Geochemical Journal, Vol. 32, pp. 125 to 133, 1998

NOTE

Sinking particles between the

(0°N-46°N) in

equatorial

the central

and subarctic regions

Pacific

HODAKA KAWAHATA,1°2 ATSUSHI SUZUKI' and HIDEKAZU OHTA3

1Marine Geology Department , Geological Survey of Japan, Tsukuba-higashi, Ibaraki 305-8567, Japan 2Graduate School of Science , Tohoku University, Sendai 980-8578, Japan

3Kansai Environmental Engineering Center , Osaka, Japan

(Received February 6, 1997; Accepted December 8, 1997)

Sinking particles play an important role in the transfer of atmospheric CO2 into the deep sea. We de

ployed six moorings of sediment traps across the transect at 175°E from 0°N to 46°N in the central Pacific. Mean organic matter fluxes along the transect generally reflected primary productivity. Mean opal fluxes showed similar profile, but increased markedly between 34°N and 46°N. The increase in mean total fluxes was accompanied with the increase in fluxes of organic matter and opal. Carbonate contents generally decreased from the equatorial to the subarctic regions. The opal/carbonate ratios increased from mid to high latitudes. These trends are essentially compatible with the prevalent plankton community structure in the upper ocean. Diatoms predominate over calcareous nannoplankton and foraminifera in higher latitudes. In spite of different plankton communities flourishing along the 175°E, C/N atomic ratios of sinking

particles varied within a small range (6.0-8.7). The high export flux of organic carbon and high Corg/ Ccarbonate ratio in sinking particles were potentially responsible for diminished partial pressure of CO2 in surface water in the middle latitudes of the central Pacific during late spring.

INTRODUCTION

Atmospheric CO2 has been rapidly increasing due to human activities. This increase threatens

to cause major changes in the global climate. Oceanic uptake of CO2 has undoubtedly slowed the accumulation of anthropogenic CO2 in the atmosphere, however, the strength of this uptake and its future behavior are uncertain. Marine biogeochemical processes may play an important role in regulating the atmospheric concentration of C02, mediated through air-sea exchange. In surface waters, photosynthesis by phytoplankton converts aqueous CO2 into organic compounds. A fraction of the biogenic material is transported out of the surface waters into deeper water masses This combination of processes tends to continually strip CO2 from the surface ocean that is in contact with the atmosphere and sequesters it in the deeper

water masses where it can no longer directly exchange with the atmosphere (Honjo, 1996). On the other hand, the formation of carbonate has

different effects on the CO2 transfer between the ocean and the atmosphere (Tsunogai and Noriki, 1991). The increase in calcareous organism such as corals, foraminifera and coccolithophorids

(Ware et al., 1992; Holligan et al., 1993; Kawahata et al., 1997a) induces the escape of CO2 from seawater to the atmosphere. Large gradients in primary productivity and

plankton community structure in association with various water masses have been identified between the equatorial and subarctic regions in the central

Pacific (Berger et al., 1989). However, little is

known about the present annual flux of sinking

particles in this area. To understand carbon cycling and fluxes of associated compounds in the central

Pacific, we deployed a total of six time-series

125

126 H.

sediment trap moorings for approximately one

year. The sites were mainly located along the longitude 175°E from the equatorial to the sub

arctic regions. In this paper we present the results

with respect to biological components from various

latitudes and compare the particle fluxes with Pco, i

n the surface waters.

AREAS OF INVESTIGATION AND

OCEANOGRAPHIC SETTING

Most of the central North Pacific has water

depths ranging from 4 to 5 km and pelagic sedi

ments are dominant. In spite of seasonal latitudinal

shifts of the boundaries between each water mass,

surface waters in the central North Pacific are di

vided into four zones: 1) equatorial region, 2) Subtropical Gyre, 3) Kuroshio Extension and 4)

subarctic region (NEDO, 1997).

There are two currents important in the equa

torial region. The eastward flowing equatorial

counter current (ECC) is predominant between 3°N

and 10°N. South of the ECC, South equatorial

current (SEC) flows westward. North equatorial current (NEC) is a westbound flow between 10°N

and 16°N. Subtropical Gyre, extending from the

NEC to about 31 °N, is the most saline water mass

among the central water masses of the oceans.

