 along an identical transect located at 12°S off the Peruvian coast near Lima, Peru. Th-234 fluxes ranged from 0 to 2088 ± 95 dpm m−2 d−1 in 2013 and 698 ± 63 to 3648 ± 113 dpm m−2 d−1 in 2017. The corresponding POC fluxes varied between 0 and 164.2 ± 7.9 mg C m−2 d−1 in 2013 and 22.7 ± 2.7 to 133.1 ± 15.2 mg C m−2 d−1 in 2017, with POC fluxes gradually decreasing with distance from the coast. Despite higher POC fluxes, the export efficiencies were found to be extremely low due to high particle remineralization rates observed within the euphotic zone.

Aquaculture organic enrichment of marine sediments: assimilative capacity, geochemical indicators, variability, and impact classification

Benthic organic enrichment at 2 high-flow Atlantic salmon Salmo salar farms and at a low-flow mussel Mytilus edulis farm was studied to assess the capacity of local physical and biological processes to assimilate organic waste inputs. Geochemical metrics served as proxies for detecting potential biological effects. High-flow sites are generally predicted to assimilate organic enrichment by flow- and wave-induced waste dispersion and metabolic processes. However, a decrease in porewater dissolved oxygen was detected out to 100 m at the salmon farm with cohesive sediments and to approximately 1000 m outside the farm with permeable sediment. Sediment oxygen consumption was responsive to the vertical flux of organic matter, resulting in hypoxic conditions. An increase in total free sulfides (H2S + HS- + S2-) in porewater was restricted to the immediate vicinity of both salmon farms. Despite exhibiting a high degree of small-scale patchiness, benthic effects were greatest at the fish farms during the pre-harvest period, regardless of season. Natural organic enrichment at the mussel farm constrained the assimilative capacity for biodeposition, resulting in substantial free sulfide accumulation. Sediment free sulfide analysis at a wide array of fish and shellfish farms showed that the ion-selective electrode method that is widely prescribed for regulatory aquaculture monitoring gave biased readings relative to methylene blue colorimetry and direct UV spectrophotometry. The ecological quality status classification system was extended to include quantitative relationships between a wide range of geochemical and biological variables employed worldwide to monitor and regulate the effects of benthic organic enrichment.

The Mesopelagic Scattering Layer: A Hotspot for Heterotrophic Prokaryotes in the Red Sea Twilight Zone

The vast majority of marine dissolved organic carbon (DOC), the largest reservoir of reduced carbon on Earth, is believed to accumulate in the abyssal layers of the ocean over timescales of decades to millennia. However, evidence is growing that small animals that migrate vertically every day from the surface to mesopelagic layers are significantly contributing to the active vertical flux of organic matter. Whether that represents an important source of carbon available for microbial production and respiration at the mesopelagic realm, and its contribution to oceanic carbon budgets and energy flows, is yet to be explored. Here we present data suggesting that Red Sea migrating animals may produce an overlooked source of labile DOC (used at a mean rate of 2.1 µmol C L-1 d-1) that does not accumulate but fuels the metabolism of prokaryotic heterotrophs in the twilight zone, generating a disregarded hotspot for heterotrophic prokaryotes.

Programmed cell death in diazotrophs and the fate of organic matter in the western tropical South Pacific Ocean during the OUTPACE cruise

