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1.
Sedimentological and micropaleontological characteristics of core sediments from the outer shelf of the Korea Strait, which connects the northern East China Sea and the East Sea (Sea of Japan), were investigated to elucidate the paleoceanographic environment, especially the timing of the Kuroshio inflow, since the last glacial maximum. The core sediments, containing continuous records of the last 15,000 years, are characterized by a relatively high mud content (more than 50%, on average) and well-developed tide-influenced sedimentary structures. Their mineralogy suggests that the material originated from the paleo-Nakdong River system, which extended across the shelf of the Korea Strait during low sea-level periods. Planktonic foraminifers reveal a series of well-defined changes in paleoceanographic conditions during the late Pleistocene–Holocene. Down-core variations in the abundance of four foraminiferal assemblages, i.e., cold, coastal, tropical–subtropical, and Kuroshio water groups comprising characteristic planktonic species, suggest the occurrence of a distinct paleoenvironmental change in the surface water at 7,000 years b.p., i.e., from 15,000 to 7,000 years b.p., the area was influenced by coastal waters whereas since ca. 7,000 years b.p., it has been under the influence of open-sea water related to the Kuroshio Current flow, associated with both higher temperature and higher salinity. In particular, Pulleniatina obliquiloculata increased markedly in abundance at this time, documenting the inflow of the Kuroshio into the study area. These data indicate that the coastal water stage terminated at ca. 7,000 years b.p. when the warm Kuroshio and its major branch, the Tsushima Current, began to flow into the East Sea, as is the case today. The intrusion of the Tsushima Current through the Korea Strait after ca. 7,000 years b.p. resulted in abrupt changes in sedimentation rates and a dramatic increase in abundance of the Kuroshio indicator species, P. obliquiloculata.  相似文献   

2.
The Storegga Slide complex is a multi-stage slope failure on the Norwegian continental margin where the most recent major event occurred 8.1 ka b.p. (calendar years before present). Its northern flank contains pockmark features that are commonly inferred to be related to the historical and modern venting of methane-bearing fluids. Three jumbo piston cores (JPC), one from a pockmark and two background cores at variable distances from this site (proximal, 5 km, and distal, 15 km) on the northern flank of the slide (806–1,524 m water depths), were sampled at 10 cm resolution to assess the geologic record of methane venting in the Nyegga pockmark field. Six down-core radiocarbon measurements on mixed planktonic foraminifer species reveal ages of 9.4–16.4 ka b.p. Bathymodiolus mussel shell horizons, indicators of methane-rich environments, have been dated at 15.8–17.6 and ~22 ka b.p. in the pockmark core. Stable isotope analyses on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Islandiella norcrossi, Melonis barleeanum) Foraminifera reveal δ18O values indicative of a clear glacial/deglacial transition (−1.5‰ shift in planktonic species). Both planktonic and benthic δ13C signatures record multiple excursions, interpreted to reflect the influence of methane in the environment; these δ13C excursions occur in the pockmark core and also in the distal background core. While authigenic calcite formation on the seafloor may play an important role in producing such excursions, these data together suggest the influence of methane seepage within the pockmark field over the past 25 ka, whereby seepage was particularly active between 13 and 15 ka. This is consistent with previously inferred regional increases in porewater pressure associated with glacial loading and higher sedimentation rates, which can cause gas hydrate and slope instability.  相似文献   

