organic carbon dynamics in shelf edge sediments off the hebrides: a seasonal perspective

Int. Revue ges. Hydrobiol. I 82 I 1997 I 3 I 425-435

LYNDA MITCHELL’, s. MARTYN HARVEY’, JOHN D. G A G E ’ and ANTHONY E. FALLICK’

‘Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, P.O. Box 3, Oban, Argyll PA34 4AD, U.K.

*Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 OQF, U.K.

Organic Carbon Dynamics in Shelf Edge Sediments off the Hebrides : a Seasonal Perspective

key words: Shelf edge, continental slope, organic carbon, biogeochemistry, benthic fluxes

Abstract

A benthic transect across the Hebridean Shelf Edge was sampled 9 times during 1995-96. Sediment samples from within the ‘surface mixed layer were analysed for organic and inorganic carbon content, porosity, grain size and stable carbon isotope ratio. The organic carbon content is always 4% dry weight. Inorganic carbon content is 17-6595 CaCO,. There is no significant seasonal variation in organic or inorganic carbon contents despite changing productivity in the water column. However, there is an inverse relationship between organic carbon content and median grain size. The isotopic composition shows strong seasonal variation which reflects the increase in phytoplankton detritus at the sediment-water interface during spring/summer. The results suggest a small but rapid burial flux. However, the study area is not a significant depocentre for organic carbon.

1. Introduction

Although occupying less than 20% of global surface area, the continental margin is thought to have a disproportionately large importance in the biogeochemical cycling of carbon and nitrogen in the oceans. Estimates from the SEEP I and SEEP I1 studies during the 1980s in the northwestern Atlantic (WALSH ef al., 1988; BISCAYE ef nl., 1994) have indi- cated a relatively high particulate carbon flux on the continental slope thought to be derived from particle rain originating from both enhanced production at the shelf edge and export from the continental shelf. Hence continental slopes have been thought to represent major depocentres for carbon (ROWE e t a / . , 1986; HENRICHS and REEBURGH, 1987; W A L S H , 1991). These studies were initiated, in part, because it was perceived that production and consumption of organic material on the continental shelf were out of balance: episodic pulses of phytoplankton detritus are known to sink in large quantities, but the shelf sediments fre- quently consist of clean, coarse relict sands. It was hypothesised that the mid slope (1 -2 km depth) might be a sink for this ‘missing’ material (WALSH et al., 1988). The fate of this material continues to be a central question in models of global carbon cycling (SIEGENTHALER

In order to quantify organic carbon deposition and biogeochemical recycling on the Hebridean Shelf Edge, or indeed on any area of the sea floor, temporal variations in the input of phytodetrital detritus must be considered. It is now well known that, far from being the constant environment once thought, the deep sea floor may experience significant seasonal intermittancy in the input of labile organic material (HONJO, 1982; GAGE, 1991). Brief, episodic inputs may be critical in sustaining the benthic community. Frequent sampling is essential in order to minimise emors arising from estimates based on single, ‘snapshot’

and SARMIENTO, 1993).

426 L. MITCHELL er af.

observations and to provide more accurate data on rates of carbon utilisation and minerali- sation (SMITH et al., 1994).

The Shelf Edge Study (SES), of which the present work is part, is a component of the Land-Ocean Interaction Study (LOIS) funded by the U.K. Natural Environment Research Council. The SES project has studied processes occurring in the continental slope region of the Hebridean shelf edge off the west of Scotland. We here present results relating to the amount, origin and fate of organic material from studies undertaken on the shelf edge sediments resulting from nine SES cruises to the Hebridean shelf edge at different times of the year during 1995/96.

