Temporal variability in dissolved organic carbon and radiocarbon in the eastern North Pacific Ocean

The factors regulating the steady state inventories and residence times of dissolved organic carbon (DOG) in the deep ocean are not well established. Previous studies of DOC have been limited to single time-point profiles that provide general information on the potential role of vertical advective-diffusive processes in controlling DOC distributions and mean apparent ages. We present results from a 2-year time series station in the eastern North Pacific (station M) where short-term (months) changes in inventories and Delta(14)C signatures of DOC as measured in deep profiles were examined in conjunction with changes in particulate organic carbon (POC) pools. Significant long-term (i.e., months to years) changes in both DOC concentrations and Delta(14)C values were observed. These changes were especially evident at mesopelagic (similar to 450 and 700 m) depths, close to the oxygen minimum. Both within the mixed layer and at mesopelagic depths, positive relationships were found between DOC Delta(14)C values and concentrations of station M, primarily reflecting diminishing vertical inputs of recent DOC throughout the main thermocline. At abyssal depths (greater than or equal to 1600 m), however, Delta(14)C was inversely correlated with DOC concentration. The Delta(14)C signature of the less abundant suspended and sinking POC pools has been observed to fluctuate over seasonal timescales at station M, presumably due:in part to sorption of DOC to POC [Druffel et al., 1996]. However, the Delta(14)C values and concentrations of the correspondingly much larger DOC pool do not appear to be related to seasonal changes in either sinking POC fluxes or suspended POC abundances. Significantly elevated concentrations of DOC were observed at station M when compared with a previously occupied site in the north central Pacific (NCP) in all regions of the water column except mesopelagic depths, where concentrations were lower. The corresponding Delta(14)C values of DOC at all depths at station M were lower than in the NCP. We speculate that dissimilarities in the size and Delta(14)C signature of the DOC pools at seasonally productive station M and the oligotrophic NCP result from differences in DOC sources and sinks between the two regions, as well as from the magnitude of interaction between DOC and POC at these sites

Temporal variability in dissolved organic carbon and radiocarbon in the eastern North Pacific Ocean

The factors regulating the steady state inventories and residence times of dissolved organic carbon (DOG) in the deep ocean are not well established. Previous studies of DOC have been limited to single time-point profiles that provide general information on the potential role of vertical advective-diffusive processes in controlling DOC distributions and mean apparent ages. We present results from a 2-year time series station in the eastern North Pacific (station M) where short-term (months) changes in inventories and Delta(14)C signatures of DOC as measured in deep profiles were examined in conjunction with changes in particulate organic carbon (POC) pools. Significant long-term (i.e., months to years) changes in both DOC concentrations and Delta(14)C values were observed. These changes were especially evident at mesopelagic (similar to 450 and 700 m) depths, close to the oxygen minimum. Both within the mixed layer and at mesopelagic depths, positive relationships were found between DOC Delta(14)C values and concentrations of station M, primarily reflecting diminishing vertical inputs of recent DOC throughout the main thermocline. At abyssal depths (greater than or equal to 1600 m), however, Delta(14)C was inversely correlated with DOC concentration. The Delta(14)C signature of the less abundant suspended and sinking POC pools has been observed to fluctuate over seasonal timescales at station M, presumably due:in part to sorption of DOC to POC [Druffel et al., 1996]. However, the Delta(14)C values and concentrations of the correspondingly much larger DOC pool do not appear to be related to seasonal changes in either sinking POC fluxes or suspended POC abundances. Significantly elevated concentrations of DOC were observed at station M when compared with a previously occupied site in the north central Pacific (NCP) in all regions of the water column except mesopelagic depths, where concentrations were lower. The corresponding Delta(14)C values of DOC at all depths at station M were lower than in the NCP. We speculate that dissimilarities in the size and Delta(14)C signature of the DOC pools at seasonally productive station M and the oligotrophic NCP result from differences in DOC sources and sinks between the two regions, as well as from the magnitude of interaction between DOC and POC at these sites

DOC cycling in a temperate estuary: A mass balance approach using natural 14C and 13C isotopes

