Plant Content

NOTES

nawa Trouth and the west side of Tsushima Warm Current,

Paleoenvironmental informa- a branch of west Kuroshio Current. The site is located 150

km away from Kyushu Island of Japan and about 600 km

tion recorded by pollen in away from the Chinese mainland. The terrigenous materi-

als come mainly from Japan[1]. Therefore, vegetation on

B-3GC gravity core in Kyushu Island has more direct effects on the characteris-

Okinawa Trough tics of sporopollen stratigraphy in B-3GC gravity core.

Modern natural vegetation in Kyushu is characterized by

1 2,3 4 mixed forest of evergreen and deciduous broadleaf. Fa-

SONG Changqing, SUN Xiangjun & Yoshiki Saito

gaceae and Theaceae are the major species below 1000 m

1. National Natural Science Foundation of China, Beijing 100085, China; a.s.l. There grow deciduous broad-leaved trees above

2. Open Lab of Marine Geology, Tongji University, Shanghai 200039,

1000 m a.s.l., in which Fagus crenata is the dominant

China;

species. Conifers consist mainly of Cryptomeria japonica,

3. Institute of Botany, Chinese Academy of Sciences, Beijing 100093,

Chamaecyparis obtusa, Pinus densiflora, Abies firma and

China;

Tsuga sieboldii[2,3]. Pollen in surface deposit of B-3GC

4. Geological Survey of Japan, Higashi 1-1-3, Tsukuba, Ibaraki, 305-

8567, Japan

gravity core come mainly from Kyushu Island and the

Correspondence should be addressed to Song Changqing (e-mail:

pollen is characterized by a combination of Pinus, Tsuga

******@****.***.**)

and Podocarpus. Since the site of B-3GC is in the west

Abstract Based on pollen records in B-3GC gravity core, Tsushima Current, this current affected directly the depo-

environmental change since 9500 aBP of Okinawa Trough sition process of terrigenous materials from Japan[1] and

and its adjacent islands was derived. The result showed that

therefore caused indirectly changes in total influx. Upon

the most time during this period was in a warm temperate

the fact, it is considered that sedimentation rate and char-

climate except in middle Holocene (6800 4400 aBP) that

acteristics of sporopollen assemblage can be used to de-

was under subtropical climate control. During 9500 8300

rive information on past climate and changes in vegetation

aBP and 3100 2000 aBP periods, it appeared colder and

as well as Kuroshio Current.

drier than the rest time. The original area of pollen sources

1 Material and method

surrounding Okinawa Trough was covered by evergreen and

deciduous broadleaf forest alternatively with mixed broad-

B-3GC gravity core was from 550 m below sea sur-

leaf-conifer forest distributed in high mountainous areas.

face with 218 cm in length. Sample was dated by radio-

Usually, these three kinds of forests existed at the same time

carbon on shell of zooplankton foraminiferan contained in

with difference in altitude. Pollen from subtropical and

the gravity core. Dating was performed by scientists from

tropical plants increased obviously in about 5000 6000 aBP,

Geological Survey of Japan with accelerator mass spec-

reflecting a great lifting of vegetation zone and expansion of

trometer in Lab of Quaternary Isotope, Washington Uni-

evergreen broad-leaf forest in the study area. However, there

versity. The results show that there is no reverse in total

was a slight descending of plant zone and shrinking of

22 data. The youngest age is 180 aBP and the oldest 9380

evergreen broadleaf forest during 9500 8300 aBP and

aBP.

3000 2000 aBP. During the remaining periods vegetation

The entire core was equally cut into 84 subsamples

zone was higher than the present but in a limited range.

and sporopollen in subsamples were treated with hydro-

Keywords: environmental change, Holocene, pollen, Okinawa

fluoric acid. The procedures are described as follows. First,

Trough.

10 15 cm3 material was taken from each sub- sample

and a piece of Lycopodium spore containing 12542 spore

As studies on paleoenvironment go on, high-resolu-

tion and short-time scale reconstruction of regional pa- was added to the selected material as applied spore to

leoenvironmental factors becomes one of the focuses in calculate total influx of the sample. Secondly, dilute hy-

recent researches. Based on the analysis of sporopollen drochloric acid was added to remove calcareous ingredi-

assemblage, the total influx and sedimentation rate ob- ent in sediments and hydrofluoric acid was used to dis-

tained from B-3GC gravity core which was taken in the solve siliceous materials. Finally, the treated samples were

BO 94-20 cruise of R/V Bosei-Maru of Tokai University shaken and filtrated using a sieve with 10 m pore in an

from September 26 to October 12, 1994 (BO means ultrasonic generator. The percentage of pollen or spore of

Bosei-maru) in north Okinawa Trouth, we discussed the each species in the sample was calculated on a cardinal

changes of paleovegetation and paleoclimate in sample number that is the sum of all pollen from seed plants on

location and the adjacent area since 9500 aBP. The rela- land.

tionships between paleoclimate change and Kuroshio

2 Results of pollen analysis

Current were also discussed in this study.

