Deep- Research II 49 (2002) 5259–5275

Sediment properties and benthic–pelagic coupling in the North Water

Jon Granta,*, Barry Hargravea,b, Paul MacPhersona a Department of , Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1 b Department of Fisheries and , Marine Environmental Sciences Division, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2

Received 11 November 2000; received in revised form 27 July 2001; accepted 29 October 2001

Abstract

Measurements of sediment oxygen consumption were made during spring and summer in the North Water, the polynya that forms between Greenland and Ellesmere Island, and used in conjunction with sediment trap data to assess benthic–pelagic coupling in this system. Bottom sediments ranged from cobble in the north to soft muds in the southern part of the sampling grid. Muddy sediments were often pelletized as shown by disaggregation. Sediment photopigments were generally lower in coarse sediment stations to the north than in finer sediments stations to the south. Shipboard 2 1 incubation of intact cores provided rates of 0.07–0.17 mmol O2 m h , with significantly greater oxygen consumption in summer than in spring. Additional incubation of macrofauna-free sediment aliquots in vials demonstrated significantly lower oxygen consumption in summer than in spring. Partitioning of benthic metabolism via these selective exclusion experiments showed a seasonal change in the response of the benthos to pelagic input, with meio-microbenthos dominating oxygen consumption in spring and macrofauna dominating in summer. Increased oxygen demand in the western polynya is suggested to coincide with the highest rates of carbon input measured by sediment traps and highest levels of sediment pigments. This region is an advective sink for particles produced in the east and subsequently transported by net polynya circulation. Although the benthos of the North Water does not display enhanced rates of carbon processing compared to other Arctic sediments, including other polynyas, the protracted production season of North Water provides a longer period over which the benthos can receive and mineralize organic carbon. Crown Copyright r 2002 Published by Elsevier Science Ltd. All rights reserved.

1. Introduction as one of the major constraints on Arctic productivity, and represent an exceptional oppor- Polynyas are Arctic regions of reduced tunity to study food webs at high latitudes. Arctic ice cover that are characterized by seasonally benthic communities receive most of their annual intense biological activity at all trophic levels food input in brief seasonal pulses, likely enhanced (Stirling, 1997). Polynyas thus constitute a ‘natural by the aggregated sinking of epontic microalgae experiment,’ in terms of removing light limitation and eventually phytoplankton following ice melt (Bauerfeind et al., 1997; Hargrave et al., 2002; *Corresponding author. Tel.: +1-902-494-2021; fax: +1- Sampei et al., 2002). The protracted production 902-494-3877. season that occurs in polynya regions may be E-mail address: [email protected] (J. Grant). expected to elevate the role of the benthos in

0967-0645/02/$ - see front matter Crown Copyright r 2002 Published by Elsevier Science Ltd. All rights reserved. PII: S 0967-0645(02)00189-3 5260 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 sequestering organic carbon relative to other polar finally disappearing as the waters of Baffin Bay regions (Ambrose and Renaud, 1995). Alterna- become open in the summer. tively, a well-developed pelagic grazer food chain The International North Water Polynya Study and microbial loop in productive waters may (NOW) was a collaborative effort designed to reduce the potential for benthic input (Grebmeier study physical, chemical, and biological aspects of and Barry, 1991; Rowe et al., 1997). In addition, this polynya. Benthic studies were undertaken to the degree of benthic–pelagic coupling that occurs quantify the role of bottom communities and in polynyas serves as a model for scenarios in sediments in the mineralization of organic carbon which global warming reduces Arctic ice cover originating in the euphotic zone. The somewhat (Rowe et al., 1997). confined area of the polynya and depths o1000 m Previous studies of polynyas have demonstrated make the benthos a potentially important sink for seasonal progression in the types of particles carbon exported from the via sinking from the euphotic zone (cells, aggregates, sinking particles. We set out to pursue the fecal pellets, etc,) and the fate of enhanced following questions relevant to location, timing, production (Grebmeier and Cooper, 1995; Bauer- and trophic structure in the NOW polynya: fiend et al., 1997; Ritzrau and Thomsen, 1997; see Spatially: Does sediment oxygen consumption also Sampei et al., 2002). Seasonal changes in (SOC) follow a pattern determined by sediment benthic carbon demand have also been examined type and organic matter, circulation, and/or by the in the Northeast Water polynya (Rowe et al., pattern of primary production and carbon input 1997), but few studies allow assessment of the role from the water column? of polynyas in benthic trophodynamics compared Temporally: Does SOC reflect the transition to other Arctic ecosystems (Grebmeier and Barry, from ice cover to open water spring/summer 1991). Arctic benthos display a diverse range in conditions and the consequent change in carbon distribution of biomass and activity between input from ice algae to phytoplankton production? bacteria, microfauna, meiofauna, and macrofau- Trophically: What is the relative importance of na, related to factors such as grain size and organic macrofauna versus meio-microbial benthos in input (Piepenburg et al., 1995; Glud et al., 1998; their contribution to benthic oxygen demand? Kroncke. et al., 2000). We approached these questions by obtaining The North Water in northern Baffin Bay benthic samples at multiple stations in spring and between Greenland and Ellesmere Island is the summer and conducting shipboard incubations for largest polynya in the Canadian Arctic, occurring measurement of SOC. These results were then over 80,000 km2 at its maximal extent. It appears related to sediment properties as well as the results to be maintained largely as a latent heat polynya, of moored sediment trap studies conducted due to the steady winds from the north that simultaneously by Hargrave et al. (2002). transport recently formed ice along the Greenland coast (Ingram et al., 2002; Bacle# et al., 2002). The ice dam across the Nares Strait also plays a role in 2. Materials and methods reducing the southern drift of pack ice. Circulation in the polynya is driven by the 2.1. Study site north along the Greenland coast, and flow is topographically steered to the west in Smith Benthic sampling was conducted from the Sound. The southern-flowing Baffin current joins CCGS icebreaker Pierre Radisson in Smith Sound the flow from western Greenland to maintain a net and northern Baffin Bay during Leg 1 (April–May; counterclockwise transport in the polynya (Bacle# spring) and Leg 4 (July; summer) of the major field et al., 2002). The seasonal development of the effort in 1998. Stations were chosen to provide polynya follows a similar pattern, occurring as north–south and east–west transects in the poly- broken or thin ice off of western Greenland and nya (Fig. 1). A total of 12 stations were sampled expanding to the southwest through the spring, during Leg 1 and seven during Leg 4, with all J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5261