Abstract. The fate of diazotroph (N2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the western tropical South Pacific Ocean was studied during OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (PCD), occurring in some diazotrophs, is an important mechanism affecting diazotroph mortality and a factor regulating the vertical flux of organic matter and, thus, the fate of the blooms. We sampled at three long duration (LD) stations of 5 days each (LDA, LDB and LDC) where drifting sediment traps were deployed at 150, 325 and 500 m depth. LDA and LDB were characterized by high chlorophyll a (Chl a) concentrations (0.2–0.6 µg L−1) and dominated by dense biomass of the filamentous cyanobacterium Trichodesmium as well as UCYN-B and diatom–diazotroph associations (Rhizosolenia with Richelia-detected by microscopy and het-1 nifH copies). Station LDC was located at an ultra-oligotrophic area of the South Pacific gyre with extremely low Chl a concentration (∼ 0.02 µg L−1) with limited biomass of diazotrophs predominantly the unicellular UCYN-B. Our measurements of biomass from LDA and LDB yielded high activities of caspase-like and metacaspase proteases that are indicative of PCD in Trichodesmium and other phytoplankton. Metacaspase activity, reported here for the first time from oceanic populations, was highest at the surface of both LDA and LDB, where we also obtained high concentrations of transparent exopolymeric particles (TEP). TEP were negatively correlated with dissolved inorganic phosphorus and positively coupled to both the dissolved and particulate organic carbon pools. Our results reflect the increase in TEP production under nutrient stress and its role as a source of sticky carbon facilitating aggregation and rapid vertical sinking. Evidence for bloom decline was observed at both LDA and LDB. However, the physiological status and rates of decline of the blooms differed between the stations, influencing the amount of accumulated diazotrophic organic matter and mass flux observed in the traps during our experimental time frame. At LDA sediment traps contained the greatest export of particulate matter and significant numbers of both intact and decaying Trichodesmium, UCYN-B and het-1 compared to LDB where the bloom decline began only 2 days prior to leaving the station and to LDC where no evidence for bloom or bloom decline was seen. Substantiating previous findings from laboratory cultures linking PCD to carbon export in Trichodesmium, our results from OUTPACE indicate that nutrient limitation may induce PCD in high biomass blooms such as displayed by Trichodesmium or diatom–diazotroph associations. Furthermore, PCD combined with high TEP production will tend to facilitate cellular aggregation and bloom termination and will expedite vertical flux to depth.

Mesopelagic Prokaryotes Alter Surface Phytoplankton Production during Simulated Deep Mixing Experiments in Eastern Mediterranean Sea Waters

Mesopelagic prokaryotes (archaea and bacteria), which are transported together with nutrient-rich intermediate-water to the surface layer by deep convection in the oceans (e.g., winter mixing, upwelling systems), can interact with surface microbial populations. This interaction can potentially affect production rates and biomass of surface microbial populations, and thus play an important role in the marine carbon cycle and oceanic carbon sequestration. The Eastern Mediterranean Sea (EMS) is one of the most oligotrophic and warm systems in the world’s oceans, with usually very shallow winter mixing (<200 m) and lack of large-size spring algal blooms. In this study, we collected seawater (0-1500 m) in 9 different cruises at the open EMS during both the stratified and the mixed seasons. We show that the EMS is a highly oligotrophic regime, resulting in low autotrophic biomass and primary productivity and relatively high heterotrophic prokaryotic biomass and production. Further, we simulated deep water mixing in on-board microcosms using Levantine surface (LSW, ~0.5 m) and intermediate (LIW, ~400 m) waters at a 9:1 ratio, respectively and examined the responses of the microbial populations to such a scenario. We hypothesized that the LIW, being nutrient-rich (e.g., N, P) and a ‘hot-spot’ for microbial activity (due to the warm conditions that prevail in these depths), may supply the LSW with not only key-limiting nutrients but also with viable and active heterotrophic prokaryotes that can interact with the ambient surface microbial population. Indeed, we show that LIW heterotrophic prokaryotes negatively affected the surface phytoplankton populations, resulting in lower chlorophyll-a levels and primary production rates. This may be due to out-competition of phytoplankton by LIW populations for resources and/or by a phytoplankton cell lysis via viral infection. Our results suggest that phytoplankton in the EMS may not likely form blooms, even after exceptionally deep winter mixing, and therefore have a very small overall effect on the vertical flux of organic matter to the deep sea.

