Stable carbon isotope ratios of plankton carbon and ... - Science Direct

Marine Chemistry, 35 (1991) 581-596 Elsevier Science Publishers RY., Amsterdam

581

Stable carbon isotope ratios of plankton carbon and sinking organic matter from the Atlantic sector of the Southern Ocean Gerhard Fischer Fachbereich Geowissenschaften, Universitdt Bremen, Klagenfurter Stmj3e, D-2800 Bremen 33, FRG (Received I September 1990;accepted 25 February 1991 )

ABSTRACT Fischer, G., 1991. Stable carbon isotope ratios of plankton carbon and sinking organic matter from the Atlantic sector of the Southern Ocean. Mar. Chetn., 35: 581-596. The stable carbon isotope composition of particulate organic carbon (POC) from plankton, sediment trap material and surface sediments from the Atlantic sector of the Southern Ocean weredetermined. Despite low and constant water temperatures, large variations in the ODC values of plankton were measured. DCenrichments of up to 10%0 coincided with a change in the diatom assemblage and a two-fold increase in primary production. Increased CO2 consumption as a result of rapid carbon fixation may result in diffusion limitation reducing the magnitude of the isotope fractionation. The 13 () C values of plankton from sea-ice cores display a relationship with the chlorophyll a content. High 'ice-algae' biomass, in combination with a limited exchangewith the surrounding seawater,results in values of about - 18 to - 20%0. It is assumed that these valuesare related to a reducedCO2 availability in the sea-ice system. In comparison with plankton, sinking krill faeces sampled by traps can be enriched by 2-5%0 in 13C (e.g, central Bransfield Strait). In contrast, the transport of particlesin other faeces, diatom aggregates or chains results in minor isotopechanges (e.g. Drake Passage, Powell Basin, NW Weddell Sea). A comparison between the (~l3C values of sinking matter and those of surface sediments reveals that DC enrichments of up to 3-4%0 may occur at the sediment-water boundary layer. These isotopic changes are attributed to high benthic respiration rates.

INTRODUCTION

Carbon isotope discrimination during photosynthesis is mainly due to enzymatic reactions, which catalyse the initial carboxylation step. According to Sackett et al. (1965), the extent of the isotope fractionation in marine plants is related to sea surface temperatures. This relationship was used by Fontugne ( 1983) for palaeoceanographic implications, supposing that only minor isotope alterations occur in the water column and during later diagenesis. However, further investigations indicated that factors other than temperature contribute to the observed J 13C variations in open-ocean plankton (discussed by Fry and Sherr ( 1984) and Descolas-Gros and Fontugne (1990)). 0304-4203/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.

582

G. FISCHER

O'Leary (1981) summarizing experimental data, concluded that the thermal effect associated with the carbon assimilation must be fairly small. Experiments by Degens et al. (1968) and others demonstrated the importance of the external CO 2 supply for the o13C composition of marine plants. According to Rau et al. (1989) , the very low o13 C values of Antarctic phytoplankton result from high CO 2 (aq) concentrations as a result oflow water temperatures . In combination with the external CO 2 supply, the cell-internal carbon demand, influenced for example by light intensity, may contribute to the carbon isotope composition in aquatic organisms. In studies by Wefer and Killingley ( 1986), Cooper and DeNiro ( 1989) and Wieneke and Fischer (1990), higher '2;~'6 ./-~~ ~ -,/

'2;'f..e ~'O

o~

~tJ

~

1. -- -'

tIl

O'

r rn

o

;>;0

to

20'

o z en

0

-l

o

-c m ;0

>-l (5

+

N

t

LO'

601

to

o-ri

-c

on

60'

L'

I

[b

I

60 '

I

I

I

30'

I

'

I5

w

ANTARCTICA

I

e

' \

w

3. Scoll. S••-Bransfleld S. •

Fig. 2. Ol3C values of plankton (6-10 m water depth) plotted vs. surface water temperature. The material was collected with an on-board pumping system during three cruises. Transects 1 and 2: more than 63 11m fraction; transect 3: more than 75 and more than 150 11m fraction. APF, Antarctic Polar Front; SuC, Subtropical Convergence; NEFZ, North Equatorial Frontal Zone.