Interpolation of 22 AMS 14C data shows that the age

B-3GC sample site (31 27.37 N, 128 31.14 E) is

located in the continental slope zone in the north of Oki- of the top layer is 232 aBP and that of the bottom is 9452

938 Chinese Science Bulletin Vol. 46 No. 11 June 2001

aBP with 110-a average resolution for the whole core. 349 reached 1.6% and 4.8%, respectively. Podocarpus began

pollen were identified from each sample on average with to occur with high concentration. The average content was

the maximum of 553 and minimum of 301. The average 0.33% and the maximum 1.9%. Deciduous Quercus pol-

sedimentation rate is 3.07 cm/100 a for material and 22 len showed continuous distribution with an average con-

grains/cm2 a for pollen with a range of 3 tent of 11% and the maximum of 18.6%. Occurrence fre-

128

quency of Artemisia, Pterocarya, and Julans decreased

grains/cm2 a. The pollen/spore influx was highly corre-

obviously and Hemlock showed a slight decrease. Abies

lated with the sedimentation rate. There total 79 genera or

was another increasing pollen type, its average content

family of pollen and 48 genera or family of spore were

reached 0.73%.

identified and 37 of 79 genera or family of pollen belong

P2 zone (126 89 cm, 6800 4400 aBP). Tropical

to woody plant and the rest belong to herbaceous plant.

and subtropical pollen increased remarkably. Evergreen

The major genera or family are Pinus, Podocarpus, Day-

Quercus pollen was distributed continuously and reached

crydium, Tsuga, Abies, Picea, Taxodiaceae, Betula,

the maximum of the whole core. The average content was

Carpinus, Corylus, Alnus, Ulmaceae, Ulmus, Celtis, Jug-

2.5% and the maximum 5.5%. Alnus and Celtis became

lans, Pterocarya, Quercus, Castanopsis, Castanea, Fagus,

common and reached the maximum of 0.8%. Abies still

Tilia, Anacardiaceae, Rhus, Hamamelidaceae, Liquid-

remained high percentage. Rhus, Liquidambar occurred

ambar, Pterolobium, Aganosma, Actinidia, Gesneriaceae,

around 5250 aBP. Common temperate tree pollen such as

Meliaceae, Moraceae, Morus, Rutaceae, Sapindaceae,

Quercus and Betula slightly changed while herbaceous

Euphorbiaceae, Geraniaceae, Liliaceae, Magnoliaceae,

Artemisia pollen was sharply decreased and occasionally

Rubiaceae, Solanum, Symplocos, Umbelliferae, Verbena-

was observed. Pollen of Compositae and Gramineae was

ceae, Caprifoliaceae Oleaceae, Artemisia, Cruciferae, Po-

fairly decreased. The total influx was very low in this

lygonaceae, Ranumculaceae, Thalictrum, Urtica, Valeri-

subzone with an average of 8.5 grains/cm2 a.

anaceae. Clearly from the results, most of cores contained

91% tree pollen in the total pollen and spore. In some case P3 zone (89 32 cm, 4400 2000 aBP). Com-

it was even up to 100%. Pinus pollen was dominant in pared with P2 zone, the total influx in this zone increased

tree pollen which usually was more than 63%, the highest obviously with an average of 20 grains/cm2 a and the

up to 95%. The rest pollen and spore mainly belonged to maximum of 39 grains/cm2 a. Deciduous Quercus de-

subtropical and temperate plants. According to the pollen posited continuously; Taxodiaceae and Hemlock almost

diagram, the core could be divided into 5 zones from bot- continued; Artemisia, Compositae and Gramineae pollen

tom to top (fig. 1). came to increase again; Podocarpus almost disappeared.

P1 zone (218 126 cm, 9500 6800 aBP). Pollen On the basis of the pollen diagram, the P3 zone could be

of subtropical plants is the principals in this zone and divided into two subzones (P3-a, P3-b).

temperate plant pollen is the next. Quercus of temperate P3-a subzone (89 5 5 cm, 4400 3 100 aBP).

deciduous forest and mountain Hemlock were distributed Pollen of evergreen Quercus still showed continuous

continuously. Abies, Betula, and Pterocarya showed deposition but the percentage decreased clearly. The av-

discontinuous distribution and high frequency of occur- erage was 1.7%. Taxodiaceae pollen appeared in a large

rence. Compositae and Gramineae shared a similar distri- amount with an average of 0.9%; Geraniaceae, Gesneri-

bution feature. Artemisia appeared discontinuous. The aceae and Moraceae occurred and deciduous Quercus

other pollen in the zone occurred scarcely. Based on the pollen slightly increased with an average of 12.7%.

pollen diagram P1 zone could be further divided into two Artemisia and Juglans increased again and were accom-

sub-zones (P1-a, P1-b). panied by Picea. The maximum of Picea content was

0.5%. Abies almost disappeared.

