pollen distribution in hemipelagic surface sediments of...

ELSEVIER Marine Geology 156 (1999) 211–226

Pollen distribution in hemipelagic surface sediments of theSouth China Sea and its relation to modern vegetation distribution

Xiangjun Sun a,b,Ł, Xun Li a, Hans-Jurgen Beug c

a Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing, 100093, Chinab Laboratory of Marine Geology, Tongji University, Shanghai, 20092, China

c Institute of Palynology and Quaternary Research, University of Gottingen, Wilhelm-Weber-Strasse 2, D-37073, Gottingen, Germany

Received 21 January 1997; accepted 13 May 1998

Abstract

This paper analyses the distribution of pollen in the surface sediments of the South China Sea as recorded in 28 samplesfrom the area 6º090–20º070N and 112º050–119º450E, at water depths of 329–4307 m. Pollen concentrations range from 444kgrains=g (dry wt) on the lower part of the continental slope in the northeast to zero in the central basin below 4000 mwater depth. Pollen distribution patterns in the concentration and percentage isopolls (incorporating data from the literature)reflect the routes and mechanisms of pollen transport, pollen source areas and considerable systematic differences betweennorth and south. The northern SCS is distinguished by very high concentrations due to the high production and effectivelong-distance transport of pine pollen and fern spores. The maximum of their concentration occurs in the north, adjacentto the convergence of the Bashi and Taiwan Straits, rather than near the estuaries of big rivers, and stretches as a saddlefrom NE to SW, consistent with the direction of the NE winter monsoon and sea current. This pattern implies that pinepollen and fern spores, adapted to wind transport and water flotation, come from the northeast through the straits borneon the winter monsoon and sea current forced by it. Their source areas should cover large regions, probably includingsouth and southeast China. Most pollen of tropical and subtropical broad-leaved trees found in the northern part of theSCS occur in low concentrations, however, these concentrations decrease uniformly offshore, implying a fluvial dischargefrom nearby lowlands in South China. In the southern part of the SCS, pollen of tropical and subtropical broad-leaved treespredominate. Total pollen concentrations, however, are much lower, only 1=10 of those of the northern part. The greatestconcentrations occur offshore north Borneo and decrease toward deep water, suggesting fluvial input from relatively localsources on the adjacent islands (e.g. Borneo). 1999 Elsevier Science B.V. All rights reserved.

Keywords: South China Sea; marine palynology; pollen transport

1. Introduction

The late Quaternary history of the South ChinaSea (SCS) has attracted increasing interest withinrecent years. A number of research papers and sev-

Ł Corresponding author. Fax: C86 10 625 90 833;E-mail: [email protected]

eral volumes have contributed to such topics as theresponse of the SCS to glacial cycles (Wang etal., 1986, 1995; Wang and Wang, 1990), the lastdeglaciation (Broecker et al., 1988; Duplessy et al.,1991), productivity (Winn et al., 1992; Thunell et al.,1992) and palaeoenvironmental interactions betweenland and sea (Wang and Sun, 1994). Pollen andspores had not been studied in the deep-water area

0025-3227/99/$ – see front matter 1999 Elsevier Science B.V. All rights reserved.PII: S 0 0 2 5 - 3 2 2 7 ( 9 8 ) 0 0 1 8 0 - 7

212 X. Sun et al. / Marine Geology 156 (1999) 211–226

of the SCS, aside from the analysis of some surfacesamples and two undated cores near Nansha Islands(Shen et al., 1991), until 1994 when palynologi-cal studies were carried out on deep-water sedimentcores taken during the Sonne-95 cruise (Sarnthein etal., 1994). The preliminary results of the studies areencouraging (Sun, 1996) but an adequate knowledgeof pollen distribution in surface sediments of theSCS is a prerequisite for their interpretation.

In this paper we present the pollen analyses ofthe surface sediments of the SCS in order to deter-mine the distribution patterns of pollen grains andspores as well as the routes and mechanisms of theirtransport from adjacent source areas.

Fig. 1. Map of the South China Sea with location of sample stations. All station numbers except 1–13 have been simplified by omissionof the first 3 digits. (Stations 1–13 are from Shen et al., 1991.)

2. Environmental setting

The SCS is one of the largest marginal seas in theWest Pacific Ocean. It is connected with the PacificOcean through the Taiwan and Bashi Straits in thenortheast, and the Indian Ocean through the SundaShelf in the south (Fig. 1).

