Inter-seasonal Variabilities in an Arctic Fjord: The Kongsfjorden System as a Natural Laboratory for Climate Change

By: K. P. Krishnan,* Rupesh Kumar Sinha** and Kuldeep Attri*
This paper presents a brief account of the inter-seasonal variability in the phytoplanktic community composition in the Kongsfjorden, an Arctic fjord. Ecologically, this Fjord represents a border area between the Atlantic and Arctic biogeographical zones. Even though records of oceanographic observations in the Kongsfjorden date back to 1905, a systematic monitoring programme for phytoplankton in conjunction with water exchange processes in the Fjord is yet to be undertaken. Hence, a programme was initiated in 2011 to study the response of the Fjord to the changing scenario in the Arctic. Water samples were collected using a Niskin sampler from predetermined depths along the major axis of the Fjord for estimation of various phytoplanktic pigments. Subsequent to preparation of pigment extracts, the samples were analysed on an Agilent 1200 series HPLC. In mid June (2011), the concentration of chlorophyll a ranged from levels of non detection to 0.5 µg/l while in early and late September the overall range was 0.01-1.3 µg/l. Diagnostic indices for diatoms, flagellates, prokaryotes and various planktic fractions were computed based on standard protocols. In mid June, the microplanktons clearly dominated the population with the diatoms and flagellate populations higher in the Fjord interior. An increase in the nanoplanktic abundance towards the Fjord interior could be attributed to the comparatively lesser concentration of chlorophyll a in the inner Fjord. In mid September, it was observed that the flagellate and prokaryotic factions showed close coupling and probably strongly influenced the Diagnostic Pigment Index. There was a significant rise in the diagnostic pigments index in late September compared to the other two periods and the abundance pattern of diatoms remained inversely related to the flagellate and prokaryotic fraction. Analysis of water column nutrients for this period indicated that the same may not be limiting (data not presented). However, in addition to the phytoplankton composition, the impact of turbidity on euphotic depth could also play a significant role on phytoplankton distribution.
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Introduction

The Kongsfjorden, a 25 km long and 5-10 km wide glacial fjord on the north-west coast of Svalbard is an established reference site for Arctic marine studies with great potential for international, multidisciplinary collaboration due to the presence of the international research platform in Ny-Ålesund (78o55′ N, 11o56′ E). Because Kongsfjorden receives variable Arctic/Atlantic climatic signals between years with measurable effects on the physical and biological systems, it functions as a climate indicator on a local scale. Kongsfjorden is an open fjord, without a sill, and therefore is largely influenced by the processes on the adjacent shelf. The Fjord is influenced by Transformed Atlantic Water (TAW) from the West Spitsbergen Current and freshwater from glacial run-off at the inner bay. Southerly winds produce downwelling at the coast and have a blocking effect on exchange processes between the shelf and the Fjord, while northerly winds move the TAW below the upper water layer towards the coast. A geostrophic control mechanism in the mouth area governs the exchange between the Fjords and adjacent coastal waters. The head of the Fjord is an active tidal glacier that causes marked environmental gradients in salinity, temperature and sedimentation rates. On a larger perspective, the Kongsfjorden-Krossfjorden system could be used as an indicator for the larger climate driven processes in the Fram Strait. Ecologically, this Fjord represents a border area between the Atlantic and Arctic biogeographical zones.

Even though records of oceanographic observations in the Kongsfjorden date back to 1905, a systematic monitoring programme for phytoplankton in conjunction with water exchange processes in the Fjord and small scale turbulences is yet to be undertaken. In addition, the alteration of algal spring bloom needs to be studied in the light of observed changing oceanographic parameters and the possible consequences for the higher trophic levels. A considerable gap in our knowledge is to quantify cause and effects of, and interaction between, each of the individual forces on the flow field. Detailed studies are needed on the exchange mechanisms to be able to distinguish the water mass exchange, which is related to wind-driven up/down welling at the coast, from that which is related to geostrophic processes in the West Spitsbergen Current.

Understanding the need to monitor the Fjord on longer time scales, the National Centre for Antarctic and Ocean Research (NCAOR) initiated a multi-institutional programme of long-term monitoring of the Kongsfjorden system in terms of its response to changing climate. The overall objective is to establish a long-term comprehensive physical, chemical, biological and atmospheric measurement programme. This could address (a) the variability in the Arctic/Atlantic climate signal by understanding the interaction between the freshwater from the glacial run-off and Atlantic water from the west Spitsbergen current; (b) the effect of interaction between the warm Atlantic water and the cold glacial-melt fresh water on the biological productivity and phytoplankton species composition and diversity within the Fjord; (c) the winter convection and its role in the biogeochemical cycling and (d) the production and export of organic carbon in the Fjord with a view to quantify the CO2 flux. This paper presents and discusses the variability in phytoplankton community structure in the Fjord during the boreal summer of 2011.