587

STABLE CARBON ISOTOPE RATIOS OF POC

with comparable scattering of b13CpOC values south of the APF has been given by Fontugne (1983). Until now, these fluctuations have remained largely unexplained. This large variability is also observed when plotting plankton b 13C values against the CO 2(aq) concentrations (Rau et al., 1989, Fig. lb ). Thus, other factors besides the external CO 2 supply must contribute to the carbon isotope compositions in Antarctic phytoplankton. Wada et al. (1987), for instance, suggested that besides other factors, the slow growth rates under low light intensities could result in the low b l3C values of Antarctic phytoplankton. In Fig. 3 the b 13C values of plankton collected with a multi-plankton net (mesh size 63 ,urn) in November 1985 in the Bransfield Strait are plotted against the Si/N ratios. Only data from the depths intervals 0-25, 25-50 and 50-100 m were used, because of a domination of zooplankton at greater depths. Generally, a correlation between the Si/N ratios and the b l3C values is observed. Samples dominated by Corethron criophilum have Si/N ratios of about 4-6 and b I 3C values of - 32 to - 35%0, whereas plankton samples with Thalassiosira spp. dominating phytoplankton biomass in late November show Si/N ratios of 1.5-3 and b 13C values of -23 to -27%0 (Fig. 3). This species succession in the Bransfield Strait, also observed in tank experiments (E.-M. Nothig, personal communication, 1989), coincided with a two-fold increase in primary production. The data of total integrated primary production were provided by von Bodungen et aI. (1987, and unpublished data, 1988). During the investigation period, total phytoplankton biomass was dominated by ·35

fir -30

e l

~ .:0 -25

•• •

•

•

~

IpP=1.5-2.5!l mol! ·20

d-ll

c. crlophllum

• Thalassloslra spp.

-+---..---"""T---r---..---"""T---r----,

o

2

3

4

5

6

7

SI/N·ratlo (atom) of particulatematter

Fig. 3. 0 l3Cvalues of phytoplankton from the Bransfield Strait plotted against the Si/N ratios. Samples were taken in November 1985 from three depth intervals between 0 and 100 m water depth with a 63 pm plankton net. Total primary production data (PP) based on 14C determinations were supplied by von Bodungen et al. (1987) and von Bodungen (unpublished data). Total phytoplankton biomass and the net phytoplankton collected were dominated by Coreth1'011 criophilum at the beginning of the investigation; 2 weeks later Thalassiosira spp. prevailed.

588

G. FISCHER

diatoms (80-90%), and flagellates contributed only about 10% to biomass (von Bodungen et al., 1987). Thus, it seems reasonable to compare total primary production rates with the o13 e compositions of plankton from the more than 63 J1m size fraction. At a few sites, Ol3C values were measured for both the greater than 63 J1m and the greater than 20 J1m size fractions (Fischer, 1989). These data show similar isotope compositions for both fractions within 1%0. The results presented above indicate that high productivity is linked to 13e enrichments in phytoplankton carbon. High internal carbon demands as a result of rapid carbon fixation may cause isotopic disequilibria in and!or around the cells, reducing the magnitude ofthe isotope fractionation (Degens et al., 1968; Deuser, 1970; Estep et al., 1978; Smith and Walker, 1980; O'Leary, 1981; Kerby and Raven, 1985). However, no general relationship between the 0 13CpOC values and primary production is found when production is low (see also Fontugne (1983) and Descolas-Gros and Fontugne (1990)).

