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1.
An historical objective analysis of subsurface temperature and salinity was carried out on a monthly basis from 1945 to 2003 using the latest observational databases and a sea surface temperature analysis. In addition, steric sea level changes were mainly examined using outputs of the objective analyses. The objective analysis is a revised version of Ishii et al. and is available at 16 levels in the upper 700 m depth. Artificial errors in the previous analysis during the 1990s have been worked out in the present analysis. The steric sea level computed from the temperature analysis has been verified with tide gauge observations and TOPEX/Poseidon sea surface height data. A correction for crustal movement is applied for tide gauge data along the Japanese coast. The new analysis is suitable for the discussion of global warming. Validation against the tide gauge reveals that the amplitude of thermosteric sea level becomes larger and the agreement improves in comparison with the previous analysis. A substantial part of local sea level rise along the Japanese coast appears to be explained by the thermosteric effect. The thermal expansion averaged in all longitudes from 60°S to 60°N explains at most half of recent sea level rise detected by satellite observation during the last decade. Considerable uncertainties remain in steric sea level, particularly over the southern oceans. Temperature changes within MLD make no effective contribution to steric sea level changes along the Antarctic Circumpolar Current. According to statistics using only reliable profiles of the temperature and salinity analyses, salinity variations are intrinsically important to steric sea level changes in high latitudes and in the Atlantic Ocean. Although data sparseness is severe even in the latest decade, linear trends of global mean thermosteric and halosteric sea level for 1955 to 2003 are estimated to be 0.31 ± 0.07 mm/yr and 0.04 ± 0.01 mm/yr, respectively. These estimates are comparable to those of the former studies.  相似文献   

2.
The UNEP in its regional seas program in 1989 has included Pakistan in a group of countries which are vulnerable to the impact of rising sea level. If the present trend of sea level rise (SLR) at Karachi continues, in the next 50 years the sea level rise along the Pakistan Coast will be 50 mm (5 cm). Since the rising rates of sea level at Karachi are within the global range of 1-2 mm/year, the trends may be treated as eustatic SLR. Historical air temperature and sea surface temperature (SST) data of Karachi also show an increasing pattern and an increasing trend of about 0.67°C has been registered in the air temperature over the last 35 years, whereas the mean SST in the coastal waters of Karachi has also registered an increasing trend of about 0.3°C in a decade. Sindh coastal zone is more vulnerable to sea level rise than Baluchistan coast, as uplifting of the coast by about 1-2 mm/year due to subduction of Indian Ocean plate is a characteristic of Baluchistan coast. Within the Indus deltaic creek system, the area nearby Karachi is more vulnerable to coastal erosion and accretion than the other deltaic region, mainly due to human activities together with natural phenomena such as wave action, strong tidal currents, and rise in sea level. Therefore, The present article deals mainly with the study of dynamical processes such as erosion and accretion associated with sea level variations along the Karachi coast and surrounding Indus deltaic coastline. The probable beach erosion in a decade along the sandy beaches of Karachi has been estimated. The estimates show that 1.1 mm/year rise in sea level causes a horizontal beach loss of 110 mm per year. Therefore, coast eroded with rise in sea level at Karachi and surrounding sandy beaches would be 1.1 m during a period of next 10 years. The northwestern part of Indus delta, especially the Gizri and Phitti creeks and surrounding islands, are most unstable. Historical satellite images are used to analyze the complex pattern of sediment movements, the change in shape of coastline, and associated erosion and accretion patterns in Bundal and Buddo Islands. The significant changes in land erosion and accretion areas at Bundal and Buddo Islands are evident and appear prominently in the images. A very high rate of accretion of sediments in the northwestern part of Buddo Island has been noticed. In the southwest monsoon season the wave breaking direction in both these islands is such that the movement of littoral drift is towards west. Erosion is also taking place in the northeastern and southern part of Bundal Island. The erosion in the south is probably due to strong wave activities and in the northeast is due to strong tidal currents and seawater intrusion. Accretion takes place at the northwest and western parts of Bundal Island. By using the slope of Indus delta, sea encroachment and the land area inundation with rising sea level of 1 m and 2 m have also been estimated.  相似文献   

