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    Review on the Study of Formation Mechanism of Coral Reefs
    ZHAO Huanting,WANG Lirong
    TROPICAL GEOGRAPHY    2016, 36 (1): 1-9.   DOI: 10.13284/j.cnki.rddl.002789
    Abstract2873)      PDF (5818KB)(1596)      
    Coral reefs have been formed through accumulation of debris of scleractinian corals and associated organism in shallow water of the tropic ocean, most of which are distributed in both sides of equator of the Pacific, the Indian Ocean and the Atlantic. The study of the formation mechanism of coral reefs is very important to understand the tectonic movement of the earth and marine dynamics. Darwin firstly gave the theory of coral reefs’ formation mechanism about 200 years ago, since then many theories have been proposed, which can be classified into 2 groups according to the relationship between the formation of coral reefs and change of sea level. The theories which are related to the change of the seal level include: Darwin’s subsidence hypothesis, Penck and Daly’s glacial-control theory, Kuenen’s glacially controlled subsidence theory, Dietz and Hess’s spreading and subsidence theory, and Morgan’s hotspot subsidence theory. And the other theories which have nothing with sea level change include: Murray’s Sea floor uplift theory, Hoffmeister and Ladd’s antecedent-platform theory, and Yabe and Asano’s Karstic saucer theory. In the past decades, the studies on the revolution of coral reefs in the Pacific, the Indian Ocean and the Atlantic showed the factors which affected the structure and morphology of the coral reefs and how the reefs developed in the extreme events. The studies on formation mechanism of the coral reefs in China were started from about 50 years ago. The records of deep drilling in South China Sea shows that the corals reefs in China may form in accord with Subsidence theory and glacial subsidence theory, that is, the development and formation of coral reefs in South China Sea are in the slow subsidence of crust for a long time and controlled by the Quaternary glacial and inter glacial epoch. The formation of the coral reefs is so complicated and one theory could not be used to explain all coral reefs. With the development of the new way for field investigation and the application of new laboratory techniques, more data can be obtained and suitable formation model for specific reefs can be reached.
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    Terrace Topography of the Ganquan Plateau in the Xisha Area of the South China Sea
    ZHANG Jiangyong,HUANG Wenxing,LIU Shengxuan,JIANG Dapeng
    TROPICAL GEOGRAPHY    2016, 36 (1): 10-18.   DOI: 10.13284/j.cnki.rddl.002810
    Abstract3401)      PDF (2835KB)(832)      

    Topography of the Ganquan Plateau in the Xisha area of the South China Sea was studied using multibeam bathymetric data. The top of the Ganquan Plateau was flat with slopes generally less than 1°, but the topography was a three-level terrace tilting toward the southwest with water depth ranging from 550–700 m. At water depth of 600–850 m, submarine terraces commonly developed with up to 5 levels recognized, and the terraces in the west were more developed than those in the east of the Ganquan Plateau. It is preliminarily believed that the top and peripheral terrace topography of the Ganquan Plateau was a result of the combined effects of the global sea level change at the time scale of glacial-interglacial cycle and the crust subsidence of the South China Sea. These two influencing factors might control the development of the other coral reefs in the South China Sea as well. Talus topography developed at the periphery of the Ganquan Plateau at water depth between 850 and 1 300 m, which is speculated to result from deposits of coral fragments transported from the top of reefs. The more developed talus topography in the northwest compared to that in the southeast might be directly related to the southwest tilt of the top of the Ganquan Plateau.

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    Review on the Coralline Algae Functions in the Development Process of Coral Reefs
    LI Yinqiang,YU Kefu,WANG Yinghui,WANG Rui
    TROPICAL GEOGRAPHY    2016, 36 (1): 19-26.   DOI: 10.13284/j.cnki.rddl.002805
    Abstract3224)      PDF (9894KB)(2004)      

    Coralline algae are common in calcified red algal groups and an essential component of coral reefs. In addition, they play an important role in the process of coral reef development: 1) Coralline algae provide calcium for building the reef body; 2) coralline algae have strong binding and gluing ability to glue the broken biological fragments together and build coral reefs that can withstand strong winds; 3) coralline algae’s hard calcareous surfaces provide rigid basements for coral larvae to attach and grow; 4) coralline algae promote energy flow in coral reef ecosystems through photosynthesis; 5) coralline algae’s high primary productivity helps to maintain the efficiency of material cycle in coral reef ecosystems. Current research on coralline algae is focused on coralline algae’s responses to environmental stresses such as global warming and ocean acidification, and on the relations between the community structure, species diversity and spatial and temporal variations of coralline algae and environment changes. Further studies will be conducive to reveal the multiple functions of coralline algae in coral reef ecosystems.

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    Sea Surface Temperature Variations during the Last 100 Years Recorded in a Porites Coral from the Mischief Reef of Sansha City
    LIN Ziyun,YU Kefu,SHI Qi,CHEN Tianran,TAO Shichen
    TROPICAL GEOGRAPHY    2016, 36 (1): 27-33.   DOI: 10.13284/j.cnki.rddl.002804
    Abstract2152)      PDF (3017KB)(915)      
    Sea surface temperature (SST) variation over the last 100 years was reconstructed with high-resolution Sr/Ca of a Porites coral from the Mischief Reef, Sansha City. The results showed that the annual average SST from 1906 to 2007 AD was 28.4°C with the maximum of 29.2°C in 1998 AD and the minimum of 27.6°C in 1917 AD. The SST of the Nansha Islands increased by 0.025°C/10 a during this period, similar to that of the Xisha Islands. The SST series displayed a significant decadal oscillation with a period of 33 years, suggesting a possible linkage between the SST and the Pacific Decadal Oscillation. In addition, in the years when ENSO occurred, the SST was high, indicating the influence of ENSO in this area. In this paper, a Sr/Ca-SST relation was first established for the Mischief Reef and then the high-resolution SST record was extended to more than 100 years in this area. The SST variations were characterized and related mechanisms were explored.
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    The Negative Correlation between SST of the Northern South China Sea and the Strength of EASM on Inter-Annual and Inter-Decadal Time Scale
    ZHANG Huiling,YU Kefu,SHI Qi,YAN Hongqiang,CHEN Tegu
    TROPICAL GEOGRAPHY    2016, 36 (1): 34-40.   DOI: 10.13284/j.cnki.rddl.002797
    Abstract2224)      PDF (3185KB)(818)      
    Based on comparison of band-SST of Porites from Northern South China Sea and δ18O records from Wanxiang Cave, Gansu province and Dongge Cave, Guizhou province, this paper revealed the relationship between SST of the Northern South China Sea and strength of East Asian Summer Monsoon (EASM). On inter-annual and inter-decadal time scale, there is a negative correlation between SST of the Northern South China Sea and the strength of EASM. When SST rises, the value of stable oxygen isotope becomes heavier and the strength of EASM weakens, and vice versa. The comparison of instrument-measured SST and δ18O record from stalagmite WX42B, Wanxiang Cave verified the relationship. ENSO influences the rainfall of the monsoon region and controls the SST of the Northern South China Sea. ENSO may directly result in the negative correlation between SST of the Northern South China Sea and the strength of EASM. But the relationship between ENSO and rainfall of the monsoon region is complicated, the relationship between SST of the Northern South China Sea and local monsoon regions still needs further study.
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    Reef Water pH Variation and Its Implications for Ocean Acidification
    CHEN Xuefei,WEI Gangjian,DENG Wenfeng,ZOU Jieqiong
    TROPICAL GEOGRAPHY    2016, 36 (1): 41-47.   DOI: 10.13284/j.cnki.rddl.002803
    Abstract2594)      PDF (4747KB)(1327)      
    In the recent century, it is calculated that reef water pH has fallen by 0.2-0.3 pH units worldwide due to the increase of atmospheric CO2 concentration, threatening the life of coral reefs. However, the long-term variation of reef water pH revealed by δ11B in the calcareous skeletons of coral demonstrates eminent interannual and decadal periodicities, and the variation was a result of the combined influences of regional marine climate processes and biological activities in the reef ecosystem. Metabolism in reef waters controls the dynamics of carbonate system parameters and regulates the variations of water pH. Influenced by global climate and environmental changes and regional marine climate processes, biological activities in reef water exert effects on variations of seawater pH, resulting in differential responses to ocean acidification from coral reef water of different sea areas. Therefore, learning the effects of the biological activities of coral reefs on marine water pH at long-term time scales is very important for understanding the acidification mechanisms of coral reef waters, and it is also an important means to learn how the coral reef ecosystem responds to ocean acidification.
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    Cited: Baidu(1)
    Isotopes of Carbon, Nitrogen, Boron in Reef Coral as Proxies of Ocean Acidification
    HAN Tao,YU Kefu,TAO Shichen
    TROPICAL GEOGRAPHY    2016, 36 (1): 48-54.   DOI: 10.13284/j.cnki.rddl.002796
    Abstract2450)      PDF (747KB)(1062)      
    Ocean acidification, caused by the increasing atmospheric CO2 levels, has not only decreased seawater pH, but also changed the carbonate equilibrium so that the aragonite saturation state has decreased, which has lead to the decrease of calcification rates. Researches show that 13C, 11B and 15N of the coral skeleton have the capacity of recording Suess Effect, productivity, seawater pH and nutrient source. The main characteristics are: its 11B records seawater pH, 13C records sea water dissolved inorganic carbon (DIC) 13C and productivity, and 15N records terrestrial input. The combination of those proxies can indicate “the shelf carbon pumping” of the South China Sea and the coastal pollution effects on ocean acidification. However, researches on records of ocean acidification in coral reefs are insufficient, our understanding of ocean acidification, climate variability and global carbon, nitrogen cycle can be deepened by the application of such combination, which may be an important tool of revealing sea water pH change regularity.
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    Sustainable Development of the Coral Reefs in the South China Sea Islands
    ZHAO Huanting,WANG Lirong,YUAN Jiayi
    TROPICAL GEOGRAPHY    2016, 36 (1): 55-65.   DOI: 10.13284/j.cnki.rddl.002800
    Abstract3575)      PDF (3162KB)(1203)      
    Coral reefs are the most productive and diverse of all marine ecosystems. In recent years, coral reefs are in degradation under the threats of natural events and human activities, such as climate change, sea-level rising, ocean acidification, over-fishing, sedimentation, contamination and regional development. How to protect coral reefs so that they can produce ecosystem goods and services sustainably to meet the needs of today and future is focused on in recent years. Related concepts and approaches of sustainable development of coral reefs are introduced in this paper. The potential of sustainable development of and the pressure faced by the coral reefs in the South China Sea Islands are also analyzed. Finally, several sustainable development methods for the coral reefs in the South China Sea Islands are proposed, such as MPA, ICZM, and EBM.
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    Cited: Baidu(3)
    Ecological Situation of Coral Reefs in the Weizhou Island Based on Reef Check
    CHEN Gang,ZHAO Meixia,LIU Bin,ZHANG Chunhua,LIANG Qun
    TROPICAL GEOGRAPHY    2016, 36 (1): 66-71.   DOI: 10.13284/j.cnki.rddl.002807
    Abstract2491)      PDF (4173KB)(743)      