The terrigenous material in the SCS is mostly car-ried there by rivers, such as the Rejang (Borneo),Mekong, Hong Ha (Indo-China Peninsula), Ehujiang(Pearl River), Hangjiang (China), very heavily ladenwith terrigenous material. However, contributions ofterrigenous clasts from the straits on its northeast bor-der should not be ignored. For example, sedimen-

X. Sun et al. / Marine Geology 156 (1999) 211–226 213

tation traps put in the northern part of the SCS(18º280N, 116º010E, 3750 m water depth, Sept. 1987–March 1988) have shown that the strong northeastwinter monsoon is able to cause the transport of largeamounts of terrigenous material into the SCS throughthe Taiwan and Bashi Straits (Jennerjahn et al., 1992).

The sea surface circulation is driven mostly by theEast Asian Monsoon. With the seasonal alternation ofprevailing wind, i.e. southwest in summer and north-east in winter, the SCS displays a transbasin pattern ofsurface currents with opposite directions in summerand winter. In summer, surface water of the tropicalIndian Ocean flows into the SCS northward and theninto the Pacific, mostly through Bashi Strait (Fig. 2a).In winter, the northeast wind drives the tropical andsubtropical Pacific waters together with colder waterof the longshore current to the SCS through Bashi andTaiwan Straits and then across the Sunda Shelf intothe Indian Ocean (Fig. 2b) (Wang et al., 1995).

The SCS is situated in the tropical and subtrop-ical areas of the northern hemisphere where hightemperature and precipitation enable rich and diversevegetation to grow on the surrounding land (Fig. 3).

Tropical rainforest grows at lower altitudes on thetropical islands such as Borneo and Sumatra and on

Fig. 2. Predominant wind and marine current patterns for the South China Sea, compiled from various sources including Hill (1979) andEditorial Board of Physical Geography of China (1979).

the Malaysian, Indo-China Peninsulas and Phillip-ines, where annual precipitation is >2500 mm andmean annual temperature ranges from 25º to 30ºC.The vegetation is very complex and the most com-mon genera are Dipterocarpus, Anisoptera, Shorea,Hopea and Vatica (Dipterocarpaceae) (Whitmore,1975). In the north, along the coastline of the Chi-nese continent, Hainan and southern Taiwan are alsoscattered tropical rainforest patches, probably not asdiverse as that in the southern islands as a result oflower annual precipitation (1800–2500 mm with ashort dry season usually <1 month) and lower meanannual temperatures (ca. 24ºC). Tarrictia parvifolia(Sterculiaceae), Vatica astrotricha, Sarcosperma lau-rinum (Sapotaceae), Diospyros hainanensis (Com-bretaceae), and Castanopsis hystris are among of themain components of this forest.

Tropical seasonal rainforest occurs in theIndo-China Peninsula, where annual precipitationvaries from 1000 to 2500 mm and where thereis a dry season during winter and spring. Xyliaspp. (Leguminosae), Tectona grandis (Verbenaceae),Hopea pierri and Parashorea stellata (Diptero-carpaceae) are characteristic of this forest. The shrublayer is rich in Palmae, wild banana and wild citrus


Fig. 3. Map of the vegetation surrounding the South China Sea, compiled from Whitmore (1975) and Wu (1980). Legend: a: cultivatedland; b: tropical rain forest; c: seasonal rainforest; d: tropical and subtropical grassland; e: subtropical evergreen forest; f: tropical andsubtropical conifers; g: mangroves.

(Whitmore, 1975). The southern part of the Chi-nese continent also has tropical seasonal rainforestalong the coast, where the climate is drier and coolerthan in the South Asian islands (annual precipitation1500–2000 mm and mean annual temperature 22º–25ºC). The forest has many Moraceae, Sapindaceae,Euphorbiaceae, Myricaceae, Lauraceae, Meliaceae,Litchi chinensis (Sapindaceae), Elaeocarpus spp.(Elaeocarpaceae), Albizia spp. (Mimosaceae), andQuercus and Castanopsis spp. (Fagaceae).

Mountain vegetation is abundant and diverse inthe regions around the SCS. In Sumatra, for exam-ple, the lower montane rainforest (1000–1800 m) isdominated by the Fagaceae (Castanopsis, Lithocar-pus, Quercus), above 1800 m Podocarpus spp. areabundant, while above ca. 2800 m is dwarf forestrich in Ericaceae and Myrica javanica (Myricaceae)(Whitmore, 1975). Another example is Hainan Is-land where, in the low mountains (<1000 m), oakforest with Castanopsis and Lithocarpus as well as


Podocarpus imbricatus is prevalent. Above 1000 mDacrydium pierrei appears together with more tem-perate elements such as Carpinus, Nyssa and Acer.On the top of the mountains, these are replaced by thedwarf forest of Enkianthus quinqueflorus (Ericaceae),Rhododendron simiarum and Pinus kwangtungensis.However, most of the montane rainforests in Chinaare highly disturbed with secondary taxa such as Al-chornea trewioides, Mallotus paniculatus and Maca-ranga (Euphobiaceae), etc., being their main compo-nents (Guangdong Institute of Botany, 1976).

