Sinking Particulate Organic Matter Research Articles

Variations in the chemistry of the Black Sea on a time scale of decades (1960–1995)

We use data collected on 52 cruises from 1960 to 1995 to analyze the decadal variability in basic chemical properties (oxygen, sulfide, nitrate, phosphate and silicate) throughout the water column of the Black Sea. This analysis reveals some new features in the recent evolution of the chemical structure of the Black Sea: an increase in the inventory of sulfide and nutrients in the anoxic zone, a decrease in the inventory of oxygen in the upper layer, and variations in the thickness of the sub-oxic zone. These changes suggest that an increase in the flux of sinking particulate organic matter (POM) has perturbed the biogeochemistry of the Black Sea. The flux balance that controlled the distribution of nutrients before the early 1970s has been modified due to intensive eutrophication. That has led to an increase in the inventory of nutrients in the anoxic zone due to an increased flux of POM. This increased flux of POM increased the rate of sulfate reduction and created an imbalance in the sulfide budget. As a result, sulfide concentrations have increased in the anoxic zone over the past 20 to 25 years. Additional anthropogenic changes are reflected in the distributions of nitrate and oxygen. Climate related and anthropogenic changes in the sources and sinks of these compounds appear to be equally important for causing variations in their inventory. Unlike oxygen and nitrate, the budget of sulfide depends primarily on the flux of sinking POM and the intensity of the lateral flux of oxygen contained in the Bosporus plume. More than 50% of sulfide production appears to be oxidized by the lateral ventilation flux of oxygen. Thus, different processes govern the dynamics of the upper and lower boundaries of the sub-oxic zone. Variations in the upper boundary of suboxic zone depend on consumption of oxygen by the flux of sinking POM, while the lower boundary is controlled by the balance between the upward flux of sulfide within the anoxic zone and the lateral flux of oxygen associated with the Bosporus plume.

Evidence for non-selective preservation of organic matter in sinking marine particles

The sinking of particulate organic matter from ocean surface waters transports carbon to the ocean interior, where almost all is then recycled. The unrecycled fraction of this organic matter can become buried in ocean sediments, thus sequestering carbon and so influencing atmospheric carbon dioxide concentrations. The processes controlling the extensive biodegradation of sinking particles remain unclear, partly because of the difficulty in resolving the composition of the residual organic matter at depth with existing chromatographic techniques. Here, using solid-state 13C NMR spectroscopy, we characterize the chemical structure of organic carbon in both surface plankton and sinking particulate matter from the Pacific Ocean and the Arabian Sea. We found that minimal changes occur in bulk organic composition, despite extensive (>98%) biodegradation, and that amino-acid-like material predominates throughout the water column in both regions. The compositional similarity between phytoplankton biomass and the small remnant of organic matter reaching the ocean interior indicates that the formation of unusual biochemicals, either by chemical recombination or microbial biosynthesis, is not the main process controlling the preservation of particulate organic carbon within the water column at these two sites. We suggest instead that organic matter might be protected from degradation by the inorganic matrix of sinking particles.

Modeling distinct vertical biogeochemical structure of the Black Sea: Dynamical coupling of the oxic, suboxic, and anoxic layers

A one‐dimensional, vertically resolved, physical‐biogeochemical model is used to provide a unified representation of the dynamically coupled oxic‐suboxic‐anoxic system for the interior Black Sea. The model relates the annual cycle of plankton production in the form of a series of successive phytoplankton, mesozooplankton, and higher consumer blooms to organic matter generation and to the remineralization‐ammonification‐nitrification‐denitrification chain of the nitrogen cycle as well as to anaerobic sulfide oxidation in the suboxic‐anoxic interface zone. The simulations indicate that oxygen consumption during remineralization and nitrification, together with a lack of ventilation of subsurface waters due to the presence of strong stratification, are the two main factors limiting aerobic biogeochemical activity to the upper ∼75 m of the water column, which approximately corresponds to the level of nitrate maximum. The position of the upper boundary and thus the thickness of the suboxic layer are controlled by upper layer biological processes. The quasi‐permanent character of this layer and the stability of the suboxic‐anoxic interface within the last several decades are maintained by a constant rate of nitrate supply from the nitrate maximum zone. Nitrate is consumed to oxidize sinking particulate organic matter as well as hydrogen sulfide and ammonium transported upward from deeper levels.

