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1.
Response of the North Pacific subtropical countercurrent (STCC) and its variability to global warming is examined in a state-of-the-art coupled model that is forced by increasing greenhouse gas concentrations. Compared with the present climate, the upper ocean is more stratified, and the mixed layer depth (MLD) shoals in warmer climate. The maximum change of winter MLD appears in the Kuroshio–Oyashio extension (KOE) region, where the mean MLD is the deepest in the North Pacific. This weakens the MLD front and reduces lateral induction. As a result of the reduced subduction rate and a decrease in sea surface density in KOE, mode waters form on lighter isopycnals with reduced thickness. Advected southward, the weakened mode waters decelerate the STCC. On decadal timescales, the dominant mode of sea surface height in the central subtropical gyre represents STCC variability. This STCC mode decays as CO2 concentrations double in the twenty-first century, owing both to weakened mode waters in the mean state and to reduced variability in mode waters. The reduced mode-water variability can be traced upstream to reduced variations in winter MLD front and subduction in the KOE region where mode water forms.  相似文献   

2.
Seasonal and interannual variations in physicochemical properties were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from December 2000 to December 2005. Physicochemical properties (i.e. temperature, salinity, density, dissolved oxygen and dissolved inorganic nutrient concentration) revealed clear seasonal variations, which were similar to each other during all 5 years. Temperature, salinity and dissolved inorganic nutrients showed rapid, drastic variations within a few days and/or weeks. These variations are related to sea levels, principally due to the shifting effects of the Kuroshio Current axis: they were strongly affected by the Kuroshio Water and other waters, when sea level difference was greater than ca. 35 cm and lower than ca. 15 cm, respectively. Temperature difference (DF T ) increased with sea level difference, and the difference of salinity and dissolved inorganic nutrients (NH4 +-N, NO3 −+NO2 −-N, NH4 ++NO3 −+NO2 −-N, PO4 3−-P and SiO2-Si) increased and decreased with DF T , respectively. All these correlations are significant. Total dissolved inorganic nitrogen (N), phosphate (P) and silicate (Si) revealed seasonal variations in the ranges of 0.57–16.08, 0.0070–0.91 and 0.22–46.38 μM, respectively. From the regression equations between these elements allowed the following relation to be obtained; Si:N:P = 14.8:13.4:1. Dissolved inorganic nutrients were characterized by Si and/or P deficiency, especially in the upper layer (0–20 m depth) during summer. Single and/or combined elements are discussed on the basis of potential and stoichiometric nutrient limitations, which could restrict phytoplankton (diatom) growth as a limiting factor.  相似文献   

3.
Seasonal and interannual variability of the Subtropical Countercurrent (STCC) in the western North Pacific are investigated using observations by satellites and Argo profiling floats and an atmospheric reanalysis. The STCC displays a clear seasonal cycle. It is strong in late winter to early summer with a peak in June, and weak in fall. Interannual variations of the spring STCC are associated with an enhanced subtropical front (STF) below the surface mixed layer. In climatology, the SST front induces a band of cyclonic wind stress in May north of the STCC on the background of anticyclonic curls that drive the subtropical gyre. The band of cyclonic wind and the SST front show large interannual variability and are positively correlated with each other, suggesting a positive feedback between them. The cyclonic wind anomaly is negatively correlated with the SSH and SST below. The strong (weak) cyclonic wind anomaly elevates (depresses) the thermocline and causes the fall (rise) in the SSH and SST, accelerating (decelerating) STCC to the south. It is suggested that the anomalies in the SST front and STCC in the preceding winter affect the subsequent development of the cyclonic wind anomaly in May. Results from our analysis of interannual variability support the idea that the local wind forcing in May causes the subsequent variations in STCC.  相似文献   

4.
Regional variations in the contribution of non-photosynthetic pigments (ā np*) to the total light absorption of phytoplankton (ā ph*) and its influence on the maximum quantum yield of photosynthesis (φ m) were investigated. In the western equatorial Pacific, the surface ā np* : ā ph* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin in the western warm pool. In the subarctic North Pacific, the ā np* : ā ph* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria were more abundant in the Western Subarctic Gyre. The values of ā np* : ā ph* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā np* : ā ph* significantly influence φ m. In comparison with φ m based on the total light absorption (φ m ph), the values corrected for the contribution of non-photosynthetic pigments (φ m ps) showed an increase in both the western equatorial Pacific and the subarctic North Pacific.  相似文献   

