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1.
The study of 134 subsurface sediment samples from three cores collected along the Coast of Kachchh, off Gujarat Province, NW India, shows the presence of 151 foraminifer species. Q-mode cluster analysis on foraminifer data for each core and radiocarbon dating at ten different downcore depths reveal an inverted sequence, with fine-grained sediments and small foraminifers sandwiched between normal detrital sediments at water depths of 10–20 m. It is postulated that ∼8,000 years B.P., sediments ranging in age from ∼10,000 to ∼12,000 years B.P. were eroded from deeper offshore deposits by storm/tsunami(s), and were subsequently transported and redeposited in shallow regions, resulting in an inverted sequence, followed by a normal detrital sequence deposited between ∼8,000 and ∼7,000 years B.P. A second, similar event resulted in the deposition of ∼10,000 year old sediments over a normally deposited, ∼7,000 year old sequence. The second inverted sequence was subsequently overlain by a normal sequence. It is hypothesised that the erosion and transportation of fine-grained sediments from deeper water, and their deposition in shallower water against the rule of gravity, are the result of storm/tsunami influence.  相似文献   

2.
The prediction results of large-scale forest fire development are given for Siberia. To evaluate the fire risks, the Canadian Forest Fire Weather Index System (CFFWIS) and the Russian moisture indices (MI1 and MI2) were compared on the basis of the data of a network of meteorological stations as input weather parameters. Parameters of active fires were detected daily from the NOAA satellite data for the period of 1996–2008. To determine the length of the fire danger season, the snow cover fractions from Terra/MODIS data (2001–2008) were used. The features of fire development on territories with different types of flammable fuel are considered. The statistical analysis of the areas and number of fires typical of each vegetation class is made with the use of the GLC2000 vegetation map. A positive correlation (∼0.45, p < 0.05) between the cumulative area of local fires and the MI1 and Canadian BUI and DMC indices is revealed. The Canadian ISI and FWI indices describe best the diurnal dynamics of fire areas. The above correlations are higher (∼0.62, p < 0.05) when we select the fires larger than 2000–10000 ha in size for the forested areas. Other cases point to the lack of a linear relation between the fire area and the values of all indices, because the fire spread depends on many natural and anthropogenic factors.  相似文献   

3.
The long-wave outgoing radiation, effective cloudiness equal to the product of the total cloud amount by their optical density, and the sea-surface temperature determined from the satellites are used to determine the annual course of the components of external heat balance on the sea surface whose climatic anomalies, parallel with the meridional heat and water transfer in the ocean-atmosphere system, specify the intraannual and interannual large-scale variations of weather in different regions of the Earth. The development of these studies is connected with the progress of satellite hydrophysics because the data obtained from the space become sufficiently exact, regular, and global. The increase in the existing data array on the external heat balance of the oceans from ∼15–20 to 100 yr and more would promote the solution of the problem of oscillations of Earth's climate. We present examples of coordinated numerical analysis of the heat balance of the upper (0–100 m ) layer of the Black Sea performed on the basis of the shipborne and satellite data. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 59–75, November–December, 2007.  相似文献   

4.
A quasiperiodic variation of 100–110 days in the Kuroshio path off Cape Ashizuri, resulting from the passage of small meanders, was detected by observation with moored current meters during 1993–1995. TOPEX/POSEIDON altimeter data covering 9 years showed that the quasiperiodic variation period was not persistent and modulated twice, with a ∼110-day period from mid-1993 to late 1996, a ∼150-day period from late 1996 to mid-1999, and a ∼110-day period from mid-1999 to late 2001. The quasiperiodic variations of the Kuroshio path migration were contemporaneous with the quasiperiodic arrivals of mesoscale eddies from the east along 27–32°N over the same ∼110- and ∼150-day period quasiperiodic variations. The periodic arrivals of the eddies configure the periodic variations of the Kuroshio path and its inter-annual modulation.  相似文献   

