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1.
To date, only a few coral proxy studies have investigated coral growth as an indicator of climate variability. This study presents the first extension-rate record (Porites lutea) from the Maldives (NW Indian Ocean), inferred from skeletal δ18O chronology for the lagoon of Rasdhoo Atoll (4°N/73°W) in the central area of the Maldives, influenced by the Indian monsoon. The record spans 90 years over the period 1917–2007. The mean annual extension over this period was 9.9 mm/year, and an increase of annual extension rates until 1990 by 3 mm/year can be explained by a rise of 0.7°C in sea surface temperature (SST) in this region. After 1990, the extension rates do no continue increasing, possibly due to ecological stress caused by progressive ocean warming and acidification. The correlation between annual extension rates and SSTs is thus significant and strong in the lower part of the record until 1955 (r = +0.69, p < 0.0001), but weaker thereafter (r = +0.44, p < 0.001). The extension rates yield a distinct interannual variability of 3–4 years, caused by interannual SST fluctuations driven by the El Ni?o-Southern Oscillation. A variability of 8–9 years is likely driven by SST variations endemic to the Indian Ocean. Spectral peaks between 18–19 years and 6–7 years cannot be explained by SST fluctuations, but by variations in the strength of the SW monsoon currents. It is suggested that during phases of stronger monsoon activity, the coral sacrificed coral extension in favor of a denser, more robust skeleton. The geomorphology of the atoll may strengthen the potential of this new coral archive to track climate variability.  相似文献   

2.
 Swath bathymetric, gravity, and magnetic studies were carried out over a 55 km long segment of the Central Indian Ridge. The ridge is characterized by 12 to 15 km wide rift valley bounded by steep walls and prominent volcanic constructional ridges on either side of the central rift valley. A transform fault at 7°45′S displaces the ridge axis. A mantle Bouguer anomaly low of −14 mGals and shallowing of rift valley over the middle of the ridge segment indicate along axis crustal thickness variations. A poorly developed neovolcanic zone on the inner rift valley floor indicate dominance of tectonic extension. The off-axis volcanic ridgs suggest enhanced magmatic activity during the recent past. Received: 24 May 1996 / Rivision received: 13 January 1997  相似文献   

3.
A total of 25 surficial sediment samples (Peterson grab, gravity and piston cores), collected during the Pilot Expedition to Southern Ocean (PESO) 2004 cruises 199C and 200 onboard the ORV Sagar Kanya along a N–S transect between 9.69°N and 55.01°S, and 80 and 40°E in the Indian Ocean sector of the Southern Ocean (SW Indian Ocean), have been investigated for various morphological features—test size, mean proloculus size and coiling direction (dextral/sinistral forms)—of the planktic indicator species Neogloboquadrina pachyderma (Ehrenberg). The results show that the coiling directions co-vary with temperature and salinity, the abundances of sinistrally coiled forms increasing towards higher latitudes (south of 40°S), whereas dextrally coiled forms show a reverse trend. Similarly, overall test and proloculus sizes depend largely on the physicochemical properties (salinity, temperature, nutrients, calcium saturation) of the ambient water masses. These observations suggest that, particularly at the boundaries between different water masses, variations in morphological features of N. pachyderma can meaningfully be used to reconstruct paleoceanographic conditions from Indian Ocean sediments.  相似文献   

4.
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   

5.
By using the NCEP/NCAR reanalysis data sets for 1951–2001, we study the characteristics of Pacific cyclones. It is shown that the northeast-southwest direction is predominant in the displacements of cyclones in the North Pacific. We study the variability of the field of surface atmospheric pressure in different phases of the Pacific decadal oscillation characterizing the temperature anomalies on the surface of the ocean in the region bounded by 20 and 60°N. It is shown that the decadal variations of the North Atlantic Oscillation supported by the large-scale anomalies of the Pacific decadal oscillation is the most important cause of natural decadal oscillations in the European region. We study and evaluate the regional response to the Pacific decadal oscillation by using, as an example, the analysis of variations of the discharge of European rivers. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 13–23, July–August, 2007.  相似文献   