Leg-4 locations having been visited during Leg 1. Table 1 Water-column depths ranged from 247 to 680 m, Benthic station location and depth during the 1998 NOW field with all stations except the most northerly, A7, study and easterly, S1, deeper than 400 m (Table 1). Ice Station Location (digital degrees) Depth range (m) cover was still present at many stations during Leg Latitude N, Longitude W 1, while during Leg 4 large areas of open water A7 78.99, 73.33 247–257 were interspersed with drifting pack ice. During N2 78.99, 73.33 517–579 Leg 4, various stations with coarse sediments E2 78.04, 73.27 450 sampled during Leg 1 were avoided to protect the A16 77.85, 74.79 680 box core from damage, resulting in incomplete A22 77.34, 76.48 420 E1 77.01, 72.63 400–532 overlap between legs for some variables. In some D2 77.00, 75.00 553–562 cases, coarse sediment was obtained for chemical S1 77.00, 75.00 259 and grain size analysis, but with insufficient S2 76.29, 72.03 563–570 quantities for core incubations. Station S4 was S4 76.28, 74.24 445–486 visited twice within 7 d during Leg 1, providing a S5 76.37, 77.28 307–370 D1 75.25, 74.95 480–499 measure of the short-term temporal variability that occurs in the polynya. Depth range refers to the variation in depths observed over multiple samples at the same general site. 2.2. Sampling

Surface sediments (up to B40 cm) were sampled southern (D1) station outside of this region with a 0.25-m2 USNEL box core at ten stations (Fig. 1). Box-core samples had varying amounts within the polynya and at a northern (A7) and of overlying water due to the presence of rocks which affected closure of the blade. Box cores drained of water raise concerns about loss of 79.00  Kane Basin A7 surficial sediments. Our samples often contained Ellesmere epifauna and intact infaunal tubes, with no 78.50 Island  Greenland n Nares Strait obvious disturbance of the sediment surface due N2 to retrieval. Sediment subsamples in general were 78.00   E2 obtained away from the edges of the box. A16 The surface of each box core was photographed 77.50 Smith Sound  immediately with a digital camera. Epifauna were A22   removed and preserved. Multiple cores (each 77.00   D2 E1 11.5 cm i.d., 30-cm length) for incubation and Latitude measurement of oxygen fluxes were collected to 76.50      B S5  13-cm sediment depth from each of the two box S4 S2 S1 76.00 cores per station and immediately placed in a dark

