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1.
Chum salmon, Oncorhynchus keta, are distributed widely in the North Pacific Ocean, and about 76% of chum salmon were caught from Russian, Japanese, and Korean waters of the northwestern Pacific Ocean during the last 20 years. Although it has been speculated that the recent increase in salmon production was aided by not only the enhancement program that targeted chum salmon but also by favorable ocean conditions since the early 1990s, the ecological processes for determining the yield of salmon have not been clearly delineated. To investigate the relationship between yield and the controlling factors for ocean survival of chum salmon, a time-series of climate indices, seawater temperature, and prey availability in the northwestern Pacific including Korean waters were analyzed using some statistical tools. The results of cross-correlation function (CCF) analysis and cumulative sum (CuSum) of anomalies indicated that there were significant environmental changes in the North Pacific during the last century, and each regional stock of chum salmon responded to the Pacific Decadal Oscillation (PDO) differently: for Russian stock, the correlations between PDO index and catch were significantly negative with a time-lag of 0 and 1 years; for Japanese stock, significantly positive with a timelag of 0–2 years; and for Korean stock, positive but no significant correlation. The results of statistical analyses with Korean chum salmon also revealed that a coastal seawater temperature over 14°C and the return rate of spawning adults to the natal river produced a significant negative correlation.  相似文献   

2.
Landlocked sockeye salmon (Oncorhynchus nerka), ranging in fork length (FL) from 105 to 313 mm, were captured in fine‐mesh gill nets set in the limnetic zone of the Waitaki hydro lakes (44° 30′ S, 170° 10’ E) in the South Island, New Zealand. A total of 443 stomachs was examined and the frequency of occurrence, volume and weight of prey items calculated. In the Ahuriri Arm of Lake Benmore the principal food (54% by weight) was zooplankton (Boeckella dilatata) whereas in the Haldon Arm of Lake Benmore it was larval and juvenile common bullies (Gobiomorphus cotidi‐anus) (73% by volume). In Lake Waitaki in winter, salmon had eaten insects (43% by volume) with smaller amounts of snails (Potamopyrgus antipo‐darum, 23%) and bullies (24%). In Lake Ohau adult insects may be an important food. There were also variations in diet with season and fish size. The stomachs of 147 brown trout (Salmo trutta) and 181 rainbow trout (S. gairdnerii) caught in the same gill nets were also examined. In contrast to sockeye salmon stomachs they contained negligible amounts of zooplankton (< 1% by weight) and large amounts of aquatic insects (50–58% by weight in the Ahuriri Arm of Lake Benmore). Comparisons with juvenile sockeye salmon and kokanee in North American lakes are made. The impact of introductions of sockeye salmon into other New Zealand lakes is discussed.  相似文献   

3.
We determined 15N/14N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (δ15N = 5‰) and the imprint of river-borne nitrogen input into the SE North Sea (δ15N up to 12‰ in estuaries of the SE North Sea) on the other hand. We compare the results with δ15N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ15N in cores from the Skagerrak – the largest sediment sink for nitrogen in the entire North Sea – was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea.  相似文献   

4.
Stable nitrogen isotopic ratios were measured in sinking particles and surface sediments from the South China Sea (SCS) in order to study recent nitrogen sources and degradation. Average δ15N values of 16 sediment traps deployed at seven locations in the northern, central and southern SCS were uniformly low, ranging between 2.7 and 4.5‰ with a winter minimum in the northern and central SCS. Enhanced nitrogen contents and δ15N values were noted in samples affected by swimmers, comprising between 5 and 20% of total nitrogen fluxes. Nitrate sources were subsurface waters from the western Pacific, which were isotopically depleted due to the remineralization of nitrogen from nitrogen fixation in surface waters. Nitrogen fixation in the SCS contributed up to 20% to the settling particles. In the southern SCS, resuspended matter close to the shelf added to the sinking particulates. The long-term trap record from the central SCS revealed decreasing δ15N values during the 1990s, which correspond with findings from the North Pacific Subtropical Gyre and may be attributable to increased nitrogen fixation due to global warming-related stratification. This trend may be restricted to the 1990s but could also persist due to the projection of more frequent occurrence of El Niño conditions.The δ15N increase from swimmer-free trap averages of 2.7–3.6‰ to values of 5–6‰ in underlying deep-sea sediments was in the same range as in other deep ocean areas. Similar to results from the northern Indian Ocean, this increase could be related to isotopic enrichment during amino acid degradation. The lowest sedimentary δ15N values characterize the Pinatubo ash layer deposited off Luzon in an event of mass sedimentation in 1991. The fast deposition of organic matter drawn from the surface waters with the ash in the form of vertical density currents evidently preserved the planktonic δ15N signal.  相似文献   