Distribution, partitioning and fluxes of dissolved and particulate organic C, N and P in the eastern North Pacific and Southern Oceans

Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POC susp), nitrogen (DON and PON susp) and phosphorus (DOP and POP susp), and of suspended particulate inorganic phosphorus (PIP susp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POM sink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POM susp) concentrations were similar. Concentrations of DOM and POM susp displayed unique C, N and P distributions, with POM susp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POM susp, POM sink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POM susp and POM sink fluxes were 8–20 and 28–52% of the total.

Amino acid and hexosamine composition and flux of sinking particulate matter in the equatorial Pacific at 175°E longitude

Sinking matter collected by sediment traps, which were deployed in the equatorial Pacific Ocean at 175°E for about 11 months during 1992–1993, were analyzed for their flux and labile components in terms of amino acids and hexosamines. The samples provided a temporal resolution of 15 days and were collected from 1357 (shallow trap) and 4363 m (deep trap) depths where sea floor depth was 4880 m. Particle flux along with major components (carbonate, organic matter, biogenic opal and lithogenic material) and amino acid parameters showed distinct temporal variations, which were more pronounced in the shallow trap relative to deep trap. A coupling between the fluxes in the shallow and deep traps was more evident during the period of maximum particle flux, which seems to be connected with the short reappearance of non-El Niño conditions in equatorial Pacific during the 1991–1993 El Niño event. The biogeochemical indicators C/N, Asp/Bala, Glu/Gaba, Bala+Gaba mol%, THAA-C% and THAA-N% implied that the increase in sinking flux was associated with upwelling and enhanced surface production. Degradation of sinking particulate organic matter between the shallow and deep traps was also evident. Occasionally higher mass and major component fluxes in the deep trap relative to the shallow trap are attributed to contribution of resuspended particulates from sea floor (nepheloid layer) or to laterally advected particulates from nearby areas. Carbonate and opal composition of the sinking flux showed a predominance of calcareous plankton; however, Asp/Gly mol ratio and Ser+Thr mol% indicated enhanced occurrence of diatoms during the periods of higher flux.

Organic geochemical studies of sinking particulate material in China sea area(I)

Sinking particulate material collected from Nansha Yongshu reef lagoon and the continental shelf of the East China Sea by sediment traps has been analyzed and studied for the first time using organic geochemical method. The results show that about half of the sinking particulate organic matter in the two study areas are consumed before reaching the depth of 5 m to the sea floor and the degree of this consumption in Yongshu reef lagoon is larger than that in the continental shelf of the East China Sea. The distributions of hydrocarbons and fatty acids indicate that the minor difference of biological sources of sinking particulate organic matter exists between Yongshu reel lagoon and the continental shelf of the East China Sea, but they mainly come from marine plankton. Stronger biological and biochemical transformations of sinking particulate organic matter are also observed and the intensity of this transformation in Yongshu reef lagoon is greater than that in the continental shelf of the East China Sea. It is found that the occurrence of C-25 highly branched isoprenoid (HBI) diene may be related to the composition of diatom species.

Long time-series monitoring of an abyssal site in the NE Pacific: an introduction

Deep-Sea Research II 45 (1998) 573—586 Long time-series monitoring of an abyssal site in the NE Pacific: an introduction K.L. Smith, Jr.!,*, E.R.M. Druffel ! Marine Biology Research Division 0202, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA Department of Earth System Science, University of California, Irvine, Irvine, CA 92697, USA Received 20 October 1997; in revised form 31 October 1997; accepted 4 November 1997 1. Introduction Abyssal regions of the world ocean cover more than 50% of the Earth’s surface (Gage and Tyler, 1991) but the biogeochemical processes in the sediments and deep water column of this vast expanse of our globe are poorly understood. The cycling of material through these deep-sea regions is intimately linked to the organic matter produced in the euphotic zone. The material sinks as particulate matter, undergoing various physical and biochemical transformations in the water column before reach- ing the seafloor. Temporal variability of plankton production in the upper ocean is well documented. The fraction of this production that escapes the euphotic zone as particulate organic matter sinking into the deep sea also exhibits temporal variability, reflecting the changes in surface water production. Independent long time-series measurements of particulate organic matter fluxes to abyssal depths (e.g. Deuser et al., 1981; Honjo, 1982; Deuser, 1986; Haake et al., 1993) and time-lapse photographic records of phytodetrital pulses reaching the sea floor (e.g. Billett et al., 1983; Lampitt, 1985; Rice et al., 1986), although taken in widely separated areas of the deep ocean, have been invaluable for predicting events in other regions. However, the cycling of organic matter in the deep ocean has been difficult to evaluate because synoptic measurements on sufficiently long time scales are rare. The lack of long time-series measurements to examine concurrently the input of a pelagi- cally derived food supply and its impact on benthic boundary layer (BBL) processes *Corresponding author. Fax: 001 619 534 7313; e-mail: ksmith@ucsd.edu. 0967-0645/98/$19.00 ( 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 - 0 6 4 5 ( 9 7 ) 0 0 0 9 4 - 5

Horizontal and Vertical Isotopic Model of Lake Biwa Ecosystem.

