The Andaman Sea has been a classic study region for internal solitary waves(ISWs)for several decades,and extraordinarily large ISWs are characteristic of the Andaman Sea in the Indian Ocean.This paper presents results...The Andaman Sea has been a classic study region for internal solitary waves(ISWs)for several decades,and extraordinarily large ISWs are characteristic of the Andaman Sea in the Indian Ocean.This paper presents results on the estimation of the propagation velocity of ISWs in the Andaman Sea that were tracked using 195 image pairs acquired by MODIS National Aeronautics and Space Administration(NASA)Terra/Aqua satellites between January 2014 and December 2018.A total of 562 ISWs were identified during the period,and the results of the propagation velocity distribution of ISWs in the Andaman Sea are presented.The estimated propagation velocity of ISWs agrees well with the theoretical results derived from the Korteweg-de Vries(KdV)equation using monthly climatology stratification data and local bathymetry.The ISW propagation velocity decreases as they propagate from deep to shallow water;the maximum propagation velocity of 3.27 m/s was estimated on the western side of the Nicobar Islands and minimum speed of 0.54 m/s occurred in the shallow water region of the southeastern Andaman Sea.The results show that the ISW propagation characteristics differ in the northern,central,and southern regions of the Andaman Sea.In the northern Andaman Sea,the velocity of ISWs propagating westward was greater than that of ISWs propagating eastward at the same water depth.In the central Andaman Sea,the propagation velocity of the ISWs differed over a small area at a depth of 2500 m,and the velocity of ISWs in the deep mixing layer in winter was higher than that in the shallow mixing layer in spring.Monthly variations in ISW propagation velocity were analyzed in the southern Andaman Sea,and the velocity of ISWs differed greatly in shallow water and was not significantly different in deep water.Water depth and monthly stratification play vital roles in controlling the phase speed of ISWs in the Andaman Sea.This study will provide a basis for the propagation and prediction of ISWs in the Andaman Sea.展开更多
Stable isotopes of carbon and oxygen variations in foraminiferal shells have been widely used in paleo-environment studies.However,studies about the shells of benthic foraminifera in methanehydrate-bearing sediments a...Stable isotopes of carbon and oxygen variations in foraminiferal shells have been widely used in paleo-environment studies.However,studies about the shells of benthic foraminifera in methanehydrate-bearing sediments as reliable geochemical proxies to reconstruct the potential methane release events in the geologic past are rare.In this study,we present the stable carbon and oxygen isotopes of fossil benthic foraminifera including one epifaunal species(Cibicidoides wuellerstorfi)and two infaunal species(Bulimina mexicana and Uvigerina peregrina)from the Site U1447 of IODP 353 Expedition to trace methane events in the Andaman Sea,where one of the thickest and deepest gas hydrate stability zones was discovered.Theδ^(13)C values of benthic foraminifera show that there are eight distinct intervals with negative values in the last~10 Myr,interpreted as a record of long-term fluctuations in methane emission.Six of these methane events occurred during the glacial sea-level lowstands in the last~1.1 Myr.We,therefore,infer that the trigger mechanism for these events might be the hydrate destabilization caused by sea level fall.The methane events that occurred at~2.11 and~5.93 Ma are more likely related to the sudden changes in sedimentation,either slide events or marked variations in sedimentation rate.展开更多
The characteristics of currents and tidal currents in the Andaman Sea（AS） are studied during the second half of2016 using observed data from a moored acoustic Doppler current profiler（ADCP） deployed at 8.6°N,...The characteristics of currents and tidal currents in the Andaman Sea（AS） are studied during the second half of2016 using observed data from a moored acoustic Doppler current profiler（ADCP） deployed at 8.6°N, 95.6°E.During the observation period, the mean flow is 5–10 cm/s and largely southward. The root mean square and kinetic energies of the low and high frequency flows, which are divided by a cutoff period of 5 d, are at the same level, indicating their identical importance to the total current. A power spectrum analysis shows that intraseasonal oscillations, a tidal-related semilunar month signal, a semidiurnal tidal signal and periods of 3–4 d are prominent. The barocliny of an eddy kinetic energy is stronger than the mean kinetic energy, both of which are the strongest on the bottom and the weakest at 70 m depth. Residual currents are largely southward（northward） during the summer（winter） monsoon season. Two striking peaks of the southward flow cause the 80 d period of meridional currents. The first peak is part of a large-scale circulation, which enters the AS through the northern channel and exits through the southern channel, and the second peak is part of a local vortex. The 40 d oscillation of the zonal current is forced by geostrophic variations attributed to local and equatorial remote forcing. The tidal current is dominated by semidiurnal constituents, and among these, M2 and N2 are the top two largest major axes. Moreover, astronomical tidal constituents MM and MSF are also significant. Diurnal constituents are weak and shallow water tides are ignorable. The aims are to introduce the new current data observed in the AS and to provide initial insights for the tidal and residual currents in the Andaman Sea.展开更多
