MARINE ECOLOGY PROGRESS SERIESMar Ecol Prog Ser

Vol. 440: 127–136, 2011doi: 10.3354/meps09385

Published October 28

INTRODUCTION

Because of the highly episodic nature of primaryproduction in seasonally ice-covered areas, the ex -port of organic carbon to the deep ocean, or its reten-tion in the upper water, is determined by the interac-tion between the development of the phytoplanktoncommunity and the seasonal dynamics of zooplank-ton (Andreassen et al. 1996, Wassmann et al. 1996,2004, Sakshaug 2004, Lalande et al. 2007). A matchor mismatch between phytoplankton blooms and zoo-plankton grazing has important consequences for theecosystem as it affects the magnitude and composi-tion of the exported particulate matter and hence the

food supply to benthic communities (Grebmeier &Barry 1991, Klages et al. 2004). The magnitude andcomposition of the exported material is particularlyimportant in the deep Fram Strait, where food avail-ability at the seafloor is the determinant factor con-trolling large-scale distribution patterns of deep-seamegafauna (Soltwedel et al. 2009).

The Fram Strait, located between Northeast Green-land and the Svalbard Archipelago, is a gateway forAtlantic Water entering the Arctic Ocean. The warmAtlantic Water (3 to 4°C) transits northward with theWest Spitsbergen Current in the eastern Fram Strait,where it merges with the cold Arctic Water (<0°C)flowing southward with the East Greenland Current

© Inter-Research 2011 · www.int-res.com*Email: catherine.lalande@awi.de

Downward particulate organic carbon export athigh temporal resolution in the eastern Fram Strait:

influence of Atlantic Water on flux composition

Catherine Lalande*, Eduard Bauerfeind, Eva-Maria Nöthig

Alfred Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany

ABSTRACT: A sediment trap was deployed at 340 m from April to July 2003 to monitor the down-ward export of particulate organic carbon (POC) at high temporal resolution in the marginal icezone of the eastern Fram Strait. Although POC fluxes remained <15 mg m−2 d−1, variations in themagnitude and composition of the exported POC were observed during deployment. A first periodof elevated POC export associated with an increase in diatom fluxes and low zooplankton fecalpellet fluxes was recorded at the beginning of May, suggesting a mismatch between phytoplank-ton production and zooplankton grazing. A second period of elevated POC export composed ofcoccolithophores, diatom resting spores and empty diatom frustules was observed in June. Thistransition in the composition of the export fluxes reflected a shift in water masses caused by theonset of an ice-edge eddy bringing warm Atlantic Water into the region at the beginning of June.The cyclonic eddy also contributed to the rapid export of Phaeocystis pouchetii, a microalga thatdoes not significantly contribute to carbon export in stratified waters. The main contributors to thezooplankton fecal pellet flux also varied according to the prevailing water mass, with copepodfecal pellets dominating throughout the deployment, except at the beginning of June, when thefecal pellet flux in Atlantic Water was dominated by appendicularian fecal pellets. These resultsindicate that a prevalence of Atlantic Water may have a large impact on the magnitude and com-position of POC export in the eastern Fram Strait.

KEY WORDS: POC export · Sediment trap · Fecal pellets · Eddy · Atlantic Water · Fram Strait

Resale or republication not permitted without written consent of the publisher

Mar Ecol Prog Ser 440: 127–136, 2011

in the western Fram Strait (Schauer et al. 2004,Polyakov et al. 2005). Sea ice conditions and the posi-tion of the ice edge in the Fram Strait are mainly de -termined by the interactions between the warmAtlantic Water and the cold Arctic Water, with perma-nent ice-covered areas in the west, permanent ice-free areas in the southeast, and seasonally varyingconditions in the central and eastern Fram Strait (Blachowiak-Samolyk et al. 2007). Therefore, sea-sonal and interannual variations in water mass distri-bution and sea ice cover are major factors constrain-ing the timing and magnitude of primary productionin the Fram Strait when sunlight is sufficient.