3.
This study correlates Holocene sedimentation with regional environmental changes for the Guadiana middle shelf, SW Iberia, based on a detailed sedimentological analysis combined with radiocarbon and amino acid racemization dating. The sedimentary record of vibrocore CRIDA16 (307 cm) from the mud patch off the Guadiana River is characterized by a transgressive signature. Terrigenous sand–gravel dominates the core base up to ca. 5,000 cal. years b.p., enriched in schist/greywackes and non-reworked quartz. The shelf area was under the direct influence of Guadiana bed load discharges, as sea level was lower than today but rising, favouring the entrapment of fines during the Guadiana estuary infilling in the early Holocene. Core upwards, fines dominate the record. Sea-level stabilization at ca. 5,700–3,700 cal. years b.p. led to estuary infilling by coarser sediments and export of suspended sediment to the middle shelf. After ca. 900–700 cal. years b.p., the formation of the Guadiana Mud Patch signifies deposition in a marine environment dominated by suspended material from the Guadiana River. Comparison with earlier publications showed that a similar evolutionary mechanism of middle shelf mud deposition occurred in other parts of the Iberian Margin, pointing to a generalized establishment of this type of sedimentary body in Iberia since the mid to late Holocene. This suggests that the formation of mud belts on the north and south Iberian Margin was to a large extent synchronous. It is likely that the evolution of the Guadiana Mud Patch on the shelf was controlled foremost by the overall climate trends identified for several parts of Iberia during the Holocene (i.e. increased aridity punctuated by significant humidity stages), and less by human occupation of the region. Enhanced humidity stages led to higher rainfall and intensified floods, with a consequent increase of discharges to the shelf which ultimately were responsible for the Guadiana Mud Patch formation. It is expected that this pattern of sedimentary dynamics has been strongly disturbed since 2002, when the closing of the Alqueva Dam (the biggest on the Iberian Peninsula) was completed in the Guadiana River basin.  相似文献   

4.
Palynological characterization of the pollen assemblages from core ZV-01 offers a reliable age record of shallow ‘gas seal’ and ‘gas reservoir’ sediments from the Ría de Vigo (NW Spain). Gassy sediments show a direct correspondence with the palynological assemblage zones (LPAZ) 2, 3 and 4, which range in age from 950 to 1510 a.d. for the interval 81–176 cm where gas is found. The facies acting as a seal would correspond to the sedimentation in the ria starting from 1510 a.d. These assemblages also provide significant data which make it possible to reconstruct the palaeoenvironmental changes recorded in the sedimentary infill of the Ría de Vigo. The gassy horizon corresponds to the phase when riparian and mesophilous forest were better represented. This coincides with a relative high abundance of Lingulodinium machaerophorum, which indicates that the waters of the ria had been less renewed by oceanic waters and had a plentiful supply of continental nutrients. At that time, anoxic conditions resulted from restricted vertical circulation of seawater and/or high biological productivity. The dinocyst assemblages overlying and underlying the gassy horizon in core ZV-01 are clearly different from those concomitant with the accumulation of the gassy sediments. This suggests that oceanographic conditions in the Ría de Vigo may have changed several times during the time interval covered by our record. The weaker relationship between L. machaerophorum/Spiniferites spp., and simultaneous significant increases in Impagidinium spp. and Bitectatodinium tepikiense may indicate a greater intrusion of colder, more oceanic waters into the Ría de Vigo, which may have provoked intensification in upwelling during two periods, ca. 700–850 a.d. and ca. 1500–1750 a.d.  相似文献   

5.
通过对位于东海内陆架泥质区中部的MZ02柱样岩芯进行粒度、常量元素、AMS14C分析,获得了粒度和常量元素随时间变化的高分辨率曲线.结果表明,近2 ka以来研究区沉积环境稳定,以沿岸流控制的浅海沉积为主,沉积物中CaO/K2O,MgO/Al2 O3和MnO/Na2 O比值的变化与我国东部气候变化序列具有较好的一致性,证...  相似文献   

6.
New, very high-resolution (25 cm) seismic profiles have revealed the internal architecture of the infilling of a macrotidal bay, the Marennes-Oléron Bay, France. Within this geometry, a major seismic unconformity has been correlated with core data. This correlation provides evidence that the seismic unconformity corresponds to a sharp grain-size decrease. Both seismic and core data indicate that this change of grain size can be interpreted as a record of a recent (around 1,000 years b.p.) decrease in hydrodynamical energy with time and/or a larger supply of fine-grained material. This recent environmental change can be related to natural infilling of the Marennes Oléron Bay, and to tidal prism decrease, increasing human activities (e.g. land reclamation, deforestation, agricultural land use) and climate fluctuations during the late Holocene, such as the transition between the cold period of the Dark Ages (1,550–1,050 years b.p.) and the Medieval warm period (1,050–550 years b.p.).  相似文献   