500 m chilling bath at near-bottom temperature (0.6 to m 500 3 75.50 0.61C). Truncated 10-cm syringe cores (tapered  2  Baffin Bay end removed; barrel area=0.0005 m ) were used to D1 75.00 sample box cores for sediment porosity, total 80.00 75.00 70.00 65.00 carbon and nitrogen ðn ¼ 122Þ; and pigments Longitude ðn ¼ 328Þ in the upper 1 cm. Where cobble was Fig. 1. Map of the polynya study area, showing sampling present, syringe cores were obtained from sand/ station locations during Leg 1 (spring, &) and Leg 4 (summer, mud patches. Samples for grain size were collected ’). Stations A7, N2, E2, and A16 were designated as north; stations A22, D2, and E1 as central; and stations S1, S2, S4, by scraping sufficient quantities of surficial sedi- and S5 as south. Station D1 was outside of the polynya during ment into plastic bags. Pigment, carbon, and grain the time frame of this study. size samples were frozen immediately. Additional 5262 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 cores (6.5 cm i.d., 3-cm length) were also taken at here are total carbon assumed to reflect each site for measurement of redox potential. organic carbon. In related sediment sampling, Due to the need for the ship to maneuver in ice, Hamel et al. (2002) analyzed sediment carbon distances between replicate box cores at a single following pre-treatment with HCl. The differences station were as great as 1 km. At stations with in results attributable to methodology are dis- heterogeneous sediment texture, this spatial dif- cussed below. Sediment photopigments were ex- ference could alter the size composition of the tracted from wet sediment overnight in a sample. This variation is considered fundamental refrigerator with 90% acetone and read fluorome- to the seafloor environment and is incorporated trically after extraction, with acidification used to into mean values of variables calculated for each distinguish chlorophyll from phaeopigments as in station. Grant et al. (1998). The sum of chlorophyll and phaeopigments is referred to as chloroplastic 2.3. Sediment analyses pigment equivalents (CPE) as in Pfannkuche and Thiel (1987). Sediment grain size was analyzed with an Sediment redox potential was measured on- expanded protocol compared to traditional ana- board in core tubes by inserting a platinum redox lyses to preserve biological structures (see also electrode with internal reference electrode Grant et al., 1987; Wheatcroft and Butman, 1997). (+247 mV) horizontally into pre-drilled holes For each station, a thawed sample was gently wet- exposed by removing sealing tape from top to sieved with tap water through a series of 63–2000- bottom. The electrode was calibrated using stan- mm sieves, with the o63-mm effluent collected and dard redox solutions made from K3Fe(CN)6, filtered. A second sample was shaken in a Calgon K4Fe(CN)6 3H2O, and KF2 2H2O (Hargrave solution (10 ml of a 6.2 g l1 stock added to 250 ml et al., 1995). Following these measurements, of DI water) in order to disperse aggregates samples were taken through the holes for profiles (largely fecal pellets) and then sieved and filtered of bulk density (Leg 4) and CHN. as the first sample. This resulted in an increase in the percentage of silt-clay in the sample, which was 2.4. Sediment oxygen consumption divided by the percentage of silt-clay in the untreated sample to calculate an aggregation index 2.4.1. Whole cores (AI). Although we calculated median sediment In the laboratory, incubation cores (n ¼ 326 grain diameters, they are not particularly mean- per station) were gently filled with filtered bottom ingful when comparing such heterogeneous sedi- water (0.2 mm) collected via rosette from the same ments among stations, since (a) representative station. A thin sheet of plastic was floated on the portions of the coarse material are impossible to sediment surface to deflect filling water and keep obtain in small samples and (b) median diameters the sediment surface undisturbed (Hulth et al., are biased when boulders are present and cobbles 1994). Cores were sealed with o-ringed lids are lumped into a >2-mm sieve category. We containing water-sampling valves and magnetic therefore express sediment texture as present stir bars and incubated in an insulated water bath weights in three categories: silt-clay (o63 mm), at constant temperature using station-specific sand (63–2000 mm), and gravel (>2000 mm). Por- bottom temperature derived from CTD casts. osity was measured as weight loss upon drying at Temperature was regulated to within 0.21C with 601C. a digital controller attached to a pump and chiller. Sediment carbon and nitrogen were measured Stirring rate in the cores was set to avoid sediment in a Perkin-Elmer 2400 elemental analyzer with resuspension. After 1 h of acclimation, initial no pre-treatment. Our initial indication was oxygen samples were drawn by depressing the lids that particulate inorganic carbon was low in with the valve open and flushing excurrent water these sediments (D. Murray, Brown University, into a 250-ml BOD bottle. Final samples were personal communication), so values reported collected the same way. In all cases, BOD bottles J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5263 were stoppered and oxygen measured immediately 2.4.2. Vials by Winkler titration (Leg 1) or by inserting an Small sediment cores incubated in vials were Orion 97–08 oxygen electrode which is tapered used to make respiration measurements that as a BOD stopper (Leg 4). Calibration of the excluded large macrofauna (Grant and Schwin- electrode was based on O2 saturation for a ghamer, 1987). Oxygen uptake in vials can be given temperature, salinity, and atmospheric pres- compared to the rates from whole cores as a means sure measured at the time of the sampling. of partitioning oxygen demand. Each vial contain- Decreases in oxygen were generally o35%, with ing the upper 2 cm of a box core sampled with a incubations that lasted up to 50 h. Sediment truncated 10-cm3 syringe (0.0005 m2) was filled oxygen demand is a measure of both aerobic and with 0.2-mm filtered bottom water and sealed anaerobic carbon respiration reactions if all without bubbles (n ¼ 5211 per station). Because reduced end products of anaerobic metabolism the oxygen probe displaced the filling water, three are oxidized. Given the generally oligotrophic vials were used to derive a mean value for initial conditions in Arctic offshore sediments and oxygen concentration. Additional vials were in- positive redox values, oxygen consumption was cubated after filling and used for final O2 assumed to be due primarily to aerobic respiration measurements. The temperature sensor of the (see Discussion). Orion oxygen probe was not immersed when Time-series sampling with this incubation sys- measurements were made in vials, so corrections tem in both coastal and shelf sediments (Hatcher for temperature differences were obtained from et al., 1994; Grant et al., 1998) indicated that linear BOD bottle incubations of bottom water con- decreases in oxygen in the cores occurred during ducted simultaneously. Following Grant and incubations. SOC was calculated as the linear Schwinghamer (1987), the respiration rate of difference in O2 concentration over the incubation sediments in vials was calculated on the basis of time and is referred to as benthic community the original area of the sediment sampled oxygen consumption (BCOC) following Piepen- (0.0005 m2). burg et al. (1995). After the incubations, cores were sieved through a 0.5-mm sieve, and macro- 2.5. Statistical analysis fauna preserved in buffered formalin. Macrofauna taxonomic and biomass data will be reported Values for oxygen consumption in cores and separately in collaboration with G. Desrosiers vials were compared using one-way analysis of (Univ. Quebec Rimouski). variance (ANOVA) for each leg with station as In a single incubation experiment at northern treatment. All sample populations were checked station N2 (Leg 4), the temperature of the for normality and equality of variance and ln- incubation chamber was raised from ambient transformed where necessary. In order to compare bottom temperature at this station (0.41C) to only stations that were sampled on both legs, a 1.91C following the first incubation. New two-way ANOVA was conducted with leg and rate measurements were started by resealing the station as treatment. In cases where the overall core to examine the temperature response of ANOVA was significant ða ¼ 0:05Þ; Bonferroni oxygen consumption. Consumption of O2 in post hoc comparisons were conducted at a ¼ 0:05; the first incubation was 8–14% of initial values adjusting for the number of comparisons. over a period of 42 h, so that depression of initial Sampling stations also were grouped by location oxygen for the second incubation was insubstan- in order to increase sample sizes for statistical tial. Temperature was raised by resetting the comparison of sediment pigment and carbon. incubator thermostat, requiring B1 h, the acclima- Stations to the north in Kane Basin and northern tion period applied to all incubations. The second Smith Sound (A7, N2, E2 and A16) were incubation at 1.91C lasted for 14 h and reduced designated ‘north’, sediments farther south in the oxygen by 7–15% of the initial values from that central region of the polynya (central Smith incubation. Sound, E1, D2, A22) were designated ‘central,’ 5264 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 and the more southern stations (southern Smith (a) Sound, S2, S4, S5) were designated ‘south’ (Fig. 1). The most easterly station S1 was considered separately in these analyses from other stations of similar latitude (S2, S4, and S5) due to its shallow depth and sandy substrate. All pigment and carbon data were ln-transformed. For sedi- ment CPE, one-way ANOVAs were conducted to compare north, central, and south locations for Leg 1, but due to inequality of variance, only between central and south locations for Leg 4. A two-way ANOVA of location and leg was conducted for central and south locations which included stations repeated between legs. Northern Baffin Bay station D1 (the most southerly) was (b) compared qualitatively due to its small sample size. Sediment carbon was compared with a two- way ANOVA between central and south locations owing to the small sample size of the north location. Bonferroni post hoc comparisons were conducted as above.

3. Results

Sediments at the polynya sampling stations were extremely heterogeneous, ranging from boulders and cobbles armouring mud, especially in the north (Fig. 2), to uniform soft muds in the south. Fig. 2. Sediment heterogeneity in samples from the northern Observation of the sediment column through clear stations of the North Water (locations in Fig. 1): (a) surface of a cores revealed generally oxidized conditions with boxcore from station A7, farthest north, showing the cobble- boulder substrate (the box is 50 cm on a side); and (b) close-up occasional striations of black reduced sediments at of a sediment incubation core from westerly station A2, several centimeters depth. Redox values were showing mud (lower left) armoured by rocky surface (distance always positive with the lowest value of +95 mV across the core is 12 cm). measured at 11.5 cm sediment depth at station D2. Surface porosities at the coarse northern stations were 20–50%, with values >60% for the muddy glaciated coasts (Bigg, 1999). Sediment texture southern stations. Some muddy stations were may be grouped into three general categories characterized by a consolidated clay layer at (Fig. 3) as allocated above, but which also 8-cm depth, where porosity decreased to 40–50%. correspond to the hydrographic regions discussed in Bacle# et al. (2002) and Hargrave et al. (2002). 3.1. Grain size Sediments in the northern group of stations were generally cobbles and boulders (Fig. 2a), in some Grain-size heterogeneity among stations was cases armouring a mud sublayer (Fig. 2b). These due in part to differing hydrodynamic regimes in sediments featured 30–76% gravel or coarser the sampling region, but also reflected the deposi- material, with a variable mud and sand content tion of rocks and other material from the (Fig. 3a). In contrast, sediments in the central numerous icebergs that calve from adjacent region of the polynya had distinctly lower gravel J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5265

