Radiocarbon in marine bacteria: Evidence for the ages of assimilated carbon

It is generally accepted that marine bacteria utilize labile, recently produced components of bulk dissolved organic matter. This interpretation is based largely on indirect measurements using model compounds and plankton-derived organic matter. Here, we present an assessment of the relative proportions of modem and older dissolved organic carbon (DOC) utilized by marine bacteria. Bacterial nucleic acids were collected from both estuarine (Santa Rosa Sound, FL) and open-ocean (eastern North Pacific) sites, and the natural radiocarbon signatures of the nucleic acid carbon in both systems were determined. Bacterial nucleic acids from Santa Rosa Sound were significantly enriched in radiocarbon with respect to the bulk DOC and were similar to the radiocarbon signature of atmospheric CO2 at the time of sampling, indicating that these bacteria exclusively assimilate a modem component of the estuarine bulk DOG. In contrast, bacterial nucleic acids from the oceanic site were enriched in C-14 relative to the bulk DOC but depleted in C-14 with respect to modem surface dissolved inorganic carbon (DIC) and suspended particulate organic carbon (POCsusp). This suggests that open-ocean bacteria assimilate both modem and older components of DOG. The distinct radiocarbon signatures of the nucleic acids at these two sites (i.e., +120 +/- 17% estuarine vs. -34 +/- 24% oceanic) demonstrate that natural C-14 abundance measurements of bacterial biomarkers are a powerful tool for investigations of carbon cycling through microbial communities in different aquatic systems

Input of particulate organic and dissolved inorganic carbon from the Amazon to the Atlantic Ocean

We report concentrations and isotope measurements (radiocarbon and stable carbon) of dissolved inorganic carbon (DIC) and suspended particulate organic carbon (POC) in waters collected from the mouth of the Amazon River and the North Brazil Current. Samples were collected in November 1991, when the Amazon hydrograph was at its annual minimum and the North Brazil Current had retroflected into the equatorial North Atlantic. The DIC D 14 C results revealed postbomb carbon in river and ocean waters, with slightly higher values at the river mouth. The low DIC delta(13)C signature of the river end-member (-11%) demonstrates that about half of the DIC originated from the remineralization of terrestrially derived organic matter. A linear relationship between DIC and salinity indicates that DIC was mixed nearly conservatively in the transition zone from the river mouth to the open ocean, though there was a small amount (\u3c= 10%) of organic matter remineralization in the mesohaline region. The POC Delta(14)C values in the river mouth were markedly lower than those values from the western Amazon region (Hedges et al., 1986). We conclude that the dominant source of POC near the river mouth and in the inner Amazon plume during November 1991 was aged, resuspended material of significant terrestrial character derived from shelf sediments, while the outer plume contained mainly marine-derived POC

Fossil and contemporary aerosol particulate organic carbon in the eastern United States: Implications for deposition and inputs to watersheds

Atmospheric particulate matter samples were collected from mid-Atlantic and northeastern U. S. (Virginia and New York, respectively) sites to assess the fossil versus contemporary sources contributing to aerosol organic carbon (OC) and the implications for its deposition to watersheds. Mean particulate matter total OC (TOC) deposition rates (wet + dry deposition) were calculated to be 1.6 and 2.4 mg C m(-2) d(-1) for the Virginia and New York sites, respectively. Wet deposition of particulate TOC was determined to be the dominant depositional mode, accounting for \u3e65% (Virginia) and \u3e80% (New York) of total aerosol TOC deposition. Isotopic mass balances suggest that, on average, the deposited aerosol TOC consisted of 66% (Virginia) and 68% (New York) contemporary biomass-derived material. The balance was fossil-derived material (34% and 32% for Virginia and New York, respectively), indicating significant anthropogenic fossil fuel contributions to aerosol TOC. When considered within representative northeastern U. S. watershed OC budgets, aerosol TOC depositional flux was up to 10% of net soil OC accumulation rates, and 5-70% of the OC throughfall flux for forested regions. When scaled to the entire Hudson and York River watersheds, estimated aerosol TOC depositional fluxes ranged from 6.1 to 9.7 x 10(10) g C yr(-1) and from 8.9 to 14 x 10(9) g C yr(-1), respectively, and were similar in magnitude to the mean annual river OC export for these two systems (Hudson, 7.2 x 10(10) g C yr(-1); York, 8.4 x 10(9) g C yr(-1)). These findings underscore the potential importance of both natural and fossil fuel-derived aerosol OC inputs to watersheds

Utilization and turnover of labile dissolved organic matter by bacterial heterotrophs in eastern north Pacific surface waters

