Long-term biogenic particle fluxes in the Bering Sea and the central subarctic Pacific Ocean, 1990–1995     

《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(9):1723-1759

Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally located subarctic pelagic Station SA (49°N, 174°W; water depth 5406 m) was simultaneously studied along with the marginal sea Station AB (53.5°N, 177°W; water depth 3788 m) in the Aleutian Basin of the Bering Sea. A mooring system was tethered to the sea-floor with a PARFLUX type trap with 13 sample bottles, which was placed at 600 m above the sea-floor at each of the two stations. Sampling intervals were synchronized at the stations, and they were generally set for 20 days during highly productive seasons, spring through fall, and 56 days during winter months of low productivity. Total mass fluxes, which consisted of mainly biogenic phases, were significantly greater at the marginal sea Station AB than at the pelagic Station SA for the first four years and moderately greater for the last year of the observations. This reflects the generally recognized higher productivity in the Bering Sea. Temporal excursion patterns of the mass fluxes at the two stations generally were in parallel, implying that temporal changes in their biological productivity are strongly governed by a large-scale seasonal climatic variability over the region rather than local phenomena. The primary reason for the difference in total mass flux at the two stations stems mainly from varying contributions of siliceous and calcareous planktonic assemblages. A significantly higher opal contribution at Station AB than at Station SA was mainly due to diatoms. Diatom fluxes at the marginal sea station were about twice those observed at the pelagic station, resulting in a very high opal contribution at Station AB. In contrast to the opal fluxes, CaCO₃ fluxes at Station AB were slightly lower than at Station SA. The ratios of C_org/C_inorg were usually significantly greater than one in both regions, suggesting that preferentially greater organic carbon from cytoplasm than skeletal inorganic carbon was exported from the surface layers. Such a process, known as the biological pump, leads to a carbon sink which effectively lowers p CO₂ in the surface layers and then allows a net flux of atmospheric CO₂ into the surface layer. The efficiency of the biological pump is greater in the Bering Sea than at the open-ocean station.  相似文献   

Long-term diatom fluxes in response to oceanographic conditions at Stations AB and SA in the central subarctic Pacific and the Bering Sea, 1990–1998     

Jonaotaro Onodera  Kozo Takahashi 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(2):189-211

Long-term monitoring of diatom fluxes during 1990–1998 was conducted at Station AB in the Bering Sea and Station SA in the central subarctic Pacific in order to decipher the relationships between sinking diatom and the upper water mass environments. The total diatom flux at Station AB was generally twice as high as that at Station SA. The dominant species in the sinking flora was primarily Neodenticula seminae at both stations, which was a significant contributor to organic carbon flux. The flora at Station AB was represented by relatively abundant coastal taxa including Chaetoceros resting spores. These results suggest more favorable conditions for diatom production at Station AB compared with those at Station SA. The possible influences of oligotrophic and temperate water masses were discerned from the positive SST anomaly and the occurrence of a few specimens of temperate species. The cumulative annual fluxes of total diatoms at Stations AB and SA are apparently related to the variation in the mean annual depth of mixed layer. At Station SA, annual mean of total diatom flux showed a negative correlation with the Pacific Decadal Oscillation (PDO) Index, which suggests a significant relationship between surface water turbidity and diatom production. At Station AB, the annual change of coastal diatom flux was correlated with the PDO and the winter value of the Arctic Oscillation, which may suggest a significant influence of Alaskan Stream waters via the Aleutian Islands and intensity of surface water mixing.  相似文献   

Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary     

Aymeric Dabrin  Jrg Schfer  Grard Blanc  Emilie Strady  Matthieu Masson  Ccile Bossy  Sabine Castelle  Naïg Girardot  Alexandra Coynel 《Estuarine, Coastal and Shelf Science》2009,84(4):429-439

Dissolved Cd (Cd_D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001–2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexation. The daily net Cd_D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd_D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd_D⁰), each representative of one distinct situation. The obtained Cd_D⁰ concentrations were relatively similar (201 ± 28 ng L⁻¹) when freshwater discharge Q was >500 m³ s⁻¹ (508 ≤ Q ≤ 2600 m³ s⁻¹), but were highly variable (340 ± 80 ng L⁻¹; 247–490 ng L⁻¹) for low discharge situations (169 ≤ Q ≤ 368 m³ s⁻¹). The respective daily Cd_D net fluxes were 5–39 kg day⁻¹, mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd_D net fluxes, we proposed an empirical model, using representative Cd_D⁰ values and daily freshwater discharges for the 2001–2007 period. Subsequent integration produced reliable Cd_D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8–5.0 t a⁻¹ in 2005 and 6.0–7.2 t a⁻¹ in 2004, depending on freshwater discharge. Comparing Cd_D net fluxes with the incoming Cd_D fluxes suggested that the annual net Cd_D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a⁻¹, without any clear temporal trend during the past seven years. The annual Cd_D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor 6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd_D net fluxes even exceeded river borne total (dissolved + particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation–resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.  相似文献   