2. Study Area and Methods

The study area is located on the Hebridean shelf edge in the north east Atlantic off the west coast of Scotland (Fig. I) . A transect was established across the shelf edge running roughly SE-NW with four stations at depths of 700, 1,000, 1,500 and 2,000 m (positions 56.47" N, 9.16" W; 56.50" N, 9.30" W; 56.74" N, 9.42" W: 57.00" N, 10.00" W, respectively). The study area was visited nine times during the period April 1995 - July 1996 (Table 1). Sampling was undertaken by multicorer (BARNETT er al., 1984), yielding sediment cores with minimal surface disturbance. The multicorer avoids the down-wash or bow wave effect associated with other sampling devices which may cause displacement of surface sediments and superficial detritus together with their associated fauna. Cores were extruded from the core tubes, sliced into I-cm sections and frozen immediately on recovery. Samples for analyses were taken from the upper 4 cm slices (mixed layer) of sediment. Porosity (grain density) measurements were calculated from weight loss on freeze drying. Elemental organic and inorganic carbon contents were determined using a Leco CHN analyser before and after acid digestion. Grain size distributions were determined by a Coulter LS 100 grain size analyser.

Stable carbon isotope analysis was carried out to determine the origin of the organic material within the sediment. This is possible because different types of plants have distinctive isotopic signatures, due primarily to different photosynthetic pathways (LAJTHA and MARSHALL, 1994). Samples for stable carbon isotope analysis were prepared for analysis by washing thoroughly in 0.5 N hydrochloric acid in

Figure 1. SES study area, west of Scotland, with detailed map of study area showing location of sampling stations S700, R1000, N1500 and N2000. Contours shown from 300 to 2000 m water depth.

Organic Carbon Dynamics in Shelf Edge Sediments 427

- .

Table 1. Summary of samples taken (station numbers indicate water depth).

1.0 - - 0.9 6 - 0.8 6 - 0.7 - 0.6 - 0.5 $ - 0.4 - 0.3 .o

+Inorganic carbon 4 0 r g a n i c carbon

0.2 5 0.1 g 0.0

Cruise Date Stations sampled

CD92A CD93B Ch120 Chl21A Chl21C Ch123B Ch124 Ch126B Ch128B

April 95 May 95 July 95 Aug 95 Sept 95 Dec 95 Jan 96 April 96 July 96

~

S700, R1000, N1500, N2000 S700, R1000, N1500 R1000, N1500, N2000 S700, R1000, N1500 S700, RlOOO S700, R1000, N1500 R 1000 R1000, N1500, N2000 S700, RlOOO

order to remove inorganic carbonates. after which each sample was placed in dialysis tubing for at least 24 hours in a bath of continuously stirred distilled water to remove traces of acid and salts. The samples were then freeze dried. Stable carbon isotope analyses were carried out at the Scottish Universities Research and Reactor Centre at East Kilbride, Scotland. Samples were placed in evacuated quartz glass tubes and oxidized with'copper oxide at 850 "C for 8 hours to produce carbon dioxide (SOFER, 1980). The carbon dioxide gas was passed through a 'slush trap' of dry ice and acetone at -78 "C to remove water vapour. Volatile gaseous contaminants were removed by vacuum pump whilst freezing the carbon dioxide to the temperature of liquid nitrogen (-197 "C). The isotopic composition of the carbon dioxide was determined using a Sira 10 mass spectrometer and recorded relative to the Pee Dee Belem- nite (PDB) standard (EPSTEIN et al., 1953).

3. Results

Organic carbon contents are less than 1 % dry wt in all samples and less than 0.2% at the 700 and 1,000 m stations. Inorganic carbon contents varied between about 2.5-8% (about 17-65% CaCO,) but were again lowest at 700 and 1,000 m, with the 1,000 m station showing the lowest values for both organic and inorganic carbon. Values for both organic and inorganic carbon were very depth specific (Fig. 2), but showed no significant seasonal variation (Fig. 3). The error bars show that variation in organic carbon within the top 4 cm is very small but greatest at the two deepest stations.

s 7 C6 $ 5 z 4

Figure 2. Organic and inorganic carbon distribution with water depth. Error bars show 1 standard deviation.

428 L. MITCHELL er al.

0 2 4 6 8 10 12 14 16 18 20

Month

Figure 3. Seasonal variability in organic carbon distribution at the four different water depths. Points show average values from the top four 1 cm sediment slices. Error bars show 1 standard deviation.

