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Science in China Ser. D Earth Sciences 2004 Vol. 47 No. 1 30—36 Palynological record during the Pleistocene (between 1.05
Ma and 0.36 Ma) from ODP1144, northern South China
Sea
1. Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China; 2. Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; 3. Key Laboratory of Marine Geology, Ministry of Education, Tongji University, Shanghai 200092, China Correspondence should be addressed to Huang Fei (email: huangfei@jlonline.com) Received September 12, 2002; revised February 10, 2003 Abstract This paper presents the pollen record from the lower section of ODP1144 (depth501.3—225.7 m, ca. 1.05—0.36 Ma). Two pollen zones (PA and PB) and eleven pollen subzonesare recognized. Within zone PB, the 11 pollen subzones (PB21—11) are defined according to thepine, fern and herb variations, and are equivalent to the marine isotope stages 21—11 (MISs21—11). The interglacial periods are typified by an increase in pine pollen and fern spores, and adecrease in herbaceous pollen, while the patterning during the glacial periods is just the opposite.
During the interglacial periods, pollen assemblages were dominated by pine similar to those ofthe present day, suggesting that the paleoenvironment of the interglacial periods was similar tothat of the present day, whereas the glacial periods are marked by an increase in herbaceouspollen, mainly Gramineae and Cyperaceae, indicating that grassland covered the exposed con-tinental shelf when sea level declined. Increased Artemisia percentages and the highest pineinflux during MIS12 may result from a stronger winter monsoon.
Keywords:
pollen record, Pleistocene, ODP1144, northern South China Sea.
DOI: 10.1360/02yd0045
Marine pollen, with the characteristics of a long, vegetation variations during interglacial and glacial continuous and chronologically controlled proxy, pro- cycles in the study area. A pollen record of the upper vides ideal data for better understanding the terrestrial section of Site 1144 (depth 225—0 mcd (mcd: meter vegetation response to climate change in Quaternary of composed depth, the depths of samples are used in interglacial-glacial cycles[1—5]. Until now, the high- mcd, but for short as m)) has been published by Sun et resolution pollen sequences around the South China al.[8] Here we present the preliminary pollen analyses Sea primarily document the last four glacial- of the lower section (depth 501.3—225.7 m, ca.
interglacial cycles since MIS 10[6,7], while those prior to MIS 10 are rare. Therefore, the high-resolution pol- Materials and methods
len analyses of deep sea sediments from ODP1144since 1.05 Ma can provide a unique opportunity to reveal terrestrial (especially exposed continental shelf) situated in the southeast of the Dongsha Islands on the Palynological record during the Pleistocene from ODP1144 northern margin of South China Sea at the water depth in case of huge amount of the latter. The percentages of 2037 m. The sediments of the site are mainly com- of each group and individual taxa were calculated posed of gray green clay. The chronological frame- based on the terrestrial seed plant pollen sum[8]. Exotic work for ODP1144 was established based mainly on Lycopodium tablets were added in order to calculate the planktonic stable oxygen isotope stratigraphy, bio- pollen concentration (grain/mL), and the age mode of stratigraphy (including mainly calcareous nannofossils, pollen influx (grain/cm2Ca−1) was calculated by linear planktonic and benthic foraminifera) and a Pleistocene interpolation. The average resolution of sample was ca.
