Samples Of Sinking Particles Research Articles

Upwelling Enhances Mercury Particle Scavenging in the California Current System.

Coastal upwelling supplies nutrients supporting primary production while also adding the toxic trace metal mercury (Hg) to the mixed layer of the ocean. This could be a concern for human and environmental health if it results in the enhanced bioaccumulation of monomethylmercury (MMHg). Here, we explore how upwelling influences Hg cycling in the California Current System (CCS) biome through particle scavenging and sea-air exchange. We collected suspended and sinking particle samples from a coastal upwelled water parcel and an offshore non-upwelled water parcel and observed higher total particulate Hg and sinking flux in the upwelling region compared to open ocean. To further investigate the full dynamics of Hg cycling, we modeled Hg inventories and fluxes in the upper ocean under upwelling and non-upwelling scenarios. The model simulations confirmed and quantified that upwelling enhances sinking fluxes of Hg by 41% through elevated primary production. Such an enhanced sinking flux of Hg is biogeochemically important to understand in upwelling regions, as it increases the delivery of Hg to the deep ocean where net conversion to MMHg may take place.

Underestimation of biogenic silica sinking flux due to dissolution in sediment traps: A case study in the South China Sea

The dissolved silicate concentrations in the supernatant of sediment trap sampling bottles retrieved from deep water (1000-3000 m) at four stations in the South China Sea (SCS) were measured to calculate the underestimated flux of biogenic silica (bSi) in sinking particles due to bSi dissolution. High dissolved silicate concentrations in the supernatant, ranging from 122.6 to 1365.8 μmol/L, indicated significant dissolution of particulate bSi in the sampling bottles. Underestimation of the bSi flux in the SCS by ~2% to ~34% (average: ~10%) due to bSi dissolution was revealed, and the degree of underestimation increased with decreasing total bSi flux. The amount of bSi dissolved within the sampling series at each station was generally positively correlated with dissolution time and to a certain extent influenced by the bSi amount collected by the sampling bottles under a low bSi sinking flux. Apparently stronger bSi dissolution was found at two of the four stations due to relatively high bSi dissolution rates, which were possibly related to a higher reactive surface area of the bSi or bacterial activity. Overall, our results demonstrated that the considerable bSi dissolution in sediment trap sampling bottles should not be ignored, especially in the low-productivity oligotrophic ocean, and bSi flux calibration via measurement of the dissolved silicate in sampling bottles is necessary. To reduce bSi flux underestimation due to the deployment of time-series sediment traps, larger-volume sampling bottles should be avoided in the oligotrophic open ocean, and sinking particle samples should be analyzed as soon as the sediment traps are recovered.

Stress factors resulting from the Arctic vernal sea-ice melt

During sea-ice melt in the Arctic, primary production by sympagic (sea-ice) algae can be exported efficiently to the seabed if sinking rates are rapid and activities of associated heterotrophic bacteria are limited. Salinity stress due to melting ice has been suggested to account for such low bacterial activity. We further tested this hypothesis by analyzing samples of sea ice and sinking particles collected from May 18 to June 29, 2016, in western Baffin Bay as part of the Green Edge project. We applied a method not previously used in polar regions—quantitative PCR coupled to the propidium monoazide DNA-binding method—to evaluate the viability of bacteria associated with sympagic and sinking algae. We also measured cis-trans isomerase activity, known to indicate rapid bacterial response to salinity stress in culture studies, as well as free fatty acids known to be produced by algae as bactericidal compounds. The viability of sympagic-associated bacteria was strong in May (only approximately 10% mortality of total bacteria) and weaker in June (average mortality of 43%; maximum of 75%), with instances of elevated mortality in sinking particle samples across the time series (up to 72%). Short-term stress reflected by cis-trans isomerase activity was observed only in samples of sinking particles collected early in the time series. Following snow melt, however, and saturating levels of photosynthetically active radiation in June, we observed enhanced ice-algal production of bactericidal compounds (free palmitoleic acid; up to 4.8 mg L–1). We thus suggest that protection of sinking sympagic material from bacterial degradation early in a melt season results from low bacterial activity due to salinity stress, while later in the season, algal production of bactericidal compounds induces bacterial mortality. A succession of bacterial stressors during Arctic ice melt helps to explain the efficient export of sea-ice algal material to the seabed.

Evaluation of particulate 137Cs discharge from a mountainous forested catchment using reservoir sediments and sinking particles

The time and size dependencies of particulate 137Cs concentrations in a reservoir were investigated to evaluate the dynamics of 137Cs pollution from a mountainous forested catchment. Sediment and sinking particle samples were collected using a vibracorer and a sediment trap at the Ogaki Dam Reservoir in Fukushima, which is located in the heavily contaminated area that formed as a result of the Fukushima Dai-ichi Nuclear Power Plant accident of 2011. The inventory of 137Cs discharged into the reservoir during the post-accident period (965 days) was estimated to be approximately 3.0 × 1012–3.9 × 1012 Bq, which is equivalent to 1.1%–1.4% of the initial estimated catchment inventory. The particulate 137Cs concentration showed a decline with time, but the exponent value between the specific surface area and the 137Cs concentration for the fine-sized (<63 μm) particle fraction remained almost constant from the immediate aftermath of the accident. These quantitative findings obtained by reconstructing the contamination history of particulate 137Cs in reservoir sediments and sinking particles have important implications for the evaluation of 137Cs dynamics in mountainous forested catchments.