5.
The δ13C and δ15N of particulate organic matter (POM) sampled from the Weddell Sea in 1986 and 1988 ranged from −30.4 to − 16.7%o and from −5.4 to +41.3%o, respectively. These large variations in POM δ13C and δ15N may reflect spatial/temporal changes in the concentrations and isotope abundances of CO2(aq.) and NH4+, respectively. Elevated isotope values were found exclusively in POM in or closely associated with sea ice, which may be the source of the 13C- and 15N-enriched sediments observed in this region.  相似文献   

6.
We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R2 = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year− 1 in the subpolar region, and 0.01 ± 0.001 nM year− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m− 2 year− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.  相似文献   

7.
Water samples from the Lena River and stratified Laptev Sea (northeastern Siberia) have been analyzed to determine their stable oxygen isotope composition (18O/16O). Measurements at the Lena River reference station give a δ18O value of −18.9‰ in both surface and bottom waters. In the brackish water surface plume, a nearly perfect correlation is found between δ18O and chlorinity
δO=−18.9+0.7C1−(n=15; r=0.999)
A few values lie distinctly below this correlation; they all correspond to surface samples collected in the semi-enclosed Buorkhaya Gulf, and they most likely reveal the occurrence of ‘old’ water masses. Some of the δ18O values in the deep waters collected in the same zone also fall below the surface-plume correlation line.Dissolved silicate concentrations exhibit a large variability. However, when they are related to the different water masses identified using oxygen isotope data, a more coherent picture is obtained. Concentrations in the surface plume decrease more or less regularly from 50 to 72 μmol in the Lena River, to 7 μmol at the ‘marine’ end-member (Cl− = 14 g l−1). Dissolved silicate results in the Buorkhaya Gulf are quite distinct, with a clear deficiency in the surface waters, and an excess in the deep waters.These δ18O and dissolved silicate variations are discussed in relation to the hydrology and the biological productivity of the investigated area.  相似文献   

8.
The ratio of oxygen-18 to oxygen-16 (expressed as per mille deviations from Vienna Standard Mean Ocean Water, δ18O) is reported for seawater samples collected from seven full-depth CTD casts in the northern North Atlantic between 20° and 41°W, 52° and 60°N. Water masses in the study region are distinguished by their δ18O composition, as are the processes involved in their formation. The isotopically heaviest surface waters occur in the eastern region where values of δ18O and salinity (S) lie on an evaporation–precipitation line with slope of 0.6 in δ18O–S space. Surface isotopic values become progressively lighter to the west of the region due to the addition of 18O-depleted precipitation. This appears to be mainly the meteoric water outflow from the Arctic rather than local precipitation. Surface samples near the southwest of the survey area (close to the Charlie Gibbs Fracture Zone) show a deviation in δ18O–S space from the precipitation mixing line due to the influence of sea ice meltwater. We speculate that this is the effect of the sea ice meltwater efflux from the Labrador Sea. Subpolar Mode Water (SPMW) is modified en route to the Labrador Sea where it forms Labrador Sea Water (LSW). LSW lies to the right (saline) side of the precipitation mixing line, indicating that there is a positive net sea ice formation from its source waters. We estimate that a sea ice deficit of ≈250 km3 is incorporated annually into LSW. This ice forms further north from the Labrador Sea, but its effect is transferred to the Labrador Sea via, e.g. the East Greenland Current. East Greenland Current waters are relatively fresh due to dilution with a large amount of meteoric water, but also contain waters that have had a significant amount of sea ice formed from them. The Northeast Atlantic Deep Water (NEADW, δ18O=0.22‰) and Northwest Atlantic Bottom Waters (NWABW, δ18O=0.13‰) are isotopically distinct reflecting different formation and mixing processes. NEADW lies on the North Atlantic precipitation mixing line in δ18O–salinity space, whereas NWABW lies between NEADW and LSW on δ18O–salinity plots. The offset of NWABW relative to the North Atlantic precipitation mixing line is partially due to entrainment of LSW by the Denmark Strait overflow water during its overflow of the Denmark Strait sill. In the eastern basin, lower deep water (LDW, modified Antarctic bottom water) is identified as far north as 55°N. This LDW has δ18O of 0.13‰, making it quite distinct from NEADW. It is also warmer than NWABW, despite having a similar isotopic composition to this latter water mass.  相似文献   