microtektite abundance layer[9]. Based on the latest δ 18O data of Globigerinoides ruber1), the age of the core base has been estimated as 1.05 Ma. The mainbiostratigraphic events include the following: The last 228 pollen samples were taken at the depths of appearance of calcareous nannofossils (i.e. small between 501.3 m and 225.7 m in the lower section of Gephrocapsa Acme, Reticulofenestra asanoi, and Site 1144. About 150 pollen taxa were identified. Ex- Pseudoemiliania lacunose) at depths of 500.7, 422.7 cept Pinus pollen, arboreal pollen were classified into and 288.7 m, are dated to be 1.01, 0.90 and 0.46 Ma, the following ecological groups: (i) temperate mon- respectively. The last occurrence of benthic fora- tane conifers (TemMC, including Picea and Abies); (ii) minifer Stilostomella at 365.5 m depth is estimated to tropical montane conifers (TroMC, Podocarpus, Da- be 0.75 Ma, and the first occurrence of planktonic pink crydium, Dacrycarpus and Phyllocladus); (iii) tem- Globigerinoides ruber at 261.3 m is dated as 0.40 perate deciduous broadleaved taxa (TDT, Quercus, Betula, Alnus, Ulmus, Juglans, etc.); (iv) lower mon-tane rainforest taxa (LMRT, evergreen Quercus, Cas- The δ 18O record of G. ruber shows that there are tanopsis / Lithocarpus, Altingia, Myrica, etc.); (v) oxygen marine isotopic stages 29—11 in the lower tropical and subtropical taxa (TST, Tilia, Melia, Ilex, part of Site 1144 at depths of between 501.3 m and Elaeocarpus, Araliaceae, Sapindaceae, Gesneriaceae, 225.7 m with stages 21—11 between 405.4 m and Palmae, Euphorbiaceae, etc.). The herbaceous types 225.7 m1). Microtektite occurs at the depth of 386.2 m are primarily composed of Artemisia, Gramineae, Cy- peraceae, etc. and the ferns of Cyathea, Davalia, Pollen extraction (10 —30 mL per sample) was Pteris, Cibotium, Hicropteris, Hymenophyllum, and so completed in the Key Laboratory of Marine Geology of Tongji University following the standard method, The pollen record of the lower part at the depths including treatment with hydrochloric and hydroflu- of between 405.4 m and 225.7 m is basically similar in oric acids to remove carbonates and silicates, followed character to that of the upper one (225—0 m). The by sieving the remaining material through a 10-µ ny- pollen assemblages are characterized by a very high lon mesh in an ultrasonic bath. Two exotic Lyco- percentage of pine and herbaceous pollen (about 67%).
podium tablets were added in each sample before The temperate deciduous types (average 10.9%) are sample preparation, each containing 12542 Lyco- the next most abundant. The tropical and subtropical (average 6.1%), lower montane rainforest (average More than 200 terrestrial seed plant pollen grains 5.6%), tropical montane conifer (average 5.4%) and per sample (not including fern spores) were counted; temperate montane conifer types (average 4.3%) show moreover, no less than 100 land seed plant pollen low percentages. In addition, the percentage of pine grains were calculated per sample except pine pollen pollen is positively correlated with that of fern spores, 1) Bühring, C., Sarnthein, M., Erlenkeuser, H., Toward a high-resolution stable isotope stratigraphy of the last 1.1 million years: Site 1144, South China Sea, 2001 (submitted to ODP Sci. Res., Vol. 184).
Science in China Ser. D Earth Sciences but negatively with herbaceous pollen. Primarily based (4.7%) progressively increases. The temperate de- on the Pinus, herb and ferns variations, two pollen ciduous broadleaved (12.3%) and tropical and sub- zones and eleven subzones, equivalent to marine iso- tropical (7.1%) pollen show a gradually increasing tope stages 21—11, are defined in the lower part of the trend. Based on the pine, fern and herb value fluctua- sequence. The software TILIA is used to plot the pol- tions, PB is divided into 11 subzones, correlated with len diagram (fig. 1). Pollen zones of the lower section of Site 1144 are briefly described below: PB21 (equivalent to MIS 21, depth 405.4—394.3 PA (equivalent to MISs 29—22, depth 501.3 m, ca. 0.88—0.82 Ma) is characterized by the first —405.4 m, ca. 1.05—0.88 Ma) is distinguished by a appearance of Phyllocladus in the tropical montane predominance of Pinus pollen (48.8%). The percent- conifers. Compared with zone PA, Pinus pollen ages of herb, fern and temperate deciduous broad- (55.2%) and fern spores (34.4%) values increase, but leaved taxa are 23%, 32.2% and 8.4%, respectively.