North of the Subtropical Gyre are Kuroshio Ex

tension and Pacific subarctic water mass, which

extend over the greater part of the Pacific. The

subarctic convergence is well developed only in the central part of the North Pacific, where the

subarctic water forms by mixing of warm saline

waters of the Kuroshio Extension with the cold

less saline waters of the Oyashio current. This convergence is located around 40°N at 175°E

(NEDO, 1997). According to the global map of ocean produc

tivity by Berger et al. (1989), primary productivity has a minimum value . around 70 mg Cm-2 day-' in the Subtropical Gyre. Weak equatorial

upwelling at 175°E supports low primary produc

tivity around 140 mg Cm-2day-1. Primary

productivities are approximately 180 and 220 mg Cm-2day-1 in the Kuroshio Extension and subarc

Kawahata et al.

tic region, respectively.

Aerosol inputs are the main contributor to the

deep sea pelagic sediments of the central North

Pacific. Their quartz contents in the surface sedi

ments and 210Pb distributions in seawater in the

North Pacific suggest that the maximum of ter

restrial inputs occurs in the latitudinal range be

tween 30°N and 40°N (Nozaki and Tsunogai,

1973; Windom, 1975).

SAMPLING AND ANALYTICAL METHODS

Four PARFLUX Mark 7G-21 and six SMD21

6000 time-series sediment traps with 21 sample

bottles on each were deployed. Before deploying,

the sample bottles were filled with filtered sea

water which was collected by a deep water cast.

Then formaldehyde was added to make a 3% so

lution with sodium borate. Recovered sample bottles were immediately refrigerated on board at

approximately 2 to 4°C (Kawahata et al., 1997b).

In laboratory, samples were passed through 1 mm

sieve and the <1 mm fraction was split into

aliquots with a rotating splitter. All flux data ex

pressed in this study are based on the <1 mm size fraction, which dominated particle flux.

We used a desalted and homogenized split from each sample for the bulk analysis. Organic carbon,

carbonate and opal values were determined using

modifications of the methods developed by

Yamamuro and Kayanne (1995) and Mortlock and

Froelich (1989), respectively. The contribution of

lithogenic matter was calculated as follows:

Lithogenic = Total Carbonate Opal Organic

matter (1.8 x organic carbon). The relative standard deviations of organic carbon and total nitro

gen analyses were 3%. Several samples giving unusual opal values were analyzed three times,

providing a relative error of 3% for the measured values.

The measurement of the PCO2 in surface seawater was carried out along with that of the air

Pco2 during the cruises of the R/V Hakurei-maru

(Kawahata et al., 1997a). Seawater was pumped up continuously from the bottom of the ship and

introduced into an equilibrator. The seawater

Sinking particles in central Pacific

temperature at the water inlet and in the CO2 equilibrator was recorded using thermistors within an error of ±0.001'C. Precision measurements of CO2 were made using a nondispersive infrared gas analyzer (NDIR Model 880; Beckman). Each se

quence of measurements involved calibration using 4 standard gases, followed by an air PC-02 and a

seawater Pco2 measurement. All measurements were made at one atmospheric pressure. For the standard gases and air measurements, the gas was

pumped into the sampling cell for 4.5 minutes. Flow was then stopped and after 30 sec equili

bration the pco2 signal was integrated over a 1

minute sample period. Seawater PC02 measurements were made by circulating air in a closed loop over the seawater sample in an equilibrator chamber, then through a desiccating system and

the gas analyzer. Before each seawater PCUZ measurement the air flow was stopped, the sam

pling cell air was allowed to equilibrate for 30 sec and a measurement was integrated for 1

minute. For the seawater PCU2 measurements, a temperature correction was applied to take account of small changes (<0.5°C) between the intake temperature and the seawater temperature in the equilibrator chamber, following the equation of Gordon and Jones (1973):

8Pco2 / 8T (uatmoCl) =4.4x10-2(PC02)-4.6x10--6 (Pco2)2 (1)

where, 8T is the temperature difference in Celsius

(°C). Salinity remains constant.