    In this article, Reef Check (coral reef health survey procedure) and factor analysis of coral reef ecosystem health index were used to evaluate the health status of the coral reefs at three sites (Zhuzheliao, Gongshan and Niubeikeng) of the Weizhou Island, Beihai, Guangxi Province from 2001 to 2012, focusing on fishes, invertebrates and reef substrates. The investigation results indicated that, during the nine years, coral reef ecological conditions showed big differences in different peripheral regions of the Weizhou Island. Although coral reef coverage was stable in Zhuzheliao and Niubeikeng, dominant population changed. But in Gongshan, coral death has occurred over a large area since 2002 and has not recovered up till now. Invertebrates were at extremely low levels, and fishes were also poor in both population quantity and diversity. This indicated that in this region, the coral reef ecosystem bore a heavy pressure from human activities.

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    Cited: Baidu(1)
    A Review on the Research of Coral Reefs in the Weizhou Island, Beibu Gulf
    WANG Wenhuan,YU Kefu,WANG Yinghui
    TROPICAL GEOGRAPHY    2016, 36 (1): 72-79.   DOI: 10.13284/j.cnki.rddl.002806
    Abstract2820)      PDF (2301KB)(903)      

    The coral reefs in the Weizhou Island (WZR) are located at the northern margin of the tropical zone, and have been developing on the volcanic rocks for at least 7000 years. This paper reviewed the related studies on the coral reefs and summarized the characteristics of WZR as follows: 1) The living coral covers of WZR have substantially declined over the past two decades. For example, the coral cover reduced by 51.6% in the north (2009–2010), by 42.42% in the southeast (1991–2010), and by 71.55% in the southwest (1991–2010); 2) the relatively high-latitude Weizhou Island is an ideal site for testing the refuge hypothesis that, under the background of global warming, corals are migrating from low-latitude areas to high-latitude areas; 3) as the basement rocks of WZR are volcanic rocks, this is an excellent case for testing Darwin’s atoll origin hypothesis; 4) the Weizhou Island is experiencing heavy anthropogenic activities, thus it is a natural laboratory to study the interactions between human and coral reefs and how this relatively high-latitude coral reef responds to the global warming, extreme climatic events and anthropogenic stresses. Therefore, as an important resource, the WZR are not only of vital ecological and environmental significance as other coral reefs, but also of unique scientific value and deserve close attention for effective protection.

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    Cited: Baidu(4)
    Review on Ecological Restoration Theories and Practices of Coral Reefs
    QIN Zhenjun,YU Kefu,WANG Yinghui
    TROPICAL GEOGRAPHY    2016, 36 (1): 80-86.   DOI: 10.13284/j.cnki.rddl.002809
    Abstract3031)      PDF (534KB)(1421)      

    Coral reefs are degraded rapidly by the global warming and large-scale human activities around the world, especially in the South China Sea (SCS). Coral reef restoration has caught the attentions of researchers and volunteers in recent years. Related theories and technologies are to be developed, but undoubtedly, the most important strategy is to protect the eco-environment of coral reefs to avoid further damage. For coral reef restoration, coral transplantation is a promising way. After corals are transplanted, the damaged tissues can be repaired in a few days, the immune system can be rebuilt, and the symbiont (zooxanthellae) community structure can be changed to enhance coral’s adaptation to the new environment. Gardening and captive breeding are effective ways to provide transplantation materials while artificial reefs are an important means to help establish coral development base. Creating and maintaining the growth environment for corals can help to raise the efficiency of ecological restoration. Spread and survival of coral larva can be promoted with the help of favorable water flow, chemical induction and microtopography. The environment-tolerant capacity and recovery potential of corals and they symbiotic zooxanthellae can be improved using molecular technologies. Coral restoration technologies including coral transplantation, gardening, artificial reefs, coral repair and captive coral breeding can be employed effectively in lots of areas.