the herbaceous pollen percentage (20.4%) decreases, Gramineae (8.4%) and Artemisia (6.9%) are the main more particularly, Artemisia (2.3%) rather than Cy- elements of herbaceous pollen, and Cyperaceae is peraceae (3.6%). The tropical and subtropical pollen secondary, averaging 3%. Artemisia reaches 15.5% at percentage (5.3%) goes up slightly, while tropical depths of between 460.5 m and 439.8 m (ca. 0.98— montane conifers (4.1%) and temperate montane 0.95 Ma). Darcydium (6.5%) and Podocarpus (0.6%) conifers (3.1%) decline. Other types remain relatively dominate the tropical montane conifers (7.4%), while no Phyllocladus pollen occurs. In addition, temperate PB20 (equivalent to MIS 20, depth 394.3—385 montane conifers (4%) and tropical and subtropical m, ca. 0.82—0.79 Ma) is characterized by the facts that Pinus pollen (45.4%) and fern spores (27.7%) PB (equivalent to MISs 21—11, depth 405.4 decline, and herbaceous pollen (21.4%) increase —225.7 m, ca. 0.88— 0.36 Ma) is characterized by slightly, mainly represented by Gramineae (9.7%), the significant occurrence of Phyllocladus pollen. Ar- Cyperaceae (2.8%) and Artemisia (2.3%). The tem- temisia (1.5%) declines substantially but Cyperaceae perate deciduous broadleaved pollen (11.4%) value Pollen percentage diagram of the lower section (between 501.3 m and 225.7 m) of Site 1144. TemMC = temperate montane conifers; LMRT = lower montane rainforest taxa; TDT = temperate deciduous broadleaved taxa; TroMC = tropical montane conifers; TST = tropical and subtropical taxa.
Palynological record during the Pleistocene from ODP1144 goes up. The Phyllocladus pollen percentage only m, ca. 0.55—0.49 Ma) is distinguished by the strong reaches 0.6% in tropical montane conifers (5.9%).
increase in herbaceous pollen (25.2%), and decrease inPinus Gramineae (9.8%) and Cyperaceae (4.5%) still domi- 385—374.9 m, ca. 0.79—0.74 Ma), Cyperaceae (7.5%) nate the herbaceous taxa. The temperate deciduous percentage increases, but the Artemisia (0.4%) value broadleaved pollen percentage increases (18.4%).
declines sharply. Gramineae (7.6%) and Cyperaceaedominate the herbaceous pollen. Phyllocladus (1.7%), For PB13 (equivalent to MIS 13, depth 294.9 only less than Darcydium (1.9%), becomes the main —274.6 m, ca. 0.49—0.46 Ma), Cyperaceae (6.6%) element in the tropical montane conifers. The tropical rises, slightly more than Gramineae (6.3%), and and subtropical pollen value (6.3%) increases slightly.
dominates the herbaceous pollen (21.5%). Pinus pol- Pine pollen (46.1%) and fern spores (35.2%) increase, len (43.6%) and fern spores (31.9%) go up, and the and herbaceous pollen (22.3%) declines.
temperate deciduous broadleaved taxa (10.8%) drops.
Other types hold relatively steady.
For PB18 (equivalent to MIS 18, depth 374.9 —358.7 m, ca. 0.74—0.70 Ma), herbaceous pollen PB12 (equivalent to MIS 12, depth 274.6—251.3 (26.5%), dominated by Gramineae (8.8%) and Cyper- m, ca. 0.46—0.42 Ma) is distinguished by an obvious acerae (8.4%), goes up slightly, whereas Pinus pollen increase in Artemisia (5.1%). The herbaceous pollen (38.4%) and fern spores (26.2%) decline. The temper- percentage (30.2%) rises, dominated by Gramineae ate montane conifers show a small increase, averaging (14.2%) and Artemisia. Pinus pollen (27.3%) and fern 4.7%. Other types show relative stability.
