Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea

High-resolution sea-level data and high-precision dating of corals in the northern South China Sea(SCS)during the Holocene provide a reference and historical background for current and future sea-level changes and a basis for scientific assessment of the evolutionary trend of coral reefs in the SCS.Although sporadic studies have been performed around Hainan Island in the northern SCS,the reconstructed sea level presents different values or is controversial because the indicative meaning of the sea-level indicators were neither quantified nor uniform criteria.Here,we determined the quantitative relationship between modern living coral and sea level by measuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Island and assessed the accuracy of results obtained using coral as sea-level indicators.Additionally,three in situ fossil Porites corals were analyzed based on elevation measurements,digital X-ray radiography,and U-Th dating.The survey results showed that the indicative meanings for the modern live Porites corals is(146.09±8.35)cm below the mean tide level(MTL).It suggested that their upward growth limit is constrained by the sea level,and the lowest low water is the highest level of survival for the modern live Porites corals.Based on the newly defined indicative meanings,6 new sea-level index points(SLIPs)were obtained and 19 published SLIPs were recalculated.Those SLIPs indicated a relative sea level fluctuation between(227.7±9.8)cm to(154.88±9.8)cm MTL between(5393±25)cal a BP and(3390±12)cal a BP,providing evidences of the Mid-Holocene sea-level highstand in the northern SCS.Besides that,our analysis demonstrated that different sea-level histories may be produced based on different indicative meanings or criteria.The dataset of 276 coral U-Th ages indicates that coral reef development in the northern SCS comprised the initial development,boom growth,decline,and flourishing development again.A comparison with regional records indicated that synergistic effects of climatic and environmental factors were involved in the development of coral reefs in the northern SCS.Thus,the cessation of coral reef development during the Holocene in the northern SCS was probably associated with the dry and cold climate in South China,as reflected in the synchronous weakening of the ENSO and East Asian summer monsoon induced by the reduction of the 65°N summer insolation,which forced the migration of the Intertropical Convergence Zone.

CMIP 6 models simulation of the connection between North/South Pacific Meridional Mode and ENSO

The subtropical North and South Pacific Meridional Modes(NPMM and SPMM)are well known precursors of El Niño-Southern Oscillation(ENSO).However,relationship between them is not constant.In the early 1980,the relationship experienced an interdecadal transition.Changes in this connection can be attributed mainly to the phase change of the Pacific decadal oscillation(PDO).During the positive phase of PDO,a shallower thermocline in the central Pacific is responsible for the stronger trade wind charging(TWC)mechanism,which leads to a stronger equatorial subsurface temperature evolution.This dynamic process strengthens the connection between NPMM and ENSO.Associated with the negative phase of PDO,a shallower thermocline over southeastern Pacific allows an enhanced wind-evaporation-SST(WES)feedback,strengthening the connection between SPMM and ENSO.Using 35 Coupled Model Intercomparison Project Phase 6(CMIP6)models,we examined the NPMM/SPMM performance and its connection with ENSO in the historical runs.The great majority of CMIP6 models can reproduce the pattern of NPMM and SPMM well,but they reveal discrepant ENSO and NPMM/SPMM relationship.The intermodal uncertainty for the connection of NPMM-ENSO is due to different TWC mechanism.A stronger TWC mechanism will enhance NPMM forcing.For SPMM,few models can simulate a good relationship with ENSO.The intermodel spread in the relationship of SPMM and ENSO owing to SST bias in the southeastern Pacific,as WES feedback is stronger when the southeastern Pacific is warmer.

Paleogene transgression process and environmental evolution in the deepwater area of the Baiyun Depression in the northern South China Sea

Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea(SCS)in an effort to reconstruct transgression processes during the Paleogene based on palynalgal analysis.This study indicates that the Baiyun Depression generated a large group of palynopore assemblages and fluvial/lacustrine-related algae during the early and middle Eocene when the Wenchang Formation was deposited.The entire depression was dominated by fluvial and lacustrine facies before transgression.Its eastern and southeastern sags transitioned to shallow marine environment by generating a large abundance of marine dinoflagellates during the Enping deposition of the late Eocene.Meanwhile,the southern uplift zone simply yielded fluvial/lacustrine-related palynopores and algae,and was dominated by the fluvial and lacustrine environment during the early stage of the Enping Formation,prior to shifting into transitional setting in the later period.Northwestern sags remained extensive fluvial and delta facies without existence of marine dinoflagellates.It was until the depositional stage of the Zhuhai Formation(Oligocene)that the overall depression was strongly impacted from transgression process.Both eastern and southeastern sags were mainly under deep marine setting on a continental slope while northwestern and southern areas developed transitional facies.Although distribution and accumulation patterns varied greatly among sub-sags,the overall Baiyun Depression was characterized by widespread development of marine dinoflagellates.It should be noted that the northwestern sag also partly generated large-scale river delta deposits.Due to the eustatic rise and change of SCS spreading axis,the overall Baiyun Depression was mostly influenced by the deep marine environment on a continental slope during the early Miocene.Both northwestern sag and southern uplift zone were found plentiful marine dinoflagellates.In summary,transgression initiated from the eastern and southeastern Baiyun Depression before subsequently progressing into the farther west.Evolution of transgression process is also greatly consistent with the gradual westward expansion of the SCS.

