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1.
Data on the carbonate system of the Northwestern Indian Ocean obtained on a cruise of F.S. Meteor during SW monsoon in July/August 1995 were compared with those of George et al. [George, M.D., Kumar, M.D., Naqvi, S.W.A., Banerjee, S., Narvekar, P.V., de Sousa, S.N., Jayakumar, D.A., 1994. A study of the carbon dioxide system in the northern Indian Ocean during premonsoon. Mar. Chem. 47, 243–254] collected during intermonsoon. In general, deep water values agreed well between the two expeditions. Surface waters, however, showed a substantial increase in dissolved inorganic carbon (CT) in the coastal regions due to strong upwelling in the SW monsoon. This was also accompanied by very high CO2 partial pressures in surface waters. The north–south gradients in vertical profiles of the measured parameters in the Arabian Sea are discussed by comparing profiles from the oligotrophic equatorial region with those from the highly productive central Arabian Sea. The effect of denitrification on regenerated CT and AT is minor, with contributions of <9 and <8 μmol kg−1, respectively, to the total amount regenerated also utilizing oxygen. The dissolution of biogenic carbonates is discussed; different approaches to define the depth, where the dissolution starts (lysocline(s), carbonate critical depth (CCrD)), are compared together with the calculation of saturation depth from carbonate concentrations. It is shown, that small differences in measured CT and AT (found between our data and those measured during GEOSECS) and different calculation approaches to the CO2 system (different dissociation constants for species involved and taking into account phosphate and silicate concentrations) can produce pronounced differences in the calculated saturation depths. However, CT and AT data suggest substantial dissolution of biogenic carbonate in the water column even above the calcite lysocline, irrespective of the procedures followed to calculate this horizon.  相似文献   

2.
Historical data of total dissolved inorganic carbon (CT), together with nitrate and phosphate, have been used to model the evolution of these constituents over the year in the Atlantic water of the Norwegian Sea. Changes in nutrient concentration in the upper layer of the ocean are largely related to biological activity, but vertical mixing with the underlying water will also have an impact. A mixing factor is estimated and used to compute the entrainment of these constituents into the surface water from below. After taking the mixing contribution into account, the resulting nutrient concentration changes are attributed to biological production or decay. The results of the model show that the change in CT by vertical mixing and by biological activity based on nutrient equivalents needs another sink to balance the carbon budget. It cannot be the atmosphere as the surface water is undersaturated with respect to carbon dioxide and is, thus, a source of CT in this region. Inasmuch as the peak deficit of carbon is more than a month later than for the nutrients, the most plausible explanation is that other nitrogen and phosphate sources than the inorganic salts are used together with dissolved inorganic carbon during this period. As nitrate and phosphate show a similar trend, it is unlikely that the explanation is the use of ammonia or nitrogen fixation but rather dissolved organic nitrogen and phosphate, while dissolved organic carbon is accumulating in the water.  相似文献   

3.
This study presents the distribution and fluxes of dissolved inorganic carbon (CT), total alkalinity (AT) and anthropogenic carbon (Cant) along the Otranto strait, during February 1995. Based on a limited number of properties (temperature, dissolved oxygen, total alkalinity and dissolved inorganic carbon), the composite tracer TrOCA was used to estimate the concentration of anthropogenic CO2 in the Otranto strait.Total alkalinity exhibits high values and weak variability throughout the water column of the strait, probably associated with the dense water formation processes in the Adriatic basin that induce a rapid transport of the coastal alkalinity to the deep waters. Elevated Cant concentrations and high anthropogenic pH variations are observed in the bottom layer of the strait, associated with the presence of Adriatic Deep Water (ADW). The study shows that large amounts of Cant have penetrated the highly alkaline Eastern Mediterranean waters, thereby causing a significant pH reduction since the pre-industrial era.Estimates of the transports of CT and Cant through the strait indicate that during February 1995, the Adriatic Sea imports through the Otranto strait natural and anthropogenic carbon and acts as a net sink of carbon for the Ionian Sea. The anthropogenic carbon that is imported to the Adriatic Sea represents less than 1% of the net CT inflow. The Levantine Intermediate Water (LIW) contributes to about one-third of the total CT and Cant inflow. Although the amounts of Cant annually transported by LIW and ADW are almost equal, the contribution of Cant to the CT transported by each water mass is slightly higher in ADW (3.1%) than in LIW (2.6%), as a result of its higher mean Cant concentration. The ADW, despite its weak contribution to the total outflow of Cant, has a vital role for the sequestration and storage of the anthropogenic carbon, as this water mass is the main component of the Eastern Mediterranean Deep Waters and, thus, the anthropogenic CO2 is transferred in the deep horizons of the Eastern Mediterranean, where it remains isolated for many years.  相似文献   