PB17 (equivalent to MIS 17, depth 358.7—343.6 For PB11 (equivalent to MIS 11, depth 251.3 m, ca. 0.70—0.66 Ma) is characterized by a decrease —225.7 m, ca. 0.42 — 0.36 Ma), herbaceous pollen in herbaceous pollen (16.7%), and an increase in pine (24.6%) falls, especially Artemisia (1.1%). The per- pollen (44.3%) and fern spores (38.9%). The percent- centages of Pinus pollen (34.3%), fern spores (27.8%) ages of temperate montane conifers (3.9%) and tropi- and tropical-subtropical pollen types (8.6%) increase.
cal montane conifers (4.7%) fall, and that of temperatedeciduous broadleaved pollen (17.6%) rises.
Discussion
For PB16 (equivalent to MIS 16, depth 343.6 As explained by Sun et al.[10], pollen assemblages —325.1 m, ca. 0.66 — 0.62 Ma), herbaceous pollen in modern marine surface sediments of the northern shows a bit of increase, averaging 17.3%. Fern spores South China Sea contain much rare tropical and sub- (12.3%) fall substantially. Phyllocladus pollen only tropical as well as herbaceous pollen, except Pinus reaches 0.4% and temperate deciduous broadleaved (averaging 80%). It is, therefore, difficult to accurately reconstruct even modern vegetation on the southernmargin of the Chinese mainland based only on pollen For PB15 (equivalent to MIS 15, depth 325.1 analyses of modern marine sediments. The pollen re- —310.8 m, ca. 0.62—0.55 Ma), herbaceous pol- cord from the upper part of Site 1144[8] indicates that, len shows an obvious reduction, averaging 9.9%.
during interglacials, pollen assemblages were domi- Pinus pollen (52.4%) and fern spores (49.1%) rise.
nated by the pine similar to those of the present day; The percentages of temperate montane (8.4%) and but during glacials, pollen influx was much higher tropical montane conifer types (8.9%) go up slightly, than during interglacials. During glacials, grasslands and that of temperate deciduous broadleaved pollen covered the exposed continental shelf. It is concluded, types (10.8%) declines. Other types stay relatively therefore, that pollen spectra from Site 1144 can only provide the information for reconstructing vegetation PB14 (equivalent to MIS 14, depth 310.8—294.9 changes on the exposed continental shelf during gla- Science in China Ser. D Earth Sciences temisia, Cyperaceae and Gramineae become the maincomponents of grassland inferring a relative moist As stated above, the pollen record between 405.4 condition. As for MIS 12, increased Artemisia pollen m and 225.7 m (ca. 0.88— 0.36 Ma) follows the same results from a colder and more arid climate.
basic pattern as the upper part of Site 1144 (225— 0 m). Pine and herbaceous pollen dominate the pollen It is worth noticing that Phyllocladus in the assemblages, with distinct fluctuations throughout.
tropical montane conifers emerges and develops Interglacials are distinguished by the predominance of gradually beginning in zone PB21 (equivalent to MIS pine similar to that of the present day, from which we 21, depth 405.4—394.3 m, ca. 0.88— 0.82 Ma). Mod- infer that the conditions of the interglacials were simi- ern Phyllocladus is currently only found in the south- lar to those of the present day. Glacials are marked by ern hemisphere, with 5 species (P. alpinus, P. aspleni- an increase in herbaceous pollen, indicating that folius, P. hypophyllus, P. trichomanoids and P. toatoa) grasslands covered the continental shelf when sea extending from Tasmania to New Zealand, New level declined. In addition, evergreen forest (evergreen Guinea, Moluccas, Celebes, Borneo and the Philip- Quercus, Castanopsis/Lithocarpus, Altingia) was pre- pines[11—13]. Until now, neither Phyllocladus pollen sent. Temperate montane conifers (Picea and Abies) nor plant fossils have been documented in the Chinesemainland and Taiwan[14—16].
