DOC and its relationship to algae in bottom ice communities

arine System

9 9 ( 9997) 7 9-80

a Biology Departnlent. University qf Waterloo, Waterloo, Ont. N2L SGI, Canada ’ Oceanography Department, Unkersity of Qukbec at Rimouski. Ritnouski, Qui. C5L 3A1, Canadu ’ National Institute for Polar Research, Tokyo. Japan ’ Biology Department, Lural University, Qukbec, Qk. GlK 7P4, Canada ’ Hokkaido National Fisheries Research Institute, Kushiro 085. JUPU:I Received 7 October 1994; accepted 30 March 1995

Abstract The seasonal development of alga1 biomass and dissolved organic carbon (DOC) in bottom ice was determined for two widely separated areas of annual sea ice, Saroma-ko in northern Japan and Resolute Passage in the Canadian High Arctic, to determine the importance of DOC to estimates of primary production in sea ice communities. As algal biomass, measured either as chlorophyll a (Ckla) or particulate organic carbon (POC), increased, DOC concentrations increased to extremely high values (up to 40 mg C I- ’ DOC). The highest algal biomass and DOC concentrations were observed at Resolute under thin (4-8 cm) snow cover. Highly significant double-log linear relationships (1” = 62-8096, y < 0.01) existed between DOC and both Chla and POC, suggesting much of the DOC originated from the ice algae. A highly significant global relationship between DOC and POC ( Y’= 7496, p < 0.01) was also found when previously published data for Frobisher Bay were included, indicating substantial consistency in the relationship between DOC and algal biomass among widely separated locations and differing climatic/hydrodynamic regimes. The significance of the apparently rich production of substrates for microheterotrophic processes in the ice is unclear until the nature and origin of the DOC are better resolved. It is clear, however, that estimates of organic production in ice based only on accumulation of particulateorganic material will be seriously biased if dissolved material is ignored. Keywords:

Dissolved OrganicCarbon; sea ice; Arctic; Algae

1. Introduction It is now recognized that algae and associated organisms living in sea ice form a community of considerable importance to the ecology of polar oceans. Algae are the dominant component of the biomass of sea ice communities, but there are substantial and metabolically active populations of het-

* Correspondingauthor. Phone: 519 885 I21 1. Fax: 519 746 0614. E-mail: [email protected]. 0924-7963/97/$17.00

erotrophic microbes in the ice community (e.g., Kottmeier et al., 1987; Smith and Clement, 1990). The production of ice microbes has been estimated to contribute on the order of 15-25% of the annual primary production on the continental shelf of the Arctic Ocean (Legendre et al., 1992; Welch et al., 1992). The importance of the ice-associated production may be greater than its share of total production would suggest, due to its time of occurrence and spatially concentrated nature. Furthermore, most estimates of primary production in sea ice communities have been based mainly on changes in fne standing

Copyright 0 1997 Elsevier Science B.V. All rights reserved.