The sediments at the two shallower stations (700 and 1,000 m) are characterised by a larger grain size and lower porosity (water content) than the deeper stations (Fig. 4). Grain size distributions in the surface sediments at 700 and 1,000 m show a single peak at about 170 pm (Figs 5 a and 5b). By contrast, at 1,500 and 2,000 m the median grain size is much smaller and the grain size distribution is trimodal, the peak at 170 pm being much reduced and two larger peaks becoming evident at about 12 and 40 pm (Figs. 5c and 5d).

The median grain size shows an inverse relationship with the organic carbon content (Fig. 6) . The data lie around a curve such that the smaller the grain size, the greater the effect of a difference in grain size on the organic carbon content.

Carbon isotope data show a strong seasonal variation. Data from the summer months (April-September 1995) are closely grouped around a mean of about -22%0, with the highest value in May (the time of the phytoplankton bloom). Data from the winter months are much lower, with a mean of around -25%0, and the lowest value in January 1996 (Fig. 7).

1.0 .- E 0.9

P 0.7 ; 0.8

0.6 0.5 0.4 0.3 0.2 0.1 0.0

0 1000 2000 3000 Depth (in)

200 175 5 150

125 x 100

.-

.- 75 g 50 2 25 2 0

Figure 4. Sediment porosity and mean grain size data with water depth. Error bars show 1 standard deviation.


- ':.m q----J lOOOm

z 6

- B 4 - 3 2

0 .i i 10 100 moo .l i 10 100 woo

Particle Sic (pn) Particle Size (pm)

g q-----J q-----J 2000m

g 6 = 4 P

2

0 , .1 1 HI 100 woo .l 1 la wo 1000 Particle Sire (pm) Panicle Size (pm)

Figure 5. Grain size distributions at different water depths.

1

0.9 h

8 0.8 - f 0.7 -

0.6 -

2 0.5 -

0 0.4 -

c 0.3 -

C

2 0

m 0)

.-

6 0.2 -

0.1 - 0 1 0 50 100 150 20

Median grain size (microns)

Figure 6. Relationship between grain size and organic carbon content.

430 L. MITCHELL et al.

-20 I 1

0 2 4 6 8 10 12 14 16 18 20 22 24 month

Figure 7. Seasonal variation in stable carbon isotope results.

There is no significant downcore trend within the top 4cm of cores in any of the measured parameters. This is not surprising as all samples are from within the sediment surface mixed layer (unpublished radioisotope data).

4. Discussion

The organic carbon content of the Hebridean shelf edge sediments is low and the inorganic content fairly high when compared with other marine sediments (Table 2). In terms of organic and inorganic carbon content, mean grain size and porosity (water content), the properties of the surface sediments of the two shallower stations are significantly different from those at the two deeper stations. This may be due to differing hydrodynamic regimes: the coarser sediments at 700 and 1,000 m could be due to the effects of a northward flowing along-slope current, evidence for which has been seen from seabed photographs and current meter data at depths of 500 to 1,100 m (HOWE and HUMPHERY, 1995). The presence of specific peaks in the grain size distributions indicates the predominance of certain particles; these may be the skeletons of microfossils. Abundant foraminiferan tests are evident as a dominant constituent of the 700 and 1,000 m sediments (170 pm peak). Coccoliths, the minute calcite scales of coccolithophores, grow to a maximum of about 15 prn in diameter before being shed (BLACK, 1988) and may therefore account for the 12pm peak. Other planktonic skeletons such as diatoms may account for the 40 pm peak.

Table 2.

Study Area Organic carbon Inorganic carbon Source

Hebridean Shelf Edge O.1-0.8% 17-65 %CaCO, This study Cape Hatteras 0.9- I .3% 11-17 %CaCO, DIAZ et al., 1994 NW Arabian Sea up to 7.5% SHIMMIELD et al., 1990 NW Arabian Sea 0.7-6.8% 29-69 %CaCO, EMEIS et al., 1991 SW African Shelf 0.7-7.8% 6-42 %CaCO, EMEIS et al., 1991 Goban Spur 0.2-0.7% FLACH and HEIP, 1996

