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1.
A 12.7-year series of weekly absolute sea surface height (SSH) data in the region south of Africa is used for a statistical characterization of the location of the Agulhas Current retroflection and its variations at periods up to 2 years. The highest probability of presence of the retroflection point is at ～39.5°S/18–20°E. The longitudinal probability density is negatively skewed. A sharp eastward decrease at 22°E is related to detachments of the Agulhas Current from the continental slope at this longitude. The asymmetry in the central part of the distribution might reflect a westward increase of the zonal velocity of the retroflection point during its east–west pulsations. The western tail of the distribution reveals larger residence times of the retroflection at 14°E–15°E, possibly related to a slowing down of its westward motion by seamounts. While the averaged zonal velocity component of the retroflection point increases westward, its modulus exhibits an opposite trend, the result of southward velocity components more intense in the northeastern Agulhas Basin than farther west. These meridional motions likely reflect influences by cyclones adjacent to the Agulhas Current south of the Agulhas Bank, and farther west in the Cape Basin. In the latter area, variations of the meridional motions result in different positions of the westernmost retroflection patterns relative to the neighbouring seamounts, likely influencing the future behaviour of Agulhas rings shed at these locations. Agulhas ring formation at an average yearly rate of 5.8, similar to previous findings, was observed to occur west of ～19°E, in the western half of the retroflection probability domain. A well-defined seasonal signal of the retroflection longitude was found throughout the first 5 years of the time series, characterized by amplitudes of 1–1.3° of longitude, and western (eastern) extremes during austral summer (winter). This annual cycle was strongly phase shifted during and after the upstream retroflection event of 2000–2001.  相似文献   

2.
A long-term mean turbulent mixing in the depth range of 200–1000 m produced by breaking of internal waves across the middle and low latitudes (40°S–40°N) of the Pacific between 160°W and 140°W is examined by applying fine-scale parameterization depending on strain variance to 8-year (2005–2012) Argo float data. Results show that elevated turbulent dissipation rate (ε) is related to significant topographic regions, along the equator, and on the northern side of 20°N spanning to 24°N throughout the depth range. Two patterns of latitudinal variations of ε and the corresponding diffusivity (Kρ) for different depth ranges are confirmed: One is for 200–450 m with significant larger ε and Kρ, and the maximum values are obtained between 4°N and 6°N, where eddy kinetic energy also reaches its maximum; The other is for 350–1000 m with smaller ε and Kρ, and the maximum values are obtained near the equator, and between 18°S and 12°S in the southern hemisphere, 20°N and 22°N in the northern hemisphere. Most elevated turbulent dissipation in the depth range of 350–1000 m relates to rough bottom roughness (correlation coefficient?=?0.63), excluding the equatorial area. In the temporal mean field, energy flux from surface wind stress to inertial motions is not significant enough to account for the relatively intensified turbulent mixing in the upper layer.  相似文献   

3.
Decadal variations of the transport and bifurcation latitude of the North Equatorial Current (NEC) in the northwestern tropical Pacific Ocean over 1959–2011 are investigated using outputs of the Ocean Analysis/Reanalysis System 3 prepared by the European Centre for Medium-Range Weather Forecasts. The results indicate that the NEC transports at different longitudes have different decadal fluctuations, which are strongest around 139°E. The NEC bifurcation latitude (NBL) has its largest decadal variations around 150 m. Extremes of the decadal NEC transport and NBL before 1975 correspond to different circulation anomalies from those after 1975. The regression map against decadal NBL exhibits negative sea surface height (SSH) anomalies and a cyclonic gyre anomaly over the northwestern tropical Pacific Ocean, while that against the decadal NEC transport exhibits a dipole structure, with positive/negative SSH anomalies to the north/south of about 13°N. Furthermore, decadal variations of the NEC transport and NBL over the whole period have different correlations with Pacific Decadal Oscillation (PDO) and Tropical Pacific Decadal Variability (TPDV). Generally, the decadal NEC transport shows higher correlations with PDO than with TPDV, while the NBL has higher correlations with TPDV than with PDO. The high correlation of decadal NEC transport with PDO mainly comes from that of its northern branch with PDO, while its southern branch shows higher correlation with TPDV.  相似文献   