PfI SO924-7963(96)00029-2

concentrations of algal biomass and/or POC in the ice or on measurements of particulate carbon fixation (Cota and Smith, 1991). Production of DOC by the ice community will not be recorded in such measurements, and could conceivably lead to significant underestimates of community production. Measurements of photosynthesis and extracellular release of carbon by ice algae in incubators have indicated only low rates of DOC production by ice algae, typically 10% or less of primary production (Kottmeier et al., 1987; Smith et al., 1988). Such rates of release are within the range observed in other algal communities, although a large-scale analysis of data from the literature uggests a somewhat higher average of 13% for marine and freshwater phytoplankton (Baines and Pace, 199 1). Incubator measurements of particulate carbon fixation, when extrapolated to field conditions, have also given reasonable estimates of ice algal biomass accumuiation during the spring growth period (Smith et al., 1988; Bergmann et al., 1991). However, the uncertainties in the latter comparisons are appreciable, and direct release of recent (labelled) photosynthate by algae is only one possible mechanism of DOC production. Other mechanisms (e.g., sloppy feeding by grazers) may operate more efficiently in the natural community than in the subsample of it represented in typical primary production experiments. There is only one published report of total DOC concentrations in communities of ice biota, but it suggested relatively high DOC concentrations could develop when ice algal biomass was high (Bunch and Harlzn4, 1990). Measurement of DOC poses many methodological and analytical challenges (Wangersky, 1993). The high DOC concentrations reported by Bunch and Harland (1990) could, for example, be a result of damage to the organisms in the collection, preparation or filtration of the sample (Goldman and Dennett, 1985; Garrison and Buck, 1986; Smith et al., 1990). Alternatively, the analytical methodology employed by Bunch and Harland (UV-assisted wet oxidation) might, from the present perspective, be thought to underestimate the true DOC concentration by 10 to 60% (Kaplan, 1992; Chen and Wangersky, 1993; Sharp et al., 1993; Wangersky, 1993). Such questions are difficult to answer and are largely beyond the scope of the present paper. Instead, we

seek to determine whether the high DOC concentrations reported for bottom ice communities by Bunch and Harland are general for bottom ice communities, and whether DOC is systematically related to indices of algal abundance in the ice. The SARES project, as described more fully by Fukuchi et al. (1997-this issue), was conceived as an opportunity to compare the functioning of sea ice communities under very different climatic and hydrodynamic regimes. In the present context, it presented the possibility to monitor the development of ice algal communities and associated DOC in two widely separated systems, Saroma-ko Lagoon at a temperate latitude in Japan and Resolute Passage at a high latitude in the Canadian Arctic. By including published data from yet a third ice community, in Frobisher Bay in the low Canadian Arctic (Bunch and Hzrland, 1990), we sought to extend the analysis to be representative of events in annual ice generally, at least in the northern hemisphere.

2. Materiais anti iiWihOdS 2.1. Sampling sites and methods Data reports produced specifically for the SARES project provide much of the detail on sampling methods and background data (Shirasawa et al., 1993; Taguchi et al., 1994; Smith et al., 1995). Only the most pertinent details are given here. The sampling site at Resolute was located approximately 2 km offshore in Resolute Passage, Northwest Territories, Canada (74”41’N, 95”15’W). Water depth was about 125 m. Land-fast annual ice forms in this area in October and November and by early spring extends for typically 200 km or more in every direction. Timing of break-up is variable among years but typically occurs in July. Multi-year ice is scarce in the vicinity. An ice camp was established in Resolute Passage to permit rapid processing of samples without transport back to a land-based lab. Sampling of ice was done in areas of two contrasting snow depths. “Thin” snow was defined as 4-8 cm, while “thick” snow was 18-24 cm. Samp!ing of the water column was done through a large access hole located within the ice camp building.

formation in Saroma-ko is varia March or early April. In the year of this study (1992), Saroma-ko was completely ice covered from February 5 to April 4. The results here for Saroma-ko were based on sampling e natural snow cover, which varied considerably during the observation period, as described in Section 3. A shore lab in close proximity to t ling site enabled prompt processing of samples. At both Saroma-ko and Resolute, samples of bottom ice were obtained using SIPPE corers, with the bottom 4 cm of the core sectioned off and melted. Although such a sampling method may not always recover all of the material initially present in the undisturbed ice (Welch et al., 1988), it -‘*,I h;nma~r cxnnlipd ~~ covers > 70% of the iugul uIvIIIuI>Jtrrhnn “vsnw‘. “yp’ VW. b.. Resolute (Smith et al., 1993) and it is a standard amethod of z‘ce sannling. Samples from the water columu were obtainid using 5 1 Niskin bottles. 2.2. Ana!,ltical methods Chlorophyll t7 (Chin) samples were filtered on glass fiber filters @F/F) and frozen pending analysis. Analysis was done on site within 2 weeks of collection, Filters were extracted overnight in 90% acetone at Resolute or for 1 hour in NJV-dimethyl formamide (DMF) at Saroma-ko. Limited comparisons between acetone and DMF extraction at Saroma-ko indicated that DMF extracted more Chin, but no consistent factor to relate the two methods could be derived. Thus, some of the varistion between Resolute and Saroma-ko is due to methodological differences that cannot be quantified, but the significance to our main conclusions is not great. Chlorophyll concentration in the extracts was determined by the fluorometric method of Yentsch and Menzel (1963), with pre- and post-acidification measurements. The fluorometer was calibrated against pure chlorophyll a. Filters used for particulate organic carbon (POC) and dissolved organic carbon (DOC) analyses were pre-combusted glass fiber (GE’/F). Such filters can,