(a) content (similar to appearance of coarse stations in Leg 1 %SC 80 Leg 1 %sand Leg 1 %>2mm Fig. 2). Sediments to the south displayed many Leg 4 %SC 60 Leg 4 %sand high AI values, especially on Leg 4. Because these Leg 4 %>2mm sediments were generally finer than the northern 40 cobble, they had relatively greater material avail- able for remoulding. Seasonal changes in the % Composition 20 effects of sediment aggregation were most appar- 0 ent at stations D2 and S5 (Fig. 3b), with increased A7 N2 A16 A22 E1 D2 S1 S2 S4 S5 D1 (b) aggregation from Leg 1 to 4, wherein the 2.5 L1Agg index ostensibly high sand content of Leg 4 samples 2.0 L4Agg index (Fig. 3a) was shown to be composed of aggregated 1.5 fines. With AI values of 2, the processes respon- 1.0 sible for this coarsening, such as fecal pellet

0.5 formation, reduce the sediment silt-clay content

Aggregation index by one-half. 0.0 A7 N2 A16 A22 E1 D2 S1 S2 S4 S5 D1 There was no relationship between sediment Station composition and water depth. The northern stations with coarse sediment spanned the entire North Central South depth range, whereas other stations with similar Fig. 3. Sediment textural composition of North Water sam- depth (A7 and S1, Table 1; Fig. 3a) had quite pling stations ðn ¼ 1Þ: (a) silt-clay sand, and gravel content of different sediment composition. Similarly, the AI samples from Legs 1 and 4, spring and summer, respectively; and (b) AI derived by comparing the proportion of silt-clay showed no relationship to water depth. content in dispersed and non-dispersed sieve samples (see text for details; missing values for A7 and A22 are due to insufficient 3.2. Sediment carbon material). Location designations as in Fig. 1. Total sediment carbon (hereafter referred to as POC or simply as carbon) ranged from 1.7% to fractions (2–12%) and higher silt-clay content and/ 3.2%, except for the sandy station S1, with a POC or sand contents. Station S1 stands out among the content of only 0.5% (Fig. 4a), in keeping with the southern stations in its shallow depth and high range of 0.9–2.8% observed by Hamel et al. sand content. Finally, the southern stations and (2002). The fining trend in sediment texture from station D1 in northern Baffin Bay were classified north to south had a corresponding increase in as soft mud, with low coarse content (Fig. 3a). sediment carbon content. A two-way ANOVA Because the above sediment analyses reflect between central and southern station groups particle size state of intact biotic conditions, more (excluding S1) for both legs indicated significantly insight into the texture of these sediments was greater carbon in the south (Table 2). Sediment gained by comparing aggregated and disaggre- carbon was uniformly distributed in the upper few gated grain-size samples via the AI (Fig. 3b). centimeters of the sediment column (data not Examination of sieve contents revealed the pre- shown). For the top 1 cm, there was no relation- sence of fecal pellets in many coarse fractions, ship between sediment carbon and water column suggesting that increases in silt-clay in disaggre- depth, with the shallowest stations (A7, 245 m, and gated samples was at least in part due to break- S1, 254 m) having widely differing values. No down of biogenic particles. The lack of fine difference in carbon was apparent at station S4, content at some stations was reflected in AI values visited twice during Leg 1 (Fig. 4a). Sediment C/N close to 1 for some of the northern sites (N2). ranged from 9 to 15 (again in keeping with the Nonetheless, a value of 1.8 was determined for range of 7–12 reported by Hamel et al. (2002)), station A16, indicative of the availability of mud except at the northern rocky station A7 where for aggregation despite overall gravel and cobble C/N=23 (Fig. 4b). 5266 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275

(a) 4 Table 2 Leg 1 Analysis of variance (ANOVA) of sediment pigments (CPE) Leg 4 and total sediment carbon at stations sample in the North 3 Water during Legs 1 and 4 (spring and summer, respectively): (a) one-way ANOVA of CPE during Leg 1 analyzed as a 2 function of station; (b) one-way ANOVA of CPE during Leg 4 Carbon

% analyzed as a function of station; (c) two-way ANOVA of CPE which overlapped between legs, as a function of station and leg; 1 and (d) two-way ANOVA of carbon which overlapped between legs, as a function of station and leg 0 A7 N2 E2 A22 E1 D2 S1 S2 S4a S4b S5 D1 Treatment df Sum of squares F-value p-value

(a) CPE: Leg 1 (b) 25 Station 2 46.646 169.690 o0.001 Residual 39 5.360 20

(b) CPE: Leg 4 15 Station 1 0.540 1.930 0.182 C/N Residual 18 5.039 10

(c) CPE: Legs 1 and 4 5 Station 1 2.194 9.260 0.004 Leg 1 0.318 1.340 0.255 0 A7 N2 E2 A22 E1 D2 S1 S2 S4a S4b S5 D1 Interaction 1 0.196 0.830 0.369 Station Residual 36 8.532

North Central South (d) Carbon: Legs 1 and 4 Fig. 4. Sediment carbon and nitrogen of North Water sampling Station 1 0.167 8.140 0.011 stations during Legs 1 and 4, spring and summer, respectively Leg 1 0.009 0.420 0.524 (n ¼ 122 sediment samples per station per leg): (a) percent total Interaction 1 0.015 0.710 0.412 carbon; and (b) C/Nratio. S4a and S4b refer to two sampling Residual 18 0.370 efforts at this station during Leg 1, separated by 1 wk. Location Location refers to one of the three station groupings designated designations as in Fig. 1. Values are means+SD. as north, central, and south relative to the polynya (see text). All data were ln-transformed prior to analysis.

