In order to discriminate between graphitic black carbon (GBC) from different sources, we separated surface sediments from two contrasting environments according to size and density and analyzed the ...fractions for GBC. In Lake Washington, an urban lake, over 70% of the GBC was in the two lightest fractions (<2.0 g/cm
3), and over half the GBC was smaller than 3 μm, suggesting that most of the GBC in this lake is light, small combustion-derived soot-black carbon (BC). In contrast, over 70% of the GBC from the Washington Coast sediment fell into the two heaviest fractions (>2.0 g/cm
3), and 70% was silt-sized (3–63 μm). These data suggest that Washington Coast Slope GBC is dominated not by combustion-derived soot but by mineral-associated carbon, probably weathered out of continental rocks, and support previous research suggesting that petrogenic graphite is the source of this carbon (Dickens, A.F., Gélinas, Y., Masiello, C.A., Wakeham, S., Hedges, J.I., 2004. Reburial of fossil organic carbon in marine sediments. Nature 427 336–339). Based on the physical separation of the two types of GBC, we estimate that the Lake Washington GBC contains ∼73% soot-BC, whereas the Washington Coast GBC is ∼70% rock-derived GBC. The evidence for two different sources of sedimentary GBC indicates that this pool of carbon is not a homogenous subfraction of BC, and caution must be used when interpreting the results of this and other BC analyses. The different physical properties of the two GBC subfractions suggest that they will follow different distribution pathways in the environment.
Amino acid analyses were performed on a suite of potential organic matter sources to coastal marine environments. They yielded no source-indicative compositional parameters, but microbes produced ...markedly higher carbon-normalized yields than did vascular plant tissues. Sediment trap samples collected monthly for a year at 30 and 60 m in Dabob Bay, Washington, were also analyzed, as were subsamples from a sediment core taken at the same site. Amino acid yields from the trap samples exhibited spring and fall maxima that coincided with blooms, and a winter minimum that resembled yields in underlying sediments. Amino acids in all samples were primarily of marine origin and low yields in winter traps resulted from low planktonic production, selective amino acid loss, and resuspension of amino acid-depleted sediments. Nonprotein amino acid levels and the fraction of total N represented by amino acids are indices of diagenetic alteration. Amino acids accounted for 13-37% of the total organic C and 30-81% of the total N in the 30-m samples, and, on average, 10 and 37% of sedimentary C and N. Midwater amino acid fluxes also displayed a winter minimum and spring and fall maxima; they were more pronounced than fluxes of bulk particles or C, due to a lesser influence of resuspension. On average,$\thicksim 80%$of the total midwater particulate amino acid flux was lost prior to incorporation in surface sediments. Amino acids were degraded selectively and represented 35 and 71% of the C and N remineralized at the benthic interface. The labile fraction closely resembled fresh plankton in its amino acid composition and carbon-normalized yield. Although trapping of poisoned zooplankton may have caused some artificially high amino acid yields, diagenesis was apparently the primary control on calculated reactivities. Among the amino acids, reactivity patterns indicated relative preservation of diatom cell-wall protein. Within the sediments, amino acids were again degraded preferentially relative to organic C and N, but no downcore compositional changes were observed. Midwater and sediment burial fluxes of planktonic amino acids represented, respectively,$\thicksim 13$and 2.5% of annual mean amino acid production by primary producers.