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    Cited: Baidu(3)
    Research Progress in the Engineering Geological Characteristics of Coral Reefs
    YUAN Zheng,YU Kefu,WANG Yinghui,MENG Qingshan,WANG Ren
    TROPICAL GEOGRAPHY    2016, 36 (1): 87-93.   DOI: 10.13284/j.cnki.rddl.002808
    Abstract2571)      PDF (572KB)(1873)      
    Coral reefs are a special geological structure developed in the tropical marine environment. The structure consists of coral reef and other marine organism fragments. This review is focused on the significance of studying coral reef engineering, composition of coral reefs, the physico-mechanical properties of calcareous sands, pile foundation engineering in coral reefs, and coral concrete. Particle crushing is the most important property of calcareous sands and affects other mechanical properties directly; and in turn, it is mainly affected by confining pressure, effective stress, grain composition, initial void ratio, particle strength and particle shape. Pile foundation bearing capacity in calcareous sands is lower than that in common silica sands due to particle crushing and disturbance of calcareous sand structure by the pile-forming process. In coral concrete engineering, concrete made with sulfate-resistant cement has good strength and durability. Future research should be focused on the mechanisms and modeling of particle crushing, new types of coral reinforced concrete and pile foundation, disaster prevention and management and later maintenance of coral reef projects.
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    A Review of Recent Research on Cold-Water Coral Reefs
    ZHAO Meixia,YU Kefu.
    TROPICAL GEOGRAPHY    2016, 36 (1): 94-100.   DOI: 10.13284/j.cnki.rddl.002802
    Abstract2470)      PDF (1413KB)(1405)      
    Coral reefs are generally associated with shallow tropical seas; however, there are widespread and diverse coral ecosystems in deep waters on continental shelves, slopes, seamounts and ridges around the world. Cold-water corals have been known since the 18th century, but much fewer studies have been performed on deep-sea coral reefs compared with on tropical coral reefs. Along with the applications of modern submersibles and remotely operated vehicles (ROVs) to deep ocean exploration activities, more and more studies have been conducted and deep-sea coral reefs have become a research hotspot recently. This review includes: 1) the diversity and biogeographical distribution of cold-water corals; 2) the growth characteristics of corals and related environmental controls; 3) the initiation and development of deep-sea coral reefs; 4) the response of corals to ocean acidification; 5) corals as valuable archives for paleoceanographic reconstructions. It also highlights the future research directions of cold-water coral reefs in the South China Sea.
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    Cited: Baidu(2)
    Spatial Variability in Summer Phytoplankton Community from Offshore to Coastal Surface Waters of the Northwestern South China Sea
    LI Gang,NI Guangyan,SHEN Pingping,YI Rong,HUANG Liangmin,TAN Yehui
    TROPICAL GEOGRAPHY    2016, 36 (1): 101-107.   DOI: 10.13284/j.cnki.rddl.002811
    Abstract2263)      PDF (1095KB)(651)      
    Results are mainly presented about the spatial changes in phytoplankton chlorophyll a (chl a) concentration, community structure and picoplankton abundance (i.e. Synechococcus and pico- eucaryotes) from offshore to coastal surface waters of the South China Sea in the summer period of 2013. Total chl a concentration increased from 0.024 to 19.1 μg·L-1 from offshore to coastal waters. Coinciding well with chl a, the proportion of microplankton (>20 μm) increased from 6.0%-81%, while that of picoplankton (<3 μm) decreased from 85% to 5.1%; and the proportion of nanoplankton (3-20 μm) ranged during 9%-24% and showed no clear spatial change. There was a positive correlation of Synechococcus and pico-eucaryote abundances that increased towards the coastal waters from (2.58±0.21)×106 to (2.29±0.10)×108 cells·L-1 and from (1.62±0.91)×105 to (1.83±0.46)×107 cells·L-1, respectively. In addition, our results indicated that the spatial variability of total surface phytoplankton biomass was mainly regulated by picoplankton abundance in the surveyed waters.
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    Diversity of Ammonia-Oxidizing Archaea in the Surface Sediments of the Northern Continental Slope of the South China Sea
    LIU Guohui,WU Houbo
    TROPICAL GEOGRAPHY    2016, 36 (1): 108-113.   DOI: 10.13284/j.cnki.rddl.002801
    Abstract2501)      PDF (1902KB)(1390)      
    Surface sediment samples were taken from three sites of different water depths at the northern continental slope of the South China Sea to investigate the community structure of ammonia-oxidizing archaea (AOA). Polymerase chain reaction (PCR) was employed to amplify the archaeal ammonia monooxygenase α subunit (amoA) gene of AOA. Amplicons of the amoA gene sequences were used to understand the diversity and phylogenetic relationship of AOA. The main results were as follows: 1) All of the archaeal amoA gene sequences from the three locations were affiliated to Group I.1a Thaumarchaeota; 2) all of the archaeal amoA gene sequences from the three locations were phylogenetically closely related; and 3) the 16S rRNA gene and amoA gene phylogenetic trees were of congruent topology. Thaumarchaeota accounted for 40% of the total archaea, indicating that AOA might play an important role in the nitrogen biogeochemical cycling in the surface sediments of the northern continental slope of the South China Sea.
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    Rainfall Erosivity in the Lianjiang Watershed in Karst Areas of Northern Guangdong, China
    WANG Mingchong,ZHANG Xinchang,WANG Xizhi,WEI Xinghu,LI Huixia.
    TROPICAL GEOGRAPHY    2016, 36 (3): 495-502.   DOI: 10.13284/j.cnki.rddl.002832
    Abstract2025)      PDF (5744KB)(652)      
    One of the main ecological environment problems is soil erosion for the Lianjiang Watershed. Rainfall erosivity reflects potential ability of soil erosion caused by rainfall. Therefore it is of great significance for valuing consequences of regional soil loss caused by regional rainfall erosivity precisely and formulating measures to maintain soil and water. We arranged the data of daily precipitation from 1980 to 2013 at 35 meteorological stations along the Lianjiang river basin. Based on the data above, we got RA, RB and RC, which were calculated from daily precipitation, monthly precipitation and annually precipitation. We got the optimum R through the test of effective coefficient M accordingly. Next, we used the Inverse Distance Weighted (IDW), Spline with Tension and Ordinary Kniging for spatial interpolation and test to ensure the most accurate interpolation method, and then made interpolation analysis. The result showed that: the IDW and monthly precipitation was more suitable for the calculation and valuation of rainfall erosivity in the Lianjiang Watershed. The spatial-temporal variation of rainfall erosivity in the Lianjiang Watershed was evident. The spatial distribution of rainfall erosivity was similar to that of precipitation year-by-year. In the middle-upper reaches of the Lianjiang River, the average annual rainfall erosivity was found significantly higher in high and large mountain areas than in other places. There was more plentiful precipitation in the lower reaches of the Lianjiang River, and also the average annual rainfall erosivity in the areas was relatively high.
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    Holocene Fire History in Relation to Climate Changes and Human Activities in Southern Subtropical China
    MA Ting,ZHENG Zhuo,MAN Meiling,LI Jie,PENG Huanhuan,HAN Aiyan,HUANG Kuangyou.
    TROPICAL GEOGRAPHY    2016, 36 (3): 486-494.   DOI: 10.13284/j.cnki.rddl.002853
    Abstract2782)      PDF (3720KB)(803)      
    Three cores at different elevations were collected from different geographical locations in the mountainous regions of the South China. Micro-charcoal and pollen analyses were conducted to examine regional Holocene fire history and discuss its possible relationship with both Asian monsoon variability and anthropogenic activities. Results showed extremely low micro-charcoal concentrations at the three cores at the period between 8.0 and 3.5 ka B.P., revealing low fire frequency. Meanwhile, high proportions of arboreal pollen demonstrated expansion of subtropical evergreen broadleaf forest. This phase is consistent with the Holocene moisture optimum and abundant precipitation. Furthermore, low population in the early-mid Holocene and no evidence of slash-and-burn cultivation during the Neolithic confirm the charcoal result. After 3.5 ka B.P., the abrupt increase in charcoal concentrations of the cores from lower elevation sites was closely related with a general drying trend towards the late Holocene, which might result from EASM weakening and decreased rainfall. This timing coincided with the Shang-Zhou Bronze period, reflecting also the impact of human activity. The notable decrease of arboreal pollen demonstrates severe damage of forest by fires. After 2.0 ka B.P., the high concentrations of micro-charcoal recorded in the cores of GY1 and LTY, as well as the rapid growth of Poaceae, Dicranopteris and Pinus, demonstrate agriculture development in low-altitude plains and hills, and this period is synchronous with the first population booming and spread of cow plough and iron farm implements. Micro-charcoal and pollen records of core GT-2 at higher elevation (>1 600 m) show a high fire frequency after 0.8 ka B.P., and this period saw severe disturbance of broadleaved forest by the expansion of anthropogenic activities and agriculture development to mountainous regions.
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    Holocene Climate Records from a Mountain Wetland in Luoxiao Ranges
    HAN Aiyan,ZENG Lifeng,HUANG Kangyou,LIAO Wenbo,ZHENG Zhuo,CHEN Cong.
    TROPICAL GEOGRAPHY    2016, 36 (3): 477-485.   DOI: 10.13284/j.cnki.rddl.002855
    Abstract2674)      PDF (6839KB)(764)      
    A 150 cm core (JXA) was drilled from a mountain wetland in Jiangxi’ao, Jinggang Mountains in the southeast of mid-subtropical Luoxiao Ranges. Paleoenviromental proxies, such as loss-on-ignition (LOI), humification, organic carbon isotopic and grayscale were used to reconstruct the climatic evolution history in the study area. Based on 6 AMS 14C dating, the age of the sediment at the bottom of the core was ~11 cal. ka B.P.. The sedimentation process could be divided into four stages: 1) During the ages between 11 and 9.2 cal. ka B.P., the content of organic carbon was low and carbon isotopes were characteristic of C3 plants. The climate was relatively cool and dry; 2) in the period of 9.2–5.3 cal. ka B.P., the forest vegetation expanded according to carbon isotope, organic carbon and humification information. The peat land began to develop rapidly, and a warm and humid climate, which corresponded well to the Holocene optimum, was speculated; 3) at 5.3–2.2 cal. ka B.P., the carbon isotope curve showed changes in vegetation components between C3 and C4 plants. The climate was cool and dry; 4) during 2.2–0 cal. ka B.P., the monsoon activity tended to enhance, and the environment was possibly interfered by agricultural activities. The present study provides new paleoclimate evidence in subtropical regions, and indicated the Holocene optimum is between 9.2 and 5.3 cal. ka B.P.. The driving mechanism is mainly controlled by the insolation intensity in the northern hemisphere and summer monsoon variability.
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    Carbon Isotope Compositions and Climate Changes of the Past 20,000 Years Inferred from a Mountainous Peat Bog of Northern Guangxi
    MAN Meiling,ZHENG Zhuo,LI Jie,WANG Mengyuan.
    TROPICAL GEOGRAPHY    2016, 36 (3): 468-476.   DOI: 10.13284/j.cnki.rddl.002839
    Abstract2263)      PDF (1893KB)(973)      
    This study concerns the organic carbon isotopes, TOC and C/N in a mountainous peat bog in northern Guangxi province. Result reveals the local vegetation variations and the climate changes since the LGM in subtropical China. Positive δ13Corg indicates vegetation types change due to the cold and dry climate during the LGM. However, cold and dry condition didn’t lead to vegetation degradation from forest to grassland even during the last glacial period, as δ13Corg shows the dominance of C3 plants around the mountains, which is also proved by pollen records. It can be inferred from the lithology and TOC that local peat-land began to accumulate during the period of 14-10 cal. ka B.P., which developed at fastest speed between 10 and 9 cal. ka B.P. Carbon isotope change towards negative values occurred slightly earlier than the formation of the swamp, indicating that strengthening of summer monsoon occurred at about 14 cal. ka B.P., which is basically concordant with the record from stalagmites. Obvious variation in carbon isotopes which occurred between 9-8 cal. ka B.P. may be relative to 8.2 ka cooling event or changes of organic matter sources. High input of organic matter and negative carbon isotopes in the period during 7.0-2.8 cal. ka B.P. corresponded to the wet and warm condition. Relatively positive change of δ13Corg at 1.7 cal. ka B.P. might be caused by prehistory human impact. The comparison between the δ13Corg data and those of the coastal lowland records from the Leizhou Peninsula shows that a big difference existed between plain and mountainous areas, probably because humidity didn’t reduce too much due to the effect of orographic precipitation in the mountains even during the LGM, while decrease in precipitation and high evaporation were apparently shown in the plains. It should be pointed out that the factors are quite complicated for the interpretation of δ13Corg values in the peat records. The changes in sediment environment, origin of the organic matter and geomorphologic conditions should be taken into consideration when using δ13Corg to reconstruct paleoclimate.
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    Process of Calcitization of Aragonite Altering δ18O Records of Aragonite Stalagmites
    ZHANG Huiling,YU Kefu,ZHAO Jianxin,FENG Yuexing,LIN Yushi,ZHOU Wei,LIU Guohui.
    TROPICAL GEOGRAPHY    2016, 36 (3): 457-467.   DOI: 10.13284/j.cnki.rddl.002854
    Abstract2553)      PDF (3826KB)(684)      