7.
全新世东海内陆架泥质区有孔虫特征及其古环境意义   总被引：5，自引：0，他引：5  
东海内陆架泥质区是东海全新世高海平面以来的沉积中心,保存了冰后期海平面上升以来完整的全新世沉积记录,是研究东海古海洋环境变化的良好载体,也是研究全新世古气候、古环境变迁的绝佳材料。选取了位于东海内陆架泥质区中部的MZ02孔长岩心作为研究对象,通过对沉积物中有孔虫进行属种鉴定分析,并结合岩心沉积物的岩性特征和AMS14 C测年数据,主要依据底栖有孔虫组合,恢复了研究区全新世以来的沉积环境演化。研究表明,全新世以来东海内陆架泥质区的沉积环境呈现阶段性演化特征,经历了以下4个阶段的演化:阶段I(10.8～10.5cal.kaBP)为滨岸沉积环境;阶段II(10.5～8.3cal.kaBP)随海面快速上升沉积环境由内陆架滨岸向中—内陆架过渡;阶段III(8.3～5.2cal.kaBP)为台湾暖流十分靠近的中—内陆架沉积环境;阶段IV(5.2～0cal.kaBP)为沿岸流较强的内陆架沉积环境。暖水种丰度在8.4cal.kaBP出现高值,推测为台湾暖流形成之时。约4.0cal.kaBP以来表生种丰度呈现高值和底栖有孔虫18 O变轻,推测与沿岸流增强密切相关。  相似文献   

8.
A high-resolution sediment core (sedimentation rate ~2 mm/year) from the German Bight was analysed for its foraminiferal stable oxygen isotope (18O) composition. These data were correlated with instrumental summer sea-surface temperature and salinity data from the nearby island of Helgoland, reaching back 100 years. Comparing the isotope data with the instrumental records reveals a distinct 18O–salinity relationship (18O=0.34×S–9.36; r=0.86) for the German Bight, where salinity is mainly driven by freshwater input from the Elbe River. Thus, these findings provide the possibility for future regional paleosalinity and paleodischarge reconstructions for times far beyond the instrumental timescale.  相似文献   

9.
《Marine Geology》2005,219(1):47-69
Laminated sediments preserved in the anoxic inner basin of Effingham Inlet on the Pacific coast of Vancouver Island, British Columbia, Canada, yield a high-resolution sediment deposition record spanning about 6000 yr. The varying thickness of diatom/terrigenous mud varves in sediment cores from the basin can be interpreted in terms of annual changes in surface productivity and freshwater input within the inlet. Similarly, the occurrence of unlaminated mud units (homogenites) intercalated amongst the laminated sediments can be interpreted in terms of oceanic and climatic changes. These units appear to be associated with coastal upwelling events that result infrequently in highly oxygenated oceanic water penetrating to the bottom of the inner and outer basins of the inlet. The sedimentary record also contains massive and graded mud units considered to arise from debris flows and turbidity currents, some of which were probably initiated by seismic events, including a major event about 4500 14C yr BP which may be earthquake related. A total of seventeen oceanographic surveys of the inlet beginning in 1995 characterize the modern seasonal coastal upwelling regime and a unique bottom water oxygenation event which was recorded in January 1999, following a rapid transition from the strong El Niño event of 1997–98 to the moderate La Niña event of 1998–99. Circum-Pacific evidence suggests that a “regime shift” from warm to cold conditions occurred in the central northeast Pacific in the late 1990s, indicating that the coastal ocean processes influencing Effingham Inlet sedimentation are likely modified by climate-scale ocean variability.  相似文献   