Downward carbon transport by diel vertical migration of the copepods Metridia pacifica and Metridia okhotensis in the Oyashio region of the western subarctic Pacific Ocean     

Kazutaka Takahashi  Akira Kuwata  Hiroya Sugisaki  Kazuhisa Uchikawa  Hiroaki Saito 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1777-1791

Seasonal change in the downward carbon transport due to respiration and mortality through diel vertical migration (DVM) of the calanoid copepods Metridia pacifica and Metridia okhotensis was estimated in the Oyashio region, western subarctic Pacific during six cruises from June 2001 to June 2002. M. pacifica (C4, C5 and adult females) was an active migratory species throughout the year though its DVM amplitude varied among seasons and stages. The mean distribution depths of adult females during the daytime were positively related with the illumination level in the water column, being shallowest in April and deepest in January. M. okhotensis generally showed less-extensive migrations than M. pacifica. Therefore, together with their lower abundance, this species is considered to be a less-important mechanism of downward transport of carbon except for April when their DVM was more active and descended deeper than M. pacifica, which remained in the upper 150 m even during the daytime. The mean migrating biomass of the two Metridia species was 558 mg C m⁻² d⁻¹ and was high during summer to winter (263–1676 mg C m⁻² d⁻¹) and low during spring (59–63 mg C m⁻² d⁻¹). Total downward flux through DVM fluctuated between 1.0 and 20.0 mg C m⁻² d⁻¹ with an annual mean of 8.0 mg C m⁻² d⁻¹. Contribution of the respiratory flux was greater than the mortality flux and accounted for 64–98% of total migratory flux throughout the year except for January when contribution of both fluxes was equal. Overall the annual carbon transport by DVM of Metridia spp. was estimated as 3.0 g C m⁻² year⁻¹, corresponding to 15% of the annual total POC flux at 150 m at the study site, suggesting that DVM is a significant process for carbon export in the subarctic region as well as that in tropical and subtropical oceanic regions. Since DVM in M. pacifica is more active during the non-bloom season when the gravitational flux of particulate matter is low, this species plays an important role in driving the biological pump in the subarctic Pacific during summer to winter.  相似文献   

Remotely sensed sea-surface chlorophyll and POC flux at Deep Gulf of Mexico Benthos sampling stations     

Douglas C. Biggs  Chuanmin Hu  Frank E. Müller-Karger 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2555

Biweekly composite averages of the standing stock of sea-surface chlorophyll (SSC) were derived from SeaWiFS satellite ocean-color data at 44 benthic sampling stations occupied along the continental slope and rise by the Deep Gulf of Mexico Benthos (DGoMB) program. At the 22 DGoMB sites north of 26°N and west of 91°W in the NW Gulf of Mexico, annual average SSC was 0.19 mg m⁻³, ranging at most locations from annual highs of about 0.3 mg m⁻³ in November–February to lows of about 0.1 mg m⁻³ in May–August. Comparison of three years of SeaWiFS data (January 1998–December 2000) showed little inter-annual variation at these NW Gulf stations. In contrast, at the 22 NE Gulf sites north of 26°N and east of 91°W, SSC averaged 2.8 times higher than in the NW Gulf, showing also strong inter-annual variation. Maxima in the NE region occurred in November–February and also during summers. The summer maxima were associated with Mississippi River water transported offshore to the east and southward by anticyclonic eddies in the NE Gulf. The apparent increases in SSC in June–August at NE Gulf stations reached average monthly concentrations >50% greater than in November–February. Based on a primary productivity model and a vertical flux model, the calculated export of particulate organic carbon (POC flux reaching the seafloor) was estimated as 18 mg C m⁻² day⁻¹ at the 22 NE Gulf stations, and 9 mg C m⁻² day⁻¹ at the 22 NW Gulf stations. These estimates are comparable to fluxes measured by benthic lander by others in the DGoMB program, which may drive the differences in west versus east bathymetric zonation and community structure of macrobenthos that were sampled with large box corers by others in the DGoMB program.  相似文献   

Effects of irradiance on benthic and water column processes in a Gulf of Mexico estuary: Pensacola Bay, Florida, USA   总被引：1，自引：0，他引：1  

Michael C. Murrell  Jed G. Campbell  James D. Hagy III  Jane M. Caffrey 《Estuarine, Coastal and Shelf Science》2009,81(4):501-512