    The aragonite stalagmite has been used to be a new paleoclimate archive recently, but the problem of how the aragonite to calcite transition affects δ18O of aragonite stalagmites is still a puzzling problem. A stalagmite LH5, which was recovered from the Lianhua Cave, Central China, has been identified by XRD analyzing that its aragonite has partially inverted into calcite in the lower part in which the content of calcite ranges during 10%-27.5%. On the basis of 18 TIMS-U series ages and 311 δ18O measures of stalagmite LH5, this paper studied effects of aragonite to calcite transition on the aragonite stalagmite paleoclimate record. At first, uranium loss of aragonite in the process of aragonite-calcite transition results in radiometric ages deviating from real ages to form reversal ages. Although there are phenomena of aragonite to calcite transition in lower part of stalagmite LH5, low openness of uranium decay system (less than 10%) can’t change TIMS ages greatly which still can be used to set up time scale after eliminating abnormal ages. Secondly, through comparison of climate events during the last deglaciation,this paper revealed the aragonite to calcite transition resulting in abnormal δ18O signals which can’t record any climate events e.g. B?lling-Aller?d and Younger Dryas which have been recorded by the other stalagmites from Southern China. However, during the early Holonece, the aragonite segment of stalagmite LH5, δ18O fluctuations recorded climate change faithfully. Drip water is considered to be one of the main causes of the aragonite to calcite transition. As for stalagmite LH5, the splash erosion of cave water in collapse pit may play an important role in the process of aragonite to calcite transition. Because of intensity of penetrating and leaching of water in different part of aragonite stalagmites and heterogeneity of stalagmites, aragonite to calcite transition in aragonite stalagmite is not linear. It is the nonlinear transition of aragonite to calcite that leads to nonlinear change of δ18O, which results in δ18O signals of stalagmite in which aragonite to calcite transition occurred can’t reflect climate changes.
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    Paleoclimatic Interpretations of Speleothem δ18O Record in Monsoonal China: Controversies and Some Key Issues
    ZHOU Houyun,LIU Shuhua,PENG Xiaotao,DENG Xiaomin,CHEN Qiong,MI Xiaojian.
    TROPICAL GEOGRAPHY    2016, 36 (3): 448-456.   DOI: 10.13284/j.cnki.rddl.002835
    Abstract2077)      PDF (1649KB)(1626)      
    The paleoclimatic interpretations of speleothem δ18O in the summer monsoon (SM) area of China are widely disputed in recent years. In this paper, we first simply introduce the major viewpoints about the paleoclimatic implications of speleothem δ18O in the SM area of China. Then we raised three key questions which may be crucial to the interpretations of speleothem δ18O record in the SM area of China, such as the test of calcite precipitation under isotope equilibrium conditions, the similarity and variability of different speleothem δ18O records, and the influence of cave ventilation on speleothem δ18O record. Those questions are closely related to the connecting mechanisms between speleothem δ18O records and climate environment in the SM area of China. Answer to those questions may be helpful to settling of the disputation on paleoclimatic interpretations of speleothem δ18O record in the SM area of China. Therefore, we suggest that more attention should be paid to those questions in future.
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    Effect of Dehydration of Marine Sediments on Their Magnetic Properties
    LI Mingkun,OUYANG Tingping,TIAN Chengjing,ZHU Zhaoyu,TANG Zhihua,PENG Xuechao,QIU Yan,ZHONG Hexian.
    TROPICAL GEOGRAPHY    2016, 36 (3): 438-447.   DOI: 10.13284/j.cnki.rddl.002843
    Abstract2156)      PDF (3159KB)(701)      
    The technology of environmental magnetism has been increasingly widely applied in marine sediment research. Marine sediment contains a lot of water which is a kind of antimagnetic material. However, it’s not clear that loss of water during sample preparation and preservation is influential to its magnetic properties or not. Magnetic parameters were measured before and after drying for hundreds of marine sediment samples collected from the South China Sea. 685 samples were dried at room temperature, and their magnetic parameters κlf, κhf, SIRM, S-300 and κfd were measured every 40 days, totally 5 measurements. The other sixty samples were freeze dried and the same magnetic parameters were measured before and after drying. The results are shown as follows : 1) For samples dried at room temperature, κ decreased for most samples and increased for a few of samples while both S-300 and κfd decreased except the outliers; SIRM decreased at first 40 days and then increased, and it showed an increasing trend on the whole. 2) Magnetic parameters κ, S-300 and κfd showed an increasing trend and SIRM showed a trend of decrease for samples dried under freeze condition. 3) The variation trends of κ, SIRM and S-300 in profiles didn’t change during drying process. However, dehydration played a significant influence on profile variation of κfd. The variations of magnetic parameters may be due to comprehensive factors such as a weak oxidation during drying process, the reducing of “negative contribution” of water caused by water loss, the transition when fine magnetite and maghemite in wet state changed into paramagnetism and incomplete antiferromagnetism. Therefore, the same drying method must be used for the same batch of samples.
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    Long Scale Climatic Drought Events in the Yangtze River Delta since the Late Pleistocene: Environmental Magnetic Records from the Sediment
    ZHOU Qixian,YANG Xiaoqiang,LI Jian,LIN Qinglong,PENG Jie,WENG Yuanzhong,DING Jieying,LIU Chunlian.
    TROPICAL GEOGRAPHY    2016, 36 (3): 427-437.   DOI: 10.13284/j.cnki.rddl.002852
    Abstract2581)      PDF (3945KB)(1149)      
    Since the late Pleistocene, the Yangtze River Delta region affected by both the sea level and the East Asian monsoon, resulting in complex regional climate, has brought a lot of uncertainty for recovery of its long-term history and evaluation of future climate evolution. This article selected three long boreholes in the south Yangtze River Delta, CSB4, CSB6 and CSB8, to be studied. The analysis of environmental magnetism was for revealing the region's significant climate events recorded from the sediments since the late Pleistocene. The results showed that there were three significant low S300 areas in the three boreholes, when S300 was a low value, the magnetic susceptibility, ARM and SIRM values were low, and the ratio of IRMAF80mT/SIRM and that of ARM/ SIRM relatively were high, indicating that the concentration of magnetic minerals were reduced, particle size became small. Their sediments mainly were yellow silty clay containing ferromanganese tuberculosis. IRM acquisition curves and spectral quantitative analysis results revealed that the relative increase in the content of hematite high coercivity component in the sediments indicated that three significant dry events happened in the Yangtze River Delta. Based on the magnetic strata, AMS14C dating and optically stimulated luminescence dating, the three drought events happened in 163-121 ka B.P. (Event I), 57-42 ka B.P. (Event II) and 14-10 ka B.P. (event III), respectively. The three dry events were corresponding to a relatively low sea level, while the monsoon weakened, rainfall decreased, climate became dry, forming an oxidation-based environment.
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    Vegetation and Environmental Changes Inferred from a Holocene Pollen Spectrum in the Lower Reaches of Min River
    YUE Yuanfu,ZHENG Zhuo,Barry V ROLETT,HUANG Bojin,HUANG Kangyou,Rachid CHEDDADI.
    TROPICAL GEOGRAPHY    2016, 36 (3): 417-426.   DOI: 10.13284/j.cnki.rddl.002848
    Abstract2109)      PDF (7447KB)(792)      
    In order to reveal the Quaternary environment changes and human impact in Minhou area of the lower reaches of the Min River, Fujian Province, pollen and diatom analysis were carried out from the core FZ5 near Zhuangbianshan Neolithic site. The present result indicated that the Holocene marine transgression in Minhou began at about 9 000 cal. a B.P., and reached its maximum level at 7 500 cal. a B.P. Major marine regression occurred at about 1 900 cal. a B.P. Pollen analyses confirmed a dense evergreen broad-leaved forest during early and middle Holocene, indicating warm and humid climate condition. The optimal climate was relatively stable during the period between 7 500 and 1 900 cal. a B.P. The warm climate and local marine estuary environment were in favor of the development of the Neolithic culture (e.g. Tanshishan Culture) which was characterized with fishing and hunting economic lifestyles. Since 1 900 cal. a B.P., the pollen assemblages were mainly dominated by pioneer plants such as Dicranopteris, Poaceae and Pinus, suggesting a substantial change of the local vegetation. This forest alternation may be resulted from rapid development of human agriculture. High content of Poaceae pollen (including rice pollen type) was only found in the upper part of the profile, that confirmed the onset of large-scale development of rice cultivation at about 1 900 cal. a B.P.
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    Late Quaternary Sediment Stratigraphy and Marine Cycles in the Pingtan Island, Fujian Province
    CHEN Cong,WAN Qiuchi,ZHENG Zhuo,YU Fengling,A Switzer,WAN Yixing.
    TROPICAL GEOGRAPHY    2016, 36 (3): 406-416.   DOI: 10.13284/j.cnki.rddl.002845
    Abstract2399)      PDF (10017KB)(903)      
    A 28.3 m long core, PT01, from the Pingtan Island, Southeast China, is selected to be studied. Radiocarbon dating (AMS 14C) and optical stimulated luminescene (OSL) are used for establishing chronology. Combining age-dating results with marine microfossil and color index, we classify the Late Quaternary sediment stratigraphy in the coastal region of Fujian Province. It is suggested that the late Pleistocene marine deposit, dated back to 124 ka, and abundant marine microfossil (e.g. foraminifer and ostracods), would belong to the Marine Isotope Stages 5(MIS 5). Moreover, the late Quaternary sediment could be divided into three units based on the analysis of lithology, microfossil, grain size and color index. Our results reveal that the sediment environment during the MIS 5 was significantly controlled by global sea level change which varied among coast, tidal flat, lagoon, and eolian sand, and probably there existed weathering process. A hiatus during the last glacial (MIS 2-4) was attributed to low relative sea level. And the Holocene deposit, as thick as 3.79 m, developed poorly and was mainly comprised of swamp facies and eolian dune.
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    New Insight on the Marine Deposit in the Southern Hainan Island
    WANG Mengyuan,ZHENG Zhuo,HUANG Kangyou,ZHANG Yimeng.
    TROPICAL GEOGRAPHY    2016, 36 (3): 399-405.   DOI: 10.13284/j.cnki.rddl.002834
    Abstract2413)      PDF (6409KB)(818)      
    Based on AMS 14C and optical stimulated luminescence dating of core TLG01 from Tielu Harbor of Sanya in southern Hainan Island, this study comprehensively analyzes lithology, sediment grain size, color index, marine macrofossil and foraminifer indexes. The upper marine deposit belonging to the Holocene is thin that is interpreted as tidal sand flat. Whereas, the lower marine deposits, as thick as 38 m, are dated to MIS 5e and 5d according to optical stimulated luminescence dating. The late Pleistocene transgression-regression sequences are as follows: tidal sand flat-subtidal-tidal mud flat-tidal sand flat. The species of Mollusca living in deep-water condition are identified in late Pleistocene marine layer. The species identification and their related habitats make possible to restore the sedimentary facie. In MIS 5e, the content of silt and clay sharply increased followed by a decrease trend at MIS 5d. Sediment grain size, foraminifera abundance and sediment color index L* show that the highest sea level appeared at the beginning of MIS 5e, while from MIS 5e to MIS 5d, the sea level was lowered, accompanied by the increase in terrestrial coarse sand, indicating relative low sea level toward MIS 5d. The triangular plots of interglacial periods MIS 1 and MIS 5 are respectively consistent with modern surface sediments from the island intertidal zone of Zhanjiang and the South China Sea.
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    Dating and Sedimentary Environment Reconstruction of Holocene Beach Profile in the Pearl River Estuary Islands
    WAN Yixing,ZHENG Zhuo,XIAO Yiting,TANG Yongjie,CHEN Cong.
    TROPICAL GEOGRAPHY    2016, 36 (3): 388-398.   DOI: 10.13284/j.cnki.rddl.002851
    Abstract2638)      PDF (4689KB)(722)      
    Holocene sand flat and sand dune deposits, which may be formed during the high sea level period in Holocene, are widely distributed in the coastal zone and islands of the Pearl River Estuary. These deposits contain rich information on Holocene marine transgression and environmental changes. Furthermore, rich Neolithic remains are found in these sediments in the islands around the Pearl River Estuary. Therefore, the coastal sandy marine deposits of Holocene, with evidences of both natural and cultural histories, have drawn great attention from scientists. In this paper, optical stimulated luminescence (OSL) dating and grain-size analysis were conducted. The results showed that the bottom of the coastal sandy marine deposits of Holocene might be formed more than 9 ka B.P. ago. Most of the OSL dating results showed that the Holocene sand flat and sandy eolian deposits were older than the Neolithic remains, which indicated that the former was formed before the latter. Another finding was that the overlying strata of the coastal sandy marine deposits often shifted rapidly to alluvial face of supratidal zone or dune at about 6.5 ka B.P., resulting in worsened grain-size sorting and great parameter fluctuations. The marine facies reached +4.8 m (modern elevation), which might be related to regional tectonic movement or the descending of sea level in Holocene. Combining grain-size analysis and archaeological excavation remains with other relevant records, the Holocene sedimentary environment was reconstructed; sea level change and differential tectonic movement, and relationship between man and nature in Holocene were revealed.