Organic and inorganic carbon contents of surface sediments from selected sites

Organic Carbon Dynamics in Shelf Edge Sediments 43 1

The inverse relationship between the organic carbon content and the median grain size of the sediment suggests that the organic carbon content of these sediments may be determined by the available surface area of particles rather than being directly related to surface productivity or organic carbon flux to the sediment surface. Organic material binds to the surfaces of particles. Over 90% of the organic matter preserved in most marine sediments has been shown to be intimately associated with mineral surfaces (MAYER, 1994). Sorption of organic matter to mineral surfaces stabilizes the component molecules, slowing remine- ralisation by up to five orders of magnitude, and allowing the preservation of intrinsically labile molecules (KIEL et al., 1994). The smaller the particles, the greater the available surface area for this process. Surface productivity may play an indirect role by providing very small particles (such as coccoliths) for the organic material to bind to, but these particles will themselves be redistributed by physical and chemical processes (current activity, disso- lution).

The constant, low organic carbon content of these sediments and relationship between organic material and particle surface area suggest that, during the spring bloom, the large amount of material reaching the seabed at the Hebridean shelf edge does not become per- manently buried. Indeed, a large amount of phytodetrital material was seen resting on the surface of the sediment of some cores during the bloom in May 1995 (personal observation). The fate of this materi'al remains largely unknown: much of it may be transported further downslope or consumed at the sediment surface by the benthic community. The deep-sea benthos has long been recognised as a community dominated by detrital decomposers and deposit feeders which depend on the supply of organic material from above (PFANNKUCHE, 1993). It is now known that the deep-sea is characterised by significant seasonal pulses of phytodetritus sedimentating rapidly from the surface (ASPER et al., 1992; SMITH et af., 1994) which result in rapid increases in the biomass of benthic organisms (GRAF, 1989), and particularly microorganisms (PFANNKUCHE, 1992 ; 1993). In the North Pacific, benthic sediment community oxygen consumption showed a sharp increase between winter and summer values, and mobile epibenthic epifauna was twice as active when detrital aggregates were present on the seafloor as during the rest of the year (SMITH et nf., 1994). Labelled algae placed on the seafloor off Cape Hatteras entered the guts of deposit feeding annelids within only 1.5 days (BLAIR et af., 1996). Furthermore, benthic community biomass in the north Atlantic has been shown to correlate much better with particulate organic carbon (POC) flux than with sediment detrital organic carbon, indicating that most organic matter is consumed on the sediment surface rather than within the sediments (ROWE et al., 1991). Freshly depo- sited phytodetritus on the seafloor of the N.E. Atlantic was shown to support a considerable number of benthic organisms particularly nematodes and benthic foraminiferans (THIEL et af., 1988).

The strong seasonal variation in stable carbon isotope data indicate changes in the origin of the organic detritus within the sediment. The difference in values between April 1995 and April 1996 reflect the fact that the spring bloom occurred later the second year. Summer values (around -22%0) are typical of organic material in oceanic sediments and reflect a predominance of phytoplankton detritus (typical value -21%0). Winter values (around -25%0) are consistent with a minimum phytoplankton input and a correspondingly larger proportion of more isotopically depleted material, probably land plant detritus (typical value -27%0). These results show that some, at least, of the sedimentating phytoplankton detritus is quick- ly incorporated into the surface sediment and that the organic flux across the sediment-water interface, though small, is rapid. This could be due to physical mixing by currents or to bioturbation. Many infaunal deposit feeders take in organic material from the sediment surface whilst also returning it to the sediment surface as mounds of faecal egesta (NICKELL and ATKINSON, 1994; BE?T et al., 1995; HUGHES et al., 1996). Sediment mounds formed of faecal material from megafaunal deposit feeders can form rapidly in most deep sea environ- ments, indicating rapid recycling of organic material across the sediment-water interface


(SMITH et al., 1986). Viable diatoms have been found at depths of 14 cm in burrows off Cape Hatteras, North Carolina (CAHOON et al., 1994).