4.
To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F v/F m) and effective absorption cross-section of photosystem II (σPSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F v/F m [Z(F v/F m max)] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F v/F m at the Z(F v/F m max) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.  相似文献   

5.
Turbulent mixing in the central equatorial Pacific has been quantitatively evaluated by analyzing data from microstructure measurements and conductivity temperature depth profiler (CTD) observations in a meridionally and vertically large region. The result that strong turbulent mixing with dissipation rate ε (>O(10?7) W kg?1), continuing from sea-surface mixed layer to low Richardson number region below, in the area within 1° of the equator, shows that turbulent mixing has a close relationship to shear instability. ε > O(10?7) W kg?1 and turbulent diffusivity K ρ  > O(10?3) m2 s?1 were obtained from near-surface to 85 db at stations even southwardly beyond 3°S, where it is already far from the southern boundary (~2°S) of the Equatorial Undercurrent. Turbulence-induced heat flux and salinity flux were calculated, and both had their maxima in the equatorial upwelling region, though the former was downward and the latter was upward. Accordingly, vertical velocity in the upwelling region was estimated to be similar to the results derived by other methods. These fluxes and the vertical velocity suggest the critical importance of turbulent mixing in maintaining the well-mixed upper layer. Secondly, in the intermediate region (>500 db), turbulent eddies were investigated by applying Thorpe’s method to the CTD data. A large number of overturns were detected, with spatial-averaged K ρ (700–1,000 db) being 3.3 × 10?6 m2 s?1, and the corresponding K ρ-max reaching to O(10?4) m2 s?1 in the north (3°–13°N). The results suggest that, in the intermediate region, considerable turbulent mixing occurs and moderates the properties of the water masses.  相似文献   

6.
In this work, the vertical structure and variability along the western boundary of the Philippines are investigated using direct observations from acoustic Doppler current profiler (ADCP), Doppler volume sampler (DVS) and Aanderaa Seaguard instruments, which are mounted on a subsurface mooring deployed at 8°N, 127°3′E. In climatology, the southward Mindanao Current (MC) and northward Mindanao Undercurrent (MUC) play a dominant role in the upper layer. The mean currents at 1200 and 3500 m flow northward, whereas those at 2500 and 5600 m flow equatorward. The power spectral density (PSD) shows that an intraseasonal signal of 60–80 days is common from the sea surface to the bottom. The semiannual signals are strongest in the MUC layer, and the amplitude then decreases with depth to 3500 m. The seasonal variability at 2500 and 5600 m is similar between the two depths, suggesting a southward current in winter and northward flow in autumn. The current at 3500 m exhibits a northward direction in spring and southward flow in winter. In addition, the linear correlations between mooring data and altimetry products indicate that the variations in surface meridional currents along the western boundary of the Pacific Ocean can reach the bottom via low-frequency processes. The vertical-mode decomposition for observations indicates that the first four modes can effectively capture the original data. The relative contributions of different modes exhibit seasonal variability. The first baroclinic mode plays a dominant role in spring and autumn. In winter and summer, its contribution decreases and becomes comparable to that of the other modes.  相似文献   

7.
We measured dissolved isoprene (2-methyl-1,3-butadiene; C5H8) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35°S to 64°S and from 37°E to 111°E during austral summer 2010–2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L?1 and from 181 to 313 nmol m?2 day?1, respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll-a concentrations (r 2 = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (>53°S) we identified a significant negative correlation (r 2 = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO2), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO2 are similar within a physically stable water column.  相似文献   