Several investigations using short-term drifting orlong-term moored sediment traps have been con-ducted in the seasonally ice-covered Arctic Oceanto estimate the magnitude and seasonal variabilityof particulate organic carbon (POC) export (e.g.Wassmann et al. 2004). However, fluxes were usu-ally ob tained for brief deployments (~24 h) or forlong de ployments with low temporal resolution,whereby each flux measurement corresponds to sev-eral days or weeks. In the present study, a sedimenttrap was deployed at high temporal resolution in themarginal ice zone of the eastern Fram Strait to bet-ter evaluate the temporal variability of POC exportin relation with the development of the phytoplank-ton and zooplankton communities. This sedimenttrap was de ployed as part of a time series of sedi-

ment trap de ployments performed since 2000 atHAUSGARTEN, an observatory established by theAlfred Wegener Institute for Polar and MarineResearch to detect and track the impact of large-scale environmental changes in the transition zonebetween the northern North Atlantic and the centralArctic Ocean (Bauerfeind et al. 2009). This high res-olution investigation of the magnitude and composi-tion of the sinking material provides insight on theprocesses affecting the downward POC export inthis remote region.

MATERIALS AND METHODS

Sampling

A modified automatic Kiel sediment trap with asampling area of 0.5 m2 and 20 collection cups (Krem-ling et al. 1996) was deployed at 340 m for 80 d from25 April to 14 July 2003 at the HAUSGARTEN obser-vatory, located ~120 km west of Spitsbergen in theeastern Fram Strait (78° 59’ N, 4° 27’ E; water depth =2568 m; Fig. 1). Sediment trap sampling cups rotatedevery 4 d to measure downward export fluxes at hightemporal resolution. Sample cups were filled with fil-tered seawater poisoned with HgCl2 (0.14% finalsolution) and adjusted to a salinity of 40 with NaCl, topreserve samples during deployment and after recov-

ery. In the laboratory, swimmers wereremoved with forceps and rinsedunder a dissecting microscope beforesplitting of subsamples for the mea-surement of POC, calcium carbonate(CaCO3), biogenic particulate silica(bPSi), phytoplankton cells, and zoo-plankton fecal pellets. Preparationsand measurements of the subsampleswere per formed as described by vonBo dungen et al. (1991), with theexception of acidification of CaCO3

and POC filters, which were soakedwith 0.1 N HCl instead of fuming withconcentrated HCl. Filters for CaCO3

measurements were weighed beforeacidification, rinsed with distilledwater to re move residual CaCl2 aftertreatment, and reweighed after dry-ing at 60°C. CaCO3 values were cal-culated from the weight difference tototal mass, while POC measurementswere conducted on a Carlo Erba CHNanalyzer. POC fluxes were not cor-

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Fig. 1. Location of the sediment trap (black triangle) deployed from April to July2003 at the HAUSGARTEN observatory (black rectangle) in the eastern FramStrait west of the Svalbard Archipelago. The gray arrows represent branches of

the West Spitsbergen Current carrying Atlantic Water into the region

Lalande et al.: POC export in the Fram Strait

rected for dissolution of organic material in the sam-pling cups and should be considered as minimum values. Subsamples for bPSi were filtered on polycar-bonate filters (pore size: 0.8 µm), and bPSi mea -surements were ob tained by wet-alkaline digestionof the samples (von Bodungen et al. 1991).

Additional subsamples were used for the micro-scopic analysis of phytoplankton cells and zooplank-ton fecal pellets. Phytoplankton cells were enumer-ated by inverted microscopy according to theUter möhl (1958) method. A minimum of 50 to 100phyto plankton cells of the dominant groups werecounted at 4 magnifications (100, 160, 250, and400×) using phase contrast microscopy. Only thedominant and identifiable cells were counted,including intact cells, empty frustules, and restingspores of diatoms. Zooplankton fecal pellets wereenumerated (50 to 700 pellets depending on the sub-sample) using a dissecting scope. The length andwidth of each fecal pellet were measured at 2 mag-nifications (20 or 25×), and pellet volumes were cal-culated based on the cylindrical or ellipsoidal shapeof the pellets. According to their shape and size,cylindrical pellets were attributed to calanoid cope-pods and ellipsoidal pellets with a diameter >60 µmwere attributed to ap pen di cularians (Sampei et al.2009). Ellipsoidal pellets with a diameter <60 µmmay be attributed to the small cyclopoid copepodOi tho na similis (Sampei et al. 2009), but no pelletscorresponding to this size were measured. Fecal pel-let volumes were converted to fecal pellet carbon(FPC) using a volumetric carbon conversion factor of0.057 mg C mm−3 for copepod pellets and 0.042 mgC mm−3 for appendicularian pellets (González &Smetacek 1994, González et al. 1994). POC, CaCO3,bPSi, phytoplankton cells, and zooplankton FPCfluxes were averaged to daily fluxes for each collec-tion period.