A simple mixing model assuming two end points (pure phytoplankton and pure terrestrial detritus) can, with a few assumptions, be used to determine the approximate composition of the organic material in the sediment from its stable carbon isotope signature, and from that, the approximate seasonal variation in the amount and type of organic material at the sediment surface. It is difficuIt to estimate absolute proportions accurately as the signatures of the end points are not definitively fixed: for instance, 6I3C values on the North Carolina continental slope of -21.2, -19.6 and -18.7%0 were reported characteristic of the shelf and slope of the Eastern U.S. in an area of predominantly marine input (BLAIR et al., 1994). These values may have been influenced by a number of factors, including diagenesis, heterotro- phic activity or the presence of kelp or animal debris. However, if we assume that the phytoplankton signature is -21%0 and the terrestrial signature is -27%0, and that the movement of organic material across the sediment-water interface into the sediment is non-selective, then in winter (w),

-21a+-27b=-25,

where a is the proportion of phytoplankton detritus and b is the proportion of terrestrial detritus,

. ‘ . 2 5 = 2 7 b + 2 1 a and b = l - a ,

:. 25 = 27 - 27a + 21a = 27 - 6 a ,

:. 6a = 2, So a = 21, and b =‘I, .

-21a + -27b = -22,

.’. 2 2 = 2 7 b + 21a and b = 1 - a ,

:. 22 = 27 - 27a + 2 l a = 27 - 6a,

.*. 6a = 5 , So a = 5i, and b = ‘ 1 6 .

The simple mixing model gives a winter organic composition on the Hebridean shelf edge of approximately two thirds terrestrial to one third marine, and a summer composition of approximately one sixth terrestrial to five sixths marine. If we then assume that the amount of terrestrial detritus is constant (though this is not necessarily the case), then if x is the amount of phytoplankton detritus, y is the amount of terrestrial detritus, and z is the total amount of organic detritus, we know that

i

And in summer (s),

y, = ‘16 Z,, X, = j/6 Z,, j’, = ‘16 Z,, and X, = 2/6 2, . If

y, = yw then ’16 z, = ‘16 z, ,

... Z, = 42,

And x, = ’16 = ’16 ’ 42, ,

x, = 2 1 6 2, ,

:. x, = 5 t 6 . 4 . 3x, = lox,,

:. 2, = 3x,,

The model indicates a fourfold increase in total organic detritus at the sediment-water interface, corresponding to a tenfold increase in the amount of incoming marine phytoplankton detritus during summer. This value is consistent with the results of HONJO (1982)


based on sediment trap data from Panama Basin. However, only a small and constant subsample of this material is transported down across the sediment-water interface into the sediment, as shown by the low quantity and lack of seasonal variation in the organic carbon content of the sediment. The remaining ‘pool’ of material stays above the sediment-water interface. This material was seen as phytodetrital ‘fluff‘ resting on the surface of some of the cores taken during the spring bloom, as mentioned above (personal observation).

The fate of this material remains unclear. It is still not certain what proportion is consumed immediately by benthic and benthopelagic organisms and what proportion is transported further downslope. Downslope transport is clearly an important process : in the North Pacific, measured rates of benthic carbon oxidation near the continental margin exceeded the fluxes of organic carbon determined from sediment traps by a factor of three, indicating that near-bottom lateral transport is an important source of organic material (JAHNKE etal., 1990). It has been suggested that downslope resuspension and near bottom transport may introduce significantly more organic material than previously estimated to sediments of continental margins (WALSH et af., 1991). Indeed, this material may have already been transported from further upslope to this location. However, the SES study area is not a depocentre for burial of this material. Whether it accumulates further down the slope remains to be seen.

5 . Summary

The amount-of organic carbon residing in the sediment is small, less than 1 % dry wt in all samples and less than 0.2% dry weight at the two shallower stations (700 and 1000 m stations). Inorganic carbon contents are fairly high, between 2.5 and 8% dry weight (about 17-65% CaCO,). There is no significant seasonal variation in buried organic or inorganic carbon at any station despite changing productivity in the overlying water column. There is an inverse relationship between organic carbon content and median grain size, suggesting that the organic content may be more related to the available surface area of sediment particles rather than surface productivity. The excess incoming organic material, which does not bind to sediment particles, may be either consumed at the sediment surface or transported away by currents. A very small proportion becomes buried and the area is therefore not a significant depocentre for organic carbon.