5.
The paper presents the records of several paleoproductivity proxies (PP) (biogenic opal and Ba (Si_bio, Ba_bio), organic carbon (C_org) and carbonate Ca_carb, chlorin and benthic foraminifera abundance (BFA)) in sediments of the Okhotsk Sea for the last 80 kyr with a resolution of ∼100–300 years. The sediment age model was based on the AMS 14C data, records of benthic foraminifera δ18O, paleointensity of the Earth’s geomagnetic field and magnetic susceptibility. PP values demonstrate series of severe prolonged productivity drops in the Okhotsk Sea followed by a sharp increase during the last glaciation. On the basis of quantitative estimations of the paleoproductivity in the Okhotsk Sea during the cold MIS 2 and warm Holocene (Gorbarenko and Goldberg, 2005), it is suggested that the millennium scale relationship in productivity-climate changes of this basin was similar: an increase in the sea’s productivity was related with regional climate warming and vice-versa. The PP records of productivity/climate oscillations in the Okhotsk Sea during MIS 2–4 occurred contemporaneously with the North Atlantic cold Heinrich events (HE) and Greenland Dansgaard-Oyeshger interstadial (DOI). Observed successions of prolonged climate cooling events followed by rapid, abrupt warming are similar to climate and environmental oscillations in the N. Atlantic and Greenland, that confirms the millennium-scale climate changes synchronicities in the Northern Hemisphere including the far NW Pacific, the hydrology and climate conditions of which are close to those of the Okhotsk Sea. Synchronism of the N. Hemisphere severe cooling (including the Okhotsk Sea) with the Antarctic warming suggests that mechanisms of the “seesaw” effect (Blunier and Brook, 2001) in the low latitude heat redistribution between high latitudes of both hemispheres were more complicated than direct NADW formation forcing and encompasses the global atmospheric reorganization. Within the PP used a closer connection in the Okhotsk Sea millennium oscillations was observed for the C_org, BFA and chlorin; Ba_bio increases more closely to DOI. Si_bio variability does not show any evident correlation with productivity changes.  相似文献   

6.
A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ∼6,400 and ∼2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ∼5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay.  相似文献   

7.
《Ocean Modelling》2010,35(3-4):111-124
Icebergs are an important part of the fresh-water cycle and, until now, have not been explicitly represented in Intergovernmental Panel on Climate Change (IPCC) class coupled global circulation models (CGCMs) of the climate system. In this study we examine the impact of introducing interactive icebergs in a next-generation CGCM designed for 21st Century climate predictions. The frozen fresh-water discharge from land is used as calving to create icebergs in the coupled system which are then free to evolve and interact with the sea-ice and ocean components. Icebergs are fully prognostic, represented as point particles and evolve according to momentum and mass balance equations. About 100,000 individual particles are present at any time in the simulations but represent many more icebergs through a clustering approach. The various finite sizes of icebergs, which are prescribed by a statistical distribution at the calving points, lead to a finite life-time of icebergs ranging from weeks, for the smallest icebergs (60 m length), up to years for the largest (2.2 km length). The resulting melt water distribution seen by the ocean enhances deep-water formation, in particular on the continental shelves, relative to the model without icebergs.  相似文献   

8.
The recreational uses of coastal lagoons (also known locally as salt ponds) contribute significantly to the important tourism economy of the southern part of the US state of Rhode Island. The lagoons are valued highly for the wide range of recreational services they provide, such as fishing, clamming, rowing, boating, or merely relaxing. Outdoors on or near the water, weather conditions may influence individual recreation decisions strongly. A changing climate is expected to affect weather conditions in Rhode Island, thereby potentially influencing when, how, and how much recreation will take place in the coastal areas of the state. Through direct observations of human activities on coastal lagoons, the sensitivity of coastal recreational uses to changes in weather conditions was assessed. If future changes in climate bring warmer temperatures and more intense wind and rain events, our results suggest that there may be a decrease in relaxing, rowing, and fishing on coastal lagoons when days are hotter and a decrease in rowing and fishing when days are windier. Nevertheless, warmer temperatures also may lengthen the summers, leading to an overall increase in the peak coastal recreation season. However, during the hottest periods, there may be a shift toward more motor boating and away from other uses, motor boaters were more resistant than other users to changes when temperatures increase. Understanding how weather and climate influence coastal recreation could help coastal managers and businesses better plan for the future in Rhode Island and other coastal environments worldwide.  相似文献   