We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH₄⁺, NO₃⁻, PO₄³⁻) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O₂ m⁻² d⁻¹, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O₂ m⁻² d⁻¹ (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O₂ m⁻² d⁻¹, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O₂ m⁻² d⁻¹, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m⁻² d⁻¹ for NH₄⁺, 0.58 ± 1.08 mmol m⁻² d⁻¹ for NO₃⁻, 0.01 ± 0.09 mmol m⁻² d⁻¹ for PO₄³⁻. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems.  相似文献   

Seasonal variation of pteropods from the Western Arabian Sea sediment trap     

R. Mohan  K. Verma  L. P. Mergulhao  D. K. Sinha  S. Shanvas  M. V. S. Guptha 《Geo-Marine Letters》2006,26(5):265-273

Sediment trap samples collected from the Western Arabian Sea yielded a rich assemblage of intact and non-living (opaque white) pteropod tests from a water depth of 919 m during January to September 1993. Nine species of pteropods were recorded, all (except one) displaying distinct seasonality in abundance, suggesting their response to changing hydrographical conditions influenced by the summer/winter monsoon cycle. Pteropod fluxes increased during the April–May peak of the intermonsoon, and reached maximum levels in the late phase of the southwest summer monsoon, probably due to the shallowing of the mixed layer depth. This shallowing, coupled with enhanced nutrient availability, provides ideal conditions for pteropod growth, also reflected in corresponding fluctuations in the flux of the foraminifer Globigerina bulloides. Pteropod/planktic foraminifer ratios displayed marked seasonal variations, the values increasing during the warmer months of April and May when planktic foraminiferal fluxes declined. The variation in fluxes of calcium carbonate, organic carbon and biogenic opal show positive correlations with fluxes of pteropods and planktic foraminifers. Calcium carbonate was the main contributor to the total particulate flux, especially during the SW monsoon. In the study area, pteropod flux variations are similar to the other flux patterns, indicating that they, too could be used as a potential tool for palaeoclimatic reconstruction of the recent past.  相似文献   

Interannual and geographical variability of the brood size of the euphausiids Euphausia pacifica and Thysanoessa spinifera along the Oregon coast (1999–2004)     

Jaime Gmez-Gutirrez  Leah R. Feinberg  Tracy C. Shaw  William T. Peterson 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2145-2169

Brood sizes of 1259 adult female Euphausia pacifica and Thysanoessa spinifera were measured during 48 h incubations (10 °C, ±0.5 °C) on 27 oceanographic cruises between July 1999 and September 2004. The data set includes measurements from several stations off Newport, Oregon (Newport Hydrographic line, 44°39′N) made over a 5-year period and measurements from 14 more extensive cruises at stations representative of continental shelf, slope, and oceanic waters off Oregon and California, USA. E. pacifica had similar brood sizes at inshore (<200 m) and offshore (>200 m) stations with an average of 151 and 139 eggs brood⁻¹ fem⁻¹, respectively. T. spinifera brood sizes were considerably higher at inshore stations—particularly at Heceta Bank (44°N) and south of Cape Blanco (42°50′N)—than at offshore stations, 155 and 107 eggs brood⁻¹ fem⁻¹, respectively. Average brood sizes of E. pacifica increased during the study period, from 125 (in 2000) to 171 eggs brood⁻¹ fem⁻¹ (in 2003). Average percentage of carbon weight invested in spawning (reproductive effort) was higher in E. pacifica (14%) than in T. spinifera (6%), because both species have similar brood size but T. spinifera females are larger than E. pacifica females and produce smaller eggs. Reproductive effort for both species was higher during summer 2002, probably associated with anomalous cool subarctic waters and high chl-a concentration observed during that summer. Brood sizes and chl-a values remained relatively high in 2003–2004 compared to the 1999–2001 period. Geographical and temporal variability in brood sizes for both species were significantly correlated with in situ measurements of chl-a concentration but not with sea surface temperature. No gravid females were collected during late autumn and winter cruises, thus the spawning season along the Oregon coast appears to extend from March through September for both species. However, T. spinifera usually starts reproductive activity earlier in the spring (March) than E. pacifica. Both species had their highest brood sizes in summer during the period of most intense upwelling, which is associated with an increase in regional phytoplankton standing stock.  相似文献   

Basin-Scale Geographic Patterns of Bacterioplankton Biomass and Production in the Subarctic Pacific, July–September 1997     

Toshi Nagata  Rumi Fukuda  Hideki Fukuda  Isao Koike 《Journal of Oceanography》2001,57(3):301-313