 

 

Materials and Methods

Study site and sampling strategy

Kongsfjorden (Figure 1), is a polar fjord situated between 78°04’N-79°05’N and 11°03’E-13°03’E on the west coast of Spitsbergen, Svalbard Archipelago. The Fjord is characterised by a weak tidal range (~2 m) strongly influenced by topography and the adjacent ocean. One of the most remarkable characteristics of Kongsfjorden is that in spite of being located at high latitude it remains unfrozen in the winter in most years. At its inner end, the Kongsfjorden has mainly three glaciers viz. Kongsbreen, Conwaybreen and Blomstrandbreen draining into it and providing the major source of fresh water. Kongsbreen, situated in the innermost part of Kongsfjorden, is recognised to be the most active glacier in the Svalbard Archipelago (Lefauconnier et al., 1994).

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Hydrographic observations and water sampling was conducted during the boreal summer of 2011 at nine stations along the major fjord axis using the research boat R.V. Teisten. A Conductivity-Temperature-Depth (CTD) profiler (SBE 19 plus V2, Sea Bird Electronics, USA) equipped with a fluorescence sensor (Wet labs, Philomath, USA) was used to obtain information about the hydrographic features and fluorescence profile. Water samples were collected from various depths showing fluorescence peaks indicating enhanced biomass in terms of chlorophyll. Water samples were collected using Niskin bottles (10 L) attached onto the winch wire and triggered manually using messengers. Immediately upon collection, water samples were transferred to the precleaned carboys. The water samples were further analysed immediately after bringing to the shore laboratory (Marine Laboratory of Kings Bay AS).

 

Pigment analysis by HPLC

For the analysis of pigments, samples were immediately filtered on a GF/F filter (pore size 0.7 μm, Whatman, England) avoiding exposure of the filter paper to direct light and high temperature. The filter paper was further stored at -80oC until analysed. The frozen filters were immersed in 3 mL of 90 per cent acetone (v/v in deionized water) and kept overnight at 4oC for dissolution of pigment. Pigment extraction was done using a sonicator probe at 25 kHz for 5 seconds (Ultrasonic homogeniser model 3000, Biologics, USA) under low light and temperature (4°C). The extract was passed through a 0.22 μm syringe filter (Millex GV, Millipore, Ireland) to remove the cellular debris. The clarified extract was collected in a 2 mL amber colour glass vial and placed directly into the temperature controlled (4°C) auto-sampler tray for the (HPLC) analysis. Pigments were separated following a slight modification of the procedure of Van Hukelem et al. (2002). The HPLC system was equipped with an Agilent 1200 quaternary pump together with online degasser. Separation was achieved on a Zorbax Eclipse XDB C8 HPLC column (4.6 x 100 mm) manufactured by Agilent Technologies (USA) connected to a suitable guard column maintained at 60oC. Elution at a rate of 1.1 ml/minute was performed using a linear gradient programme over 20 minutes with 5/95 per cent and 95/5 per cent of solvents B/A being the initial and final compositions of the eluant, where solvent B was methanol and solvent A was (7:3) methanol and 1 M ammonium acetate (pH 7.2) instead of 28 mM solution as recommended in the protocol. After returning to the initial condition (5 per cent solvent B) by 21 minutes, the column was equilibrated for 9 minutes prior to next analysis. The eluting pigments were detected at 445 and 665 nm (excitation and emission) by the diode array detector. All chemicals used were of HPLC-grade, procured from Sigma-Aldrich (USA). Commercially available standards obtained from DHI Inc (Denmark), were used for the identification and quantification of pigments. Solutions of chlorophyll a (Chl a), chlorophyll b (Chl b), fucoxanthin (Fuco), 19’-hexanoyloxyfucoxanthin (19’-Hex), 19’- butanoyloxyfucoxanthin (19’-But), peridinin (Per), alloxanthin (Allo), Zeaxanthin (Zea) and lutein (Lut) were run in order to obtain calibration curves and absorption spectra and to determine detection limits. Identification was based on the retention time and peak shape, i.e. through fingerprint matching with known peak shape from the diode array spectra library created by running pure standard of individual pigments. The concentrations of the pigments were computed from the peak areas.

In order to know the contribution of each community, biomass proportion (BP) was determined for each station using diagnostic pigment (DP). The DP is defined as the sum of seven pigments as follows:

 

DP = Zea+ Chl b + Allo + 19’-Hex + 19’ But + Fuco + Per

 

The biomass proportion associated with each size class [picoplankton (<2 μm), nanoplankton (2-20 μm) and micropankton (20-200 μm)] is defined as:

 

BPpico = (Zea+Chl b)/DP

BPnano = (Allo + 19’-Hex+19’-But)/DP

BPmicro = (Fuco+Per)/DP.