9.
Indian monsoon precipitation fluctuated significantly during the Holocene and a reliable reconstruction of the timing of the events and their implications is of great benefit to our understanding of the effect and response of low latitude climate systems to the forcing factors. We have carried out high-resolution terrigenous proxy studies on a laminated sediment core from the Oxygen Minimum Zone of the eastern Arabian Sea margin to reconstruct the summer monsoon-controlled precipitation changes during the Holocene. The temporal variation in the terrigenous proxy indicators of this core, in combination with other high-quality cores from the Arabian Sea, suggests several abrupt events in monsoon precipitation throughout the Holocene. The early Holocene monsoon intensification occurred in two abrupt steps at 9500 and 9100 years BP and weakened gradually thereafter, starting at 8500 years BP. A weakening in precipitation recorded at ∼7000 years BP, synchronous with similar conditions in India. One of the most significant weak monsoon periods recorded in our studies lies between 6000 and 5500 years BP. Spectral analysis of the precipitation records reveals statistically significant periodicities at 2200, 1350, 950, 750, 470, 320, 220, 156, 126, 113, 104 and 92 years. Most of these millennial-to-centennial cycles exist in various monsoon records as well as the tree ring Δ14C data and/or other solar proxy records. We suggest that throughout the Holocene, externally, small changes in solar activity controlled the Indian monsoon to a large extent, whereas internally, non-solar causes could have influenced the amplitude of decadal-to-centennial oscillations.  相似文献   

10.
Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO4 l−1 yr−1 and 0.01∼0.04 μmol-NO3 l−1 yr−1 with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48 mg-Chl m−2 yr−1 and 0.08∼0.47 g-C-NCP m−2 yr−1 with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O2 over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over the western North Pacific.  相似文献   

11.
The seasonal climatic circulation of the sea reconstructed on the basis of assimilation of new arrays of many-year average hydrological data in a model is analyzed. Five layers are discovered in the structure of climatic currents in the sea in depth: the surface Ekman layer (∼ 10 m), a layer with small vertical gradients of the kinetic energy (∼ 10–60 m), a layer with relatively high vertical gradients of the kinetic energy (∼ 60–150 m), a layer with gradual decrease in the kinetic energy and intensification (from 250–350 m) of the east cyclonic gyre and Batumi anticyclonic eddy (∼ 150–1000 m), and an abyssal layer characterized by an almost barotropic velocity (∼ 1000–2000 m). The specific features of the seasonal evolution of currents at these depths are investigated. It is shown that the key role in the formation of deep-water circulation of the sea is played by the south east flow, east cyclonic gyre, and Batumi anticyclonic eddy. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 28–45, November–December, 2005.  相似文献   

12.
利用NCEP FNL、ECMWF的预报资料、NMWW3(Multi-grid WAVEWATCHⅢ)模式的后报海浪资料和JMH气象传真,对2010年1月东亚的两次冷空气过程进行了对比分析,详细分析了天气形势和对西北太平洋海况的影响,揭示了影响程度差异的本质。对比分析表明:长波槽在东亚大槽气候位置的维持有利于西北太平洋发生恶劣海况;孟加拉湾上空南支槽的增强,下游半个波长处副高脊增强,进一步加强我国东部地区500 hPa上的西南气流,造成冷空气南侵减弱;EC-MWF对两次冷空气过程高低空96 h和168 h形势预报准确,240 h的海平面形势预报也有较高的参考价值。  相似文献   

13.
The tectonic and seismological aspects of the Great Japan Earthquake, which occurred on March 11, 2011 (M w = 9.0), at the Pacific margin of the northeastern part of Honshu Island, are discussed. The structure and seismotectonic data, seismicity, and the reccurence rate of the great (M ≥ 7.6) earthquakes throughout history and in modern times are represented. It is shown that the reccurence rate of the great events is about 40 years, and that of megaearthquakes is 1000 years or more. A seismic gap of about 800 km in length is found in the region under study, located to the south of latitude 39° N and full of aftershocks to the megaearthquake of March 11, 2011. This event is probably connected with the deep thrust along the Benioff zone and its structural front (Oyashio nappe at the middle Pacific continental slope). The aftershock sequences of this megaearthquake and the Sumatra-Andaman (2004) megaearthquake are compared. It is found that several of their key characteristics (the number of aftershocks, the magnitude of the strongest aftershock, and the time of its occurrence) for 25 days are comparable for both cases with a significant difference in the energies of aftershock processes. A probable scenario for the origination of a repeated shock with M ∼ 8.0 in the Japan Trench is discussed.  相似文献   