3.3. Sediment photopigments the southern polynya regardless of leg (Table 2). Total pigments had no relationship to station Total sediment pigments (CPE) had a strong depth, but were exponentially related to sediment latitudinal spatial pattern with low values at the carbon when excluding the northern cobble station northern stations, steadily increasing toward the (A7), indicating that for a given carbon level, the south (Fig. 5a). ANOVA of Leg 1 samples and southern polynya stations contained excess pig- post hoc testing indicated significant differences ment (Fig. 6). Pigment values for station A7 were between sampling regions with northocentra- relatively low for the amount of POC contained in losouth CPE (Table 2). During Leg 4, there was these sediments. On this bouldery substrate no significant difference between central and (Fig. 2a), the carbon in the subsurface fine material southern stations. Northern stations were not had a high C/N(Fig. 4b) and the low CPE had no included in this Leg 4 comparison, but appear to chlorophyll component (Fig. 5a and b). be only slightly less in pigment content that central Sediment chlorophyll a displayed spatial and stations (Fig. 5a). A two-way ANOVA of CPE temporal patterns similar to those of CPE using stations repeated between Legs 1 and 4 (Fig. 5b). Chlorophyll was only a small part of (comparing central to south) was significant only the CPE signal, indicating the domination of for location, indicating greater pigment levels in degraded pigments. The similarity of pattern J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5267

(a) between the two pigment measures suggested that 40 Leg 1 )

-1 Leg 4 chlorophyll deposition was not a unique signal of

g 30 instantaneous sedimentation events. As with CPE, µ the easternmost polynya station (S1) and station 20 D1 beyond the southern limit of the polynya, had minimal chlorophyll content (o0.5 mgg1). Varia- 10 tion between replicates was usually higher for chlorophyll than for carbon, suggesting greater Total pigments ( 0 A7 N2 E2 A22 E1 D2 S1 S4a S4b S5 D1 patchiness of pigment accumulation on the sea- (b) floor. The difference between legs was similar to 4 the variation within a single station sampled twice ) -1 over a brief time period (S4a and b; Fig. 5b), 3 g

µ reiterating the lack of temporal change suggested

2 by the two-way ANOVA of CPE.

1 3.4. Sediment oxygen consumption Chlorophyll ( 0 0 Rates of BCOC derived from cores (excluding A7 N2 E2 A22 E1 D2 S1 S4a S4b S5 D1 the raised temperature manipulation) ranged from Station 2 1 0.07 to 0.17 mmol O2 m h , equivalent to North Central South 1.68–4.08 mmol m2 d1 (Fig. 7). One-way ANO- Fig. 5. Sediment photopigments of North Water sampling VA of BCOC from core incubations showed no stations during Legs 1 and 4, spring and summer, respectively significant difference among stations for Leg 1 (n ¼ 328 samples per station per leg): (a) chlorophyll a; and (b) (Table 3). During Leg 4, significant differences total pigments (chlorophyll a+phaeopigments)=CPE. S4a and S4b refer to two sampling efforts at this station during Leg 1, were detected in BCOC among stations (Table 3). separated by 1 wk. Location designations as in Fig. 1. Values Post hoc tests showed that the northern station N2 are means+SD. had significantly lower oxygen demand than the other stations (Fig. 7), which were not significantly different from each other. A second incubation of 35 cores from station N2, elevated from 0.4 to )

-1 30 1.91C, resulted in a doubling of oxygen consump-

g tion (Fig. 7). For the stations that were repeated

µ 25 between, legs, two-way ANOVA showed that both 20 leg, station, and the interaction term were sig- nificant (Table 3). Multiple comparison tests 15 revealed that the interaction was due to signifi- 10 cantly higher rates (mean increase of 101%) at

Total pigments ( stations E1 (central) and S5 (south) for Leg 4 5 compared to Leg 1 (Fig. 7). BCOC did not 0 correlate with sediment pigments, carbon, C/N, 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 or AI (all stations and legs combined). % Carbon The results of macrofauna-free sediment ali- Fig. 6. Sediment carbon content versus total photopigments quots incubated in vials also indicate temporal (CPE) at North Water sampling stations. Data from the changes between Legs 1 and 4 (Fig. 8). During Leg northernmost gravel station (A7) were excluded from the 1, one-way ANOVA showed that there were regression line (&), since it had no chlorophyll and its relict carbon does not represent recent deposition (see text). Equation significant differences among stations in rates of of the line is CPE=2.21 (Carbon)2.26 ðn ¼ 13; r2 ¼ 0:555; p ¼ oxygen consumption in vials (Table 3). Bonferroni 0:002Þ: multiple comparisons revealed that northern 5268 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275

0.30 1.9°C Table 3 Analysis of variance (ANOVA) of sediment oxygen consump- ) 0.25 Leg 1 -1 Leg 4 tion rates derived from incubated cores (BCOC) and from h -2 0.20 aliquots of sediments containing only meio-microbenthos m 2 incubated in scintillation vials during Legs 1 (spring) and 4 0.15 -0.4°C (summer): (a) one-way ANOVA of BCOC in cores during Leg 1 analyzed as a function of station; (b) same as in (a) but for Leg 0.10 4; (c) two-way ANOVA of BCOC in cores which overlapped BCOC (mM BCOC (mM O 0.05 between legs, as a function of station and leg; (d) one-way ANOVA of oxygen consumption in vials during Leg 1 analyzed 0.00 N2 N2 A16 A22 E1 S4a S4b S5 as a function of station; (e) same as in (d) but for Leg 4; and (f) Station two-way ANOVA of oxygen consumption in vials which overlapped between legs, as a function of station and leg North Central South Treatment df Sum of squares F-value p-value Fig. 7. BCOC in shipboard core incubations from North Water sampling stations during Legs 1 and 4, spring and summer, (a) Cores: Leg 1 respectively (n ¼ 326 cores incubated per station per leg). The Station 5 1.726 1.900 0.142 two values for station N2 refer to incubations conducted at Residual 19 3.452 temperatures of 0.4 and 1.91C as specified. Location designa- tions as in Fig. 1. Values are means+SEM. (b) Cores: Leg 4 Station 3 0.972 8.350 0.002 Residual 15 0.582