Sea-ice poe In Fig. 4,

·32

-34

·26

aea 500

I

·26

0

~278

277

I""

613C (%0 POS) ·24

-30

-32

·34

600

i

"~

:: 1000

2000 Plankton

1400 JV85

~

KG65

0

Sinking

Sinking Plankton

mailer 2500

PB63

0

OP80·61

0

mailer

o

•

Fig. 5. Ol3C values of net plankton (open symbols) and sinking matter collected by sediment traps (filled symbols) from various water depths. (a) Bransfield Strait: JV85, Joinville Shelf 1985; KG85, King George Basin 1985. Plankton net samples 277 and 278 (greater than 63/-lm fraction) were taken from the depth interval 0-50 m. (b ) Drake Passage /Powell Basin: DP8081, Drake Passage 1980- I981; PB83, Powell Basin 1983. The plankton sample 263 was collected from the depth interval 0-50 m (greater than 63/-lm fraction) . Sample M8 101 was taken from 6 m water depths using a 75 pm screen .

of selective respiration of 12C by krill. In this case, respired CO 2 should be isotopically lighter relative to phytoplankton (McConnaughey and McRoy , 1979). Indeed, the few measurements made by Mosara et al, (1971) and DeNiro & Epstein (1978) on respired CO 2 indicate a 13C depletion of 0.11%0 for respired CO 2 compared with the ingested food. According to Eadie (1972), McConnaughey and McRoy (1979) and Rau et al. (1983), zooplankton reveals 13C enrichments of a few per mil relative to phytoplankton. This was also found by Fischer ( 1989) for Antarctic zooplankton, which shows 1-3.5%0 higher e5 13C values than the food source. McConnaughey and McRoy (1979) treated the food web as an isotopic balance, where the consumer and the egested detritus are most enriched with 13C, if the consumer respires high amounts of carbon (y=respirationjassimilation is high). Thus, these 13C enrichments must reflect the carbon budget of the consumer. With the equation of McConnaughey and McRoy ( 1979), the present carbon isotope data of phytoplankton, zooplankton and krill faeces and a literature e5 13C ratio for respired CO 2 ( - 1%0 relative to the food), a ratio of res-


591

pi ration to assimilation of 0.75 for krill is calculated. This seems to be a reasonable value for Antarctic krill (see von Bodungen et al., 1987). Comparing opaljC Org ratios of phytoplankton and krill faeces, and assuming that biogenic opal is rather insoluble with regard to gut passage, it can be estimated that only one-third of the carbon ingested by krill is excreted in faeces. These findings are largely consistent with the y-value calculated above. In the deeper waters of the King George Basin, another 13C enrichment of about 3%0 is observed (Fig. 5a). This change, also indicated in a carbon isotope profile of POC collected in 1983, is due to a lateral influx of benthic macroalgae from the nearby shelf areas. These mostly brown macroalgae show carbon isotope ratios around - 20%0 and contribute 50% or more of the total carbon flux to the deeper water of the King George Basin (Fischer, 1989). In contrast to the Bransfield Strait, smaller carbon isotope alterations in the water column are observed in the Powell Basin and the Drake Passage (Fig. 5b). In the Drake Passage, sinking matter is composed of spherical pellets of unknown origin containing undamaged diatom valves (Gersonde and Wefer, 1987). This transport of phytoplankton to the deeper waters apparently results in a minor biomodification of the surface carbon isotope signal, possibly as a result of a different metabolism of the consumer producing the pellets. In the Powell Basin (Fig. 5b), trapped particles are composed of diatom chains, aggregates and a few unidentified small pellets (Gersonde and Wefer, 1987). As in the Drake Passage, krill pellets were not found. The opaljCorg ratios of the surface water plankton and trapped material are very similar (Fischer, 1989), which, in contrast to the Bransfield Strait, indicates that only a slight carbon biomodification in the food web occurred. Consequently, no isotope difference between surface plankton and sinking matter was measured. A comparable situation is observed in the northwestern Weddell Sea (trap site WSl), where sedimentation occurred mainly through pellets of unknown origin containing pennate diatoms released from the sea ice (Fischer et al., 1988). The stable carbon isotope composition of these particles, calculated for 1 year according to carbon fluxes, is about - 28%0, corresponding to the value of the surface plankton. These ratios are largely consistent with data from Biggs et al. (1987), who measured POC from the Weddell Sea summer surface waters sampled by sediment traps (100 and 200 m water depth) during ocean drilling project Leg 113. Part of the trapped material contained high percentages of Nitzschia curta, which was found to be a good indicator of pack/ sea ice and ice-edge bloom conditions (Biggs et al., 1987). JI