6.
Abstract

In the present study, mean rainfall for the months of June-July-August-September (JJAS) during summer monsoon is simulated over India and its adjoining regions for a period between 1982 and 2006. The study was carried out using Regional Climate Model (RegCM) version 4.6 at a resolution of 25?km. The simulated mean JJAS monsoon rainfall was validated against the observational IMD data. Comparison of JJAS seasonal mean summer rainfall for the first decade 1982–1991, with the later decade 1997–2006 indicate that the intensity of rainfall increases over Indian land-mass during the later decade under the forced conditions of Era-Interim. The observed JJAS mean rainfall indicates two maximum rainfall areas i.e. the Western Ghats and the Himalayan region. A significant bias is observed in the central and Jammu and Kashmir (J&K) region. The JJAS mean seasonal surface air temperature distribution at 0.25?×?0.25-degree grids resolution shows a decreasing trend of temperature over the Indian landmass.  相似文献   

7.
A contrasting study of the large-scale circulation features responsible for months with many typhoons and months with tew typhoons has revealed that the frequency of typhoon formation over the Northwest Pacific is related to the following conditions:Over the Northwest Pacific, a well-defined ITCZ (Intertropical Convergence Zone) extending eastward to 160°E was displaced to 20°N. At 200 mb, an extensive anomalous anticyclonic circulation prevails over the western and central Pacific. The condition characteristic of a break in the monsoon prevailed in India. The monsoon trough at 500 mb and at the surface over the Indian Peninsula was relatively weak and was accompanied by higher-than-normal rainfall in the northern part of India and lower-than-normal rainfall over the peninsula. In addition, the polar vortex tends to be weak and move to the side of the Northern Hemisphere, opposite to the North Pacific. Finally, abnormally warm water was observed over the Central and Eastern Pacific and abnormally cold  相似文献   

8.
Down-core variations in illite, chlorite, smectite and kaolinite (the major clays) in two 14C-dated cores collected along the SW continental margin of India show that illite and chlorite have enhanced abundance during 20–17, 12.5, 11–9.5, and 5–4.8 ka b.p., whereas smectite accumulation is higher between 17 and 12.5, and after 9 ka b.p. The climate may have been predominantly arid at 17 (20–17), 12.5, 10.5 (11–9.5), and 4.8 ka b.p. The first three dates correspond to the last glacial maximum, Bolling-Allerod, and Younger Dryas events, respectively. The SW monsoon was variable between 17 and 15 ka b.p., and it was more stable and intense after the Younger Dryas until about 6 ka b.p. Received: 2 December 1999 / Revision accepted: 11 April 2000  相似文献   

9.
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   

10.
东亚边缘海区浮游植物春华的纬向与年际变化   总被引：1，自引：1，他引：0  
Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.  相似文献   

11.
In this paper we investigated the variations of summer montoon in the South China Sea. We found that there are two kinds of oscillations in the intensity of the monsoon, one has a period of forty days, the other, fourteen days. We also found that the oscillation of a period of forty days is caused by the alternative extension of the monsoon trough eastward in the South China Sea and the extension of the subtropical anticyclone westward in the West Pacific.It is our opinion that the summer monsoon in the West Pacific and the South China Sea is a system which is independent - of the Indian monsoon and that the dividing line between these two monsoon systems is at the longitude 100°E.  相似文献   