(c) Cores: Legs 1 and 4 station A7 was lower than all other stations and Station 2 0.869 13.020 o0.0001 that oxygen consumption was higher at southern Leg 1 1.537 46.010 o0.0001 station S5 than at S4. During Leg 4, ANOVA Interaction 2 0.712 10.670 o0.0001 indicated that there was a significant effect of Residual 20 0.668 station on oxygen consumption in vials (Table 3). (d) Vials: Leg 1 Post hoc tests revealed that E2 (northern) and D1 Station 5 39.062 15.210 o0.001 (south of polynya) had significantly higher rates Residual 42 21.575 than other stations ðpo0:001Þ: Station S1 with lower pigments than the other southern station S5 (e) Vials: Leg 4 did not differ significantly in vial respiration from Station 5 0.034 30.970 o0.0001 Residual 42 0.009 S5. A two-way ANOVA using the data from temporally overlapping stations E1 and S5 in- (f) Vials: Legs 1 and 4 dicate that there was not significant station or Station 1 0.513 1.750 0.194 interaction term, but that there was a significant Leg 1 8.444 28.760 o0.0001 time treatment (Leg), indicating a 61% decrease in Interaction 1 0.266 0.910 0.347 Residual 37 10.863 mean rates at these stations between Legs 1 and 4 (Fig. 8). In summary, incubation of sediment cores Data were ln-transformed prior to analysis, except in (e) where showed increased BCOC from spring to summer, untransformed data conformed better to ANOVA assumptions. while macrofauna-free sediments incubated in vials had decreased oxygen consumption from spring to summer. component. This comparison indicated that at Sediment respiration data can be interpreted the northern stations and at southern S4, macro- further by comparing vial and core incubation fauna respiration accounted for 63–73% of BCOC results on the same areal basis (Fig. 9). Incuba- in data from both legs. In contrast, at stations E1 tions in vials consisted of a 2-cm deep sediment (central) and S5 (southern), community respira- column compared to >10 cm in the cores, such tion was dominated by the meio-microbial com- that conversion of vial data to areal rates provides munity in Leg 1 (87–100%), but macrofauna a conservative estimate of the meio-microbial dominated oxygen consumption during Leg 4 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5269

0.12 70 Input Leg 1 Leg 1 Demand Leg 1 ) 0.10 60

-1 Leg 4 Input Leg 4 h ) -2

-1 50 Demand Leg 4

m 0.08 d 2 -2 40 0.06 30

0.04 (mg C m 20 Vial SOC (mM O 0.02 demand or Carbon input 10

0.00 0 A7 N2 E2 A16 A22 E1 S1 S4 S5 D1 A16/N2 S4 S5 Station Station

North Central South Fig. 10. Comparison of benthic community carbon consump- tion based on mean of sediment core incubations (demand) and Fig. 8. SOC in shipboard incubations of scintillation vials 2 carbon deposition based on sediment trap data (input) from the containing 0.0005 m of sediment (2-cm sediment depth) from same North Water sampling stations and times (Legs 1 and 4, North Water sampling stations during Legs 1 and 4, spring and spring and summer, respectively) (Hargrave et al., 2002). To ¼ summer, respectively (n 5211 vials per station per leg). broaden comparisons for Leg 1, data on oxygen consumption Macrofauna presence was minimized by aliquot size; rates were at station A16 were used as representative of station N2, due to considered to reflect meio-microbenthic respiration. Location their similarity in sediment type and location. designations as in Fig. 1. Values are means+SEM.

100 Leg 1 micro were made (N2, A16, A22) showed that macro- Leg 1 macro Leg 4 micro faunal respiration was relatively more important 80 Leg 4 macro in both legs (Fig. 9).

60 Rates of organic carbon deposition from sedi- ment trap studies at 50 m above bottom at various 40 North Water stations (Hargrave et al., 2002) were % Total BCOC used to compare carbon input to utilization in the 20 sediment at the three stations where concurrent 0 data were available. Since all BCOC was assumed 0 N2 A16 A22 E1 S4 S5 to be due to aerobic respiration, sediment oxygen Station demand was converted to carbon consumption

North Central South using a respiratory quotient of 0.85 (Rowe et al., 1997). In order to broaden the comparisons for Fig. 9. Partitioning of BCOC between meio-microbenthos (rate Leg 1, data on BCOC at station A16 were used as from incubations of macrofauna-free sediment aliquots in vials) and macrofauna (whole core rate minus rates from incubations representative of station N2, due to their similarity in vials) from North Water sampling stations during Legs 1 and in sediment type and location. Sediment trap 4, spring and summer, respectively. The calculated macrofauna results show that for station A16/N2 carbon input component for station E1 during Leg 1 was zero. Values are was slightly higher during Leg 1 than Leg 4, derived from mean rates per station, with n ¼ 325 cores and whereas input rates were much greater at southern 5–10 vials per station. stations S4 and S5 in Leg 4 compared to Leg 1 (Fig. 10). At A16/N2 and S4 carbon demand (79–84%) (Fig. 9). The significant decrease in the exceeded carbon supply by 5–40 times, but at S5 meio-microbial component from Legs 1 to 4 supply and demand were reasonably similar. (Fig. 8), with simultaneous higher whole core rates Moreover, BCOC was similar between stations of BCOC during Leg 4 (Fig. 7), account for (Leg 1, A16/N2 versus S5; Leg 4, S4 versus S5) macrofaunal domination of partitioning (Fig. 9). despite very different levels of organic carbon The coarsest sediments in which these comparisons sedimentation (Fig. 10). 5270 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275