5.
To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80 -100 E along 7 S, and 7 -18 S along 80 E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168 ± 0.095) mg/m 3 s.d. (range: 0.034-0.475 mg/m 3 ), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034-0.066 mg/m 3 ) in the region to the south of 16 S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant: correlation and regression analysis suggests that it was primarily affected by PO 3 4 , N(NO 3 -N+NO 2 -N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.  相似文献   

6.
The global distributions of the major semidiurnal (M2 and S2) and diurnal (K1 and O1) baroclinic tide energy are investigated using a hydrostatic sigma-coordinate numerical model. A series of numerical simulations using various horizontal grid spacings of 1/15–1/5° shows that generation of energetic baroclinic tides is restricted over representative prominent topographic features. For example, nearly half of the diurnal (K1 and O1) baroclinic tide energy is excited along the western boundary of the North Pacific from the Aleutian Islands down to the Indonesian Archipelago. It is also found that the rate of energy conversion from the barotropic to baroclinic tides is very sensitive to the horizontal grid spacing as well as the resolution of the model bottom topography; the conversion rate integrated over the global ocean increases exponentially as the model grid spacing is reduced. Extrapolating the calculated results in the limit of zero grid spacing yields the estimate of the global conversion rate to be 1105 GW (821, 145, 102, 53 GW for M2, S2, K1, and O1 tidal constituents, respectively). The amount of baroclinic tide energy dissipated in the open ocean below a depth of 1000 m, in particular, is estimated to be 500–600 GW, which is comparable to the mixing energy estimated by Webb and Suginohara (Nature 409:37, 2001) as needed to sustain the global overturning circulation.  相似文献   

7.
We provide an expert quality assessment of the data for 1932–1993 and used these data to perform the numerical analysis of the carbonate system of the aerobic zone in the Black Sea. The intraannual and long-term variations of the carbonate system are studied in the abyssal part of the sea for 1960–1993. We propose explanations of the intraannual variations of the analyzed system for various layers of the aerobic zone and reveal long-term variations of the pH values, total alkalinity, and the ratios of the components of the carbonate system. We discover and explain the observed increase in the concentrations of TCO2 and CO2 and the partial pressure of carbon dioxide pCO2, as well as a decrease in pH values and the concentration of CO32− in waters of the aerobic zone of the Black Sea.  相似文献   

8.
We have measured inorganic nitrogen (IN) content and the isotope ratio of IN (δ15NIN) in a sediment core covering the last 145 kyr in the western subarctic Pacific (WSAP). IN content was generally high during glacial periods and shows positive correlations with both eolian dust content and the ratio of organic carbon (C) to organic nitrogen (ON) (C/ON) found in our previous studies. This means that IN was transported from continental areas to the WSAP together with eolian dust and that the IN was not contaminated by volcanic materials, because the eolian dust content was reconstructed using metal components to remove contaminating volcanic materials. Therefore, IN content in the WSAP sediments, the clay fraction of which is not greatly affected by drift deposits seen at the other sites in this region, may potentially be an effective proxy for eolian dust, without the need to consider contamination by volcanic materials. δ15NIN was generally low during glacial periods and shows negative correlations with IN, eolian dust, and C/ON. The possible causes of the observed variations in δ15NIN are as follows: (1) authigenic fixation of NH4 + in water-column and pore water of sea-floor sediments to clay minerals; (2) contamination of measured IN by highly resistant organic matter; or (3) variations in the continental source region of the eolian dust supplied to the WSAP and climatically induced changes in δ15N of soil organic matter there. The last mechanism shows the potential for δ15NIN to be used as a proxy for climate change on land, and is consistent with other published explanations of the spatial distribution of δ15NIN in modern sea-floor sediments.  相似文献   

9.
Data from the R/V Mirai cruise (May–June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics direct affect the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air pCO2 difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate show that the anticylonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and DIC between the upper (σθ = 26.7–27.0) and lower (σθ = 27.1–27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