9.
Genetic stock identification studies have been widely applied to Pacific salmon species to estimate stock composition of complex mixed-stock fisheries. In a September-October 2004 survey, 739 chum salmon (Oncorhynchus keta) specimens were collected from 23 stations in the western Bering Sea. We determined the genetic stock composition of immature chum salmon based on the previous mitochondria DNA baseline. Each regional estimate was computed based on the conditional maximum likelihood method using 1,000 bootstrap resampling and then pooled to the major regional groups: Korea - Japan - Primorie (KJP) / Russia (RU) / Northwest Alaska (NWA) / Alaska Peninsula - Southcentral Alaska - Southeast Alaska - British Columbia - Washington (ONA). The stock composition of immature chum salmon in the western Bering Sea was a mix of 0.424 KJP, 0.421 RU, 0.116 NWA, and 0.039 ONA stocks. During the study period, the contribution of Asian chum salmon stocks gradually changed from RU to KJP stock. In addition, North American populations from NWA and ONA were small but present near the vicinity of the Russian coast and the Commander Islands, suggesting that the study areas in the western Bering Sea were an important migration route for Pacific chum salmon originating both from Asia and North America during the months of September and October. These results make it possible to better understand the chum salmon stock composition of the mixed-stock fisheries in the western Bering Sea and the stock-specific distribution pattern of chum salmon on the high-seas.  相似文献   

10.
Carbon and nitrogen stable isotope ratios of particulate organic matter (POM) were studied approximately weekly during spring and summer 2003 and 2004 in the Gulf of Trieste (northern Adriatic Sea) in order to track the temporal variations and differences between two years. In parallel, particulate organic carbon (POC) and particulate nitrogen (PN), phytoplankton biomass (chlorophyll a), and N and P nutrients were monitored. All studied parameters, especially N and P nutrients and chlorophyll a, showed higher concentrations and larger variability in spring 2004. As a consequence the macroaggregates were produced in late spring 2004. The C and N isotope composition of POM was not directly linked to phytoplankton biomass dynamics. The δ13CPOC values covaried with temperature. In 2004, δ13CPOC variations followed the δ15NPN values as well as the δ13CDIC values which were probably more dependent on the photosynthetic use of 12C. Variations in δ15NPOM values were most probably the consequence of variations in N nutrient sources used in phytoplankton assimilation. The significant correlation between δ15NPN values and nitrate concentrations in 2004 implies intense nitrate assimilation in the presence of higher nitrate concentration. This suggests nitrate as the key nutrient in the »new primary production«, later producing macroaggregates with a mean δ13C and δ15N values of − 19‰ and 5‰, respectively. A low fractionation factor ε, < 1‰, lower than that reported in other marine and lacustrine systems, was found probably to be a consequence of distinct phytoplankton species, i.e. several classes of autotrophic nanoflagellates, and specific growth conditions present in the Gulf of Trieste. The tentative use of C isotope composition of POM revealed a higher contribution of allochthonous organic matter in 2004 compared to 2003 due to higher riverine inflow.  相似文献   

11.
The trophic position of Calanus finmarchicus in the Trondheim Fjord in 2004 was determined through stable isotope analyses. Wild specimens were sampled monthly in the fjord and δ13C and δ15N signatures of the developmental stages from CIII to adults were measured. There were statistically significant differences in the δ13C and δ15N signatures of three identified groups: overwintered parental generation, developing new generation and new generation preparing for overwintering. C. finmarchicus individuals raised in a laboratory on a pure algal diet (Dunaliella tertiolecta and Isochrysis galbana) provided stable isotope signatures for purely herbivorous copepods. With these signatures as comparison, the trophic position of C. finmarchicus in the Trondheim Fjord in 2004 was determined as trophic level 2.4, thus indicating omnivory under natural conditions. Additionally, our data suggest that seasonal differences in the δ13C signatures of C. finmarchicus are due to the varying lipid content of the different developmental stages.  相似文献   

