arctic marine ecosystems in an era of rapid climate change

Progress in Oceanography 90 (2011) 1–17

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Arctic marine ecosystems in an era of rapid climate change q

1. Introduction

Countless documents have focussed upon the rapid changes thatare being observed in the Arctic (e.g. ACIA, 2004). Atmosphericwarming has increased Arctic Ocean (AO) temperature and resultedin decreased extent and thickness of sea ice (Comiso, 2003; Kwokand Rothrock, 2009). Sea ice extent is now decreasing at a rate ofabout 10% per decade (Stroeve et al., 2007; Comiso et al., 2008). Afterthe rapid melting in 2007, a slower negative trend was re-established in 2008–2010, but the AO (covered mostly by first-yearice) will probably be largely ice-free in late summer in a few decades.In addition, the average thickness of the ice has decreased steadily(Kwok and Rothrock, 2009), freshwater inputs have increased(McPhee et al., 2009; Yamamoto-Kawai et al., 2009) and transporttowards the Fram Strait has increased (von Eye et al., 2009). Thesestriking changes in physical forcing have left marine ecological foot-prints of climate change in the Arctic ecosystem (Wassmann et al.,2010b). However, predicting the future of the pan-Arctic ecosystemremains a challenge not only because of the ever-accelerating natureof both physical and biological alterations, but also because of a stag-gering lack of marine ecological knowledge.

The AO is a circular system engirdled by land, i.e. a mediterra-nean sea (sensu Dietrich et al., 1980; Tomczak and Godfrey,2001), encompassing several distinctive characteristics that cannotbe revealed by research in its various sectors. At present theamount of scientific exploration that has been done is inadequatein terms of geographic coverage, time coverage and precision todescribe the circumpolar features, local/regional disparities andthe complexities of the AO ecosystem (Wassmann, 2006). How-ever, recent studies on biogeochemistry, marine ecology and phys-ical forcing in the pan-Arctic region (e.g. through the 4thInternational Polar Year (IPY), that just has come to the end of itsexploratory phase) have led to a rapid increase in knowledge aboutregion as a whole. The international symposium C flux and climatechange: The Nordic contribution to a pan-Arctic perspective in 2002was crucial in the development of the marine pan-Arctic perspec-tive. That was the meeting where Arctic oceanographers sincerelystarted using the now-ubiquitous term ‘pan-Arctic’. Here the ideawas broached to synthesize the emerging image of pan-Arctic foodwebs and ecosystem structure in a dedicated volume: Structure andfunction of contemporary food webs on Arctic shelves (Wassmann,2006). Pan-Arctic overviews on ecosystems and food webs were

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q Finally, since zoogeography is a study of a dynamic, not a static, phenomenon,and since changes in the distribution of marine animals can be of decisive economicimportance, it is necessary to keep routine observations going every year, or atregular intervals, not only upon the fauna itself, but upon the hydrographicconditions which, more than anything else, determine the composition of the fauna(Arctic and Subarctic marine ecology: immediate problems (Dunbar, 1953)).

assembled for the first time. Based upon this exercise, increasedinterest in the Arctic and some of the scientific endeavours of the4th IPY an attempt was made to convene central projects andkey oceanographers operating in the pan-Arctic region at the sym-posium Arctic Marine Ecosystems in an Era of Rapid Climate Change(www.arctic-frontiers.com) in Tromsø in January 2009. Buildingupon the foundation presented in Wassmann (2006) efforts weremade to encourage further pan-Arctic integration. To this end, se-lected scientists working throughout the pan-Arctic were asked tosummarize their information on the ecology of the pan-Arctic. It isthe extraordinary atmosphere and the enthusiastic character of theTromsø conference that is embodied in the present volume. Thepresent synopsis is based upon the comprehensive perspectivesand unifying concepts presented by Carmack and Wassmann(2006). It focuses on how the pan-Arctic is depicted today, summa-rizing available investigations done in the various national sectorsor in AO as a whole. We also highlight some of the major ecologicalquestions that are common for the pan-Arctic region as well as theecological implications of climate change. Towards the end of thesynopsis we converge upon future research challenges and arguefor a change in the international attitude towards Arctic oceanog-raphy in general and marine ecosystem research in particular.

2. Pan-Arctic ecosystems: what do we know?

Fig. 1 provides an overview over regions for which publicationssummarizing the ecosystems are already available, or are beingmade available through this volume. Most of them are centeredon the Fram Strait – Svalbard – Barents Sea (BS) region. Also inthe Bering Strait – Chukchi Sea, Canadian Beaufort Sea and south-western Greenland overviews and progress summaries on ecosys-tems are available, but many recent intensive investigations havenot been summarized as yet. There are two key regions from whichonly a dearth of ecosystem information is available: the wide cen-tral AO and the extensive Siberian shelf. The lack of ecosystemsoverview from the central AO is understandable in view of thedifficulty of gaining access to the productive zones of this vast re-gion, and doing so not just once but repeatedly over several years.Current ecological information is often based on snapshots derivedfrom periodic visits of icebreakers (e.g. Gosselin et al., 1997) orpainstakingly assembled collages of data sets for some of themore long-lived organisms such as copepods (e.g. Kosobokovaand Hopcroft, 2010). From the immense Siberian shelf only twosummaries are available (Hirche et al., 2006; Schmid et al., 2006),but even these consider only a narrow annual time window or onlya selection of ecological elements. Biological data from the centralArctic Basin and the Russian shelves appear to exist mainly in re-ports and field work journals that are scattered, frequently notcompiled and basically never published, not even in Russian.

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Fig. 1. The Arctic Ocean with the Canadian, Makarov, Amundsen and Nansen Basin, separated by the Alpha, Lomonosov and Nansen–Gakkel Ridges. The Arctic shelvesencircle the deep basins. Red dots and numbers indicate regions where the structure and function of contemporary food webs is adequately known and the information hasbeen published. 1: Fram Strait/western Spitsbergen (Hop et al., 2006); 2: Barents Sea (Wassmann et al., 2006); 3: Kara Sea (Hirche et al., 2006); 4: Laptev Sea (Schmid et al.,2006); 5: East Siberian and Chukchi Sea (Grebmeier et al., 2006a,b); 6: Beaufort Sea (Dunton et al., 2006); 7: Canadian Archipelago (Michel et al., 2006); 8: Baffin Bay andNorth Water Polynya (Tremblay et al., 2006); 9: North-eastern Greenland and Young Sound (Rysgaard and Nielsen, 2006). The blue dots indicate ecosystems for whichinformation on the structure and function of contemporary food webs is provided in this volume: 10: Fram Strait (Mauritzen et al., 2011); 11: Polar Front region of the BarentsSea (Drinkwater, 2011); 12: Rijpfjorden, representative of the Arctic coastal waters north of Spitsbergen (Leu et al., 2011); 13: the marginal ice zone of the northern BarentsSea (Reigstad et al., 2011). The blue line indicates the Arctic cross-section of the IPY project Canada’s Three Oceans (Carmack and McLaughlin, 2011).

2 Editorial / Progress in Oceanography 90 (2011) 1–17

Russia’s national plans for marine ecological research on the exten-sive Siberian shelf and adjacent AO have not been made available tothe international scientific community. The prospects for a rapidincrease in essential knowledge from the entire AO are thus unsat-isfactory and will require major impetus, also after the end of the4th International Polar Year. Meanwhile, we must try to be patientuntil a more comprehensive picture becomes available.

Despite of the alarming nature of warming and its strong poten-tial effects in the AO the research effort aimed at describing andunderstanding Arctic marine ecosystems is rather limited (see Sec-tion 5 and Fig. 8). If we are to attain fuller insight into the workingsof pan-Arctic ecosystems, data and investigations must be madeaccessible in a comprehensive manner. The main aim of this vol-ume is to contribute towards this goal.

3. Fundamental elements of pan-Arctic ecosystems

To obtain a better overview over pan-Arctic ecosystems in thisera of rapid climate change it seems important to organize

investigations into broad, unifying categories. In Section 3.1 we ad-dress three shelf investigations dealing with the seasonal ice zone(SIZ) (Leu et al., 2011; Reigstad et al., 2011; Drinkwater, 2011). Wepresent the contributions regarding the in- and out-flow processesin Section 3.2 (Mauritzen et al., 2011; Carmack and McLaughlin,2011). The complex coupling inside the AO itself demands thatproductivity regimes and food webs be considered through a mac-roecological perspective. This is done in Section 3.3, where wepresent evidence from two additional publications (Bouchard andFortier, 2011; Slagstad et al., 2011).