In southern China, there are tropical and subtropi-cal coniferous forests of Pinus (Pinaceae), Podocar-pus (Podocarpaceae) and Cephalotaxus (Cephalotax-aceae) with Dacrydium (Podocarpaceae) (only onhigh mountains of Hainan), most of which are mixedwith broad-leaved trees. Only a few species of Pinus(P. ikedai, P. kwangtungensis) and Podocarpus nagiare able to form pure coniferous forest on Hainan andthe Leizhou Peninsula. In southeast Asia as a whole,pine is very widely distributed, some species extend-ing far southward into the tropics, with P. kesiya andP. merkusii reaching the Malesian archipelago (Whit-more, 1975). Moreover, there are also large areas ofpine plantation in the southern part of the continent.

Mangroves are commonly found around the south-ern SCS, particularly along the coast of the MalaysianPeninsula and adjacent islands, but are only scatteredaround its northern part, such as in suitable loca-tions along the coastline of Hainan, Taiwan and thesouth-eastern coast of the continent. Some species ofRhizophora, Sonneratia, Avicennia, Zylocarpus andBruguiera often occur in the mangroves. Coral reefislands in the SCS are usually covered by luxurianttrees, shrubs and herbs, such as Cocos nucifera (Pal-mae), Ipomoea pes-caprae (Convolvulaceae), Piso-nia alba (Nyctaginaceae), Euphorbia atoto and Phyl-lanthus niruri (Euphorbiaceae), etc.

Subtropical forest occurs on the hills and table-lands of southeast China between 24º and 25ºNlatitude, where the warm and humid climate (annualprecipitation >1500 mm and almost no dry season)enables the forest to be evergreen. The principal fam-ily is Fagaceae (Castanopsis spp. and Quercus spp.):Lauraceae, Theaceae, Magnoliaceae and Hamameli-daceae are also important there. Some tropical ferns(Cyathea spp.) and wild bananas also grow in theforest.

The whole area around the SCS is very denselypopulated, so the forests have been subjected toa great deal of disturbance and destruction for along time. For example, in south China, borderingthe sea, there are large areas of tropical grasslandwith scattered trees and shrubs and subtropical hillyor montane grassland dominated by Dicranopterislinearis as well as grasses with sparsely dispersedPinus massoniana. Most grasslands are consideredto be secondary, resulted from human activities, suchas burning, cutting and hunting.

3. Materials and methods

The sediment samples on which this paper isbased were obtained on ‘Sonne Cruise 95’ fromthe continental slopes and deep-sea basin. Waterdepths of the sample stations range from 329 to4307 m (Table 1). The samples were taken fromthe very tops of the 45 box cores (box sized as0:5 ð 0:5ð 0:6 m3). Only 28 pollen counts are usedin this paper due to the absence of pollen in theremaining samples mainly from the deep-sea basin,sites in the eastern part close to Philippines, and nearthe Nansha coral reefs. Two samples (nos. 17951,17952 in Table 1) on the western side near Vietnamcontain such high concentrations of diatoms thatmake pollen counting impossible (Fig. 1). Table 1shows the locations of sample stations, their waterdepths and pollen counts. Percentage pollen data ofthe surface sediment samples from southern Nansha(south of 6ºN latitude) are incorporated into thediscussion of the percentage pollen results and indrawing the pollen percentage isopoll maps (Shen etal., 1991).

Pollen preparation was carried out in the Labora-tory of the Institute of Palynology and QuaternarySciences, Gottingen University and followed its tech-niques for processing Quaternary marine samples,including the use of hydrochloric and hydrofluoricacids to remove carbonates and silicates. The ma-terial remaining after the cold hydrofluoric reactionwas sieved through a 10 µm mesh in an ultrasonicbath.

