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Chinese Science Bulletin

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Palaeoenvironmental changes from pollen record in

deep sea core PC-1 from northern Okinawa Trough,

East China Sea during the past 24 ka

XU HongYan1,4, CHANG FengMing2, LUO YunLi1 & SUN XiangJun1,3

1

State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093,

China;

2

Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071,

China;

3

State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;

4

Graduate University of Chinese Academy of Sciences, Beijing 100049, China

A pollen record of core PC-1 from the northern Okinawa Trough, East China Sea (ECS), provides in-

formation on vegetation and climate changes since 24 cal. kaBP. A total of 103 samples were paly-

nologically analyzed at 8 cm intervals with a time resolution of 230 a. Four pollen zones are recognized:

zone I (812 715 cm, 24.2 21.1 cal. kaBP), zone II (715 451 cm, 21.1 15.2 cal. kaBP), zone III (451 251

cm, 15.2 10.8 cal. kaBP), zone IV (251 0 cm, 10.8 0.3 cal. kaBP), corresponding to Late MIS 3, Last

Glacial Maximum (LGM), deglaciation and Holocene, respectively. The LGM is characterized by the

dominance of herbs, mainly Artemisia, and high pollen influx, implying an open vegetation on the ex-

posed continental shelf and a cool and dry climate. The deglaciation is a climate warming stage with

Pinus percentage increased and Artemisia percentage decreased and a rapid sea-level rise. The Holo-

cene is characterized by predominance of tree pollen with rapid increase in Castanea-Castanopsis in-

dicating the development of mixed evergreen and deciduous broad-leaved forest and a warm, humid

climate. Low pollen influx during the Holocene probably implies submergence of the continental shelf

and retreat of the pollen source area. The vegetation indicated by pollen assemblage found in this up-

per zone is consistent with the present vegetation found in Kyushu, Japan. Originating from the humid

GEOLOGY

mountain area of North Luzon of the Philippines, Tasmania and New Zealand, Phyllocladus with spo-

radic occurrence throughout PC-1 core probably suggests the influence of Palaeo-Kuroshio Current or

intense summer monsoon. The observed changes in Pinus and Herbs percentage indicate fluctuations of

the sea level, and high Pinus percentage corresponds to high sea level. Spectrum analysis of the pollen

percentage record reveals many millennial-scale periodicities, such as periodicities of 6.8, 3.8, 2.2, 1.6 ka.

East China Sea, Okinawa Trough, palynology, Kuroshio, palaeoenvironment, MIS

The topography of the East China Sea (ECS) is charac- was always below the sea level, so it was a good place to

terized by wide continental shelf area, extending up to research the palaeoenvironmental changes and palaeo-

500 km. The total area of the ECS is about 770 000 climatic evolution. There are controversies over the Pa-

km2[1]. Water depth is

Received November 25, 2008; accepted March 2, 2009; publsihed online July 27, 2009

and >800 m in the Okinawa Trough. Sea level during the

doi: 10.1007/s11434-009-0227-y

last glacial maximum (LGM) was 120 130 m lower

Corresponding author (email: ***@*****.**.**)

Supported by the National Natural Science Foundation of China (Grant Nos.

than the present[2], consequently most of the continental 40671198 and 40506015) and National Basic Research Program of China (Grant No.

shelf changed into land. However, the Okinawa Trough 2007CB815906)

Citation: Xu H Y, Chang F M, Luo Y L, et al. Palaeoenvironmental changes from pollen record in deep sea core PC-1 from northern Okinawa Trough, East China Sea

during the past 24 ka. Chinese Sci Bull, 2009, 54: 3739 3748, doi: 10.1007/s11434-009-0227-y

laeo-Kuroshio Current in previous palynological and the major species of Castanopsis, Quercus-evergreen

foraminiferal studies[3 7]: one opinion is that during the and Machilus. Above 1000 m a.s.l. grows deciduous

LGM the Kuroshio Current was not present in the Oki- broad-leaved forest dominant by Fagus, incidental by

nawa Trough but shifted to a position east of the Ryukyu Quercus-deciduous, Acer, Betula, Carpinus. Man-made

Islands[3 5] because of the land bridge between Ryukyu conifers mainly Larix leptolepis, Cryptomerica japonica,

Islands and Taiwan Island[3]; the other is just contrary[6,7]. Chamaecyparis obtuse, Pinus densiflora, Abies firma,

Kawahata et al.[6] and Deng et al.[8] revealed that it was Tsuga sieboldii, etc. develop in areas where deciduous

grassland on the exposed continental shelf of the ECS broad-leaved forest had been destroyed[10,11].

during the MIS 2. L et al.[9] considered during the last

20 ka oceanographic changes of the ECS lagged behind

the epicontinent climate changes by 1000 a through pa-

lynology and phytolith, diatom and foraminifera data.