3.1. Regional and time variation studies in the seasonal ice zone

The features and dynamics of the SIZ impose severe limitationson the marine autotrophs that form the base of the marine foodweb. Reigstad et al. (2011) assess internal and spatial variabilityand pathways of carbon flow within lower tropic levels and be-tween plankton and benthos of the ice-covered waters of thenorthern BS (Fig. 1). In regions influenced by non ice-covered

Fig. 2. (A) The average gross primary production in the European Arctic Corridor for the period 1995–2007. Scale to the lower left (g C m�2 year�1). Redrawn from Wassmannet al. (2010a). (B) The coefficient of variation (standard deviation/mean) of the annual gross primary production in the European Arctic Corridor for the period 1995–2007.Scale to the lower left. Redrawn from Wassmann et al. (2010a).

Editorial / Progress in Oceanography 90 (2011) 1–17 3

Atlantic water (AW) the range of annual primary production is110–130 g C m�2 year�1 with low interannual variability. Season-ally ice-covered regions exhibit higher interannual variability,but lower productivity (55–65 g C m�2 year�1). Three basic pri-mary production domains can be distinguished in the BS and adja-cent regions (Fig. 2A): (i) an extensive domain dominated by AW(red), (ii) an elongated domain roughly corresponding to the SIZ(yellow) and (iii) a compact perennial ice zone (blue) (>100, be-tween 100 and 30, and <30 g C m�2 year�1, respectively).

Ecological groups that differ in terms of biomass and carbonturnover were compared. Despite the fact that larger planktonand benthos often represent a large proportion of the total biomass

(average 50%), small planktonic organisms (algae <10 lm and bac-teria, proto- and small mesozooplankton) are major players in car-bon turnover (average 77%) in the northern BS. The significance ofsmall algae in ice-covered waters, at least in the European ArcticCorridor (eastern Greenland coast to Kara Sea; EAC; Fig. 2) withits low silicate surface water concentrations, deviates from earlierviews. Despite of the periodic significance of larger life forms suchas diatoms, microbial food webs may play a greater role in pelagicecosystems than previously believed. Carbon budgets illustrate theimportance of grazers for vertical flux regulation, as highest down-ward export coincided with lowest heterotroph consumption rela-tive to autotroph biomass. However, the mesozooplankton

Fig. 3. Conceptual overview of the primary production regimes of ice algae andphytoplankton in the European Arctic Corridor along a latitudinal gradient reachingfrom the southern seasonal ice zone (D) to the central Arctic Ocean (A). Both icecover and the open, stratified surface waters are indicated (beta ocean, see Fig. 6).Panel E exemplifies the course of primary production in the scenario of continu-ously open water in the Barents Sea, characterized by no major freshwater source(alpha ocean, see Fig. 6). The variable production in June arises through variations innutrient supply caused by vertical mixing events triggered by low-pressure passageafter the end of the spring bloom. Panel F projects future primary production at70�N (E) after global warming leads to increasing thermal stratification. Panels A–Eshow present-day spatial variability in the European Arctic Corridor. Panels A–Fshow temporal development during global warming. Modified from Fig. 1 in Leuet al. (2011).


biomass in the Marginal Ice Zone (MIZ) may vary greatly betweenyears. The overwintering success of the key herbivore in Arcticshelf seas, the copepod Calanus glacialis, appears to have a signifi-cant influence on spring bloom development due to an earlier graz-ing impact compared to its Atlantic congener, Calanus finmarchicus.The pelagic–benthic coupling in MIZ is therefore highly variableand the presence and absence of ice-algae may add to thisvariability.

Sediment carbon burial rates reflect a longer time-scale (years),and these rates are relatively constant in the northern BC.Topography can provide environmentally favourable conditionsfor benthos by creating regions of local accumulation and/or sub-ducted AW and thus ‘override’ productivity regimes in the surfacewater. Thus simulated patterns in annual productivity do notcorrespond with observed sedimentation patterns, e.g. increasedcarbon burial in regions with high productivity. However, benthicbiomass was higher in stations influenced by AW, in good agree-ment with higher annual primary production and carbon exportflux.

Leu et al. (2011) focussed upon the timing, quantity, and qualityof primary and secondary producers in the European Arctic shelfseas, exemplified by one of the northernmost fjords in Svalbard:Rijpfjorden (Fig. 1). Sea-ice algae begin to grow in early springwithin and beneath the ice, producing a substantial amount of bio-mass despite very low light intensities. Pelagic algal blooms, incontrast, normally occur after ice breakup, at high latitudes as lateas July–September (Fig. 3). The timing of these blooms is crucial forthe quantity and quality of primary and secondary production, andtherefore for the transfer of energy and matter to higher trophiclevels. It is suggested that ice algae, rather than pelagic algae,trigger the reproduction of Arctic zooplankton around Svalbard.C. glacialis timed its seasonal migration, foraging, and reproductionin perennial ice-covered regions to ice algal blooms, which pre-ceded the pelagic algal bloom by 2 months. The growth of this sec-ondary producer’s offspring, however, was dependent on the laterbloom of phytoplankton and higher seawater temperatures. In2007, reproduction and growth of C. glacialis and the primary pro-duction regime matched perfectly. The persistent ice cover in thesummer of 2008, however, led to a mismatch between the pelagicalgal bloom and the growth of the new copepod generation, result-ing in a fivefold lower biomass of C. glacialis in August 2008compared to 2007. The initiation of the ice algal bloom is mainlydetermined by the solar angle and snow cover, whereas the pelagicalgal bloom requires more light and is therefore governed to alarger degree by ice thinning and less predictable ice breakup.

The ecology of the SIZ in the EAC is characterized by an intimatecoupling between the solar cycle, ice and snow cover, the onset ofprimary production in ice and open water, seawater temperatures,and the reproductive success and growth of C. glacialis. A futurereduction of the Arctic ice cap and sea-ice thickness will changethe timing of key processes, including an earlier ice breakup and,as a consequence, an earlier onset of the pelagic bloom. For ice al-gae, however, the growth season will become shorter because itsonset is limited by a critical amount of available light that, beingrestricted by the low solar angle at high latitudes, will remain un-changed. In a future warmer climate, more precipitation is pre-dicted, which will lead to a thicker snow cover, or to anacceleration of ice breakup due to melting processes induced byrain. Either way, the result will restrict the ice algal bloom growthseason further. Years with less extreme ice conditions in terms ofeither an earlier ice breakup or a reduced ice and snow cover orboth, will thus lead to a reduced time lag between ice algal andphytoplankton blooms, resulting in a potential mismatch, particu-larly between the phytoplankton peak and the ontogenesis of C.glacialis. A warmer climate with less extensive ice cover leads toa higher total primary production (Arrigo et al., 2008; Slagstad

et al., 2011), which again will increase the overall secondaryproduction. The other extreme, as experienced in 2008, i.e., anextensive ice cover with ice breakup in August–September, leadsto low overall primary and secondary production, and does notlead to a high recruitment grazers. The findings of Leu et al.(2011) suggest that timing is probably the single most essentialfactor deciding the recruitment success or failure in secondary pro-ducers, and hence, the efficiency of transfer of biomass and energyto higher trophic levels. However, the quantity and quality of thealgal food available, together with seawater temperatures, havealso been shown to be crucial for optimal reproduction anddevelopment.

The Polar Front in the Barents and Norwegian Seas restricts thesouthern section of the SIZ in the EAC. In this region Drinkwater(2011) worked with the aim to quantify the impact of climate var-iability on the structure and function of the marine ecosystem(Fig. 1). New insights were provided on the role of large-scaleatmospheric forcing on the physical oceanography including theeffect of Arctic and Atlantic cyclones on the variability of the ice ex-tent in the BS and the nonlinear response of the sub-polar gyre toNorth Atlantic Oscillation forcing. In addition, the North AtlanticOscillation was shown to influence biological factors, for exampleshrimp recruitment in the BS and primary production in the NordicSeas, with the strength and sign of the correlations being spatiallydependent. The importance of longer-term climate variability inthe form of the Atlantic Multi-decadal Oscillation (60–80 year per-iod) was stressed, as it leads to significant changes in fish produc-tion, shifts in distribution and changes in spawning sites in the BSas well as other northern Atlantic ecosystems.