12.
The stable carbon isotope ratios (δ13C) of the organic fraction of intertidal sediments in the Forth Estuary and the Firth of Forth, Scotland, were measured to determine if terrestrially derived carbon was present in the estuarine sediments. It was hypothesised that differences in the inputs from marine vs. terrestrial sources to the organic carbon of estuarine and marine sediments, as well as differences in ambient seawater stable oxygen isotope (δ18O) ratios between the estuary and the Outer Firth, would allow the use of these two stable isotopes as habitat markers for juvenile plaice (Pleuronectes platessa), to allow determination of nursery habitats. Muddy and sandy sediments from the estuary and sandy sediments from the Outer Firth were sampled and δ13C measured. Juvenile plaice were caught at two estuarine sites and at two Outer Firth sites and otoliths were removed for δ13C and δ18O analysis. The sandy sediments in the estuary showed a strong gradient of δ13C enrichment with distance down the estuary, while the muddy sediments showed a much shallower gradient. δ13C and δ18O measured in the carbonate of juvenile plaice otoliths showed no clear difference between otoliths of fish caught at one of the estuarine sites and at the two Outer Firth sites. However, the isotope ratios of both carbon and oxygen in plaice otoliths from the other estuarine site showed the expected trend of depletion in the heavier isotopes. While the measurements recorded here did not conclusively distinguish between otoliths from juveniles caught in the estuarine site and those caught in the other three sites, they show that stable isotopes have potential to distinguish between estuarine habitats with terrestrial carbon inputs, and coastal marine habitats with predominantly marine carbon inputs.  相似文献   

13.
The isotopic composition (δ15N) of dissolved nitrate was measured at five stations within the oxygen-deficient region of the eastern tropical North Pacific Ocean (ETNP) and at one station 900 km northeast of Hawaii, which was considered to be representative of all major water masses of the Pacific. At this last station, the δ15N composition of dissolved nitrate decreased systematically from about +6‰ at 400 m to approximately +5‰ at 5,000 m; these results are consistent with other estimates from the western Pacific.In contrast, vertical profiles of δ15N of dissolved nitrate from the ETNP showed marked departure from the above observed trend and correlated with losses of nitrate arising from denitrification. Instantaneous fractionation factors (α) were estimated, using the one dimensional vertical diffusion-advection model. These results suggest that 14NO3− is consumed 3–4% faster than 15NO3−, significantly larger than fractionations (2%) observed under laboratory conditions.Maximum rates of denitrification at 100 m were also evaluated and ranged from 0.6 to 8 μg-at 1−1 yr−1 for the stations investigated. The above upper limit is probably excessive, but the average maximum for the four stations analyzed is estimated to be 3.5 μg-at NO3− 1−1 yr−1. These results compare favorably with suitably corrected oxygen utilization rates derived from electron transport activity measurements.  相似文献   

14.
Nitrogen isotope compositions of particulate organic matter and nitrate were analyzed for seawater sampled at five stations at the Alaskan Gyre, Western Subarctic Gyre and East China Sea, focusing on the samples from the surface to 5000 m water to characterize the nitrogen cycling in the subarctic North Pacific Ocean and its marginal sea. The 15N of particulate organic matter showed little agreement with a conceptual closed model that interprets isotopic variation as being caused by isotope discrimination on nitrate utilization. The 15N and 13C of particulate organic matter varied with the water depth. A correlation between isotope compositions and C/N elemental ratio was found generally at all stations, although some irregular data were also found in deep layers. We developed a hypothetical nitrogen balance model based on N2 fixation and denitrification in seawater and attempted to apply it to distinguish nutrient cycling using both 15N-NO3 – and N* variation in seawater. This model was applied to the observed data set of 15N-NO3 – and N* in the North Pacific water and estimated the 15N-NO3 – of primordial nitrate in the North Pacific deep water as 4.8. The North Pacific intermediate water for all stations showed similar 15N-NO3 – and N* values of 6 and –3 µmol/kg, respectively, suggesting a similar nitrogen biogeochemistry. In the East China Sea, analysis showed evidence of water exchange with the North Pacific intermediate water but a significant influence of nitrogen from the river runoff was found in depths shallower than 400 m.  相似文献   