4.
The uptake of atmospheric carbon dioxide in the water transported over the Bering–Chukchi shelves has been assessed from the change in carbon-related chemical constituents. The calculated uptake of atmospheric CO2 from the time that the water enters the Bering Sea shelf until it reaches the northern Chukchi Sea shelf slope (1 year) was estimated to be 86±22 g C m−2 in the upper 100 m. Combining the average uptake per m3 with a volume flow of 0.83×106 m3 s−1 through the Bering Strait yields a flux of 22×1012 g C year−1. We have also estimated the relative contribution from cooling, biology, freshening, CaCO3 dissolution, and denitrification for the modification of the seawater pCO2 over the shelf. The latter three had negligible impact on pCO2 compared to biology and cooling. Biology was found to be almost twice as important as cooling for lowering the pCO2 in the water on the Bering–Chukchi shelves. Those results were compared with earlier surveys made in the Barents Sea, where the uptake of atmospheric CO2 was about half that estimated in the Bering–Chukchi Seas. Cooling and biology were of nearly equal significance in the Barents Sea in driving the flux of CO2 into the ocean. The differences between the two regions are discussed. The loss of inorganic carbon due to primary production was estimated from the change in phosphate concentration in the water column. A larger loss of nitrate relative to phosphate compared to the classical ΔN/ΔP ratio of 16 was found. This excess loss was about 30% of the initial nitrate concentration and could possibly be explained by denitrification in the sediment of the Bering and Chukchi Seas.  相似文献   

5.
The relation between the nitrate and phosphate concentrations in the Sea of Okhotsk and the bordering waters of the Pacific Ocean were studied. The surveys were carried out in the autumn, spring, and summer of 2001–2002. For the deepwater part of the sea, the relation [NO? 3] = ((14.88 ± 0.07) × [PO3? 4] ? 5.46 ± 0.17) was found. The coefficients in the equation given are statistically different from those in the similar equation for the Pacific waters: [NO? 3] = (16.05 ± 0.15) × [PO3? 4]-(7.23 ± 0.36). In the northern part of the sea; on the shelf; in the slope area; and, especially, in the deep waters of the TINRO Depression, the linear dependence between the phosphate and nitrate concentrations was distorted. This feature was described in terms of nitrate deficiency. The maximum values of this deficiency were found in the near-bottom waters. The principal processes that might cause the nitrate deficiency were considered: the difference in the oxidation rates of the nitrogen and phosphorus organic compounds, the matter transfer between the continent and the sea, the different efficiency of the biogenic burial of nitrogen and phosphorus in the bottom sediments, and the denitrification in the upper layer of the bottom sediments. It was shown that the most probable cause of the nitrate deficiency was the denitrification. The loss of inorganic nitrogen owing to the supply of the waters of the Sea of Okhotsk to the Pacific Ocean was estimated as ～2.5 × 1011 mol N/year.  相似文献   

6.
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7.
In January 1982, sediment microbial N transformations and inorganic N fluxes across the sediment/water interface were studied at nine sites off the South Island West Coast, New Zealand. The sediments showed a great variety in physical, chemical and biological properties. The sediment organic matter had a molar CN ratio of 5.9–10.9, and the total NP ratio was 1.2–4.0. The denitrification capacity in the top 7.5 cm of sediment was 0.1–77.2 mmol N m?2 day?1 and generally declined with increasing sediment depth. The in situ denitrification rate was 0.02–1.84 mmol N m?2 day?1 and highest activities were generally found in surface sediments and at 6–7.5 cm depth. Denitrification accounted for 82–100% of total nitrate reduction. Net N mineralization was indirectly estimated at 0.6–2.4 mmol N m?2 day?1, and the experimental determination of this N transformation gave 0.6–3.2 mmol N m?2 day?1. Denitrification accounted for 3–75% of net N mineralization. The diffusive flux of ammonium and nitrate across the sediment/water interface was 0.1–0.7 and 0.1–0.6 mmol N m?2 day?1, respectively.  相似文献   