Advection of AW is essential to explain the recent warming andhigh salinities in the BS. An important determinant of the annualprimary productivity in the Barents and Norwegian seas is thecombination of lower nutrient concentrations in the deep AW, low-er light levels in the south, and stratification and ice-cover north ofthe Polar Front. Along the topographically controlled Polar Frontaround Svalbard primary production is particularly high. The in-creased primary productivity in the BS during the recent warmingis due to the reduction in sea ice. Zooplankton biomass appears tobe controlled by both top-down (predation by fish) and bottom-upforcing (advection and temperature) in the Barents and NorwegianSeas. The poleward movement of zooplankton and fish during therecent warming period in the BS is confirmed as a general responsethroughout all the ecosystems investigated.

3.2. Large-scale advective regulation of the Arctic Ocean ecosystems

As we have seen in Section 3.1, food web dynamics in the AO arestrongly influenced by ice regimes and connections with the Pacificand Atlantic Oceans. An important factor in these impacts is theadvective nature of the AO (Fig. 4). The AO is an open, circular sys-tem where >80% of the in- and outflow proceeds through thenortheastern North Atlantic. There is growing acceptance that thepan-Arctic system is tightly connected to the subarctic bythrough-flowing Atlantic and Pacific water masses. Thus, changeswithin the AO cannot be fully understood in regional isolation;rather, changes within its ice-cover, water column and marine eco-systems are inextricably linked to the global system in general andto the bordering subarctic Pacific and Atlantic in particular. Tounderstand the AO we must study the bordering oceans as well.Two lines of logic underpin this argument. First, as shown by bothobservational and modelling results, one major impact of climatechange on the marine system will be the redistribution of oceanicboundaries and habitats/biomes; this emphasizes the need fortime-series observations over broad spatial domains (Sarmientoet al., 2004; Carmack and McLaughlin, 2011). Second, high-latitudeoceans share the common trait of salinity-dominated stratification(beta ocean), which, in turn, strongly influences all processes asso-ciated with horizontal and vertical flux (Carmack, 2007). The AO it-self acts a ‘double estuary’ where waters entering from the NorthAtlantic either become denser through cooling (negative estuary)or lighter become by mixing with river, sea ice melt and Pacificwaters (positive estuary). Atlantic waters are thus modified as theycirculate within the Arctic basin and return to the North Atlantic tojoin the global thermohaline circulation (Aagaard and Carmack,1989; Carmack and Wassmann, 2006; Yamamoto-Kawai et al.,2006). It is within this interconnected system, wherein localchange has far-reaching effects across interacting space and timescales that the effects of climate change have to be interpreted.

Here we summarize the marine ecological information fromtwo papers that describe the status of the research activities ofthe Norwegian IPY projects iAOOS-Norway, POLEWARD and MEOP(Mauritzen et al., 2011) and the IPY projects Canada’s Three Oceansand Joint Ocean Ice Study (Carmack and McLaughlin, 2011). The firstreport focuses on the role of advection into and out of the AOthrough the inadequately studied Fram Strait, while the secondtakes a look at the entire Canadian coast, bordering three oceans(Fig. 1). The advection of parent subarctic water masses, their sub-sequent modification upon entering the AO and their transitthrough the pan-Arctic system is investigated. In both cases weemphasize ecosystem properties and dynamics rather thanphysics.

For the Fram Strait region, recent simulations suggest a produc-tivity regime of 100–140 g C m�2 year�1 in the waters influencedby northward-flowing AW, with a sharp decrease towards westclose to the East Greenland Shelf Break (Mauritzen et al., 2011;

Fig. 2A). In the out-flow region on the North-East Greenland Shelf,the simulated annual primary production drops to about half thevalues to the east, 40–60 g C m�2 year�1. The main regulating fac-tors are the duration, thickness and characteristics of the ice cover,which determines the length of the productive season and watercolumn stratification. The East Greenland Shelf and Shelf Breakare covered by dense drift ice from the AO, making sunlight thelimiting factor for biological production in spring. A considerableincrease in the biological production, biomasses and vertical exportof organic matter was observed from April to May 2007 within thedrift ice, illustrated a highly dynamic system with chlorophyll aconcentrations increasing from <0.05 to 10 mg m�3 within a fewweeks. The algal community changed from a dominance of small(<10 lm) cells to large cells over this period and vertical exportof organic matter increased by a factor of 10–100. At one stationvertical export of particulate organic carbon, pigments and faecalpellets from zooplankton increased by a factor of >10 over a fewdays. The pelagic spring bloom is of short duration and intense.

Owing to differences in their physiological optima, the copepodcommunity composition should change across Fram Strait, withAtlantic species such as C. finmarchicus on the eastern side, andArctic species such as C. glacialis on the western side (Hircheet al., 1991; Falk-Petersen et al., 2009). However, due to the com-plex current system in the Fram Strait, Atlantic species are ad-vected and redistributed to the East Greenland side with theAtlantic return flow (Hop et al., 2006; Hirche and Kosobokova,2007). A change in ice conditions in the AO and the Fram Strait,with less multi-year ice (MYI), thinner and smaller ice floes, andin particular less or changing snow cover, can create a situationthat favours earlier blooms and alters which species dominatethe East Greenland Shelf and the SIZ. While winter concentrationsof 10–12 lM NO3 are typical for the BS and AW (Reigstad et al.,2002), the nitrate concentrations on the East Greenland shelf de-creased from similar concentrations in the AW water at the shelfbreak to concentrations <3 lM NO3 on the shelf. With such lowconcentrations of winter-accumulated nitrate on the shelf, the po-tential productivity in this region will be considerably constrained.Similar low nitrate concentrations are reported from Canadian Arc-tic surface waters (Tremblay et al., 2008; Li et al., 2009). This sup-ports a scenario of compellingly nutrient-limited primaryproduction and short, transient spring blooms for major regionsof the AO.

Across the Fram Strait and in the BS, highly different productionsystems exist at similar latitudes, because of advection of AW andice and Arctic Water (ArW) (Hirche et al., 1991; Hop et al., 2006).Comparative studies of these systems can help in identifying po-tential consequences of future change in sea ice extent and sea-sonal dynamics. High spatial and temporal variability as well asshort spring blooms and reduced primary production are the rulein the heterogeneous environments of the ArW outflow, but withincreased light availability due to reduced ice discharge one mayexpect earlier phytoplankton blooms. This contrasts with the AWadvective regime of the eastern Fram Strait and that through theBS, where primary production is 2–3 times higher, the productiveseason longer and the onset of the bloom is less variable.

Carmack and McLaughlin (2011) present data and conceptualframeworks for interpretation and future comparison along a tran-sect that connects subarctic and Arctic domains from the North Pa-cific to the North Atlantic, showing the present-day distributions oftemperature, salinity, nitrate, oxygen and chlorophyll data, andestablishing an initial step towards a true baseline against whichto gauge future change. The focus is to observe and categorizephysical and chemical change. The relationship between thesechanges and their impacts on high-latitude ecosystems is por-trayed through indications of ecosystem changes. With oceanwarming, altered salt-stratification, increased sea ice melting and

Fig. 4. The import of Pacific and Atlantic Water into the Arctic Ocean (solid lines) and the export of Arctic Water from the Arctic Ocean into the North Pacific and Atlantic(dotted lines). In addition to the export of Arctic Water through Fram Strait, the Transpolar Drift is indicated. Subduction of imported Pacific and Atlantic Water takes place inthe Arctic Ocean (dashed lines). Perhaps as much as 90% of the import comes through the northeastern North Atlantic. The export is mainly through the western section ofFram Strait, but also through Nares Strait and the Canadian Archipelago. Northerly winds along the west side of Bering Strait occasionally give rise to the Siberian CoastalCurrent, a short-lived, southward-flowing current that penetrates to the Bering Strait (Weingartner et al., 1999).


ice retreat, alterations in circulation and fronts, and shifts in advec-tion patterns, the three oceans of Canada are already subject to sig-nificant change, and face even more change in the near future.Within the Canada Basin, a core region of the AO, the largestchanges in water column properties are due to advection. Forexample, the first signal of far-field effects on Canada Basin waterswas the increased ventilation of Atlantic-origin BS waters in the1990s (McLaughlin et al., 2002). Significantly warmer Atlantic-origin Fram Strait water, first observed in the Nansen Basin duringthe early 1990s, reached the western parts of the Canada Basin in2002 (Shimada et al., 2004) and subsequently spread across mostof the interior of the southern basin by 2007 (McLaughlin et al.,2009). Advective processes naturally also affect biological distribu-tions. One example is the advection of Pacific haplotype C. glacialisas far north as the western Canada Basin, though the copepod doesnot yet reproduce there (Nelson et al., 2009). Another example isthe advection of euphausids through Bering Strait and into theChukchi Sea, where they are grazed by bowhead whales (Bluhmand Gradinger, 2008).