Bacterial biomass and production rate were measured in the surface (0–100 m) and mesopelagic layers (100–1,000 m) in the subarctic Pacific and the Bering Sea between July–September, 1997. Depth profiles were determined at stations occupied in oceanic domains including the subarctic gyres (western, Bering Sea, and Gulf of Alaska) and a boundary region south of the gyres. In the surface layer (0–100 m), both bacterial biomass and production were generally high in the western and Bering Sea gyres, with the tendency of decrease toward east. This geographic pattern was consistent with the dominant regime of phytoplankton biomass at the time of our survey. A significant portion of variation in bacterial production was explained by the concentration of chlorophyll a (r ² = 0.340, n = 60, P < 0.001) and, to the greater extent, by the concentration of semilabile total organic carbon (SL-TOC = TOC at a given depth—TOC at 1,000 m, r ² = 0.488, n = 59, P < 0.0001). Temperature significantly improved the regression model: temperature and chlorophyll jointly explained 60% of variation in bacterial production. These results support the hypothesis that bacteiral growth is largely regulated by the combination of temperature and the supply of dissolved organic carbon in subarctic surface waters. In the mesopelagic layer (100–1,000 m), the geographic pattern of bacterial production was strikingly different from the surface phytoplankton distribution: the production was high in the boundary region where the phytoplankton biomass was lowest. Bacterial growth appeared to be largely controlled by the supply of organic carbon, as indicated by the strong dependency of bacterial production on SL-TOC (r ² = 0.753, n = 75, P < 0.0001). The spatial uncoupling between surface phytoplankton and mesopelagic bacterial production suggests that the supply rate of labile dissolved organic carbon in the mesopelagic zone does not simply reflect the magnitude of the particulate organic carbon flux in the subarctic Pacific.  相似文献   

Impact of the Mediterranean Outflow Water on particle dynamics in intermediate waters of the Northeast Atlantic, as revealed by Th and Th     

Sabine Schmidt   《Marine Chemistry》2006,100(3-4):289

Over the last decade ²³⁴Th has become increasingly used to study particle transport in the ocean on a timescale of weeks. The application of ²³⁴Th is mainly focused on the determination of particle and associated carbon fluxes from oceanic surface water. However, ²³⁴Th is also suitable for investigating particle dynamic from the upper ocean down to interface sediments, as illustrated by the present work which reports unexpected behavior of ²³⁴Th in intermediate waters associated with the Mediterranean Outflow Water (MOW). Concentration profiles of dissolved ²³⁸U and ²²⁸Ra, and dissolved and particulate ²³⁴Th and ²²⁸Th were measured in the Mediterranean Outflow Water (MOW) near the Gibraltar Straits and at two sites (36°30′N–15°35′W, Nicole; 36°27′N–10°35′W, Yseult) which had hydrographic characteristics of Meddies, i.e. MOW that propagates as eddies in the Northeastern Atlantic at intermediate depths.There are marked differences in the distribution of thorium between MOW and the surrounding Atlantic waters. At the youngest Meddy Nicole salinity maximum at 1000 m depth, ²³⁴Th(total) : ²³⁸U and ²²⁸Th(total) : ²²⁸Ra activity ratios are significantly lower than radioactive equilibrium, indicating an unusual deficit of short half-life thorium nuclides. This implies an export of thorium, presumably on particles, from intermediate Meddy Nicole waters. This process is supported by an increase of particulate thorium fluxes measured in sediment traps deployed for two weeks above and within Meddy Nicole. In contrast, offshore Meddy Yseult has more typical profiles of both thorium nuclides that are nearly in equilibrium with their parents. These results indicate that at intermediate depths, the presence of MOW affects the exchange of reactive elements between particles and dissolved forms and enhances the downward flux of particles from intermediate waters in the Northeast Atlantic.  相似文献   

Biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean from 2004 to 2013     

Masahide Wakita  Makio C. Honda  Kazuhiko Matsumoto  Tetsuichi Fujiki  Hajime Kawakami  Sayaka Yasunaka  Yoshikazu Sasai  Chiho Sukigara  Mario Uchimiya  Minoru Kitamura  Toru Kobari  Yoshihisa Mino  Akira Nagano  Shuichi Watanabe  Toshiro Saino 《Journal of Oceanography》2016,72(5):665-685