and tropical montane conifers (Podocarpus, Dacry- dium, Dacrycarpus and Phyllocladus) together with It is necessary to understand the processes by temperate deciduous broadleaved forest (Quercus, which terrestrial pollen and spores are transported in Betula, Alnus, Ulmus and so on) expanded in response marine environments, and where potential pollen source areas are when interpreting past vegetation andclimate changes inferred from the marine pollen re- Although the subdivision of pollen assemblages cord[10,17]. Pollen analyses of modern marine sedi- between 405.4 m and 225.7 m is arranged to be in ments in the South China Sea show that Darcydium agreement with marine isotope stages 21—11, that transport is directly influenced by its modern distribu- between 501.3 m and 405.4 m is not easy to compare tion and its pollen grains are primarily carried by the to marine isotope stages due to the low resolution of summer monsoon and ocean current[10,17]. However, the samples. However, based on the pollen records the modern distribution of Darcydium, more similar to below the depth of 405.4 m, the amounts of Artemisia, especially at the depths of between 460.5 m and 439.8 mountainous areas of the Hainan Island[18]. With the m (ca. 0.98—0.95 Ma), may be from the exposed con- help of the modern Darcydium pollen transport pattern, tinental shelf during the glacials. The Artemisia pollen we deduce that Phyllocladus pollen is also transported during MIS 20, drops sharply and is replaced by the by the summer monsoon and ocean currents. Thus, the Cyperaceae pollen. After MIS 20, Cyperaceae in- significant emergence of Phyllocladus pollen since creased progressively, and Gramineae and Cyperaceae MIS 21 indicates a stronger summer monsoon. A dominated the grassland covering the continental shelf stronger summer monsoon since MIS 21 is also sup- during the later glacials (except MIS 12, for which the ported in the herbaceous pollen, as Cyperaceae re- Artemisia percentage is high).
placed Artemisia and was favored on the grassland As indicated by Sun et al.[8], Artemisia prefers a covering the continental shelf; meanwhile, tropical and cooler and semiarid environment. A high percentage of subtropical forests expanded gradually. In subzone Gramineae in the pollen assemblage indicates grass- PB19 (equivalent to MIS 19) (fig. 1), high percentages land, while the high percentage of Cyperaceae implies of Phyllocladus and Cyperaceae as well as tropi- a swampy or wet environment. Before MIS 20, a large cal-subtropical fern spores are interpreted as an in- amount of Artemisia reflects a cold arid environment, crease in the strength of the summer monsoon during but after MIS 20, with the remarkable decrease of Ar- MIS 19, with warmer and wetter conditions.
Palynological record during the Pleistocene from ODP1144 Pollen analyses on modern marine surface sedi- curred both on the exposed continental shelf and on ments of the northern South China Sea demonstrate the Chinese mainland due to dry conditions. In general, the relationship between pollen mechanisms and during MIS 12, the winter monsoon became the source areas. As explained by Sun et al.[10,17], Pinus, strongest and the climate was coldest and most arid as the principal pollen element of marine sediment in the shown by the lower part of Site 1144, the temperate northern South China Sea, is concentrated at the con- montane conifers expanded, Artemisia flourished on vergence of the Bashi and Taiwan Straits, indicating the exposed, grassy continental shelf, and the intensity that it is transported into the marine environment of natural fires from the exposed continental shelf and mainly by winter monsoon and sea currents. Thus, the Chinese mainland was the strongest.
Pinus pollen influx is the best palynological proxy forevaluating the intensity of winter monsoon[5].