Regional warming may lead to the breakdown of current barri-ers at gateways, and the invasion of new species. An example of a

dispersal barrier breakdown and downstream consequences is de-scribed by Grebmeier et al. (2006a,b) who note that the near-bottom ‘cold pool’ – formed by wintertime sea-ice formation onthe Bering shelf under current ‘normal’ climate conditions – mayblock southern pelagic species and strengthen pelagic–benthiccoupling farther north in the Chukchi Sea. Possible adaptations tochanging physical environments might include Pacific salmonentering and surviving in the Beaufort Sea (Irvine et al., 2009) orkiller whales moving into the eastern Canadian Arctic Archipelago(Higdon and Ferguson, 2009).

A basic but nonetheless difficult challenge is to predict whethernew primary production will increase or decrease under conditionsof temporally and spatially reduced ice cover and increased advec-tive throughflow. Carmack and McLaughlin (2011) suggest thatthere is no single answer and – recalling that the AO is mainly ni-trate-limited (Carmack et al., 2004; Tremblay and Gagnon, 2009) –that the response will depend on regional conditions. On thepan-Arctic shelves removal of ice cover beyond the shelf break willenhance wind and ice-forced shelf-break upwelling; the resultingincreases in both nutrient fluxes and solar radiation should thusincrease new production. In the deep central basins the increased


addition of freshwater from ice melt will increase surface layerstratification, particularly in the Pacific Arctic sector; the resultingdecrease in vertical nutrient flux to the euphotic zone should thusdecrease new production. In many passages and channels of theCanadian Arctic Archipelago in which strong flows and tidal mixingforce nutrients into the surface layer, reduced ice cover and a long-er growing season should increase new production. Finally, in thesub-basins of the Canadian Arctic Archipelago increased ice meltand a stronger regional precipitation and river discharge will in-crease surface layer stratification; the resulting decrease in verticalnutrient flux should thus decrease new production. This highlysimplified concept admittedly ignores other regional processes(e.g. increased turbidity from river discharge, altered convectiveprocess, etc.) but at least serves as a starting point for analysis.

3.3. Over-arching issues and themes in the pan-Arctic realm

The circular and mediterranean structure of the AO requiresholistic, not sectorwise accounts (Wassmann, 2006). The complexnature of the AO, the fact that investigations are not evenly distrib-uted over the geographic regions of the AO and the sheer shortageof knowledge hamper our ability to make well-balanced evalua-tions. To exemplify over-arching issues, a circum-arctic compari-son of the hatching season of polar cod Boregadus saida(Bouchard and Fortier, 2011) and an evaluation of primary and sec-ondary production in an AO void of summer sea ice by Slagstadet al. (2011) are presented in this volume. Both papers belong tothe few that so far have addressed over-arching issues and themesthroughout the AO.

The polar cod B. saida plays a central role in the relatively sim-ple pelagic food web of the AO, channelling a major fraction of theenergy flow between plankton and vertebrates (Bradstreet et al.,1986; Welch et al., 1992). Starting in late summer, polar cod fryare preyed upon by seabirds in the surface layer (Karnovsky andHunt, 2002) and then by their adult congeners as they migrate atdepth to their overwintering grounds (Baranenkova et al., 1966).A large size at the end of the short Arctic summer should reducethe vulnerability of juveniles to avian predation, cannibalism, andwinter starvation. Hence, selection pressures should push hatchingto occur as early in winter or spring as environmental conditionswill allow, so as to maximize the duration of the growth seasonand late-summer size (Fortier et al., 2006). Bouchard and Fortier(2011) test the hypothesis exposed in Bouchard and Fortier(2008) that salinity-induced variations in sea surface temperaturesdictate regional differences in the hatching season of polar cod. Incoastal seas influenced by large rivers (Laptev/East Siberian Seas,Hudson Bay, and Beaufort Sea) brackish conditions in under-iceriver plumes would provide the larvae with temperatures onlyslightly below 0 �C, accelerating embryonic development andallowing successful first feeding and survival in winter. In regionswith less freshwater input (Canadian Archipelago, North BaffinBay, and Northeast Water) the �1.8 �C temperature prevailing un-der the ice in winter would slow egg development and limit firstfeeding and survival. In such regions, hatching would have to bedelayed until the vernal warming of the surface layer for the larvaeto survive.

The review of hatching seasons of polar cod in relation to fresh-water input generally supports the hypothesis that under-ice riverplumes provide a thermal refuge that enables some polar cod tohatch, initiate first feeding and grow in winter. In southeasternHudson Bay in spring (late April to early June), newly hatched polarcod larvae occur in the coastal zone influenced by the turbid fresh-water plume of the Great Whale River that extends over the 0–5 mdepth layer immediately under the ice cover (Fortier et al., 1996).The seemingly euryhaline first-feeding larvae congregate indaytime in the brackish halocline between the plume and the

underlying marine layer, where the prey density is greatest (Pon-ton and Fortier, 1992). These observations support the assumptionthat polar cod larvae associate with under-ice river plumes in win-ter as well. However, a definitive test of the winter thermal refugehypothesis would entail the direct verification that polar cod hatch,feed successfully, and grow in the halocline of the under-iceplumes of rivers in Arctic coastal seas in winter. The Laptev Sea,the area of the Beaufort Sea inside the stamukhi, and Hudson Baywould be particularly well suited to deploy the overwinteringexpeditions needed to sample polar cod larvae under sea ice inthe extreme winter conditions of the AO.

In the other paper, a physically–biologically coupled 3D modelwas applied to the entire AO for the first time (Slagstad et al.,2011). Three highly relevant and timely questions related to cli-mate change are raised: (1) How will productivity change in a war-mer, future AO? (2) Which key processes and players thatdetermine productivity are the most variable? (3) Where and whenwill changes be observed? The study focuses mainly on gross pri-mary and secondary production and the key mesozooplankton spe-cies C. finmarchicus (Atlantic) and C. glacialis (Arctic). The modelwas applied in an experimental setting where a control run hadatmospheric forcing from the European Centre for Medium-RangeWeather Forecasts reanalysis data. In order to test how atmo-spheric temperature increase and retreating ice cover in the forth-coming century might affect productivity through physicalprocesses in the AO, Slagstad et al. (2011) added a latitude-dependent air temperature increase starting at +1 �C at 40�N andincreasing to +2, +4, +6 and +8 �C at 90�N to the temperature forc-ing. The model indicates that gross primary production increasesalong the temperature gradient both in the Arctic Basins and alongthe Eurasian shelves from approximately 10 to 40 and from 30 to60 g C m�2 year�1, respectively (Fig. 5A). In contrast, primary pro-duction in the BS was more or less constant (ca100 g C m�2 year�1). For secondary production the results of theexperimental runs are more complex. With an air temperature in-crease towards +8 �C secondary production of C. glacialis in the BSdropped from about 3.9 to 0.3 g C m�2 year�1, while that in theArctic Basin and Eurasian shelf increased from approximately�0.1 to 1.5 and 1.4 to 2.4 g C m�2 year�1, respectively. Secondaryproduction changes are unevenly distributed spatially during fu-ture warming with the most significant increases occurring alongthe Eurasian shelves and the Chukchi Sea. Reductions are predictedfor the Kara Sea and northern Baffin Bay. During warming andamong the key mesozooplankton species the distribution of C.finmarchicus is constrained to the BS and eastern Fram Strait whileC. glacialis almost disappears from the northern BS, the westernFram Strait and northern Baffin Bay. In contrast, this typical Arcticspecies expands to the Arctic Basin and on and off the Eurasianshelf, in particular the Chukchi and East Siberian Seas.

The application of the SINMOD model provides guidelines forfuture primary and secondary production research efforts in theAO. It provides scientists and mangers with a tool to maximizethe effects of research efforts geared to find answers to the vitalquestion as to which role the AO plays in the global climate system.The major findings of the model experiments are: (1) In a warmerAO the overall primary production will double or even triple(Fig. 5B). (2) The key processes that determine primary productionin a warming ocean are ice cover (light), stratification (ice melt),wind (vertical supply of nutrients) and the heterotrophs (respira-tion). (3) Primary production increases on most shelves and alongthe Eurasian shelf break (Fig. 5B), but less on the Canadian andGreenland side, and C. glacialis expands its domain into theEurasian shelves and the Chukchi Sea. One of the surprising resultsfrom the model experiment is the minor increase in primary pro-duction in the entire BS during global warming (Fig. 5B). The BSprimary production is sensitive to winter and spring ice cover,

Fig. 5. (A) Simulated annual gross primary production (g C m�2) in the Arctic Ocean(today’s average). (B) Difference between the simulated average annual grossprimary production of today and the average annual gross primary production ofthe Arctic Ocean forced by an 8 �C air temperature increase towards the end of thiscentury (A2 model projection of IPPC). The difference is given in g C m�2. Redrawnand recalculated from Slagstad et al. (2011).


but not to increased air temperature. Reduced ice cover will in-crease the primary production in the previously ice-covered north,but this is compensated for by decreased production in thesouthern BS due to reduced supply of nutrients from deep water(increased stratification).