8.
The distribution of pH and alkalinity has been used to calculate the distribution of total inorganic carbon (TC) and fugacity of carbon dioxide (fCO2) in the upper 200 m of the water column in coastal upwelling areas off northern Chile (23–24°S, near Antofagasta) and central Chile (30–31°S, near Coquimbo) during austral summer 1997. In these upwelling areas, colder surface waters were oxygen poor and strongly CO2 supersaturated (100% near Antofagasta and 200% near Coquimbo), although below the pycnocline the CO2 supersaturation invariably exceeded 200% in both areas. The larger surface CO2 supersaturation and outgassing at 30°S were associated with stronger winds that promoted the upwelling of denser water (richer in CO2) as well as a higher air–sea CO2 transfer velocity. The consistent decrease in intensity of the southerly winds (as derived from NSCAT scatterometer data) from 30–31°S to 23–24°S suggests a corresponding decline in the intensity of the CO2 outgassing due to upwelling. Additionally, we suggest here that the intensity of the local upwelling forcing (i.e. alongshore–equatorward winds) plays a role in determining the water mass composition and phytoplankton biomass of the coastal waters. Thus, while deep upwelling of salty and cold water resulted in high fCO2 (up to 1000 μatm) and very low phytoplankton biomass (chlorophyll a concentration lower than 0.5 mg m−3), the shallow upwelling of less salty (e.g. salinity <34.5) and less CO2-supersaturated water resulted in a higher phytoplankton biomass, which further reduced surface water fCO2 by photosynthesis.  相似文献   

9.
Hydrographic, geochemical, and direct velocity measurements along two zonal (7.5°N and 4.5°S) and two meridional (35°W and 4°W) lines occupied in January–March, 1993 in the Atlantic are combined in an inverse model to estimate the circulation. At 4.5°S, the Warm Water (potential temperature θ>4.5°C) originating from the South Atlantic enters the equatorial Atlantic, principally at the western boundary, in the thermocline-intensified North Brazil Undercurrent (33±2.7×106 m3 s−1 northward) and in the surface-intensified South Equatorial Current (8×106 m3 s−1 northward) located to the east of the North Brazil Undercurrent. The Ekman transport at 4.5°S is southward (10.7±1.5×106 m3 s−1). At 7.5°N, the Western Boundary Current (WBC) (17.9±2×106 m3 s−1) is weaker than at 4.5°S, and the northward flow of Warm Water in the WBC is complemented by the basin-wide Ekman flow (12.3±1.0×106 m3 s−1), the net contribution of the geostrophic interior flow of Warm Water being southward. The equatorial Ekman divergence drives a conversion of Thermocline Water (24.58⩽σ0<26.75) into Surface Water (σ0<24.58) of 7.5±0.5×106 m3 s−1, mostly occurring west of 35°W. The Deep Water of northern origin flows southward at 7.5°N in an energetic (48±3×106 m3 s−1) Deep Western Boundary Current (DWBC), whose transport is in part compensated by a northward recirculation (21±4.5×106 m3 s−1) in the Guiana Basin. At 4.5°S, the DWBC is much less energetic (27±7×106 m3 s−1 southward) than at 7.5°N. It is in part balanced by a deep northward recirculation east of which alternate circulation patterns suggest the existence of an anticyclonic gyre in the central Brazil Basin and a cyclonic gyre further east. The deep equatorial Atlantic is characterized by a convergence of Lower Deep Water (45.90⩽σ4<45.83), which creates an upward diapycnal transport of 11.0×106 m3 s−1 across σ4=45.83. The amplitude of this diapycnal transport is quite sensitive to the a priori hypotheses made in the inverse model. The amplitude of the meridional overturning cell is estimated to be 22×106 m3 s−1 at 7.5°N and 24×106 m3 s−1 at 4.5°S. Northward heat transports are in the range 1.26–1.50 PW at 7.5°N and 0.97–1.29 PW at 4.5°S with best estimates of 1.35 and 1.09 PW.  相似文献   

10.
Composite analysis was conducted using high-frequency radar data obtained during 2006–2015 in order to gain a better understanding of the current field in the Ariake Sea. The seasonally averaged surface current in the Ariake Sea was directed southward in all seasons, except around river mouths during summer. Heavy rainfall enhanced the outflow along the eastern coast of the Shimabara Peninsula from Isahaya Bay to the southern area 2–5 days after heavy rainfall. Spring–neap differences were clearly seen in the southward current along the Shimabara Peninsula. Interannual variation in the M2 tidal current amplitude was synchronized with the lunar nodal cycle.  相似文献   