In this paper, we present the palynological record of

gravity core PC-1 from the northern end of the ECS, and

discuss the floral evidence of terrestrial environmental

changes around the ECS continental margin and Kyushu

Island. An emphasis of our discussion will be laid on the

paleoceanographic and terrestrial environmental changes

since 24 cal. kaBP in the region.

1 General situation of study areas

PC-1 core (31 27.50 N, 128 24.80 E) is located at the

continental slope zone in the northern Okinawa Trough

at a site to the east side of Tsushima Warm Current, a

branch of Kuroshio Current (Figure 1). The core site is

150 km away from Kyushu Island of Japan, 600 km Figure 1 Map showing the present Kuroshio Current in the East

from the mainland of China. The Kuroshio Current ori- China Sea and the location of PC-1 core site (according to ref. [12]).

Also shown in + are sites of cores MD982195 (31 38.33 N,

ginates from western equatorial Pacific, flows northward

128 56.63 E) and DGKS-9602 (28 07.491 N, 127 22.13 E).

off the Philippines, enters the Okinawa Trough, flows

northeastward along the edge of the ECS continental

2 Materials and methods

shelf, and finally offsets into several branches around

29 30 N. The mainstream then turns eastward across Gravity core PC-1 was obtained by the Institute of

the Tokara Strait and flows along the southern sea of the Oceanology, Chinese Academy of Sciences in March

main islands of Japan. The branch with the ECS surface 1990 from a water depth of 590 m (Figure 1). The core

water together constitutes the Tsushima Warm Current, is 812 cm in length. The lithology is characterized by

which enters the Sea of Japan through the Tsushima

silty clay ooze (0 165 cm), clayey silt (165 410 cm),

Strait and runs along the northern Japanese coast. The

silty clay (410 610 cm) and fine silt (610 812 cm).

Kuroshio Current carries a huge amount of thermal en-

Foraminifers and bioclasts occur throughout the core,

ergy from the equatorial to mid-latitudinal regions, di-

while volcanic glass and detritus are mainly confined to

rectly influences the oceanographic setting and the dis-

123 130 cm, 315 330 cm, 735 cm and 746 748 cm.

tribution of ocean sediments and palaeoclimatic changes

A total of 103 samples were palynologically analyzed

of the ECS.

at 8 cm intervals, with 4 6 cm intervals individually

The terrigenous materials at PC-1 core mainly come

from Japan[1]. The natural vegetation on Kyushu Island is with heavy-liquid separation. First, 4 8 g dry material

characterized by evergreen and deciduous broad-leaved from each sample was added with a piece of Lyco-

forest. Evergreen broad-leaved forest mainly Fagaceae, podium spore (University of Lund, batch 483216) stan-

Theaceae and Lauraceae grows below 1000 m a.s.l., with dard containing 18583 spores as additional spore for

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calculating the total influx in the sample. Then dilute fied and 56 genera or family of pollen belong to woody

plant, 19 belong to herbaceous plant and 4 belong to

hydrochloric acid was added to remove calcareous ma-

aquatics and 22 genera or family of spore belong to

terials and hydrofluoric acid was used to dissolve sili-

ferns. The dominant species are Pinus and Artemisia.

ceous ingredient. Finally, floral ingredients were sepa-

rated using heavy liquid with the density of 2.0 g/cm3 Pollen of Picea, Abies, Betula, Castanea-Castanopsis,

Quercus, Gramineae, Cyperaceae, Compositae and

before identified with an Olympus CX31 microscope.