P1-a subzone (218 179 cm, 9500 8300 aBP).

Warm temperate pollen prevailed in this subzone. P3-b subzone (55 3 2 cm, 3100 2 000 aBP).

Continuously distributed deciduous Quercus pollen took Tropical and subtropical plant pollen decreased

the highest composition with an average of 15.7%, the sharply and evergreen pollen such as Quercus, Podocar-

highest 27.5% and the lowest 8.3% in the profile. Ptero- pus and Moraceae came to disappear. No Picea pollen

carya, Juglans and Betula presented in discontinuity with was identified in the sample. On the contrary, deciduous

high frequency. Subtropical pollen included evergreen Quercus and Carpinus were increased. Pinus and Taxodi-

Quercus, Moraeae and Hemlock. Artemisia pollen was aceae were still on high percentage with the average of

close to continuous distribution with an average of 0.23% 80.3% and 1.0%, respectively. The total influx was high

and the highest of 0.8%. up to 19.4%.

P1-b subzone (179 126 cm, 8300 6800 aBP). P4 zone (32 17 cm, 2000 600 aBP). The total

Compared with P1-a subzone, tropical and subtropi- influx was low in this zone with an average of 10.1%. Still,

cal pollen were increased in this subzone, especially for Pinus pollen remained high percentage with an average of

evergreen Quercus. Its average and the highest content 85.5% and Hemlock reached its maximum content. Ever-

Chinese Science Bulletin Vol. 46 No. 11 June 2001 939

NOTES

Fig. 1. Pollen diagram of B-3GC of Okinawa Trough.

940 Chinese Science Bulletin Vol. 46 No. 11 June 2001

green Quercus began to appear and deciduous Quercus ous broad-leaf forest. In the mountainous area it devel-

decreased, which was accompanied by an increase in Ge- oped mixed broadleaf-conifer forest. Such climate varia-

raniaceae and Gesneriaceae. Artemisia disappeared from tions were also observed in central Inner Mongolia of

China[4,5].

sediment while a small amount of Picea came to appear.

P5 zone (17 9 cm, 600 230 aBP). The total in- 6800 4400 aBP. Subtropical plants prevailed in

flux increased rapidly in this zone with an average rate of this period. Pollen of evergreen Quercus deposited con-

63.3%. Pinus pollen reached the maximum in the whole tinuously and reached its maximum percentage in the

core with an average of 90%. Constituent of tropical and whole gravity core. Podocarpus, Alnus and Celtis begin to

subtropical plants such as evergreen Quercus decreased exit in a large amount and tropical Anacardiaceae and

rapidly. Artemisa and Picea reappeared with the high per- Liquidambar appeared in about 5250 aBP. Correspond-

centage of 0.4% and 0.2%, respectively. ingly, pollen of temperate land plants decreased and Ar-

temisia was nearly extinct. High mountainous plants like

3 Paleoenvironmental significance of pollen record of

Abies became abundant. Such a pollen combination pat-

B-3GC gravity core

tern indicates that the climate in this period was domi-

Pollen deposited in B-3GC core came mainly from

nated by south subtropical climate with temperature and

Kyushu Island, located in the southern part of Japan. Ac-

humidity reaching their maximum. In accordance with the

cording to China vegetation classification, vegetation on

climate, vegetation in this period consisted mainly of ev-

Kyushu Island belongs to evergreen broad-leaf forest of

ergreen broad-leaf forest. Similar warm and humid cli-

middle subtropical zone in base zone (which is equal to

mate was reported for central Africa[6] but opposite for

warm temperate vegetation in Japan s classification sys-

central North America[7].

tem) and deciduous broad-leaf forest of warm temperate

4400 3100 aBP. Tropical and subtropical plants

in places above 1000 m a.s.l. Long-term meteorological

decreased and pollen from evergreen Quercus, Gesneri-

observations in Kagoshima (31 34 N, 130 33 E) show

aceae and Moraceae occurred in a small amount. Espe-

that mean annual temperature, mean January temperature

cially pollen of hygrophilous Liquidambar became to ex-

and mean July temperature are 17.0, 6.7 and 27.3,

ist. Pollen of temperate plants such as Juglans, Pterocarya,

respectively.