The annual flux of biologically produced organic carbon from surface waters is equivalent to annual net community production (NCP) at a steady state and equals the export of particulate and dissolved organic carbon (POC and DOC, respectively) to the ocean interior. NCP was estimated from carbon budgets of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using quasi-monthly biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO₂ exchange, net CaCO₃ production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.49 ± 0.42 mol m^?2 year^?1) was lower than S1 (2.81 ± 0.53 mol m^?2 year^?1) (p < 0.001 based on t test). These fluxes consist of three components: vertically exported POC fluxes (K2: 1.43 mol m^?2 year^?1; S1: 2.49 mol m^?2 year^?1), vertical diffusive DOC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.25 mol m^?2 year^?1), and suspended POC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.07 mol m^?2 year^?1). The estimated POC export flux at K2 was comparable to the sum of the POC flux observed with drifting sediment traps and active carbon flux exported by migrating zooplankton. The export fluxes at both stations were higher than those reported at other time-series sites (ALOHA, the Bermuda Atlantic Time-series Study, and Ocean Station Papa).  相似文献   

Factors influencing benthic bacterial abundance, biomass, and activity on the northern continental margin and deep basin of the Gulf of Mexico     

Jody W. Deming  Shelly D. Carpenter 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2597

As part of a larger project on the deep benthos of the Gulf of Mexico, an extensive data set on benthic bacterial abundance (n>750), supplemented with cell-size and rate measurements, was acquired from 51 sites across a depth range of 212–3732 m on the northern continental slope and deep basin during the years 2000, 2001, and 2002. Bacterial abundance, determined by epifluorescence microscopy, was examined region-wide as a function of spatial and temporal variables, while subsets of the data were examined for sediment-based chemical or mineralogical correlates according to the availability of collaborative data sets. In the latter case, depth of oxygen penetration helped to explain bacterial depth profiles into the sediment, but only porewater DOC correlated significantly (inversely) with bacterial abundance (p<0.05, n=24). Other (positive) correlations were detected with TOC, C/N ratios, and % sand when the analysis was restricted to data from the easternmost stations (p<0.05, n=9–12). Region-wide, neither surface bacterial abundance (3.30–16.8×10⁸ bacteria cm⁻³ in 0–1 cm and 4–5 cm strata) nor depth-integrated abundance (4.84–17.5×10¹³ bacteria m⁻², 0–15 cm) could be explained by water depth, station location, sampling year, or vertical POC flux. In contrast, depth-integrated bacterial biomass, derived from measured cell sizes of 0.027–0.072 μm³, declined significantly with station depth (p<0.001, n=56). Steeper declines in biomass were observed for the cross-slope transects (when unusual topographic sites and abyssal stations were excluded). The importance of resource changes with depth was supported by the positive relationship observed between bacterial biomass and vertical POC flux, derived from measures of overlying productivity, a relationship that remained significant when depth was held constant (partial correlation analysis, p<0.05, df=50). Whole-sediment incubation experiments under simulated in situ conditions, using ³H-thymidine or ¹⁴C-amino acids, yielded low production rates (5–75 μg C m⁻² d⁻¹) and higher respiration rates (76–242 μg C m⁻² d⁻¹), with kinetics suggestive of resource limitation at abyssal depths. Compared to similarly examined deep regions of the open ocean, the semi-enclosed Gulf of Mexico (like the Arabian Sea) harbors in its abyssal sediments a greater biomass of bacteria per unit of vertically delivered POC, likely reflecting the greater input of laterally advected, often unreactive, material from its margins.  相似文献   

Seasonal variations in dimethylsulfoniopropionate and dimethylsulfide concentrations in relation to the plankton community in the St. Lawrence Estuary   总被引：1，自引：1，他引：1  

Sonia Michaud  Maurice Levasseur  Guy Cantin   《Estuarine, Coastal and Shelf Science》2007,71(3-4):741-750

Weekly variations in total dimethylsulfoniopropionate (DMSPt) and dimethylsulfide (DMS) were investigated in relation to the phytoplankton assemblage from spring to fall 1994 at a coastal fixed station in the St. Lawrence Estuary. DMSPt and DMS concentrations showed a strong seasonality and were tightly coupled in time. Maximum concentrations of DMSPt and DMS were observed in July and August, during a period of warm water and low nutrient concentrations. Seasonal maxima of 365.4 nmol l⁻¹ for DMSPt and 14.2 nmol l⁻¹ for DMS in early August coincided with the presence of many phytoplankton species, such as Alexandrium tamarense, Dinophysis acuminata, Gymnodinium sp., Heterocapsa rotundata, Protoperidinium ovatum, Scrippsiella trochoidea, Chrysochromulina sp. (6 μm), Cryptomonas sp. (6 μm), a group of microflagellates smaller than 5 μm (mf < 5), many tintinnids, and Mesodinium rubrum. The abundance of mf < 5 followed the general trend of DMS concentrations. The temporal occurrence of high P. ovatum abundance and DMSPt concentrations suggests that this heterotrophic dinoflagellate can either synthesize DMSP or acquire it from DMSP-rich prey. The calculated sea-to-air DMS flux reached a maximum of 8.36 μmol ⁻² d⁻¹ on August 1. The estimated annual emission from the St. Lawrence Estuary is 77.2 tons of biogenic sulfur to the atmosphere.  相似文献   