12.
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   

13.
The Sea Surface Temperatures (SST) and currents are simulated over the north Indian Ocean, during the onset phase of southwest monsoon for the three years 1994, 1995, and 1996, using daily Special Sensor Microwave/Imager (SSM/I) winds and National Center for Environmental Prediction (NCEP) heat fluxes as forcings in the 2½ layer thermodynamic numerical ocean model. The results are discussed for the 30-day period from 16 May to 13 June for all the three years, to determine the ocean state during the onset phase of SW monsoon. The maximum variability in the simulated SST is found along the Somali coast, Indian coasts, and equatorial regions. The maximum SST in the North Arabian Sea is found to be greater than 30°C and minimum SST in the west equatorial region is 25°C during the onset phase of all three years. Model SSTs are in agreement with Reynolds SST. SST gradients in the north-south as well as in the east-west directions, west of 80°E are found to change significantly prior to the onset. It can be inferred from the study that the SST gradient of 2.5°C/2000 km is seen due north and due west of the region 2° - 7°S, 60° - 65°E, about 8 to 10 days prior to the arrival of SW monsoon near Kerala coast. Upper and lower layer circulation fields do not show prominent interannual variability.  相似文献   

14.
The objective of the paper is to use the data collected along two meridional sections (45° E and 57°30′ E) during the austral summer (January–March) 2004 to understand the influence of seabed topography across the Madagascar and Southwest Indian Ridges on hydrographic parameters. The study was supplemented by World Ocean Circulation Experiment (WOCE) Conductivity-Temperature-Depth data collected during February–March 1996 along 30° E, as well as Levitus climatology. A southward shift of 2° latitude (between 45° E and 57°30′ E) was recorded for the two predominant frontal structures, i.e., the Agulhas Return Front and Southern Subtropical Front, which is attributed to the influence of seabed topography on hydrographic parameters. No significant spatial variation of these fronts was noted between the 30° E and 45° E meridional sections. Between latitudes 31° S and 42° S, the temperature and salinity structures show deepening over the ridges. The Antarctic Circumpolar Current core was detected between 40°15′ S and 43° S.  相似文献   

15.
黑潮延伸体海表温度锋位置的变化特征   总被引：2，自引：1，他引：1  
High spatial resolution sea surface temperature(SST) data from 1993 to 2013 are used to detect the position of the Kuroshio Extension sea surface temperature front(KEF) from 141°E to 158°E,and the seasonal,monthly and interannual-to-decadal variations of the KEF position are investigated.The latitudinal position of the KEF varies with longitudes:the westernmost part of the KEF from 141°E to 144°E is relatively stable,whereas the easternmost part from 153°E to 158°E exhibits the largest amplitude of its north-south displacement.In the light of the magnitudes of the standard deviations at longitudes,then the KEF is divided into three sections:western part of the KEF(KEFw,141°–144°E),central part of the KEF(KEFc,144°–153°E) and eastern part of the KEF(KEFe,153°–158°E).Further analysis reveals that the KEFw position is dominated by the decadal variability,while the KEFc and KEFe positions change significantly both on interannual and decadal time scales.In addition,the KEFw position is well correlated with the KEF path length.The possible mode leading to the decadal oscillation of the KEFw is further discussed.The KEFw position exhibits significant connections with the Pacific decadal oscillation(PDO) index and the north Pacific gyre oscillation(NPGO) index with a time lag of 40 and 33 months,respectively.  相似文献   

16.
Interannual variability(IAV) in the barrier layer thickness(BLT) and forcing mechanisms in the eastern equatorial Indian Ocean(EEIO) and Bay of Bengal(BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January(NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode(IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth(ILD). Moreover, the variability in the mixed layer depth(MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December–February(DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Ni?o-Southern Oscillation(ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations.  相似文献   

17.
 Magnetic data over the eastern continental margin of India and adjacent Bengal fan demarcate two major lineaments. A high amplitude N–S-trending lineation of the Cauvery offshore Basin corresponds to the offshore fragment of the 80°E lineament recorded onland. A N–S lineation of very high amplitude anomaly off Chilka lake considered as the possible northward extension of the 85°E ridge delineated, hitherto in Bengal Fan. A subdued magnetic anomaly zone is demarcated seaward of the continent–ocean boundary (COB) in the Bengal Fan. Over the northern Bengal Fan this zone is delineated east of 85°E lineation. This quiet zone might have evolved during the Early Cretaceous period of normal magnetic polarity between M0 and 34 (120–84 Ma) anomalies. Received: 6 April 1995 / Revision received: 3 September 1996  相似文献   