Remote sensing

Daily sea ice concentrations in the sampling regionwere obtained by analysis of satellite-derivedAdvanced Microwave Scanning Radiometer for EOS(AMSR-E) data provided by the National Snow andIce Data Centre. The 89 GHz AMSR-E sensor and theARTIST Sea Ice (ASI) algorithm were used, yieldinga spatial resolution of 6.25 × 6.25 km (Spreen et al.2008). Satellite-derived chlorophyll a concentrations(chl a) above the sediment trap were obtained from 7April to 15 July 2003 from the GlobColour Project(ESA). Chl a concentrations were retrieved at a reso-

lution of 4 km and for 8 d binning periods using thesemi-analytical GSM algorithm (Garver & Siegel1997, Maritorena et al. 2002) applied to mergedwater leaving reflectance spectra from SeaWiFS,MODIS and MERIS datasets (Maritorena & Siegel2005). GSM was selected over usual empirical algo-rithms to minimize the impact of optical constituents(colored detrital material and non-algal particles).Although the GSM algorithm has not been validatedfor the Arctic Ocean, the semi-empirically derivedchl a concentration patterns are more realistic thanthe ones obtained using empirical algorithms (Bé lan -ger et al. 2008).

RESULTS

Ice and chl a concentrations

Ice concentration in the sampling region was ~20%during the first weeks of deployment, in creased to~40% at the beginning of June, and remained at thisconcentration for the rest of the deployment period(Fig. 2a). Chl a concentrations were >1 mg m−3 atthe start of the deployment and ranged between 0.5and 1.5 mg m−3 for most of the deployment period(Fig. 2b). The highest chl a concentration wasobserved in May, while the lowest chl a concentra-tion was measured in June (Fig. 2b).

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Fig. 2. Temporal variations in satellite-derived (a) sea ice con-centration averaged over the sampling region (78.5 to79.5° N, 2.5 to 6.5° E) and (b) chl a concentration averagedover the sampling region (78 to 80° N, 2 to 7° E) in the easternFram Strait in 2003. The bars represent standard deviations

Mar Ecol Prog Ser 440: 127–136, 2011

CaCO3, bPSi, and phytoplankton cell fluxes

CaCO3 fluxes were high at the end of April,decreased during the month of May, and increasedagain at the beginning of June, while bPSi fluxeswere elevated at the beginning of May and low inJune and July (Fig. 3). Concurring with the elevatedbPSi fluxes, an enhanced export of diatoms was ob -served at the beginning of May (Fig. 4). Pennatediatoms, mainly the chain-forming Fragilariopsiscylinders and F. oceanica, and centric diatoms of thegenus Thalassiosira spp. reached their highest fluxvalues in the first week of May, while empty diatomfrustules and resting spores of Chaetoceros spp.mostly contributed to the phytoplankton flux in June.Elevated fluxes of Phaeocystis pouchetii were ob -served at the beginning of June, while increasedcocco lithophore fluxes (mainly of Emiliania huxleyiand a few Coccolithus pelagicus) were observed dur-ing most of the month of June. Fluxes of large identi-fiable phytoplankton cells decreased to low valuesduring the month of July (Fig. 4).