8.
By transforming fixed nitrogen (N) into nitrogen gas, the biochemical processes that support denitrification provide a function critical to maintaining the integrity of ecosystems subjected to increased loading of N from anthropogenic sources. The Louisiana coastal region receives high nitrate (NO3?) concentrations (> 100 µM) from the Mississippi–Ohio–Missouri River Basin and is also an area undergoing high rates of wetland loss. Ongoing and anticipated changes in the Louisiana coastal region promise to alter biogeochemical cycles including the net rate of denitrification by ecosystems. Projecting what these changes could mean for coastal water quality and natural resources requires an understanding of the magnitude and patterns of variation in denitrification rates and their connection to estuarine water quality at large temporal and spatial scales under current conditions. We compile and review denitrification rates reported in 32 studies conducted in a variety of habitats across coastal Louisiana during the period 1981– 2008. The acetylene inhibition and 15N flux were the preferred techniques (95%); most of the studies used sediment slurries rather than intact sediment cores. There are no estimates of denitrification rates using the N2/Ar ratio and isotope pairing techniques, which address some of the problems and limitations of the acetylene inhibition and 15N flux techniques. These studies have shown that sediments from estuaries, lakes, marshes, forested wetlands, and the coastal shelf region are capable of high potential denitrification rates when exposed to high NO3? concentrations (> 100 µM). Maximum potential denitrification rates in experimental and natural settings can reach values > 2500 µmol m2 h? 1. The lack of contemporary studies to understand the interactions among critical nitrogen transformations (e.g., organic matter mineralization, immobilization, aquatic plant assimilation, nitrification, nitrogen fixation, dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (annamox) limits our understanding of nitrogen cycling in coastal Louisiana, particularly the role of respiratory and chemolithoautotrophic denitrification in areas undergoing wetland restoration.  相似文献   

9.
N2 fixation is an important biological process that adds new nitrogen to oceans and plays a key role in modulating the oceanic nitrate inventory. However, it is not known how, when, and where N2 fixation rates have varied in response to past climate changes. This study presents a new record of nitrogen isotopic composition (δ15N) over the last 83 kyr from a sediment core (KH02-4 SUP8) taken in the Sulu Sea in the western equatorial Pacific region; data allow the N2 fixation variability in the sea to be reconstructed. Sediments, sinking, and suspended particulate organic matter (POM) all have lighter isotopic values compared to the δ15N values of substrate nitrate (av. 5.8‰) in North Pacific Intermediate Water. These lighter δ15N values are regarded as reflecting N2 fixation in the Sulu Sea surface water. A δ15N mass balance model shows that N2 fixation rates were significantly enhanced during 54–34 kyr in MIS-3 and MIS-2. It has been speculated that higher interglacial denitrification rates in the Arabian Sea and the eastern tropical Pacific would have markedly decreased the global oceanic N inventory and contributed to the increase in N2 fixation in oligotrophic regions, but such a model was not revealed by our study. It is possible that changes in N2 fixation rates in the Sulu Sea were regional response, and accumulation of phosphate in the surface waters due to enhanced monsoon-driven mixing is thought to have stimulated enhancements of N2 fixation during MIS-3 and MIS-2.  相似文献   