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    Paleoenvironment Reconstruction and Sedimentary Record in the Wanqingsha Area of the Pearl River Estuary
    YU Shaohua,CHEN Fang,XIE Yecai,ZHOU Yang,WU Cong,CHEN Chixin,LONG Gui.
    TROPICAL GEOGRAPHY    2016, 36 (3): 374-387.   DOI: 10.13284/j.cnki.rddl.002844
    Abstract2354)      PDF (4017KB)(1148)      
    In order to reconstruct the eustatic change and paleoenvironment of the estuary of Pearl River since the late Pleistocene, the Core ZK 316-2, which is located in the Wanqingsha district of the Pearl estuary, was chosen to carry on pollen analysis combining with diatom and lithological analyses. Results of diatom and pollen analyses as well as lithological analysis showed that the late Pleistocene experienced a large sea level transgression and regression and two smaller eustatic changes. During the transgression period in the late Pleistocene the pollen assemblages indicated warm and rainy climate, when vegetation was dominated by south sub-tropical Asian evergreen forest, including sub-tropic pollen types Cyclobalanopsis, Altingia, and Hamamelidaceae, etc. The appearing of Sonneratia in this period was deduced from the littoral face, and it represented the altitude of relative sea level. Although the dating year from 14C results in this oceanic layer was more than 30 ka, the regional pollen assemblages and diatom signals as well as the altitude of global sea level demonstrated that the deposition in the transgressive period during the late Pleistocene was more likely from MIS5, and the two shorter low sea level records probably corresponded to 5b and 5d. The upper layer of the core (less than 13.9 m in depth) was deposited since 2 232 cal. a B.P., and the pollen analysis demonstrated that the vegetation was still dominated by the subtropical evergreen forest, when the climate was colder and dryer during this period as compared with that in the transgressive period of the late Pleistocene. The flourishing of Poaceae, Pinus and Dicranopteris as well as fire records (charcoal) which indicated the anthropogenic disturbance during this period indicated that human activities and cultivated agriculture bloomed, almost synchronizing with the regression of sea level and deposition of the Pearl River delta.
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    Holocene Paleoenvironment Reconstruction Based on Pollen Data in the Sanshui Basin, Northern Pearl River Delta
    HUANG Kangyou,HE Jiahui,ZONG Yongqiang,ZHENG Zhuo,ZHANG Guifang,CAO Linglong.
    TROPICAL GEOGRAPHY    2016, 36 (3): 364-373.   DOI: 10.13284/j.cnki.rddl.002849
    Abstract2299)      PDF (4126KB)(1297)      
    Sanshui basin is located on the convergence of Xijiang and Beijiang Rivers of the northern Pearl River delta, where the sediment recorded the sea level changes during Holocene. Based on 12 AMS 14C dating results, pollen and diatom analyses were used to reconstruct paleoenvironment and seal level change during early Holocene. The results showed that because of the rapid sea-level rise Sanshui basin was inundated and the onset of rapid deltaic accumulation was at ~9 000 cal. a B.P. and 3 000 cal. a B.P. respectively. The environment varied as an evolution process of fluvial - river bay - estuarine - tidal-flat - estuarine- alluvial flat facieses. The sediment rate was at 1.6 cm/a in early Holocene, the sediment was mainly composed of fine silt. The marine transgression occurred at ~8 700 cal. a B.P., and reached the highest sea level stand at ~7 600 cal. a B.P. The mangrove forest was distributed around the seacoast, but the regional vegetations were characterized by subtropical evergreen forest which was dominated by Castanopsis and Quercus-evergreen type. The sediment consisted of silty peat at mid- and late Holocene (6 500-2 200 cal. a B.P.), with the sediment rate of 0.2-0.5 cm/a. The mangrove forest disappeared and the swamp developed, which was composed of Cyperaceae, Poaceae and spores. Since the age of ~2 200 cal. a B.P., the sediment rate has reached the highest value (1.7 cm/a) and the delta plain expended rapidly. Pollen evidence showed that the natural forest was likely disturbed by agricultural development during the late Holocene.
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    Holocene Mollusc Records and Palaeoenvironmental Changes in the Pearl River Delta
    LIU Chunyao,YIN Jian,LIU Chunlian,HUANG Yi,WU Yueqin.
    TROPICAL GEOGRAPHY    2016, 36 (3): 355-363.   DOI: 10.13284/j.cnki.rddl.002830
    Abstract2690)      PDF (4971KB)(1162)      
    A study has been carried out on the sediments and molluscs of core PRD11 drilled in the central Pearl River Delta plain. The results suggest that the sea level fluctuations, fluvial processes, and tectonic uplift and subsidence led to the environmental changes of the study area during the Holocene. Five environmental stages can be recognized: 1) Before 9 010 cal. a B.P., the sediments were subaerially exposed and experienced weathering process, which is indicated by the mottled clay in the lower part of core PRD11. 2) From 9 010 to 7 000 cal a. B.P.,an estuary environment began to develop at the site of core PRD11. 3) From 7 000 to 5 460 cal. a B.P., a decrease in water depth occured. 4) From 5 460 to 3 340 cal. a B.P., water depth increased again, with the largest water depth at around 4 546 cal. a B.P.. 5) Since 3 340 cal. a B.P., the environment gradually changed into an alluvial plain setting, with enhanced fluvial influence.
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    Major and Trace Elements Geochemistry and Paleoenvironmental Implications of Borehole ZK19 in the Lingdingyang Bay of the Pearl River Estuary
    WAXI Lali,WANG Jianhua,CHEN Huixian,WU Jiaxue,TAO Hui.
    TROPICAL GEOGRAPHY    2016, 36 (3): 343-354.   DOI: 10.13284/j.cnki.rddl.002841
    Abstract2333)      PDF (3236KB)(620)      
    The research on Late Quaternary sediments of borehole ZK19 in the Lingdingyang Bay of the Pearl River Estuary has shown that the formation of the borehole revealed mainly on the upper Pleistocene Series and Holocene Series. Bounded by the weathering layer formed during the last glacial period, it has demonstrated the two important transgressive events during the Late Pleistocene and Holocene respectively. The distribution of major, trace elements and their ratios (e.g. Al2O3/Na2O ratio, MgO/Al2O3 ratio, Sr/Ba ratio and V/Cr ratio), Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) were used to reconstruct the paleo-climate and environment changes. Paleo-environmental changes were reconstructed: 1) Middle Stage of Late Pleistocene MIS4-early MIS3: sedimentary facies changed from continental facies to coastal beach facies; gradually warming from cooler climate, sea level rose slowly; 2) MIS3 stage of Middle-late Stage of Late Pleistocene, sedimentary environment showed an estuarine facies, climate got warmer, sea level rose significantly; 3) Late Stage of Late Pleistocene MIS2 stage, during the Last Glacial Maximum the sea level dropped significantly, and the climate was cooler; 4) MIS1 (8-12 cal. ka B.P.), the climate was warmer, sea level rose fast, sedimentary environment consisted of fluvial facies-coastal tidal flat-estuarine shoal-estuarine facies; 5) The Middle Holocene sediment is lacked in the borehole, probably due to an underwater erosion of migration of estuarine shoal - channel; 6) Late Holocene (since 3 cal. ka B.P.) sedimentary environment was estuarine facies - delta front slope facies - delta front shoal facies, climate overall was relatively stable, and warmer than that in early Holocene.
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    Late Quaternary Tectonic Movements in the Pearl River Delta, China, Revealed from Stratigraphic Profiles
    YU Zhangxin,ZHANG Ke,LIANG Hao,LI Zhongyun.
    TROPICAL GEOGRAPHY    2016, 36 (3): 334-342.   DOI: 10.13284/j.cnki.rddl.002850
    Abstract2138)      PDF (24282KB)(583)      
    The Pearl River Delta is located at north margin of the South China Sea. Neotectonic movements play important role on the evolution of the delta featured as fault-blocks differential uplift and subsidence. Some critical topics, e.g. the active variation of different fault groups, the pattern of fault-blocks movements, are still debatable. Recently some Quaternary depositional terraces were discovered on Panyu Platform in the north Pearl River Delta. Those terraces can be identified into several stratigraphic layers: A. migmatite or granite bedrocks which have been deeply weathered into vermicular red soil, B. greyish white and yellow medium/coarse sand, cross-bedding structure, with weathering surfaces, C. dark grey to black silt with a few fine sand lense, wood fragments layer in the bottom, and D. dark grey silt, rhythmically intercalated by greyish white sand layers. Study on sedimentary facies of those layers shows that this sequence belongs to the Pearl River Delta lower marine transgressive cycle, which means the delta deposits was tilted after the 1st transgressive deposition, due to the NNW trending Hualong-Huangge fault zone. Other W-E and N-S trending terrace-borehole stratigraphic profiles in the Pearl River Delta area reveal the active variation of different fault groups. The W-E and NE-SW trending faults control the edge of the Pearl River Delta, while little influence on the pattern of delta deposition process and river channel distribution. The NNW-SSE and NEE-SWW trending faults are still active since the 1st marine transgression, making the delta deposits weekly tilt. The comparison of sedimentary sequence in the Pearl River Delta with continental shelf of the Northern South China Sea illustrates that besides the 2 cycles in the Pearl River Delta, there are much older cycles on the continental shelf due to intensive activities of the Littoral Fault Zone.
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    Relationship between Late Quaternary Lithostratigraphy, Sea-level Change and Tectonics in the Pearl River Delta
    ZONG Yongqiang,HUANG Guangqing,XIONG Haixian,LI Xiaoyun,SUN Yiying.
    TROPICAL GEOGRAPHY    2016, 36 (3): 326-333.   DOI: 10.13284/j.cnki.rddl.002842
    Abstract3002)      PDF (3276KB)(2012)      
    Based on a review of the lithostratigraphic data from the coastal area and the continental shelf of northern South China Sea, this paper has examined the Late Quaternary evolutionary history of the Pearl River Delta. Results show that: 1) the deltaic basin of the Pearl River contains two marine sequences, the upper (younger) one belongs to the present interglacial (the past 10.5 ka B.P.) deposit and the lower (older) one most likely is that of the high sea level period during the last interglacial (126–120 ka B.P.); 2) the burial depth of the older marine sequence within the deltaic basin is recorded at 10-15 m below present sea level, whilst the depth in the mouth region is found below 20 m, implying geological subsidence because the height of sea level during the last interglacial was close to that of the present; 3) within the tectonic framework of southeastward continental extension of the Eurasian Plate during the Cenozoic, the coast and continental shelf of northern South China Sea has experienced a continuous subsidence at a long-term average rate of 0.12 mm/a, which is similar to that measured by GPS at present; 4) on top of the continental subsidence, fault activity has enhanced the localized subsidence of the deltaic basin, which led to the creation of accommodation space for marine inundation during interglacial high sea levels.
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    Environmental Changes Inferred from Spatial-temporal Distribution of Holocene Buried Peat Layers in Lower Reaches of the Xijiang and Beijiang and the River Confluence of Pearl River Delta
    ZHENG Zhuo,TANG Yongjie,ZHENG Yanwei,HUANG Kangyou,HAN Ziyun,ZONG Yongqiang,LI Pingri,TAN Huizhong.
    TROPICAL GEOGRAPHY    2016, 36 (3): 313-325.   DOI: 10.13284/j.cnki.rddl.002840
    Abstract2555)      PDF (16108KB)(610)      
    The buried peat and wood layers of Holocene are found widespread mainly in lower Xijiang and Beijiang Rivers, as well as in the confluence areas of northwestern part of Pearl River delta. In this paper, detailed studies of sedimentary facies, combined with radiocarbon dating, have enabled us to reconstruct the Holocene environment and evaluate the distribution of Holocene buried peat and wood layers in the study region. Four conclusions can be drawn as follows: 1) The terrestrial sedimentary sequences located in the northern boundary of Holocene Marine transgression and downstream areas of the Xijiang and Beijiang Rivers show the thick bedded peat which have the earliest age in the mid-late Holocene (7.5-1.5 cal. ka B.P.) and the main deposit period centered at 5.0-1.5 cal. ka B.P.; 2) In the marginal region of Pearl River Delta, terrestrial peat swamps emerged mainly due to the Holocene marine transgression, and the high sedimentation rate during the early Holocene (around 9-7 cal. ka B.P.) provided fertile mud for further development of brackish water swamp. In addition, the alluvial or flood deposits situated in downstream area of the Xijiang and Beijiang Rivers expanded after 8 cal. ka B.P., which also led to the prosperity of the Chinese cypress (Glyptostrobuspensilis) peat swamp; 3) The study area is considered to be a transitional region of ancient estuary and floodplain in the lower reaches of Xijiang and Beijiang Rivers during the mid-Holocene, that caused an emergence of peat swamp in a large scale, especially under its interaction between riverine and tidal currents; 4) The peatland was inundated by alluvial sediments at around 2-1.5 cal. ka B.P. under the process of aggradation in Pearl River Delta, that can be attributed to the destruction of tidal-fluvial balance, as well as the change in hydrological conditions. Moreover, the increasing human activity, deforestation and soil erosion should be also taken into consideration.
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    Seasonal Patterns and Major Environmental Influences of Skeletal Density Bands of Coral Porites from the South China Sea
    WEI Wenwen,SHI Qi 1,YU Kefu,TAO Shichen,WAN Yang
    TROPICAL GEOGRAPHY    2016, 36 (6): 923-934.   DOI: 10.13284/j.cnki.rddl.002893
    Abstract2725)      PDF (3953KB)(1133)      