3.
IPCC气候情景下全球海平面长期趋势变化   总被引：5，自引：1，他引：4  
利用CCSM3 (Community Climate System Model version 3)气候系统模式模拟20世纪海平面变化,在IPCC SRES A2 (IPCC,2001)情景假设下预测21世纪全球海平面长期趋势变化。模拟显示20世纪海平面上升约4.0 cm,且存在0.004 8 mm/a2的加速度,这个结果仅为热盐比容的贡献。在A2情景假设下,21世纪海平面上升存在很大的区域特征,呈纬向带状分布;总体上北冰洋上升大,南大洋高纬度海区上升小,大西洋上升值比太平洋的大;整个21世纪全球平均比容海平面上升了约30 cm,且呈加速上升的趋势。同时发现,中深层水温度和盐度变化对区域比容海平面变化具有重要贡献。北太平洋增暖主要集中在上层700 m以内,而北大西洋的增暖可达2 500 m的深度,南大洋南极绕极流海区热盐变化则是发生在整个深度。  相似文献   

4.
Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.  相似文献   

5.
For ocean and climate research, it is essential to get long-term altimetric sea level data that is as accurate as possible. However, the accuracy of the altimetric data is frequently degraded in the interior of the Arctic Ocean due to the presence of seasonal or permanent sea ice. We have reprocessed ERS-1/2/Envisat satellite altimetry to develop an improved 20-year sea level dataset for the Arctic Ocean. We have developed both an along-track dataset and three-day gridded sea level anomaly (SLA) maps from September 1992 to April 2012. A major improvement in data coverage was gained by tailoring the standard altimetric editing criteria to Arctic conditions. The new reprocessed data has significant increased data coverage with between 4 and 10 times the amount of data in regions such as the Beaufort Gyre region compared with AVISO and RADS datasets. This allows for a more accurate estimation of sea level changes from satellite altimetry in the Arctic Ocean. The reprocessed dataset exhibit a mean sea level trend of 2.1 ± 1.3 mm/year (without Glacial Isostatic Adjustment correction) covering the Arctic Ocean between 66°N and 82°N with significant higher spatial coherency in the ice-covered regions than the RADS and DUACS datasets.  相似文献   

6.
Sea level variations in the regional seas around Taiwan   总被引：2，自引：0，他引：2  
The patterns and trends of sea level rise in the regional seas around Taiwan have been investigated through the analyses of long-term tide-gauge and satellite altimetry data. Series of tide-gauge data extending over 50 years reveal decadal and interannual variations and spatially-inhomogeneous patterns of generally rising sea level. The East Asia tide-gauge stations around Taiwan show an average trend of +2.4 mm/yr from 1961–2003, which is larger than the reported global rate of +1.8 mm/yr for the same period. These stations also show significantly larger sea level rise rates (+5.7 mm/yr) than global values (+3.1 mm/yr) during the period from 1993–2003. Consistent with the coastal tide-gauge records, satellite altimetry data show similar increasing rates (+5.3 mm/yr) around Taiwan during the same period. Comparisons with temperature anomalies in the upper ocean suggest that thermal expansion and heat advection in the upper layer contribute significantly to the long-term sea level variations in this area with correlations >0.9 for observations after 1992. Thermosteric sea level variations may also explain the interannual and decadal variations of the observed sea level rises around Taiwan. Our analysis also indicates that the altimetry data are only part of a long-term, larger-scale signal. Finally, we have found that a non-linear smoother, LOESS, is more suitable for extracting long-term trends in sea level than the traditional linear regression approach.  相似文献   