collected in pre-combusted glass vials,

aterial retained on the filter was

on a Dohrman DC-80 reagent and ultraviolet radiation to oxidize organic carbon to CO,, which is subsequently quantified with a non-dispersive detector, very si UV-assisted wet oxidation method of @hen and Wangersky (1993). Benzoic acid was used as a standard and all measurements reported here were made within the linear response range of the instrument. Recent comparisons among alirzlytical methods would suggest that the wet oxidariun system used here for DOC would yield lower ttshuXr; :hz:r?snmr alternative methods, particularly high temperature catalyzed oxidation (HTCO) methods (Kaplan, 1992; Sharp et al., 1993; Wangersky, 1993). Chen and Wangersky ”1993) found that their HTCO method yielded 560% (but usually lo-40%) more DOC than the wet oxidation method on samples from algal cultures and from inshore and offshore North Atlantic waters. However, the aim of the present study was to determine relatively gross changes associated with very large changes in algal biomass, and current information indicates the wet combustion method is adequate for nur purpose. Other sorts of analytical uncertainty, particularly related to sample preparation, are probably more important and are considered in the discussion. The results shown here for all the chemical analyses are the means of duplicate determinations, unless otherwise specified.

R. E. H. !hitlr et al. / Jmrmal oj’bfarine Systems I I f 1997) 71-80

74

11.8

3. Results , Chl

Sampling at Resolute commenced in mid-April, 1992, when relatively little algal biomass had accumulated (Fig. 1). Under thin snow cover (4-8 cm), Chla concentrations in the bottom ice increased rapidly from 0.054 mg l- ’ on April 13 to over 1.33 mgl-* on April 29. Chla concentrations declined after April 29 until a renewed increase led to the maximum observed concentration of 2.48 mg 1-l. Particulate organic carbon (POC) measurements commenced later than the Chla measurements and did not reveal any increase of POC parallel to the earlier phase of Chla increase (Fig. 1). Instead, POC decreased from the initial value of nearly 50 mg Cl-’ on April 20 to a minimum of 30 mg Cl-’ on May 6; it subsequently increased to the maximum observed concentration of 64 mg C l- * on May 18, declining thereafter to a value of 58 mg C l- * on May 22. Seasonal changes in dissolved organic carbon (DOC) concentration in bottom ice under thin snow cover broadly paralleled the changes in Chla (Fig. 1). although precise comparisons were hindered by differences in sampling frequency. The minimum concentration of 3.95 mg C I- ’ was observed on our initial sampling date (April 13) and the maximum concentration of 40.3 mg C l- ’ was observed on May 14, with a subsequent decline to 23.8 mg C l- ’ 3

2.5

2

1.5 f! 0

\\ \

------ , IJ---_-i,

DOC i

1

20.

0.5

10

I---l----&Apr 1 SApr

29-Apr 09.May SAMPLING DATE

lSM;yy

DOC w

t;pay

Fig. 1. The time course of chlkrophyll n (CM& particulate organic carbon ( POC.) and dissolved organic carbon in bottom ice (DOC i) and in under-ice surface seawater (DOC w), all in mgl-‘, near Resolute, N.W.T., in 1992. Snow depth was 4-8 cm. Points are means of triplicate (Chkr, POC) or duplicate (DOC) samples.