3

C alterations at the sediment-water interface

In Fig. 6, the J 13C ratios of POC sampled by sediment traps (mostly from 1 year deployments) are compared with those of the surface sediments. It

592 -30

-28

10 0

D-

G. FISCHER

0

sinkIng matter

0

surface sediments

~ l f

o

0 0

~

oC'l

0

·26

0

0

0 0

0

-24

0

0

, 0

0

~

-22

, 0

0

-20 Trap statIons

KG1b

KG95

JV95

N'Sranslleld Strait Area KG-Sasln

Shelf

OP80·81 Drake Passage

WS1

KN1

Weddell Sea open

Shelf

PF1 Polar Front

Fig. 6. Comparison between the Ol3C values from POC sampled by sediment traps and the surface sediment carbon (0-1 cm). For traps collecting over I year (KGl b, WSI and PFI), average isotope values according to the carbon fluxes were calculated. For site KG 1, the value of the deeper trap (1588 m-KO Ib) was used. The sediment traps deployed for only weeks to a few months sampled the period of highest fluxes (austral spring/summer; see Wefer et aI., 1990).

must be emphasized that no direct information is available on the age of the sediments. However, it is evident that the upper 1 cm of the sediment is generally older and covers a larger time-span than 1 year, especially in the slowly accumulating sediments ofthe central Weddell Sea site WS 1 (see Rutgers van der Loeff and Berger, 1991). The J13C values of all sediments are higher than for POC from the water column. In the Bransfield Strait, where the sediment accumulation rates are very high (Rutgers van der Loeff and Berger, 1991), these isotope alterations are less than 1%0, whereas they reach 3-4%0 at all other sites. These large isotope shifts are comparable with changes discussed above in the surface water J l3C po c induced by zooplankton respiration (krill). The extent of 13C enrichments is attributed to the intensity and/or the mode of benthic respiration. As emphasized by McConnaughey and McRoy (1979), carbon reaching the benthos is mostly respired rather than returned to macrofaunal food. Furthermore, if CO 2 respired by bacteria is more depleted in 12C relative to the food, then the remaining carbon in the sediments must be largely enriched in 13C, as seen for the sites outside the Bransfield Strait. However, longer food chains involving bacteria and meiofauna may also be the reason for a strong biomodification of the carbon isotope signal as a result of cumulative 13C enrichments (Rau et al., 1983). In the Bransfield Strait, this biomodification is less evident than in the other areas (Fig. 6). The reasons for the different J13C alterations at the sediment-water interface remain unexplained. The

593


following explanations may be taken into account: (1) lower rate of microbial degradation because of very high sedimentation rates, (2) shorter food chains, (3) different types of bacteria reworking the accumulated carbon, (4) a more refractory type of organic carbon accumulated (more than 50% is benthic macroalgal carbon). Similarly, large carbon isotope shifts between sinking POC and surface sediment carbon from the Antarctic were measured by Eadie (1972) and Eadie and Jeffrey ( 1973). They attributed isotope alterations of 2-6.6%0 to the metabolism of bacterial populations at the sediment-water interface. Thus, it appears that this biologically highly active zone deserves more detailed study of stable carbon isotopes. Experiments on the t5 13 C composition of respired CO 2 under different conditions in relation to the accumulated detritus and the remaining carbon could be of great importance. CONCLUSIONS