10.
Two gravity cores (CAG-3 and C-15) from the tectonically active, 1,276-m deep Çınarcık Basin of the Marmara Sea each include three sandy turbiditic mud units (1 mm–2 cm thick) with sharp basal contacts. The high benthic foraminifer content of these units suggests that the sediments were transported by turbidity currents from the upper slope region. These units represent the thin edges of turbidites thickening towards the subsiding north-eastern part of the basin, and contain quartz, detrital calcite, intact shells and shell fragments, smectite, pyrite framboids, muscovite, biotite, epidote and garnet. Their clay fractions are more enriched in smectite than those of adjacent layers. AMS 14C ages (957±43 a.d. and 578±31 a.d.) of two upper and middle turbiditic units in core C15 overlap with the historical İstanbul-Thrace (intensity=10) and İstanbul-Kocaeli (intensity=9) earthquakes of 26 October 986 and 15 August 553, respectively. This overlap, together with sedimentological characteristics, strongly suggests that the turbiditic units are related to the tectono-seismic activity of the North Anatolian Fault. The age of the lowest turbiditic unit in core C-3 was found to be 6,573±87 a b.p. (calendar) by AMS 14 C. In terms of chronostratigraphic relationships and lithological composition, the turbiditic units in core CAG-3 cannot be correlated with those in C15. This can be explained by gravity-controlled sedimentation causing wedging out of turbidites towards the edge of the basin.  相似文献   

11.
《Marine Geology》2007,236(1-2):15-26
The South American coast between Brazil and Venezuela is affected by longshore migrating mud banks derived from the fine-grained Amazon sediment discharge. Onshore mud migration prevails over shallow ‘bank’ areas alternating alongshore with deeper ‘inter-bank’ areas. The transport on the inner shelf, and attachment to the shoreline, of this migrating mud has been attributed mainly to wind waves. However, the lack of in situ data on waves hampers understanding of the relationship between waves and mud dynamics. A 44-yr record (1960–2004) of the ERA-40 wave dataset generated by the European Centre for Medium-Range Weather Forecasts (ECMWF) was used, in conjunction with field investigations in French Guiana, to define both event-scale and longer-term patterns of mud mobilisation induced by waves. The ratio H03 / T2, combining wave height H and period T, and the angle of wave incidence α, were singled out as the most relevant parameters for describing wave forcing. Typical ‘bank’ and ‘inter-bank’ profiles and corresponding mud densities, and a 3-month record of changes in the thickness of the fluid mud layer in an estuarine navigation channel were monitored by echo-sounding from October 2002 to January 2003. An 80-day record of bed-level changes in the intertidal zone was obtained from August to November 2004 using a pressure transducer. The results on the wave regime of French Guiana confirm a distinctly seasonal pattern, and highlight an increase in H03 / T2 over the 44-yr period related to an increase in trade-wind velocities determined from corresponding trends in Atlantic wind pseudo-stress off the South American coast. Wave forcing over bank areas leads to the liquefaction of a 1–3 m-thick layer of mud that is transported onshore (and alongshore by the longshore component of wave energy). The episodic nature of high wave energy events generally results in the formation of mud bar features from the shoreward mobilisation of gel-like fluid mud. The effect of waves on mud is particularly marked following long periods of low energy, and especially at the onset of the high wave energy season (October to May), when even moderate wave energy events can lead to significant mobilisation of mud.Significant phases of increased wave energy are attended by higher long-term (annual) rates of longshore mud bank migration but the correlation is rather poor between the wave forcing parameter H03 / T2 and migration rates because stronger wave forcing is generally associated with low angles of wave incidence. This suggests a complementary role of other hydrodynamic mechanisms, such as geostrophic and tidal currents, in longshore mud bank migration.  相似文献   