U-Pb zircon geochronology of basaltic pyroclastic rocks from the basement beneath the Xisha Islands in the northwestern South China Sea and its geological significance

As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone(0–888.4 m) and the underlying basement rocks(888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha microblock. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206Pb/238U age of(36.3 ± 1.1) Ma,Mean Squared Weighted Deviations(MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons(116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.

The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea

Highly productive estuaries facilitate intense decomposition of dissolved organic matter(DOM) as a carbon source.However,the specific impacts of typhoons on DOM decomposition in eutrophic bays remain unclear.To address this issue,we investigated the spectral characteristics of DOM before and after Typhoon Ewiniar in Zhanjiang B ay,a eutrophic semi-enclosed bay in the northwestern South China Sea.The results revealed that intense microbial decomposition of DOM occurred during the pre-typhoon period because high nutrient inputs facilitated the mobilization of DOM in the bay.However,the intrusion of external seawater induced by the typhoon diluted the nutrient levels in Zhanjiang B ay,reducing the impact of microbial decomposition on DOM during the post-typhoon perio d.Nevertheless,the net addition of DOM occurred in Zhanjiang Bay during the post-typhoon period,possibly because of the decomposition of particulate organic matter(POM) and desorption of particulate matter.In addition,an increase in apparent oxygen utilization,a decrease in DO saturation and the reduced level of Chl a indicated that organic matter(OM) decomposition was enhanced and OM decomposition shifted to POM decomposition in Zhanjiang Bay after the typhoon.Overall,our study highlighted the shift in the intense OM decomposition from DOM to POM decomposition before and after typhoons in eutrophic bays,providing new insights into the response of typhoons to biogeo chemistry.

Detection of a mud volcano in the Weitan Banks area of the northern South China Sea

Situated between the petroliferous Cenozoic Zhujiang(Pearl)River Mouth Basin and the mud volcano-rich Mesozoic Dongsha Basin in the middle sector of the northern South China Sea,the Weitan Banks area has been previously mapped as a basement high that is composed of Mesozoic magmatic rocks.In this study,we present several favorable indicators for petroleum geology that were detected from geophysical profiling and benthic sampling in the area.A conspicuous hill was discovered,named“Zhongwei Hill”,~80 m high above the~340 m deep seafloor and~1 km broad,in a depression with more than 7 km thick sedimentary strata.The Zhongwei Hill was seismically imaged with a mushroom-shaped structure and containing a cake-like crown,fluid flow pipes,and an~10 km broad anticline at depth.Thus,the hill represents a source-plumbing-eruption system.Shallow gas zones linked to deep fracture were found at or near the hill.Stratigraphic correlation indicates that the deep strata comprise the Jurassic and Paleogene strata,the major hosts of hydrocarbon source rocks.In addition to the hill,there are number of mounds from which three bottom water samples were collected and the samples are rich in dissolved methane with concentrations high up to~900 nmol/L,much higher than the background level(0.5–2 nmol/L).The benthic samples are rich in coarse sediment clastics,authigenic carbonate nodules,and deep-water habitats likely feeding on methanotrophic community.Given these observations and the context,we propose that the Zhongwei Hill represents a mud volcano,likely thermally driven,that seeps methane from Jurassic and Paleogene source layers,thus poses a favorable clue for significant hydrocarbon generation capacity in transitional zone of the Zhujiang River Mouth Basin and the Dongsha Basin.

A case study of continental shelf waves in the northwestern South China Sea induced by winter storms in 2021

This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.