Nitrogen and carbon isotope ratios of organisms were measured in order to elucidate and illustrate the food web structure in Lake Biwa. Samplings of particulate organic matter (POM), zooplankton, and fish were performed at the north basin from 1993 to 1994. The food web structure of Lake Biwa (north basin) was divided into five parts judging from carbon and nitrogen isotope ratios. A clear trophic effect of ca. 3‰ was found as δ15N for the pelagic food chain in the following order : small POM (2.7 to 40 μm) →Eodiaptomus japonicus → Plecoglossus altivelis altivelis, Hypomesus transpacificus → Salmo masou macrostomus, and Silurus biwaensis (euphotic zone food chain - 1). This was considered the major food chain and was manifested in the surface layer. The other food chains in the euphotic zone, hypolimnion, lake bottom and coastal zone were described as follows ; POM with low δ15N → Daphnia galeata (euphotic zone food chain -2), sinking large POM (40 to 150 μm) and organic matter in mud →Jesogammarus annandalei (hypolimion food chain), organic matter in mud → oligocheata (lake bottom food chain), and attached algae →Sarcocheilichthys variegatus and Rhinogobius sp. (coastal zone food chain). The above mentioned food web structure seems to reflect physical environment at factors such as vertical and horizontal water movements, the sinking of particulate organic matter, and the geographical setting of Lake Biwa.

Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δ15N, δ13 and δ14

Sinking particles were analyzed for their nitrogen isotopic ratio δ 15N) of total particulate nitrogen (PN), stable carbon isotopic ratio ( δ 13C) and radioactive isotopic ratio ( δ 14C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ 15N and δ 13C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ 15N and δ 13C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ 14C of sinking POC. After this correction, common downward decreasing trends in δ 15N and δ 13C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ 15N and δ 13C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of 15N- and 13C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.

Organic geochemical studies of sinking particulate material in China sea area II

We have for the first time studied the compositions of ketone, aldehyde and alcohol lipid compounds in sinking particulate materials from Yongshu Reef lagoon and the continental shelf of the East China Sea collected by sediment trap sampling apparatus. The results indicate that sinking particulate materials contain abundant isoprenoid ketone, aldehyde and alcohol lipid compounds which take part in marine chemical cycling. The compositional features of these compounds show that sinking particulate organic matter mainly comes from autochthonous marine organisms and Yongshu Reef lagoon has more submerged macrophytes-derived component, while the continental shelf of the East China Sea contains more dinoflagellate-derived constituent. The contribution of higher land plant to sinking particulate organic matter may be very small. In contrast, it is greater in Yongshu Reef lagoon than that in the continental shelf of the East China Sea. Sinking particulate organic matter in the two regions undergoes strong biochemical transformation processes before reaching the depth of 5 m to the sea floor, and its intensity is greater in Yongshu Reef lagoon than in the continental shelf of the East China Sea. These results have certain reference value to the researches of marine chemistry, marine biology and marine sedimentology in China, and reveal the importance of organic geochemistry to the study of oceanology.

What controls dissolved iron concentrations in the world ocean?