    Porites corals are dominant in the South China Sea (SCS) coral reef systems. Porites have been widely used in the coral-based high-resolution paleo-climate reconstructions, based on their seasonal skeletal density bands. There were local difference and contradictions on the seasonal skeletal density bands of Porites attributing to the single sample site in the previous studies. In this paper, gray value and geochemical proxies (Sr/Ca and δ 18 O) were analyzed by using digital image processing, inductively coupled plasma atomic emission spectrometry and gas isotope ratio mass spectrometer in 4 living Porites collected from four typical coral reef sites in the northern, middle and southern SCS respectively, including Wenchang, Yongxing Island, Panshiyu Reef, and Meiji Reef. As compared with the sea surface temperatures, the skeletal density showed significant seasonal variations in all samples, but the seasonal pattern of skeletal density band varied within the different sites. The high and low skeletal density bands formed separately in summer and winter in the Porites sample from Wenchang in the northern SCS; the high and low density bands developed separately in autumn and spring in the skeletal samples from Yongxing Island and in spring and autumn in the sample from Panshiyu Reef respectively in the middle of the SCS; and the high and low density bands of the skeletal sample occurred separately in winter and summer at Meiji Reef in the southern SCS. The Generalized Additive Mixed Model was applied to reveal the relationship of skeletal density to sea surface temperature, sea surface salinity and net shortwave radiation, respectively. Regardless of the random effects from sample individuals and sites, the results showed the different relationship between skeletal gray values and environmental factors in four sites: sea surface temperature and net shortwave radiation had negative correlation to the skeletal gray values in Wenchang; while skeletal gray values in Meiji Reef had strongly positive correlation with sea surface temperature and negative with net shortwave radiation; in Yongxing Island, significant positive correlation existed between skeletal gray values and sea surface salinity; and there was positive correlation between skeletal gray values and sea surface temperature in Panshiyu Reef, showing the distinctly different responses of skeletal density to the environmental factors in the four sites. However, when the random effects of the sample individuals and sites were taken into account, non-linear relationship was found between the skeletal density and the sea surface temperature and net shortwave radiation on the whole, but there was no positive or negative relationship between salinity and skeletal gray values. It means that over the large spatial scale in the SCS, the temperature and radiation were the possible major influences on seasonal skeletal density of coral Porites samples. Coral skeletal density increased with the rising sea surface temperature, when the temperature was higher than 27℃, the slope of density/SST decreased. In addition, the optimal radiation for the Porites was found to be 150 W/m 2 , coral density decreased when the radiation was higher than the optimum, in contrast, the density increased with the increase of the radiation when the radiation was lower than the optimum.