-OkApr

19-Apr

’ 29,Apr 09.May SAMPLING DATE

a

It1.6

-7-y-

Fig. 2. The time course of Chlorophyll n (Chkah particulate organic carbon ( POC) and dissolved organic carbon in bottom ice ( DOC i) and in under-ice surface seawater ( DOC MS), all in mgl-‘. near Resolute, N.W.T.. in 1992. Snow depth was 18-24 cm. Points are means of triplicate (C/da, POC) or duplicate ( (KM3 samples.

on the last sampling date (May 22). By comparison, there was little variation in DOC concentration in surface seawater beneath the ice (Fig. 1) with :l seasonal average concentration of 4.38 f 0.76 (95% CL) mg C l- I. Under thick snow cover (18-24 cm) the seasonal increase of Chla and POC was delayed and smaller compared to that under thin snow cover (Fig. 2). Chl a increased from a minimum of 0.001 mg I- ’ observed on the initial sampling date (April 20) to the maximum of 1.55 mg l- ’ observed on the last sampling date (May 22). POC increased from a minimum of 1.5 mg C 1-l observed OJ the initial sampling date (April 24) to a maximum of 28 mg C l- ’ observed on the last sampling date (May 22). DOC in bottom ice under thick snow cover again broadly paralleled the changes in Chla and POC (Fig. 2). The minimum concentration was 2.08 mg C 1-l on April 13 and the maximum was 20.05 mg Cl-’ on May 22. Air temperatures remained consistently below freezing during the observation period at Resolute. There was no observed melting or loss of snow cover (Shirasawa and Ingram, pers. commun.). As expected, the seasonal increase of algal biomass, as judged by Chla, was earlier at the low-latitude site in Saroma-ko (Fig. 3). Chla increased rapidly from about 0.2 mg 1-l on the initial sampling date (February 20) to a seasonal maximum

301--

--

__

-~

1.6 14

t

0.6

’ i, 0.4 W

I

0.2

o--_

l&Feb

.7-.---_1--7-_.-__ 23-Feb

------T-28-Feb 05-Mar 1O-Mar SAMPLING DATE

15Mar

JO PO-fvlar

Fig. 3. The time ccursc of Chlorophyll II (C/I/U), particulate and dissolved organic carbon in bottom ice (DOC i) and in under-ice surface seawater (DOC WQ),all in in Saroma-ko in 1992. Depth of snow cover varied as mgl-‘, described in text. Points are means of triplicate (Cltltr, P(?C) or duplicate ( DOC) samples.

organic carbon (POC)

of 1.6 mgl-’ on February 28. Chla decreased nearly 50% over the following two days ar;rl remained nearly constant at about 0.8 mg 1 - ’ thereafter (Fig. 3). POC d ata were available for only the last three sampling dates, but indicated a substantdal increase from 5.9 mg Cl-’ on March 9 to 10.5 mg c’I - ’ on the last sampling date, March 16. Samp’ling for DOC in Saroma-ko did not commence tlntil the seasonal maximum in Chla had been attained (Fig. 3). DOC in bottom ice showed little trend over the observation period, but there was a major increase from 11.3 mg C 1- ’ on the date of the Chla maximum (February 28) to 27.5 mg Cl-’ on the next sampling date (March 2), simultaneous with the large decrease in Chla concentration. Subsequently, there was a large decrease in DOC to the seasonal minimum of 4.8 mg C 1 - ’ observed on March 6, and then a recovery KOhigher values for the remainder of the observation period. The large changes in Chla and DOC in Saroma,-ko from February 28 to March 6 coincided with a major snowfall on March l-3, which increased the average snow depth from a,n initial value of less than 10 cm to a maximum of 40 cm on March 3. Snow depth gradually decreased thereafter and was again less than 10 cm by the end of the observation period. During the later part of the storm, on March 3, water appeared on the ice and was attributed to melting of snow and infiltration of seawater due to depression

unstable variance. Log-log transformation corrected both problems and led to the regression models reported in Table I, with the fitted lines shown in Figs. 4 and 5. The significance of the models is determined mainly by the Resolute data, but the Saroma-ko data fall in reasonable agreement with the overall relationship. Chla was a better predictor of DOC in bottom ice than was POC, with an r2 of 80 VS. 62% (Table 1). Both relationships have regression coefficients significantly less than unity (Table l), indicating that the “yield” of DOC per unit Chla or POC declines as algal biomass increases.