10.
In the Mediterranean Sea the carbon chemistry is poorly known. However, the impact of the regional and large-scale anthropogenic pressures on this fragile environment rapidly modifies the distribution of the carbonate system key properties like CT (total dissolved inorganic carbon), AT (total alkalinity), CANT (anthropogenic CO2), and pH. This leads inexorably to the acidification of its waters. In order to improve our knowledge, we first develop interpolation procedures to estimate CT and AT from oxygen, salinity, and temperature data using all available data from the EU/MEDAR/MEDATLAS II database. The acceptable levels of precision obtained for these estimates (6.11 ??mol-kg−1 for CT and 6.08 ??mol kg−1 for AT) allow us to draw the distribution of CANT (with an uncertainty of 6.75 ??mol kg−1) using the Tracer combining Oxygen, inorganic Carbon, and total Alkalinity (TrOCA) approach. The results indicate that: 1) all Mediterranean water bodies are contaminated by anthropogenic carbon; 2) the lowest concentration of CANT is 37.5 ??mol kg−1; and 3) the western basin is more contaminated than the Eastern basin. After reconstructing the distribution of key properties (CT, AT, CANT) for four periods of time (between 1986 and 2001) along a west-east section throughout the whole Mediterranean Sea, we analyze the impact of the Eastern Mediterranean Transient (EMT). Not only has the concentration of CANT increased (especially in the intermediate and the bottom layers of the eastern basin, during and after the EMT), but also the distribution of all properties has been considerably perturbed. This is discussed in detail. For the first time, the level of acidification is estimated for the Mediterranean Sea. Our results indicate that for the year 2001 all waters (even the deepest) have been acidified by values ranging from −0.14 to −0.05 pH unit since the beginning of the industrial era, which is clearly higher than elsewhere in the open ocean. Given that the pH of seawater may affect a very large number of chemical and biological processes, our results stress the necessity to develop new programs of research to understand and then predict the evolution of the carbonate system properties in the Mediterranean Sea.  相似文献   

11.
Nitrous oxide (N2O) is a trace gas that is increasing in the atmosphere. It contributes to the greenhouse effect and influences the global ozone distribution. Recent reports suggest that regions such as the Arabian Sea may be significant sources of atmospheric N2O.In the ocean, N2O is formed as a by-product of nitrification and as an intermediary of denitrification. In the latter process, N2O can be further reduced to N2. These processes, which operate on different source pools and have different magnitudes of isotopic fractionation, make separate contributions to the 15N and18O isotopic composition of N2O. In the case of nitrification in oxic waters, the isotopic composition of N2O appears to depend mainly on the 15N/14N ratio of NH+4 and the 18O/16O ratio of O2 and H2O. In suboxic waters, denitrification causes progressive 15N and 18O enrichment of N2O as a function of degree of depletion of nitrate and dissolved oxygen. Thus the isotopic signature of N2O should be a useful tool for studying the sources and sinks for N2O in the ocean and its impact on the atmosphere.We have made observations of N2O concentrations and of the dual stable isotopic composition of N2O in the eastern tropical North Pacific (ETNP) and the Arabian Sea. The stable isotopic composition of N2O was determined by a new method that required only 80–100 nmol of N2O per sample analysis. Our observations include determinations across the oxic/suboxic boundaries that occur in the water columns of the ETNP and Arabian Sea. In these suboxic waters, the values of δ15N and δ18O increased linearly with one another and with decreasing N2O concentrations, presumably reflecting the effects of denitrification. Our results suggest that the ocean could be an important source of isotopically enriched N2O to the atmosphere.  相似文献   

12.
为获得反硝化脱氮效率较好的菌株,实验从海水螺旋藻培养体系中分离获得一株嗜碱兼性好氧反硝化菌, 通过观察细菌形态以及16S rRNA基因序列的同源性分析, 鉴定该菌株为海杆菌属, 命名为Marinobacter sp. B3。为明确该海杆菌的反硝化性能及氮转化途径, 研究开展了溶解氧(DO), 碳氮摩尔比(C/N), pH和温度等不同单因素对反硝化性能影响实验和氮平衡实验。单因素影响实验结果表明, 当硝酸钾(KNO3)作为唯一氮源, NO3--N的初始浓度为100 mg/L, 盐度32, 振荡速度为150 r/min (初始DO质量浓度是5.6 mg/L), C/N=10, pH=8.0±0.2, 温度为35 °C时, 可获得最大脱氮效果。氮平衡实验结果得出, 在好氧环境下, 有20.11%的NO3--N转化为胞内氮, 5.58 mg/L的NO3--N转化为其他形态(NO2--N、NO4+-N和有机氮), 74.72%转化为N2释放; 厌氧环境下, 有26.65%的NO3--N转化为胞内氮, 72.86%的NO3--N转化为气态产物释放。最终实验结果表明, Marinobactersp. B3在好氧和厌氧条件下, 48 h对NO3--N的去除率分别为99.89%和93.80%, 具有较好的反硝化脱氮能力, 且在好氧条件下NO3--N去除效率更高, 在海水工厂化循环水养殖尾水处理方面具有良好的应用前景。  相似文献   