POC and FPC fluxes

POC fluxes were <15 mg C m−2 d−1 during the com-plete deployment (Fig. 5a). Periods of increased POCexport were observed at the beginning of May (12 d>5 mg C m−2 d−1) and at the end of June (16 d >10 mgC m−2 d−1). FPC fluxes remained <5 mg C m−2 d−1 dur-ing the deployment, were highest at the end of Mayand in June, and de creased considerably in July

(Fig. 5a). The contribution of FPC to the POC fluxranged between 10 and 30% at the beginning of thedeployment, substantially increased to supply >85%of the POC flux at the end of May, and remainedbetween 40 and 70% until mid-June when the contri-bution of FPC to the POC flux decreased to an aver-age of 10% for the rest of the deployment (Fig. 5b).Copepod fecal pellets were present in all samplesand dominated the FPC fluxes, except during a short

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Fig. 4. Temporal variations in cell fluxes of (a) Thalassiosiraspp., (b) Chaetoceros spp., (c) pennate diatoms, (d) cocco litho -phores, and (e) Phaeocystis pouchetii measured at 340 m in

the eastern Fram Strait in 2003. Note the different scales

Lalande et al.: POC export in the Fram Strait 131

period at the beginning of June when they werenearly absent from the samples (Fig. 5c). Appendicu-larian fecal pellets completely dominated the FPCfluxes at the beginning of June but were nearlyabsent at the start of the deployment (Fig. 5c). Cope-pod and appendicularian fecal pellet volumessteadily increased with time until a rapid de cline inJune (Fig. 5d). The low copepod fecal pellet volumerecorded at the beginning of June re sulted from thesmall fragments of broken fecal pellets collected inthe sample (Fig. 5d).

DISCUSSION

An unusual increase in ice concentration in thesampling region, instead of the expected decrease inice cover due to melting at the beginning of June, in -dicated the formation of an ice-edge eddy, a commonfeature along the ice edge in the Fram Strait (Wad -hams & Squire 1983, Johannessen et al. 1987a,b). In-deed, ice concentration maps revealed the presence

of a cyclonic eddy transporting ice over a large areadirectly above the sediment trap from 2 June to 2 July(Fig. 6). With typical scales of from 30 to 40 km and alifetime of at least 20 to 30 d, mesoscale eddies have alarge impact on ice distribution in the Fram Strait (Johannessen et al. 1987a,b, Shuchman et al. 1987).In addition to dragging ice away from the main icepack, cyclonic eddies transport warm Atlantic Waterbeneath the ice (Wadhams & Squire 1983, Johan-nessen et al. 1987b). Therefore, the coincident de-ployment of the sediment trap with the occurrence ofan ice-edge eddy provided a unique opportunity toassess the influence of the advection of warm AtlanticWater on POC export in the eastern Fram Strait.

POC export prior to the ice-edge eddy

The enhanced diatom and diatom-specific bPSifluxes at the beginning of May suggest that thedeployment of the sediment trap coincided with theonset of a bloom. Although satellite-derived measure-ments have limited viewing conditions and were par-tially hindered by ice cover, the chl a concentrationrecorded at the end of April was above the thresholdvalue of 1.0 mg m−3 defining a bloom (Wu et al. 2007),supporting an enhanced primary production at thetime of the deployment. A phytoplankton bloomoccurs when nutrient-rich water is exposed to lightduring ice break-up and water from the melting icegives rise to strongly stratified surface water (Peinertet al. 2001, Fortier et al. 2002, Sakshaug 2004, La -lande et al. 2007). The influence of ice on primaryproduction was reflected by the export of ice-associ-ated pennate diatoms Fragilariopsis spp. known to bequantitatively important during the spring bloom inthe Arctic Ocean (von Quillfeldt 2000). A largeexport of pennate diatoms recorded from the end ofApril to the beginning of May 2003 by another long-term sediment trap deployed at the HAUSGARTENobservatory emphasizes the importance of the springbloom for POC export in the region (Bauerfeind et al.2009). The elevated CaCO3 fluxes ob served prior tothe increase in diatom-specific bPSi fluxes at the startof the deployment may reflect the release of forami-nifera from melting sea ice. High benthic foraminif-era fluxes due to sea-ice rafting were observed fromJanuary to May in the eastern Fram Strait (Hebbeln2000); however, the low abundance of foraminiferacollected in the sediment trap was not sufficient toexplain the elevated CaCO3 fluxes observed duringthe first days of deployment in our study, and thesehigh CaCO3 fluxes remain unexplained.