Dissolved (< 0.4 μm) iron has been measured in 354 samples at 30 stations in the North and South Pacific, Southern Ocean and North Atlantic by the Trace Metals Laboratory at Moss Landing Marine Laboratories. These stations are all more than 50 km from a continental margin. The global distribution of dissolved iron, which is derived from these profiles, is remarkable for several reasons. The dissolved iron profiles have a uniform shape with a nutrient-like profile at each station. Concentrations at the surface are all < 0.2 nmol kg −1 and average 0.07 nmol kg −1 . Below 500 m, the average concentration is 0.76 nmol kg −1 . The largest value in the data set is 1.38 nmol kg −1 . There is no inter-ocean fractionation, which is unique for an element with a nutrient-like profile. Published estimates of the iron residence time are on the order of 100 to 200 yr, indicative of rapid removal. Other elements with such short residence times are characterized by vertical profiles that decrease with depth and deep concentrations that decrease with age as water passes from the Atlantic to the Pacific. This is not the case for iron. The largest horizontal changes in dissolved iron are observed in gradients from the continental margin. There is only a factor of three difference between the minimum (0.4 nmol kg −1 ) and maximum (1.3 nmol kg −1 ) value in the data set at a depth near 750 m, where variability is at a maximum. The minimum concentrations are found at stations in the remote central Pacific and the maximum values occur at stations adjacent to the continental margin. The major source of iron in the deep sea is generally aeolian deposition. Integrated (surface to 500 m) concentrations of iron at each station are only weakly correlated with the aeolian iron deposition flux, however. This contrasts with other elements such as lead that also have strong atmospheric sources. These observations lead us to conclude that the nutrient-like profile is maintained by a mechanism that reduces the scavenging rate of dissolved iron at concentrations less than 0.6 nmol kg −1 . This mechanism may be complexation by strong iron binding ligands, which have been found in both the Atlantic and Pacific at concentrations near 0.6 nM. This apparent solubility would act to diminish inter-ocean fractionation. It would allow a nutrient-like profile to develop before scavenging began to remove iron. In order to test the concept, we developed a numerical model to make quantitative predictions of dissolved iron concentrations from place to place. The dissolved iron source in the ocean interior is remineralization from sinking particulate organic matter. Scavenging removes dissolved iron only at concentrations greater than the apparent solubility. The only geographically variable parameter in the model is the export flux of carbon from the surface layer, which carries iron with it. The model generated dissolved iron profiles, based on measured or estimated values of the carbon export flux, are in remarkable agreement with the observed profiles at all stations from the North Atlantic through the Southern Ocean to the North Pacific.

Radiocarbon in organic compound classes in particulate organic matter and sediment in the deep northeast Pacific Ocean

Radiocarbon (Δ14C) and stable carbon isotopes (δ13C) were measured for total amino acids, carbohydrates, lipids and acid‐insoluble organic fractions separated from sinking particulate organic matter (POMsink), detrital aggregates, sediment floe and sediments collected from the deep Northeast Pacific Ocean. The results show distinct Δ14C signatures among these organic compound classes. Bomb 14C, produced 3–4 decades ago in the atmosphere, was present in all organic fractions in the POMsink in the deep sea. Δ14C values decrease with depth, from the sediment trap POMsink (3450 m) to the sediment (4100 m), with rapid changes occurring at the sediment‐water interface. Total lipid had much ‘older’ Δ14C values than those of amino acid and carbohydrate fractions in detrital aggregates, sediment floe and sediments. These data demonstrate that two processes may be occurring: 1) preferential decomposition of organic matter at the sediment‐water interface, and 2) incorporation of ‘old’ organic carbon into POM and sediment. The alteration of carbon found in these organic compound classes suggests that differences in decomposition and chemical behavior exist for each of these compound classes in the deep ocean.

Zooplankton biomass and grazing at the JGOFS Sargasso Sea time series station

We examined the variability in zooplankton biomass and grazing in the upper 200 m at the JGOFS time series station off Bermuda during 3 week periods in August 1989 and in March/April 1990. The average-integrated 64 μm zooplankton biomass was similar in August (571 mg C m −2) and March/april (592 mg C m −2). However, macrozooplankton (200 μm) represented a greater portion of total (64 μm) zooplankton biomass in March/April (75%) as compared to August (30%). The average estimated rate of phytoplankton ingestion was higher in March/April (3.7 mg C m −2 h −1) compared to August (0.6 mg C m −2 h −1), with macrozooplankton (200 μm) contributing more to the estimated flux in March (65%) compared to August (14%). Our estimates of 3 times greater macrozooplankton biomass in March/April is similar in magnitude to the differences in the estimated flux of organic material from the photic zone during these seasons. In addition, short-term changes in the sinking of particulate organic matter during our March/April cruise were consistent with increases/decreases in macrozooplankton biomass and grazing.

Vertical fluxes of biogenic particles and associated biota in the eastern North Pacific: Implications for biogeochemical cycling and productivity