11.
Between November 2001 and March 2002 an Australian/Japanese collaborative study completed six passes of a transect line in the Seasonal-Ice Zone (south of 62°S) along 140°E. Zooplankton samples were collected with a NORPAC net on 22–28 November, and a Continuous Plankton Recorder on 10–15 January, 11–12 February, 19–22 February, 25–26 February, and 10–11 March. Zooplankton densities were lowest on 22–28 November (ave=61 individuals (ind) m−3), when almost the entire transect was covered by sea ice. By 10–15 January sea surface temperature had increased by ∼2 °C across the transect line, and the study area was ice-free. Total zooplankton abundance had increased to maximum levels for the season (ave=1301 ind m−3; max=1979 ind m−3), dominated by a “Peak Community” comprising Oithona similis, Ctenocalanus citer, Clausocalanus laticeps, foraminiferans, Limacina spp., appendicularians, Rhincalanus gigas and large calanoid copepodites (C1–3). Total densities declined on each subsequent transect, returning to an average of 169 ind m−3 on 10–11 March. The seasonal density decline was due to the decline in densities of “Peak Community” taxa, but coincided with the rise of Euphausia superba larvae into the surface waters, increased densities of Salpa thompsoni, and an increased contribution of C4 to adult stages to the populations of Calanoides acutus, Calanus propinquus and Calanus simillimus. The seasonal community succession appeared to be influenced by the low sea ice extent and southward projection of the ACC in this region. The relatively warm ACC waters, together with low krill biomass, favoured high densities of small grazers during the January/February bloom conditions. The persistence of relatively warm surface waters in March and the seasonal decrease in chlorophyll a biomass provided favorable conditions for salps, which were able to penetrate south of the Southern Boundary.  相似文献   

12.
Satellite ocean colour remote sensing can serve as a powerful tool to assess river plume characteristics because it provides daily mapping of surface suspended particulate matter (SPM) concentration at high spatial resolution. This study’s ultimate objective was to better understand daily and seasonal particle dynamics in a coastal area strongly influenced by freshwater discharge and wind—the Rhône River (France), this being the major source of terrestrial input to the Mediterranean Sea. SPM concentrations and biogenic composition (chlorophyll a, organic carbon) were investigated during several bio-optical field campaigns conducted in spring–autumn of 2010 both from aboard a research vessel and by means of an autonomous profiling float. Freshwater discharge and wind velocities varied significantly during the year, associated with marked fluctuations in surface SPM (upper 1 m), even within hours and not restricted to any specific season. Thus, the range was ca. 12–25 g m–3 (dry mass basis) on 9 April (spring), and ca. 3–39 g m–3 on 4–5 November (late autumn). Short-term variations were observed also in SPM composition in terms of POC (albeit not chl a), with POC/SPM ratios ranging between ca. 3 and 11% over ca. 3 weeks in spring. Nevertheless, the particulate backscattering coefficient (b bp) proved to be a robust proxy of SPM concentration in the river plume (b bp(770)?=?0.0076?×?SPM, R2?=?0.80, N?=?56). It has recently been demonstrated that 80% of the Rhône’s terrestrial discharge occurs during flood events. The results of the present study revealed that, under these conditions, SPM is constrained largely within surface waters (i.e. at depths <5 m), with only weak daily vertical variability. By implication, ocean colour satellite data are highly suitable in meaningfully estimating the overall SPM load exported by the Rhône River to the Mediterranean. These findings make a solid contribution to future improvements of three-dimensional sediment transport models for the region and similar settings.  相似文献   

13.
This study compares the seasonal and interannual-to-decadal variability in the strength and position of the Kuroshio Extension front(KEF) using high-resolution satellite-derived sea surface temperature(SST) and sea surface height(SSH) data. Results show that the KEF strength has an obvious seasonal variation that is similar at different longitudes, with a stronger(weaker) KEF during the cold(warm) season. However, the seasonal variation in the KEF position is relatively weak and varies with longitude. In contrast, the low-frequency variation of the KEF position is more distinct than that of the KEF strength even though they are well correlated. On both seasonal and interannual-to-decadal time scales, the western part of the KEF(142°–144°E) has the greatest variability in strength, while the eastern part of the KEF(149°–155°E) has the greatest variability in position. In addition, the relationships between wind-forced Rossby waves and the low-frequency variability in the KEF strength and position are also discussed by using the statistical analysis methods and a wind-driven hindcast model. A positive(negative) North Pacific Oscillation(NPO)-like atmospheric forcing generates positive(negative) SSH anomalies over the central North Pacific. These oceanic signals then propagate westward as Rossby waves, reaching the KE region about three years later, favoring a strengthened(weakened) and northward(southward)-moving KEF.  相似文献   