10.
The light-saturated maximum value (P B max) and initial slope (α) of the photosynthesis-irradiance (P-E) curve were examined in a warm streamer, a cold streamer and a warm core ring off the Sanriku area in the subarctic western North Pacific Ocean during an ADEOS/OCTS Sanriku field campaign in early May 1997. BothP B max and α were within the ranges of temperate populations. A regional difference was apparent inP B max: populations in the warm streamer tended to show higher value ranging between 1.92 and 4.74 mgC (mgChla)−1h−1 than those in the cold streamer and the warm core ring (1.35–2.87 mgC (mgChla)−1h−1). A depth variation was also observed in α in both the warm streamer and the warm core ring: shallow populations tended to have lower α than deep populations. The depth variations in bothP B max and α resulted in a lower light intensity of the light saturation in a deeper population than that of a shallower one. These depth-related variations in the P-E parameters were likely a manifestation of “shade-adaptation” of photosynthesis. Photoinhibition was not observed over in situ surface light intensity varying below ca 1600 μmol photon m−2s−1. Water-column primary productivity was biooptically estimated to be 233 to 949 mgC m−2d−1 using vertical distributions of the P-E parameters, chlorophylla, phytoplankton light absorption and underwater irradiance. Applicability of surface data sets for estimation of water-column productivity is discussed.  相似文献   

11.
Satellite instruments for the routine global monitoring of NO2 in the atmosphere—the Global Ozone Monitoring Experiment (GOME) on the ERS-2 satellite, the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on the ENVISAT satellite, the Ozone Monitoring Instrument (OMI) on the AURA satellite, and the GOME-2 on the MetOp satellite—are briefly described. It is shown that the error of measuring the NO2 total column amount (∼10% for the background conditions in the troposphere) substantially increases in regions subject to anthropogenic pollution. Examples of practically using multiyear satellite measurements for the regional monitoring of NO2 in the troposphere are presented, including mapping the tropospheric NO2 in Russia, identifying the weekly and annual cycles in tropospheric NO2 variations for megalopolises (St. Petersburg, Moscow, Paris), and estimating the long-term linear trend in 1995–2007.  相似文献   

12.
Rare earth elements (REEs) of 91 fine-grained bottom sediment samples from five major rivers in Korea (the Han, Keum, and Yeongsan) and China (the Changjiang and Huanghe) were studied to investigate their potential as source indicator for Yellow Sea shelf sediments, this being the first synthetic report on REE trends for bottom sediments of these rivers. The results show distinct differences in REE contents and their upper continental crust (UCC)-normalized patterns: compared to heavy rare earth elements (HREEs), light rare earth elements (LREEs) are highly enriched in Korean river sediments, in contrast to Chinese river sediments that have a characteristic positive Eu anomaly. This phenomenon is observed also in primary source rocks within the river catchments. This suggests that source rock composition is the primary control on the REE signatures of these river sediments, due largely to variations in the levels of chlorite and monazite, which are more abundant in Korean bottom river sediments. Systematic variations in ΣLREE/ΣHREE ratios, and in (La/Yb)–(Gd/Yb)UCC but also (La/Lu)–(La/Y)UCC and (La/Y)–(Gd/Lu)UCC relations have the greatest discriminatory power. These findings are consistent with, but considerably expand on the limited datasets available to date for suspended sediments. Evidently, the REE fingerprints of these river sediments can serve as a useful diagnostic tool for tracing the provenance of sediments in the Yellow Sea, and for reconstructing their dispersal patterns and the circulation system of the modern shelf, as well as the paleoenvironmental record of this and adjoining marginal seas.  相似文献   

13.
A complex analysis of the hydrooptical and dynamic parameters of the Atlantic surface waters has been made on the basis of experimental data. It is shown that the structural properties of the distribution of the basic hydrooptical parameters—such as the optical water-type index m (according to Prof. V.N. Pelevin’s classification), surface-water transparency (the depth of white-disc visibility Z σ), circulation parameter (the dynamic height D at a depth of 100 m), and flow fields—are similar. On the basis of this, in the authors’ previous studies, relations between these parameters were obtained and the empirical dependences Z σ(m) and D(m) were found. These dependences and the earlier obtained relationships between biological and optical parameters-chlorophyll concentrations c p (m) and the indices of light attenuation by a soluted “yellow substance” a ys (m) and suspended matter a sm (m)—were combined and formed the basis of a method to determine them at any point of the open ocean from the measured (also remotely) parameter m. The results of the measurements of hydro-optical parameters (which were taken as part of the Meridian project from the Akademik Ioffe during its 14th voyage in October-November 2003) supported the validity of calculations of variations in the five parameters indicated above from the values of the index m. Thus, the efficiency of the developed rapid method of estimating variations in a set of parameters according to the optical water-type index m was demonstrated. In addition, the water’s “health” index H w proposed by Pelevin in 2002, which is equal to the ratio between chlorophyll concentrations and soluted yellow substance, proved to be efficient at identifying the ecological state of the near-surface waters.  相似文献   