The characteristics of the T/S structures,water mass exchange and deep circulation in the Andaman Sea are investigated based on the simulation from a high-resolution general circulation model(MITgcm).The results show ...The characteristics of the T/S structures,water mass exchange and deep circulation in the Andaman Sea are investigated based on the simulation from a high-resolution general circulation model(MITgcm).The results show that,below 1000 m,the water mass is saltier,warmer and more homogeneous in the Andaman Sea than that in the Bay of Bengal,attributing to the strong vertical mixing at the depth of^1800 m.The water mass exchange between the Andaman Sea and the Bay of Bengal goes through three major channels,which manifests itself as follows:the northern channel(Preparis Channel)is the main passage of water mass transport from the Bay of Bengal to the Andaman Sea,whereas the Middle Channel(the south of Andaman Islands and the north of Nicobar Islands)has an opposite transport;the southern channel(Great Channel)features with a four-layer water exchange which results in the least net transport among the three channels;all the transports through the three channels have an intra-annual variation with a period of half a year.At 1000-m depth,the entire Andaman Sea is occupied by a cyclonic circulation in January and July while by an anticyclonic one in April and October.The semiannual cycle found in both the deep circulation and water mass exchange is likely associated with the downwelling eastward-propagating Kelvin waves induced by the semiannual westerly component in the equatorial Indian Ocean during intermonsoon seasons.展开更多
Internal solitary waves(ISWs)are ubiquitous in the Andaman Sea,as revealed by synthetic aperture radar images;however,their generation mechanisms and corresponding influencing factors remain unknown.Based on a nonhydr...Internal solitary waves(ISWs)are ubiquitous in the Andaman Sea,as revealed by synthetic aperture radar images;however,their generation mechanisms and corresponding influencing factors remain unknown.Based on a nonhydrostatic two-dimensional model,the generation of ISW packets along the transect of a channel lying between Batti Malv Island and Car Nicobar Island is investigated.Moreover,the influences of topographic characteristics,seasonal stratifications,and tidal forcings are analyzed through a series of sensitivity runs.The simulation results indicate that bidirectional rank-ordered ISW packets are generated by the nonlinear steepening of internal tides.An east-west ISW asymmetry is observed,which is attributed to distinct topographic characteristics.The surrounding sills can also generate internal wave beams,which modulate the intensity of ISWs.However,the topographic structure of the west flank of the ridge mainly contributes to the suppression of westward ISWs,which decreases the modulating effect of internal wave beams.During the spring tide,the generation of ISWs is enhanced.During the neap tide,ISWs are weak,and the east-west ISW asymmetry is less obvious.Moreover,seasonal stratification only has a minor effect on the generation and evolution of ISWs.展开更多
Box jellyfish Chiropsoides buitendijki from the coastal zone along the Andaman Sea, southwestern Thailand are characterized by a box-shaped body with unilateral branched tentacles and lack of interradial furrows. Tent...Box jellyfish Chiropsoides buitendijki from the coastal zone along the Andaman Sea, southwestern Thailand are characterized by a box-shaped body with unilateral branched tentacles and lack of interradial furrows. Tentacular banding was first reported in the present study with 1-3-2-3-2-3-2-3-1 patterns （1-major band, 2-thicker minor band and 3-thinner minor band）. The DNA sequences of 18 S ribosomal RNA genes indicated that the specimen examined were genetically similar to C. buitendijki that was previously identified from the Nam Bor Bay, Phuket, Thailand, and distinct to the other known taxa in the order Chirodropida. In addition, a significant genetic divergence based on 16S mitochondrial gene was observed within the C. buitendijki samples. This indicates a population genetic differentiation but needs further confirmation.展开更多
The horizontally variable density stratification and background currents are taken into the variable-coefficent extended Korteweg-de Vries(evKdV)theory to obtain the geographical and seasonal distribution of kinematic...The horizontally variable density stratification and background currents are taken into the variable-coefficent extended Korteweg-de Vries(evKdV)theory to obtain the geographical and seasonal distribution of kinematic parameters of internal solitary waves in the Andaman Sea(AS).The kinematic parameters include phase speed,dispersion parameter,quadratic and cubic nonlinear parameters.It shows that the phase speed and dispersion parameter are mainly determined by the topographic feature and have limited seasonal variation.The maximum phase speed is 2.6 m/s,which occurs in the cool season(November)in the middle of the AS,while the phase speed in the cool season is slightly larger than those in other seasons,up to 11.4%larger than that in the rainy season(July)in the southern AS.The dispersion parameter in the cool season can be 22.3%larger than that in the hot season.The nonlinear parameters have significant seasonal variation,and they can even change their signs at the continental slope in the north of the AS,from season to season.Meanwhile,the algebraic solitons dominate in the AS with minimum amplitudes(aal)ranging from 0.1 m to 102 m,and the maximum aal occurs in the cool season in the southern AS.The effect of the background flow on the parameters is also studied.The background flow has a great influence on the nonlinear parameters,e.g.,the value of cubic nonlinear parameter can be reduced by 1/3 when the background flow is not considered.展开更多
A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Chann...A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Channel(TDC),and the Great Channel(GC),based on the daily averaged simulation results ranging from 2010 to 2019.Spectral analysis and Empirical Orthogonal Function(EOF)methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms.The results of model simulation indicate that the net average transports of the PC and GC,as well as their linear trend,are opposite to that of the TDC.This indicates that the PC and the GC are the main inflow channels of the AS,while the TDC is the main outflow channel of the AS.The transport variability is most pronounced at surface levels and between 100 m and 200 m depth,likely affected by monsoons and circulation.A 182.4-d semiannual variability is consistently seen in all three channels,which is also evident in their second principal components.Based on sea level anomalies and EOF analysis results,this is primarily due to equatorial winds during the monsoon transition period,causing eastward movement of Kelvin waves along the AS coast,thereby affecting the spatiotemporal characteristics of the flow in the AS.The first EOF of the PC flow field section shows a split at 100 m deep,likely due to topography.The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series.Meanwhile,the first EOF of the GC flow field section indicates a stable surface inflow,probably influenced by the equatorial Indian Ocean’s eastward current.展开更多