As the upper layers of the AO receive more light, heat and fresh-water, vertical mixing processes cannot provide sufficient nutri-ents for phytoplankton growth. Increased light will thus increasenew production only to a limited degree. Net-heterotrophy in the

AO will increase due to: (i) increased import of mesozooplankton,(ii) increased respiration of heterotrophs (in particular microbes)and (iii) relatively small increases in primary production causedby stratification that limits nutrient supply. To achieve more pre-cise primary production estimates for the AO the model must beimproved with regard to its physical forcing, e.g. photosyntheticavailable light affected by low sun angle, an atmosphere with highprobability of fog formation and a variable thickness and variablesnow cover on ice. There is a need for more information on temper-ature-dependent respiration and metabolism at low temperatures,and stage-structured models are needed for key zooplanktonstages in order to simulate their ability to conquer new geograph-ical areas. Finally, basic data from the entire AO have to be ob-tained in order to validate the models. This essential exercise ishardly possible with the current knowledge, except for a few ofthe investigated regions.

4. Rapid climate change of Arctic Ocean ecosystems: trends andexpectations

Global climate change is amplified in the Arctic by several posi-tive feedbacks, including ice and snow melting that decreases sur-face albedo, atmospheric stability that traps temperatureanomalies near the surface, and cloud dynamics that magnifychange (Overpeck et al., 1997). Consequently, the temperature inthe Arctic is increasing at a rate of two to three times that of theglobal average temperature, estimated to be 0.4 �C over the past150 years (ACIA, 2004). Atmospheric warming has increased AOtemperature and resulted in decreased extent and thickness ofsea ice prompting concern that the AO could be ice-free in summerby 2050 (Arzel et al., 2006) or even earlier. How then will Arcticmarine ecosystems be affected by these changes? And given ourinadequate comprehension of the ecology of the AO as a whole,what can we already now foresee?

Wassmann et al. (2010b) list what changes may be expectedwithin the subarctic/Arctic region: (a) northward displacement(range shifts) of subarctic and temperate species, and cross-Arctictransport of organisms; (b) increased abundance and reproductiveoutput of subarctic species, decline and reduced reproductive suc-cess of some Arctic species associated with the ice and species nowpreyed upon by predators whose preferred prey have declined; (c)increased growth of some subarctic species and primary producers,and reduced growth and condition of animals that are bound to,associated with, or born on the ice; (d) anomalous behaviour ofice-bound, ice-associated, or ice-born animals with earlier springevents and delayed fall events; (e) changes in community structuredue to range shifts of predators resulting in changes in the preda-tor–prey linkages in the trophic network. The detailed investiga-tion of these changes is demanding and no breakthrough is likelyin the nearest future. At present it appears less problematic to as-sess the climatic effects on the overall functioning of the AO eco-systems. This can be achieved by investigating: (a) conceptualmodels and (b) numerical models.

4.1. Conceptual models

Fig. 6 illustrates the ecological development of a partly ice-cov-ered pelagic zone at about 78�N in the BS throughout the year. Anice algae bloom characterizes today’s scenario in the SIZ when rel-atively thick ice thins and the snow cover disappears, followed by astrong but brief phytoplankton bloom (Fig. 6A). The water depth towhich nutrients are depleted (roughly the euphotic zone) de-creases continuously during the productive period. Heterotrophicprocesses (red) take over the spring dominance of autotrophy(green). The decline of the ice algae bloom is accompanied by a dis-tinct vertical export of algae. The production, consumption and

Fig. 6. (A) Schematic illustration of principal processes regulating biogeochemical cycling in the upper layers of the seasonal ice zone (modified from Wassmann et al., 2004). Thedark period, the height of the sun and changing thickness of snow and ice are shown. The growth of ice algae in spring (strong because of available nutrients) and autumn (weakdue to nutrient shortage) reduces the incident light. Phytoplankton development leads to vertical export of fresh material in spring (e.g. phytoplankton cells). In summer and earlyautumn, more degraded material is exported (e.g. faecal pellets from zooplankton grazing and detritus). The depth of the zone where nutrients such as nitrate limit primaryproduction is indicated. This line also illustrates the depth of the euphotic zone. The arrows indicate the changing dominance of autotrophic (green) and heterotrophic (red)processes in the euphotic zone. Most of the primary production and pelagic–benthic coupling is phased to the months June–August, characterized by intense biological activity.(B) The same schematic illustration as A, but climate warming has increased the ice-free period. Stratification hampers nutrient supply and primary production in scenario A andthe situation is similar in scenario B. Mesozooplankton can enjoy an earlier spring bloom, but food availability is spread over a longer period. There is scarcely any ice algae growthin autumn due to late ice formation and limited light. Primary production and pelagic–benthic coupling are more evenly distributed over the months May–September. Organismsare forced to develop strategies that allow them to live with food concentrations that are smaller, but are available over longer time periods. (C) Climate warming also results in athinning of sea ice cover. Sea-ice algae can start to grow already from mid March (provided that snow cover is not too thick). They may grow for 2 months, partly in concert withplanktonic algae. Vertical export will not be as strong, since the spring bloom extends over 2 months or even longer.


regeneration cycles in the pelagic zone are reflected in the quantityand quality of vertically exported biogenic matter that leaves theeuphotic layers. Two distinct pulses of biogenic matter dominatedby autotrophic cells are followed by less distinct pulses of

degrading matter (faecal pellets, aggregates, detritus). Climatechange first prolongs the ice-free period (Fig. 6B). As a consequenceboth the ice and plankton algae blooms start earlier and the periodwhen heterotrophic processes dominate lasts longer. Stratification


by melting sea ice persists and nutrient availability will not in-crease with the increase of photosynthetically active radiation(PAR). The vertical export of the two vernal blooms takes place ear-lier in the season and the time interval dominated by regeneratedproduction becomes longer. This must have consequences for ben-thos (earlier food after winter depletion) and zooplankton (longerperiod of food availability but at lower concentrations). Further cli-mate warming reduces the thickness of the ice cover and this re-sults in ice algae blooming even earlier and over longer periodsof time (Fig. 6C). More of the slowly growing ice algae will proba-bly be consumed by pelagic heterotrophs and less will be exportedvertically. The ice thickness determines whether ice algae andplankton algae can thrive in concert. Nutrient availability will notincrease and primary production will be spread over lengthy peri-ods of time. This will favour smaller organisms and remove thestrong pulsing of the present scenario that supports large meso-zooplankton and benthos. Consequently, the strong phasing of to-day’s SIZ will be replaced by more evenly distributed (nutrientlimited) primary production and food availability.

The specific dynamics between ice algae and plankton algae as afunction of ice cover in the EAC is presented in Fig. 3. Ice algaegrowth depends on the solar angle, ice thickness and snow cover.Ice algal production may equal phytoplankton production in dura-tion, but the production and biomass of phytoplankton, normalizedto a per area basis, usually exceeds that of ice algae. The productionof ice algae is patchy and highly variable, averaging 5–10 g C m–

2 year–1; the production of Arctic phytoplankton is higher, averag-ing 12–50 g C m–2 year–1, depending on latitude and the durationof ice-free periods (Legendre et al., 1992; Gosselin et al., 1997)while in areas with more extensive ice cover, ice algae are of com-paratively greater importance. In the multi-year ice pack of thecentral AO, for instance, ice algae contribute on average 57% ofthe total primary production (Gosselin et al., 1997). Fig. 3 showsthe temporal development of ice and plankton algae along a tran-sect through the SIZ from the southernmost, stratified domain (D)where sea-ice melts early in the season, to the central AO close tothe North Pole (A). As the sea ice cover shrinks due to global warm-ing we may find that the seasonal development of ice and planktonalgae at a specific latitude of the SIZ changes from one of the sce-narios in the middle of the figure (C and D) into one without anysea ice cover (E). As global warming progresses the open, non-stratified water of the southern BS will become increasingly proneto thermal stratification, resulting in decreased primary production(compare to Fig. 5B).