We measured dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and their corresponding D14C and d13C values in order to study the sources and fates of DOC in the York River Estuary (Virginia, U.S.A.). The D14C and d13C values of DOC and DIC at the freshwater end-member indicate that during periods of moderate to high flow, riverine DOC entering the York was composed of decadal-aged terrestrially organic matter. In nearly all cases, DOC concentrations exceeded conservative mixing lines and were therefore indicative of a net DOC input flux from within the estuary that averaged 1.2 mM L21 d21 . The nonconservative behavior of DOC in the York River Estuary was also apparent in carbon isotopic mixing curves and the application of an isotopic mixing model. The model predicted that 20–38% of the DOC at the mouth of the estuary was of riverine (terrestrial 1 freshwater) origin, while 38–56% was added internally, depending on the isotopic values assigned to the internally added DOC. Measurements of D14C and d13C of DOC and DIC and marsh organic matter suggest that the internal sources originated from estuarine phytoplankton and marshes. The isotopic mixing model also indicates a significant concomitant loss (27–45%) of riverine DOC within the estuary. Changes in DOC concentration, D14C-DOC, and d13C-DOC were also measured during incubation experiments designed to quantify the amounts, sources, and ages of DOC supporting the carbon demands of estuarine bacteria. Results of these experiments were consistent with an estuarine source of phytoplankton and marsh DOC and the preferential utilization of young (14C-enriched) DOC in the low-salinity reaches of the York. However, the average removal of riverine DOC by bacteria accounts for only ;4–19% of the riverine pool; therefore, other significant sinks for DOC exist within the estuary

A Suggested Criterion for Selecting between E-V and Stochastic Dominance Analysis Tools

Research Methods/ Statistical Methods,

Atmospheric CO2 evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary

Direct measurements of the partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) were made over a 2‐yr period in surface waters of the York River estuary in Virginia. The pCO2 in surface waters exceeded that in the overlying atmosphere, indicating that the estuary was a net source of CO2 to the atmosphere at most times and locations. Salinity‐based DIC mixing curves indicate there was also an internal source of both DIC and alkalinity, implying net alkalinity generation within the estuary. The DIC and alkalinity source displayed seasonal patterns similar to that of pCO2 and were reproducible over a 2‐yr study period. We propose that the source of inorganic carbon necessary for both the sustained CO2evasion to the atmosphere and the advective export of DIC is respiration in excess of primary production (e.g., net heterotrophy). The rates of CO2 evasion and DIC export were estimated to provide an annual rate of net heterotrophy of ~100 g C m−2 yr−1. Approximately 40% of this excess inorganic carbon production was exported as DIC to the coastal ocean, whereas 60% was lost as CO2 evasion to the atmosphere. The alkalinity generation needed to sustain the export of inorganic carbon, as HCO3− , is most likely provided by net sulfate reduction in sediments. Accumulation of sulfide in the sediments of a representative site directly adjacent to the York River estuary is sufficient to account for the net export of alkalinity. The seasonality of net heterotrophy causes large variations in annual CO2 and DIC concentrations, and it stresses the need for comprehensive temporal data sets when reporting annual rates of CO2 evasion, DIC advection, and net heterotrophy

Assessing sources and ages of organic matter supporting river and estuarine bacterial production: A multiple-isotope (D14C, d13C, and d15N) approach

We used radiocarbon (D14C) and stable isotopic (d13C, d15N) signatures of bacterial nucleic acids to estimate the sources and ages of organic matter (OM) assimilated by bacteria in the Hudson River and York River estuary. Dualisotope plots of D14C and d13C coupled with a three-source mixing model resolved the major OM sources supporting bacterial biomass production (BBP). However, overlap in the stable isotopic (d13C and d15N) values of potential source end members (i.e., terrestrial, freshwater phytoplankton, and marsh-derived) prohibited unequivocal source assignments for certain samples. In freshwater regions of the York, terrigenous material of relatively recent origin (i.e., decadal in age) accounted for the majority of OM assimilated by bacteria (49–83%). Marsh and freshwater planktonic material made up the other major source of OM, with 5–33% and 6–25% assimilated, respectively. In the mesohaline York, BBP was supported primarily by estuarine phytoplankton–derived OM during spring and summer (53–87%) and by marsh-derived OM during fall (as much as 83%). Isotopic signatures from higher salinity regions of the York suggested that BBP there was fueled predominantly by either estuarine phytoplankton-derived OM (July and November) or by material advected in from the Chesapeake Bay proper (October). In contrast to the York, BBP in the Hudson River estuary was subsidized by a greater portion (up to ;25%) of old (;24,000 yr BP) allochthonous OM, which was presumably derived from soils. These findings collectively suggest that bacterial metabolism and degradation in rivers and estuaries may profoundly alter the mean composition and age of OM during transport within these systems and before its export to the coastal ocean