This paper describes investigations of the internal waves in the Andaman Sea using Moderate Resolution Imaging Spectroradiometer(MODIS)imagery over the period of June 2010 to May 2016.Results of the spatial and tempor...This paper describes investigations of the internal waves in the Andaman Sea using Moderate Resolution Imaging Spectroradiometer(MODIS)imagery over the period of June 2010 to May 2016.Results of the spatial and temporal distribution,generation sources and propagation characteristics of internal waves are presented.The statistical analysis shows that internal waves can be observed in almost the entire area of the Andaman Sea.Most internal waves are observed in the northern,central and southern regions of the Andaman Sea.A significant number of internal waves between 7°N and 9°N in the East Indian Ocean are also observed.Internal waves can be observed year-round in the Andaman Sea,while most of internal waves are observed between February and April,with a maximum frequency of 15.03%in March.The seasonal distribution of the internal waves shows that the internal waves have mostly been observed in the dry season(February to April),and fewer internal waves are observed in the rainy season(May to October).The double peak distribution for the occurrence frequency of internal waves is found.With respect to the lunar influence,more internal waves are observed after the spring tide,which implies the spring tide may play an important role in internal wave generation in the Andaman Sea.Generation sources of internal waves are explored based on the propagation characteristics of internal waves.The results indicate that six sources are located between the Andaman Islands and the Nicobar Islands,and one is located in the northern Andaman Sea.Four regions with active internal wave phenomenon in the Andaman Sea were presented during the MODIS survey,and the propagation speed of internal waves calculated based on the semidiurnal generation period is smaller than the results acquired from pairs of the images with short time intervals.展开更多
In this study, we assess coral health by detecting the severity of coral diseases and compromised health states on massive Porites. Field surveys are conducted at twenty-two sites covering the eastern, inner and weste...In this study, we assess coral health by detecting the severity of coral diseases and compromised health states on massive Porites. Field surveys are conducted at twenty-two sites covering the eastern, inner and western Gulf of Thailand as well as the Andaman Sea during 2010–2015. A total of nine coral diseases and signs of compromised health are observed in the waters of Thailand, consisting of pigmentation responses(pink lines, pink patches,pink spots and pink borers), white syndromes(white patches, white bands and ulcerative white spots), growth anomalies, and unusual bleaching patterns. The highest severity of all observed coral diseases and signs of compromised health are found at Ko Khang Khao in the inner Gulf of Thailand, while that observed in the Andaman Sea is relatively low. Composition of the diseases vary across the study sites. Four groups of study sites,in which there is an 80% similarity of diseases or signs of compromised health composition, are clustered and detected based on the Bray-Curtis similarity. The canonical analysis of principal coordinates reveal that most study sites in the Gulf of Thailand, especially the inner Gulf of Thailand, tend to show a high severity of the diseases. The association of disease severity and composition and the level of human impact are also detected.The study sites located near the shores and/or the areas with intensive tourism tend to have higher human impact, especially on poor water quality, which may be linked to the higher severity and composition of coral diseases and signs of compromised health in the Gulf of Thailand. Fish bites are also observed in many study sites.The severity of fish bites in the Gulf of Thailand is much lower compared to the Andaman Sea. Ko Rawi exhibits the highest severity, following by Ko Surin Nua and Ko Butang. The study sites within marine national park boundaries have a significantly higher severity of fish bites than those outside of the marine national park boundaries. This study suggests that higher coral diseases and signs of compromised health severity might be linked to anthropogenic disturbances on coral communities in the waters of Thailand.展开更多
The Facetotecta is among the lesser known groups in the world ocean. The present study recorded two types of Facetotecta in the Andaman Sea, off Andaman Islands. These two types of Facetotecta were observed during the...The Facetotecta is among the lesser known groups in the world ocean. The present study recorded two types of Facetotecta in the Andaman Sea, off Andaman Islands. These two types of Facetotecta were observed during the period of August 2015, July 2016 and October 2017 and identified as Type I Hansenocaris corvinae and Type IX Hansenocaris leucadea. However, the cursory analysis suggested that the Type IX is a new type of Facetotecta and named it as Type XII Hansenocaris portblairenae sp. (nov). This finding suggests that this Facetotecta observation is the first report in the Andaman Sea, as well as in the Indian Ocean Region.展开更多