Iron deficiency in micro-sized diatoms in the Oyashio region of the Western subarctic Pacific during spring     

Ai Hattori-Saito  Jun Nishioka  Tsuneo Ono  R. Michael L. McKay  Koji Suzuki 《Journal of Oceanography》2010,66(1):105-115

In order to detect iron (Fe) stress in micro-sized (20–200 μm) diatoms in the Oyashio region, western subarctic Pacific during spring, immunological ferredoxin/flavodoxin assays were applied to samples collected from the surface layer in May 2005. Concomitantly, the community composition of the micro-sized phytoplankton and hydrographic conditions, including dissolved Fe and macronutrient concentrations, were also examined. Chlorophyll (Chl) a concentrations were <2 mg m⁻³ at all sampling stations, except at a station where the Chl a level was 9.0 mg m⁻³ and a micro-sized diatom bloom occurred. A high abundance of ferredoxin in micro-sized diatoms was detected only at a rather near-shore station where dissolved Fe and macronutrient concentrations were higher, indicating that the micro-sized diatoms did not suffer from iron deficiency. On the other hand, flavodoxin in micro-sized diatoms was often observed at the other stations, including the bloom station, where macronutrients were replete but dissolved Fe concentration was low (0.31 nM). A significant amount of chlorophyllide a, a degradation product of Chl a, was also observed at the bloom station, suggesting a decline of the diatom bloom. The micro-sized phytoplankton species at all the stations were mainly composed of the diatoms Thalassiosira, Chaetoceros, and Fragilariopsis spp. Our study indicates that micro-sized diatoms were stressed by Fe bioavailability during the spring season in the Oyashio region  相似文献   

On Seasonal and Year to Year Variation in Flow of the Alaskan Stream in the Central North Pacific   总被引：1，自引：0，他引：1  

Hiroji Onishi  Kiyotaka Ohtani 《Journal of Oceanography》1999,55(5):597-608

The Alaskan Stream is the westward boundary current of the North Pacific subarctic gyre. In the central region of the North Pacific, the Alaskan Stream serves as a connection between the Alaskan gyre, Western subarctic gyre and Bering Sea gyre. Its volume transport is very important in estimating the magnitude of the subarctic circulation in the North Pacific. In order to clarify its seasonal and interannual variation, we conducted observations along a north-south section at 180° during June from 1990 to 1997. Moorings were deployed from 1995 to 1997. Hydrographic casts were made at intervals of 37 km to a depth of 3000 m. Moorings were set between CTD stations, with Moor1 (Moor2) at the center (southern edge) of the Alaskan Stream. Geostrophic volume transport (referred to 3000 m) revealed large interannual variability in the Alaskan Stream. Average volume transport over the 8 years was 27.5 × 10⁶ m³s^-1 with a standard deviation of 6.5 × 10⁶ m³s^-1. Maximum transport was 41.0 × 10⁶ m³s^-1 (1997) and minimum was 21.7 × 10⁶ m³s^-1 (1995). Stable westward flows were observed at Moor1 1500 m (259°, 11.7 cm s^-1) and 3000 m (240°, 3.7 cm s^-1, 1996–1997 year average). The ratio of eddy to mean kinetic energy (KE/ ) was very small (<0.6) throughout the year. A relatively weak and unstable westward flow was observed at Moor2 at 3000 m depth. Conversely, the average flow direction at Moor2 5000 m was eastward.  相似文献   

Air-sea exchange of mercury in Tokyo Bay     

Masahiro Narukawa  Masahiro Sakata  Kohji Marumoto  Kazuo Asakura 《Journal of Oceanography》2006,62(3):249-257

In Tokyo Bay the concentrations of dissolved gaseous mercury (DGM) in the surface seawater and total gaseous mercury (TGM) over the sea were measured during December 2003, October 2004 and January 2005. Based on these data, the evasional fluxes of mercury from the sea surface were estimated using a gas exchange model. In addition, an automatic wet and dry deposition sampler was used to measure the wet and dry depositional fluxes of mercury from December 2003 to November 2004 at three locations in and near Tokyo Bay. The results indicate that the average DGM and TGM levels of seven locations are 52 ± 26 ng m⁻³ and 1.9 ± 0.6 ng m⁻³, respectively, which shows that the surface seawater in Tokyo Bay is supersaturated with gaseous mercury, leading to an average mercury evasional flux of 140 ± 120 ng m⁻²d⁻¹. On the other hand, the annual average wet and dry depositional fluxes of mercury at three locations were 19 ± 3 μg m⁻²yr⁻¹ and 20 ± 9 μg m⁻²yr⁻¹, respectively. These depositional fluxes correspond to the daily average total depositional flux of 110 ± 20 ng m⁻²d⁻¹. Thus, it is suggested that in Tokyo Bay, the evasional fluxes of mercury are comparable to the depositional fluxes.  相似文献   