A laboratory experiment was conducted in which14C-labeled diatoms (Thalassisora weissflogii) were fed to an herbivorous copepod zooplankton (Calanus pacificus). Digestion efficiencies, as defined by ...changes in concentration relative to biogenic silica from the diet to fecal pellets, were calculated for14C, organic carbon, nitrogen, and chlorophyll-type pigments as well as proteins (as amino acids) and polysaccharides (as aldoses). The majority of organic material ingested (≥ 65% of all components except pigments, 30%) was digested. Digestion efficiencies were similar to reactivity patterns observed in previous studies of the same organisms (total N > organic C > total chlorophyll-type pigments). Polysaccharides and particularly amino acids were clearly important nutrients for copepods. However, together with chlorophyll-type pigments, these biochemicals accounted for only 57% of organic C in the diatom and only 35% in fecal pellets. Although lipids represented some fraction of the uncharacterized materials, an important, relatively stable diatom component remained unidentified and apparently was concentrated in the fecal pellets. Individual amino acids and especially aldoses were digested to differing degrees, apparently due to preferential digestion of intracellular materials with concomitant preservation of cell-wall polymers in the fecal pellets. Overall, egested materials were dramatically altered in composition relative to the diet. Digestion efficiencies for all components were similar in magnitude and patterns to reactivities observed in temperate coastal sites in which diatoms and copepods are important contribution to plankton population and sinking particle fluxes.
In simulation studies of the ocean's role in the global carbon cycle, predicting the depth-distribution for remineralization of particulate organic carbon (POC) is of particular importance. Following ...Sarmiento et al. (Global Biogeochemical Cycles 7 (1993) 417), most simulation models have the power-law curve of Martin et al. (Deep-Sea Research 34 (1987) 267) for this purpose. The Martin et al. curve is an empirical fit to data, most of which is from shallow floating sediment traps. Using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself, so that the organic-carbon flux
F
OC(
z) at any depth
z can be predicted from the flux of organic carbon
F
OC(
z
0) at some near-surface depth
z
0. Here, we challenge this basic premise, arguing that fluxes of ballast minerals (silicate and carbonate biominerals, and dust) determine deep-water POC fluxes, so that a mechanism-based model of POC flux must simultaneously predict fluxes of both POC and ballast minerals. This assertion is based on the empirical observation that POC fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean. Here, we develop a model structure that incorporates this observation, and fit this model to US JGOFS EqPac data. This model structure, plus the preliminary parameter estimates we have obtained, can be used to explore the implications of our model in studies of the ocean carbon cycle.
Biogeochemistry of Carbon in the Amazon River Richey, Jeffrey E.; Hedges, John I.; Devol, Allan H. ...
Limnology and oceanography,
March 1990, Letnik:
35, Številka:
2
Journal Article
Recenzirano
Depth-integrated, discharge-weighted water samples were collected over 1,800 km of the Amazon River on eight cruises at different stages of the hydrograph, 1982-1984. Fine (FPOC, $< 63 \mu m$) and ...coarse (CPOC, $> 63 \mu m$) particulate organic carbon as weight percentage of suspended sediment varied between 0.9-1.5% for FPOC and 0.5-3.4% for CPOC. Concentrations of FPOC ranged from $5 mg liter^-1$ upriver to $2 mg liter^-1$ downriver in the mainstem and from $6 mg liter^-1$ in the Rio Madeira to < 1 in the Rio Negro. CPOC had similar distribution patterns, but with concentrations 15-30% those of FPOC. Dissolved organic carbon (DOC) averaged $4-6 mg liter^-1$ in the mainstem and up to $12 mg liter^-1$ in the Rio Negro. Upriver dissolved inorganic carbon (DIC) concentrations of about $1,200 \mu M$ were diluted by tributaries and floodplain drainage to $600 \mu M$ at the most downriver site. Evasion of $CO_2$, invasion of $O_2$, and in situ oxidation were of comparable magnitude, $3-8 \mu mol m^-2 s^-1$. The average export of total organic carbon (TOC) was $36.1 Tg yr^-1$ $(8.5 g m^-2 yr^-1)$, of which 62% was DOC, 34% was FPOC, and 4% was CPOC. TOC inputs were insufficient to support in situ oxidation by a factor of at least two. A relatively small, rapidly cycling pool of labile organic matter may coexist with a much larger pool of more refractory material.