ARTICLES

Chenopodiaceae occur quite often, while others occur

About 200 or more pollen grains were identified for

rather rare, particularly some of the tropical-subtropical

each sample, and the pollen percentage of each species

taxa and ferns. For easier interpreting the pollen diagram,

was calculated on a cardinal number that is the sum of

several groups of taxa are presented according to their

all pollen from seed plants on land. Pollen percentage

plant ecology and modern distribution except Pinus as

and influx diagrams were drawn with Tilia software.

follows:

Foraminifers including Neogloboquadrina dutertrei

Montane conifers: Abies, Picea, Tsuga and Larix.

or mollusk shells with the diameter >250 m were

Tropical montane conifers: Podocarpus, Phyllocladus

picked for 14C dating using the National Ocean Sciences

and Taxodiaceae.

AMS Facility, Woods Hole Oceanographic Institution.

Temperate broad-leaved taxa: Quercus-deciduous,

The results show that two ages are reverse among the

eleven dataset (405 cm: 9360 50 14C aBP; 809 cm: 13 Betula, Alnus, Carpinus, Corylus, Fagus, Juglans, Ul-

650 80 14C aBP) and may not be reliable. Age calibra- mus, Salix, Acer, Tilia, Pterocarya, Rosaceae, etc.

tion was carried out by using the Calib5.1.0 soft- Tropical and subtropical taxa: Quercus-evergreen,

ware[13,14] after considering an adopted AMS 14C reser- Castanea-Castanopsis are main species, others quite

voir effect of 400 years (Table 1, Figure 2). Linear in- rare, such as Euphorbiaceae, Altingia, Ilex, Carya, Pla-

terpolation and extending of radiocarbon dates indicate tycarya, Engelhardtia, Mallotus, Palmae, Moraceae,

351 cal aBP at the core top and 24280 cal. aBP for bot- Myrtaceae, Proteaceae, Rutaceae, Theaceae, Anacardi-

tom sediments, respectively. The time resolution of pa- aceae, Araliaceae, Sapindaceae, etc.

lynological samples is 230 a and the sedimentation rate Aquatics: Alisma, Typha, Myriophyllum and Spar-

is 33 cm/ka on average. Two ash layers with ages of 6.1 ganiaceae.

14

C ka BP (123 130 cm) and 11.5 14C kaBP (315 330 Herbs: Artemisia, Gramineae, Cyperaceae, Composi-

cm) are very close to that of the K-Ah (6.3 14C kaBP) tae, Chenopodiaceae, Polygonum, Cruciferae, Thalic-

and U-Oki (9.3 14C kaBP) tuffs[15], respectively. The trum, Sanguisorba, Umbelliferae, Ranunculaceae, Ane-

calibrated ages for the two ash layers are 6.5 cal. kaBP,

mone, Liliaceae, Labiatae, Geraniaceae, etc.

12.8 cal. kaBP, respectively.

Ephedra and Nitraria represent very dry climate, so

GEOLOGY

they are specially grouped together.

3 Results of pollen analysis

Ferns: P olypodium, H icriopteris, P yrrosia, S e-

3.1 Pollen species laginella, Pteris, Lycopodium, Dicranopteris, Osmunda,

Total 103 genera or family of sporopollen were identi- Cibotium, Cyathea, Davaliaceae, Dryopteridaceae, The-

Table 1 Radiocarbon dating and sedimentation rate of PC-1core

AMS 14C age (aBP)

Depth (cm) Species Cal. age (cal. aBP) Sedimentation rate (cm/ka)

836 (793 883)*

10 1290 30

N. dutertrei

3851 (3806 3905)

66 3880 30 18.6

N. dutertrei

7496 (7452 7546)

150 7000 50 23.1

N. dutertrei

9965 (9885 10072)

222 9160 40 29.2

N. dutertrei

13600 (135**-*****)

351-*****-** 35.5

N. dutertrei

15978 (157**-*****)

500-*****-** 62.7

N. dutertrei

19693 (195**-*****)

598 Mollusc 17000 60 26.4

20888 (206**-*****)

708 Mollusc 18100 60 92.1

22340 (222**-*****)

752-*****-** 30.3

N. dutertrei

* showing the data with 1 error range.

Xu H Y et al. Chinese Science Bulletin October 2009 vol. 54 no. 20 3741

grains (g/cm) 1 a 1, with herbaceous pollen influx 80.7

and arboreal 91.4 grains (g/cm) 1 a 1, respectively.