SINKING PARTICLES ALONG 175°E

Site 3 (0°00.2' N, 175°09.7' E): Site 3 was located in the equatorial region. Sediment traps were deployed at water depths of 1,357 m and 4,363 m for 0.8 year from 1 June 1992 to 1 April 1993. Mean total, carbonate, organic matter (OM) and opal fluxes at shallow trap were 40.1, 30.2, 4.4, and 3.5 mg m-2day-1, respectively (Table 1, Fig. 1). These fluxes were fairly low, although

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Comparison of the mean values of (a) C/N and opal/carbonate ratios, (b) the contents of

carbonate, organic matter (OM), opal and lithogenics, (c) carbonate, (d) organic matter (OM), (e) opal, (f)lithogenic and (g) total mass fluxes along 175°E.

128 H. Kawahata et al.

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Sinking particles in central Pacific 129

the site was located at the western end of the

equatorial upwelling zone (Berger et al., 1989).

Site 4 (7°55.6' N, 175°00.4' E): At Site 4, also

located in the equatorial region, the successful

sampling duration was only 29 days for the shal

low trap due to a fish, which plugged the rotary

collector of the trap. On the other hand, deep trap

was successfully deployed at a water depth of

4,743 m from 25 September 1993 to 13 April

1993. No definite seasonality was observed at Site

4. Total, carbonate, OM and opal fluxes at deep

trap averaged 15.8, 10.1, 1.4 and 3.5 mg m-2

day-1, respectively (Table 1, Fig. 1).

Site 6 (30°00.1' N, 174°59.7' E): The location

of Site 6 was at the northern end of the Subtropical

Gyre. One trap was deployed at a water depth of

3,873 m from 16 June 1993 to 1 June. 1994. Total

flux exibited one broad maxima with relatively

intermediate values from January through March,

when the Kuroshio Extension was shifted south

of Site 6 (Meteorological Institute, personal communication). The Subtropical Gyre, whose surface

water is depleted in nutrients, was predominant at

Site 6 during the rest of the year. Total, carbonate,

OM and opal fluxes were on the average 47.4,

30.2, 4.8 and 4.2 mg m-2day-1, respectively

(Table 1, Fig. 1). Site 5 (34°25.3' N, 177°44.2' E): Site 5 was

situated within the Kuroshio Extension between

30°N and 40°N. Sediment traps at Site 5 were

deployed on 16 June 1992 for 0.9 year. Shallow

and deep trap depths were 1,342 m and 2,848 m, respectively. Two flux maxima with relatively high

and intermediate fluxes in June and March were

observed at the shallow trap of Site 5. Mean total,

carbonate, OM and opal fluxes at shallow trap

were 41.1, 23.3, 5.2 and 3.7 mg m 2day-1, respectively (Table 1, Fig. 1).

Site 7 (37°24.2' N, 174°56.7' E): Total flux at

Site 7, also situated within the Kuroshio Extension,

showed a seasonal pattern similar to that at Site

5. Traps were deployed at water depths of 1,482

m and 4,588 m from 1 June 1992 to 9 April 1993.

Mean total, carbonate, OM and opal fluxes at

shallow trap were 94.6, 41.5, 11.6 and 17.5 mg

m-2day-1, respectively (Table 1, Fig. 1).

Site 8 (46°07.2' N, 175°01.9' E): Surface water of Site 8 was located in the subarctic water mass. Trap deployment at a water depth of 1,412 m started in 16 June 1993 and ended in 16 April 1994. One large distinct peak was observed spanning from July to December with another small

peak in April. Total, carbonate, OM and opal fluxes averaged 207.7, 38.5, 14.6 and 143.4 mg m-2day-1, respectively (Table 1, Fig. 1).

Mean component fluxes for total, carbonate, OM, opal and lithogenics are plotted in Fig. 1. Fluxes and compositions of major components in the deep traps deployed about 500 m above the seafloor sometimes showed appreciable contribution of resuspended matter from the bottom sediment at Sites 3 and 5 (Table 1). Therefore, only data obtained from shallow traps are presented when data from both shallow and deep traps are available. Mean OM fluxes generally reflect primary

productivity. Minimum flux was recorded at Site 4 (8°N) and mean OM fluxes generally increased

from south to north. Mean opal fluxes showed a

similar profile, however, they increased markedly between 34°N and 46°N. Opal accounted for ap

proximately 70% of total mass at Site 8. Increase in annual total fluxes was accompanied with the

increase in fluxes of OM and opal. Mean total

flux at Site 8 was the largest, 16 times of that

observed at Site 4. Carbonate was generally the

largest component of settling particles except at

Site 8. Carbonate fluxes observed along 175°E were between 23 and 42 mg m-2day-1 except at