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    Seasonal Responses of Symbiodinium in Stress-tolerant Porites lutea to Environmental Factors on Fringing Reefs of the Hainan Island
    XU Lijia,YU Kefu,LI Shu
    TROPICAL GEOGRAPHY    2016, 36 (6): 915-922.   DOI: 10.13284/j.cnki.rddl.002900
    Abstract3027)      PDF (2841KB)(901)      

    Due to global warming and increase in human activities, coral reefs worldwide have experienced severe declines recently,and scientific studies on their important causes keep on increasing. In this study, 194 samples of stress-tolerant Porites lutea were collected seasonally between October 2013 and August 2014 at fringing reefs in Sanya and Wenchang, Hainan Island, northern South China Sea (SCS), and their algal symbiont density and effective photochemical efficiency (Φ PSII ) were measured. The results indicated that both the Symbiodinium density and Φ PSII of P. lutea were subject to significant seasonal and spatial variations (Scheffe test,p<0.05). Seasonally, the mean Symbiodinium density in P. lutea varied from (2.23 ± 0.18) × 10 6 cells/cm 2 to (6.08 ± 0.36) × 10 6 cells/cm 2 , with the lowest density occurring in winter but a higher value in summer; the mean Φ PSII of Symbiodinium in P. lutea varied from (0.599 ± 0.01) to (0.717 ± 0.002) during seasons, with a higher Φ PSII in winter yet a lower value in spring and summer. Spatially, the mean Symbiodinium densities in P. lutea at the two reefs were (4.54 ± 0.33) × 10 6 cells/cm 2 (Wenchang, 1-2 m depth), (4.65 ± 0.33) × 10 6 cells/cm 2 (Sanya, 1-2 m depth), and (3.75 ± 0.29) × 10 6 cells/cm 2 (Sanya, 4-6 m depth). Although there were not significant differences between Wenchang and Sanya areas, the mean Symbiodinium densities of corals within 1-2 m depth were higher when compared to corals within 4-6 m depth. The mean Φ PSII of Symbiodinium in P. lutea at the two reefs were (0.625 ± 0.009) (Wenchang, 1-2 m depth), (0.680 ± 0.005) (Sanya, 1-2 m depth), and (0.672 ± 0.004) (Sanya, 4-6 m depth), indicating Φ PSII of corals in Sanya area were higher as compared to corals in Wenchang. Cumulation over the month before sampling showed high correlations with the Symbiodinium density and Φ PSII of P. lutea suggesting that there was a time-lag effect of environmental factors on coral symbiont. Further analysis suggested that SST and nutrients in the reefs were responsible for the observed seasonal variations in symbiont density and Φ PSII of P. lutea, while the spatial difference of Φ PSII probably reflected the coral’s photo acclimation; besides, the cold-water upwelling (Qiongdong upwelling, QDU) had to be taken into account for the variations as well. As the reefs have been experiencing coastal constructing, significant marine culturing and tourist diving activities, the reef waters are at the risk of anthropogenic nutrification, thus, the viability of P. lutea is facing severe threat by the effects of nutrient enrichment and temperature increase. Since local management of nutrient enrichment could reduce the effects of global warming on coral reefs, efficient nutrient management strategies are urgently required to be developed and the action should be taken immediately.