Fig. 7 illustrates how physical forcing – through vertical mixing,stratification and ice-cover – determines primary production. Atthe southernmost end of the south-north gradient through the Arc-tic SIZ find open ocean in the Pacific and Atlantic Ocean sectors;these areas are never influenced by ice cover (alpha oceans, sensuCarmack (2007)) and are characterized by extensive vertical mix-ing, high productivity, but relatively low phytoplankton biomass,and a deep euphotic zone (Fig. 7A). North of the alpha ocean liethe outskirts of the AO, a region where seasonal sea ice leaves aclear signal in the form of strong vertical stratification, a beta ocean(sensu Carmack, 2007). Vertical mixing ceases, the euphotic zone iscloser to the surface, primary production decreases (per m2), butphytoplankton biomass may be high (per m3). North of the SIZ withits strong stratification, relatively shallow euphotic zone and in-tense, transient phytoplankton bloom. Under the ice the euphoticzone is extremely shallow and productivity and phytoplanktonbiomass are low.

Future decrease in sea ice cover will influence primary produc-tion and suspended phytoplankton biomass in two phases. Duringthe first phase the thinning of sea ice and the receding MIZ willwiden the SIZ, resulting in increased primary production towardsthe north (Fig. 7B). In the second phase the MIZ will disappear

and the stratification in the outer reaches of the SIZ will be erodedby wind, particularly during passage of low-pressure systems. Con-sequently, the alpha ocean will expand northwards (Fig. 7C). Thismay result in markedly increased primary production in the south-ernmost realms of today’s SIZ, but will also result in decreased ver-tical mixing in the southern region of the alpha ocean (caused byincreased thermal stratification). Primary production will decrease(see Fig. 5B suggests reduction in primary production of up toabout 30% for the most productive region of the southern BarentsSea).

4.2. Coupled physical–biological ecosystem models

Considering the vastness of the AO and the logistic challengesposed by ice cover, we are unlikely to acquire sufficient in situ eco-logical measurements in the near future. This may leave us nochoice but to use inadequately validated physico-biologically cou-pled models to shed light on the magnitude and temporal and spa-tial variation of fundamental biological processes in the AO, nowand in the future. To indicate trends and predicted developmentsin the AO in an era of climate change we apply two versions ofthe SINMOD model. Here we focus first upon the EAC for whichthe SINMOD model was developed.

The average decadal primary production in the EAC roughlyparallels three major physico-chemical domains: regions influ-enced by AW are most productive (100–150 g C m�2 year�1), theSIZ is moderately productive (50–100 g C m�2 year�1) and themore or less permanently sea ice covered AO has low primary pro-duction (<50 g C m�2 year�1; Fig. 2A). How will this rather simpledistribution pattern change in decades to come? The interannualcoefficient of variation for primary production in the 100–150 g C m�2 year�1 domain was <0.1, and increased northwards to-wards >0.6 in the northwesternmost and northeasternmost fringeof the SIZ (Fig. 2B). The main anomalies in primary productionare found early in the productive season and in sections of theSIZ with low primary production, which again reflects variabilityin ice cover. The highest coefficient of variation for primary pro-duction is found in regions where changes in ice cover are largest,but where the average primary production is lowest. It is in the re-gion where the coefficient of variation for primary production is>0.3 that the largest relative changes in primary production canbe expected. But also in regions where primary production is lessvariable (coefficient of variation >0.2), changes caused by globalwarming and ice reductions may have great impact, since primaryproduction is far greater there than in the central AO.

Ice cover is by far the single most important factor for primaryproduction in the AO. Recently Ellingsen et al. (2008) demon-strated that the correlation between observed annual ice coverand the SINMOD model ice cover in the BS and adjacent regionsis good (R2 = 0.88). With regard to the most prominent source ofprimary production variability, i.e. the interannual variation inice cover, there is therefore relatively good agreement betweenthe model and nature. A shrinking and thinning future ice coverwill result in the establishment of provinces with increased pro-ductivity. Fig. 2 suggests where the greatest changes in primaryproduction will occur (B) and how much primary production cansoon be expected in what is currently the SIZ (A).

After the EAC we focus on the central AO. Despite the growinginterest in biogeochemical changes in the AO as the climatewarms and the ice melts, surprisingly few attempts have beenmade to apply numerical ecosystem or biogeochemical modelsto the entire region. The only exception is the SINMOD model(Slagstad et al., 2011). As an attempt to address the question ofhow and when marine ecosystems may be affected by climatechanges, the experimental simulation approach of Slagstad et al.(2011) is of interest. Provided that the atmospheric temperature

Fig. 7. (A) Generic scheme illustrating the basic features and function of the multi-year ice zone, seasonal ice zone, and permanently open water outside the seasonal ice zonecontinuum, with the marginal ice zone towards open water being its most conspicuous feature. Zonation, functional ocean types (alpha/beta) and ice cover are indicated atthe top. Primary production, the depth of the euphotic zone and the mixed layer are also shown, as are phytoplankton concentrations and ice algae. (B) The generic schemeafter shrinkage of the multi-year ice zone. The seasonal ice zone expands and primary production increases. (C) The generic scheme after the loss of the multi-year ice. Theentire Arctic Ocean turns into a seasonal ice zone. Erosion of stratification in the outer section of the seasonal ice zone results in an expansion of the alpha ocean northwards,but there is a simultaneous increase of thermal stratification in the south. Redrawn from Carmack and Wassmann (2006).


increases by 8 �C (as it might towards the end of this century) theSINMOD model indicates an increase in primary production in thecentral AO, particularly around Franz Josef Land and the EastSiberian and Beaufort Seas (over +40 g C m�2 year�1; Fig. 5B). Inthe central AO, primary production may increase less (+20–40 g C m�2 year�1). Of equal interest is that primary productionwill decrease in some currently productive regions of the BS andSvalbard. While the limited increase in the central AO is caused

by low nutrient concentrations and increased PAR, the decreaseoutside the SIZ is triggered by increased stratification due toatmospheric warming (see Fig. 5B). Also, the increased dischargeof nutrients with the larger rivers that enter the AO yields littleincrease in primary production along the inner coastal shelves.This is because of the concurrent discharge of detritus that waspreviously stored in permafrost, but is increasingly dischargedduring global warming.

(a)

(b)

(c)

Fig. 8. An example of time series data. Daily maximum rates of gross primaryproduction calculated for the HAUSGARTEN mooring site and daily vertical fluxes ofparticulate organic carbon (POC) and biogenic particulate silicon (bPSi) at �300 mdepth at this station from 2000 to 2005. Adapted and redrawn from Forest et al.(2010).


4.3. Trends and expectations

In the absence of adequate time series containing detailed dataon Arctic and subarctic species, it will be difficult to detect changesin their range, abundance, growth and condition; behaviour andphenology; community composition and regime shifts. However,it is already possible to predict how and when marine ecosystemswill be affected by climate change and what trends can beexpected.

� The largest changes will take place in the northern sections oftoday’s SIZ, which will expand to cover the entire AO. Primaryproduction will increase by up to 60 g C m�2 year�1 in whatare currently low-productive AO basins, but will not increaseany further as surface waters will remain stratified and nutrientconcentrations are generally low [with the exception of theregions subjected to large-scale advection (e.g. the ChukchiSea, the southern BS, western Spitsbergen and possibly partsof the Canadian Archipelago)].

� Notably, the new production of the AO will remain low. Thefisheries of the subarctic regions – currently the world’s richest– will thus not expand into the AO when the ice cover shrinks.

� Mesozooplankton productivity will increase over the entirecentral AO, in particular along the shelf breaks, but boreal formsmay not be able to penetrate into the AO and reproduce there.

� Over time today’s highly productive subarctic region willdecrease its productivity due to increased thermal stratification.The southernmost sector of what is now the SIZ will turn into analpha ocean because of low-pressure passage will erode

stratification. Today’s southern subarctic regions will experi-ence more thermal stratification and receive fewer nutrients.Primary production will thus increase in the former anddecrease in the latter zone.

� Due to the thinning of the ice, the significance of ice algae forthe total primary production of the AO may increase in the cen-tral AO, but decrease in the outer SIZ. The blooms of ice andplankton algae will stretch over longer periods of time.

� The weakening of today’s highly episodic primary productionand algae blooms in the SIZ will result in lower food concentra-tions for heterotrophic organisms and more recycling of avail-able energy, changes in life cycle strategies and less variablevertical export.

� Increased freshwater discharge by rivers along with freshwaterinput due to ice melt may improve the overwintering condi-tions of larger organisms such as fish.