Site 4. Carbonate contents generally decreased

from the equatorial to the subarctic sites. The ratio

of opal to carbonate in weight (opal/carbonate)

increased from the Kuroshio Extension to subarctic

region. This essentially reflects the prevalent

plankton community structure in the upper ocean

(Tanaka and Eguchi, personal communication). Our study indicates a predominance of diatoms

over carbonate and calcareous nannoplankton (high

opal/carbonate ratio) in higher latitudes, which is

consistent with the results obtained by floating trap

experiments (Bernstein et al., 1990). In spite of

different plankton communities existing along the

130 H.

175°E, C/N atomic ratios of sinking particles var

ied within a small range (6.0-8.7). Lithogenic

fluxes exhibited maximum in the middle latitude,

which corresponded to the position of the westerly

wind over the Pacific. The maximum wind velocity

in the modern climate zone is located around

30°N-40°N at high altitude (Rex and Goldberg,

1958). This supports the idea that the pelagic

sedimentary particles in the central North Pacific

are mainly transported from the Asian continent

through the atmosphere.

EXPORT OF ORGANIC CARBON AND PC02

IN MAY ALONG 175°E

Carbon cycling in the ocean is often affected

by the fluxes and composition of the primary

producers; settling of particulate organic carbon decreases the concentrations of total CO2 and

partial pressure of CO2 (Pco2) in surface waters, whereas removal of carbonate from surface waters

raises PC02 by shifting the carbonate ion equilib

ria. Therefore, variations in organic carbon flux and in the initial production ratio of organic carbon

to carbonate carbon (Corg/Ccarbonate) can result in

a significant variation in PC02 in surface waters.

Measurement of PC02 in surface water was

carried out from 0°N to 8°N at the end of May,

1992 and from 8°N to 48°N in May, 1993 (Fig.

2). Surface water PCO, was lower than the atmospheric PC02 between 0°N and 46°N. PC02 was around 340 µatm in the equatorial region and de

creased gradually northward in the Subtropical

Gyre. Its profile exhibited a definite minimum with

less than 300 µatm within the Kuroshio Extension

and a significant increase to 370 Jtatm at 48°N.

The difference between the surface ocean PCOZ and the atmospheric PCO2 was the largest between 30°N and 40°N. This feature indicates that the

surface seawater potentially works as a sink of CO2 in the middle latitude during late spring.

Sea surface temperature (SST) is one of the

important factors controlling PC02. SST profile exhibited a slight decrease from the equatorial re

gion to 25°N and a continuous decrease to the

Kawahata et al.

subarctic region. On the contrary, PC02 profile showed a significant increase between 35°N and

the subarctic region (Fig. 2). This trend demon

strates that the distribution of PC02 should not be

determined only by SST.

The organic and carbonate fluxes and Corg/

Ccarbonate ratios observed between 0°N and 8°N

from 15th to 30th of June, 1992 and between 8°N

and 48°N from 15th to 30th of June, 1993, are

presented in Fig. 2. The residence time of particles between the upper water column and the

trap depth is often an order of two weeks, because

sinking speed ranges from 185 m day-' to 200 m

day-1 depending on sample resolution, employing

diatoms, silicoflagellates and radiolarians

(Takahashi, 1986, 1987, 1989). Therefore, this comparison may be valid although crude. Organic

carbon and carbonate fluxes at shallow traps were

2.39 and 35.4 mg m-2day-1 at Site 3, 1.45 and 16.8

mg m-2day-1 at Site 6, 10.8 and 50.3 mg rn-2 day-1 at Site 5, 22.9 and 115.6 mg m-2day 1 at Site