Zone II: 715 451 cm, 21.1 15.2 cal. kaBP (MIS 2,

LGM). Herbaceous pollen increases to the dominance

(39.6% 64.9%) with average 54.5% and Artemisia

36.1%. Arboreal pollen such as Pinus (10.1%), Picea

(6.8%) and Tsuga (2.5%) decreases, while Quercus-de-

ciduous (12%), Castanea-Castanopsis (4%) and Ulmus

(1.1%) increases. Ferns are 4.9%. Other groups change

little and are still at low abundance. Montane conifers

(9.9%) decrease, but pollen influx increases up to ses-

quialter (276.4 grains (g/cm) 1 a 1), herbaceous pollen

influx 147.1 and arboreal 117.2 grains (g/cm) 1 a 1,

respectively), the sedimentary quantity is as high as zone I.

Zone III: 451 251 cm, 15.2 10.8 cal. kaBP (De-

Figure 2 Map showing sample age and sedimentation rate of

glaciation). Herbaceous pollen decreases to 37.7%

PC-1 core.

(28.6% 48.6%), lower than zones I and II, with main

lypteridaceae, etc. Most of them are difficult to identify

species like Chenopodiaceae (2.2%), Compositae (1.6%)

which genera or family belongs to, so just grouped to and Artemisia (28.4%). Arboreal pollen increases, such

Monolete-spores or Trilete-spores respectively. as Pinus (24.6%), temperate broad-leaved taxa (22.3%)

What s more, Concentricystes, Zygnema and Antho- like Quercus-deciduous (15.9%) and tropical and sub-

ceros are rarely seen in several samples. tropical taxa (10%) like Castanea-Castanopsis (5.1%)

and Quercus-evergreen (2%). While montane conifers

3.2 Pollen assemblage zones

gradually decreases to 4.8%, such as Picea (2.3%) and

Based on the pollen percentage and influx diagrams

Tsuga (1.6%). Ferns gradually increase to 7.2%. Total

(Figures 3 and 4), the core could be divided into 4 zones

pollen influx reaches to an climax (343.7 grains (g/cm) 1

from bottom to top. Zones I, II and III are characterized

a 1), and herbs (123.5 grains (g/cm) 1 a 1) decrease

by high herbaceous pollen percentage; whereas arboreal

while trees (195.4 grains (g/cm) 1 a 1) increase.

pollen predominates in zone IV.

Zone IV: 251 0 cm, 10.8 0.3 cal. kaBP (Holocene).

Zone I: 812 715 cm, 24.2 21.1 cal. kaBP (Late

Marine Oxygen Isotope Stage 3). Herbaceous pollen The most obvious change is arboreal pollen (69.7%

percentage is rather high (39.6% 56.5%) with an av- 95.2%) increases to an absolute dominance at an average

erage value 46.5%, Artemisia (32.3% on average, the of 86.3%. Herbaceous pollen decreases to 13.7% like

same below), Chenopodiaceae (4.8%), Cyperaceae Artemisia (9.8%) and Chenopodiaceae (1.2%), and ferns

(3.2%), Compositae (2.5%), Gramineae (1.3%) and grow up to 12.7% like Polypodium (1.6%). Arboreal

Thalictrum (1.1%) are predominant species. Arboreal pollen such as Pinus (37.4%) and Quercus-evergreen

pollen such as Pinus (18.6%), montane conifers (16.4%), (4%) increase and Castanea-Castanopsis sharply in-

temperate broad-leaved taxa (14%) and tropical and creases to 23.6%. While temperate broad-leaved taxa

subtropical taxa (3.9%) are major ones, such as Tsuga (16.8%) and montane conifers (2.9%) decrease. Total

(3.2%), Abies (1.6%), Quercus-deciduous (7%), Betula pollen influx decreases to 172.8 grains (g/cm) 1 a 1

(1.6%), Alnus (2.1%), Corylus (1%), Quercus-evergreen with herbaceous pollen influx 20.8 and arboreal 132.4

(1.4%) and Castanea-Castanopsis (1.6%). Another cha- grains (g/cm) 1 a 1 respectively.

racter is high percentage of Picea (11.7%) and spo- radic

occurrence of Phyllocladus. Other groups like aquatics

4 Discussion and conclusions

(0.6%), Ephedra and Nitraria (0.1%) and tropi- cal

4.1 Pollen indication of palaeoenvironmental changes

montane conifers (0.5%) are quite low. Ferns (3.3%) are

at low abundance. The total pollen flux is up to 174.7 Pollen assemblage in ECS surface sediments near PC-1

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ARTICLES

Pollen percentage diagram of PC-1 core.