Diel Patterns in Chlorophyll <Emphasis Type="Italic">a</Emphasis> Specific Absorption Coefficient and Absorption Efficiency Factor of Picoplankton     

Nobuaki?OhiEmail author  Hiroaki?Saito  Satoru?Taguchi 《Journal of Oceanography》2005,61(3):379-388

Diel patterns in the chlorophyll a specific absorption coefficient of surface picoplankton, a*_pico (γ) (m²·[mg chlorophyll a]⁻¹), were studied at 7 stations under daily cycle of in situ light condition in the western subarctic Pacific and Japan Sea. All the data were normalized by dividing the anomaly with daily averaged a*_pico (γ). Opposite diel patterns were observed for the normalized a*_pico (443) and a*_pico (675) with maximum toward dawn or dusk and minimum toward midday at 4 stations under low-irradiance (LI) conditions and vice versa at 3 stations under high-irradiance (HI) conditions. The absorption efficiency factors at red absorption peak, Q _a (675), were determined by reconstruction with intracellular chlorophyll a concentration and cell diameter. The normalized Q _a (675) also showed diel pattern with maximum toward midday and minimum toward dawn or dusk under LI. The diel pattern in a*_pico (675) and Q _a (675) were primarily caused by changes in intracellular chlorophyll a concentration due to photoadaptation under LI. The diel pattern in a*_pico (443) was influenced by pigmentation, as recognized by blue to red ratio [a*_pico (443)/a*_pico (675)] under HI. This study proposed that the opposite diel pattern in a*_pico (γ) might occur for a wide range of algal species. The results presented here have important consequences for the interpretation of diel variations in optical properties observed in the open ocean.  相似文献   

Particle export within cyclonic Hawaiian lee eddies derived from Pb–Po disequilibrium     

E. Verdeny  P. Masqu  K. Maiti  J. Garcia-Orellana  J.M. Bruach  C. Mahaffey  C.R. Benitez-Nelson 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1461

Particle export from the upper waters of the oligotrophic ocean may play a crucial role in the global carbon cycle. Mesoscale eddies have been hypothesized to inject new nutrients into oligotrophic surface waters, thereby increasing new production and particle export in otherwise nutrient deficient regimes. The E-Flux Program was a large multidisciplinary project designed to investigate the physical, biological and biogeochemical characteristics of cold-core cyclonic eddies that form in the lee of the Hawaiian Islands. There, we investigated particle dynamics using ²¹⁰Pb–²¹⁰Po disequilibrium. Seawater samples for ²¹⁰Pb and ²¹⁰Po were collected both within (IN) and outside (OUT) of two cyclones, Noah and Opal, at different stages of their evolution as well as from the eddy generation region. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO₂) export fluxes were determined using water-column PC, PN, and bSiO₂ inventories and the residence times of ²¹⁰Po. PC and PN fluxes at 150 m ranged from 1.58±0.10 to 1.71±0.16 mmol C m⁻² d⁻¹ and 0.22±0.02 to 0.30±0.02 mmol N m⁻² d⁻¹ within Cyclones Opal and Noah. PC and PN fluxes at OUT stations sampled during both cruises were of similar magnitudes, 1.69±0.16 to 1.67±0.16 mmol C m⁻² d⁻¹ and 0.30±0.03 to 0.26±0.03 mmol N m⁻² d⁻¹. The bSiO₂ fluxes within Cyclone Opal were 0.157±0.010 mmol Si m⁻² d⁻¹ versus 0.025±0.002 mmol Si m⁻² d⁻¹ at OUT stations. These results of minimal PC and PN export, but significant eddy-induced bSiO₂ fluxes, agree very well with other studies that used a variety of direct and indirect methods. Thus, our results suggest that using elemental inventories and residence times of ²¹⁰Po is another independent and robust method for determining particle export and should be investigated more fully.  相似文献   

Recent sediments, sediment accumulation and carbon burial at Goban Spur, N.W. European Continental Margin (47–50°N)     

Tj. C. E. van Weering  I. R. Hall  H. C. de Stigter  I. N. McCave  L. Thomsen 《Progress in Oceanography》1998,42(1-4)