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Fig. 5. Temporal variations in (a) particulate organic carbon(POC) and fecal pellet carbon (FPC) flux, (b) contribution ofFPC to the POC flux, (c) contribution of copepod and appen-dicularian FPC, and (d) average copepod and appendicular-ian fecal pellet (FP) volume measured at 340 m in the eastern

Fram Strait in 2003

Mar Ecol Prog Ser 440: 127–136, 2011

Because zooplankton fecal pellets sink rapidly(Turner 2002), the absence of a coincident increase inzooplankton fecal pellet fluxes with the increase indiatom fluxes at the beginning of May suggests thatfecal pellets were retained in the upper water columnor were not abundantly produced. However, theenhanced export of diatoms implies a lack of reten-tion, and low fecal pellet fluxes likely reflect low zoo-plankton biomass and fecal pellet production at the

start of the deployment. In fact, the proportion offecal pellets in the POC flux remained low until itabruptly increased above 85% at the end of May dueto a considerable increase in fecal pellet fluxes, sug-gesting that zooplankton biomass was low during thefirst weeks of deployment and rapidly increased inMay. This large increase in fecal pellet fluxes mayreflect the advection of zooplankton in the region,but most likely reflects the seasonal ontogenetic mi -

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Fig. 6. Ice concentration maps for the complete deployment period showing the presence of an ice-edge eddy above the sediment trap from 2 June to 2 July 2003. The location of the sediment trap is indicated by a yellow dot

Lalande et al.: POC export in the Fram Strait

gra tion of copepods. Hirche (1997) reported a south−north gradient in the timing of the ascent of the pop-ulation of the copepod Calanus hyperboreus from theNorwegian Sea to the central Arctic Ocean, with theascent beginning in March in the Norwegian Sea, inApril in the Greenland Sea, and in June in the centralArctic Ocean. Given the location of the Fram Straitbetween the Greenland Sea and the central ArcticOcean, it is probable that the overwintering cope-pods surfaced in May in the region.

The plausible mismatch between zooplanktongrazing and the phytoplankton bloom before thereturn of the overwintering copepods resulted in anincreased export of intact phytoplankton cells andPOC at the beginning of May. Previous investiga-tions in the Arctic Ocean have also shown that arapid increase in food supply and low zooplanktonbiomass during the spring bloom may cause a largeexport of ungrazed phytoplankton cells (Olli et al.2002, Wassmann et al. 2004, Lalande et al. 2007).This mismatch period is commonly followed by aperiod of reduced POC export and elevated fecal pel-let fluxes due to the extensive grazing pressureresulting from higher abundances of large copepodsand sufficient feeding conditions. The increase in thecontribution of fecal pellets to the POC flux at theend of May, with fecal pellets comprising nearly theentire POC flux, reflects this expected match be -tween phytoplankton and zooplankton. In the east-ern Fram Strait, zooplankton abundance and bio-mass is dominated by calanoid copepods (Hop et al.2006), as reflected by a majority of copepod fecal pel-lets exported at that time. This large contribution ofcopepod fecal pellets to the POC flux is comparableto the export of fecal pellets from the copepodCalanus finmarchicus, which accounted for 92% ofthe total carbon export at the end of a spring bloom inMay in the Norwegian Sea (Graf 1989).

Despite the low amount of diatoms collected in thesediment trap following the elevated diatom and di-atom-specific bPSi fluxes measured in the first weeksof May, another increase in bPSi fluxes was observedat the end of May. The almost complete contributionof fecal pellets to the POC flux at that time suggeststhat the bPSi was exported through fecal pellets.Thus, fecal pellets enhanced the export of bPSi in theeastern Fram Strait, similar to previous observationsmade at a nearby station off northern Spitsbergen,where fecal pellets were the most prominent sourceof sinking particulate silicate (Andreas sen et al.1996), and in the Antarctic Polar Front region, wherefecal pellets contributed significantly to biogenic sil-ica and POC fluxes during spring (Dagg et al. 2003).