Conclusions
Fig. 2 shows the influx variations of main pollen (1) Based on the main ecological types, pollen types. Glacials are characterized by high pollen influx, assemblages from the lower part of Site 1144 (depth but the influx during interglacials is lower. The highest 501.3—225.7 m, ca. 1.05—0.36 Ma, corresponding to pine influx occurred during MIS 12, secondarily MIS MISs 29—11) are divided into two pollen zones and 16. The pollen influxes of temperate montane conifers eleven subzones. The subzones are correlated with (Picea and Abies) and Artemisia also show the highest marine isotope stages 21—11. Interglacials are distin- values during MIS 12. Based on the charcoal record guished by an increase in pine pollen and fern spores, between 501.3 m and 225.7 m[19], the highest influxes and a decrease in herbaceous pollen, indicating that of coarse, medium and fine charcoal particles during the paleoenvironment of the interglacials was similar MIS 12 indicate that the strongest natural fires oc- Pollen influx diagram of the main types of the lower section (between 501.3 m and 225.7 m) of Site 1144. TemMC = Temperate montane Science in China Ser. D Earth Sciences (2) Grasslands, mainly represented by Gramineae, 4. Hooghiemstra, H., Vegetational and climatic history of the high Artemisia and Cyperaceae, covered the exposed con- plain of Bogota, Colombia: A continous record of the last 3.5 tinental shelf when sea level lowered during the gla- million years, Dissertactioes Botanicae, 1984, 79: 1—368.
5. Hooghiemstra, H., Agwu, C., Changes in the vegetation and trade cials. The components of grassland varied signifi- winds in equatorial northwest Africa 140000—70000 yrB.P. as cantly throughout the lower section of Site 1144. Be- deduced from two marine pollen records, Palaeogeography, Pa- fore MIS 20, Artemisia dominated the grassland; after laeoclimatology, Palaeoecology, 1988, 66: 173—213.
MIS 20, Cyperaceae replaced Artemisia, and was pro- 6. Wang, X., van der Kaars, S., Kershaw, P. et al., A record of fire, gressively increasing, Gramineae and Cyperaceae be- vegetation and climate through the last three glacial cycles from Lombok Ridge core G6-4, eastern Indian Ocean, Indonesia, Pa- came the main elements of the grassland.
laeogeography, Palaeoclimatology, Palaeoecology, 1999, 147: (3) The significant occurrence of Phyllocladus 7. Zheng, Z., Lei, Z. Q., A 400000 year record of vegetational and since MIS 21 is correlated with a stronger summer climatic changes from a volcanic basin, Leizhou Peninsula, monsoon. The summer monsoon was intensified dur- South China, Palaegeography, Palaeoclimatology, Palaeoecology, 8. Sun, X. J., Luo, Y. L., Pollen record of the last 280 ka from (4) Pinus pollen influx is the best palynological deep-sea sediments of the northern South China Sea, Science in proxy for documenting the intensity of the winter China, Ser. D, 2001, 44(10): 779—888.
monsoon. During MIS 12, the winter monsoon was 9. Wang, P. X., Prell, W. L., Blum, P. et al., Proc. ODP Init. Repts., strongest throughout the lower part of the present Site 184 College Station TX (Ocean Drilling Program), 2000, 1—77.
1144. Temperate montane conifers developed and Ar- 10. Sun, X. J., Li, X., The differences of modern pollen transport mechanism and distribution pattern between the northern and temisia flourished on the exposed continental shelf.
southern South China Sea, Science in China, Ser. D (in Chinese), Acknowledgements
This work was supported by the National Natu- ral Science Foundation of China (Grant No. 49999560) and the State 11. Sinnott, E. W., The morphology of the reproductive structure in Key Basic Research and Development Plan of China (Grant No.
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2000078503). The authors are grateful to the shipboard scientists and 12. Keng, H., On the family Phyllocladaceae, Taiwania, 1973, 18: technicians of ODP Leg184 for providing the samples for the study, and especially appreciate Dr. Lisa Kealhofer for improving the English 13. Keng, H., A new scheme of classification of the conifers, Taxon, References
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