( 1) There is no well-defined overall relationship between the t513Cpoc values and the surface water temperature range of 30 to - 1 C. (2) The t5 13C values of Antarctic plankton are highly variable, although water temperatures are nearly uniform. These carbon isotope changes are attributed to different diatom communities with different carbon demands. High primary production associated with Thalassiosira spp, resulted in t5 13C values of about - 24%0, and low production in values of about - 34%0 (dominance of Corethron criophilum i . ( 3) Besides the internal carbon demand, the external CO 2 supply must influence the stable carbon isotope composition of POc. Highest biomasses in sea-ice cores dominated by pennate diatoms resulted in t5 13C values of about - 18%0. They are assumed to be due to CO 2 limitations in the more or less closed sea-ice system. (4 ) 13C enrichments of 3-4%0 may occur when phytoplankton is transformed to sinking krill faeces (e.g. Bransfield Strait). These alterations are apparently due to a preferred respiration of 12C by krill. Almost no isotope changes are observed when POC sinks as non-krill faeces, diatom chains or aggregates (e.g. Drake Passage, Powell Basin and NW Weddell Sea). ( 5 ) 13C enrichments at the sediment-water interface may be less than 1%0 (e.g. Bransfield Strait) or may reach 3-4%0 in the other areas. These alterations are possibly dependent on the intensity and/or the mode of benthic respiration. 0

ACKNOWLEDGEMENTS

I thank the officers and the crew of R/V "Polarstern" and R/V "Polar Duke" for their friendly help during the work on board. I am also indebted to

594

G. FISCHER

E. Steen, H. Berner, B. von Bodungen and G. Wefer for their work on the moorings, and to M. Segl and B. Meyer for stable carbon isotope analysis. H. Schmidt, J. Patzold, G. Wefer and two anonymous referees made critical suggestions to improve the manuscript. This work was funded by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 261 at Bremen University, Contribution 26).

REFERENCES Bathrnann, V., Fischer, G., Miiller, P.M. and Gerdes, D., 1991. Short-term variations in particulate sedimentation off Kapp Norvegia, Weddell Sea, Antarctica: relation to water mass advection, ice cover, plankton biomass and feeding activity. Polar Biol., II: 185-195. Biggs, D.C., Berkowitz, S.P., Altabet, M.A., Bidigare, R.R., DeMaster, D.1., Dunbar, R.B., Leventer, A., Macko, SA, Nittrouer, C.A. and Ondrusek, M.E., 1987. A cooperative study of upper-ocean particulate fluxes in the Weddell Sea. Ocean Drilling Project Initial Rep., 113: 77-86. Bishop, J.K.B., Edmond, J.M., Ketten, D.R., Bacon, M.P. and Silker, W.B., 1977. The chemistry, biology and vertical flux of particulate matter from the upper 400 m of the Equatorial Atlantic Ocean. Deep-Sea Res., 24: 511-548. Cooper, L.W. and DeNiro, M.J" 1989, Stable carbon isotope variability in the seagrass Posidonia oceanica: evidence for light intensity effects. Mar. Ecol. Prog, Ser., 50: 225-229. Craig, H., 1957. Isotopic standards for carbon and oxygen and correction factors for mass spectrometry analysis of carbon dioxide, Geochim. Cosmochim. Acta, 3: 133-149, Degens, E,T., Guillard, R.R.L., Sackett, W.M. and Hellebust, J.A., 1968. Metabolic fractionation of carbon isotopes in marine plankton-I. Temperature and respiration experiments. Deep-Sea Res., IS: 1-9. DeNiro, M.1. and Epstein, S., 1978. Influence of diet on the distribution of carbon isotopes in animals. Geochim. Cosmochim. Acta, 42: 495-506. Descolas-Gros, C. and Fontugne, M., 1990. Stable carbon isotope fractionation by marine phytoplankton during photosynthesis. Plant, Cell Environ., 13: 207-218. Deuser, w.G., 1970. Isotopic evidence for diminishing supply of available carbon during diatom bloom in the Black Sea. Nature, 225: 1069-1070. Eadie, B.1., 1972. Distribution and fractionation of stable carbon isotopes in the Antarctic ecosystem. Ph.D. Dissertation, A & M University, College Station, TX, 109 pp. Eadie, B.1. and Jeffrey, L.M., 1973. 6 13C analysis of oceanic particulate organic matter. Mar. Chern., I: 199-209. Eadie, B.1., Jeffrey, L.M. and Sackett, W.M., 1978. Some observations on the stable carbon isotope composition of dissolved and particulate organic carbon in the marine environment. Geochim. Cosmochim. Acta, 42: 1265-1269. Estep, M.F., Tabita, R.F., Parker, P.L. and Van Baalen, C; 1978. Carbon isotope fractionation by ribulose-I ,5-biphosphate carboxylase from various organisms. Plant Physiol., 61: 680687. Fischer, G., 1989. Stabile Kohlenstoff-Isotopen-Verhaltnisse in partikularer organischer Substanz aus dem Siidpolarmeer (Atlantischer Sektor). Berichte, Fachbereich Geowissenschaften, V niversitat Bremen, 161 pp. Fischer, G., Fiitterer, D., Gersonde, R., Honjo, S., Ostermann, D. and Wefer, G., 1988. Seasonal variability of particle flux in the Weddell Sea and its relation to ice cover. Nature, 335: 426428.