4. Discussion ments oxygen consumption, especially relative to depth. No relationship between water depth and 4.1. Rates of BCOC and partitioning BCOC is apparent in our study, but the depth range was relatively small and the effects of depth Our measurements of BCOC in the North are confounded by grain size. Water sediments produced rates of 1.68– Of interest is that stations with coarse sediments 2 1 4.08 mmol O2 m d . These values are within did not have consistently lower BCOC, e.g., the range of rates of SOC for Arctic slope central station A22 had the highest gravel content sediments at depths from 200 to 1000 m (0.5– but was not significantly different in core respira- 2 1 7.8 mmol O2 m d ) complied in Boetius and tion from other stations of Leg 1. The presence of Damm (1998). In the Northeast Water Polynya, glacial dropstones obscures the traditional rela- Rowe et al. (1997) measured lower minimum rates tionship between BCOC and grain size, which is 2 1 (0.7–4.3 mmol O2 m d ) for stations of 300– forced more consistently by hydrodynamics at 490-m depth, but rates of primary and export lower latitudes (Grant et al., 1991). The AI production were also substantially less in the suggested that the poorly sorted coarse sediments Northeast Water than in the North Water (Klein of North Water stations have fine components et al., 2002). Shallower Arctic sites display (and associated carbon) that are amenable to expectedly higher rates of BCOC (see compilation reworking and aggregation. in Glud et al., 1998), including the St. Lawrence Organic matter and fine mineral grains trapped Island Polynya with rates of oxygen demand in the interstices of coarse sediment are potentially 1 1 >30 mmol O2 m d at water depths o70 m important at many of the sites sampled herein. (Grebmeier and Cooper, 1995). A useful compar- Hamel et al. (2002) indicated that inorganic ison for our values of BCOC is our previous work carbon content was higher in northern sediments using the identical incubation set-up with sampling of the sampling grid, a finding that affects our use from a box core (Grant et al., 1998). A station at of total carbon as a proxy for organic carbon. We the mouth of the Gulf of St. Lawrence (Cabot suggest that their use of acidification in sample Strait) had June oxygen consumption rates pre-treatment is only a semi-quantitative method equivalent to B48 mg C m2 d1 at comparable for distinguishing inorganic carbon, since some depths to the North Water (494–531 m) and organic carbon is likely digested. Regardless of similar to the rates in Fig. 10. Duineveld et al. these procedural differences, sampling of coarse (1997) plotted BCOC versus depth for several sediments for carbon analysis is notoriously North Atlantic sites. Values for depths of difficult, since the isolation of sand and mud from 500–1000 m were in the range of 2 mmol the gravel matrix is required for the small sample 2 1 O2 m d , including the post-bloom depositional capacity of the elemental analyser. Our previous season. Our North Water values at slightly work indicates that although sedimentary fine shallower depths were somewhat higher. material is richer in carbon on a percentage weight Taken together, these data support previous basis, most of the organic material is in the coarse suggestions that oxic mineralization in Arctic fraction (gravel) by virtue of its weight dominance sediments is not inherently lower than in temperate (Grant et al., 1987). The carbon content of the sediments under similar depth ranges (Thamdrup sample is thus heavily influenced by the selection and Fleischer, 1998; Glud et al., 1998; Rysgaard of mud versus sand from the gravel background. et al., 1998). The North Water stations occupy a This variation is compounded by km-scale changes somewhat intermediate position between shelf and in sediment texture at some stations, as mentioned deep-sea depths and have a constant temperature above. characteristic of deep-sea environments. In gen- Recent published observations suggest that eral, they appear to have a higher supply of temperature is not limiting for rate processes in organic matter than slope sites at temperature Arctic sediments because bacterial activity is latitudes, accounting for the high rates of sedi- comparable to temperate rates (Thamdrup and J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5271

Fleischer, 1998; Rysgaard et al., 1998). There are, that most of the oxygen demand probably however, several indications of temperature-lim- occurred in the upper sediment column. Oxygen ited rates in cold-water environments including consumption in coastal Greenland sediments bacterial decomposition (Pomeroy and Wiebe, (36-m water depth) was concentrated in the upper 2001) and meio-microbenthic turnover rates centimeters of sediment, although subaerobic and (Pfannkuche and Thiel, 1987). Our measurements anaerobic respiration at greater depth in the of oxygen uptake at station N2 were for a period sediment column were significant in carbon dominated by macrofaunal respiration (Fig. 9), mineralization (Rysgaard et al., 1998; Glud et al., demonstrating a doubling of BCOC with a 2000). Chemical oxidation of reduced end pro- temperature increase of only 2.31C (Fig. 7). These ducts accounted for 63% of SOC at their site. results are by no means definitive, but they suggest If chemical oxidation is important in our cores, that temperature can limit oxygen consumption in then the oxygen consumption attributed to macro- Arctic sediments. fauna (core minus vial rates) will be overestimated. A wide range of estimates exist for macrofauna However, the entire difference in rates between contribution to BCOC in Arctic sediments (Glud cores and vials cannot be attributed to this effect, et al., 1998). We recognize that the BCOC in cores since oxygen consumption in vials in some cases excludes the megafauna and their role in benthic exceeds that in cores on an areal basis. Another metabolism (Grant et al., 1991), and that our source of uncertainty occurs in that isolation of results apply mostly to small infauna. Various small quantities of sediment for measurement of studies (Grebmeier and McRoy, 1989; Piepenburg rate processes may stimulate microbial oxygen et al., 1995; Migne and Devoult, 1998) have consumption by changing solute gradients or other suggested that macro- and megafaunal respiration aspects of sediment chemistry (Grant et al., 1998). are relatively greater in coarse sediments; our This would cause the meio-microbial component results are in agreement with macrofaunal dom- of benthic metabolism to be overestimated. We ination of BCOC in coarse sediments (63–73%, cannot estimate the magnitude of these effects in Fig. 9). However, our data indicate that macro- our calculations, but the exclusion of macrofauna faunal prominence also can occur on fine sedi- intended in comparing oxygen demand in small ments and further introduce a seasonal component versus large cores was an attempt to apply a broad to partitioning in that there is a shift from meio- approach to partitioning. The significant seasonal microbial domination of BCOC in spring to decrease in respiration in vials and seasonal macrobial domination in summer (Fig. 9). increase in whole cores, coupled with the postu- The use of selective exclusion as a means of lated time-scale of response to input, is compelling partitioning benthic metabolism has been at- evidence of the legitimacy of this approach. tempted infrequently (Grant and Schwinghamer, 1987), but it adds a unique perspective to our work 4.2. Benthic–pelagic coupling beyond that of BCOC in larger incubation cores. Glud et al. (1998) conducted another approach to That bacteria and microfauna would have a exclusion by comparing oxygen consumption in more rapid response to carbon input during spring large in situ chambers (microelectrode profiles) to is reasonable, considering their asexual reproduc- estimates from incubation of laboratory cores. tion and potentially rapid doubling times. This They attributed increased estimates in field mea- response should occur via increased cell size and surements to macrofauna that were excluded from higher cell numbers, although Boetius and Lochte cores. Subsequent work suggests that the increases (1996) found the latter to be more important in in BCOC due to macrofauna are the result of slope sediments at 821N. Coastal sediments may bioturbation and its enhancement of oxygen show an almost immediate response to organic diffusion rather than to the respiration of macro- input at temperate latitudes (Graf, 1987) or in the fauna (Glud et al., 2000). In our study, despite the Arctic (Rysgaard et al., 1998), but Arctic slope shallow sampling depth of vials (2 cm), we expect sediments with a time lag of days to weeks are 5272 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 similar to deep-sea sediments at other latitudes The spatial and temporal pattern of benthic (Boetius and Lochte, 1996). Nonetheless, Ritzrau oxygen demand fits the currently understood and Thomsen (1997) found rapid response of pattern of primary production and circulation in boundary layer microorganisms to summer sedi- the North Water. Decreased ice cover in April– mentation in the Northeast Water Polynya at May leads to a diatom bloom in the nutrient-rich depths similar to our study sites. waters off the west coast of Greenland. Through We would expect macrofauna to have a longer the summer, the bloom propagates across the lag in response time to organic sedimentation polynya to the west with retreating ice cover, but is than the microbial community, given that game- attenuated due to nutrient depletion (Tremblay togenesis and reproduction occur over periods of et al., 2002; Klein et al., 2002). Sediment-trap weeks to months. There are increases in the AI fluxes are thus enhanced in the western region off from Legs 1 to 4 at some of the muddy stations Ellesmere Island (Hargrave et al., 2002), where that may reflect increased faunal activity. Rowe particle aggregation and advection optimize con- et al. (1997) found a time lag of several months for ditions for sinking fluxes, presumably supplemen- macrofauna response to food input in models of ted by continuing local production. benthic food chains in the Northeast Water Hargrave et al. (2002) discussed some of the Polynya. Ambrose and Renaud (1997) found that reasons why North Water traps may have under- peaks of polychaete reproduction in that polynya estimated depositional fluxes, including high near- were offset from peaks in phytodetrital deposition bottom flow. In the present study, we emphasize by several months. The response of the meiofauna the spatial and temporal pattern of deposition, to enrichment is of the order of 1 month in rather than its absolute magnitude as a means of temperate environments (Webb, 1996) and not understanding the contemporaneous patterns of necessarily evident in benthic respiration, since benthic carbon demand. The linkage between there are few examples where they play a dominant pelagic production and benthic response is appar- role in whole community rates (Piepenburg et al., ent in that southern stations S4 and S5 with 1995). maximum sedimentation of organic matter and Sediment pigments provide a useful indicator of highest sediment photopigments also had the organic input to sediments (Sun et al., 1991) and highest levels of BCOC. Moreover, they contained have been used previously to characterize food ‘excess’ pigment relative to their carbon contents, deposition to Arctic benthos (Table 4). In general, i.e. more than would be expected if the carbon– the total sediment pigments in the North Water pigment relationship were linear (Fig. 6). Station are within the ranges seen in measurements made E1, a sandy-mud location in the centre of the in other Arctic sediments (Table 4). The similarity polynya, also had high BCOC (Fig. 7), but was not of North Water chlorophyll and CPE to pigment included in coverage by sediment trap moorings. levels from the Northeast Water is perhaps This region may be somewhat transitional between surprising given that primary and export produc- the coarse northern sediments and the finer muds tion is so much higher in the North Water (Klein of the southern polynya, occupying the eastern et al., 2002; Amiel et al., 2002). Two other results area of high primary production in the overlying of interest in these literature comparisons are that water column (Klein et al., 2002). Station D1 deeper sediments (>1000 m) still have relatively outside of the polynya (in the time frame of this high CPE and that areas of semi-permanent ice study) had low CPE, consistent with reduced cover (lower slope Laptev sea and central Arctic phytoplankton production in the south (Klein Ocean) display a range of values from low to et al., 2002). Oxygen consumption in vials, medium CPE (Table 4). These results suggest that however, was among the highest of summer the relationship between CPE, sedimentation, and stations. benthic response may be more robust within There are few examples of comparisons between basins or shelf regions than over broader Arctic BCOC and primary production for Arctic waters. spatial scales. Grant et al. (1991) estimated that Labrador Sea J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275 5273