Geometry and 3D seismic characterisation of post-rift normal faults in the Pearl River Mouth Basin,northern South China Sea

Based on high-resolution 3D seismic data acquired in the Pearl(Zhujiang)River Mouth Basin of the northern South China Sea,this study investigated the geometry,spatial extension,and throw distribution of the post-rift normal fault through detailed seismic interpretation and fault modeling.A total of 289 post-rift normal faults were identified in the study area and can be classified into four types:(1)isolated normal faults above the carbonate platform;(2)isolated normal faults cutting through the carbonate platform;(3)conjugate normal faults,and(4)connecting normal faults.Throw distribution analysis on the fault planes show that the vertical throw profiles of most normal fault exhibit flat-topped profiles.Isolated normal faults above the carbonate platform exhibit roughly concentric ellipses with maximum throw zones in the central section whereas the normal faults cutting through the carbonate platform miss the lowermost section due to the chaotic seismic reflections in the interior of the carbonate platform.The vertical throws of conjugate normal faults anomalously decrease toward their intersection region on the fault plane whereas the connecting normal faults present two maximum throw zones in the central section of the fault plane.According to the symmetric elliptical distribution model of fault throw,an estimation was made indicating that normal faults cutting through the carbonate platform extended downward between-1308 s and-1780 s(two-way travel time)in depth and may not penetrate the entire Liuhua carbonate platform.Moreover,it is observed that the distribution of karst caves on the top of the carbonate platform disaccord with those of hydrocarbon reservoirs and the post-rift normal faults cutting through the carbonate platform in the study area.We propose that these karst caves formed most probably by corrosive fluids derived from magmatic activities during the Dongsha event,rather than pore waters or hydrocarbons.

Freshening of the Intermediate Waters in the Northern South China Sea over the Past Six Decades

The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the long-term changes in the intermediate water in the SCS have not been thoroughly studied due to limited data,particularly in relation to its thermodynamic variations.This study utilized reanalysis data products to identify a 60-year trend of freshening in the intermediate waters of the northern South China Sea(NSCS),accompanied by an expansion of low-salinity water.The study also constructed salinity budget terms,including advection and entrainment processes,and conducted an analysis of the salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of the intermediate water in the NSCS.The analysis revealed that the freshening in the northwest Pacific Ocean and the intensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes in the NSCS.Additionally,a weakened trend in the intensity of vertical entrainment also contributes to the freshening in the NSCS.This study offers new insights into the understanding of regional deep sea changes in response to variations in both thermodynamics and oceanic dynamic processes.

Preliminary Study of Microzooplankton Grazing and Community Composition in the North of South China Sea in Autumn

Microzoopiankton community composition in the north of South China Sea was investigated during autumn （between September and October）, 2004. Dilution technique using chlorophyll a （Chl a） was employed to estimate grazing rates and grazing pressure. The results showed that Polymenophorea Oligotrichida was the dominant group with 16 species, and there were 4 species in Oligotrichina and 11 species in Tintinnina. The ciliates abundance ranged from 9 to 102 ind/m^3, instantaneous growth rates of phytoplankton （k） varied from 0.03 / d to 2.13 / d. Grazing rates of microzooplankton（g） ranged between 0.01 / d and 1.06 / d. The grazing pressure on initial phytoplankton stock （Pi） and primary production （Pp） was 0.089 % - 65.23 % and 33.63 % - 86.04 %, respectively. The grazing of microzooplankton was mainly limited by ciliates abundance. Results of grazing pressure on primary production indicated that microzooplankton played an improtant role in transmitting primary production in the north of South China Sea.

Distribution and composition of tintinnids ciliates in the northern South China Sea during summer

Tintinnids were enumerated and identified in samples collected from 36 stations between 18°-22°N, 107°-122 °E in the northern South China Sea （NSCS）. 44 species belonging to 24 genera of tintinnids were recorded. The dominant species were He/icostome/la /onga and Tintinnopsis radix. Tintinnids abundance ranged from 0 to 2 200 cell/L, and mean abundance was 221cell/L in the surface water. Tintinnids abundance and species numbers decreased from coast to offshore. Upwelling and Pearl River discharge influenced the distribution of tintinnids by regulating nutrients supply. Maximum abundance （2 200 cell/L） was found in the surface water of A1. Tintinnids abundance showed positive relationship with chlorophyll a （Chl a） concentration, and no significant relationship was found between tintinnids abundance and temperature.