7 and 3.90 and 26.9 mg m-2day-1 at Site 8, re

spectively. The Corg/Ccarbonate ratios peaked within

the Kuroshio Extension, which means a dominance

of organic carbon over carbonate carbon in the export flux in the middle latitude. Due to rather

rapid degradation of OM, the organic carbon fluxes

measured with traps were strongly depth depen

dent. Therefore, organic carbon fluxes were nor

malized to 100 m water depth (Corgloo), using the

relationship given by Pace et al, (1987). Although

there are several equations for organic carbon

depth dependency, the equation proposed by Pace

et al. (1987) is the best fit for the data set on

sinking particles from the western Pacific (Honda

et al., 1997). Corgloo values were 11, 12, 47, 106 and 18 mg m-2day1 at Sites 3, 6, 5, 7 and 8, re

spectively. Both organic carbon fluxes and Corgloo

values peaked around 37°N within the Kuroshio Extension. These enhanced organic carbon fluxes

in this region were potentially responsible for

transport of CO2 from surface water into the ocean

interior in the middle latitude during the month of

May.

Net production of organic matter and carbon

ate modifies alkalinity and total CO2 in seawater,

Sinking particles in central Pacific 131

N

N

a

400

380

360

340

320

300

280

Ma y May : 1992 1993 SST

PCO2

a

pCO2 r -r

'fl-V -it

50

40

30

20 U yFO

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10

0 10 20 30 40

0

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20

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10

5

0

June1992.

June..1993

• b i

1

...............

i •0 20 3010. 40 5

125

100 „ti

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50 '

25 ^'

0

150

c 100 Cq N

50

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0

June

1992June C1993

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40 50

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a 1.4

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0.0

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Fig. 2. PCp2 in the surface water, atmospheric pCp2 and sea surface temperature (SST) in carbon flux (solid) and export organic carbon flux (normalized at 100 m water depth) (shaded) ate flux (shaded) and CorglCcarbonate ratios (solid square) (c) observed in June.

May

(b),(a), organic and carbon

which leads to changes in PC02. If we assume that

one hundred meter deep water column provided

the export flux of organic carbon and carbonate,

we can calculate reduction rate in PC02 . Although

the vertical change in carbonate flux was suggested

by Honda et al. (1997), biogenic calcareous tests

such as foraminifera and coccoliths obtained dur

ing this sediment trap experiment remained definitely fresh and therefore any calibration is not

made for the following calculation. Assuming that

all particulate carbon collected by sediment traps

is produced in the 100 m thick upper water layer and transported vertically and that carbon leaving

the upper water layer does not come back (Honda

132 H. Kawahata et al.

et al., 1997), when we adopt the method of Suzuki

(1994), using the Corgloo and carbonate flux at Site 7, the Pco2 would be reduced by no more than 0.8 patm week-1 under the initial conditions of

SST of 15°C, salinity of 34.5%0, total CO2 of 2,050

µmol 1-1, total alkalinity of 2,306 jimol 1-1, and Pco 2 of 340 ,uatm. This result indicates that it takes 38 weeks to reduce Pco

2 from 340 ,uatm to approximately 310 uatm. This is not plausible

because Pco 2 profile along the 175°E demonstrates definite seasonality (Harada et al., 1996).

One possible explanation is that much thinner

upper water layer exports much of organic carbon. If the thickness of the upper water layer is con

sidered to be ten meter in the same computation , the Pco 2 would be reduced by 8 patm week-1, which enables Pco 2 to reduce to 300 uatm in a month.

Acknowledgments-The authors express their appreciation to Prof. K. Takahashi and Dr. M. Honda for valuable comments to improve the manuscript. This study was supported by the following research pro

grams; "Northwest Pacific Carbon Cycle study" consigned to the Kansai Environmental Engineering Center Col. Ltd. by the New Energy and Industrial Technology Development Organization and "Study on Paleoceanography" by the Geological Survey of Japan.

REFERENCES

Bernstein, R. E., Betzer, P. R. and Takahashi, K . (1990)Radiolarians from the western North Pacific Ocean:

a latitudinal study of their distributions and fluxes . Deep-Sea Res. 37, 1677-1696.

Berger, W. H., Smetacek, V. S. and Wefer, G. (1989) Ocean productivity and paleoproductivity an over view. Productivity of the Ocean: Present and Past (Berger, W. H., Smetacek, V. S. and Wefer, G., eds.), 1-34, Wiley, Chichester.