In situ camera observations reveal major role of zooplankton in modulating marine snow formation during an upwelling-induced plankton bloom

Particle aggregation and the consequent formation of marine snow alter important properties of biogenic particles (size, sinking rate, degradability), thus playing a key role in controlling the vertical flux of organic matter to the deep ocean. However, there are still large uncertainties about rates and mechanisms of particle aggregation, as well as the role of plankton community structure in modifying biomass transfer from small particles to large fast-sinking aggregates.Here we present data from a high-resolution underwater camera system that we used to observe particle size distributions and formation of marine snow (aggregates >0.5 mm) over the course of a 9-week in situ mesocosm experiment in the Eastern Subtropical North Atlantic. After an oligotrophic phase of almost 4 weeks, addition of nutrient-rich deep water (650 m) initiated the development of a pronounced diatom bloom and the subsequent formation of large marine snow aggregates in all 8 mesocosms. We observed a substantial time lag between the peaks of chlorophyll a and marine snow biovolume of 9–12 days, which is much longer than previously reported and indicates a marked temporal decoupling of phytoplankton growth and marine snow formation during our study. Despite this time lag, our observations revealed substantial transfer of biomass from small particle sizes (single phytoplankton cells and chains) to marine snow aggregates of up to 2.5 mm diameter (ESD), with most of the biovolume being contained in the 0.5–1 mm size range. Notably, the abundance and community composition of mesozooplankton had a substantial influence on the temporal development of particle size spectra and formation of marine snow aggregates: While higher copepod abundances were related to reduced aggregate formation and biomass transfer towards larger particle sizes, the presence of appendicularia and doliolids enhanced formation of large marine snow.Furthermore, we combined in situ particle size distributions with measurements of particle sinking velocity to compute instantaneous (potential) vertical mass flux. However, somewhat surprisingly, we did not find a coherent relationship between our computed flux and measured vertical mass flux (collected by sediment traps in 15 m depth). Although the onset of measured vertical flux roughly coincided with the emergence of marine snow, we found substantial variability in mass flux among mesocosms that was not related to marine snow numbers, and was instead presumably driven by zooplankton-mediated alteration of sinking biomass and export of small particles (fecal pellets).Altogether, our findings highlight the role of zooplankton community composition and feeding interactions on particle size spectra and formation of marine snow aggregates, with important implications for our understanding of particle aggregation and vertical flux of organic matter in the ocean.

To what extent can specialized species succeed in the deep sea? The biology and trophic ecology of deep-sea spiny eels (Notacanthidae) in the Mediterranean Sea

The population structure, reproductive biology and feeding ecology of the two notacanthids inhabiting the deep Mediterranean, Notacanthus bonapartei and Polyacanthonotus rissoanus, were analyzed in the Balearic Basin at depths from 579 to 2233m (mainly pristine depths or subjected to low fishing impact), including seasonal variations. Preferred average depths (Centres of Gravity, CoG) of Notacanthusbonapartei were situated over the middle slope (942m) and of P. rissoanus on the lower slope (1680m). For both species, bigger individuals collected at the deepest depths had the highest values of a gonadosomatic index (GSI), suggesting that in reproductive periods adults migrate into deeper waters. The reproductive season for N. bonapartei was late summer and autumn; that of P. rissoanus was narrower, restricted to summer. N. bonapartei exploited benthic prey, among identified prey mainly echinoderms (e.g., Penilpidia ludwigi, Hymenodiscus coronata) and sessile benthic organisms (e.g., actinians and polyps of the bamboo coral Isidella elongata). Consumption of bamboo coral polyps by N. bonapartei constitutes a unique specialized trophic strategy and a direct link with such corals. Some differences in the diet composition related to depth were observed, as were a few differences related to periods of water-column stratification and homogenization. Gut fullness (F) of this species was mainly correlated with surface Chlorophyll a recorded 2–3 months before sampling date and somewhat but less so with river discharges 1 month before sampling. That suggests that vertical flux of organic matter was the food source for prey exploited by N. bonapartei. Diet of P. rissoanus was based on epibenthic-suprabenthic crustaceans, e.g. tanaids (Apseudes spp.), isopods (Munnopsurus atlanticus) and amphipods (Rhachotropis caeca) and on polychaetes (Polynoidae, Harmothoe spp.), all these prey more mobile than consumed by N. bonapartei. No significant differences in diet composition were found related with either depth or homogenization/stratification of the water column. This lack of changes in diet is probably attributable to the greater stability of the lower slope where P. rissoanus lives. Gut fullness was mainly correlated with surface Chlorophyll a recorded simultaneously with the fish sampling. Lactate dehydrogenase (LDH) activity was similar in the muscle of the two notacanthids (N. bonapartei=3.72–8.75µmol/min/mg prot; P. rissoanus=7.56µmol/min/mg prot). Values for N. bonapartei were the highest found compared to other deep-sea fish in the deep Mediterranean. This could be related with the special feeding behaviour of this species when it removes sessile prey from substrate.