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    Influencing Factors of SST Variation along the South China Coast during 1960-2013
    CHENG Zemei,TANG Chaolian,CAI Bing,SHEN Dongfang
    TROPICAL GEOGRAPHY    2016, 36 (6): 906-914.   DOI: 10.13284/j.cnki.rddl.002897
    Abstract2451)      PDF (6049KB)(1318)      

    Sea Temperature is a conventional subject of ocean research, and sea surface temperature (SST) research is the focus in the study of ocean temperature, which is the most valuable ocean hydrological element in the research of oceanographic physics and global climate change. With the observational data of SST from seven Marine Environmental Monitoring Stations (MEMS) along South China coast, Global average surface temperature, Pacific Decadal Oscillation (PDO), El Ni?o Southern Oscillation (ENSO), SCSH index and sea surface wind-speed during the period 1960-2013, we used the methods of linear regression,Yamamoto mutation test,wavelet analysis and correlation analysis to analyze the relationship between SST and global climate change, temperature of South China coast, SST of the South China Sea and SCSH index along the South China coast over the past 54 years, we also discussed the reasons for warming hiatus phenomenon in South China coast during the period from 1998 to 2013. The conclusions were as follows: 1) The annually averaged SST of all the MEMS showed a quasi-synchronous changes and significant warming trend over the past 54 years, the climate had an tendency rate of 0.08-0.17℃/10 a, with an average of 0.12℃/10 a, the most significant warming was in winter (0.20℃/10 a), secondly in autumn (0.14℃/10a), and minimum in spring and summer (0.09℃/10 a, 0.08℃/10 a); 2) The mutation of SST occurred in 1997/1998; 3) The character of SST variation was multi-spatiotemporal, with the main cycle of 2-4 years; 4) SST changes were influenced by ENSO events, and lagged behind MEI index by about 2-4 months; 5) We also found that the main factors affecting SST were global warming, PDO, enhancement of the subtropical high and sea surface wind-speed along the South China coast.

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    Cited: Baidu(2)
    Projections of Maximum Sea Level Recurrence Intervalnear Shenzhen at the End of the 21 th Century
    NIE Yuhua,TANG Chaolian,CHENG Zemei
    TROPICAL GEOGRAPHY    2016, 36 (6): 901-905.   DOI: 10.13284/j.cnki.rddl.002895
    Abstract2252)      PDF (1177KB)(929)      
    The Chi-wan tide gauge station is the only oceanic tidal observation site on the west coast of Shenzhen that belongs to the State Oceanic Administration. Due to its special geological location, the Chi-wan Station is of significant importance in many fields, including sea level rise, storm tide prediction, and so on, in our country. In the present study, the tidal data of Chi-wan station ever since it was established were analyzed using a P-III curve-fitting method. The maximum sea level recurrence intervals at this station during 1965-2014 were obtained. The maximum sea level was 2.31 m for a one-hundred-years return period and 2.18 m for a fifty-years return period. Using an interpolation method, the yearly maximum sea levels at Chi-wan Station (x) and North Point/Quarry Bay Station (y) in Hong Kong during 1965-2011 were analyzed. It was found that there existed a significant correlation between x and y. The maximum sea levels in the recent one hundred years at Chi-wan station can thus be hindcast to be 2.7 m in 1962 and 2.34 m in 1937. According to the RCP2.6 in IPCC-AR5, the maximum sea level recurrence interval at Chi-wan Station at the end of the 21 th century (during 2081-2100) was also projected. It is projected to be 2.55 m for a one-hundred-year return period if the global sea level rises by 0.24 m and 2.71 m if the global sea level rises by 0.4 m. Finally, the influence of land reclamation on the sea level rising rate in the Ling-Ding waters and the influence of the No.0814 typhoon Hagupit on the storm tide at Chi-wan were discussed. The near shore terrain of Xixiang, which is located at the north part of Chi-wan, is very low. When the sea level exceeds 1.40 m, sea water will flow backwards in this area. That is to say, sea level rise in the future will increase the frequency of seawater flowing-backward near Chi-wan Station. Also, by analyzing the tidal observation data when typhoon passed by, it was found that, when typhoon Hagupit passed the Pearl River Estuary, the maximum sea level at Chi-wan Station increased by 1.46 m. In the present study, the maximum sea level recurrence interval at Chi-wan station was revised. This can not only improve the accuracy of water level warning in this area, but also provide reference for the prediction and precaution of storm tide in this sea area.
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    Trends of Rainfall at Shantou and Their Relationships with Global Surface Temperature during 1880–2015
    XIE Jianqun,OUYANG Yujie,CHEN Xiuyun,ZHAO Meixia,CHEN Tegu
    TROPICAL GEOGRAPHY    2016, 36 (6): 895-900.   DOI: 10.13284/j.cnki.rddl.002899
    Abstract2635)      PDF (576KB)(820)      

    In recent years, some investigations have been carried out to study the inter-decadal variability of precipitation in China. The earliest record of rainfall was from 1880 and a total of 127 years of complete records were taken for Shantou. This long precipitation sequence was very important for exploring the rainfall regime for the whole eastern region of Guangdong Province. The long-term changes in precipitation during a whole year, the pre-flood period (Apr.-Jun.), or the post-flood period (Jul.-Sep.), and their relationships with global surface temperature during 1880-2015 were analyzed using precipitation data from the Central Weather Bureau (for years of 1881-1943) and Shantou Meteorology Station (for years of 1951-2015) and global surface temperature data from HadCRUT 4 dataset. The methods of filtering analysis, linear regression analysis, spectral analysis and correlation analysis were adopted in this study. The following findings were highlighted: 1) The inter-annual and inter-decadal variations in precipitation during a whole year, the pre-flood period or the post-flood period were obvious during 1880-2015, and the primary periods for the annual precipitation sequence were 6, 8, 13, and 26 years during 1880-1938 and were 7, 8, 11 and 17 years during 1951-2015. There was no significant long-term increasing or decreasing tendency basing on this long precipitation sequence. For example, the precipitation during a whole year, the pre-flood period or the post-flood period fluctuated after treatment in filtering analysis. 2) The relationship between precipitation during a whole year, the pre-flood period or the post-flood period and global warming was complicated. There was a significant positive correlation between precipitation and global surface temperature during cold periods (1880-1939), especially in the pre-flood periods (Apr.-Jun.). There was no significant correlation between precipitation and global surface temperature during warm periods (1977-2015). But the variation magnitude of precipitation in the pre-flood period and the post-flood period increased with the increase of temperature, which suggested that the risk of drought or flood would increase accordingly. 3) According to the long-term changes in precipitation during a whole year, the pre-flood period or the post-flood period and the current precipitation evaluation standard adopted by the Guangdong Meteorology Administration, the frequency of normal precipitation in the pre-flood period would increase under the background of global warming, and the probability of less precipitation in the post-flood period would increase at the same time. These results were important for exploring the variation characters of precipitation for the eastern region of Guangdong over a long term period and useful for evaluating the possible effect of global warming on precipitation at Shantou in the near future.

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