Seawater incubation experiments were conducted in June and October 1992 to examine bacterial utilization of labile dissolved organic matter (DOM) in open ocean surface waters of the eastern North Pacific. Natural plankton extract-DOM (PE-DOM) and selected model compounds were added to seawater samples to evaluate bacterial utilization and respiration rates relative to bacterial carbon production rates for the various amendments. PE-DOM always stimulated bacterial production and DOM utilization, and the primary nitrogen source supporting this bacterial production was dissolved organic nitrogen (DON). Utilization of DON during exponential growth was balanced by the production of ammonium for samples amended with PE-DOM. Bacterial growth efficiencies for samples amended with PE-DOM ranged between 3.4 and 8.8 % and generally were slightly higher in June than in October. Of the model compounds tested, net bacterial biomass production was observed only in samples amended with glucose, glucose plus ammonium (glucose+NH4+), and dissolved free amino acids (DFAA). Bacterial growth efficiencies for these amendments were 0.8, 1.9, and and 9.3.%, respectively. Bacterial production at in situ DOM concentrations was observed in June but not in October. Using the bacterial dissolved organic carbon (DOC) utilization rates observed in this study together with other detailed information pertaining to bulk DOC at our study site, we estimate that the turnover time for labile DOC in these surface waters ranges from approximately 2 to 6 d depending on the labiliity of the standing stock of DOC. On the basis of (a) the exclusive use of DON as a nitrogen source in PE-DOM amendments, (b) the stimulation of ammonium utilization in the glucose+NH4+ amendment, and (c) the higher growth efficiencies observed for samples amended with either PE-DOM or DFAA, we suggest that bacterioplankton biomass production in eastern North Pacific surface waters is primarily energy limited. As a result of this energy limitation, bacterial production appears to be additionally constrained by the quality of the nutrients available for assimilation. Thus, the quality of the DOM substrate, specifically the DOC:DON ratio, can be a major determinant of bacterial production in pelagic marine systems

Dissolved and particulate organic matter source-age characterization in the upper and lower Chesapeake Bay: A combined isotope and biochemical approach

In order to characterize the sources and ages of organic matter contributing to river and estuarine outflow waters, the present study investigated Delta C-14 and delta C-13 signatures of the major operationally defined biochemical classes of ultrafiltered dissolved organic matter (UDOM) in conjunction with lipid biomarker and elemental compositions of UDOM and suspended particulate organic matter (POM) in the Chesapeake Bay. Freshwater (Susquehanna River) UDOM was dominated by a molecularly uncharacterized (MUC) fraction, followed by total carbohydrate (TCHO), total hydrolysable amino acid (THAA) and total lipid (TLE) components. In contrast, UDOM at the bay mouth (salinity similar to 22-24) was comprised mainly of TCHO, followed by MUC, THAA, and TLE. The Delta C-14 and delta C-13 signatures of both UDOM and its major biochemical classes indicate that Susquehanna DOM is derived in part from old allochthonous terrestrial sources, whereas young marine sources dominate at the bay mouth. In contrast to the other biochemical classes, lipophilic DOM at both sites was very old (similar to 5,000-7,000 years B.P.). In addition, factor analysis of lipid biomarker compounds revealed unique signatures for the UDOM and POM pools that imply disparate source and/or recycling properties as well as potential influences due to physical partitioning. Lipid biomarker compounds showed that although autochthonous riverine/estuarine sources dominated both the UDOM and POM pools, terrigenous lipids were elevated in the Susquehanna during high flow conditions. The presence of lipid biomarkers diagnostic of fresh algal material in UDOM further suggested its greater reactivity than POM. The observed biochemical and lipid biomarker compositions and isotopic signatures of UDOM and POM are consistent with previous findings suggesting that these two major organic matter pools have dissimilar reactivities and cycling times, and they derive from comparatively unique source-age materials in rivers and estuaries

Bioreactivity of estuarine dissolved organic matter: A combined geochemical and microbiological approach

An integrated multidisciplinary study utilizing geochemical and microbial ecological approaches was conducted to characterize the origins, chemical nature, and quantities of dissolved and particulate organic matter (OM) utilized by heterotrophic bacteria in a temperate estuary. C: N, stable isotope (delta C-13), and lipid biomarker analyses revealed differences in the inferred reactivity of autochthonous versus allochthonous OM sources. Isotopic comparison of OM size fractions and bacterial nucleic acids suggests that high-molecular-weight dissolved OM (DOM) is consistently linked to bacterial biomass synthesis along the estuarine salinity gradient. Polyunsaturated fatty acids (as percent of total fatty acids, FA) were a reliable predictor of DOM decomposition in bioassays, thus providing an indicator directly linking DOM reactivity to its composition. Significant positive correlations between FA diagnostic of bacterial sources and lipid biomarker compounds diagnostic of planktonic origin indicate a systematic bacterial response to autochthonous DOM sources along the estuarine continuum. These findings further suggest that, although the geochemical signature of algal-derived OM in the dissolved phase may appear quantitatively insignificant, this fraction may nevertheless represent a principal source of bioreactive OM to heterotrophic bacteria in estuarine waters