Gordon, L. I. and Jones, L. B. (1973) The effect of temperature on carbon dioxide partial pressures in

sea water. Mar Chem. 1, 317-322.Harada, K., Murayama, S. and Goto, K. (1996) The

change in Pco 2 in the surface water observed along 175°E in the North Pacific. Kaiyo-Monthly 314 , 472

475 (in Japanese).Holligan, P. M., Fernandez, E., Aiken, J., Balch , W. M., Boyd, P., Burkill, P. H., Finch, M., Groom , S. B., Malin, G., Muller, K., Purdie, D. A., Robinson,

C., Trees, C. C., Turner, S. M. and van der Wal, P.

(1993) A biogeochemical study of the coccolithophore, Emiliania huxleyi, in the North Atlantic. Global Biogeochem. Cycles 7, 879-900.

Honda, M., Kusakabe, M., Nakabayashi, S., Manganini, S. J. and Honjo, S. (1997) Change in pco 2 through bi

ological activity in the marginal seas of the west ern North Pacific: The efficiency of the biological

pump estimated by a sediment trap experiment. J. Oceanogr. 53, 645-662.

Honjo, S. (1996) Fluxes of particles to the Interior of the open oceans. Particle Flux in the Ocean (Ittekkot ,

V., Schafer, P., Honjo, S. and Depetris, P. J., eds .), 91-154, SCOPE, John Wiley & Sons Ltd., England.

Kawahata, H., Suzuki, A. and Goto, K. (1997a) High Pco2 in the lagoonal surface water of Palau Barrier Reef and Majuro Atoll-Coral reef ecosystem works as a source of atmospheric CO2. Coral Reefs 16, 261 266.

Kawahata, H., Yamamuro, M. and Ohta, H. (1997b) Seasonal and vertical variations of sinking particle fluxes in the West Caroline Basin. Oceanologica Acta

(in press).Mortlock, R. A. and Froelich, P. N. (1989) A simple method for the rapid determination of biogenic opal

in pelagic marine sediments. Deep-Sea Res . 36, 1415-1426.

NEDO (1997) Reports on North Pacific Carbon Cycle Study (New Energy and Industrial Technology De velopment Organization, eds.), 1-272, Ministry of International Trade and Industry (in Japanese).

Nozaki, Y. and Tsunogai, S. (1973) Lead-210 in the North Pacific and the transport of terrestrial material through the atmosphere. Earth Planet . Sci. Lett. 20, 88-92.

Pace, M. L., Knauer, G. A., Karl, D. M. and Martin , J. H. (1987) Primary production, new production and vertical flux in the eastern Pacific Ocean. Nature 325 , 803-804.

Rex, R. W. and Goldberg, E. D. (1958) Quartz con tents of pelagic sediments of the Pacific Ocean .

Tellus 10, 153-159.Suzuki, A. (1994) Seawater CO2 system and its trans

formation caused by photosynthesis and calcification in coral reefs.-theory and measurements of reef

metabolism. Bull. Geol. Surv. Jpn . 45, 573-623 (in Japanese with English abstract).

Takahashi, K. (1986) Seasonal fluxes of pelagic diatoms in the subarctic Pacific, 1982-1983. Deep-Sea Res.

33, 1225-1251.Takahashi, K. (1987) Radiolarian flux and seasonality:

climatic and El Nino response in the subarctic Pa cific, 1982-1984. Global Biogeochemical Cycles 1 , 213-231.

Sinking particles in central Pacific 133

Takahashi, K. (1989) Silicoflagellates as productivityindicators: evidence from long temporal and spatial

flux variability responding to hydrography in the

northeastern Pacific. Global Biogeochemical Cycles

3,43-61.

Tsunogai, S. and Noriki, S. (1991) Particulate fluxes of carbonate and organic carbon in the ocean. Is the marine biological activity working as a sink of the atmospheric carbon. Tellus 43B, 256-266.

Ware, J. R., Smith, S. V. and Reaka-Kudla, M. L.

(1992) Cora, reefs: sources or sinks of atmospheric C02? Coral Reefs 11, 127-130.

Windom, H. L. (1975) Eolian contributions to marine sediments. J. Sed. Petrol. 45, 520-529.

Yamamuro, M. and Kayanne, H. (1995) Rapid direct determination of organic carbon and nitrogen in car bonate-bearing sediments using Yanako MT-S CHN analyzer. Limnol. Oceanogr. 40, 1001-1005.