To quantify recent sediment accumulation, carbon fluxes and cycling, three N.W. European Continental Margin transects on Goban Spur and Meriadzek Terrace were extensively studied by repeated box- and multicore sampling of bottom sediments. The recent sediment distribution and characteristics appear directly related to the near-bed hydrodynamic regime on the margin, which at the upper slope break on the Goban Spur results in along-slope and periodic off-slope directed transport of particles, possibly by entrainment of particles in a detached bottom or intermediate nepheloid layer. From the shelf to the abyssal plain the surface sediments on the Goban Spur change from terrigenous sandy shelf sediments into clayey silts. ²¹⁰Pb activity decreases exponentially down core, reaching a stable background value at 10 cm (shallower stations) to 5 cm (deeper stations) sediment depth. ²¹⁰Pb profiles of repeatedly sampled stations indicate negligible annual variability of mixing and flux. The ²¹⁰Pb_xs flux to the sediment shows a decreasing trend with increasing water depth. Below about 2000 m the average ²¹⁰Pb_xs flux is about 0.3 dpm cm⁻² y⁻¹, a third of the fluxes measured on the shelf and upper slope stations. Sediment mixing rates (D_b) correlate with macro- and meiofaunal density changes and are within the normal oceanic ranges. Lower mixing rates on the lower slope likely reflect lower organic carbon fluxes there. Mass accumulation rates on Meriadzek Terrace are at maximum 80 g m⁻² y⁻¹, almost twice as high as at Goban Spur stations of comparable depth. A minimum accumulation rate of 16.6 g m⁻² y⁻¹ is found at the Goban Spur upper slope break. Organic carbon burial rates are low compared to other margins and range from a lowest value of 0.05 g m⁻² y⁻¹ at the upper slope break to 0.11 g m⁻² y⁻¹ downslope. A maximum organic carbon burial rate of 0.41 g m⁻² y⁻¹ is found on Meriadzek Terrace. Carbonate burial rates increase along the northern transect from the shelf (13 g m⁻² y⁻¹) via a low (9.3 g m⁻² y⁻¹) on the upper slope break to the deep sea (30.7 g m⁻² y⁻¹). Carbonate burial is highest on Meriadzek Terrace (44.5 g m⁻² y⁻¹). The N.W. European Margin at Goban Spur and Meriadzek Terrace cannot be considered a major carbon depocenter.  相似文献   

Calcareous nannofossil and planktonic foraminiferal distributional patterns during deposition of sapropels S6, S5 and S1 in the Libyan Sea (Eastern Mediterranean)   总被引：1，自引：1，他引：0  

Maria V. Triantaphyllou  Assimina Antonarakou  Margarita Dimiza  Christos Anagnostou 《Geo-Marine Letters》2010,30(1):1-13

In core ADE3-23 collected in the Libyan Sea, the nannofossil species Coccolithus pelagicus, Coronosphaera spp., Helicosphaera spp., Syracosphaera spp., Calcidiscus spp., small Gephyrocapsa spp., and the planktonic foraminifers Globigerina bulloides, Neogloboquadrina pachyderma, Globorotalia scitula, Turborotalita quinqueloba and Neogloboquadrina dutertrei prevail in sapropel S6 (midpoint at 172 ka b.p.), indicative of cold and highly productive surface conditions. Warm and highly stratified water-column conditions are recorded by the characteristic assemblage of Globigerinoides ruber, Globoturborotalita rubescens, Florisphaera profunda, Rhabdosphaera spp. during the sapropel S5 depositional interval (midpoint at 124 ka b.p.). Compared with S5, Globigerinita glutinata, Globorotalia inflata, Globigerinella siphonifera, Globorotalia truncatulinoides and the calcareous nannofossil Emiliania huxleyi characterise less stratified conditions within sapropel S1 (midpoint at 8.5 ka b.p.). Multivariate statistical analyses of calcareous nannofossil and planktonic foraminifers in core ADE3-23 identify planktonic assemblages which typify sapropels S6, S5 and S1 in the Libyan Sea. A warmer interval is recognised in the middle part of the cold S6, and can be associated with an influx of less saline waters and the occurrence of a faint, temporary deep chlorophyll maximum. Evidence for enhanced surface productivity and breakdown of stratification is observed in the middle–upper part of the warm S5, associated with climatic deterioration. Moreover, an increase in surface productivity in the upper S1 implies weak stratification. Our combined calcareous nannofossil and planktonic foraminiferal data add to the evidence that climate variability was more pronounced than commonly considered to date for all the three studied Eastern Mediterranean sapropel depositional intervals.  相似文献