Figure 3

GEOLOGY

Xu H Y et al. Chinese Science Bulletin October 2009 vol. 54 no. 20 3743

Pollen influx diagram of PC-1 core.

Figure 4

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core site is predominant by Pinus, Quercus and Cas- based on palynological data displays that steppe and

tanopsis. The abundance of evergreen broad-leaved taxa desert expanded southwards and eastwards reaching the

like Castanopsis (11%) and Quercus glauca (>10%) is northern margin of the present evergreen broad-leaved

high, while herbaceous pollen is very low[16]. This floral forest; evergreen broad-leaved forest retracted south-

assemblage is consistent with the vegetation found in wards to the present tropical zone and needle-broad

Kyushu and the pollen assemblage zone IV at PC-1 site leaved mixed forest retracted to the evergreen broad-

ARTICLES

leaved forest zone[17,18]. These results imply that grass-

and provides a reference for paleoenvironmental inter-

pretation of the pollen zones in the core. land developed in the middle-lower Yangtze area. An-

other pollen study has shown that even the Japanese Ar-

Zone I (812 715 cm, 24.2 21.1 cal. kaBP) corre-

chipelago was almost entirely covered with coniferous

sponded to Late MIS 3 with an average sedimentation

forests during the LGM, and Kyushu was covered by

rate of 31 cm/ka. The predominant are arboreal pollen

temperate coniferous-deciduous broad-leaved forests

(53.5%), including montane conifers (16.4%) and tem-

including Picea polita, Abies firma, Tsuga sieboldii, Pi-

perate broad-leaved taxa (14%). Artemisia is the main

nus, Fagus, Ulmus and Quercus and over 95% of arbo-

taxon in nonarboreal pollen. Sea level at that time was

real pollen[19]. High percentage of herbaceous and tem-

about 80 m lower than today[2] and the distance from the

perate broad-leaved taxa pollen in zone II of PC-1 might

mainland of China to PC-1 core site would be shortened

reflect different sources of pollen: herbs from the ex-

by about 400 km, with a large area of the continental

posed continental shelf and arboreal pollen from vegeta-

shelf becoming silty land. The pollen assemblage indi-

tions on Kyushu.

cates that the exposed shelf was covered with grass-

Zone III (451 251 cm, 15.2 10.8 cal. kaBP) cor-

land mainly Artemisia, and temperate needle-broad

leaved mixed forest developed at higher altitude areas responded to the Last Deglaciation with an average se-

around the area. dimentation rate of 46 cm/ka. With the decrease of

montane conifers and herbaceous pollen, Pinus, tropical

Zone II (715 451 cm, 21.1 15.2 cal. kaBP) corre-

and subtropical taxa, temperate broad-leaved taxa and

sponded to the LGM with an average sedimentation rate

ferns increase, implying warmer and moister climate and

of 45 cm/ka. Herbaceous pollen such as Artemisia shows

higher sea level during this period. But grassland still

higher abundance and arboreal pollens such as Pinus has

grew on the rest exposed continental shelf and temperate

the lowest percentage in the core, implying wider exten-

deciduous broad-leaved forest grew in its surrounding

sion of grassland even onto the coastal region. It is quite

areas. High pollen influx and sedimentation rate were

interesting that the percentage of temperate broad-leaved

ascribed to increased rainfall. Foraminiferal study of

taxa and tropical and subtropical taxa increases while

KH82-4-14 core (31 44.4 N, 129 02.1 E) and RN80-

montane conifers decreases although its sedimentary

GEOLOGY

PC3 core (29 04.1 N, 127 22.6 E) revealed that during

quantity stays almost the same as before. These paly-

19.5 10.5 cal. kaBP high abundance of foraminifer

nologic characteristics imply that sparse deciduous

broad-leaved forest might develop around the grassland species preferring low sea-surface salinity and temperate

and needle-broad leaved mixed forest might grow at water conditions was due to increased river and sedi-

ment discharge[20].

high altitude areas such as Kyushu Island and upper-

middle reaches of the Yangtze River. As sea level was Zone IV (251 0 cm, 10.8 0.3 cal. kaBP) corre-

about 120 m lower than today at LGM[2], the continental sponded to the Holocene with an average sedimentation

shelf was entirely exposed, resulting in the coastal line rate of 24 cm/ka. Pinus and ferns continually increase