595

Fontugne, M., 1983. Les isotopes stables du carbone organique dans l'ocean, Applications ala paleoclimatologie. These Doctorat D'Etat, Universite Paris XI, 224 pp. Fontugne, M. and Duplessy, J.-C, 1978. Carbon isotope ratios of marine plankton related to surface water masses. Earth Planet. Sci. Lett., 41: 365-371. Fry, B. and Sherr, E.B., 1984. 8 13C measurements as indicators of carbon flow in marine and freshwater ecosystems. Contrib. Mar. Sci., 27: 13-47. Gersonde, R. and Wefer, G., 1987. Sedimentation of biogenic siliceous particles in Antarctic waters from the Atlantic sector. Mar. Micropaleontol., II: 311-332. Honjo, S. and Doherty, K.W., 1988. Large aperture time-series sediment traps; design objectives, construction and application. Deep-Sea Res., 35: 135-149. Jeffrey, A.W.A., Pflaum, R.C., Brooks, J.M. and Sackett, W.M., 1983. Vertical trends in particulate carbon 13C; 12C ratios in the upper water column. Deep-Sea Res., 30: 971-983. Kerby, N.W. and Raven, J.A., 1985. Transport and fixation of inorganic carbon by marine algae. In: J.A. Callow and A.W. Woolhouse (Editors), Advances in Botanical Research, Vol. 11. Academic Press, London, pp. 71-123. McCave, LN., 1975. Vertical fluxes of particles in the ocean. Deep-Sea Res., 22: 491-502. McConnaughey, T. and McRoy, C.P., 1979. Food-web structure and the fractionation of carbon isotopes in the Bering Sea. Mar. BioI., 53: 257-262. Mosara, F., Lacroix, M. and Duchesne, J., 1971. Variations isotopiques 13C/12C du CO2 respiratoire chez le rat, sous l'action d'hormones. CR. Acad. Sci., 273: 1752-1753. Mtiller, P.J., Suess, E. and Ungerer, A.C., 1986. Amino acids and amino sugars of surface particulate and sediment trap material from waters of the Scotia Sea. Deep-Sea Res., 33: 8 I9838. O'Leary, M.H., 1981. Carbon isotope fractionation in plants. Phytochemistry, 20: 553-567. Rau, G.H., Sweeney, R.E. and Kaplan, LR., 1982. Plankton 13C: 12C ratio changes with latitude: differences between northern and southern oceans. Deep-Sea Res., 29: 1035-1039. Rau, a.H., Mearns, A.J., Young, D.R., Olson, R.J., Schafer, H.A. and Kaplan, LR., 1983. Animal 13C/12C correlates with trophic level in pelagic food webs. Ecology, 64: 1314-13 I8. Rau, G.H., Takahashi, T. and Des Marais, DJ., 1989. Latitudinal variations in plankton 0 13C: implications for CO 2 and productivity in past oceans. Nature, 341: 516-518. Reimers, C.E. and Suess, E., 1983. Spatial and temporal patterns of organic matter accumulation on the Peru continental margin. In: E. Suess and J. Thiede (Editors), Coastal Upwelling, Part B. Plenum, New York, pp. 3 11-346. Rutgers van der Loeff, M.M. and Berger, G.W., 1991. Scavenging and particle flux: seasonal and regional variations in the Southern' Ocean (Atlantic sector). Mar. Chern., 35: 553-567. Sackett, W.M., Eckelmann, W.R., Bender, M.L. and Be, A.W.H., 1965. Temperature dependence of carbon isotope composition in marine plankton and sediments. Science, 148: 236237. Sarnthein, M., Winn, K., Duplessy, J.-C and Fontugne, M.R., 1988, Global variations of surface ocean productivity in low and mid latitudes: influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years. Paleoceanography, 3: 361-399. Smith, FA and Walker, N.A., 1980. Photosynthesis by aquatic plants: effects of unstirred layers in relation to assimilation of CO 2 and HCOj' and to carbon isotopic discrimination. New Phytol., 86: 245-259. Suess, E., 1980, Particulate organic carbon flux in the ocean-surface productivity and oxygen utilization. Nature, 288: 260-263. von Bodungen, 8., Fischer, G., Nothig, E.-M. and Wefer, G., 1987. Sedimentation of krill faeces during spring development of phytoplankton in Bransfield Strait, Antarctica. In: E.T. Degens, E. Izdar and S. Honjo (Editors), Particle Flux in the Ocean. Mitt. Geol-Palaontol, Inst. Univ. Hamburg, SCOPE UNEP Sonderband, 62: 243-257. Wada, E., Terazaki, M., Kabaya, Y. and Nernoto, T., 1987. 15N and 13C abundances in the