14.
Shells of the rocky shore intertidal gastropod Osilinus turbinatus (von Born), often abundant in archaeological deposits in the Mediterranean region, are a potential source of data on palaeotemperature, palaeoseasonality and archaeological seasonality. To evaluate this species as a climate archive, investigations of annual patterns of shell growth and of monthly variations in oxygen isotopes in shell carbonates were made on different populations in NW Sicily. Mark-recapture experiments at San Vito lo Capo and Mazzaforno show that O. turbinatus grows almost continuously throughout the year but at different rates in different seasons. Around 75% of the yearly shell growth occurs in the autumn and winter. On average, larger/older shells produce narrower annual growth increments than smaller/younger ones. Conspicuous growth lines in larger/older shells show that growth stops during the hottest part of the summer. Oxygen isotope analyses on monthly collected shells of O. turbinatus from three shores (Cala Grande, Monte Cofano and Mazzaforno) show that the isotope values record temperature variations through the year. In all the datasets, surface seawater temperatures (SSTs) calculated from δ18OSHELL mostly underestimate measured SSTs, offsets being generally greater in summer. Minimum annual offsets range from 0.0°C to 0.7°C and maximum annual offsets from 3.1°C to 8.7°C. δ18OSHELL values fail to record temperatures higher than 25°C. Careful selection of shells to be analysed can reduce offsets between δ18OSHELL temperature estimates and measured SSTs for many parts of the year, except the hottest. Allowing for this, shells of O. turbinatus offer good potential as climate archives and for archaeological studies of seasonal patterns of human foraging for shellfish.  相似文献   

15.
The spatiotemporal variability of equatorial Pacific upper ocean heat content (HC) and subsurface heat during two types of El Niño-Southern Oscillation (ENSO), namely eastern and central Pacific (EP and CP) types, is investigated using subsurface ocean heat budget analysis. Results show that HC tendencies during both types of ENSO are mainly controlled by oceanic heat advection beneath the mixed layer to the thermocline, and the role of net surface heat flux can be neglected. The most important three terms are the zonal and vertical advections of anomalous heat by climatological currents (QU 0 T′, QW 0 T′) and zonal advection of climatological heat by anomalous current (QU′T 0). The large contribution of QU 0 T′ extends from west to east along the equatorial Pacific. The considerable contribution of QU′T 0 is confined to the east of 160°W, and that of the QW 0 T′ is observed in the central Pacific between 180°E and 120°W. In particular, a major contribution of QW 0 T′ is also observed in the far eastern Pacific east of 100°W during EP ENSO. There is also a small contribution from meridional advection of climatological heat by anomalous current (QV′T 0). In contrast, the meridional advection of anomalous heat by climatological currents (QV 0 T′) and vertical advection of climatological heat by anomalous current (QW′T 0) are two damping factors in the HC tendency, with the former dominating. Differences in spatial distribution of the heat advection associated with the two types of ENSO are also presented. We define a warm water heat index (WWH) as integrated heat content above 26 kg m?3 potential density (26σ ? ) isopycnal depth within 130°E–80°W and 5°S–5°N. Further examination suggests that the recharge–discharge of WWH is involved in both types of El Niño, though with some differences. First, it takes about 42 (55) months for the evolution of a recharge–discharge cycle during an EP (CP) ENSO. Second, the EP El Niño event peaks during the discharge phase, 7–8 months after the recharge time. The CP El Niño peaks during the recharge phase, 4–5 months before the recharge time. The locations of HC anomalies in the El Niño mature phase relative to those at recharged time explain why the EP and CP El Niño peak in different stages of the recharge–discharge process.  相似文献   

16.
The Arctic Ocean is connected to the Pacific by the Bering Sea and the Bering Strait. During the 4th Chinese National Arctic Research Expedition, measurements of carbon tetrachloride (CCl4) were used to estimate ventilation time-scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution method. The profile distribution showed that there was a high-CCl4 tongue entering through the Canada Basin in the intermediate layer (27.6?<?σθ?<?28), at latitudes between 78 and 85°N, which may be related to the inflow of Atlantic water. Between stations B09 and B10, upwelling appeared to occur near the continental slope in the Bering Sea. The ventilation time scales (mean ages) for deep and bottom water in the Arctic Ocean (~?230–380 years) were shorter than in the Bering Sea (~?430–970 years). Higher mean ages show that ventilation processes are weaker in the intermediate water of the Bering Sea than in the Arctic Ocean. The mean Cant column inventory in the upper 4000 m was higher (60–82 mol m?2) in the Arctic Ocean compared to the Bering Sea (35–48 mol m?2).  相似文献   