7.
The UNEP in its regional seas program in 1989 has included Pakistan in a group of countries which are vulnerable to the impact of rising sea level. If the present trend of sea level rise (SLR) at Karachi continues, in the next 50 years the sea level rise along the Pakistan Coast will be 50 mm (5 cm). Since the rising rates of sea level at Karachi are within the global range of 1-2 mm/year, the trends may be treated as eustatic SLR. Historical air temperature and sea surface temperature (SST) data of Karachi also show an increasing pattern and an increasing trend of about 0.67°C has been registered in the air temperature over the last 35 years, whereas the mean SST in the coastal waters of Karachi has also registered an increasing trend of about 0.3°C in a decade. Sindh coastal zone is more vulnerable to sea level rise than Baluchistan coast, as uplifting of the coast by about 1-2 mm/year due to subduction of Indian Ocean plate is a characteristic of Baluchistan coast. Within the Indus deltaic creek system, the area nearby Karachi is more vulnerable to coastal erosion and accretion than the other deltaic region, mainly due to human activities together with natural phenomena such as wave action, strong tidal currents, and rise in sea level. Therefore, The present article deals mainly with the study of dynamical processes such as erosion and accretion associated with sea level variations along the Karachi coast and surrounding Indus deltaic coastline. The probable beach erosion in a decade along the sandy beaches of Karachi has been estimated. The estimates show that 1.1 mm/year rise in sea level causes a horizontal beach loss of 110 mm per year. Therefore, coast eroded with rise in sea level at Karachi and surrounding sandy beaches would be 1.1 m during a period of next 10 years. The northwestern part of Indus delta, especially the Gizri and Phitti creeks and surrounding islands, are most unstable. Historical satellite images are used to analyze the complex pattern of sediment movements, the change in shape of coastline, and associated erosion and accretion patterns in Bundal and Buddo Islands. The significant changes in land erosion and accretion areas at Bundal and Buddo Islands are evident and appear prominently in the images. A very high rate of accretion of sediments in the northwestern part of Buddo Island has been noticed. In the southwest monsoon season the wave breaking direction in both these islands is such that the movement of littoral drift is towards west. Erosion is also taking place in the northeastern and southern part of Bundal Island. The erosion in the south is probably due to strong wave activities and in the northeast is due to strong tidal currents and seawater intrusion. Accretion takes place at the northwest and western parts of Bundal Island. By using the slope of Indus delta, sea encroachment and the land area inundation with rising sea level of 1 m and 2 m have also been estimated.  相似文献   

8.
Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.  相似文献   

9.
Spatial Variation of Sea Level Trend Along the Bangladesh Coast   总被引：1，自引：0，他引：1  
O. P. Singh 《Marine Geodesy》2002,25(3):205-212
The Bangladesh coast is threatened by rising sea level due to various factors. The results based on the analysis of past 22 years of tidal data of the Bangladesh coast reveal that the annual mean tidal level in the eastern Bangladesh coast is rising at an alarmingly high rate of 7.8 mm/year, which is almost twice the observed rate in the western region. This type of sea level trend seems to be the result of changing local conditions like increased precipitation and land subsidence during the recent decades. It seems that the higher rate of land subsidence in the eastern Bangladesh coast is the main causative factor for the steeper sea level trends there. The differential sea level trends show that the subsidence component in the sea level rise may be as high as 4 mm/year in the eastern Bangladesh coast. However, this needs to be verified with actual geological observations.  相似文献   

10.
Data derived from altimetry shows that since 1993 the mean sea level over the East /Japan (EJS) Sea is increasing at a rate of ~3 mm/year, but tide gauge records indicate that a multidecadal reversal trend occurred prior to the early 1980s. We here characterize and quantify the multi-decadal trend of mean sea level in the EJS from the reconstructed sea levels and the in-situ ocean profiles over the past 60 years. Our analysis shows that sea level trends have undergone a shift, revealing a declining trend before the early 1980s, followed by a rising trend from the early 1980s onward with a near basin-wide sea level fluctuation. The trend reversal strongly corresponds to changes in the upper-ocean heat content over the EJS, revealing a negative correlation with the Pacific Decadal Oscillation (PDO) index that correlates negatively with wind stress curl (WSC) in the subtropical North Pacific. The PDO-related WSC, which changes the transport of the western boundary current in the subtropical gyre, may account for the observed trend reversal in the EJS sea level on a multi-decadal time scale.  相似文献   

11.
O. P. Singh 《Marine Geodesy》2013,36(3):205-212
The Bangladesh coast is threatened by rising sea level due to various factors. The results based on the analysis of past 22 years of tidal data of the Bangladesh coast reveal that the annual mean tidal level in the eastern Bangladesh coast is rising at an alarmingly high rate of 7.8 mm/year, which is almost twice the observed rate in the western region. This type of sea level trend seems to be the result of changing local conditions like increased precipitation and land subsidence during the recent decades. It seems that the higher rate of land subsidence in the eastern Bangladesh coast is the main causative factor for the steeper sea level trends there. The differential sea level trends show that the subsidence component in the sea level rise may be as high as 4 mm/year in the eastern Bangladesh coast. However, this needs to be verified with actual geological observations.  相似文献   