Influence of Atlantic Water on POC export

The advection of warm Atlantic Water due to theformation of an ice-edge eddy at the beginning ofJune directly in the collection area of the sedimenttrap rapidly modified the composition of the POC flux.The first effect associated with the onset of the eddywas the large collection of the haptophyte Phaeocystispouchetii in the sediment trap. Although blooms of P.pouchetii are often recorded in the Fram Strait (Hopet al. 2006), P. pouchetii does not contribute signifi-cantly to carbon export unless deep mixing acceler-ates the downward export (Reigstad & Wassmann2007). Because Phaeocystis spp. cells are typically re-tained in the upper 50 to 100 m (Reigstad & Wass-mann 2007), P. pouchetii cells collected at 340 m werelikely exported within the downwelling columnsfound on either side of a cyclonic eddy (Niebauer &Smith 1989). In fact, P. pouchetii cells were potentiallyexported deeper than the sediment trap depth, as thecyclonic motion and warm water influence of eddieswere previously observed beyond 600 m in the east-ern Fram Strait (Wadhams & Squire 1983, Johan-nessen et al. 1987b). The large P. pou chetii exportwas followed by a period of elevated coccolithophoreand CaCO3 fluxes, suggesting that a coccolithophorebloom was taking place at the surface and that theeddy contributed to the rapid export of these smallcells. Typically observed in the warmer waters of thenorthern North Atlantic and the Norwegian Sea,cocco litho phore blooms were recently ob served fur-ther north (Hegseth & Sundfjord 2008). In their study,Hegseth & Sundfjord (2008) concluded that the coc-colithophore bloom observed in the marginal ice zoneof the Barents Sea in August 2003 was due to the sub-surface circumpolar boundary current carrying waterof Atlantic origin west of Svalbard and then east -wards along the Eurasian Shelf break. The sameboundary current explains the presence of a cocco -litho phore bloom in the Atlantic Water of the easternFram Strait in June 2003, which was probably carriedto the sediment trap by the ice-edge eddy.

Appendicularian fecal pellet fluxes abruptly domi-nated the export of fecal pellets at the onset of the ice-edge eddy. Appendicularians are soft-bodied zoo-plankton commonly abundant in the cold waters ofsub-Arctic and Arctic seas that often contribute sub-stantially to carbon export through fecal pellets andwhich were also abundant in the Fram Strait inspring 2003 (Bauerfeind et al. 1997, Vargas et al.2002, Hopcroft et al. 2005, Blachowiak-Samolyk et al.2007). The dominance of appendicularian fecal pel-lets and the near absence of copepod fecal pellets in

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the fecal pellet fluxes during several days suggest ahigher grazing pressure from appendicularians. In -deed, these filter-feeders are capable of much higherrates of ingestion, growth, and reproduction thancopepods, allowing them to respond more rapidly toshifts in primary productivity (Hopcroft et al. 2005).Thus, it appears that appendicularians were eitheradvected with the Atlantic Water or were betteradapted to take advantage of the change in phyto-plankton composition associated with the rapid inputof Atlantic Water, which contributed to a large exportof carbon through appendicularian fecal pellets inJune. Another possible explanation for the nearabsence of copepod fecal pellets in fecal pellet fluxesmay be the fragmentation of the copepod fecal pel-lets due to orbital currents of up to 40 cm s−1 associ-ated with the eddy (Johannessen et al. 1987a,b), apossibility supported by the fragmented copepodfecal pellets collected in the sediment trap at theonset of the eddy.

After several days, the almost total contribution ofappendicularian fecal pellets to fecal pellet fluxesdecreased toward an equal contribution of copepodsand appendicularians, and eventually back to a pre-dominance of copepod fecal pellets in the fecal pelletfluxes. This shift in the composition of the fecal pelletfluxes possibly reflects a decrease in the influence ofAtlantic Water, with fecal pellet fluxes returning totheir pre-eddy proportions after 20 to 24 d. Althoughice concentration maps indicate the presence of theeddy until the beginning of July, the material col-lected in the sediment trap suggests that the eddy sig-nal disappeared earlier at depth. Concurrently withthe increasing proportion of copepod fecal pellets,the fecal pellet fluxes and the average size of fecalpellets rapidly decreased at the end of June. Whilethe steady increase in fecal pellet size from May toJune probably reflected the increasing size of thezooplankton present in the community, the rapid de -crease in the size of zooplankton fecal pellets in Junemay reflect fragmentation processes above the sedi-ment trap. Indeed, the small pieces of pellets col-lected in the sediment trap, the steady decrease infecal pellet fluxes, and the low proportion of fecal pel-lets in the POC flux suggest that coprophagy, theingestion of fecal pellets by copepods, and/orcoprorhexy, the fragmentation of fecal pellets bycope pods, occurred in June (Noji et al. 1991, Turner2002, Wexels Riser et al. 2002). The fragmentation offecal pellets through coprophagy and coprorhexylikely contributed to the retention of fecal pellets inthe upper water column by lowering their sinkingrates (Noji et al. 1991, Turner 2002, Wexels Riser et al.

