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Contrasting zooplankton communities (Arctic vs. Atlantic) in the European Arctic Marginal Ice Zone

KEYWORDS

Zooplankton communities Arctic Marginal Ice Zone (MIZ) Barents Sea Fram Strait Arctic waters Atlantic waters

Katarzyna Blachowiak-Samolyk

Institute of Oceanology, Polish Academy of Sciences,

Powstancow Warszawy 55, PL-81-712 Sopot, Poland; e-mail: kasiab@iopan.gda.pl

Received 1 April 2008, revised 11 August 2008, accepted 18 August 2008.

Abstract

Relationships between the zooplankton community andvarious environmental fac­tors (salinity, temperature, sampling depth and bottom depth) were established in the European Arctic Marginal Ice Zone (MIZ) using multivariate statistics. Three main zooplankton communities were identified: an Atlantic Shallow Community (AtSC), an Arctic Shallow Community (ArSC) anda Deep Water Community (DWC). All species belonging to AtSC andArSC were pooledandtheir relative abundances in the total zooplankton calculated with respect to a particular layer (surface, midanddeep strata), regions (the Barents Sea, Fram Strait andthe waters off northern Svalbard), years (1999 or 2003) and seasons (spring or autumn). Mapping of the proportions of Arctic andAtlantic species ledto the conclusion that zooplankton from the MIZs do not exactly follow complementary water masses, although the general pattern of AtSC and ArSC dominance accords with the physical oceanography of the study area (AtW and ArW respectively). The mid layer proved to be a better predictor of mesozooplankton distribution than the unstable conditions near the surface.

The complete text of the paper is available at http://www.iopan.gda.pl/oceanologia/

1. Introduction

It is widely believed that the effect of global climate change will be perceptible first andforemost in the Polar Regions (ACIA 2005). In this context, seasonally ice-coveredshelf seas are of special interest, since they are more productive than the deep Arctic Ocean, which is almost permanently coveredby multi-year ice (Hegseth 1998, after Gosselin et al. 1997).

The Marginal Ice Zone (MIZ) is the key productive area of Arctic shelf seas (Slagstad& Stokke 1994, Loeng et al. 1995, Falk-Petersen et al. 2000). As a transitional area, between ice-free andpermanently ice-coveredsea (Frankenstein et al. 2001), MIZ is influencedby both Atlantic (AtW) andArctic waters (ArW), andthe plankton community comprises associatedfauna from both the North Atlantic and the Arctic domains (Stromberg 1989, Walkusz et al. 2003, Daase & Eiane 2007). The ongoing warming of Arctic regions is expectedto leadto a northwardretreat of the MIZ and, in consequence, to the expansion of the geographical ranges of many temperate marine species associatedwith the displacement of Arctic species (Drinkwater 2006). The current study integrates substantial mesozooplankton data from the MIZ of the Barents Sea, Fram Strait and northern Svalbardwaters.

The Barents Sea is one of the most productive regions in the world and one of two major routes by which Atlantic waters enter the Arctic Ocean. Large variations in zooplankton abundance and biomass structures have been recorded on various temporal and spatial scales (Hassel 1986, Skjoldal et al. 1987, Skjoldal & Rey 1989, Arashkevich et al. 2002, S0reide et al. 2003, Blachowiak-Samolyk et al. 2006). The relationship between physical and biological conditions in the Barents Sea has been addressed in several studies (e.g. Unstad & Tande 1991, Pedersen et al.  1995, Hansen et al.

1996, Falk-Petersen et al. 1999, S0reide et al. 2003, Ellingsen et al. 2008,

Blachowiak-Samolyk et al. 2008a,b).

Even though Fram Strait is the most important passage, andthe only deep one, between the Arctic Ocean and the Nordic Seas (Morison 1991), information on the structure of the pelagic biota in this region is still limited (e.g. Smith et al. 1985, Smith 1988, Hirche et al. 1991, Blachowiak-Samolyk et al. 2007, Blachowiak-Samolyk et al. 2008b). The pelagic ecosystem of Fram Strait, highly influencedby advection, has recently been reviewed thoroughly by Hop et al. (2006), but knowledge of the north-eastern Svalbard region remains relatively poor. Apart from the studies on lipids in Clione limacina and Limacina helicina (Falk-Petersen et al. 2001) andon Calanus feeding strategies (S0reide et al. 2008), the only results to date on

the relationship between hydrodynamics and the zooplankton community structure from the north-eastern Svalbardarea have been publishedby

Daase & Eiane (2007).