17.
The seasonal variability of the carbon dioxide (CO2) system in the Southern Ocean, south of 50°S, is analysed from observations obtained in January and August 2000 during OISO cruises conducted in the Indian Antarctic sector. In the seasonal ice zone, SIZ (south of 58°S), surface ocean CO2 concentrations are well below equilibrium during austral summer. During this season, when sea-ice is not obstructing gas exchange at the air–sea interface, the oceanic CO2 sink ranges from −2 to −4 mmol/m2/d in the SIZ. In the permanent open ocean zone, POOZ (50–58°S), surface oceanic fugacity fCO2 increases from summer to winter. The seasonal fCO2 variations (from 10 to 30 μatm) are relatively low compared to seasonal amplitudes observed in the subtropics or the subantarctic zones. However, these variations in the POOZ are large enough to cross the atmospheric level from summer to winter. Therefore, this region is neither a permanent CO2 sink nor a permanent CO2 source. In the POOZ, air–sea CO2 fluxes calculated from observations are about −1.1 mmol/m2/d in January (a small sink) and 2.5 mmol/m2/d in August (a source). These estimates obtained for only two periods of the year need to be extrapolated on a monthly scale in order to calculate an integrated air–sea CO2 flux on an annual basis. For doing this, we use a biogeochemical model that creates annual cycles for nitrate, inorganic carbon, total alkalinity and fCO2. The changing pattern of ocean CO2 summer sink and winter source is well reproduced by the model. It is controlled mainly by the balance between summer primary production and winter deep vertical mixing. In the POOZ, the annual air–sea CO2 flux is about −0.5 mol/m2/yr, which is small compared to previous estimates based on oceanic observations but comparable to the small CO2 sink deduced from atmospheric inverse methods. For reducing the uncertainties attached to the global ocean CO2 sink south of the Polar Front the regional results presented here should be synthetized with historical and new observations, especially during winter, in other sectors of the Southern Ocean.  相似文献   

18.
Phytoplankton fluorescence, temperature and salinity were measured from December through February using in situ instruments deployed at two locations in the southern Ross Sea, Antarctica during the austral summers of three consecutive years (2003–2004, 2004–2005, and 2005–2006) to assess the short-term, seasonal and interannual variations in phytoplankton biomass and oceanographic conditions. The seasonal climatologies of physical forcing variables were also determined from satellite measurements, and the data from the two sites compared to the 2000–2009 mean. In situ fluorometers were deployed at three depths at 77°S, 172.7°E and 77.5°S, 180°. Significant differences between the two sites were consistently observed, confirming the anticipated high level of spatial and temporal heterogeneity. Chlorophyll fluorescence was maximal in late December, and generally decreased rapidly to modest levels in January and February. However, during 1 year (2003–2004) a secondary bloom was found, with summer maxima being similar to those observed during spring. Fluorescence displayed a strong diel cycle, with strong quenching during periods of maximum irradiance. The magnitude of this reduction was large (the minimum average fluorescence was 25% of the daily mean) and decreased with depth. Fluorescence varied interannually, with the absolute levels and temporal patterns being different among years. The two sites had different temperature/salinity properties as measured at 24 m, and both variables changed with time. During 2004–2005 we were able to continuously measure the photosynthetic quantum efficiency of PSII (Fv/Fm) at 11 m, which revealed a minimum in December, and an increase in January, whereas the absolute fluorescence (Fo) decreased simultaneously. We suggest that this reflected a mixing event, whereby available irradiance increased, allowing a short period of growth in a more favorable optical environment. While substantial variations from the mean physical forcing were observed, the linkage of these physical variations with fluorescence was not always clear. Short-term (over 24-h) changes in fluorescence occurred, and were likely related to advective events. Wind events altered fluorescence in the surface layer, and these redistributed phytoplankton in the surface. The variability in chlorophyll fluorescence and physical forcing over a variety of scales in the Ross Sea provides insights into temporal–spatial coupling of phytoplankton.  相似文献   