The isotopic composition of the organic carbon shows significant seasonal variation, suggesting a small but rapid flux of organic material into the sediment, due to either physical mixing or bioturbation. Stable carbon isotope results from sediment organics show that the buried material is dominated by phytoplankton detritus in summer. Winter values, in the absence of such large amounts of phytoplankton detritus, show a larger proportion of more isotopically depleted material which is probably terrestrial in origin. Using a simple mixing model, isotope values suggest a winter composition of organic material of one third marine to two thirds terrestrial, and a summer composition of five sixths marine to one sixth terrestrial. These figures suggest a possible tenfold proportional increase in phytoplankton detritus, and a corresponding fourfold increase in total organic detritus, at the seabed from winter to summer. However only a small subsample of this material is transported across the sediment-water interface into the sediment. Organic carbon burial is not a significant process in this area.

6. Acknowledgements

Thanks are due to the officers, crews and scientists on board the Royal Research Ships Charles Dar- win and Challenger. This work was funded by NERC Research Grant (GST/02/734) ‘Benthic Fluxes at


the Hebridean Shelf Edge' awarded to JDG. The Isotope Geosciences Unit at SURRC is supported by NERC and the consortium of Scottish Universities. The manuscript was improved after comments by 0. PEPPE and two anonymous reviewers.

7. References

ASPER, V.L., W.G. DEUSER, G.A. KNAUER and S.E. LOHRENZ, 1992: Rapid coupling of sinking particle fluxes between surface and deep ocean waters. - Nature 357: 670-672.

BARNETT, P.R.O., J. WATSON and D. CONNELLY, 1984: A multiple corer for taking virtually undisturbed samples from shelf, bathyal and abyssal sediments. - Oceanologica Acta 7: 399-408.

BEIT, B.J., A.L. RICE and M.H. THURSTON, 1995: A quantitative photographic survey of 'spoke burrow' type Lebensspuren on the Cape Verde Abyssal Plain. Int. Revue ges. Hydrobiol. 80: 153-170.

BISCAYE, P.E., C.N. FLAGG and P.G. FALKOWSKI, 1994: The Shelf Edge Exchange Processes experiment, SEEP 11: an introduction to hypotheses, results and conclusions. - Deep-sea Research I1 41:

BLACK, R.M., 1988: The Elements of Palaeontology. - Cambridge, Cambridge University Press,

BLAIR, N.E., L.A. LEVIN, D.J. DEMASTER and G. PLAIA, 1996: The short-term fate of fresh algal carbon in continental slope sediments. - Limnology and Oceanography 41: 1208- 1219.

BLAIR, N.E., G.R. PLAIA, S.E. BOEHME, D.J. DEMASTER and L.A. LEVIN, 1994: The remineralization of organic carbon on the North Carolina continental slope. - Deep-sea Research 41: 755-766.

CAHOON, L.B., R.A. LAWS and C.J. THOMAS, 1994: Viable diatoms and chlorophyll a in continental slope sediments' off Cape Hatteras, North Carolina. - Deep-sea Research 41: 767-782.

DIAZ. R.J., G.R. CUTTER and D.C. RHOADS, 1994: The importance of bioturbation to continental slope sediment structure and benthic processes off Cape Hatteras. North Carolina. - Deep-sea Research 41 :

EMEIS, K.C., J.W. MORSE and L.L. MAYS, 1991: Organic carbon, reduced sulfur, and iron in Miocene to Holocene upwelling sediments from the Oman and Benguela upwelling systems. - Proceedings of the Ocean Drilling Program, Scientific Results 117, 517-527.

EPSTEIN, S . , R. BUCHBAUM, H.A. LOWENSTAM and H.C. UREY, 1953 : Revised carbonate-water isotopic temperature scale. - Bull. Geol. SOC. Amer. 64: 1315-1326.

FLACH, E.. and C. HEIP, 1996: Seasonal variations in faunal distribution and activity across the continental slope of the Goban Spur area (NE Atlantic). - J. Sea Res. 36: in press.

GAGE, J.D., 1991: Biological rates in the deep sea: A perspective from studies on processes in the benthic boundary layer. - Reviews in Aquatic Sciences 5: 49-100.