Numerous internal solitary waves(ISWs)have been observed in the southern Andaman Sea.In this study,the twodimensional Massachusetts Institute of Technology general circulation model is applied to investigate the dynam...Numerous internal solitary waves(ISWs)have been observed in the southern Andaman Sea.In this study,the twodimensional Massachusetts Institute of Technology general circulation model is applied to investigate the dynamics of ISWs and explore the effects of the bottom topography and tidal forcing on the generation and propagation of ISWs in the southern Andaman Sea.The results show that the large-amplitude depression ISWs are mainly generated via the oscillating tidal flow over the sill of the Great Channel,and the generation of ISWs is subject to the lee wave regime.The Dreadnought Bank cannot generate ISWs itself;however,it can enhance the amplitudes of eastward-propagating ISWs generated from sill A,owing to constructive interference of internal tide generation between the sill of the Great Channel and the Dreadnought Bank.The eastward-propagating ISWs generated by the eastern shallow sill near the continental shelf can propagate to the shelf,where they evolve into elevation waves because of the shallow water.Sensitivity runs show that both the semidiurnal and diurnal tides over the sill of the Great Channel can generate ISWs in this area.However,the ISWs generated by diurnal tides are much weaker than those generated by semidiurnal tides.Mixed tidal forcing has no significant effect on the generation of ISWs.展开更多
Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （...Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （ANSR） are analyzed to investigate the hydrographic responses to the topography in this region. The results show that the topography of ANSR can induce internal waves around the submarine ridge that have a maximum current velocity of 1 m s 1 The spatial struc- ture of the turbulent kinetic energy （TKE） and shear in this region during 2010 is investigated using the high-resolution Princeton Ocean Model （POM） forced by the satellite-based Advanced Scatterometer （ASCAT） winds including the tide, The results show that the model successfully simulates the internal waves around the ANSR. Numerical experiments further indicate that both the topography and tide play an important role in the gen- eration of the internal waves in this region.展开更多
Andaman and Nicobar Islands, the gastropod diversity is high, due to the majority of shores are rocky. The wet rocky shore promotes algal growth, which is ultimate for feeding ground for gastropod growth and developme...Andaman and Nicobar Islands, the gastropod diversity is high, due to the majority of shores are rocky. The wet rocky shore promotes algal growth, which is ultimate for feeding ground for gastropod growth and development leading to more diversity. The global warming, anthropogenic activities, industrial and domestic pollution, etc., have accelerated the loss of coastal and marine biodiversity components over the last few decades which has been of great concern. However, except global warming, the other factors were of least concern with reference to Andaman and Nicobar Islands biodiversity due to a pristine environment. Therefore, exploration of biodiversity in these islands is essential to create a baseline data for record and future research. Four locations of south to north Andaman Islands which represented Carbyns Cove from south Andaman, Rangat and Mayabunder from the Middle Andaman and Diglipur from the North Andaman were selected for this study. Gastropoda species were collected for a period of one year in three prevailing seasons of Andaman and Nicobar Islands. They are South West Monsoon (SW monsoon), North East Monsoon (NE Monsoon) and Non Rainy Seasons (NR Seasons). The present study of gastropods distribution in the South, Middle and North Andaman groups of Islands suggested that there are 71 species belonging to 52 genus and 33 families. At any one of the time and any one of the locations, only one occurrence was noticed for 38 species and remaining 33 species were overlapping with respect to stations and seasons. Evaluation of the cluster suggested that Cluster A (NR season in Carbyns Cove) and Cluster B (NE and SW Monsoon in Mayabunder) as a separate entity among the 12 combinations of stations and seasons due to their species representation. It was also concluded that out of 71 studied species, 3 species were not reported till date in these Island environment and 2 species from any other parts of India.展开更多
基金Supported by the National Key Research and Development Program of China(No.2017YFC1405102)the National Natural Science Foundation of China(No.42006164)+1 种基金the Global Change and Air-Sea Interaction Program of China(No.GASI-02-IND-YGST2-04)the Chinese Association of Ocean Mineral Resources R&D(No.DY135-E2-4)。
文摘The Andaman Sea has been a classic study region for internal solitary waves(ISWs)for several decades,and extraordinarily large ISWs are characteristic of the Andaman Sea in the Indian Ocean.This paper presents results on the estimation of the propagation velocity of ISWs in the Andaman Sea that were tracked using 195 image pairs acquired by MODIS National Aeronautics and Space Administration(NASA)Terra/Aqua satellites between January 2014 and December 2018.A total of 562 ISWs were identified during the period,and the results of the propagation velocity distribution of ISWs in the Andaman Sea are presented.The estimated propagation velocity of ISWs agrees well with the theoretical results derived from the Korteweg-de Vries(KdV)equation using monthly climatology stratification data and local bathymetry.The ISW propagation velocity decreases as they propagate from deep to shallow water;the maximum propagation velocity of 3.27 m/s was estimated on the western side of the Nicobar Islands and minimum speed of 0.54 m/s occurred in the shallow water region of the southeastern Andaman Sea.The results show that the ISW propagation characteristics differ in the northern,central,and southern regions of the Andaman Sea.In the northern Andaman Sea,the velocity of ISWs propagating westward was greater than that of ISWs propagating eastward at the same water depth.In the central Andaman Sea,the propagation velocity of the ISWs differed over a small area at a depth of 2500 m,and the velocity of ISWs in the deep mixing layer in winter was higher than that in the shallow mixing layer in spring.Monthly variations in ISW propagation velocity were analyzed in the southern Andaman Sea,and the velocity of ISWs differed greatly in shallow water and was not significantly different in deep water.Water depth and monthly stratification play vital roles in controlling the phase speed of ISWs in the Andaman Sea.This study will provide a basis for the propagation and prediction of ISWs in the Andaman Sea.