15.
Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.  相似文献   

16.
Extensive artificial waterways have replaced natural wetlands and created new estuarine habitats on the southern Queensland coast, Australia. Economically important fish species found in adjacent natural wetlands of mangrove, saltmarsh and seagrass also occur in the artificial waterways. Stable isotope analyses (δ13C, δ15N) were used to test whether the relative importance of basal sources of energy varied for foodwebs found in artificial (canals and tidal lakes) and natural waterways. None of the fish species differed in their isotope values between artificial waterways. In contrast, isotopic signatures of snub-nosed garfish (Arrhamphus sclerolepis; Hemiramphidae) varied greatly between natural and artificial waterways, having highly enriched δ13C values (−10.5‰) in natural wetlands, demonstrating reliance on seagrass (−11.4‰), and significantly less enriched values (−19.0‰) in artificial waterways, consistent with either local algal sources (−19.8 to −20.4‰) or a mixture of seagrass and other less enriched autotrophs from adjacent natural wetlands. Isotopic signatures of sand whiting (Sillago ciliata; Sillaginidae) were also significantly more enriched in natural (−18.2‰) than artificial (−21.0‰) habitats, but means were not far enough apart to distinguish between different sources of nutrition. δ13C values of yellowfin bream (Acanthopagrus australis; Sparidae) did not differ between artificial and natural habitats (about −20‰ in both). δ15N values of fish varied among habitats only for A. sclerolepis, which in artificial waterways had values enriched by 2‰ over those in natural waterways. This was consistent with a shift from seagrass (relatively depleted δ15N) as a source in natural habitat to algal sources (relatively enriched δ15N) in artificial habitats. This study provides some of the first evidence that at least some fish species rely on different autotrophs in artificial waterways than in adjacent natural wetlands.  相似文献   

17.
The C/N and stable C and N isotope ratios (δ13C, δ15N) of sedimentary and suspended particulate matter were determined in the Schelde Estuary. Suspended matter was divided into 2 to 5 size fractions by centrifugation. Four major pools of organic matter were recognized: riverine, estuarine, marine and terrestrial materials. Terrestrial organic matter (δ13C≈−26‰, δ15N≈3.5‰, C/N≈21) is important for the sedimentary pool, but suspended matter is dominated by the marine (δ13C≈−18‰, δ15N≈9‰, C/N≈8), riverine (δ13C≈−30‰, δ15N≈9‰, C/N≈7.5) and estuarine (δ13C≈−29‰, δ15N≈15‰, C/N≈8) end-members. In the upper estuary, the suspended matter size fractions vary systematically in their carbon and nitrogen biogeochemistry, with the small particles having low C/N ratios, depleted δ13C and enriched δ15N values relative to large particles. Moreover, sedimentary and suspended matter differ significantly in terms of C/N ratios (17 vs. 8.9), δ13C (−26.3 vs. −28.9‰) and δ15N (+6.9 vs. 12.0‰). In the lower estuary, suspended matter fractions are similar and sedimentary and suspended organic matter differ only in terms of δ13C (−23.5 vs. −20.1‰). Our data indicate that autochthonous organic matter contributes significantly to the total suspended matter and that the suspended organic matter composition cannot be explained in terms of conservative mixing of riverine and terrestrial sources on the one hand and marine sources on the other hand.  相似文献   

18.
We examined stable carbon and nitrogen isotopic signatures of 17 fish and 16 invertebrate taxa common to the Newfoundland and Labrador (NL) continental shelf food web. Particular sampling emphasis was placed on Atlantic cod (Gadus morhua) and related prey species (e.g. shrimp, Pandalus borealis, and capelin, Mallotus villosus). We found highly significant (p < 0.0001) differences between near-shore (bays) and offshore (shelf edge) δ15N signatures for cod, ‘other fish’ (pooled) and invertebrates (pooled). In contrast, there were only minor differences in δ13C signatures of ‘other fish’ (p < 0.05) and no difference for cod and invertebrates among the two habitats. We sampled at two times of the year (January and June) and found no systematic effect of season on both δ13C and δ15N in cod, ‘other fish’ and invertebrates. We calculated isotopic fractionation factors for cod from the entire shelf (mixed diet) and for cod with diets composed mainly of capelin or shrimp. These values ranged between 2.2‰ and 3.9‰ for δ15N and −0.4‰ and 0.8‰ for δ13C and, for δ15N, may reflect diet-related differences in bioenergetic status. We discuss potential mechanisms for near-shore versus offshore enrichment of δ15N signatures, and demonstrate the implications of this spatial variation on δ15N-derived trophic position estimates.  相似文献   