Observations of carbon export by small sinking particles in the upper mesopelagic

Carbon and nutrients are transported out of the surface ocean and sequestered at depth by sinking particles. Sinking particle sizes span many orders of magnitude and the relative influence of small particles on carbon export compared to large particles has not been resolved. To determine the influence of particle size on carbon export, the flux of both small (11–64μm) and large (>64μm) particles in the upper mesopelagic was examined during 5 cruises of the Bermuda Atlantic Time Series (BATS) in the Sargasso Sea using neutrally buoyant sediment traps mounted with tubes containing polyacrylamide gel layers and tubes containing a poisoned brine layer. Particles were also collected in surface-tethered, free-floating traps at higher carbon flux locations in the tropical and subtropical South Atlantic Ocean. Particle sizes spanning three orders of magnitude were resolved in gel samples, included sinking particles as small as 11μm. At BATS, the number flux of small particles tended to increase with depth, whereas the number flux of large particles tended to decrease with depth. The carbon content of different sized particles could not be modeled by a single set of parameters because the particle composition varied across locations and over time. The modeled carbon flux by small particles at BATS, including all samples and depths, was 39±20% of the modeled total carbon flux, and the percentage increased with depth in 4 out of the 5months sampled. These results indicate that small particles (<64μm) are actively settling in the water column and are an important contributor to carbon flux throughout the mesopelagic. Observations and models that overlook these particles will underestimate the vertical flux of organic matter in the ocean.

Factors controlling interannual variability of vertical organic matter export and phytoplankton bloom dynamics – a numerical case-study for the NW Mediterranean Sea

Abstract. Mid-latitude spring blooms of phytoplankton show considerable year-to-year variability in timing, spatial extent and intensity. It is still unclear to what degree the bloom variability is connected to the magnitude of the vertical flux of organic matter. A coupled three-dimensional hydrodynamic-biogeochemical model is used to relate interannual variability in phytoplankton spring-bloom dynamics to variability in the vertical export of organic matter in the NW Mediterranean Sea. Simulation results from 2001 to 2010, validated against remote-sensing chlorophyll, show marked interannual variability in both timing and shape of the bloom. Model results show a tendency for the bloom to start later after cold and windy winters. However, the onset of the bloom occurs often when the mixed layer is still several hundred metres deep while the heat flux is already approaching zero and turbulent mixing is low. Frequency and intensity of wind episodes control both the timing and development of the bloom and the consequent export flux of organic matter. The wintertime flux is greater than zero and shows relatively low interannual variability. The magnitude of the interannual variability is mainly determined in March when the frequency of windy days positively correlates with the export flux. Frequent wind-driven mixing episodes act to increase the export flux and, at the same time, to interrupt the bloom. Perhaps counterintuitively, our analysis shows that years with discontinuous, low-chlorophyll blooms are likely to have higher export flux than years with intense uninterrupted blooms. The NW Mediterranean shows strong analogy with the North Atlantic section within the same latitude range. Hence, our results may also be applicable to this quantitatively more important area of the world ocean.