基金supported by the National Key R&D Program of China(No.2018YFC031000404)the National Natural Science Foundation of China(No.42276068)State Key Laboratory of Marine Geology,Tongji University(No.MGK202206)。
文摘Stable isotopes of carbon and oxygen variations in foraminiferal shells have been widely used in paleo-environment studies.However,studies about the shells of benthic foraminifera in methanehydrate-bearing sediments as reliable geochemical proxies to reconstruct the potential methane release events in the geologic past are rare.In this study,we present the stable carbon and oxygen isotopes of fossil benthic foraminifera including one epifaunal species(Cibicidoides wuellerstorfi)and two infaunal species(Bulimina mexicana and Uvigerina peregrina)from the Site U1447 of IODP 353 Expedition to trace methane events in the Andaman Sea,where one of the thickest and deepest gas hydrate stability zones was discovered.Theδ^(13)C values of benthic foraminifera show that there are eight distinct intervals with negative values in the last~10 Myr,interpreted as a record of long-term fluctuations in methane emission.Six of these methane events occurred during the glacial sea-level lowstands in the last~1.1 Myr.We,therefore,infer that the trigger mechanism for these events might be the hydrate destabilization caused by sea level fall.The methane events that occurred at~2.11 and~5.93 Ma are more likely related to the sudden changes in sedimentation,either slide events or marked variations in sedimentation rate.
基金The National Key Research and Development Program of China under contract No.2017YFC1405100the National Natural Science Foundation of China under contract No.41406034the Basic Scientific Research Fund for National Public Institutes of China under contract No.GY0215P05
文摘The characteristics of currents and tidal currents in the Andaman Sea（AS） are studied during the second half of2016 using observed data from a moored acoustic Doppler current profiler（ADCP） deployed at 8.6°N, 95.6°E.During the observation period, the mean flow is 5–10 cm/s and largely southward. The root mean square and kinetic energies of the low and high frequency flows, which are divided by a cutoff period of 5 d, are at the same level, indicating their identical importance to the total current. A power spectrum analysis shows that intraseasonal oscillations, a tidal-related semilunar month signal, a semidiurnal tidal signal and periods of 3–4 d are prominent. The barocliny of an eddy kinetic energy is stronger than the mean kinetic energy, both of which are the strongest on the bottom and the weakest at 70 m depth. Residual currents are largely southward（northward） during the summer（winter） monsoon season. Two striking peaks of the southward flow cause the 80 d period of meridional currents. The first peak is part of a large-scale circulation, which enters the AS through the northern channel and exits through the southern channel, and the second peak is part of a local vortex. The 40 d oscillation of the zonal current is forced by geostrophic variations attributed to local and equatorial remote forcing. The tidal current is dominated by semidiurnal constituents, and among these, M2 and N2 are the top two largest major axes. Moreover, astronomical tidal constituents MM and MSF are also significant. Diurnal constituents are weak and shallow water tides are ignorable. The aims are to introduce the new current data observed in the AS and to provide initial insights for the tidal and residual currents in the Andaman Sea.
基金The National Natural Science Foundation of China under contract Nos 41931182,41521005 and 41676016Guangdong Key Project under contract No.2019BT2H594+2 种基金the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract Nos GML2019ZD0303 and GML2019ZD0304the Chinese Academy of Sciences under contract Nos ZDRW-XH-2019-2 and ISEE2018PY05the Independent Research Project Program of State Key Laboratory of Tropical Oceanography under contract Nos LTOZZ1902 and LTOZZ1802。
文摘The characteristics of the T/S structures,water mass exchange and deep circulation in the Andaman Sea are investigated based on the simulation from a high-resolution general circulation model(MITgcm).The results show that,below 1000 m,the water mass is saltier,warmer and more homogeneous in the Andaman Sea than that in the Bay of Bengal,attributing to the strong vertical mixing at the depth of^1800 m.The water mass exchange between the Andaman Sea and the Bay of Bengal goes through three major channels,which manifests itself as follows:the northern channel(Preparis Channel)is the main passage of water mass transport from the Bay of Bengal to the Andaman Sea,whereas the Middle Channel(the south of Andaman Islands and the north of Nicobar Islands)has an opposite transport;the southern channel(Great Channel)features with a four-layer water exchange which results in the least net transport among the three channels;all the transports through the three channels have an intra-annual variation with a period of half a year.At 1000-m depth,the entire Andaman Sea is occupied by a cyclonic circulation in January and July while by an anticyclonic one in April and October.The semiannual cycle found in both the deep circulation and water mass exchange is likely associated with the downwelling eastward-propagating Kelvin waves induced by the semiannual westerly component in the equatorial Indian Ocean during intermonsoon seasons.