12.
A bottom pressure gauge (BPG) was installed in proximity (3.7 km at closest approach) of Jason-1 and formerly TOPEX/Poseidon (T/P) ground track No. 238 at the Wusi site, located ∼ 10 km offshore off the west coast of Santo Island, Vanuatu, Southwest (SW) Pacific. Sea level variations are inferred from the bottom pressure, seawater temperature, and salinity, corrected for the measured surface atmospheric pressure. The expansion of the water column (steric increase in sea surface height, SSH) due to temperature and salinity changes is approximated by the equation of state. We compare time series of SSH derived from T/P Side B altimeter Geophysical Data Records (GDR) and Jason-1 Interim Geophysical Data Records (IGDR), with the gauge-inferred sea level variations. Since altimeter SSH is a geocentric measurement, whereas the gauge-inferred observation is a relative sea level measurement, SSH comparison is conducted with the means of both series removed in this study. In addition, high-rate (1-Hz) bottom pressure implied wave heights (H1/3) are compared with the significant wave height (SWH) measured by Jason-1. Noticeable discrepancy is found in this comparison for high waves, however the differences do not contribute significantly to the difference in sea level variations observed between the altimeter and the pressure gauge. In situ atmospheric pressure measurements are also used to verify the inverse barometer (IB) and the dry troposphere corrections (DTC) used in the Jason IGDR. We observe a bias between the IGDR corrections and those derived from the local sensors. Standard deviations of the sea level differences between T/P and BPG is 52 mm and is 48 mm between Jason and BPG, indicating that both altimeters have similar performance at the Wusi site and that it is feasible to conduct long-term monitoring of altimetry at such a site.  相似文献   

13.
A comprehensive set of 456 monthly tide gauge records is analyzed for trend and acceleration over the same period that satellite altimetry was analyzed (1993 to 2011). Additionally, a 90 tide gauge record subset is analyzed for which GPS data are available. The selection criterion for the tide gauge data is 85% data completion. All measurements are adjusted for vertical land motion. Results from 456 pairs of tide gauges, adjusted for Global Isostatic Adjustment, and satellite recordings located within 1° root-mean-square latitude and longitude separation differences are compared. The tide gauge trends and accelerations are adjusted for spatial bias using the more globally dense satellite data.The average trends of the 456 and 90 gauge sets (3.26 and 2.68 mm/year, respectively) agree reasonably well with the global trend average of the satellite data (3.09 mm/year). Average trends for the 456 tide gauges are also in good agreement (within 95% confidence limits) with trends based on satellite data within the 1° satellite proximity criterion (3.26 and 3.31 mm/year, respectively). The trends for the 90 gauges with GPS nearby and qualifying satellite locations are 2.68 and 2.74 mm/year, respectively. For all datasets analyzed, the accelerations are quite strongly negative but the uncertainty is relatively large. Adjustment of the tide gauge trends for spatial bias modified both trends and accelerations significantly and decreased trend differences between the 456 and 90 gauge datasets. The spatially adjusted tide gauge trends (2.95 and 2.72 mm/year, respectively for the 456 and 90 tide gauges sets) are somewhat less than the 1° spatially adjusted satellite data (3.09 mm/year). Whether the increased sea level trend of approximately 3 mm/year measured by the satellites since the 1990's is a long-term increase from the 20th Century value of approximately 1.7 mm/year or part of a cycle will require longer records; however, the negative accelerations support some cyclic character.  相似文献   