Vertical flux regulation by zooplankton in the northern Barents Sea during Arctic spring

Abstract The influence of zooplankton on vertical carbon export was investigated during three field investigations conducted on and off the northern Barents Sea shelf during bloom conditions in July 2003, 2004 and May 2005. Short-term patterns in vertical flux of organic matter were measured at high vertical resolution (eight depths) in the upper 200 m at 11 stations. Vertical flux of particulate organic carbon (POC) was highly variable between stations and depths, depending on water mass characteristics such as stratification, phytoplankton bloom development, and zooplankton-related activities. Detailed investigations of the vertical flux composition revealed that faecal pellets (FPs) produced by larger meso- and macrozooplankton comprised on average 20% of the vertical POC flux (average for all depths and stations). The relative importance of FP carbon (FPC) increased with depth, and at depths >60 m FPC comprised ∼30% of the vertical POC flux. The main contributors to the FPC flux varied depending on the prevailing water masses and the phytoplankton bloom stage. FPs produced by older copepodite stages of Calanus spp. dominated at most stations, while FP produced by appendicularians and euphausiids dominated at certain depths and stations. A conservative grazing estimate obtained by calculating the ingestion necessary to support the measured FPC at 50 m depth, suggests that average zooplankton community carbon ingestion equals the vertical POC export. This study clearly shows that zooplankton is important for vertical flux regulation. Zooplankton ingest POC in the range of 22–44% of the daily primary production, but accelerate the vertical flux through production of fast-sinking FP.

Effects of organic effluents from a salmon farm on a fjord system. III. Linking deposition rates of organic matter and benthic productivity

The vertical flux of organic matter and infauna production, biomass and abundance at six stations along a gradient away from a salmon farm, located in a western Norwegian fjord at a depth of 230 m and which produced 2910 tonnes of fish in 19 months, was measured repeatedly during an entire on-growth cycle. The study showed that large increases in benthic secondary production can result from the loading of organic waste in nutrient-poor systems like fjords and a strong correlation between annual sedimentation rates of particulate organic matter (carbon and nitrogen) and annual benthic secondary production was found. At the stations that received the bulk of the waste matter (stations situated within 250 m from the mooring point of the farm) infauna production followed feeding regimes at the farm and in 2004 annual benthic secondary production was 40 g ash-free dry weight m − 2 , 50 times as high as the production 550 to 3000 m away from the farm. Production close to the farm was mainly due to the polychaete Heteromastus filiformis and the bivalve Abra nitida in periods with moderate loadings of organic matter, and by the polychaete Capitella capitata in periods with high loadings. The results of the study further indicate that the threshold for increased infauna production in this deep benthic ecosystem had been reached at an annual flux of 500 g C m − 2 and that continuous loadings at this magnitude over time might cause overloading of fish farm localities.

Sediment oxygen consumption and vertical flux of organic matter in the Seto Inland Sea, Japan

Vertical flux of organic matter and rates of sediment oxygen consumption (SOC) were measured in summer 2000 at a muddy sediment site (21 m depth) in the Seto Inland Sea, Japan. During the 26-day experimental period (15 July to 9 August), a diatom bloom occurred, lasting for about a week. The vertical flux of organic carbon and chlorophyll a ( F C and F chl), measured at 12.5 m depth, showed a sharp peak following the development of the bloom. Under these conditions, SOC ranged from 1.4 to 3.0 mmol O 2 m −2 h −1, and it was strongly influenced by the biomass of macrozoobenthos present in the experimental chambers used for SOC measurements. However, macrozoobenthic oxygen consumption made up only 5% of SOC. SOC variations were not coupled with corresponding changes in F C or F chl. The effects of other factors, such as water temperature, as well as levels of sediment chlorophyll a and bacterial abundance, were minor, presumably because these parameters did not vary strongly during the study period. The average SOC value corrected for macrozoobenthos oxygen consumption (1.8 mmol O 2 m −2 h −1) and converted into the decomposition rate of organic material was nearly balanced with the F C averaged over the experimental period (0.7 C m −2 day −1). This indicates that this muddy sediment area in the Seto Inland Sea plays an important role in the degradation of organic material supplied from the water column.