596

G. FISCHER

Antarctic Ocean with emphasis on the biochemical structure of the food web. Deep-Sea Res., 34: 829-841. Wefer, G. and Killingley, J.S., 1986. Carbon isotopes in organic matter from a benthic algae Halimeda incrassata (Bermuda): effects of' light intensity. Chern. Geol. (Isot. Geosci. Section), 59: 321-326. Wefer, G., Suess, E., Balzer, W., Liebezeit, G., MUller, P.J., Ungerer, A. and Zenk, W., 1982. Fluxes of biogenic components from sediment trap deployment in circumpolar waters of the Drake Passage. Nature, 299: 145-147. Wefer, G., Fischer, G., Fiitterer, D., Gersonde, R., Honjo, S. and Ostermann, D., 1990. Particle sedimentation and productivity in Antarctic waters of the Atlantic Sector. In: U. Bleil and J. Thiede (Editors), Geological History of the Polar Oceans: Arctic Versus Antarctic. Kluwer, Dordrecht, pp. 363-379. Wieneke, C. and Fischer, G., 1990. Growth and stable carbon isotope composition of coldwater macroalgae in relation to light and temperature. Mar. Ecol. Prog. Ser., 65: 283-292. Wong, W.W. and Sackett, W.M., 1978. Fractionation of stable carbon isotopes by marine phytoplankton. Geochim. Cosmochim. Acta, 42: 1809- I 815. Zeitzschel, B., Dieckmann, P. and Uhlmann, L., 1978. A new multisample sediment trap. Mar. BioI., 45: 285-288.