~_

__~__.

- - .;_

1.5 CHLOROPHYLL a

1ii

2

I 2.5

+ l-siiizrj HES-THIN

Fig. 4. Concentration of DOC (mgl- ’) in bottom ice versus simultaneous concentmtion of chlorophyll a (mg l- ’) for Resolute and Saroma-ko. The line shown was fitted by linear regression to log-transformed data and is described by the Chin @ARES only, n = 20) equatton in Table 1. Points are means for individual dates and sample sites.

20

10

30

50

40

60

POC

=

RES-THIN

+

RES-THICK

--

SAROMA - ---

-- .-

FROBISHER 1 .J

Fig, 5. Concentration of DOC in bottom ice versus simultaneous POC concentration (both in mgl -’ ) for Resolute, Saroma-ko and Frobisher Bay. The lines were fitted by linear regression of log-transformed data and are described by the POC (Aif data) equation (solid line) and the POC iSARES only1 equation idotted line) in Table 1. Points are means for Individual sampling dates and sites.

The analyses in Fig. 4 necessarily excluded some of our data, corresponding to dates with Chla but not POC data. This resulted in the exclusion of fully half the data from Saroma-ko. In order to make use of more of the Saroma-ko data, a log-log regression model on Chla only was also fitted to all our data. As might be expected from the less orderly seasonal changes in Saroma-ko, this modification resulted in a lower r2 (75%), but the relationship was still highly significant and the regression coefficient still significantly less than unity (Table 1). To further explore the generality of the relationships in Table 1, we then included previously published data for DOC and POC in bottom ice of

Table 1 Parameters of log-log linear regression models for predicting DOC in bottom ice: log(DOC) = CI+ 6 log( X 1 Predictor, X

a

6*95%

POC (all data) POC @ARES data only) Chla @ARES only) chla @ARES only) G

0.385 0.5 10 1.197 1.155

0.591 f0.154 0.487 f O.t40 0.401f0.126 0.324f0.086

CL

r’ (%‘c) II

74 62 80 75

22 12 12 20

Dissolved organic carbon (DOC), particulate organic carbon (POC) and chlorophyll n (Chla), all in mg l- I, a Includes dates with Chla but not POC data.

Frobisher Bay (Bunch and Harland, 1990). Anaiysis of residuals covtinued to indicate that a linear regression of untra&formed variables was inappropriate, so we fitted t&e log-log linear regression model to obtain highly significant results (Table 1; Fig. 5). The Frobisher Bay data appeared to fall in reasonable agreement with the overall relationship which was, in turn, in reasonable agreement with the results for Resolute and Saroma-ko only. The regression coefficient was significantly larger than for Resolute and Saroma-ko only, but still significantly less than unity. The y2 was actually higher (74%) for the combined data set. No Chla values were reported for Frobisher Bay, so comparison of Chla vs. POC based models could not be done for the combined data.

4. Discussion The only previously published report of DOC in sea ice (Bunch and Harland, 1990) showed that relatively high concentrations were associated with the development of ice algal populations. The seasonal dynamics of DOC in bottom ice at Resolute similarly suggested a roughly parallel development of’ ice algae and DOC. Together with the highly significant reluti;lnships between DOC and both POC and Chla, the results support the interpretation that most of the DOC originates from the ice algae. The Resolute site has consistently shown development of algal crops considerably larger than those reported from almyother Arctic site (Smith et al., 1988), and the maximum DOC concentrations there were similarly the largest yet reported for a sea ice community (cf. Runch and Harland, 1990). They were far higher thagl typical DOC concentrations (l-2 mg C 1- ’) for the marine water column in general, even allowing for methodological uncertainties (Chen and Wangersky, 1993; Kepkay et al.. 1993; Sharp ct. al., 1993). The concentrations reported here are for the melted sea ice samples and are uncorrected for the diluting effect of the melted ice or ,for any leakage or loss of material while sampling. Given a typical porosity of roughly 10% for bottom ice (Maykut, 1985) and assuming that the DOC partitions into the liquid brine rather than the ice crystals, the actual in situ