14.
Experiments in reconstructing twentieth-century sea levels   总被引：3，自引：0，他引：3  
One approach to reconstructing historical sea level from the relatively sparse tide-gauge network is to employ Empirical Orthogonal Functions (EOFs) as interpolatory spatial basis functions. The EOFs are determined from independent global data, generally sea-surface heights from either satellite altimetry or a numerical ocean model. The problem is revisited here for sea level since 1900. A new approach to handling the tide-gauge datum problem by direct solution offers possible advantages over the method of integrating sea-level differences, with the potential of eventually adjusting datums into the global terrestrial reference frame. The resulting time series of global mean sea levels appears fairly insensitive to the adopted set of EOFs. In contrast, charts of regional sea level anomalies and trends are very sensitive to the adopted set of EOFs, especially for the sparser network of gauges in the early 20th century. The reconstructions appear especially suspect before 1950 in the tropical Pacific. While this limits some applications of the sea-level reconstructions, the sensitivity does appear adequately captured by formal uncertainties. All our solutions show regional trends over the past five decades to be fairly uniform throughout the global ocean, in contrast to trends observed over the shorter altimeter era. Consistent with several previous estimates, the global sea-level rise since 1900 is 1.70 ± 0.26 mm yr−1. The global trend since 1995 exceeds 3 mm yr−1 which is consistent with altimeter measurements, but this large trend was possibly also reached between 1935 and 1950.  相似文献   

15.
Observed subsurface signature of Southern Ocean sea level rise   总被引：1，自引：0，他引：1  
Satellite altimetry data show a strong increase in sea level in various parts of the Southern Ocean over the 1990s. In this paper, we examine the causes of the observed sea level rise in the region south of Australia, using 13 years of repeat hydrographic data from the WOCE SR3 sections, and the SURVOSTRAL XBT and surface salinity data. The hydrographic data show a poleward shift in the position of the Subtropical and the Subantarctic Fronts over the period. In the Antarctic Zone, the Antarctic Surface Water has become warmer and fresher, and the Winter Water tongue has become warmer, fresher, thinner and shallower. Increased freshening south of the Polar Front is linked to increased precipitation over the 1990s. Temperature changes over the upper 500 m account for only part of the altimetric sea level rise. The CTD sections show that the deeper layers are also warmer and slightly saltier and the observed sea level can be explained by steric expansion over the upper 2000 m. ENSO variability impacts on the northern part of the section, and a simple Sverdrup transport model shows how large-scale changes in the wind forcing, related to the Southern Annular Mode, may contribute to the deeper warming to the south.  相似文献   

16.
Tide gauge observations usually include temperature and density measurements. As an example of such data, a time series of sea surface temperature (SST) from 1855 to 1877 and from 1921 to 1993 at Fort Point, San Francisco, California (the longest U.S. record), and mean air temperature at Mission Dolores (San Francisco), California, from 1936 to 1990, were analyzed. Annual mean Fort Point SST increased at a rate of 0.3°C per century, but the coefficient of determination (r2) was below 0.06; for air temperature the results were 1.6°C per century and r2 = 0.16 respectively. Evidence of El Niño were found in the periodogram of the mean annual SST but not in the air temperature. The annual and semiannual peaks in the monthly time‐series analysis of SST and air temperature dominate their periodograms, and the cross‐correlation between them has r2 = 0.47. Of the 1.3 mmlyr sea level rise over the same time period. 0.003°C/yr accounts for 0.04 mmlyr in thermal expansion if the upper 100 m of the water column were uniformly warmed.  相似文献   

17.
热带印度洋降水、蒸发的时空特征及其对海表盐度的影响   总被引：3，自引：2，他引：1  
许金电  高璐 《海洋学报》2018,40(7):90-102
本文利用降水、蒸发等资料分析热带印度洋年降水量、蒸发量、净淡水通量的分布特征，并选取4个典型海域来分析降水量、蒸发量、净淡水通量的季节变化和年际变化。结果表明:东印度洋的苏门答腊岛西部海域年降水量最大，季节变化较小，属全年降雨型；孟加拉湾的东北部和安达曼海的北部海域年降水量较大，其年际变化以4.2 mm/a的速率增长，强降水出现在5-9月；阿拉伯海的西部海域年降水量较小；南印度洋东部（20°~30°S，80°~110°E）海域年降水量较小，年蒸发量较大，年蒸发量在2000年之前以5.1 mm/a的速率增长，之后以4.5 mm/a的速率减小。本文还采用Argo盐度等资料探讨降水、蒸发对海表盐度的影响，研究结果表明:降水量远大于蒸发量的海域，海表盐度较低；降水量远小于蒸发量的海域，海表盐度较高。表层水平环流是导致高净淡水通量中心与低盐中心并不重合的主要原因，也是导致强蒸发中心与高盐中心并不重合的主要原因。选取的4个典型海域海表盐度的季节变化与净淡水通量关系不大，而是与表层水平环流有关。孟加拉湾强降水对表层盐度的影响显著，强降水发生后表层盐度降低0.2~0.8，其影响深度为30~50 m。  相似文献   