13.
Benthic Nutrient Recycling in Port Phillip Bay, Australia   总被引：8，自引：0，他引：8  
Benthic chamber measurements of the reactants and products involved with biogenic matter remineralization (oxygen, ammonium, nitrate, nitrite, phosphate, silicate, TCO2and alkalinity) were used to define solute exchange rates between the sediment and overlying water column of Port Phillip Bay, Australia. Measurements at various sites throughout the bay, conducted during the summers of 1994 and 1995, indicate that the variability in flux values within a site is comparable to year-to-year variability (±50%). Four regions of the bay were distinguished by sediment properties and the northern region was identified as having 3–30 times greater nutrient regeneration rates than the other regions. Benthic recycling accounted for 63 and 72% of the annualized N and P input, respectively, to the entire bay as determined by summing benthic, dissolved riverine, atmospheric and dissolved effluent sources. However, bay-wide sedimentary denitrification accounted for a loss of 63% of the potentially recyclable N. This fraction is higher than many other coastal regions with comparable carbon loading. Denitrification efficiency is apparently not enhanced by benthic productivity nor by bio-irrigation. The rate of bio-irrigation is negatively correlated with denitrification efficiency. Bio-irrigation was studied using radon-222 and CsCl spike injection chamber measurements. Radon fluxes from sediments in Port Phillip Bay were enhanced over the diffusive flux by 3–16 times. The modelled rate of loss of Cs from chamber water was positively correlated with radon flux enhancement results. Both methods identify regions within Port Phillip Bay that have particularly high rates of non-diffusive pore-water overlying water solute exchange.  相似文献   

14.
Recent studies of the nitrogen gas excess produced during water column denitrification have indicated that water column denitrification rates calculated using nitrate deficit-type methods could be a substantial underestimate. Since there are no other significant processes that produce (or consume) N2 in the oxygen deficient zone (ODZ), its excess above background can be used to estimate the amount of denitrification, avoiding assumptions made in nitrate deficit calculations of the composition of the respired organic matter and also uncertainties in the nitrogen removal pathways. Dissolved N2, Ar, and nutrient concentrations were measured at 2 stations in the ODZ of the eastern tropical South Pacific (ETSP) in order to compare the nitrogen gas excess with the dissolved inorganic nitrogen (DIN) deficit due to denitrification. In contrast with previous findings in the Arabian Sea ODZ, the shapes of the N2 excess and DIN deficit profiles were similar in the ETSP ODZ, with maxima at the top of the ODZ. Maximum DIN deficits at each station were 19 and 18 μM N compared to the maximum N2 excesses of 15 and 20 μM N, respectively. Given the same considerations of the volume and residence time for the oxygen deficient zone waters, denitrification rates for the ETSP estimated from the N2 excess would be comparable or no greater than 30% larger than the one determined using the DIN deficit. This implies that the source of the DIN removed from the ODZ is either deep sea nitrate or organic matter with an N:P ratio close to Redfield.  相似文献   

15.
The rate of benthic denitrification in slope and rise sediments of a transect across the N.W. European Continental Margin (Goban Spur) was evaluated from 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and denitrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 μmol N cm−2 y−1 and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation. Denitrification rates in a nearby canyon, which did not follow these relationships, were estimated to be much higher as a result of erosion and redistribution of organic matter. Denitrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17% of the particulate organic nitrogen input (8.93 μmol N cm−2 y−1) is denitrified and only 1% is buried, the rest being released as nitrate. Although being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf.  相似文献   

16.
Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ13COC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O2 uptake (5.2 to 29.3 mmol m−2 d−1) and NH4+ release (−0.1 to −3.5 mmol m−2 d−1) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ13COC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms.  相似文献   

17.
High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO3 contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High Corg/N ratios and low δ13C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ15N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ15N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high Corg/N ratios and low δ13C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ15N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.  相似文献   