In recent decades, the influx of AtW to the Arctic Ocean has increased (Morison et al. 2000, Schauer et al. 2004), but it remains unclear how flux variability affects its pelagic ecosystem. The current paper was initiated by the question whether Atlantic Shallow Community (AtSC) andArctic Shallow Community (ArSC) mesozooplankton follow complementary water masses (AtW andArW, respectively) in the European Arctic. In this context, the main aim of the investigation was to compare contrasting mesozooplankton communities (Arctic vs. Atlantic) from different MIZ of Fram Strait, the waters off northern Svalbardand the Barents Sea with respect to vertical stratification and different hydrographic regimes.

2. Material and methods

2.1. Description of the study areas

This study was based on a compilation of mesozooplankton data collectedduring two projects carriedout in the Marginal Ice Zones (MIZs) of the Barents Sea, Fram Strait andthe waters off northern Svalbard by the Norwegian Polar Institute: 'Spatial andtemporal variability of the ice-ocean system in the Marginal Ice Zone of the Barents Sea' (MARIN0K) and'On Thin Ice' (OTI).

The MARIN0K survey was conducted in the central Barents Sea in May 1999. The physical conditions of this continental shelf sea (av. depth 230 m) have already been described (Loeng 1991, Rudels et al. 1991, Steele et al. 1995), so only a brief description of the hydrographic features prevailing at the time of the survey is given here. Typically, in the central Barents Sea warm Atlantic water (AtW) from the south encounters coldwater from the north over the Hopen Trench, forming the Polar Front, approximately at the 250 m isobath. The warm, saline AtW is advected northwards by the Norwegian Atlantic Current, which splits at the Bear IslandChannel. Part of the branch entering the Barents Sea flows northwards along the axis of the Hopen Trench, andthen to the west andnorth of the Central Bank.

'On Thin Ice' (OTI) was carriedout in May 2003 in the eastern Fram Strait, the most important gateway between the Atlantic andArctic oceans, which is influencedby the West Spitsbergen Current (WSC), and is a continuation of the North Atlantic Current (Figure 1) andthe major pathway of heat to the interior of the Arctic Ocean (Aagaardet al. 1987, Schauer et al. 2004). Warm, saline andnutrient-rich water ofAtlantic origin follows the continental shelf slope of West Spitsbergen (Mosby 1938).

20o 30o 40'

longitude E

extensions of sea ice: - maximum--minimum

currents: Atlantic Arctic

stations:  MARIN0K, May 1999     О OTI, May 2003     О   OTI, August 2003

Figure 1. Sampling area in the Arctic Marginal Ice Zone (MIZ) of the Barents Sea (May 1999), Fram Strait (May 2003 andAugust 2003) andoff northern Svalbardwaters (August 2003)

During the autumn OTI cruise (August 2003) the study area covered Fram Strait dominated by AtW and the area north of Svalbard, where Arctic waters (ArW) of low temperature andmoderate salinity prevail. North of Svalbard, the AtW mass submerges below the Arctic water (ArW) and forms a relatively warm and saline intermediate layer that is detectable throughout the Arctic Ocean (Rudels et al. 1991). During the summer ice melt, a thirdwater mass is formedin the surface layer. This surface mix water (MW) is characterisedby low salinity (typically < 34.3 PSU) (Loeng

1991, Harris et al. 1998).

In the northern Barents Sea andover the Great Bank, the upper 150 m

of the water column is colder and less saline; it is also defined as ArW (Loeng 1991). This coldArW layer is initially formedby the freshening of Atlantic water as a result of ice melt, by net precipitation, andperhaps also by mixing with less saline water advected from the Kara Sea (Rudels et al. 1991, Steele et al. 1995); it is subsequently homogenisedduring winter by haline convection in the area of origin, the northern Barents Sea. Then, mainly as a result of the northerly winds prevailing in winter and spring, it is transportedsouthwards, forming the northern component of the Polar Front (Vinje & Kvambekk 1991).