Pollen concentration values were calculated us-ing the exotic Lycopodium tablet technique and areexpressed as numbers of pollen grains per gram of


Table 1Sample stations, locations, water depths (Sarnthein et al., 1994), and pollen counts for surface sediment samples

Sample station Location Water depth Arboreal pollen Nonarboreal pollen Spores(m) (grains) (grains) (grains)

17940 20º07.00N, 117º23.00E 1728 193 8 18517938 19º47.20N, 117º32.30E 2835 332 4 101717937 19º30.10N, 117º40.00E 3428 118 0 12417924 19º24.70N, 118º50.80E 3438 186 3 12617929 20º40.90N, 115º42.00E 371 187 31 23617930 20º20.00N, 115º46.90E 629 169 16 21217931 20º06.00N, 115º57.80E 1005 256 3 8917934 19º01.90N, 116º27.70E 2665 124 0 12217935 18º52.70N, 116º31.60E 3143 142 5 111917928 18º16.30N, 119º44.70E 2486 280 3 12917927 17º15.00N, 119º27.20E 2800 286 22 26417942 19º20.00N, 113º12.10E 329 185 12 18717943 18º57.00N, 117º33.20E 917 142 8 69217944 18º39.50N, 113º38.30E 1219 159 7 45017945 18º07.60N, 113º46.60E 2404 185 7 123117948 16º42.50N, 114º53.80E 2841 185 6 152617922 15º25.00N, 117º27.50E 4221 0 0 017923 15º08.30N, 117º25.20E 1839 0 0 017953 14º35.80N, 115º08.60E 4307 0 0 017950 16º05.60N, 112º53.80E 1868 80 5 75017954 14º45.50N, 111º31.60E 1517 198 8 40617955 14º07.30N, 112º10.60E 2404 107 8 25417956 13º50.90N, 112º35.30E 3387 68 22 29717958 11º37.30N, 115º04.90E 2581 57 14 27917959 11º08.30N, 115º17.20E 1957 80 19 56017957 10º53.90N, 115º18.30E 2197 66 15 60117960 10º07.20N, 115º33.50E 1707 89 14 32717961 08º30.40N, 112º19.90E 1795 44 24 17817964 06º09.50N, 112º12.80E 1556 64 37 48517965 06º09.40N, 112º33.30E 889 74 27 66617963 06º10.00N, 112º40.00E 1233 83 17 336

sediment dry weight. The percentages of total ar-boreal and herbaceous pollen and fern spores werecalculated on the sum of all pollen and spore taxa,while the percentages of individual taxa of trees,herbs and ferns were estimated on their group to-tals.

4. Results

From the 28 samples used in the study, about 72pollen taxa (Appendix A) were identified with only25 taxa occurring in more than 20% of the samples.Pollen concentrations and relative abundances werecalculated and summarized by isopoll maps.

4.1. Pollen and spore concentration

4.1.1. Total concentration (Fig. 4)Maximum pollen concentration (Fig. 4a) occurs

on the lower part of the continental slope in thenortheastern part of the SCS, adjacent to the Taiwanand Bashi Straits. The high concentration stretchesas a saddle from NE to SW, with the peak abundance(443,900 grains=g) appearing at its extreme northernend (station 17924). North of this strip, even at thosesample sites situated on the upper part of the slopeand closer to the mainland, pollen concentrationis lower, averaging 5320 grains=g (highest 26,100grains=g). To the south of the strip, spores andpollen are almost absent. Another area with high


Fig. 4. Maps of pollen concentration isopolls (103 grains=g dry sediment) for (a) total; (b) trees; (c) herbs, and (d) ferns.

pollen concentration is found in the south of themarine realm, clustered on the northern slope of theLuconia shoals north of Borneo, but compared withthe northern SCS, pollen concentrations are muchlower, the maximum value only one tenth of that ofthe northern centre. Pollen concentration normallydecreases northward off the coast, and extends downto 500 grains=g in the Nansha island region northof 9ºN. West of Luzon, the pollen concentration (in

station 17927) is very unusual (Fig. 4a) but the lackof adjacent data prevent explanation.

The distribution patterns of tree pollen (Fig. 4b)and fern spore taxa (Fig. 4c) are the main determi-nants of the total distribution pattern of pollen andspores, although their values on the northern up-per continental slope are rather erratic. Herb pollenseem to decrease seaward from all directions (>200grains=g to <30 grains=g).


4.1.2. Pinus (Fig. 5a)Pinus is widely spread in the northern tem-

perate zone but only two species, Pinus kesiyaand P. merkusi, extend southward to 20ºS (Kowal,1966; Cooling, 1968). Accordingly, the great major-ity of pine pollen is concentrated in the north of the

Fig. 5. Maps of pollen concentration isopolls (103 grains=g dry sediment) for (a) Pinus; (b) Podocarpus; (c) Dacrydium, and (d) Quercus.