GRAF, G., 1989: Benthic-pelagic coupling in a deep sea benthic community. - Nature 341: 437-439. HENRICHS, S.M., and W.S. REEBURGH, 1987: Anaerobic mineralization of marine sediment organic mat-

ter: rates and the role anaerobic prosesses in the oceanic carbon economy. - Geomicrobiology Jour- nal 5: 191-237.

HONIO, S., 1982: Seasonality and interaction of biogenic and lithogenic particulate flux at the Panama Basin. - Science 218: 883-884.

HOWE, J.A., and J.D. HUMPHERY, I995 : Photographic evidence for slope-current activity, Hebrides Slope, NE Atlantic Ocean. - Scottish Journal of Geology 30: 107- 115.

HUGHES, D.J., A.D. ANSELL and R.J.A. ATKINSON, 1996: Sediment bioturbation by the echiuran worm Maxmiielleria lunkesreri (HERDMAN) and its consequences for radionuclide dispersal in Irish Sea sediments. -Journal of Experimental Marine Biology and Ecology 195: 203-220.

JAHNKE, R.A., C.E. REIMERS and D.B. CRAVEN, 1990: Intensification of recycling of organic matter at the sea floor near ocean margins. - Nature 348: 50-54.

KIEL. R.G., D.B. MONTLUCON, F.G. PRAHL and J.I. HEDGES, 1994: Sorbtive preservation of labile organic matter in marine sediments. - Nature 370: 549-552.

LAJTHA, K., and J.D. MARSHALL, 1994: Sources of variation in the stable isotopic composition of plants. - In: K. LAJTHA and R.H. MITCHENER (eds.), Stable Isotopes in Ecology and Environmental Science, Black- well Scientific Publications. pp. 1-21.

MAYER, L.M., 1994: Surface area control of organic carbon accumulation in continental shelf sediments. - Geochimica et Cosmochimica Acta 58: 1271-1284.

231 -252.

404 PP.

7 19-734.


NICKELL, L.A. and R.J.A. ATKINSON, 1994: Observations on the behaviour of Thalassema rhalassernum (Echiua: Echiuridae). -Journal of the Marine Biological Association of the U.K. 74: 963-966.

PFANNKUCHE, O., 1992: Organic carbon flux through the benthic community in the temperate abyssal northeast Atlantic. - In: G.T. ROWE and V. PARIENTE (eds.), Deep-sea Food Chains and the Global Carbon Cycle, Kluwer Academic Publishers. pp. 183- 198.

PFANNKUCHE, 0.. 1993: Benthic response to the sedimentation of particulate organic matter at the BIOT- RANS station, 47" N, 20" W. - Deep-sea Research 40: 135-149.

ROWE, G., M. SIBUET, J. DEMING, A. KHRIPOUNOFF, J. TIETJEN, S . MACKO and R. THEROUX, 1991 : 'Total' sediment biomass and preliminary estimates of organic carbon residence time in deep-sea benthos. - Mar. Ecol. Prog. Ser. 79: 99- 114.

ROWE, G.T., S . SMITH, P. FALKOWSKI, T. WHITLEDGE, R. THEROUX, W. PHOEL and H. DUCKLOW, 1986: Do continental shelves export organic matter? - Nature 324: 559-561.

SHIMMIELD, G.B., N.B. PRICE and T.F. PEDERSEN, 1990: The influence of hydrography, bathymetry and productivity on the sediment type and composition on the Oman Margin and in the Northwest Ara- bian Sea. - In: The Geology and Tectonics of the Oman Region, Geol. SOC. Special Publication 49:

SIEGENTHALER, U. and J.L. SARMIENTO, 1993: Atmospheric carbon dioxide and the ocean. - Nature 365:

SMITH, C.R., P.A. JUMARS and D.J. DEMASTER, 1986: In sirir studies of megafaunal mounds indicate rapid sediment turnover.and community response at the deep-sea floor. - Nature 323: 25 1-253.

SMITH, K.L., R.S. KAUFMANN and R.J. BALDWIN, 1994: Coupling of near-bottom pelagic and benthic processes at abyssal depths in the eastern North Pacific Ocean. - Limnol. Oceanogr. 39: 1101-1118.