19.
Tangential-flow ultrafiltration was used to isolate particulate and high-molecular-weight dissolved material from seawater collected at various depths and geographic regions of the Pacific and Atlantic Oceans. Ultrafiltration proved to be a relatively fast and efficient method for the isolation of hundreds of milligrams of material. Optical and electron microscopy of the isolated materials revealed that relatively fragile materials were recovered intact. Depth-weighted results of the size distribution of organic matter in seawater indicated that ˜ 75% of marine organic carbon was low-molecular-weight (LMW) dissolved organic carbon (< 1 nm), ˜ 24% was high-molecular-weight (HMW) dissolved organic carbon (1–100 nm), and ˜ 1% was particulate organic carbon (> 100 nm). The distribution of carbon in surface water was shifted to greater relative abundances of larger size fractions, suggesting a diagenetic sequence from macromolecular material to small refractory molecules. The average C:N ratios of particulate organic matter (POM) and HMW dissolved organic matter (DOM) were 7.7 and 16.7, respectively. Differences in C:N ratios between POM and HMW DOM were large and invariant with depth and geographic region, indicating that the aggregation of HMW DOM to form POM must be of minor significance to overall carbon dynamics. The stable carbon isotope composition (δ13C) of POM averaged −22.7%. in surface water and −25.2%. in subsurface water. Several possible explanations for the observed isotopic shift with depth were explored, but we were unable to discern the cause. The δ13C of HMW DOM samples was relatively constant and averaged −21.7%., indicating a predominantly marine origin for this material. The δ15N values of POM were highly variable (5.8–15.4%.), and the availability of nitrate in surface waters appeared to be the major factor influencing δ15N values in the equatorial Pacific. In the upwelling region nitrate concentrations were relatively high and δ15N values of POM were low, whereas to the north and south of the upwelling nitrate concentrations were low and δ15N values were high. The δ15N values of HMW DOM reflected the same trends observed in the POM fraction and provided the first such evidence for biological cycling of dissolved organic nitrogen (DON). Using the observed δ15N values and an estimate of meridional advection velocity, we estimated a turnover time of 0.3 to 0.5% day−1 for HMW DON. These results suggest a major role for DON in the upper ocean nitrogen cycle.  相似文献   

20.
One of the motivations of the GLOBEC Northeast Pacific program is to understand the apparent inverse relationship between the increase in salmon catches in the Gulf of Alaska and concurrent declines in the California Current System (CCS). We therefore used coded wire tag (CWT) data to examine the spatial and temporal patterns of covariability in the survival of hatchery coho salmon along the coast from California to southeast Alaska between release years 1980 and 2004. There is substantial covariability in coho salmon survival between neighboring regions along the coast, and there is clear evidence for increased covariability within two main groups – a northern and southern group. The dividing line between the groups lies approximately at the north end of Vancouver Island. However, CWT survivals do not support inverse covariability in hatchery coho salmon survival between southeast Alaska and the CCS over this 25 year time span. Instead, the hatchery coho survival in southeast Alaska is relatively uncorrelated with coho survival in the California Current System on inter-annual time scales. The 50% correlation and e-folding scales (distances at which magnitude of correlations decreases to 50% and e−1 (32.8%), respectively) of pairwise correlations between individual hatcheries were 150 and 217 km, which are smaller than that reported for sockeye, pink, and chum salmon. The 50% correlation scale of coho salmon is also substantially smaller than those reported for upwelling indices and sea surface temperature. There are also periods of 5–10 years with high covariability between adjacent regions on the scale of hundreds of km, which may be of biological and physical significance.  相似文献   

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