Penetration of anthropogenic carbon into organic particles of the deep ocean

] In the late 1980s, bomb C-14 was present in suspended particulate organic carbon (POC) from the North Central Pacific (NCP) and Sargasso Sea ( SS) throughout most of the water column, demonstrating that deep POC had exchanged with atmospheric CO2 in the past 30 years. Upon reoccupation of these sites in 1999 and 2000, respectively, we observed that the delta(13)C values of suspended POC were lower than those measured a decade earlier. This demonstrates that anthropogenic CO2 from fossil fuel and biomass burning has penetrated a major organic matter pool in the deep ocean. Delta(14)C measured in the suspended POC showed similar or higher values in the deep Sargasso Sea and decreased values in the deep NCP compared to those measured previously. We use a box model to show that the differences in the radiocarbon results are likely due to the presence of resuspended sediment that is laterally advected from the continental margin to the deep Sargasso Sea

Chemical and Structural Stability of CsPbX3 Nanorods during Postsynthetic Anion-Exchange: Implications for Optoelectronic Functionality.

We examine halide anion-exchange reactions on CsPbX3 nanorods (NRs), and we identify reaction conditions that provide complete anion exchange while retaining both the highly quantum-confined 1-D morphology and metastable crystal lattice configurations that span a range between tetragonal structures and thermodynamically preferred orthorhombic structures. We find that the chemical stability of CsPbBr3 NRs is degraded by the presence of alkyl amines that etch CsPbBr3 and result in the formation of Cs4PbBr6 and 2-D bromoplumbates. Our study outlines strategies for maintaining metastable states of the soft lattices of perovskite nanocrystals undergoing exchange reactions, despite the thermodynamic driving force toward more stable lattice configurations during this disruptive chemical transformation. These strategies can be used to fine-tune the band gap of LHP-based nanostructures while preserving structure-property relationships that are contingent on metastable shapes and crystal configurations, aiding optoelectronic applications of these materials

Gas chromatographic isolation of individual compounds from complex matrices for radiocarbon dating

This paper describes the application of a novel, practical approach for isolation of individual compounds from complex organic matrices for natural abundance radiocarbon measurement. This is achieved through the use of automated preparative capillary gas chromatography (PCGC) to separate and recover sufficient quantities of individual target compounds for C-14 analysis by accelerator mass spectrometry (AMS). We developed and tested this approach using a suite of samples (plant lipids, petroleums) whose ages spanned the C-14 time scale and which contained a variety of compound types (fatty acids, sterols, hydrocarbons), Comparison of individual compound and bulk radiocarbon signatures for the isotopically homogeneous samples studied revealed that Delta(14)C values generally agreed well (+/- 10%). Background contamination was assessed at each stage of the isolation procedure, and incomplete solvent removal prior to combustion was the only significant source of additional carbon, Isotope fractionation was addressed through compound-specific stable carbon isotopic analyses, Fractionation of isotopes during isolation of individual compounds was minimal (\u3c 5 parts per thousand for delta(13)C), provided the entire peak was collected during PCGC, Trapping of partially coeluting peaks did cause errors, and these results highlight the importance of conducting stable carbon isotopic measurements of each trapped compound in concert with AMS for reliable radiocarbon measurements, The addition of carbon accompanying derivatization of functionalized compounds (e.g., fatty acids and sterols) prior to chromatographic separation represents a further source of potential error, This contribution can be removed using a simple isotopic mass balance approach, Based on these preliminary results, the PCGC-based approach holds promise for accurately determining C-14 ages on compounds specific to a given source within complex, heterogeneous samples

Temporal variability of Delta C-14, delta C-13, and C/N in sinking particulate organic matter at a deep time series station in the northeast Pacific Ocean

A 6-year time series of Delta(14) C, delta(13) C, and C/N measurements in deep sinking particulate organic matter ( POM) is presented for an abyssal site, Station M in the northeast Pacific Ocean. The Delta(14)C values revealed that sinking POM at 3450 m depth ( 650 m above bottom) contained old carbon despite its presumed short transit time in the water column. The isotopic and chemical properties of the sinking POM varied with time and appear to be controlled by more than one major process. In 1993, 1994, and late 1996, isotopic signatures and C/N molar ratios indicate negligible or vertically homogeneous influence of resuspended particles from the bottom or particles laterally transported from the margin to the study site. However, during early 1995 and 1998, Delta(14)C values were lower than those during other periods and C/N values at three deep depths were not equal, indicating that the study site was influenced by resuspended sediments more severely than during other periods. During mid-1995 to mid-1996, delta(13)C values decreased abruptly while Delta(14)C values increased slightly, and C/N values were extremely high ( up to -80) at 50 and 600 m above bottom; these results suggest input of degraded, modern, terrestrial organic matter. The periods of anomalous isotopic signatures, as well as vertically heterogeneous C/N values [ Smith et al., 2001], were correlated with high discharge periods of California rivers with a time lag of 2 to 4 months. The correlation suggests that regional meteorological events are important in controlling the biogeochemical properties of particles at Station M by varying the intensity of resuspension and transport of organic matter from the continental margin