14.
Concentrations of particulate organic nitrogen (PN), dissolved inorganic nitrogen (DIN), and their nitrogen isotope ratios (δ 15N) in the Kiso-Sansen Rivers were determined from monthly observations over the course of a year to assess variations in the form and sources of riverine nitrogen discharged into Ise Bay. The δ 15N values of NO3 − observed in the Kiso-Sansen Rivers showed a logarithmic decreasing trend from 8 to 0‰, which varied with the river discharge, indicating mixing between point sources with high δ 15N and non-point sources with low δ 15N. The influence of isotope fractionation of in situ biogeochemical processes (mainly DIN assimilation by phytoplankton) on δ 15N of NO3 − was negligible, because sufficient concentrations of NH4 + for phytoplankton demand would inhibit the assimilation of NO3 −. A simple relationship between river discharge and δ 15N of NO3 − showed that the fraction of total NO3 − flux arising from point sources increased from 4.0–6.3% (1.1–1.8 tN day−1) during higher discharge (>600 m3 s−1) to 30.2–48.3% (2.6–4.1 tN day−1) during lower discharge (<300 m3 s−1). Riverine NO3 − discharge from the Kiso-Sansen Rivers can explain 75% of the variations in surface NO3 − at the head of Ise Bay over the year.  相似文献   

15.
Numerical study of baroclinic tides in Luzon Strait   总被引：6，自引：1，他引：5  
The spatial and temporal variations of baroclinic tides in the Luzon Strait (LS) are investigated using a three-dimensional tide model driven by four principal constituents, O1, K1, M2 and S2, individually or together with seasonal mean summer or winter stratifications as the initial field. Barotropic tides propagate predominantly westward from the Pacific Ocean, impinge on two prominent north-south running submarine ridges in LS, and generate strong baroclinic tides propagating into both the South China Sea (SCS) and the Pacific Ocean. Strong baroclinic tides, ∼19 GW for diurnal tides and ∼11 GW for semidiurnal tides, are excited on both the east ridge (70%) and the west ridge (30%). The barotropic to baroclinic energy conversion rate reaches 30% for diurnal tides and ∼20% for semidiurnal tides. Diurnal (O1 and K1) and semidiurnal (M2) baroclinic tides have a comparable depth-integrated energy flux 10–20 kW m−1 emanating from the LS into the SCS and the Pacific basin. The spring-neap averaged, meridionally integrated baroclinic tidal energy flux is ∼7 GW into the SCS and ∼6 GW into the Pacific Ocean, representing one of the strongest baroclinic tidal energy flux regimes in the World Ocean. About 18 GW of baroclinic tidal energy, ∼50% of that generated in the LS, is lost locally, which is more than five times that estimated in the vicinity of the Hawaiian ridge. The strong westward-propagating semidiurnal baroclinic tidal energy flux is likely the energy source for the large-amplitude nonlinear internal waves found in the SCS. The baroclinic tidal energy generation, energy fluxes, and energy dissipation rates in the spring tide are about five times those in the neap tide; while there is no significant seasonal variation of energetics, but the propagation speed of baroclinic tide is about 10% faster in summer than in winter. Within the LS, the average turbulence kinetic energy dissipation rate is O(10−7) W kg− 1 and the turbulence diffusivity is O(10−3) m2s−1, a factor of 100 greater than those in the typical open ocean. This strong turbulence mixing induced by the baroclinic tidal energy dissipation exists in the main path of the Kuroshio and is important in mixing the Pacific Ocean, Kuroshio, and the SCS waters.  相似文献   