基金This work was supported by the National Natural Science Foundation of China(No.41876012)the National Basic Research Program of China(973 Program)(No.2017YFC1405605)the Fundamental Research Funds for the Central Universities(No.202061001).
文摘Internal solitary waves(ISWs)are ubiquitous in the Andaman Sea,as revealed by synthetic aperture radar images;however,their generation mechanisms and corresponding influencing factors remain unknown.Based on a nonhydrostatic two-dimensional model,the generation of ISW packets along the transect of a channel lying between Batti Malv Island and Car Nicobar Island is investigated.Moreover,the influences of topographic characteristics,seasonal stratifications,and tidal forcings are analyzed through a series of sensitivity runs.The simulation results indicate that bidirectional rank-ordered ISW packets are generated by the nonlinear steepening of internal tides.An east-west ISW asymmetry is observed,which is attributed to distinct topographic characteristics.The surrounding sills can also generate internal wave beams,which modulate the intensity of ISWs.However,the topographic structure of the west flank of the ridge mainly contributes to the suppression of westward ISWs,which decreases the modulating effect of internal wave beams.During the spring tide,the generation of ISWs is enhanced.During the neap tide,ISWs are weak,and the east-west ISW asymmetry is less obvious.Moreover,seasonal stratification only has a minor effect on the generation and evolution of ISWs.
基金China-ASEAN Maritime Cooperation Fundthe Tropical Marine Ecosystem Collaborative Study(TiME)of the Thailand-China Joint Laboratory for Climate and Marine Ecosystem+2 种基金the Public Science and Technology Research Funds Projects of Ocean under contract No.201505004the fund from Phuket Marine Biological Centerthe Miscellaneous Contribution No.60 from Phuket Marine Biological Center
文摘Box jellyfish Chiropsoides buitendijki from the coastal zone along the Andaman Sea, southwestern Thailand are characterized by a box-shaped body with unilateral branched tentacles and lack of interradial furrows. Tentacular banding was first reported in the present study with 1-3-2-3-2-3-2-3-1 patterns （1-major band, 2-thicker minor band and 3-thinner minor band）. The DNA sequences of 18 S ribosomal RNA genes indicated that the specimen examined were genetically similar to C. buitendijki that was previously identified from the Nam Bor Bay, Phuket, Thailand, and distinct to the other known taxa in the order Chirodropida. In addition, a significant genetic divergence based on 16S mitochondrial gene was observed within the C. buitendijki samples. This indicates a population genetic differentiation but needs further confirmation.
基金The Key Research Program of Frontier SciencesChinese Academy of Sciences under contract No.QYZDJ-SSWDQC034+9 种基金the Grant from Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0304the National Natural Science Foundation of China under contract Nos 41521005,41776007 and 41776008the Guangdong Natural Science Foundation under contract No.2020A1515010495the Grant from Chinese Academy of Sciences under contract No.ISEE2021PY01the Guangzhou Science and Technology Program under contract No.201804010373the Youth Science and Technology Innovation Talent of Guangdong Te Zhi Plan under contract No.2019TQ05H519the Pearl River S&T Nova Program of Guangzhou under contract No.201806010091the Rising Star Foundation of South China Sea Institute of Oceanology under contract No.NHXX2019WL0201the Youth Innovation Promotion Association of Chinese Academy of Sciences under contract No.2018378the State Key Laboratory of Tropical Oceanolography Independent Research Program under contract No.LTOZZ2001。
文摘The horizontally variable density stratification and background currents are taken into the variable-coefficent extended Korteweg-de Vries(evKdV)theory to obtain the geographical and seasonal distribution of kinematic parameters of internal solitary waves in the Andaman Sea(AS).The kinematic parameters include phase speed,dispersion parameter,quadratic and cubic nonlinear parameters.It shows that the phase speed and dispersion parameter are mainly determined by the topographic feature and have limited seasonal variation.The maximum phase speed is 2.6 m/s,which occurs in the cool season(November)in the middle of the AS,while the phase speed in the cool season is slightly larger than those in other seasons,up to 11.4%larger than that in the rainy season(July)in the southern AS.The dispersion parameter in the cool season can be 22.3%larger than that in the hot season.The nonlinear parameters have significant seasonal variation,and they can even change their signs at the continental slope in the north of the AS,from season to season.Meanwhile,the algebraic solitons dominate in the AS with minimum amplitudes(aal)ranging from 0.1 m to 102 m,and the maximum aal occurs in the cool season in the southern AS.The effect of the background flow on the parameters is also studied.The background flow has a great influence on the nonlinear parameters,e.g.,the value of cubic nonlinear parameter can be reduced by 1/3 when the background flow is not considered.