18.
In the southern Arabian Sea (between the Equator and 10°N), the shoaling of isotherms at subsurface levels (20 °C isotherm depth is located at ∼90 m) leads to cooling at 100 m by 2–3 °C relative to surrounding waters during the winter monsoon. The annual and interannual variations of this upwelling zone, which we call the Arabian Sea dome (ASD), are studied using results from an eddy-permitting ocean general circulation model in conjunction with hydrography and TOPEX/ERS altimeter data. The ASD first appears in the southeastern Arabian Sea during September–October, maturing during November–December to extend across the entire southern Arabian Sea (along ∼5°N). It begins to weaken in January and dissipates by March in the southwestern Arabian Sea. From the analysis of heat-budget balance terms and a pair of model control experiments, it is shown that the local Ekman upwelling induced by the positive wind-stress curl of the winter monsoon generates the ASD in the southeastern Arabian Sea. The ASD decays due to the weakening of the cyclonic curl of the wind and the westward penetration of warm water from the east (Southern Arabian Sea High). The interannual variation of the ASD is governed by variations in the Ekman upwelling induced by the cyclonic wind-stress curl. Associated with the unusual winds during 1994–1995 and 1997–1998 Indian Ocean dipole (IOD) periods, the ASD failed to develop. In the absence of the ASD during the IOD events, the 20 °C isotherm depth was 20–30 m deeper than normal in the southern Arabian Sea resulting in a temperature increase at 97 m of 4–5 °C. An implication is that the SST evolution in the southern Arabian Sea during the winter monsoon is primarily controlled by advective cooling: the shoaling of isotherms associated with the ASD leads to SST cooling.  相似文献   

19.
The seasonal and interannual variation of upwelling along the west coast of India between 8°N and 24°N was studied for the period 1985 through 2003 using NOAA-AVHRR sea surface temperature data. The seasonal migration of pronounced upwelling, which follows the seasonal shift of the winds in southwest monsoon period and northeast monsoon, was confined. The temporal mean sea surface temperature images clearly show the upwelling season, as does the seasonal sea surface temperature anomaly. These dominate features of the upwelling system are also the most variable, with most of the variance being explained by the seasonal cycle. Quasi-cyclic behavior of seas surface temperature on interannual scales has also been observed.  相似文献   

20.
The influences of the large-scale interannual variations in the eastern Indian Ocean on the variability of the Indonesian throughflow are investigated by using an ocean general circulation model, driven by the ERS satellite winds from July 1992 to June 1997. The empirical orthogonal function (EOF) analysis of the simulated surface dynamic height variability captures two dominant modes on an interannual time scale, which are quite consistent with the available observations. The first mode indicates large amplitude in the western tropical Pacific and has a strong relation to the El Niño events, while the second EOF exhibits the large amplitude in the eastern Indian Ocean. The simulated net Indonesian throughflow shows an interannual variation of amplitude of about 15 Sv, with large transport from the Pacific to the Indian Ocean during 1994/95 and small transport during 1992 and 1997. It turns out that the net throughflow variation shows a high correlation with the second EOF mode (r = 0.51) for the whole five-year simulation. On the other hand, the correlation with the first mode is rather low (r = ?0.07). However, the relative importance of the EOF modes to the throughflow variability changes with time. The upper-layer transport above a depth of 230 m in the Indonesian archipelago is also affected by the second mode. The difference in the upper-layer transport across 1°S and 110°E generates warm water convergence/divergence with a magnitude of 4 Sv within the Indonesian Seas on the interannual time scale, which shows good correspondence with sea surface temperature variation averaged over the Indonesian archipelago.  相似文献   

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