Results and Discussion

The Kongsfjorden is influenced by Atlantic-derived water masses covered by thin layer of freshwater from the glaciers. Though the Kongsfjorden as well as other fjords in the Svalbard show a similar stratification, the amount of Atlantic-derived water in the fjords depend on the general oceanographic situation in the North Atlantic (Cottier et al., 2005). Closer to the glaciers, where the great discharge of freshwater occurs, strong stratification in temperature and salinity is observed, but this gradient diminishes towards the fjord opening (Swerpel 1985; Svendsen et al., 2002). Together with the melting waters, vast amounts of inorganic sediments are released (Zajaczkowski 2008). The resulting turbidity controls the depth of the euphotic zone as well as the spectral composition of penetrating radiation (Urbajski et al., 1980; Svendsen et al., 2002), which directly influences phytoplankton composition and primary production. Relatively clean and blue waters are encountered at the mouth of the Kongsfjorden but the inner basins are turbid with a reddish brown coloration (Piwosz et al., 2008).

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Figures 2 (A-C) illustrates the concentration of Chlorophyll a at various depths along the major axis of the Fjord. The concentration ranged from levels of non detection to 0.5 µg/l averaging at 0.1±0.1 µg/l. In mid June there appeared to be a comparatively low Chlorophyll a zone at the 10 m sandwiched between productive layers (Figure 2A). In early September (Figure 2B), the biomass was higher but confined mostly to shallow depths. The overall range of Chlorophyll a in the Fjord during this period was 0.01-1.28 µg/l. Analysis of water column nutrients for this period indicated that the same may not be limiting (data not presented). It could be discerned that the biomass of phytoplankton increased with time and there was a considerable amount of biomass build up 0.6±0.3 µg/l in late September (Figure 2C). The biomass also increased on a spatial scale from the head to the mouth of the Fjord and ranged from 0.12-1.3 µg/l. Hence a systematic assessment of the effect of sunlight and particle flux into the Fjord would be vital in understanding the key elements governing production.

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Computations based on the concentration of pigments (diagnostic index) indicated that during mid June at 5 m along the Fjord major axis, the population distribution of diatoms and flagellates were comparable while the prokaryotic component oscillated inversely (Figure 3). The microplanktons clearly dominated the population with the pico and nanoplankton abundance fluctuating in a mutually exclusive pattern. The diatoms continued to be the most abundant fraction at 40 m; however the population significantly dwindles at 150 m followed by concomitant rise in the flagellate fraction. It was also interesting to note that irrespective of the depth under consideration the diatoms and prokaryotes dominated the Fjord interior. Piwosz et al. (2008) had reported that the diatoms and autotrophic dinoflagellates are more important in the outer basins during July. In early September (Figure 4), contrary to the observations in June, at 5 m the diatoms and flagellates oscillated mutually exclusively at 10 and 60 m, while the prokaryotic fraction followed the flagellate fraction almost closely at 10 m. It was also observed that the flagellate and prokaryotic factions showed close coupling and probably strongly influenced the DP index. However, the diatoms appeared to be having a significantly different abundance pattern. Like in June, the microplanktons clearly dominated the population with the nanoplankton abundance fluctuating in a mutually exclusive pattern. The picoplankton load was comparatively less compared to the observations in June. Though there was a significant rise in the DP index in late September compared to the other two periods (Figure 5), the abundance pattern of diatoms remained inversely related to the flagellate and prokaryotic fraction. Similar to the early September scenario, the abundance pattern of diatoms did not match well with the diagnostic index. However, there was a significant similarity between them same at 5 m. The microplanktons continued to dominate the Fjord waters with the pico and nano plankton exhibiting a fairly uniform distribution at both the depths. The nanoplanktons were more dominant in the inner Fjord during mid June and a similar observation was also made by Piwosz et al. (2008) in the Kongsfjorden during late July. This could be one of the reasons for comparatively lesser Chlorophyll a values in the inner Fjord. However, in addition to the phytoplankton composition, the impact of turbidity on euphotic depth could also play a significant role on phytoplankton distribution.

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Conclusion

Chlorophyll a concentration in the Fjord was found to increase from mid June to late September with the biomass more concentrated and confined to the shallower depths. Chlorophyll a concentration in the outer regions of the Fjord was higher compared to in the inner Fjord in late September while there was not significant spatial variability in mid June. Irrespective of the time of sampling, the microplanktic fraction always dominated the Fjord with the picoplantonic fraction gradually increasing towards late September. Analysis of water column nutrients indicated that the same may not be limiting. However, in addition to the phytoplankton composition, the impact of turbidity on euphotic depth could also play a significant role on phytoplankton distribution.

 

 

Acknowledgement

The authors wish to express their gratitude to Dr. S.Rajan, Director, National Centre for Antarctic and Ocean Research for his interest in this work. This work was carried out as a part of the project “Long term monitoring of Kongsfjorden system of Arctic region for climate change studies” supported by grants from the Ministry of Earth Sciences, Government of India. We acknowledge the Kings Bay AS for their field and laboratory support.

 

 

References

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