eucaryotic microbes assimilate weight organic molecules in be ice community (Homer and Alexander, 1972; lmisano and Sullivan, 1985; Smith and Clement, By contrast to the apparent substrates for growth, the bio of heterotrophic bacteria in bottom ice communities are not particularly high. Area1 and volumetric concentrations of bacterial biomass are high in absolute terms, when compared to concentrations in the water column, but not when compared to the si abundance of ice algae (Kottmeier et al., 1987; Smith et al.. 1989: Bunch and Harland, 1990; Smith and Clement, 1990). Inhibition of bacterial growth and/or substrate utilization efficiency at low temperatures (Pomeroy and Deibel, 1986; Nedwell and Rutter, 1994) may be a factor, but the temperature sensitivity of bacterial and a!gal productivity in bottom ice (Kottmeier and Sullivan, 1988) suggests that other factors are more important in restraining bacterial activity. The: nature of the DO@ is unknown, and much of it may be relatively refractory to bacterial metabolism or even inhibitory, despite its apparent origin from the algae within the limited time period of the bloom (e.g., Bell et al., 1974; Sundh, 1992; Amon and Benner, 1994). It is also possible that most of the apparent DUG measured in GF/F filtrates is not truly dissolved in the natural community environment but is either small particulate material or dissolved material that is released from algae in the process of sample preparation and filtration (Goldman and Dennett, 1985; Isao et al., 1990; Wangersky, 1993). Studies of dissolved inorganic nutrients in bottom ice samples have suggested that osmotic shock during melting of samples is not criticai, but that the fiitration step itself may be responsible for the appearance of substantial amounts of low molecular weight dissolved materials (Smith et al., 1990). The data currently available cannot resolve the proportion of the measured DOC that may originate in such artifacts, which are a general problem in DOC determinations (Wangersky, 1993).

derive from the ice algae, there may be additional mechanisms operating to enrich the bottom ice with C. As sea ice forms, dissolved salts are largely e ice crystals, resulting in brine salinity of the youngest and most porous bottom ice is only about 25% of that of the seawater from which it is formed. if DOC were similarly excluded during ice formation, then DOC concentrations in bottom ice without ice algae should be about 1.1 to 1.25 mg C I-‘, based on observed surface seawater DOC concentrations at Resolute and Saroma-ko, respectively. Our log-log regression models must by their nature predict intercepts at the origin, which seems unlikely to be truly accurate even though the models appeared to fit the functional form of the response quite well over the observed range of the variables. The fitted models predicted a high ratio of DOC to POC at very low biomass concentrations (e.g., 2.43.2mgCl-’ ofDOCatPOC= l.OmgU-’ forthe global and SARES model, respectively) and much lower ratios at higher biomass (e,.g., 9.2-9.9 mg C I- ’ of DOC at POC = 10.0 mg C l- ‘). Such strong non-linearity of the response may in fact owe partly to some mechanism or process that acts to retain or even produce DOaC in ice when algae are scarce or absent. The alternative explanation would be a relatively greater release of DOC at low algal biomasses than at higher, for which no obvious reason exists. Direct observations of DOC in ice with low algal biomass ( < 0.015 mg I- ’ of Chla) at Resolute indicated an average of 3.2 & 1.2 (95% C.I.) mg Cl-‘, which is significantly higher than the expected concentration for algae-free ice. The data published by Bunch and Harland (1990) for early season samples with low algal biomass also suggest higher DOC