Table 4 Levels of chlorophyll a and total CPE in offshore polar sediments

Location Depth (m) Date Chlorophyll a CPE Reference (mg m2) (mg m2)

Ellesmere Island-W 247–680 Leg 1 (April–May) 0–2 4–30 This study Greenland (North Leg 4 (July) o1–5 11–42 Water) NE Greenland 150–515 July–August 9–46 Ambrose and Renaud (1995) (Northeast Water) NE Greenland 290–340 May–August o1–3 12–44 Ambrose and Renaud (1997) (Northeast Water) Barents Sea slope 1,400 July 66–102 Thomsen et al. (1995) NE Greenland 183–774 September 6–33 Brandt and Schnack (1999) 1098–1965 3–7 Laptev Sea 50 August–September 45 100 Boetius and Damm (1998) (Eurasian Arctic) 1000–3500 o2 10–40

Central Arctic 1055–4180 August–September 1–12 Soltwedel and Schewe (1998) Ocean Northern Barents 226–405 July–August 1–4 7–23 Pfannkuche and Thiel (1987) Sea (Svalbard Shelf) 854–3920 o1–1 1–7 Arctic Ocean 68 July–August o1 7 Clough et al. (1997) section 540–4190 0 p1 Values from other studies are means estimated from tables or graphs therein. All values are from the upper 1 cm of sediment or less, except for samples in Pfannkuche and Thiel (1987) which are the top 5 cm, Thomsen et al. (1995) which are integrated over the top 10 cm, and Clough et al. (1997) which are the top 2 cm.

benthos required B8% of annual primary produc- appropriate sediment type and boundary layer tion. In the North Water, benthic consumption of conditions to allow deposition of surface produc- organic matter accounts for B5% of seasonal (ice- tion. As shown for the St. Lawrence Island free) primary production using a value of Polynya (Grebmeier and Cooper, 1995), the high- B1000 mg C m2 d1 for the western polynya est input of organic carbon to the benthos is not (Klein et al., 2002), where benthic carbon demand necessarily beneath productive waters, but dis- was B50 mg C m2 d1 (Fig. 10). Rowe et al. placed by advection. Similarly, highest carbon (1997) estimated that the benthos of the Northeast deposition and benthic oxygen consumption in the Water Polynya consumed 5–15% of net primary North Water occurred at the western side of the production at stations from 145 to 490 m, while polynya (Fig. 10), which was the site of lowest benthic oxygen consumption at 40-m depth in a primary production in the overlying water column Greenland fjord was equivalent to 12% of primary (Klein et al., 2002). The polynya permits a production (Rysgaard et al., 1996). In Svalbard prolonged production season compared to other fjords ranging from 115 to 329 m depth, Glud et al. Arctic environments, allowing an earlier ramping (1998) calculated that sediment remineralization up of benthic energy flow. Resulting rates of consumed 25–58% of primary production, but benthic metabolism are not necessarily enhanced, speculated that sediment focusing may have so that in climate change scenarios of reduced ice concentrated organic input. cover, the benthos will occupy a position of similar The net benefit to the benthos of increased relative importance, but like the pelagic system, primary production in the polynya requires the with a longer season over which to act. 5274 J. Grant et al. / Deep-Sea Research II 49 (2002) 5259–5275

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