SCS, largely between 16ºN and 19ºN and more than300 km from the coast. The highest concentration isnear Bashi Strait (50,800 grains=g), whereas all thesamples in the south are much lower, mostly <250grains=g, except near Borneo where values up to1180 grains=g were recorded.


4.1.3. Podocarpus (Fig. 5b)Podocarpus now grows all around the SCS reach-

ing as far as the Himalayas and Japan from its centrein the south (Florin, 1963). Coinciding with thepresent distribution, the greatest number of Podocar-pus pollen occurs southwest of the Taiwan Straitbut decreases southward, eastward and northwest-ward. Podocarpus pollen is also localized (>1000grains=g) in other three offshore areas, namely Lu-zon, Indo-China and Borneo, but sharply decreasesto 100 grains=g seaward.

4.1.4. Dacrydium (Fig. 5c)Dacrydium trees are ubiquitous in the tropical ar-

eas of the southern hemisphere, and extend north ofthe equator as far as Hainan Island (Florin, 1963).As a result, the maximum pollen concentration ofDacrydium (1720 grains=g) occurs south of 7ºN,close to Borneo. Another high concentration stripcrosses the northern SCS from SW to NE. Althoughthis coincides with the high concentrations of totalpollen and spores, the gradient is in the reverse direc-tion, values falling quickly to zero northeast from themaximum at Macclesfield Bank (16º–18ºN). Almostno Dacrydium grains were found in sediments fromthe eastern or central parts of the SCS.

Fig. 6. Maps of pollen concentration isopolls (103 grains=g dry sediment) for (a) Dicranopteris, and (b) tropical complex.

4.1.5. Quercus (Fig. 5d)Quite different from other taxa, the distribution

of Quercus pollen is very simple, clustering alongthe north and south margins of the SCS. Pollenconcentrations reach>100 grains=g in both areas butdecrease uniformly offshore to <10 grains=g. Fromthe trend of the 100 grains=g isopoll in the north,Quercus pollen concentration is probably controlledby rivers such as the Pearl River.

4.1.6. Dicranopteris (Fig. 6a)The distribution pattern of Dicranopteris spores

is similar to that of the total pollen concentrationexcept that, along the northern continental margin,the spore concentration decreases off the coast atfirst and then rises to much higher values at greaterdistance.

4.1.7. Tropical components (Fig. 6b)Since the vegetation in tropical rainforests is so

diverse with most species having low pollen pro-duction and mostly growing as scattered individuals,the pollen concentrations of many typical taxa arevery low. Consequently, the pollen concentrationsof all tropical components (Appendix A), exclud-ing Quercus, are summed to give a single isopoll


map. The relatively common taxa are Gesneriaceae,Elaeagnaceae, Castanopsis, Euphorbiaceae, Myrsi-naceae, Moraceae, Engelhardtia (Juglandaceae) andLiquidambar (Hamamelidaceae). The greatest num-ber of tropical pollen (>20,000 grains=g) occurs inthe offshore area in the south and northeast. Never-theless, some northwestern stations have concentra-tions between 100 and 1600 grains=g although fewreach 5000 grains=g.

4.2. Pollen and spore percentages

Among the spore and pollen assemblages, fernspores (Fig. 7) predominate. About 85% of all sam-ples contain >50% fern spores and 44% of the

Fig. 7. Maps of spore percentage isopolls (based on the sum of total pollen and spores).

samples have >70% ferns. The relative frequency offerns increases uniformly offshore to >70% alongboth the northern continental slope and the Luco-nia shoals. The subdominant components are trees.The percentage of trees reaches 40% in the northern,southern and eastern margins of the SCS but dimin-ishes seaward to 10% around the deep-sea basin andfinally to zero within it. In 88% of the samples, herbscontribute <10% of the total: in the southern part,herbs are relatively more abundant than elsewherebut everywhere have higher concentrations near theshores.

Pinus is most common among tree pollen(Fig. 8a). In the northern part of the SCS it reaches>80% in most of the samples with a maximum of


Fig. 8. Maps of pollen percentage isopolls for (a) Pinus, (b) Podocarpus, (c) Dacrydium, and (d) Quercus (based on the sum of treepollen).