500 km away from the mainland of China. More denu- and Castanea-Castanopsis increases sharply; herba-

dated substance from the exposed continental shelf was ceous pollen decreases and pollen influx and sedimenta-

deposited at the PC-1 site because of shorter distance, so tion rate decrease significantly. Due to the continuous

did the pollen influx. rise in sea level, the exposed continental shelf was sub-

Palynological analysis of DGKS-9602 core in the merged again, and the distance between PC-1 site and

middle of Okinawa Trough also indicates the develop- the mainland of China increased, resulting in low pollen

ment of grassland on the exposed continental shelf at the influx and low sedimentation rate in the core. Pollen at

LGM[8]. The biome reconstruction of China at the LGM PC-1 core mainly comes from Kyushu Island, and ever-

Xu H Y et al. Chinese Science Bulletin October 2009 vol. 54 no. 20 3745

green and deciduous broad-leaved forests were now between the PC-1 site and coastal line due to the sea

better developed there with main species of Quercus and level changes, and H/P variation is comparable with the

Castanopsis. From a nearby core B-3GC, palynological oxygen isotopic curve. Similar conclusions have been

reported from palynological analyses of core DGKS-

analysis also shows that evergreen and deciduous broad-

9602 and cores in the South China Sea[8,21,22]. The H/P

leaved forests developed alternately in the Holocene on

land[10]. ratio has been considered by Sun[23] to indicate the dis-

To sum up, during glacial times high pollen influx tance changes between study sites and the coastline: rise

and sedimentation rate were due to shorter distance be- of H/P values is related to marine regression, exposure

tween material sources and the core site, and high per- of the continental shelf and inland shifting of the coast-

centage of herbaceous pollen implies grassland grew on line, while falling of H/P values indicates marine trans-

the exposed continental shelf, while pollen of montane gression, submergence of the continental shelf and off-

conifers and temperate broad-leaved taxa indicates nee- shore shifting of the coastline. And during a glacial and

dle-broad leaved mixed forests probably developed on interglacial cycle, the more the amplitude of H/P values

changed, the wider the continental shelf was[23]. In core

Kyushu Island. During the Holocene, however, sea level

rise led to the submergence of the exposed continental PC-1, the average H/P values are 2.5 for Late MIS 3, 5.4

shelf, resulting in low sedimentation rate and pollen in- in the LGM which is the highest, 1.7 in Deglaciation and

flux, when Kyushu Island was inhabited mainly by 0.4 during the Holocene, indicating the wide continental

evergreen and deciduous broad-leaved forests. shelf of the ECS broadly exposed during the glacial

times.

4.2 Sea level fluctuations indicated by herbs/Pinus

ratio 4.3 Phyllocladus pollen

The Pinus percentage curve overall is in a consistent Phyllocladus has never occurred in the Quaternary-Ter-

tiary sediments in Japan. In modern conditions, Phyllo-

changing trend with the oxygen isotopic curve from core

MD982195 (Figure 5). During glacial times Pinus is low, cladus vegetation is distributed in the humid mountain

and oxygen isotopic value is high, indicating cold cli- area of North Luzon of the Philippines, Tasmania and

New Zealand, and is not distributed in Taiwan Island[24].

mate. From deglaciation to Holocene Pinus gradually

The Phyllocladus pollen is about 35 m with two small

rises and the oxygen isotopic value decreases, indicating

airsacs (Figure 6). The sporadic occurrence of Phyllo-

a warming stage. As discussed above, the alternation of

herbs/Pinus (H/P) indicates the comparative distances cladus in the whole PC-1 core (Figure 3, Table 2) might

18 [12]

Figure 5 Comparison of pollen percentage, H/P ratio and influx of PC-1 core with O curve of MD982195 core (YD and OD indicate

Younger and Older Dryas periods, respectively).

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ARTICLES

Figure 6 Pollen morphology of Phyllocladus.