The area investigatedduring the MARIN0K project comprisedthe inner part of the Hopen Trench surrounded by the Barents Sea banks between 76°03'N-77°31/Nand26°53/E-33°08'E (Table 1, Figure 1). Zooplankton andoceanographic parameters were collected with the ice-strengthened r/v 'Lance' from 9 to 22 May 1999. Two transects (A - eastern at 33°E, andB - western at 27°E near Hopen), each consisting of four stations, were sampledfrom north to south across the MIZ. During two OTI cruises zooplankton was collectedfrom the waters north ofSvalbard(Figure 1). The spring cruise with r/v 'Jan Mayen' was carriedout in May 2003, whereas the autumn cruise (August 2003) took place on boardr/v 'Lance'.

For the present work, a set of zooplankton samples from four May stations andeleven August stations was selected(Table 1). In spring, sampling was carriedout on the shelf (station 405), on the continental slope (stations 411 and441) of Fram Strait andover deep water in Sofiadjupet (station 419). In autumn, a transect from the shelfwaters over Norskebanken (station N1) to deep waters (stations N2, N3 and Ice3) was sampled together with two stations on the slope of Flaket (stations FL1 andFL2). Additionally, zooplankton from a few stations situated in north-eastern Svalbardwaters was sampled: on the slope of Hinlopen (station H1), as well as in the shallow areas of Erik Eriksen Strait (station EE4), Rijpfjorden (stations Outer-R1 andInner-R2) andnorthern Kvit0yrenna (station Ice1).

2.2. Oceanographic conditions and sea ice

During the MARIN0K cruise, ice concentration, ice thickness andfloe size were measuredandrecordedevery three hours (Hop & Falk-Petersen 2003). Estimates of ice concentration were basedon schematic diagrams from the National Oceanic andAtmospheric Administration (NOAA 2001).

During OTI cruises, sea ice concentrations were derived from satellite data on two spatial scales: the 25 km grid from the Special Sensor Microwave Imager (SSM/I), andthe 1.1 km gridfrom the AdvancedVery High Resolution Radiometer (AVHRR), provided by the National Snow and Ice

Data Centre (NISDC) andNOAA respectively.

Table 1. Stations, sample (replication) ID, dates, water mass classification, bottom depth, position andice concentration in the Barents Sea, Fram Strait andoff northern Svalbardwaters

Project/Area

Station

Date

Latitude

Longitude

Bottom

Water

Ice

 

 

ID

 

[°N]

[°E]

depth [m]

mass

[%]

MARIN0K -

May

 

 

 

 

 

 

Barents

Sea

A31-01

09.05.1999

76.92

32.92

162

ArW

100

Barents

Sea

A31-03

09.05.1999

76.96

33.00

169

ArW

100

Barents

Sea

A31-05

09.05.1999

76.99

33.03

158

ArW

100

Barents

Sea

A31-07

10.05.1999

77.01

33.08

150

ArW

100

Barents

Sea

A31-09

10.05.1999

77.01

33.07

141

ArW

100

Barents

Sea

A33-01

11.05.1999

76.82

32.82

191

ArW

50

Barents

Sea

A33-02

11.05.1999

76.80

33.53

186

ArW

50

Barents

Sea

A33-03

12.05.1999

76.79

32.97

170

ArW

50

Barents

Sea

A33-04

12.05.1999

76.75

33.07

151

ArW

50

Barents

Sea

A33-05

12.05.1999

76.75

33.13

147

ArW

50

Barents

Sea

A34-01

12.05.1999

76.64

32.89

182

ArW

10

Barents

Sea

A34-03

13.05.1999

76.64

33.09

186

ArW

10

Barents

Sea

A34-05

13.05.1999

76.63

33.12

187

ArW

10

Barents

Sea

A34-07

13.05.1999

76.65

33.31

162

ArW

10

Barents

Sea

A34-09

13.05.1999

76.64

33.30

166

ArW

10

Barents

Sea

A35-01

14.05.1999

76.09

32.65

317

ArW

0

Barents

Sea

A35-03

14.05.1999

76.11

32.39

319

ArW

0

Barents

Sea

A35-05

14.05.1999

76.08

32.67

312

ArW

0

Barents

Sea

A35-06

14.05.1999

76.05

32.37

312

ArW

0

Barents

Sea

A35-07

15.05.1999

76.09

32.69

316

ArW

0

Barents

Sea

B49-01

17.05.1999

77.43

27.03

188

ArW

100

Barents

Sea

B49-03

17.05.1999

77.43

27.07

187

ArW

100

Barents

Sea

B49-05

17.05.1999

77.45

27.00

196

ArW

100

Barents

Sea

B49-07

17.05.1999

77.48

27.00

188

ArW

100

Barents

Sea

B49-09

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