Laboratory and field experiments were conducted to determine the effectiveness of various poison, preservative, and antibiotic treatments currently in common use in sediment work. Our results agree ...with previous reports that most biological activity in sediment traps can be inhibited by appropriate concentrations of formaldehyde, chloroform, or mercuric chloride. Sodium azide probably too ineffective for long-term deployments. On the basis of laboratory experiments, effective concentrations when sustained throughout the deployment are 50% saturated chloroform, 37 mM formaldehyde, or$180 \muM HGCl_2.$Our results also indicate, however, that the weight of swimmers (zooplankton which swim into the trap and die there from contact with the poison) collected in sediment traps is higher when more effective treatments are used. The presence of large numbers of swimmers can greatly affect the flux and composition of particulate organic matter collected in sediment traps is higer when more effective treatments are used. The presence of large numbers of swimmers can greatly affect the flux and composition of particulate organic matter collected in sediment traps and may decrease the effectiveness of the various treatments in inhibiting microbial activity in the traps.
Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed ...for lignin oxidation products as well as elemental and stable carbon isotope compositions. The sediment core was compositionally uniform over its entire 50-cm length. The elemental and lignin compositions of the sediment trap and core samples indicate nitrogen-rich $(atomic C:N\cong 7.5)$ plankton-derived organic matter mixed with vascular plant debris. At most, vascular plant debris accounts for 10% (nonwinter months) to 35% (winter months) of the total organic carbon in the upper water column (30 m) sediment trap samples and consists predominantly of gymnosperm wood along with some nonwoody gymnosperm tissues and angiosperm woods. Bulk land-derived organic matter in Dabob Bay contains a maximum of 50% vascular plant debris and comprises an average of one-third of the total organic carbon in the sediment trap samples and two-thirds of the total organic carbon in the underlying sediments. Lignin in the sediment trap and core samples shows evidence (from elevated vanillic acid-vanillin ratios) of white-rot fungal degradation before (but not after) introduction to the water column at the study site. Vascular plant debris introduced to the bay has already lost almost half of its initial bulk polysaccharide. Glucose yields are particularly low whereas rhamnose and fucose are obtained in excess of expected yields and must have additional sources. Lignin and neutral sugars together account for $<20%$ of the total organic carbon in the sediment trap and core samples. Overall, the sediments of Dabob bay compositionally resemble the gymnosperm wood-rich particulate material introduced to the overlying water column during winter and poorly record the input of plankton and other types of vascular plant debris during nonwinter months.
The performance of a dissolved organic carbon (DOC) analyzer operating on the principle of high-temperature combustion (HTC) is subject to numerous design and operation characteristics. Here we ...describe modifications and performance tests of a commercial HTC analyzer (MQ Scientific, model MQ-1001), many of which are applicable to other HTC instruments. Design improvements include a new combustion column, auto-sampler needle assembly, and a smaller sparger/water trap that automatically maintains constant water level and pH. Techniques for monitoring and compensating for carrier gas flow rate fluctuations, as well as electronic improvements to the auto-sampler advance control and the high-pressure injection gas pulse, are also described. A new model LICOR 7000, nondispersive IR (NDIR) detector is shown to provide a 50-fold increase in sensitivity over the previous LICOR 6252 model.
The total blank for the modified instrument is initially ∼27 ng C and declines during use to ∼9 ng C as the combustion column ages. For an instrument with a well-conditioned combustion column, approximately half of this background is resolvable into a reagent component coming largely from the deionized, UV-irradiated (DUV) water used to rinse the sample onto the combustion column: the other half is intrinsic to the instrument and appears associated with the quartz bead packing. Injection of varying volumes of DUV water with and without an added constant C background, indicates that our DUV water contains between 2 and 9 μM DOC, depending on the variable performance of the water purifier. Similar experiments indicate that the intrinsic instrument blank is variable over time and depends complexly on both the wait time between individual water injections and the overall time that the combustion column has been conditioned. The modified instrument fitted with the new LICOR 7000 detector measures 46.1±1.3 μM DOC in Sargasso Sea water reference material (44–45 μM) against a total instrument blank equivalent to about a fourth of this value. Overall, the modified MQ-1001 analyzer is capable of dependable, automated analysis of relatively challenging deep seawater samples with an average accuracy of about ±3.8% of the consensus value.
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