Seasonal variation in production, retention and export of zooplankton faecal pellets in the marginal ice zone and central Barents Sea

Vertical distribution and sedimentation of faecal pellets (FPs) as well as the production rates of FPs by larger copepods were studied during three cruises to the Barents Sea in March and May 1998, and July 1999. Three to five 24-h stations were selected during each cruise, where at least one main station was located in Arctic water (ArW), one in the polar front region (PF) and one in Atlantic water (AW). A winter scenario was encountered in March with very low concentrations of FPs in the water column, most of the time well below 0.1 mg faecal pellet carbon (FPC) per cubic meter, and with sedimentation rates below 3 mg FPC m −2 day −1 at all depths and stations. Increased concentrations of FPs were observed in May and the maximum biomass of FPs was found in ArW (4.8 mg FPC m −3). This was reflected in high vertical flux of FPs in the ArW, just below the chlorophyll maximum (∼150 mg FPC m −2 day −1). FPC sedimentation explained ∼40% of the total particulate organic carbon (POC) export at 90 m depth at this station. Copepod FP production was moderate to high in May, reflecting favourable feeding conditions. Large spatial variation in the estimated retention potential of FPs was observed, ranging from 96% in AW to ∼40% in the PF region. The July scenario did not differ very much from that observed in May. The lowest suspended concentrations and vertical flux of FPs were again observed in AW, in spite of the high pellet-production rate. FPC explained 34% of the POC export out of the upper layer in ArW, 40% in the PF region, but only 8% in AW. The calculated retention potential of 70% of the produced copepod FPs in AW decreased to 60% and 47% in the PF region and ArW, respectively. Krill FPs comprised a significant fraction of both suspended and sedimented FPC throughout the central Barents Sea. The data show that spatial and temporal variations in the FP “retention filter” are extensive and evidently of importance for the patterns of vertical flux of organic matter and the regulation of pelagic–benthic coupling in the Barents Sea.

Particle transport processes at slope environments — event driven flux across the Barents Sea continental margin

Recent studies of the vertical flux of organic matter into the deep ocean have prompted the search for key organic compounds (biomarkers) as tracers for its production, flux and burial into the sediment. Particulate matter was collected with sediment traps moored at the Barents Sea continental margin (75°11.78′N/12°29.21′E; water depth 2050 m) at 610, 1840 and 1950 m depth. The compositions of the organic material in the two bottoms near traps differ significantly. This difference cannot be the result of a change of the vertical sedimentation alone. A combination of biomarker analyses, quantitative microscopy and bulk parameter determinations on water and sediment trap samples is used in this study to demonstrate that a turbidity plume event at the shelf edge is a vehicle to transport organic and lithogenic particles at high velocities to the benthos of the lower continental margin. It is suggested that fine particles were advected into the trap at 1850 m, whereas the coarser fraction of higher settling velocities, passing several resuspension loops entered the lower trap.

Distribution and sedimentation of faecal on the Nordvestbanken shelf, northern Norway, in 1994

Abstract A close seasonal coherence between mesozooplankton and abundance of faecal pellets was encountered at Nordvestbanken, northern Norwegian shelf, in 1994. Mesozooplankton at Nordvestbanken influenced the vertical flux of organic matter by production, consumption, modification, and destruction of faecal pellets. On average, 11-37% of particulate organic, vertical carbon flux was comprised by faecal pellets. The pelagic degradation of organic matter at Nordvestbanken appears to be reduced due to the low pelagic residence time in the upper 100 m of the water column of faecal pellets ( 1.3-8.3 d). The specific seasonal sinking rates of faecal pellets (12-77 m d-1)fell well into the range of in situ and in vitro sinking rates reported in the literature for the dominating classes of faecal pellets al Nordvestbanken, i.e. from calanoid copepods and pteropods. The shape, colour, density, and degree of fragmentation of faecal pellets appears to reflect variations and changir1g preferences in the diet of mes...