Table 2 Pollen percentage and influx of Phyllocladus in PC-1 core

Pollen influx

Depth Cal. Age Density Percentage

(grains (g/cm) 1 a 1)

(cm) (cal. a BP) (grains/g) 131 6670 15 0.3 0.3

155 7667 16 0.3 0.4

275-*****-** 0.7 1.3

459-*****-** 0.5 1.1

Figure 7 Spectrum analysis of Pinus pollen percentages showing

715-*****-** 0.3 0.4

periodicity at millennial scales (Dashed line represents 95% level of

significance).

be mainly ascribed to ocean current. They are trans-

ported to the coastal region by large amounts of river subtropical taxa percentages are performed, which show

water and then to the hemipelagic region and/or open the similar periodicity. Figure 7 shows the millennial

ocean by ocean current. The Kuroshio Current could climatic fluctuations reflected by Pinus percentage: the

play an important role in transporting Phyllocladus to cycle of 6.8 ka might correspond to the cycle of Hei-

the ECS, which implies that the Kuroshio Current influ- nrich events found in the northern Atlantic deep-sea se-

enced the sedimentation environment of North Okinawa diments[26 28], while the 3.8 ka and 2.2 ka cycles might

Trough since 24 cal. kaBP. The same conclusion was correspond to the cycle of Dansgaard-Oscheger (D-O)

found in the MD982195 core[6] and supported by fo- events found in Greenland iceberg[29,30]; the 1.6 ka cycle

raminiferal research[7,12,20]. However, another factor as- might be correlated with the 1.5 ka cycle found in some

cribed to the occurrence of Phyllocladus might be in- areas of the tropical ocean[5,31]. 0.7 ka cycle is less cred-

tense summer monsoon. ible because of 230 a of sample resolution. Millen-

4.4 Spectrum analysis nial-scale climatic fluctuations have been testified by

many researches, might be ascribed to the monsoon pe-

GEOLOGY

Percentage of different pollen species fluctuates obvi-

riods and correlated with the sun activity, atmospheric

ously in different stages (Figure 3), especially alternat-

circulation and instability inside the ocean, etc. Its origin,

ing lifting of Pinus and Artemisia in the last deglaciation

mechanism and paleoclimatic significance are still un-

and the fluctuations of Pinus, Quercus-deciduous and

clear, and need further research.

Castanea-Castanopsis in Holocene. With univariate

spectrum analysis from the SPECTRUM program[25]

The authors express their great appreciation to Prof Li Qianyu for im-

s pectrum analyses of P inus, A rtemisia, Q uercus - provement of the text, Prof. Kong Zhaochen for professional guidance and

deciduous, temperate broad-leaved taxa and tropical and to Profs. Xi Yizhen and Zhang Yulong for pollen identification.

1 Qin Y S, Zhao Y Y, Chen L R, et al. Geology of the East China Sea 4 Jian Z M, Saito Y, Wang P X, et al. Shifts of the Kuroshio axis over

(in Chinese). Beijing: Science Press, 1987. 1 200 the last 20 000 years. Chin Sci Bull, 1998, 43: 1053 1056

2 Saito Y, Katayama H, Ikehara K, et al. Transgressive and highstand 5 Jian Z M, Wang P X, Saito Y, et al. Holocene variability of the Ku-

systems tracts and post-glacial transgression, the East China Sea. roshio Current in the Okinawa Trough, northwestern Pacific Ocean.

Sediment Geol, 1998, 122: 217 232 Earth Planet Sci Lett, 2000, 184: 305 319

3 Ujiie H, Ujiie Y. Late Quaternary course changes of the Kuroshio 6 Kawahata H, Ohshima H. Vegetation and environmental record in

Current in the Ryukyu arc region, northwestern Pacific Ocean. Mar the northern East China Sea during the late Pleistocene. Glob Planet

Micropaleontol, 1999, 37: 23 40 Change, 2004, 41: 251 273

Xu H Y et al. Chinese Science Bulletin October 2009 vol. 54 no. 20 3747

7 Li T G, Sun R T, Zhang D Y, et al. Evolution and variation of the 1201 1209

Tsushima warm current during the late Quaternary: Evidence from 19 Tsukada M. Vegetation and climate during the Last Glacial Maxi-

planktonic foraminifera, oxygen and carbon isotopes. Sci China Ser mum in Japan. Quat Res, 1983, 19: 212 235

D-Earth Sci, 2007, 50: 725 735 Xu X D, Oda M. Surface-water evolution of the eastern East China

20

8 Deng Y, Zheng Z, Suc J P, et al. Pollen assemblages of the Last Sea during the last 36,000 years. Mar Geol, 1999, 156: 285 304