98%, but in the south values are <10%. Representa-tion of Pinus increases off the coast reaching highestvalues on the continental slope. Unlike Pinus, thehighest percentage (>60%) of tropical components(excluding Quercus and mangroves) (Fig. 9a) occursin the south of the region very close to Borneo, fromwhere it decreases seaward to 1% at the edge of

the deep-sea basin. The percentage of Podocarpus(Fig. 8b) is relatively high adjacent to the south-east coastline and gradually decreases seaward. Thesame pattern exists in the northern and eastern partsbut high abundances are restricted to water depths>2000 m in the northwest. The variation within per-centages of Quercus (Fig. 8d) is more or less the


Fig. 9. Maps of pollen percentage isopolls for (a) tropical complex (excluding Quercus and mangroves), and (b) mangroves (based on thesum of total tree pollen).

same, but the peak abundances lie south of 6ºN: al-most no Quercus pollen is found in the extreme east.Both mangroves (Fig. 9b) and Dacrydium (Fig. 8c)diminish obviously northeastward from maxima of10% south of 7ºN. Mangrove pollen are absent innorthernmost sites, and pollen of Dacrydium form<1% of the total north of 19ºN. From the coast, therelative frequency of Dacrydium increases gradually,similar in that respect to Pinus and ferns.

5. Discussion

The distribution pattern of pollen concentrationis quite different between the northern and southernSCS. The maximum concentration of palynomorphsof trees, herbs and ferns occurs in the north, adjacentto the convergence of the Taiwan and Bashi Straitsrather than the estuaries of big rivers. Consistent withthe currents in winter (Fig. 2), the tongue of isopollsextends southwestward from the area with the high-est concentration. Measuring lithogenous particle in-flux (Jennerjahn et al., 1992) by sediment traps at1000 and 3000 m water depth in the north-centralSCS (18º280N, 116º010E in 3750 m water depth), Suand Wang (1994) show that the maximum sediment

influx in this region occurs during winter (Nov.–Jan.), when runoff from the adjacent rivers such asthe Pearl River is at a minimum (Editorial Boardof Physical Geography of China, 1979). They there-fore postulate that quantities of terrestrial particlesare brought to the SCS by strong winter monsoonwinds and marine currents through the Taiwan andBashi Straits. Pine trees bloom during the earlyspring when the NE winter monsoon is still verystrong, so this can also account for the high concen-tration of pine pollen in the northern area: aeolianand current transport are primarily responsible for itsdistribution. In the south, the concentration of pollenuniformly decreases with distance from the shore orwith depth of water, which implies that it probablycomes mainly from adjacent islands, such as Borneo.The rivers running into the SCS from Borneo arerelatively small but very energetic so a large amountof terrestrial material, including pollen, is dischargedfrom them. Hence, the pollen distribution pattern inthe south is more a result of fluvial and offshorecurrent transport.

Concentrations of individual pollen taxa are dif-ferentially affected by the above factors. The north-eastern winter monsoon and monsoon-forced cur-rents are the main factors controlling the transport


of those pollen types adapted to wind transport andwater flotation, such as Pinus and Dicranopteris.Isopolls of pine pollen and fern spores more or lesscoincide with the orientation of the winter monsoonand sea currents. Pinus is a large pollen producer andits pollen grains are easily dispersed by wind and onwater surface and is over-represented in almost allpollen assemblages. Pinus blooms in early springwhen the winter monsoon from the northeast is stillpowerful and its pollen grains are carried to the SCSby wind and longshore currents through the Taiwanand Bashi Straits. Fern spores are produced in enor-mous numbers and, adapted to flotation, thus seemto be dispersed more easily by water. In HangzhouBay, percentages of fern spores increase obviouslyfrom the supratidal to the subtidal zone (Yang andChen, 1985). Dicranopteris is a fern which grows inopen places especially following forest clearance. Inthe south of China it occupies large areas of exposedhills. Transported by long-shore currents, its sporesare concentrated on the northern continental slopeof the SCS. Podocarpus is similarly distributed withthe exception that, besides a high concentration men-tioned above, its pollen grains are localized in placesadjacent to Luzon to the east, Indo-China to the westand Borneo to the south, indicating that fluvial andoffshore currents also play an important role in itsdispersal.

By contrast, pollen grains of tropical and sub-tropical broad-leaved trees found in the SCS aredispersed mainly by fluvial transport. Thus, Quercusis found in the greatest quantity some distance offthe mouth of the Pearl River, reflecting the influenceof fluvial transport. The distribution of herbaceouspollen may be due to the combined effects of wind,currents and rivers.