Castanea and Carpinus became abundant again, which

From the above-listed pollen analysis, the study site

was accompanied by occurrence of mountain conifer

and its surrounding region was characterized by subtropi-

Picea. It thus can be concluded that the climate in this

cal temperature in the recent 10000 a. The climate change

period was humid and land was covered by evergreen

during this period could be divided into the stages as fol-

broad-leaf forest with deciduous broad-leaf forest cover-

lows:

ing mountainous area. This tendency of climate change

9500 8300 aBP. Pollen from temperate trees were

was typically reflected in central Inner Mongolia of Chi-

rich in the pollen diagram and representative temperate

na[8].

trees included deciduous Quercus, Pterocarya and Julans

3100 2000 aBP. Subtropical pollen decreased

besides Pinus. There were also a small amount of Compo-

further and evergreen Quercus disappeared completely.

sitae and Gramineae. Pollen of subtropical trees consisted

However, temperate component increased and Artemisia

mainly of evergreen Quercus and mountain Hemlock.

appeared again, indicating a relatively dry warm temper-

Thus it can be concluded that during this period the base

ate climate with land covered mainly by deciduous

zone on which the pollen was produced was covered by

broad-leaf forest. Such climate was just opposite to that

warm temperate deciduous broad-leaf forest and that the

reported from Central America[9].

mountainous region was covered by temperate mixed

2000 560 aBP. Pollen of evergreen Quercus oc-

broadleaf-conifer forest.

curred continuously and Hemlock showed an obvious in-

8300 6800 aBP. Pollen of temperate plants such

crease, reaching their maximum percentage of the whole

as deciduous Quercus and Julans were on the decrease

gravity core. At the same time, Picea began to exist and

while mountain plants such as Abies slightly increased.

Pinus content was very high. Deciduous plants included

Artemisia appeared in a regular off and on way. Subtropi-

Carpinus, Quercus and Betula. It can be concluded that

cal constituent began to increase. Evergreen Quercus and

south subtropical temperate prevailed in this period and

Podocarpus pollen appeared intermittently, which was

humidity was higher than the earlier stage. The lower al-

alternated with Artemisia. These characteristics indicated

titude land was covered mainly by evergreen broad-leaf

frequent fluctuation in temperatures and it was more hu-

forest while dominant vegetation was mixed broadleaf-

mid than before. Generally, vegetation in this period was

conifer forest in high altitudes.

characterized by alternative occurrence of subtropical

560 230 aBP. Pinus pollen accounted for more

evergreen broad-leaf forest and warm temperate decidu-

Chinese Science Bulletin Vol. 46 No. 11 June 2001 941

NOTES

sample site had been dominated in alternation between

than 90% of the total and the others included Carpinus,

evergreen broad-leaf forest and deciduous broad-leaf for-

Quercus, Picea and Artemisia, which reflected a dry cli-

est with mixed broadleaf-conifer forest in some high

mate. Vegetation in base zone was dominated by ever-

mountainous area since 9500 aBP. These three types of

green broad-leaf forest while in high mountainous area

forests usually existed at the same time but different in

mixed broadleaf-conifer forest was developed.

altitude. At present, the altitude boundary between ever-

4 Discussion and conclusion

green broad-leaf forest and deciduous broad-leaf forest is

Study on the modern process showed that pollen of about 1000 m. But this limit had a great up-shift in about

B-3GC gravity core came mainly from southern Japan 5000 6000 aBP and down a little in about 9500 8300

with a little from the Chinese mainland. Therefore, pa- aBP and 3000 2000 aBP. In remaining periods the limits

leoenvironmental information recorded by pollen in the shifted up in a small range.

core has limitation in area. Because B-3GC is located in Generally, paleoenvironment change revealed by

the west of Tsushima Current, sediment deposition in pollen records of B-3GC gravity core synchronizes with

sample site was mainly influenced by path and strength of findings in central Africa and has great difference with the

Tsushima Current[10,11]. The stronger Tsushima Current,

change in Central America.

the less material in the sample site from south Japan rivers.

Acknowledgements We would like to thank Y. Kato of Tokai Univer-

Sample analysis indicated that there was a significant

sity, H. Katayama of the Geological Survey of Japan and the crew of

positive correlation between the sedimentation rate and R/V Bosei-Maru for their support in sampling which was done as part of

the total influx. Thus, information from the total influx the Marginal Sea Flux Experiment in the West Pacific (MASFLEX).

This work was supported by the Special Coordination Funds for Pro-

cannot be directly applied to revealing changes in climate

moting Science and Technology of the Science and Technology Agency

and vegetation whereas the pollen diagram can provide

of Japan and by the National Natural Science Foundation of China

more practical environmental information. (Grant Nos. 49732060 and 49894170).

Researches showed that during the Holocene, when

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The pollen records in this study showed that vegetation in

942 Chinese Science Bulletin Vol. 46 No. 11 June 2001

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