Vegetation Evolution in the Northern South China Sea Region Since 40 ka BP - An Attempt to Reconstruct Palaeovegetation Based on Biomization

Vegetation evolution in the northern South China Sea region since 40 500 a BP is reconstructed using biomization procedure based on pollen data from deep sea core 17940. The result shows that, it is feasible to reconstruct palaeovegetation using biomization procedure, when pollen, particularly Pinus pollen, transported by mind over long distance is excluded. Results from factor analysis suggest that humidity and temperature are the two main factors determining vegetation evolution on land around the northern South China Sea. From 40 500 a BP to 11 100 a BP, broad-leaved evergreen forest (WAMF), and montane conifers(MGRF) occurred on hills and low mountains; while steppe (STEP) predominated on the exposed shelf. The main feature of the vegetation evolution is the frequent alternation between MGRF (or WAMF) and STEP, implying abrupt changes in millennium scale between humid/cold and dry/temperate climate. All abrupt climate events could be broadly correlated with Henrich events and Dansggard-Oscherge events. One of the events around 12 700 a BP, sees the occurrence of MGRF, suggesting that climate turned humid and cold rapidly. This may be correlated with the Younger Dryas event; Broad-leaved evergreen (WAMF) predominates since 11 000 a BP. During the early Holocene and late Holocene tropical rainforest (TRFO) or tropical seasonal forest (TSFO) occurred several times.

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.

Internal tides in the northern South China Sea from 20-day in-situ mooring observations in 1998

20-day in-situ ADCP current and CTD data are used to investigate the characteristics and energy of the internal tides in the northern South China Sea （NSCS）. The results show that the O1, K1, M2 and S2 constituents of internal tides are energetic and diurnal constituents （O1 and K1） are dominating. In the observational period, the current vectors of these four constituents all rotate clockwise and the maximum semi-major axe of internal tidal ellipses is more than 14 cm/s. The variation of ocean temperature shows that the internal tides present obvious quasi-diurnal oscillation and the average amplitude reaches 50 m. Furthermore, these internal tides carry high energy and appear to be intermittent. The maximum values of KE （PE） during the observational period are up to 2 （3.5） k J/m^2 for diurnal internal tides, and up to 1 （1.5） k J/m^2 for semidiurnal internal tides.

Development of Sedimentary Environment in the Northeastern South China Sea Since the Last Glacial Stage

Core D （21°23′02″N, 116°47′13″E, water depth 405 m） was sampled from the upper slope from the northeastern South China Sea （SCS） and applied to analyze the sedimentary environmental change in this sea area since the last glacial stage. The results of grain size analysis, diatom analysis and detrital mineral analysis were well matched. We divided the core D into two layers. The surface sand layer （0 - 2 cm） consisted of residual sediments, which might be originally the sediment in the late Pleistocene and later suffered from being transformed in the post glacial transgression. The lower layer （2 - 130 cm） was quite different from the surface one, which might mainly result from a neritic sedimentary environment in the last glacial stage. Two sedimentary cycles could be detected in the core D： regression during Marine isotope stage （MIS） 4 to transgression during MIS 3 and regression during MIS 2 to transgression during the post glacial.

血红蛋白变异体Hb Fukuyama和Hb North Manchester干扰糖化血红蛋白检测2例报道

糖化血红蛋白(glycated hemoglobin A1c,HbA_(1c))可反映患者近2~3个月的血糖控制情况[1]。美国糖尿病协会(American Diabetes Association,ADA)在2010年就推荐将HbA_(1c)≥6.5%作为糖尿病的补充诊断标准[2]。血红蛋白(hemoglobin,Hb)病是珠蛋白基因发生突变引起的一组溶血性遗传性疾病[3]。

DEFINITING AND ITS GEOLOGIC MEANING OF SOUTH-NORTH TREND FAULTED STRUCTURE BELT IN QIANGTANG BASIN, NORTH PART OF TIBET

There were more expounding to north—west (west) trend fault and north\|east trend fault within Qiangtang Basin, North Part of Tibet, in the past literature. With increasing of geophysical exploration data, nearly east\|west trend structure began to be taken note to. Since the year of 1995, by a synthetic study to geophysical and geological data, that south\|north trend faulted structures are well developed. These structures should be paid much more attention to, because they have important theoretical meaning and practical significance.1 Spreading of south\|north faulted structure belt According to different geological and geophysical data, the six larger scale nearly south\|north faulted structure belt could be distinguished within the scope of east longitude 84°～96° and near Qiangtang Basin. The actual location of the six belts are nearly located in the west of the six meridian of east longitude 85°,87°,89°,91°,93°,95° or located near these meridian. The six south\|north faulted structure belts spread in the same interval with near 2° longitude interval. The more clear and much more significance of south\|north trend faulted structure belts are the two S—N trend faulted structure belts of east longitude 87° and 89°. There are S—N trend faulted structure belts in the west of east longitude 83°,81°, or near the longitudes. The structure belts spreading features,manifestation,geological function and its importance, and inter texture and structure are not exactly so same. The structure belts all different degree caused different region of geological structure or gravity field and magnetic field. There is different scale near S—N trend faulted structure belt between the belts.