Diatom fluxes to the deep sea in the oligotrophic North Pacific gyre at Station ALOHA

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 182:55-67 (1999) - doi:10.3354/meps182055 Diatom fluxes to the deep sea in the oligotrophic North Pacific gyre at Station ALOHA Renate Scharek*, Luis M. Tupas, David M. Karl Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822, USA *Present address: Institut de Ciències del Mar, Passeig Joan de Borbó s/n, E-08039 Barcelona, Spain. E-mail: rscharek@cucafera.icm.csic.es ABSTRACT: Planktonic diatoms are important agents of vertical transport of photosynthetically fixed organic carbon to the ocean's interior and seafloor. Diatom fluxes to the deep sea were studied for 2 yr using bottom-moored sequencing sediment traps located in the vicinity of the Hawaii Ocean Time-series (HOT) program station 'ALOHA' (22°45'N, 158°W). The average flux of empty diatom frustules was around 2.8 x 105 cells m-2 d-1 in both years, except in late summer when it increased approximately 30-fold. Flux of cytoplasm-containing diatom cells was much lower (about 8 x 103 cells m-2 d-1) but increased 500-fold in late July 1992 and 1250-fold in August 1994. Mastogloia woodiana Taylor, Hemiaulus hauckii Grunow and Rhizosolenia cf. clevei var. communis Sundström were the dominant diatom species observed during the July 1992 event, with the former 2 species again dominant in August 1994. The 1994 summer flux event occurred about 3 wk after a documented bloom of H. hauckii and M. woodiana in the mixed-layer and a simultaneous increase in vertical flux of these species. This surface flux signal was clearly detectable at 4000 m, suggesting rapid settling rates. A further indication of very high sinking speeds of the diatoms was the much larger proportion of cytoplasm-containing cells in the bottom-moored traps during the 2 summer events. Cells of H. hauckii and R. cf. clevei var. communis frequently contained endosymbiotic cyanobacteria with heterocysts (cf. Richelia), similar to the cells of these species in the mixed-layer. Our data show for the first time that diatoms containing nitrogen-fixing cyanobacteria contribute directly to the vertical flux of organic matter to the deep sea in the oligotrophic regions. The peak of diatom flux coincided with a significant flux increase of biogenic silica in both years. During periods of rapid sinking, the vertical flux of diatom assemblages out of the uppermost water column seems to be more important than the diatom flux out of the deep chlorophyll maximum layer (DCML). Aggregate formation may be responsible for the fast sinking of the diatoms. KEY WORDS: Biogenic silica · Bottom-moored sediment traps · Deep sea · Diatoms · Vertical particle flux Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 182. Publication date: June 11, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Photosynthesis, respiration, and carbon turnover in sinking marine snow from surface waters of Southern California Bight:implications for the carbon cycle in the ocean

Photosynthesis and respiration were measured in 1 to 6 mm large aggregates (marine snow) collected in the Southern Californian Bight, USA. The aggregates were freely sinking in a vertical flow system with an upward flow velocity which opposed the sinking velocity of individual aggregates during the measurements. The aggregates were net heterotrophic communities at light intensities 500 μE m 2 S 1 . Bacterial densities on aggregates were >2000-fold higher than in the surrounding water. Cytophaga was highly abundant in the aggregate-associated bacterial community as identified by in situ hybridization techniques. Both the respiration rate per aggregate volume and the bacterial densities decreased with increasing aggregate size. The respiration rates normalized to the number of bacteria in single aggregates were 7.4 to 70 fmol C cell 1 d -1 , The aggregate community respired 433 to 984 ng C d -1 per aggregate in darkness, which yielded a turnover time of 8 to 9 d for the total organic carbon in aggregates. Thus, marine snow is not only a vehicle for vertical flux of organic matter; the aggregates are also hotspots of microbial respiration which cause a fast and efficient respiratory turnover of particulate organic carbon in the sea.