基金The Joint Advanced Marine and Ecological Studies(JAMES)in the Bay of Bengal and eastern equatorial Indian Ocean supported by the Global Change and Air-Sea InteractionⅡProgram under contract Nos GASI-01-EIND-STwin and GASI-04-WLHY-03Zhejiang Provincial Ten Thousand Talents Plan under contract No.2020R52038.
文摘A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Channel(TDC),and the Great Channel(GC),based on the daily averaged simulation results ranging from 2010 to 2019.Spectral analysis and Empirical Orthogonal Function(EOF)methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms.The results of model simulation indicate that the net average transports of the PC and GC,as well as their linear trend,are opposite to that of the TDC.This indicates that the PC and the GC are the main inflow channels of the AS,while the TDC is the main outflow channel of the AS.The transport variability is most pronounced at surface levels and between 100 m and 200 m depth,likely affected by monsoons and circulation.A 182.4-d semiannual variability is consistently seen in all three channels,which is also evident in their second principal components.Based on sea level anomalies and EOF analysis results,this is primarily due to equatorial winds during the monsoon transition period,causing eastward movement of Kelvin waves along the AS coast,thereby affecting the spatiotemporal characteristics of the flow in the AS.The first EOF of the PC flow field section shows a split at 100 m deep,likely due to topography.The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series.Meanwhile,the first EOF of the GC flow field section indicates a stable surface inflow,probably influenced by the equatorial Indian Ocean’s eastward current.
基金The National Key Research and Development Program of China under contract No.2017YFC1405102the National Natural Science Foundation of China under contract No.61471136the Global Change and Air-Sea Interaction Program of China under contract No.GASI-02-IND-YGST2-04
文摘This paper describes investigations of the internal waves in the Andaman Sea using Moderate Resolution Imaging Spectroradiometer(MODIS)imagery over the period of June 2010 to May 2016.Results of the spatial and temporal distribution,generation sources and propagation characteristics of internal waves are presented.The statistical analysis shows that internal waves can be observed in almost the entire area of the Andaman Sea.Most internal waves are observed in the northern,central and southern regions of the Andaman Sea.A significant number of internal waves between 7°N and 9°N in the East Indian Ocean are also observed.Internal waves can be observed year-round in the Andaman Sea,while most of internal waves are observed between February and April,with a maximum frequency of 15.03%in March.The seasonal distribution of the internal waves shows that the internal waves have mostly been observed in the dry season(February to April),and fewer internal waves are observed in the rainy season(May to October).The double peak distribution for the occurrence frequency of internal waves is found.With respect to the lunar influence,more internal waves are observed after the spring tide,which implies the spring tide may play an important role in internal wave generation in the Andaman Sea.Generation sources of internal waves are explored based on the propagation characteristics of internal waves.The results indicate that six sources are located between the Andaman Islands and the Nicobar Islands,and one is located in the northern Andaman Sea.Four regions with active internal wave phenomenon in the Andaman Sea were presented during the MODIS survey,and the propagation speed of internal waves calculated based on the semidiurnal generation period is smaller than the results acquired from pairs of the images with short time intervals.
基金The budget for research promotion from the Government of Thailand to Ramkhamhaeng University
文摘In this study, we assess coral health by detecting the severity of coral diseases and compromised health states on massive Porites. Field surveys are conducted at twenty-two sites covering the eastern, inner and western Gulf of Thailand as well as the Andaman Sea during 2010–2015. A total of nine coral diseases and signs of compromised health are observed in the waters of Thailand, consisting of pigmentation responses(pink lines, pink patches,pink spots and pink borers), white syndromes(white patches, white bands and ulcerative white spots), growth anomalies, and unusual bleaching patterns. The highest severity of all observed coral diseases and signs of compromised health are found at Ko Khang Khao in the inner Gulf of Thailand, while that observed in the Andaman Sea is relatively low. Composition of the diseases vary across the study sites. Four groups of study sites,in which there is an 80% similarity of diseases or signs of compromised health composition, are clustered and detected based on the Bray-Curtis similarity. The canonical analysis of principal coordinates reveal that most study sites in the Gulf of Thailand, especially the inner Gulf of Thailand, tend to show a high severity of the diseases. The association of disease severity and composition and the level of human impact are also detected.The study sites located near the shores and/or the areas with intensive tourism tend to have higher human impact, especially on poor water quality, which may be linked to the higher severity and composition of coral diseases and signs of compromised health in the Gulf of Thailand. Fish bites are also observed in many study sites.The severity of fish bites in the Gulf of Thailand is much lower compared to the Andaman Sea. Ko Rawi exhibits the highest severity, following by Ko Surin Nua and Ko Butang. The study sites within marine national park boundaries have a significantly higher severity of fish bites than those outside of the marine national park boundaries. This study suggests that higher coral diseases and signs of compromised health severity might be linked to anthropogenic disturbances on coral communities in the waters of Thailand.