SOFER, Z., 1980: Preparation of carbon dioxide for stable isotope analysis of petroleum fractions. - Ana- lytical Chemistry 52: 1389-1391.

THIEL, H., 0. PFANNKUCHE, G. SCHRIEVER, K. LOCHTE, A.J. GOODAY, C. HEMBLEBEN, R.F.G. MANTOURA, C.M. TURLEY,' J.W. PATCHING and F. RIEMANN, 1988: Phytodetritus on the deep-sea floor in a central oceanic region of the northeast Atlantic. - Biological Oceanography 6 : 203-239.

WALSH, J.J., 1991: Importance of continental margins in the marine biogeochemical cycling of carbon and nitrogen. - Nature 350: 53-55.

WALSH, J.J., P.E. BISCAYE and G.T. CSANADY, 1988: The 1983- 1984 Shelf Edge Exchange Processes (SEEP)- I experiment: hypotheses and highlights. - Continental Shelf Research 8: 435-456.

WALSH, J.J., D.A. DIETERLE and J.R. PRIBBLE, 1991 : Organic debris on the continental margins: a simu- lation analysis of source and fate. - Deep-sea Research 38: 805-828.

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Manuscript received March 20th, 1997; revised June 16th, 1997: accepted June 18th. 1997

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y 19

98

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issi

on of

man

uscr

ipts

3

Aug

ust 1

998

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fere

nce

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pt 1

998

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mes

1.

Sha

llow

lake

s in

low

land

rive

r lak

e

2. C

atch

men

t ar

ea

and

nutr

ient

3. A

biot

ic st

ruct

ure

(hyd

rody

nam

ics

4. S

edim

ent-

wat

er i

nter

acti

ons1

5. B

lue-

gree

n al

gae

and

com

petit

ion

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enth

ic-p

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tera

ctio

ns

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ttora

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coup

ling (

esp.

Fish)

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ole

of m

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phyt

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bio

tic a

nd

9. B

istab

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of sh

allo

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kes

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-lake

syst

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load

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and

unde

r-w

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ligh

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ent fluxes

with

oth

er au

totro

phs

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tic in

tera

ctio

ns

mea

sure

s

0 rg

an iz

ing

Com

mit

tee

Ch

airp

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ns:

Inst

itute

of F

resh

wat

er E

colo

&

and

Inla

nd F

ishe

ries

Brig

itte N

ixdo

rf

Bra

nden

burg

Tec

hnic

al U

nive

rsity

of

Cot

tbus

, Wat

er P

rote

ctio

n

,1

Nor

bert

Walz

.

Adv

isor

y B

oard

: H

orst

Beh

rend

t Fr

ank

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uais

M

icho

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upfe

r T

hom

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endr

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chub

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n St

einb

erg

Secr

etar

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: In

stitu

te of F

resh

wat

er E

colo

gy a

nd

Inla

nd F

ishe

ries

Mue

ggel

seed

amm

260

1256

2 B

erlin

(Ger

man

y)

Tel.:

+49

30

- 64

19 05

11

E-m

ail:

wal

z@ig

b-be

rlin.

de

Fax.:

+49

30

- 64

19 05

23

Fir

st A

nnou

ncem

ent

Shal

low

Lakes ‘

98

Inte

rnat

iona

l Con

fere

nce

on

Trophic

Inte

ract

ions

in

Sha

llow

Fre

shw

ater

an

d B

rack

ish

Lak

es

3 - 8

Au

gu

st 1998

Surr

ound

ings

of B

erlin

(G

erm

any)

Org

aniz

ed b

y In

stitu

te of

Fre

shw

ater

Ec

olog

y an

d In

land

Fis

herie

s Ber

lin

Bra

nden

burg

Tec

hnic

al U

nive

rsity

of

Cot

tbus

unde

r the

aus

pice

s of

The

Inte

rnat

iona

l Ass

ocia

tion

of Th

eore

tical

and

A

pplie

d Li

mno

logy

(SIL

)

organic carbon dynamics in shelf edge sediments off the hebrides: a seasonal perspective

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