16.
The predictability of catastrophic earthquakes according to data on time variations in tidal response is discussed. We present the results of a harmonic analysis of (1) a one-year record of tide-gauge observations with the use of two long-term vertical seismometers at the MAJO station on Honshu Island near the epicenter of the M w = 9 catastrophic earthquake of March 11, 2011, and (2) a 0.5-year record of horizontal pendulum observations at the ERM station near Hokkaido Island from March 13, 2010, to March 12, 2011, and from April 26, 2010, to August 3, 2010, respectively. The relative changes in the tidal amplitudes are found to be about 3 and 4%. The identification of distinct prognostic attributes awaits much more representative spatiotemporal statistics. These results can be adequately and reliably interpreted by analyzing “background” variations in the tidal amplitudes at these stations and, in particular, their possible seasonal variations. This requires at least several years of observations.  相似文献   

17.
A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH4 +−N, (NO3 −+NO2 −)−N, PO4 3−−P and Si (OH)4−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r 2=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r 2=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.  相似文献   

18.
Large eddy simulation (LES) of the resonant inertial response of the upper ocean to strong wind forcing is carried out; the results are used to evaluate the performance of each of the two second-order turbulence closure models presented by Mellor and Yamada (Rev Geophys Space Phys 20:851–875, 1982) (MY) and by Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) (NN). The major difference between MY and NN is in the formulation of the stability functions and the turbulent length scale, both strongly linked with turbulent fluxes; in particular, the turbulent length scale in NN, unlike that in MY, is allowed to decrease with increasing density stratification. We find that MY underestimates and NN overestimates the development of mixed layer features, for example, the strong entrainment at the base of the oceanic mixed layer and the accompanying decrease of sea surface temperature. Considering that the stability functions in NN perform better than those in MY in reproducing the vertical structure of turbulent heat flux, we slightly modify NN to find that the discrepancy between LES and NN can be reduced by more strongly restricting the turbulent length scale with increasing density stratification.  相似文献   

19.
The wave friction factor is commonly expressed as a function of the horizontal water particle semi-excursion (A wb) at the top of the boundary layer. A wb, in turn, is normally derived from linear wave theory by \fracU\textwbT\textw2p \frac{{{U_{\text{wb}}}{T_{\text{w}}}}}{{2\pi }} , where U wb is the maximum water particle velocity measured at the top of the boundary layer and T w is the wave period. However, it is shown here that A wb determined in this way deviates drastically from its real value under both linear and non-linear waves. Three equations for smooth, transitional and rough boundary conditions, respectively, are proposed to solve this problem, all three being a function of U wb, T w, and δ, the thickness of the boundary layer. Because these variables can be determined theoretically for any bottom slope and water depth using the deepwater wave conditions, there is no need to physically measure them. Although differing substantially from many modern attempts to define the wave friction factor, the results coincide with equations proposed in the 1960s for either smooth or rough boundary conditions. The findings also confirm that the long-held notion of circular water particle motion down to the bottom in deepwater conditions is erroneous, the motion in fact being circular at the surface and elliptical at depth in both deep and shallow water conditions, with only horizontal motion at the top of the boundary layer. The new equations are incorporated in an updated version (WAVECALC II) of the Excel program published earlier in this journal by Le Roux et al. Geo-Mar Lett 30(5): 549–560, (2010).  相似文献   

20.
A Subtropical Countercurrent (STCC) is a narrow eastward jet on the equator side of a subtropical gyre, flowing against the broad westward Sverdrup flow. Together with theories, recent enhanced observations and model simulations have revealed the importance of mode waters in the formation and variability of North Pacific STCCs. There are three distinct STCCs in the North Pacific, maintained by low potential vorticity (PV) that mode waters carry from the north. Model simulations show that changes in mode water ventilation result in interannual to interdecadal variations and long-term changes of STCCs. STCCs affect the atmosphere through their surface thermal effects, inducing anomalous cyclonic wind curl and precipitation along them. Thus, mode waters are not merely passive water masses but have dynamical and climatic effects. For temporal variability, atmospheric forcings are also suggested to be important in addition to the variability of mode waters. STCCs exist in other oceans and they are also flanked by mode waters on their poleward sides, suggesting that they are maintained by similar dynamics.  相似文献   

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