� Freshening of the AO, nutrient limitation and a prolonged grow-ing season will shift the community composition towards smal-ler phyto- and zooplankton forms.

5. The legacy of marine ecosystem research in the pan-Arcticrealm

It has been evident for some time that the Arctic is warming attwo to three times the global rate (ACIA, 2004; Trenberth et al.,2007). The most striking evidence of abrupt climate change hasso far occurred at sea, where the rapid reduction of Arctic seaice in 2007 generated worldwide concern (Stroeve et al., 2007;Comiso et al., 2008) and where the volume of sea ice has beenhalved (Kwok and Rothrock, 2009). It is therefore logical thatthe AO is the focus of special attention. Although the vulnerabilityof Arctic marine biota to climate change is clearly established(Vibe, 1967; Gradinger, 1995) the rather limited marine ecologi-cal research done so far has not provided much evidence of theeffects of global warming in the AO. A recent review evaluatingthe availability of reliable baseline information located only 51published reports of documented changes in Arctic marine biotain response to climate change (Wassmann et al., 2010b). Despitethe nature of warming and its strong potential effects in the AO,marine ecological research on the effects of climate change islimited.

Today’s knowledge about AO ecology is patchy at best; the fieldis still in its infancy. Nonetheless, gathering the information thatwill be required for adequate comprehension of the future marineecology in the AO appears not to be a matter of public concern atpresent. As we face the prospect of widespread change, will scien-tists be able to provide the knowledge needed to support wisemanagement of the AO? This would demand an intensification ofresearch pace to match the swiftness of climate change.

6. Future research needs for pan-Arctic integration

6.1. Filling the geographic and seasonal gaps

The geographic inadequacy of marine ecological knowledge ofthe pan-Arctic region is clearly illustrated by Fig. 1. Of greatest con-cern is the lack of data from the Siberian shelf. Although it com-prises almost half of the pan-Arctic perimeter is up to >1000 kmwide, there are very few dedicated programmes of oceanographicand marine ecological research along and across the Siberian shelf.The paucity of reports on ecological developments in the Arctic ba-sin derives from the lack of the sustained research efforts in this re-gion that would be required to detect change. Although there havebeen a few expeditions to the high Arctic (e.g. Carmack et al., 1997;Anderson et al., 2003), these mainly provided isolated data on


physical and chemical properties that are marginally useful to as-sess climate change impacts on biota (but see e.g. Gosselin et al.,1997; Wheeler et al., 1997; Olli et al., 2007).

We need first of all basic marine ecological knowledge fromthree key regions: (a) the Fram Strait area, which accounts formore than 50% of all exchanges of water to and from the centralAO (Schauer et al., 2004); (b) the extensive Siberian shelf, a keyarea to detect changes caused by climate warming [extensive in-crease in river discharge and input of materials, e.g. sediments, dis-solved organic matter, nutrients, toxic substances (Peterson et al.,2002; Vincent and Pedrós-Alió, 2008)]; and (c) the Central AO,arguably the least studied region, for which almost no informationon ecological impacts of climate change is available. These threeareas, which constitute >60% of the AO, are expected to experienceparticularly large changes, but unless baseline research is done andthe results are made available we will have little opportunity totrace ecological change.

Marine ecosystem studies in the AO also suffer from inadequateseasonal coverage. For example, good winter data are only avail-able from the Chukchi Sea (SHEBA), Franklin Bay (CASES), the Nan-sen and Amundsen Basins (DAMOCLES) and off Banks Island (CFL).In addition, some investigations, such as those from the Kara (e.g.Hirche et al., 2006) and Laptev Seas (Schmid et al., 2006) and thecentral AO (e.g. Olli et al., 2007) only cover short spans of time.Good as they are, these studies do not provide enough informationfor us to understand the dynamics of marine ecosystems in the AO.The investigations reflect the marine ecosystem function in latesummer or autumn, whereas occurrences during the most impor-tant time period – the spring bloom – remain basically unknown.The spring bloom in densely ice-covered regions is a brief butessential event for both primary and secondary production in mar-ine Arctic ecosystems. It is also notoriously difficult to study be-cause of its variation in space and time.

In conclusion, it appears that it will be some time before wehave all the information we need to grasp the entire geographic ex-tent and seasonality of the AO. Obtaining that knowledge will re-quire major research efforts, even when all the data gatheredduring the 4th IPY have been published.

6.2. Time series: continuation, start off and analysis

Time series analysis comprises methods for extracting mean-ingful statistics and other characteristics from time series data.The physical environment of the AO is under the influence of mul-ti-annual to decadal oscillatory atmospheric processes that mayconfound the interpretation of changes. The effects of human-induced climate change are superimposed on those of climaticfluctuations on a shorter time-scale. To discriminate between theecological effects of multi-annual to decadal oscillations in climateand those of the more one-directional anthropogenic climatechange, we need time series of climatic drivers and potential bio-logical responses spanning several decades. To gather this data,multidisciplinary teams must carry out annual cruises with ice-breakers and cover regular stations and transects. We can also im-prove our capacity to derive appropriate Arctic baselines byincreased data mining in historical records from surveys that havenot yet been fully incorporated into the scientific literature.

Data series in the AO are few and derive almost entirely fromnational climate monitoring programmes. One of these few is theworld’s longest oceanographic time series, the Kola section, runby Norway and Russia in the southern BS (Loeng and Sætre,2001). Another emanates from the Hausgarten observatory (e.g.Bergmann et al., 2009; Forest et al., 2010), a long-term deep-seasite with various moorings (Fig. 8). A third example is Canada’sThree Oceans (Carmack and McLaughlin, 2011) which is based onthe notion that the waters from the Pacific flow through the AO

and out to the Atlantic, representing a great continuum of watermoving around Canada.

It is vital to continue the few existing time series at permanentstations in the AO (e.g. Canada’s Three Oceans, those of Hausgarten(Fram Strait) and Kongsfjord (Svalbard), St. Lawrence Island (Ber-ing Strait), and Kola section (BS). The international community alsoought to start new time series in AO regions that are most likely tobe strongly affected (or are already affected) by climate change.The implementation of state-of-the-art technology [e.g. SvalbardIntegrated Arctic Earth Observing System (SIOS), Integrated ArcticOcean Observing System (iAOOS-Norway; http://www.iaoos.no)and Developing Arctic Modeling and Observing Capabilities forLong-term Environmental Studies (DAMOCLES; http://www.damocles-eu.org)] will be indispensable in supporting theseendeavours, but they do not eliminate the need for logisticallydemanding marine ecological investigations.

Time series are also essential to evaluate ecosystem resilienceunder environmental change. Scarcely any adequate time seriesfrom the AO are available that would make it possible to evaluatethe effects of future environmental change on the structure andresilience of AO ecosystems, but in subarctic regions such as theBering Strait, off southern Greenland and the BS the effects of pastchanges in climate and fisheries can be studied by developing indi-cators of ecosystem resilience, diversity and structure. For the BSthis will be carried out by the BarEcoRe project (http://www.imr.no/forskning/prosjekter/barecore/en), which seeks to answer ques-tions about what determines robustness and resilience of the BSecosystem and how these might be affected by future changes inclimate and fisheries regimes. BARECORE will also attempt to de-tect early warning signals of abrupt ecosystem changes and evalu-ate management strategies with regard to ecosystem resilience.

In conclusion, a plethora of international statements argue forimmediate actions to slow the pace of change (e.g. ACIA, 2004;AMAP, 2009; Allison et al., 2009), but an important role of the sci-entific efforts must be to provide the knowledge necessary to takesuch actions. There is therefore an urgent need for heightened ef-forts to detect marine ecological variability and changes inducedby climate change in the AO (Wassmann et al., 2010b). Future ef-forts will necessarily require international collaboration and sup-port, in particular to continue existing time series and to startessential new ones.

6.3. Seasonal and marginal ice zones

The SIZ system currently engirdles the AO in an uninterruptedband that undulates annually over almost the entire expanse ofthe pan-Arctic shelves (Carmack et al., 2006). The physical/biolog-ical characteristics of this key feature of AO ecology deserve partic-ular attention as the most significant functional changes areexpected to take place in the SIZ. It has been commonly assumedthat the outer part of the SIZ, the MIZ, is highly productive andmore so than open waters (e.g. Ferreyra et al., 2004), but this viewhas been rejected (Carmack and Wassmann, 2006; Reigstad et al.,2011; Wassmann et al., 2010b). This is clearly demonstrated inFig. 2A where the wide, yellow band of reduced primary produc-tion is the SIZ. The sediments underlying the SIZ are rich in bio-genic matter, diatoms and benthos (Reigstad et al., 2011), butthis does not reflect increased primary production but, rather, effi-cient vertical export.