Evaluation of particulate 137Cs discharge from a mountainous forested catchment using reservoir sediments and sinking particles

The time and size dependencies of particulate 137Cs concentrations in a reservoir were investigated to evaluate the dynamics of 137Cs pollution from a mountainous forested catchment. Sediment and sinking particle samples were collected using a vibracorer and a sediment trap at the Ogaki Dam Reservoir in Fukushima, which is located in the heavily contaminated area that formed as a result of the Fukushima Dai-ichi Nuclear Power Plant accident of 2011. The inventory of 137Cs discharged into the reservoir during the post-accident period (965 days) was estimated to be approximately 3.0 × 1012–3.9 × 1012 Bq, which is equivalent to 1.1%–1.4% of the initial estimated catchment inventory. The particulate 137Cs concentration showed a decline with time, but the exponent value between the specific surface area and the 137Cs concentration for the fine-sized (<63 μm) particle fraction remained almost constant from the immediate aftermath of the accident. These quantitative findings obtained by reconstructing the contamination history of particulate 137Cs in reservoir sediments and sinking particles have important implications for the evaluation of 137Cs dynamics in mountainous forested catchments.

Relationships between microbial extracellular enzymatic activity and suspended and sinking particulate organic matter: seasonal transformations in the North Water

Abstract Despite the importance of hydrolytic activities by bacterial extracellular enzymes (EE) in the temperate ocean, little is known about the role of extracellular enzymatic activity (EEA) in determining the fate of particulate organic matter (POM) in polar seas. To explore the issue further, we measured various chemical and bacterial parameters in the near-0°C waters of the North Water during the months of May and July of 1998. Seawater (SW) samples were collected by Niskin bottle at the depth of the chlorophyll fluorescence maximum (8–90 m), while samples of sinking particles and aggregates were collected in short-term (0.5–1.2 d), unpoisoned, floating sediment traps deployed at depths typically below the mixed layer (50–136 m). Samples were analyzed for POC, PON, and abundance of total and actively respiring bacteria. They were also incubated with fluorescently tagged substrate analogs to measure potential maximal rates of three classes of EE (leucine-aminopeptidase, chitobiase, and β -glucosidase) at –1°C. The percentage of actively respiring bacteria was always higher in sediment trap samples than in SW (medians of 38% and 24% versus 10% and 12% in May and July, respectively). Cell-specific rates of EEA were also higher in the trap samples and, for both sample types, similar to published rates from temperate waters. Rates of EEA when scaled to the abundance of actively respiring bacteria, however, did not differ between sample types, suggesting that the elevated EEA associated with sinking material is due to the greater abundance of metabolically active cells supported by such material and not due to enhanced enzyme expression in general, as suggested by previous studies. In this study, leucine-aminopeptidase activity was always much higher than the other classes of EEA, becoming even more dominant later in the season; it always correlated positively with the abundance of both total and actively respiring bacteria. Enzyme ratios indicating protease dominance corresponded with the seasonal increases in C/N ratios of both suspended and sinking POM. Overall the results suggest bacterial responses to seasonal changes in POM quality through differential expression of EE and an important role for proteases in influencing the nitrogen content of organic matter even at near-0° temperatures in this polynya.

Characterization of sinking particles in the ocean by pyrolysis-gas chromatography/mass spectrometry

Pyrolysis-gas chromatography/mass spectrometry was applied to the study of the composition, source and chemical changes of organic matter in sinking particles, as part of efforts towards the understanding of the transport processes of organic carbon from surface waters to the sea-floor. Sinking particle samples were collected using sediment traps from the Japan Trench (site JT; water depths of 4519 and 8798 m) located in the northern Pacific Ocean. Trap samples from a coastal region of Japan were also analyzed for comparison purposes. The analysis was conducted using a CDS Pyroprobe connected to a gas chromatograph/mass spectrometer. The trap samples produced phenols, aromatic hydrocarbons, nitrogenous compounds, furans, alkenes/alkanes and aliphatic cyanides/fatty acids. These products are largely categorized into three classes of precursor: proteins (nitrogenous compounds such as pyrroles, pyridines, phenylalkyl nitriles and indoles), carbohydrates (furan derivatives) and lipids (alkenes/alkanes, alkyl nitriles/fatty acids). The degree of freshness (FD), defined as the ratio of pyrolysis product x (where x is pyrrole, indole, pyridine, furfural normalized by the sum of the alkanes and alkenes) in a sample to that in a reference material; or the ratio of a pyrrole/pyridine or alkene/alkane in a sample to that in a reference material, was proposed to characterize the trapped organic matter. The results revealed that the FD of organic matter in sinking particles at site JT varies over time.