12.
Mud volcanoes (MVs) are abundant along the eastern Mediterranean subduction zones, recording mud breccia extrusion over long timescales (106 years), but to date relatively few have been recognised in the northern Ionian Sea on the Calabrian accretionary prism (CAP). In the present study, the seafloor distribution and recent activity of MVs is investigated across a 35,600 km2 sector of the CAP using a regional acoustic dataset (multibeam bathymetric and backscatter imagery, integrated with subbottom profiles) locally ground-truthed by sediment cores. A total of 54 MVs are identified across water depths of 150–2,750 m using up to four geophysical criteria: distinctive morphology, high backscatter, unstratified subbottom facies and, in one case, a hydroacoustic flare. Fourteen MVs are identified from 3–4 criteria, of which five have been previously proven by cores containing mud breccia beneath up to 1.6 m of hemipelagic sediments (Madonna dello Ionio MVs 1–3, Pythagoras MV and the newly named Sartori MV), while nine others are identified for the first time (Athena, Catanzaro, Cerere, Diana, Giunone, Minerva, ‘right foot’, Venere 1 and 2). Forty other as yet unnamed MVs are inferred from 1–2 geophysical criteria (three from distinctive morphology alone). All but one possible MV lie on the inner plateau of the CAP, landwards of the Calabrian Escarpment in a zone up to 120 km wide that includes the inner pre-Messinian wedge and the fore-arc basins, where they are interpreted to record the ascent from depth of overpressured fluids that interacted with tectonic structures and with evaporitic or shale seals within the fore-arc basins. The rise of fluids may have been triggered by post-Messinian out-of-sequence tectonism that affected the entire pre-Messinian prism, but Plio-Quaternary sedimentation rates and depositional styles support the inference that significant mud volcanism has taken place only on the inner plateau. Sedimentation rates across the CAP applied to a 12 khz sonar detection depth of 225 cm imply that all MVs with backscatter signatures (50 of 54) have erupted mud breccias within the last 56 ka, and within the last 12.5 ka in the fore-arc basins. Ages of eruption estimated from the depth of cored mud breccias at five MVs, and a seismo-stratigraphic relationship at a sixth, indicate episodes at the last glacial maximum ca. 20 ka BP and during the postglacial period. Eruptive episodes within the Calabrian MV province constitute recurrent geohazards, separated by longer periods of quiescent (subdued) fluid seepage that are likely to support gas hydrate formation and chemosynthetic ecosystems.  相似文献   

13.
The compilation of results obtained on three giant piston cores from the Whittard, Shamrock and Guilcher turbidite levees reveals a high-resolution stratigraphic record for the Bay of Biscay. Due to the abundance of reworked sediments in these sedimentary environments, a specific methodological approach, based on an X-ray-assisted subsampling phase associated with sedimentological, geochemical and micropalaeontological analyses, was implemented. With an accurate chronological framework, this multi-proxy investigation provides observations on the ‘Fleuve Manche’ palaeoriver and the British-Irish Ice Sheet (BIS) histories over the last 20,000 years. The results obtained highlight the direct influence of the decay of the BIS on the Bay of Biscay deep-sea clastic sedimentation during the last European deglacial phase. During this period, the annual BIS cycle of meltwater seems enough to generate seasonal turbidity currents associated with exceptional sedimentation rates in all the Celtic and Armorican turbidite systems. With very high sedimentation rates, the turbidite levees represent the main deep-sea clastic depositional area. Long coring combined with a very careful subsampling method can provide continuous high-resolution palaeoenvironmental signals.  相似文献   

14.
Rapid shifts in past climate recorded in polar ice sheets have elicited various explanations relating to either thermohaline circulation changes by ice-rafting or natural greenhouse gas concentrations modulated by climatic conditions in the tropics. To compare the tropical paleoclimate record with the polar record, one must choose sediment cores from highly productive ocean regions. Necessarily, such regions reflect the wind records in the tropics, because high productivity is associated with upwelling driven by winds. Comparing tropical precipitation records with high-latitude records is, however, a more difficult task because sediments recording paleoprecipitation usually have low sedimentation rates, and offer coarser resolution relative to polar ice cores. Here, we present δ 18O data of three planktonic species of Foraminifera (a proxy for precipitation) from such a sediment core, spanning the past 35 ka for the equatorial Indian Ocean, which falls under the southwest monsoon (SWM) realm. Results show that minimum SWM precipitation occurred at the Last Glacial Maximum, with a subsequent increase at Termination IA. During the Holocene, SWM precipitation intensified uniformly up to the core top (∼2.2 ka b.p.), as revealed by generally decreasing δ 18O values. Variations in precipitation are consistent with climate changes recorded in polar ice sheets. Although the different resolutions of the two records preclude a rigorous comparison, abrupt cooling/warming events appear to be accompanied by sudden reduction/enhancement in (SWM) rainfall. Thus, mechanisms with time scales much shorter than a millennium, such as natural greenhouse warming (e.g., CH4 concentration), controlled by emissions from the tropics, could have played a major role in high-latitude climate change.  相似文献   