14.
Several researchers have investigated morphological changes on the south-eastern Mediterranean coast during the late Holocene. However, very few of these studies include quantitative data covering the last 200 years. In this study, topographical maps, nautical charts and aerial photographs are used to estimate the shoreline migrations and beach–nearshore sand balance over the last 200 years in Haifa Bay, Israel, the northernmost final depositional sink of the Nile littoral cell. The findings reflect two main periods. During the first period, between 1799 and 1928, human intervention along the bay’s coast was negligible, a significant coastal expansion of ∼50 to 150 m (averages of 0.4–1.2 m/year) was measured, and sand accumulation was estimated at ∼70,000 m3 annually in the beach–nearshore area. A dramatic change in the sedimentological pattern was observed during the second period, between 1928 and 2006, following the completion of Haifa Port’s main breakwater (1929–1933). During this period, most of the bay’s coast was in a steady state, with seasonal fluctuations of less than about ±20 m, and slight erosion of ∼7,000 m3 annually. These findings are consistent with previous studies which conclude that from approximately 4,000 years ago until the construction of Haifa Port, sea level remained relatively stable, and a continuous accumulation of Nile-derived sand dried up the Zevulun Plain and shifted the Haifa Bay shoreline westwards to its present location. This long-term trend ceased after completion of the Haifa Port main breakwater.  相似文献   

15.
From April 2005 to March 2006, the concentration of dissolved cadmium (Cd) was monitored in the surface seawater of Urasoko Bay, which is in a subtropical area of the North Pacific Ocean and is surrounded by a well-developed fringing reef. During this period, the observed salinity and Cd concentrations varied in a range of approximately 16–34.5 and 4.8–77.8 pM, respectively. The concentration range of Cd obtained in this study was considered to be too low to damage the coral species, and its variation throughout the year did not show any seasonality and was not connected with climate data. The Cd-salinity plot for all the data in the salinity range over 26 showed apparent non-conservative behavior, which suggests a possible irregular input of Cd from a solid phase through streams and groundwater, release from bottom sediments, and atmospheric deposition into the bay.  相似文献   

16.
詹国能 《台湾海峡》1996,15(4):352-356
本文应用任意３ａ中８５０ｈＰａ上的风及５００ｈＰａ和地面气象资料，对台湾海峡地区出现低空急流的天气气候特征，形成急流的天气背景及其影响下的天气进行初步分析。结果表明，台湾海峡地区８５０ｈＰａ低空急流具有明显的季风特征和特定的地理影响。  相似文献   

17.
南海南部海区气候要素的变化和分布特征   总被引：1，自引：0，他引：1  
南海南部海区属较典型的区域性热带和赤道带海洋性季风气候区。各气候要素的变化特征与冬、夏季风气流的转换关系密切。汇集沿岸各站和海岛站以及近15年来的考察资料，对气候要素的变化和分布特征作了初步的统计分析，为科研和海洋天气预报提供了许多实用的数据。  相似文献   

18.
We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976–1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976–1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean.  相似文献   

19.
The effect of air-sea temperature differences on the ocean microwave brightness temperature (Tb) was investigated using the Advanced Microwave Scanning Radiometer (AMSR) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) during a period of seven months. AMSR Tb in the global ocean was combined with wind data supplied by the scatterometer SeaWinds aboard ADEOS-II and air temperature given by a weather forecast model. Tb was negatively correlated with air-sea temperature difference, its ratio lying around −0.4K/°C at the SeaWinds wind speed of 14 m/s for the 6 GHz vertical polarization. Tb of AMSR-E aboard AQUA during 3.5 years was combined with ocean buoy data, and similar results were obtained.  相似文献   

20.
Reanalysis data obtained from data assimilation are increasingly used for diagnostic studies of the general circulation of the atmosphere, for the validation of modelling experiments and for estimating energy and water fluxes between the Earth surface and the atmosphere. Because fluxes are not specifically observed, but determined by the data assimilation system, they are not only influenced by the utilized observations but also by model physics and dynamics and by the assimilation method. In order to better understand the relative importance of humidity observations for the determination of the hydrological cycle, in this paper we describe an assimilation experiment using the ERA40 reanalysis system where all humidity data have been excluded from the observational data base. The surprising result is that the model, driven by the time evolution of wind, temperature and surface pressure, is able to almost completely reconstitute the large-scale hydrological cycle of the control assimilation without the use of any humidity data. In addition, analysis of the individual weather systems in the extratropics and tropics using an objective feature tracking analysis indicates that the humidity data have very little impact on these systems. We include a discussion of these results and possible consequences for the way moisture information is assimilated, as well as the potential consequences for the design of observing systems for climate monitoring. It is further suggested, with support from a simple assimilation study with another model, that model physics and dynamics play a decisive role for the hydrological cycle, stressing the need to better understand these aspects of model parametrization.  相似文献   

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