18.
On the rocky coasts of the northwestern Mediterranean basin, biogenic littoral rims built by the coralline rhodophyte Lithophyllum lichenoides develop, whose remains may be preserved for millennia when submerged in a rising sea environment. These remains can be used as biological indicators of recent sea-level variations. Our survey of the continental coasts of Var and Bouches du Rhône, west of Marseilles (southern France) and of northern Corsica shows that relative sea level rose about 1.6 m in the study area during the last 4500 years without exceeding the present datum. The rate of sea-level rise was 0.4 mm per year between 4500 and 1500 yr B.P. and slowed down to 0.2 mm per year from 1500 yr B.P. to present time. There are also morphological indications of an acceleration of the rate of sea-level rise during the last century, supporting the evidence of tide gauges. Regions at the periphery of the above zone (Alpes Maritimes, Italian border zone, and the French and Spanish Catalonia regions) were also surveyed, but a weaker development of Lithophyllum rims and bad preservation of algal remains led to unconvincing dates which could also be linked to regional tectonic trends.  相似文献   

19.
The plate culture method using the two formulae for non-nitrogenous media was adopted in this investigation for the purpose of counting and isolating nitrogen-fixing bacteria distributed in the open sea. Sea water samples were collected at eighteen different stations in the region of Lat. 50°N–15°S along Long. 155°W and two other stations in the Pacific Ocean. In order to compare with those samples from the open sea, water samples were also obtained at four stations in Suruga and Sagami Bays. Nitrogen-fixing bacteria appear to be widely but very unevenly distributed at all depths in sea water, in numbers approximately ranging from nil to 104 per 100 ml of sea water, and denser vertical populations have been found in the area of Lat. 40°N and 5°N along Long. 155°W, even at depths from 2,000 to 3,000m. A conparatively denser population of bacteria was found in sea water from Suruga Bay and Sagami Bay. The bacteria associated with plankton were abundantly demonstrated, in numbers ranging from 106 to 108 per 1 ml settling volume of plankton, in many plankton samples collected at four stations in the southern parts of the Pacific Ocean. Almost all the bacteria isolated from the samples of blue green algal colonies,Trichodesmium, sp., were able to grow on nonnitrogeneous media.  相似文献   

20.
Bangladesh, one of the most densely populated countries in the world, is a victim of frequent natural calamities like tropical cyclones, tornadoes, floods, storm surges and droughts. Now the sea level rise (SLR) has also been included in these natural calamities. The SLR is likely to have greater impact on that part of Bangladesh having low topography and a wide flood plain. Since 21% of the population lives in the low coastal belt, any increase in sea level will be a problem of ominous proportion for Bangladesh. Since the cyclogenesis enhances over the Bay of Bengal during May and November, the sea level and sea surface temperature (SST) trends of these two months have been analyzed and calculated. The results of the selected stations one in the eastern coast and another in the western coast of Bangladesh show that Bangladesh coastal sea level is rising in the same way as the global sea level, but the magnitude is quite different. The difference in the behavior of sea level rise along the Bangladesh coast and the global trend may be due to the tectonic activity such as subsidence of the land. The mean tide level at Hiron Point (in Sunderbans) has shown an increasing trend of about 2.5 mm/year in May and 8.5 mm/year in November. Similarly near Cox?s Bazar (in the eastern coast of Bangladesh) it has registered a positive trend of about 4.3 mm/year in May and 10.9 mm/year in November. Thus the increment in the sea level along the Bangladesh coast during cyclone months is much more pronounced. In coastal waters near Hiron Point the SST has registered an increasing trend of about 1°C in May and 0.5°C in November during the 14-year period from 1985?1998. Near Cox?s Bazar, SST has shown a rising trend of about 0.8°C in May and about 0.4°C in November during the same 14-year period. The magnitude of SST trend is slightly more along the west coast. Any change in the frequency and intensity of tropical cyclones will have far reaching implications in the South Asian region. The rise in SST in the cyclone months seems to be correlated with the frequency and intensity of tropical cyclones. During these months, an increasing trend in the frequency and intensity of severe cyclones has been observed.  相似文献   

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