15.
１９８９年３－５月在海南岛三亚浅钻取心,用岩石地层学和地质年代学方法研究了海南岛周缘珊瑚礁的基本特征和成礁时代,在此岩心的基础上进一步研究珊瑚礁的ＥＳＲ谱学特征。结果表明,珊胡礁Ｍｎ＾２＋的ＥＳＲ信号和古气候变化直接相关,在１００％文石基础上归一的Ｍｎ＾２＋ＥＳＲ信号是一种新的灵敏的古气候指示物,其指示的古气候变化和前人发表的研究成果相一致,海南岛三亚珊瑚礁的Ｍｎ＾２＋ＥＳＲ信号表明,中国全新世大  相似文献   

16.
Modern tidal rhythmites deposited in a deep-water estuary   总被引：1，自引：0，他引：1  
 The sedimentary record in Muir Inlet, a macrotidal fjord in Alaska, is dominated by cyclic silt–mud rhythmites. Couplet thicknesses vary systematically in a vertical sequence and reflect a semidiurnal tidal regime. Semimonthly, monthly, bimonthly, and annual cycles can be identified both visually in cores and by spectral frequency analysis. An average annual sedimentation of 22.5 cmyr-1 occurs over a four-month meltwater season and is confirmed by 210Pb dating. These modern deep-water tidal rhythmites can be used to verify interpretations made on ancient rhythmites in the stratigraphic record, and they also provide a dating tool to interpret high latitude successions for high-resolution climate change. Received: 20 February 1997 / Revision received: 1 October 1997  相似文献   

17.
《Marine Geology》2003,193(1-2):61-91
The Gargano subaqueous delta formed on the eastern and southeastern sides of the Gargano promontory, in the western Adriatic. This subaqueous deposit represents the southernmost portion of the late-Holocene highstand systems tract (HST) growing along the western side of the Adriatic as an extensive wedge of deltaic and shallow-marine mud. The late-Holocene HST rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5.5 cal. kyr BP, at the end of the late-Pleistocene–Holocene sea-level rise. High-resolution seismic–stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5.5 and 3.7 cal. kyr BP over much of the basin. Above this unit, sediment accumulation rates increased to high values (as much as 1.5 cm yr−1) reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics. The late-Holocene mud wedge, of which the Gargano subaqueous delta is a significant component, reaches up to 35 m in thickness and has a volume of ca 180 km3. The shore-parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources (with a combined modern delivery of 51.7×106 t yr−1 of mean suspended load). In sections perpendicular to the coast the late-Holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets (typically 0.5°). The Gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25–28 m, and accounts for about 1/7th of the total volume of the late-Holocene mud wedge, despite the absence of direct river supply to the Gargano area. In the area of maximum interaction between shore-parallel currents and basin morphology, progradation occurs onto a flat and barren bedrock outcrop in about 50–80 m water depth. The rapid transition from a thickness of 30 m of late-Holocene mud to nil is a good indication of the role of southward-flowing bottom-hugging shelf currents in causing the redistribution of sediment along the Adriatic inner shelf. Additional evidence of this regime comes from: (1) the most recent sigmoid (defined at seismic–stratigraphic scale) deposited since the onset of the Little Ice Age, showing a shore-parallel thickness distribution and a main depocentre to the southeast of the Gargano promontory; (2) the maximum values of sediment accumulation rates over the last century (documented by 210Pb measurements) defining a narrow shore-parallel belt immediately seaward of the depocentre of the most recent sigmoid. The Gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones. The Gargano subaqueous delta differs from other documented late-Holocene subaqueous deltas because its growth reflects: (1) sediment transport dominated by bottom currents sub-parallel to the strike of the composing clinoforms; (2) a complex supply regime including the Po delta (350 km to the north) and several coalescing Apennine rivers acting as ‘line source’; (3) several alternating intervals of enhanced outbuilding and condensed deposition; and (4) an in-phase growth of the most recent sigmoid with the major progradation of the Po delta during the Little Ice Age.  相似文献   