Glacial Maximum in Okinawa Trough and their implication on pa- 21 Sun X J, Luo Y L, Huang F, et al. Deep-sea pollen from the South

leoenvironment (in Chinese). Earth Sci-J Chin Univ Geosci, 2005, China Sea: Pleistocene indicators of East Asian monsoon. Mar Geol,

30: 597-***-****, 201: 97 118

9 L H Y, Liu Z X, Liu B Z, et al. Asynchrony of the marine and epi- 22 Luo Y L, Sun X J. Vegetation evolution and millennial-scale climatic

continental climate records in the east Asia during the last 20 ka (in fluctuations since Last Glacial Maximum in pollen record from

Chinese). Mar Geol Quat Geol, 2002, 22: 17 23 northern South China Sea. Chin Sci Bull, 2005, 50: 793 799

10 Song C Q, Sun X J, Saito Y. Paleoenvironmental information re- 23 Sun X J, Luo Y L. Pollen record of the last 280 ka from deep sea

corded by pollen in B-3GC gravity core in Okinawa Trough. Chin sediments of the northern South China Sea. Sci China Ser D-Earth

Sci Bull, 2001, 46: 938 942 Sci, 2001, 44: 879 888

11 He F. Forest Vegetations in Japan (in Chinese). J Sichuan For Sci 24 Delectis Florae Reipublicae Popularis Sinicae Agendae Academiae

Technol, 2006, 27: 38 41 Sinicae Edita. Flora Reipublicae Popularis Sinicae (Tomus 1) (in

12 Ijiri A, Wang L J, Oba T, et al. Paleoenvironmental changes in the Chinese). Beijing: Science Press, 2004. 112

northern area of the East China Sea during the past 42000 years. 25 Schulz M, Stattegger K. Spectrum analysis of unevenly spaced pa-

Palaeogeogr Palaeoclimatol Palaeoecol, 2005, 219: 239 261 leoclimatic time series. Comput Geosci, 1997, 23: 929 945

13 Hughen K A, Baillie M G L, Bard E, et al. MARINE04 marine ra- 26 Heinrich H. Origin and consequence of the cyclic ice rafting in the

diocarbon age calibration, 0 26 cal kyr BP. Radiocarbon, 2004, 46: Northeast Atlantic Ocean during the past 130000 years. Quat Res,

105*-****-****, 29:142 152

14 Reimer P J, Baillie M G L, Bard E, et al. INTCAL04 Terrestrial 27 Elliot M, Labeyrie L, Bond G, et al. Millennial-scale iceberg dis-

Radiocarbon age calibration, 0 26 cal kyr BP. Radiocarbon, 2004, charges in the Irminger Basin during the last glacial period: Rela-

46: 1029 1058 tionship with the Heinrich events and environmental settings.

15 Machida H, Arai F. Extensive ash falls in and around the Sea of Ja- Plaeoceanography, 1998, 13: 433 446

pan from large late quaternary eruptions. J Volcanol Geotherm Res, 28 Broecker W S. Massive iceberg discharge as triggers for global

1983, 18: 151 164 climate change. Nature, 1994, 372: 421 424

16 Wang K F, Sun Y H, Zhang Y L, et al. The Spore-Pollen and Algal 29 Dansgarrd W, Johnsen S J, Clausen H B, et al. Evidence for general

Assemblage in the East China Sea Sediments (in Chinese). Beijing: instability of past climate from a 250-kyr ice-core record. Nature,

Ocean Press, 1987. 1 139 1993, 364: 218 220

17 Sun X J, Song C Q, Chen X D. China Quaternary Pollen Database 30 Bond G, Broecker W S, Johnsen S, et al. Correlations between cli-

(CPD) and Biome 6000 Project (in Chinese). Adv Earth Sci, 1999, mate records from North Atlantic sediments and Greenland ice.

14: 407 411 Nature, 1993, 365: 143 147

18 Members of China Quaternary Pollen Data Base. Pollen-based bi- 31 Pterson L C, Huang G H, Hughen K, et al. Rapid changes in the

ome reconstruction at Middle Holocene (6 kaBP) and Last Glacial hydrologic cycle of the tropical Atlantic during the last glacial.

Maximum (18 kaBP) in China (in Chinese). Acta Bot Sin, 2000, 42: Science, 2000, 290: 1947 1951

3748 www.scichina.com csb.scichina.com www.springer.com/scp www.springerlink.com

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