Previously published data on vertical fluxes of particulate carbon (PC), nitrogen (PN), organisms (MICRO), and extracted adenosine triphosphate (ATP) into screened sediment traps (335 μm) from the VERTEX 5 and ADIOS I programs are reexamined as they relate to biogeochemical cycling and oceanic productivity. The four stations discussed represent an oligotrophic to mesotrophic gradient in total primary production (PT), ranging from 245 to 1141 mg Cm−2 d−1 and a gradient in PC flux from the euphotic zone, ranging from 12 to 164 mg Cm−2 d−1 for particles &lt;335 μm in diameter. Vertical fluxes of PC, PN, MICRO, and ATP decreased as negative power functions of depth with significantly higher depth‐dependent losses for ATP fluxes. The flux of intact biota (free, particle‐associated, and some active “swimmers,” measured microscopically and by extracted ATP) decreased rapidly in the upper 200 m, contributing as much as 52.4% at the most productive station and as little as 1.6% to the flux of PC at oligotrophic stations, remaining relatively constant or increasing slightly (to 3.4 ‐ 9.6% PC flux) between 200 and 2000 m. Multiple regression analyses, expressing fluxes as functions of depth and PT or new production, PN, demonstrated that MICRO and ATP fluxes were more dependent on PT, PN, and depth than bulk PC or PN fluxes. The present analysis illustrates that while sinking particulate organic matter (POM) undergoes rapid attrition in the upper water column, the fluxes of sedimenting biota decrease at even higher rates. Findings support the hypothesis that in oceanic waters, POM sinking from the euphotic zone rapidly becomes a poor habitat for associated microbes, and mechanisms other than remineralization by attached microbes must be invoked to explain observed fluxes and attrition rates. This study also supports the hypothesis that the vertical flux of intact organisms is a more sensitive and less ambiguous record of upper ocean processes than bulk flux measurements of total mass, PC, or PN. Therefore time‐resolved measurement of the flux of biota may be useful in estimating PT and PN in the overlying waters.

Particulate organic sulfur in the waters of the Southern California Bight

The organic sulfur content of suspended and sinking particulate matter was examined in the upper 1000 m of the water column in the Southern California Bight. Depth distributions of suspended particulate organic sulfur (POS) showed a subsurface maximum in most stations that deepened offshore. POS concentrations in suspended matter averaged 1.26 ± 0.50 μg S L−1 within the euphotic zone during the two cruises analyzed (August and October, 1987). The downward fluxes of mass, carbon, nitrogen and sulfur of sinking particulate matter increased with increasing sample depth to 350 m in the water column. Fluxes were similar during the three deployments. POS was correlated with and directly proportional to POC, PON, and chlorophyll a in the suspended material. Similar correlations were obtained in the trap material although a positive POC intercept value suggested the presence of more refractory material, with sulfur being selectively removed relative to carbon. The average molar ratios were C : N : S = 224 : 27: 1 in suspended and 119 : 17 : 1 in sinking particulate organic matter. Particulate organic sulfur appeared to have a biological origin, most likely planktonic.

Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity.

The sinking of particulate organic matter from the euphotic zone is an important pathway for the vertical transport of many elements and organic compounds in the sea. Many natural and artificial radionuclides in surface waters are readily adsorbed onto suspended particles and are presumably scavenged and removed to depth on time scales commensurate with both particle sinking rate and retention time of the radionuclide on the particle. Previously, abyssal benthic organisms from the northeast Pacific were found to contain short-lived fission products which entered the sea surface as fallout from nuclear testing. The presence of these radionuclides at great depth could not be explained by Stokesian settling of small fallout particles and it was hypothesized that zooplankton grazing in the surface layers packaged these particle-reactive radionuclides into large, relatively dense faecal pellets which rapidly sank to depth. We report here data from a time-series sediment trap experiment and concomitant zooplankton collections which show conclusively that Chernobyl radioactivity, in particular the rare earth nuclides 141Ce and 144Ce, entering the Mediterranean as a single pulse, was rapidly removed from surface waters and transported to 200 m in a few days primarily by zooplankton grazing.

Lipid composition of the pelagic crab Pleuroncodes planipes, its feces, and sinking particulate organic matter in the Equatorial North Pacific Ocean

Fecal pellets from the pelagic crab Pleuroncodes planipes were a substantial portion of the particulate organic matter in a sediment trap deployed at the bottom of the mixed layer in the eastern tropical North Pacific Ocean. The lipids of fresh P. planipes feces were compared to lipids of the sediment trap material, of mixed zooplankton which may comprise part of the diet of the crab, and of the crab itself in order to elucidate the source of organic compounds found in the trap. Hydrocarbons, wax esters, triacylglycerols, steroidal alcohols, steroidal ketones, and fatty acids were determined by capillary gas chromatography and gas chromatography/mass spectrometry. Significant input of lipids via sedimentation of crab fecal material is indicated, and modification of dietary lipid within the gut of the crab is inferred. Labile dietary fatty acids are depleted and sterols enriched in the fecal pellets and trap material relative to the zooplankton and crab. Nuclear saturated and unsaturated 3-ketosteroids and unsaturated steroidal hydrocarbons were detected in the crab, its feces, and in the sediment trap particulate material.