concentrations than expected if DOC behaves like salt during ice formation. When corrected for the average porosity ( 10%) of bottom ice, the DOC concentrations that can apparently be attained even with minimal algal influence are far larger than those in the water column. Although the mechanism is unclear, it thus appears that a substantiai enrichment of the bottom ice environment with DOC can occur even with only minimal algal growth. In more operational terms, the results clearly indicate that organic production inferred from POC or Chla changes in sea ice can be greatly underestimated if the dissolved fraction is ignored. Based on the present and previous seasonal studies at Resolute and elsewhere (e.g., Hsiao, 1980; Smith et al., 1988; Bunch and Harland, 1990?, we may assume that the spring growth period begins with 1.O mg C l- I of POC due to scavenging from the water column and overwinter accumulation. Then a spring algal bloom that produces an accumulated biomass of 10 mg cl-’ of POC (t ypical of maximum reported POC for Frobisher Bay and Saroma-ko) would produce 7.47.8 mg Cl-’ of additional organic material in the form of DOC, depending on whether we use the global or SARES regression model. The yield of DOC, relative to POC, decreases as biomass increases, according to the regression mod&. Still, a bloom producing 60 mg C 1” of POC (the maximum observed under thin snow at Resolute in 1992) would produce an additional 27 to 35 mg C 1 - ’ as DOC according to our regression models, Kepkay et al. (1993) reported similar proportions of DOC production for a bloom of coastal marine phytoplankton: 30 to 80 PM POC and an additional 25 p,M DOC. While the DOC production inferred here is not likely to greatly alter the perceived status of ice communities as contributors to basin-scale primary production estimates (e.g., Legendre et al., 1992), it is of considerable significance to carbon budgets for sea ice communities. Chla proved a better predictor of DOC than was POC for the SARES data, where both measures of algal biomass were available. POC was still a better predictor of total organic carbon (TOC) concentration (r* = 94%) than was Chl a ( r2 = 78%), according to log-log linear regression analysis, because most of the TOC was in the form of POC. Nonetheless, the predictive power of Chla, which is rela-

tively quick and cheap to determine, was quite respectable. It is not clear why Chla should be more closely related to DOC than is POC, or whether the result was peculiar to the Resolute data, which dominated the SARES analysis. The density of data for the individual sites is insufficient to resolve whether relationships between DOC and indices of algal biomass may vary substantially between locations. The sparse data for Saromako suggest that events such as snowfall and associated melting and infiltration can induce large and rapid changes in biomass and its relationship to DOC. In Saroma-ko, such events appeared to lead to an appreciable loss of algal biomass from the ice but an increase, possibly due to release from stressed algae, of DOC over an interval of only a few days in early March. Thus, the peculiarities of hydrodynamic and climatic regimes may influence events at different locations. Our analysis does show, however, that a single, global relationship reasonably encompasses the results available to date, despite major differences in the climatic and hydrodynamic regimes and in sampling and analytical methods.

Acknowledgements We thank the many organizations and individuals who contributed financial support and logistical help in both Japan and Canada. In Japan, the Monbusho International Scientific Research Program, the Sukekawa Scientific Research Grant of the National Institute for Polar Research, the Saroma Research Centre of Aquaculture and the Hokkaido Tokoro Shounen-shizen-no Iye all provided assistance. In Canada, the Department of External Affairs Canada, the Natural Science and Engineering Research Council, the Fonds FCAR of Quebec, the Groupe Interuniversitairc de Recherches Oceanographiques du QuGbec (GIROQ), the Department of Fisheries and Oceans Canada and the Polar Continental Shelf Project (P.C.S.P.) all provided financial and/or logistical assistance. Special thanks to Dr. H.E. Welch of the Freshwater Institute and Dr. R.J. Conover of the Bedford Institute of Oceanography for providing working space and equipment in Resolute and to the personnel of P.C.S.P. for their generous help.

99

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