Vertical distribution of microbial and meiofaunal populations in sediments of a natural coastal hydrocarbon seep

We studied the vertical distribution of microbes and meiofauna in natural hydrocarbon seep sediments to determine if there was a relationship between profiles of benthic trophic structure and the unique biogeochemical conditions present at the seep. Three stations in the Santa Barbara Channel represented a gradient of natural petroleum seepage, from very active, to moderate, to none. Seasonal differences were examined by sampling in the three major oceanographic seasons, upwelling (April), mixed (July), and Davidson (December). Densities of microbes and meiofauna were highest in July, and decreased in winter. All population sizes decreased with increasing depth in the sediment. Harpacticoids and Chl a were practically restricted to the surface sediments. Harpacticoids and Chl a were more dense (number per unit volume or strata of sediment) and abundant (number per unit area of sediment or sum of the strata) at the comparison site than at the seep sites. Density and abundance of nematodes, bacteria cell counts, and bacterial biomass were greater at the station with the most active seepage rates. Bacterial biovolumes appeared constant among sediment depths and stations, but cell biovolumes were larger in July. The data are consistent with the hypothesis that organic enrichment via petroleum utilization is responsible for increased abundances of bacteria and nematodes at the seep. There were strong correlations between densities of harpacticoids and microalgae, and densities of nematodes and bacteria. These links indicate that seeping petroleum might have an enhanced effect on the detrital (bacterial based) food web, but a toxic effect on the grazing (microalgal based) food web

QUANTITATION AND IMMUNOCYTOCHEMICAL LOCALIZATION OF HUMAN SKIN COLLAGENASE IN BASAL CELL CARCINOMA

Human skin collagenase was quantitated by radioimmunoassay in 21 basal cell carcinomas. Immunoreactive collagenase protein was found to be approximately 2-fold greater in extracts of these tumors than in extracts of normal skin, suggesting that this enzyme may be important in the pathogenesis of soft tissue destruction in vivo. To further define the role of collagenase in such destruction, immunofluorescent staining with specific antiserum to human skin collagenase was used to localize collagenase in the basal cell carcinomas. The enzyme was found only in the stromal elements surrounding the tumor islands. No staining of the epithelial components of the basal cell carcinomas was found. These findings suggest that the normal connective tissue elements may have been stimulated to produce an increased amount of collagenase and emphasize the importance of epithelial-stromal interaction in soft tissue invasiveness

Temporal variability and the relationship between benthic meiofaunal and microbial populations of a natural coastal petroleum seep

Previous studies of the Isla Vista petroleum seep in the Santa Barbara Channel found much higher abundances of macrofauna and concentrations of adenosine triphosphate (ATP) in sediments near petroleum seepage compared to those from nonseep areas. To further assess the possible effect of petroleum on organisms at the base of benthic food webs, population abundances of meiobenthos and their suspected microbial food (bacteria and diatoms) were measured biweekly for one year at three stations with differing petroleum exposure. Determinations of suspended particulate matter and the abundance and gut contents of juvenile fishes were also made at seep and nonseep stations. Nematodes and bacteria had higher abundances in areas of active petroleum seepage than in areas of moderate seepage (within 20 m) or no seepage (1.4 km away). Bacterial productivity (based on the frequency of dividing cells) was 340% greater in sediments from areas of active seepage compared to those from a nonseep station. Sediments within the seep, but away from active seepage, had rates of bacterial productivity 15 times greater than a nonseep comparison site. Densities of harpacticoid copepods and their probable principal food, diatoms, were not affected by petroleum seepage. Suspended organic matter caught in settling traps was not different between seep and nonseep stations. In addition, there was no evidence that predation pressure by juvenile fish on meiofauna was different between stations. The higher bacterial biomass and productivity in areas of petroleum seepage are consistent with the hypothesis that petroleum carbon is available for assimilation by sediment bacteria. The enhanced level of microbial carbon associated with the petroleum seep is available for consumption by benthic invertebrates and could explain the higher abundances of macrofauna and meiofauna found there