文摘The Facetotecta is among the lesser known groups in the world ocean. The present study recorded two types of Facetotecta in the Andaman Sea, off Andaman Islands. These two types of Facetotecta were observed during the period of August 2015, July 2016 and October 2017 and identified as Type I Hansenocaris corvinae and Type IX Hansenocaris leucadea. However, the cursory analysis suggested that the Type IX is a new type of Facetotecta and named it as Type XII Hansenocaris portblairenae sp. (nov). This finding suggests that this Facetotecta observation is the first report in the Andaman Sea, as well as in the Indian Ocean Region.
基金supported by the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDJ-SSW-DQC034)the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(Grant No.GML2019ZD0304)+8 种基金the National Natural Science Foundation of China(Nos.41521005,41776007 and 41776008)the Chinese Academy of Sciences(Grant No.ISEE2021-PY01)the Guangzhou Science and Technology Program(Grant No.201804010373)the Guangdong Natural Science Foundation(Grant No.2020A1514010495)the Youth Science and Technology Innovation Talent of Guangdong TeZhi Plan(Grant No.2019TQ05H519)the Pearl River S&T Nova Program of Guangzhou(Grant No.201806010091)the Youth Innovation Promotion Association of CAS(Grant No.2018378)the LTO Independent Research Program(Grant No.LTOZZ2001)the Rising Star Foundation of SCSIO(Grant No.NHXX2019WL0201).
文摘Numerous internal solitary waves(ISWs)have been observed in the southern Andaman Sea.In this study,the twodimensional Massachusetts Institute of Technology general circulation model is applied to investigate the dynamics of ISWs and explore the effects of the bottom topography and tidal forcing on the generation and propagation of ISWs in the southern Andaman Sea.The results show that the large-amplitude depression ISWs are mainly generated via the oscillating tidal flow over the sill of the Great Channel,and the generation of ISWs is subject to the lee wave regime.The Dreadnought Bank cannot generate ISWs itself;however,it can enhance the amplitudes of eastward-propagating ISWs generated from sill A,owing to constructive interference of internal tide generation between the sill of the Great Channel and the Dreadnought Bank.The eastward-propagating ISWs generated by the eastern shallow sill near the continental shelf can propagate to the shelf,where they evolve into elevation waves because of the shallow water.Sensitivity runs show that both the semidiurnal and diurnal tides over the sill of the Great Channel can generate ISWs in this area.However,the ISWs generated by diurnal tides are much weaker than those generated by semidiurnal tides.Mixed tidal forcing has no significant effect on the generation of ISWs.
基金supported by the Ministry of Science and Technology of the People's Republic of China(MOST)(Grant No.2011CB403504)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant Nos. KZCX2-EW-208 and KZCX2-YW-Q11-02)+1 种基金the National Natural Science Foundation of China(Grant No.41076009)100 Talent Program of the Chinese Academy of Sciences
文摘Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （ANSR） are analyzed to investigate the hydrographic responses to the topography in this region. The results show that the topography of ANSR can induce internal waves around the submarine ridge that have a maximum current velocity of 1 m s 1 The spatial struc- ture of the turbulent kinetic energy （TKE） and shear in this region during 2010 is investigated using the high-resolution Princeton Ocean Model （POM） forced by the satellite-based Advanced Scatterometer （ASCAT） winds including the tide, The results show that the model successfully simulates the internal waves around the ANSR. Numerical experiments further indicate that both the topography and tide play an important role in the gen- eration of the internal waves in this region.
文摘Andaman and Nicobar Islands, the gastropod diversity is high, due to the majority of shores are rocky. The wet rocky shore promotes algal growth, which is ultimate for feeding ground for gastropod growth and development leading to more diversity. The global warming, anthropogenic activities, industrial and domestic pollution, etc., have accelerated the loss of coastal and marine biodiversity components over the last few decades which has been of great concern. However, except global warming, the other factors were of least concern with reference to Andaman and Nicobar Islands biodiversity due to a pristine environment. Therefore, exploration of biodiversity in these islands is essential to create a baseline data for record and future research. Four locations of south to north Andaman Islands which represented Carbyns Cove from south Andaman, Rangat and Mayabunder from the Middle Andaman and Diglipur from the North Andaman were selected for this study. Gastropoda species were collected for a period of one year in three prevailing seasons of Andaman and Nicobar Islands. They are South West Monsoon (SW monsoon), North East Monsoon (NE Monsoon) and Non Rainy Seasons (NR Seasons). The present study of gastropods distribution in the South, Middle and North Andaman groups of Islands suggested that there are 71 species belonging to 52 genus and 33 families. At any one of the time and any one of the locations, only one occurrence was noticed for 38 species and remaining 33 species were overlapping with respect to stations and seasons. Evaluation of the cluster suggested that Cluster A (NR season in Carbyns Cove) and Cluster B (NE and SW Monsoon in Mayabunder) as a separate entity among the 12 combinations of stations and seasons due to their species representation. It was also concluded that out of 71 studied species, 3 species were not reported till date in these Island environment and 2 species from any other parts of India.