18.
Benthic fluxes of dissolved inorganic carbon, total alkalinity, oxygen, nutrients, nitrous oxide and methane were measured in situ at three sites of Río San Pedro salt marsh tidal creek (Bay of Cádiz, SW Spain) during three seasons. This system is affected by the discharges of organic carbon and nutrients from the surrounding aquaculture installations. Sediment oxygen uptake rates and inorganic carbon fluxes ranged respectively from 16 to 79 mmol O2 m? 2 d? 1 and from 48 to 146 mmol C m? 2 d? 1. Benthic alkalinity fluxes were corrected for the influence of NH4+ and NO3? + NO2? fluxes, and the upper and lower limits for carbon oxidation rates were inferred by considering two possible scenarios: maximum and minimum contribution of CaCO3 dissolution to corrected alkalinity fluxes. Average Cox rates were in all cases within ± 25% of the upper and lower limits and ranged from 40 to 122 mmol C m? 2 d? 1. Whereas carbon mineralization did not show significant differences among the sites, Cox rates varied seasonally and were correlated with temperature (r2 = 0.72). During winter and spring denitrification was estimated to account for an average loss of 46% and 75%, respectively, of the potentially recyclable N, whereas during the summer no net removal was observed. A possible shift from denitrification to dissimilatory nitrate reduction to ammonium (DNRA) during this period is argued. Dissolved CH4 and N2O fluxes ranged from 5.7 to 47 μmol CH4 m? 2 d? 1 and 4.3 to 49 μmol N–N2O m? 2 d? 1, respectively, and represented in all cases a small fraction of total inorganic C and N flux. Overall, about 60% of the total particulate organic matter that is discharged into the creek by the main fish farm facility is estimated to degrade in the sediments, resulting in a significant input of nutrients to the system.  相似文献   

19.
Net community production (NCP) and nutrient deficits (Def(X)) were calculated using decreases in dissolved CO2 and nutrient concentrations due to biological removal in the upper 200 m of the water column during four cruises in the Ross Sea, Antarctica along 76°30′S in 1996 and 1997. A comparison to excess dissolved and particulate organic carbon showed close agreement between surplus total organic carbon (TOC) and NCP during bloom initiation and productivity maximum; however, when TOC values had returned to low wintertime values NCP was still significantly above zero. This seasonal NCP, 3.9±1 mol C m−2, must be equivalent to the particle export to depths greater than 200 m over the whole productive season. We estimate that the annual export was 55±22% of the seasonal maximum in NCP. The fraction of the seasonal maximum NCP that is exported through 200 m is significantly higher than that measured by moored sediment traps at a depth of 206 m. The removal of carbon, nitrate and phosphate (based on nutrient disappearance since early spring) and their ratios showed significant differences between regions dominated by diatoms and regions dominated by the haptophyte Phaeocystis antarctica. While the ΔC/ΔN removal ratio was similar (7.8±0.2 for diatoms and 7.2±0.1 for P. antarctica), the ΔN/ΔP and ΔC/ΔP removal ratios for diatoms (10.1±0.3 and 80.5±2.3) were significantly smaller than those of P. antarctica (18.6±0.4 and 134.0±4.7). The similarity in ΔC/ΔN removal ratios of the two assemblages suggests that preferential uptake of phosphate by diatoms caused the dramatic differences in ΔC/ΔP and ΔN/ΔP removal ratios. In contrast to low ΔC/ΔP and ΔN/ΔP removal ratio in diatom-dominated areas early in the growing season, deficit N/P and C/P ratios in late autumn indicate that the elemental stochiometry of exported organic matter did not deviate significantly from traditional Redfield ratios. Changes in biologically utilized nutrient and carbon ratios over the course of the growing season indicated either a substantial remineralization of phosphate or a decrease in phosphate removal relative to carbon and total inorganic nitrogen over the bloom period. The species dependence in C/P ratios, and the relative constancy in the C/N ratios, makes N a better proxy of biological utilization of CO2.  相似文献   

20.
Alkenone unsaturation indices (UK37 and UK′37) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between UK37 (and UK′37) values and temperature, and a significant negative correlation between UK37 (and UK′37) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. UK37 relationships (UK37=0.018 (T)−0.162, R2=0.84, UK′37=0.013 (T)−0.04, R2=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index UK′37 based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the UK37 vs. temperature slope, or nutrient levels are the main controller of the UK37 index. In addition, particularly high abundances (>5% of total C37 alkenones) of the tetra-unsaturated ketone, C37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones.  相似文献   

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