2002). These processes possibly occurred in responseto a decline in food availability at this time, as re -flected by the diatom resting spores and emptydiatom frustules collected in the sediment trap.

A significant decrease in POC, phytoplankton cell,and fecal pellet fluxes occurred during the last daysof the short deployment in July. This decline mayreflect the prevalence of a retention food chain due toa more complex zooplankton community, with ahigher capacity of recycling in summer compared tospring, which is in accordance with observations pre-viously made in the Barents Sea (Olli et al. 2002). Onthe other hand, the reduced fecal pellet fluxes in Julymay reflect the onset of the descent of copepods todepth, as supported by observations of the prepara-tion for the descent of Calanus hyperboreus in July inthe Greenland Sea (Hirche 1997), the aggregation ofC. hyperboreus over the ocean floor of the GreenlandSea in late July (Hirche et al. 2006), and the accumu-lation of overwintering stock of Calanus spp. at depthin July in the Barents Sea (Arashkevich et al. 2002).However, it is more likely that the low export fluxesobserved in July reflect the retention capacity of thehigher zooplankton abundance and biomass ob -served later in the season in the eastern Fram Strait(Blachowiak-Samolyk et al. 2007).

CONCLUSIONS

The deployment of a sediment trap at a high tempo-ral resolution allowed us to better assess the develop-ment of the phytoplankton and zooplankton commu-nities and their influence on the magnitude andcomposition of the downward POC export in the east-ern Fram Strait. Although high POC export was asso-ciated with the sinking of the diatom bloom at thebeginning of May, most of the POC export was asso-ciated with the advection of Atlantic Water in thesampling region due to an ice-edge eddy. The inputof Atlantic Water affected the composition of theexported phytoplankton cells and zooplankton fecalpellets, underscoring the importance of water massesin shaping POC export in the eastern Fram Strait. Asimilar influence of water masses was observed inthe Barents Sea, where the composition of the sink-ing particles was different in Arctic and Atlanticwaters (Olli et al. 2002) and where the main contribu-tors to the fecal pellet flux varied depending on theprevailing water masses and phytoplankton bloomstage (Wexels Riser et al. 2008). Although watermasses strongly influence export fluxes, ice coveralso affects POC export in the eastern Fram Strait,

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Lalande et al.: POC export in the Fram Strait

mainly through the release of particles during icemelt (Bauerfeind et al. 2009). Nonetheless, ourresults suggest that the recent increases in the vol-ume and temperature of the Atlantic Water flowinginto the Arctic Ocean through the Fram Strait (Wal-czowski & Piechura 2006) likely affected the composi-tion of the POC flux, and that potential ‘atlantifica-tion’ of the Fram Strait could significantly influencePOC export in this region.

Furthermore, the immediate shift in the composi-tion of the export fluxes during the formation of theice-edge eddy suggests that such events lead to rapidPOC export. Smith et al. (1987) concluded that, sinceapproximately 10 to 20% of the marginal ice zone ofthe Fram Strait is impacted by cyclonic eddies, thesefeatures may introduce large spatial and temporalvariability into biological processes and may havesignificant impact on the entire food web of theregion. This hypothesis was confirmed by our results,which clearly showed that eddies are important forthe downward export of small phytoplankton cells,further implying that their effect should be consid-ered in the estimation of annual POC export.

Acknowledgements. We thank the crew of the RV ‘Polar -stern’ and the late J. Wegner for the deployment and recov-ery of the sediment trap. We thank L. Kaleschke for provid-ing sea ice concentration data and C. Lorenzen forlaboratory work. This study was funded by the HGF MPGJoint Research Group on Deep Sea Ecology and Technology.C.L. received financial support from the Alexander vonHumboldt Foundation.

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Editorial responsibility: Marsh Youngbluth, Fort Pierce, Florida, USA

Submitted: April 5, 2011; Accepted: September 5, 2011Proofs received from author(s): October 20, 2011