The characteristic differences of tropical cyclones forming over the western North Pacific and the South China Sea

The best track dataset of tropical cyclones in the western North Pacific （WNP） and the South China Sea （SCS） from 1977 to 2005 during the satellite era, the NCEP/NCAR reanalysis dataset and the extended reconstructed sea surface temperature dataset are employed in this study. The main climatological characteristics of tropical cyclone formation over the WNP and the SCS are compared. It is found that there is obviously different for the locations of tropical cyclone origins, achieving the lowest central pressure and termination points between over the WNP and over the SCS. The annual number of tropical cyclones forming over the SCS is obviously less than over the WNP, and there is a significant negative correlation with the correlation coefficient being - 0.36 at the 5% significance level between over the WNP and over the SCS. The mean speed of tropical cyclone moving is 6.5 m/s over the WNP and 4.6 m/s over the SCS. The mean lowest central pressure of tropical cyclones is obviously weaker over the SCS than over the WNP. The tropical cyclone days per year, mean total distance and total displacement of tropical cyclone traveled over the WNP are all obviously longer than those over the SCS. Tropical cyclone may intensify to Saffir - Simpson hurricane scale 5 over the WNP, but no tropical cyclone can intensify to Saffir - Simpson hurricane scale 3 over the SCS. The changing ranges of the radii （R15,R16） of the 15.4 m/s winds them and the 25.7 m/s winds over the WNP are obviously wider than those over the SCS, and the median values of the radii over the WNP are also larger than those over the SCS. For the same intensity of tropical cyclones, both radii have larger medians over the WNP than over the SCS. The correlations of annual mean tropical cyclone size parameters between over the WNP and over the SCS are not significant. At the same time, the asymmetric radii of tropical cyclones over the WNP are different from those over the SCS.

Impact of the eastern water diversion from the south to the north project on the saltwater intrusion in the Changjiang Estuary in China

The south to the north project (WDP) on the saltwater intrusion in the Changjiang Estuary is studied by the improved three-dimensionai (3D) numerical model.The net unit width flux in the Changjiang Estuary as well as the sectional salt flux is calculated in the North Branch (NB),the South Branch (SB),the North Channel (NC),the South Channel (SC),the North Passage (NP) and the South Passage (SP),respectively.The net seaward water flux in the SB is reduced,and the net water flux spilling over from the NB to the SB is enhanced after the eastern WDP.Under the mean river discharge condition in the dry season,the net salt flux spilling over from the NB to the SB is increased by 2.09 t/s and 0.52 t/s during the spring and neap tides,respectively,due to the eastern WDP.The saltwater intrusion in the Changjiang Estuary is enhanced by the eastern WDP.Compared with that during the spring tide,the net water diversion ratio during the neap tide in the NC is smaller,and thus the enhancement of the saltwater intrusion by the eastern WDP is smaller in the NC,and larger in the NP and the SP.The tidally averaged surface salinity at the water intakes of the Dongfengxisha Reservoir,the Chenhang Reservoir and the Qingcaosha Reservoir rises both during the spring and neap tides.

Evolution of the Madrean-Tethyan disjunctions and the North and South American amphitropical disjunctions in plants

The present paper reviews advances in the study of two major intercontinental disjunct biogeographic patterns： （i） between Eurasian and western North American deserts with the Mediterranean climate （the Madrean- Tethyan disjunctions）; and （ii） between the temperate regions of North and South America （the amphitropical disjunctions）. Both disjunct patterns have multiple times of origin. The amphitropical disjunctions have largely resulted from long-distance dispersal, primarily from the Miocene to the Holocene, with available data indicating that most lineages dispersed from North to South America. Results of recent studies on the Mediterranean disjuncts between the deserts of Eurasia and western North America support the multiple modes of origin and are mostly consistent with hypotheses of long-distance dispersal and the North Atlantic migration. Axelrod＇s Madrean-Tethyan hypothesis, which implies vicariance between the two regions in the early Tertiary, has been favored by a few studies. The Beringian migration corridor for semiarid taxa is also supported in some cases.