From work carried out in the delta of the HanjiangRiver, sediments during the Holocene are dominatedby Castanopsis, Lithocarpus and Quercus, while therelative abundance of Pinus pollen is only 10% andno Podocarpus pollen occurs, although trees of Pi-nus and Podocarpus occur at many places upstream(Zheng and Li, 1992). This supports our sugges-tion that conifers e.g. Pinus and Podocarpus, aretransported less by rivers than Quercus pollen.

In many cases fluvial transport is a very importantfactor in determining pollen distribution in marinesediments (Heusser, 1988). In the SCS, the fluvial

role is not significant in comparison with the effectsof wind and sea currents. The strong winter monsoonand sea currents bring enormous numbers of airborneand buoyant palynomorphs into the sea and therebydiminish the apparent importance of the fluvial com-ponent. The fact that the samples were collected faroffshore under deep water might also have affectedthe results (cf. Melia, 1984).

In addition, the present-day distribution and abun-dance of vegetation affects the concentration of in-dividual pollen taxa. For the tropical and subtrop-ical pollen complex, the high concentrations occurmostly in the south and east which are largely occu-pied by tropical rainforests, but on the northern con-tinental slopes, where other taxa are most abundant,the concentrations are very low, even zero. Tropicalevergreen and seasonal rainforests are largely re-stricted to quite small areas south of 18ºN in China,while rainforest in particular, is widely distributedin Borneo, Sumatra and New Guinea. This is themain determinant for their pollen distribution pat-tern. Pollen grains of Dacrydium also appear to bevery restricted to the area where the parent plant oc-curs (Fig. 8): since Dacrydium does not grow northof 20ºN, most Dacrydium pollen grains are found inthe south.

Compared with pollen concentration, relativeabundance is more closely related to the compo-sition of terrestrial vegetation (Heusser and Balsam,1977; Mudie, 1982; Mudie et al., 1994). Such rela-tionships are commonly found in most pollen taxain the SCS though they are transported in differentways.

As mentioned by Muller (1959) in his Orinocodelta study, the pollen distribution pattern of man-grove shows very high values within the source area.Study of pollen distribution from NW Africa alsorevealed a close relationship between the distributionof Rhizophora and the distribution of its pollen inmarine sediments (Hooghiemstra et al., 1986). Sucha situation also occurred in the SCS. The percent-ages of mangrove pollen (Fig. 9) seems to correlatedirectly with the distribution of its source vegetation.Mangrove grows along the coast line of the south-ern SCS, especially in Sumatra and southwesternIndo-China but only rarely on the northern coast.Even though pollen grains of Rhizophora, the mainspecies in mangroves, are very small and easily


transported over a long distance by wind (Muller,1959), the high percentage of mangrove pollen (10–20%) is restricted to the southern SCS. Most ofthe pollen are derived from the nearby source ar-eas. It seems that, as suggested by Hooghiemstraet al. (1986), mangrove pollen transport by watercurrents is relatively important. Though low in pro-duction, tropical and subtropical pollen seems to bepresented in much higher proportions adjacent tosouthern islands occupied by tropical rainforests anddecreases northward. Both Podocarpus and Dacry-dium are principal components of montane evergreenrainforests. In the south they grow in different foresttypes but on the northern continental margin, Dacry-dium is restricted to the high mountains of HainanIsland while patches of Podocarpus forest extendfurther north. The relative importance of source veg-etation is reflected by the isopolls of Podocarpus andDacrydium; Podocarpus forms >40% and Dacry-dium nearly 20% adjacent to major areas of tropicalevergreen forest but these taxa are only locally im-portant in the north.

The relative abundance of Pinus (Fig. 8) is ex-tremely high in northern areas, part of which can beascribed to the existence of temperate conifers andplanted pine trees on subtropical hills and their vo-luminous production of pollen. Even in areas wherepine trees are absent, e.g. near Borneo, the percent-age of pine pollen is still >20%. Since pine pollendispersal is relatively efficient in both eolian andfluvial transport (Heusser, 1988), the extension ofthe distribution area of Pinus pollen grains beyondthe area of present-day occurrence of pine forestin the SCS thus probably indicates transport of thepollen by wind and sea currents, as suggested byHeusser and Balsam (1977) on the basis of Pacificcoast data. Similar observations on the effect of eo-lian and marine current transport of pine pollen werealso made by Mudie (1982) from eastern Canadaand Traverse and Ginsburg (1966) on the Great Ba-hama Bank. A large input of pine pollen by thewinter monsoon and sea currents is the direct causeof the high percentages of Pinus pollen. Thereforethe contribution of pollen grains of other taxa witha northern distribution, such as Quercus, is verymuch reduced. Quercus is dominant in both southerntropical montane rainforest and northern subtropicaland temperate forests, yet the percentage of Quer-

cus near Borneo is 10 times higher than that inmost northern areas. This difference is the effectof the high representation of Pinus in the north. Infact there is a sufficient correspondence between thedistribution area of Quercus forest and the distribu-tion area of its pollen in the SCS. It may also beconcluded that there is a good correlation betweenareas with relative abundance of Podocarpus, Dacry-dium and tropical pollen grains and their sourceareas.