19.
汪金涛  陈新军  高峰  雷林 《海洋与湖沼》2014,45(6):1185-1191
东南太平洋茎柔鱼(Dosidicus gigas)是短生命周期种类,其资源量极易受到海洋环境变化的影响。根据2003—2012年我国鱿钓船在东南太平洋的生产统计数据,以及茎柔鱼栖息地的海表温度(SST)、海面高度(SSH)、叶绿素a浓度(chl a)数据,利用相关性分析法分析茎柔鱼资源丰度和补充量(以单位捕捞努力量渔获量为指标,t/d)与栖息海域20°S—20°N、110°W—70°W的SST、SSH、chl a浓度的相关性,获取相关系数大的关键海区位置,同时加入茎柔鱼产卵场、索饵场最适表层水温范围占总面积的比例(分别用PS、PF表示)两个参数,建立三种基于主要环境因子的误差反向传播(EBP)神经网络资源补充量预报模型,进行了比较。结果表明:茎柔鱼资源丰度与SST、SSH、chl a浓度的相关系数最大值海域为7月份的Point1(13°N,102°W)海区、9月份的Point3(11°N,102°W)海区和3月份的Point5(8°S,107°W)海区;资源补充量与SST、SSH、chl a浓度的相关系数最大值海域为6月份的Point2(8°N,103.5°W)海区、2月份的Point4(12°N,97.5°W)海区和10月份的Point6(10°S,93.5°W)海区。EBP神经网络预报模型结果认为:基于产卵环境关键影响因子的方案2(以Point2的SST、Point4的SSH、Point6的chl a浓度、PS作为模型输入因子)和基于全部环境关键影响因子的方案3(以Point1与Point2的SST、Point3与Point4的SSH、Point5与Point6的chl a浓度、PS、PF作为模型输入因子)的两种神经网络预报模型均方误差较小,其准确率可达90%左右。  相似文献   

20.
Variations in the distribution of chemotaxonomic pigments were monitored in the Arabian Sea and the Gulf of Oman at the end of the SW monsoon in September 1994 and during the inter-monsoon period in November/December 1994 to determine the seasonal changes in phytoplankton composition. The Gulf of Oman was characterized by sub-surface chlorophyll maxima at 20-40 m during both seasons, and low levels of divinyl chlorophyll a indicated that prochlorophytes did not contribute significantly to the total chlorophyll a. Prymnesiophytes (19′-hexanoyloxyfucoxanthin), diatoms (fucoxanthin) and chlorophyll b containing organisms accounted for most of the phytoplankton biomass in September, while prymnesiophytes dominated in November/December. In the Arabian Sea in September, high total chlorophyll a concentrations up to 1742 ng l-1 were measured in the coastal upwelling region and a progressive decline was monitored along the 1670 km offshore transect to oligotrophic waters at 8°N. Divinyl chlorophyll a was not detected along this transect except at the two most southerly stations where prochlorophytes were estimated to contribute 25–30% to the total chlorophyll a. Inshore, the dominance of fucoxanthin and/or hexanoyloxyfucoxanthin indicated that diatoms and prymnesiophytes generally dominated the patchy phytoplankton community, with zeaxanthin-containing Synechococcus also being important, especially in surface waters. At the southern oligotrophic localities, Synechococcus and prochlorophytes dominated the upper 40 m and prymnesiophytes were the most prominent at the deep chlorophyll maximum. During the inter-monsoon season, total chlorophyll a concentrations were generally half those measured in September and highest levels were found on the shelf (1170 ng l-1). Divinyl chlorophyll a was detected at all stations along the Arabian Sea transect, and we estimated that prochlorophytes contributed between 3 and 28% to the total chlorophyll a, while at the two oligotrophic stations this proportion increased to 51–52%. While procaryotes were more important in November/December than September, eucaryotes still accounted for >50% of the total chlorophyll a. Pigment/total chlorophyll a ratios indicated that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were the dominant group, although procaryotes accounted for 65% at the two southerly oligotrophic stations.  相似文献   

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