18.
Rates of short-term (up to 2 years) bed elevation change and sedimentation from mudflats to salt marshes were measured in a rapidly infilling macrotidal estuary using an original combination of three high-resolution techniques: an ultrasonic altimeter, the Rod Surface-Elevation Table (RSET) method, and filter traps. The Authie estuary is located on a straight, sand-rich coast and is undergoing rapid infill under the influence of flood-dominant tides reinforced by wave action. The estuarine sediment suite consists of both mud and sand derived from the sea, of sand derived from storm wave erosion of dunes lining the north bank of the estuary, and, to a much smaller extent, of mud from the river catchment. Bed elevation change and sedimentation rates show an expected increase with the duration of tidal flooding (hydroperiod) in both space and time. The estuarine bed sediment suite changes from sandy at the mouth to muddy within the low-energy inner estuary, where mudflats are rapidly accreting, paving the way for the formation of increasingly denser and mature salt marshes from the high-sedimentation pioneer zone to the upper marsh where annual sedimentation is very low. Recorded variability in rates of bed elevation change and sedimentation reflect the influence of estuarine macro-scale and local sediment transport and depositional processes in a macrotidal context dominated by high inputs of allochthonous sediments.  相似文献   

19.
A considerable number ofEuphausia similis G. O. Sars were found to be infected with a parasite in the samples collected in the summer of 1969 in Suruga Bay. The same species was also parasitized by an ellobiopsid,Thalassomyces fagei (Boschma), but it was rare in occurrence. The former parasite is slightly oval in shape with the longer diameter ranging between 1.0 and 1.5 mm, average diameter 1.35 mm. It infests cardiac region, rarely gastric region, of the host. It has been preliminarily identified by Drs.T. Oshima andT. Shimazu of the Shinshu University as the progenetic metacercaria of a trematode species very closely related toPseudopecoelus japonicus; its adult was originally reported to infest several bathypelagic fishes and the encysted stage was also found in jack mackerel from Suruga Bay byYamaguti (1938). The occurrence of the metacercaria inE. similis from the area may be new to science, althoughG. O. Sars (1885) has reported the immature forms ofDistomum filiferum G. O. Sars inNematoscelis megalops G. O. Sars andThysanoessa gregaria G. O. Sars and the crustaceans of wide variety have been proved to serve as the second intermediate host of various trematodes. The euphausiids infected with the metacercaria were concentrated in the innermost part of the bay. This might suggest the presence of the euphausiid population which is confined to the geographical area for some period. The metacercaria may be used as a “biological tag” to trace the migratory range of the host when the life history of the parasite is elucidated. The finding ofT. fagei in the area may be the first record of occurrence of the species in the western North Pacific, andE. similis is now recorded as the fourteenth known host euphausiid of the ellobiopsid.  相似文献   

20.
采用超低本底液闪β计数的方法,测定了春季黄海、东海海水中溶解态、悬浮物、筛绢颗粒物和雨水中天然32P和33P的比活度.结果显示,上层海水各相33P,32P的比活度相当低,其中TDP的32P,33P比活度的浓度最高,悬浮物次之,筛绢颗粒物最低.海水各相中33P与32P活度比值从TDP到悬浮物、筛绢颗粒物逐渐增大,反映出食物链传递过程中磷的年龄逐渐增加.根据稳态模式的估算结果,海水各相中磷的停留时间具有明显的区域变化特征,其中近岸和内陆架溶解磷的停留时间比外陆架短,仅为3~4 d,意味着近岸和内陆架海区低浓度的磷也可能维持高生物生产力的运转.利用稳态模式还估算出浮游植物的碳同化通量为189~814 mg/(m2·d),浮游动物的碳摄食通量为10~161 mg/(m2·d).此外,通过比较雨水32P,33P的输入通量和海水32P,33P积存量,利用质量平衡方法估算出上层海水POC输出通量为102~972 mg/(m2·d).  相似文献   

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