6. Conclusions

Abundant pollen grains and spores have beenfound in most of the analyzed surface sedimentsamples from 329 to 4307 m water depth. Pollenconcentration decreases markedly below about 3500m water depth and becomes extremely low in thecentral deep-water basin below 4000 m. The pollenassemblages in most of the deep-sea samples havemany taxa in high concentrations and, therefore,make pollen analyses in the SCS very promising forpalaeoenvironmental studies.

The northern part is distinguished by very highconcentrations of pine pollen and fern spores whichare adapted to wind transport and water flotation.Their distribution patterns imply that they werebrought by winter monsoon and sea currents forcedby it from large and regional source areas. By con-trast, for most pollen from tropical and subtropicalbroad-leaved trees, fluvial transport is more respon-sible for their distributions.

In the southern part of the SCS, pollen of tropicaland subtropical broad-leaved trees predominate andpollen concentrations are much lower. The greatestconcentrations occur in the offshore areas north ofBorneo and decrease toward deep water, suggestingfluvial transport from relatively local sources on ad-jacent islands (e.g. Borneo). The high proportions oftropical plants, mangroves and Dacydium in pollenassemblages correspond well with the distribution ofthe vegetation on the surrounding islands.

Understanding the relationship between modernpollen distribution in surface sediments and the dis-tribution of source vegetation is essential for theinterpretation of fossil pollen assemblages in theSCS in terms of palaeoclimate and palaeovegetation.


Acknowledgements

This study is the result of the joint project‘Monitor Monsoon’ of Kiel University, Germanyand Tongji University, China. The laboratory workand pollen counts were completed in the Instituteof Palynology and Quaternary Research, GottingenUniversity, and financially supported by the Ger-man Ministry of Education, Science and Technology.The National Natural Science Foundation of China(Grant No. 49732060) and a key grant of the ChineseAcademy of Sciences supported part of the researchactivities performed in China.

Appendix A

Identified pollen taxa from surface sediment samples in the South China Sea

Tropical and subtropical components Temperate components Alpine conifers Herbs Ferns

Podocarpaceae Fagaceae Taxodiaceae Pinaceae Asteraceae DicranopterisPodocarpus Quercus Abies ArtemisiaDacrydium Castanopsis Ulmaceae Picea CyatheaPhyllocladus Ulmus Pinus ChenopodiaceaeDacrycarpus Tsuga HemenophyllumJuglandaceae Myricaceae Fagaceae GramineaeCarya Myrica Fagus CeratopterisEngelhaldtia Juglandaceae Cyperaceae

Myrsinaceae Pterocarya AngiopterisEuphorbiaceae Juglans CampanulaceaeMallotus Gesneriaceae Betulaceae LygodiumMagnoliaceae Alnus CaryophyllaceaeMagnolia Hammamelidaceae Betula Pteris

Altingia Corylus LabiataeLiquidambar Carpinus Selaginella doederleiniiElaeagnaceae Plantaginaceae

Moraceae Araliaceae Aquifoliaceae PlantagoPadanaceae Meliaceae Ilex Umbelliferae Aleuritopteris subargenteaPandanus

Palmae RanunculaceaeMimosaceae Thalictrum Stenochlaena type

SapodaceaeSolanaceae Polygonaceae

Rubiaceae Polygonum Other typesPiperaceae

LecythidaceaeAncistrocladaceaeAncistrocladusRhizophoraceaeRhizophoraSonneratiaceaeSonneratiaOleaceaeRutaceae

We sincerely acknowledge Prof. M. Sarnthein andProf. Wang Pinxian for providing research samplesand encouraging discussion and advice. Dr. WangLuejing is indebted for his kind assistance withsampling and dating. We also wish to sincerelythank Prof. D. Walker, Prof. H. Hooghiemstra andProf. P.A. Kershaw for reviewing the manuscript andassistance with the English. Mrs. Hongsernant issincerely thanked for arranging the senior author’svisit to Germany.


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