Degradation of faecal pellets in Pegea confoederata (Salpidae, Thaliacea) and its implication in the vertical flux of organic matter

Faecal pellets of P. confoederata were maintained in suspension for 10 days and changes in their morphological, microbiological and fatty acid characteristics as well as their resulting sinking rates were followed during this period. Among the morphological characteristics measured, the perimeter, the surface area and the longest dimension decreased linearly with time but their form remained unchanged. The weight decreased. Microbiological concentrations showed three stages, a rapid increase was followed by a rapid decrease and then finally a small re-increase for heterotroph populations and stabilization for autotrophs. Total fatty acid concentration followed a similar pattern to that of microbial concentrations with some exceptions for individual fatty acids. These three stages in degradation were attributed to incubation conditions as well as to trophic relationships. The sinking rates, measured in different turbulent conditions, varied from 2706 to 3646 m day −1 for the fresh faecal pellets and decreased 30% after 10 days incubation whatever the turbulent kinetic energy dissipation rate. For fresh faecal pellets, the observed sinking rates were greater in highly turbulent conditions than in moderately turbulent or in calm conditions. At the beginning of incubation, minimal sinking rates were observed in moderately turbulent conditions and after four days in calm conditions. This was attributed to the state of degradation of the faecal pellets. Considering the wind induced turbulence for the 0 to 200 m layer, high wind speeds delay sinking rates and increase residence times when compared to moderate or low wind speeds. According to our calculations, the residence times in this superficial layer of faecal pellets of P. confoederata, an oceanic salp species, never exceed 100 min (calculated for wind speeds varying from 0 to 24 m s −1).

Oxygen budget methods to determine the vertical flux of particulate organic matter with application to the coastal waters off western Scandinavia

Oxygen budget methods to determine the vertical flux of particulate organic matter in the sea are presented and discussed. Most attention is devoted to oxygen budgets for aphotic stagnant waters, e.g. in fjordic sill basins, but oxygen budgets for the photic layer are also covered. Overall results on the vertical flux of organic matter obtained from the two oxygen budget methods are presented. It is found that the vertical flux of organic matter generally decreases with depth. This should be an effect of pelagic remineralization. Starting in the Baltic Sea, the contemporary vertical flux of organic matter along the Scandinavian west coast shows a minimum in Öresund from where it increases to a maximum in the coastal zone of eastern and northern Skagerrak. Along the Norwegian west coast the vertical flux appears to be approximately constant and about the same as in the open Skagerrak. The vertical flux of organic matter has increased in the Baltic since the 1950s and there is strong evidence that there has been an increase along the eastern and northern coasts of Skagerrak and in Kattegat during the last 15 years, approximately. The open Skagerrak, less influenced by outflowing Baltic Sea water, showed a decrease in the vertical flux of organic matter in the period 1957–1982. Highly elevated rates of oxygen consumption are found in some fjordic sill basins. For fjords discharging directly into the open sea, it is thought that this may be due to transient transport of large quantities of macroalgae into the fjords which had previously been dislodged in the coastal zone during events of extremely strong winds and waves.

Influence of dissolved silicate on vertical flux of particulate biogenic matter

The influence of dissolved silicate (DSi) addition on primary production, phytoplankton development and subsequent vertical export of particulate matter was studied in enclosures. Blooms of different phytoplankton communities were initiated in the upper part of 10 m deep enclosures supplied with nitrate and phosphate (NP) and nitrate, phosphate and silicate (NPS). Primary production was 31% higher in the NPS enclosure as compared to the NP enclosure over the experimental period of 27 days. Increased phytoplankton growth was mainly caused by mass development of diatoms in the NPS enclosure. Enhanced growth was accompanied by an increased vertical flux of organic matter (86, 15.9 and 16.9% in terms of chlorophyll, particulate nitrogen and particulate carbon, respectively) and was dominated by diatoms. The present study indicates that for each gram of DSi added, vertical flux was enhanced by 3.6 g C, implying that the ratio of DSi added/carbon exported was close to the Redfield ratio. Thus DSi presence appears to decrease the nutrient turn-over time in the euphotic zone by increasing vertical export. This may improve water quality of the surface layer of eutrophicated environments, but can lead to oxygen depletion of bottom waters.