The annual undulation of the SIZ presently has an amplitude ofseveral hundred to a few thousand kilometres, but the thinning ofthe annual sea ice and the current decline of the MYI gives rise tothe prospect of an AO entirely devoid of ice cover at the end ofsummer within a few decades. This implies that the SIZ will soonexpand to cover the entire AO, which will have consequences fortotal primary production, the ratio between sea ice and plankton

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http://www.imr.no/forskning/prosjekter/barecore/en


algae and the timing and duration of blooms. It will further influ-ence the life cycles of zooplankton, the role of the microbial loop,the pelagic–benthic coupling and benthic communities. What willhappen when the SIZ withdraws from the shelves entirely duringsummer? Will upwelling at the shelf edge advect nutrients ontothe shelf, as predicted by Carmack et al. (2004)?

In conclusion, the lack of basic knowledge regarding the possi-ble consequences of the SIZ withdrawing from the shelves in sum-mer is probably the greatest challenge for AO marine ecology andbiogeochemical cycling. It deserves the greatest possible interna-tional attention. Figs. 3, 6 and 7 are intended to stimulate develop-ment of future SIZ research programmes.

6.4. Large-scale regulation of ecosystem function

The AO is basically the final extension of the North Atlantic,with some influence from the Pacific Ocean. AW, passing throughthe Norwegian and Iceland Seas, enters the AO through Fram Straitand across the BS (Fig. 4). Upon entering the AO the AW flows un-der fresher waters derived from ice melt, river inflow and theinflowing Polar Water (from the North Pacific). It generally movesas topographically steered boundary currents, following the conti-nental margins and trans-basin ridges (Fig. 4). Along this pathwaythe original source waters are rendered either denser, primarily bycooling (a negative estuary) or lighter, by mixing with fresherwaters (a positive estuary). This complex, double estuary functionforms the dominant physical backdrop for the marine ecology ofthe AO (Carmack and Wassmann, 2006). Aagaard and Carmack(1994) hypothesized that changes in ice extent and freshwater ex-port from the AO might alter the sites of deep thermohaline over-turning, which currently occurs in the Nordic Seas. A similarargument can be made for the coupled Bering/Chukchi systemshould sites of dense water formation change.

Physical processes may contribute both toward local productionof biomass by bringing nutrients into the euphotic zone or enhanc-ing light conditions through stratification, and local accumulationof biomass, by advection. The advected water carries not only sig-nificant amounts of allochthonous nutrients and suspended bio-mass into the AO, but also substantial quantities of zooplanktonfrom the North Atlantic (Wassmann, 2001; Olli et al., 2007) and,less so, from the Pacific Ocean (Ashjian et al., 2005; Nelson et al.,2009; Bluhm and Gradinger, 2008). Among the mesozooplanktonthe larger Calanus species constitute a significant proportion of ad-vected biomass and play an important role in the bands of positiveand negative zooplankton production that engirdle the AO (seeSlagstad et al., 2011). Not all advection is northwards. AO copepodsare also advected southwards through Fram Strait and into theGreenland Sea and perhaps also through the Bering Strait intothe Bering Sea (e.g. Weingartner et al., 1999; Nelson et al., 2009).The characteristics of the AO, a rotating, quasi land-locked, deepocean where productivity is low, mean that advection from outsidehas crucial consequences for ecosystem function. The advection ofArctic or Pacific water into the basically boundary current-engirdled AO has a pace-making and climatically variable ‘spin-up’ effect on the biogeochemical and ecological function of theAO. Climate change in an ‘orbiting’ ocean has impact on how muchwater is advected to and from the AO and how fast the gyresspin, and this determines the residence times of water, the poten-tial for biogeochemical change and the living conditions for keyspecies.

In conclusion, since advection governs the AO, moving frontsand changing currents will have disproportionate influences onecosystems. Species distributions will change and new speciesmay be introduced. The AO can thus not be studied in isolationand its large-scale regulation is obviously a research topic that de-serves increased attention.

6.5. Over-arching themes

The circumpolar features, local/regional disparities and the com-plexities of the AO ecosystem are not well known (Wassmann,2006; Wassmann et al., 2010a). The reasons are multiple, includingthe logistics associated with international cooperation and re-stricted access to the Arctic during the Cold War period and beyond.Investigations are traditionally limited to national territories andare primarily carried out along south-north transects rather thanthe basin-wide approaches that are essential to address the natureof the land-engirdled AO (Carmack and Wassmann, 2006). The 4thIPY and the mounting evidence of warming, accelerated ice loss andclimatic change have stimulated Arctic marine biology and ecologyresearch in recent years, but these efforts failed to address over-arching themes. The legacy of the 4th IPY will obviously enrichthe peer-reviewed literature gradually over time, but reversingthe negative trend in the number of ecological studies (see Fig. 8)demands particular commitment.

It is not surprising that few marine ecological investigations fo-cus on the AO as a single entity. In one of these few, Pabi et al.(2008) estimated based on remotely sensed pigments that the pri-mary production of the AO increased by 23% in 2006 as comparedto the 1998–2002 average. Significant trends towards earlier phy-toplankton blooms have been detected in coastal regions such asHudson Bay, off Greenland, in the Kara Sea and around NovayaZemlya (Kahru et al., 2010). These areas coincide with areas whereice concentration has decreased in early summer, thus making ear-lier blooms possible. The annual phytoplankton bloom maximumhas advanced by up to 50 days in these coastal regions.

The physical–biological coupled 3D SINMOD model is anotherapproach that addresses over-arching themes, such as primaryand secondary production, over the entire AO (Slagstad et al.,2011). Despite its limitations the modelling approach provides sci-entists a long-awaited opportunity to address ecosystem dynamicsof the entire AO. The model can be applied 1D to study ecosystemprocesses in greater detail and to simulate/understand them a pos-teriori. However, provided one accepts the uncertainty that is partof any projection, one can also apply the model with atmosphericforcing of the IPPC future climate scenarios to study how Arcticecosystems may develop during climate change. With this caveat,marine ecosystem models are an extraordinarily useful tool withwhich to explore phenomena in the AO and adjacent regions.

In conclusion, far stronger emphasis should be placed on phys-ical–biological coupled 3D and remote sensing models of the AO.

6.6. Comparative investigations

An important way to move from geographically isolated studiesto pan-Arctic integration is to perform comparative studies. Thisalternative has not yet been fully exploited and only some first at-tempts have been published. In order to understand the dynamicsof the SIZ, flow-through shelves (best described in the EAC) have tobe compared with the other major flow-through shelf, the BeringSea. Evidence from outflow shelves, such as the Canadian Archipel-ago, is available and should be contrasted with evidence from in-flow shelves. Meanwhile we have to wait for more in-depthdescription of the manifold interior shelves of Siberia. The bestavailable evidence is from the Kara Sea (Hirche et al., 2006), whichhas both flow-through and interior shelf characteristics. Whilestudies on individual ecosystems can increase our knowledgeand understanding, comparative studies offer an opportunity todetermine which processes are fundamental and which are uniqueto a particular ecosystem. Examining different ecosystems in-creases the degrees of freedom in a statistical sense when testingand determining relationships between climate forcing, physicaloceanography and biological responses. For the ice-free, subarctic


waters south of the pan-Arctic region the biological responses tothe recent warming appear to be more direct and more pro-nounced in higher latitude systems, i.e. the BS (Drinkwater,2009; Drinkwater et al., 2009). The importance of large calanoidcopepods, small pelagic fishes and gadids, which is seen in theBS, is common to all the ecosystems investigated. Temporal stockpatterns, often of the same species or functional group, are out ofphase between the Pacific and Atlantic northern ecosystems, butindicate large-scale connectivity, likely through atmosphericforcing.

In conclusion, systematic comparison of marine Arctic ecosys-tems should be initiated. The assessments should be contrastedand compared with those from subarctic ecosystems that are al-ready underway.

7. Outlook

In addition to the publications presented in this volume, a fewothers address the ecological changes taking place in the AO inan era of climate change. Drinkwater et al. (2009) discuss linkagesbetween oceanic variables and ecosystem responses (e.g. distribu-tion, reproduction, growth, activity, recruitment and mortality ofArctic cod). Grebmeier et al. (2010) describe how recent changesin sea ice extent in the Bering and Chukchi Seas affect the distribu-tion of zooplankton, fish, benthic organisms, and the habitat of ice-associated mammals. Wassmann et al. (2010b) review accounts ofobserved impacts of anthropogenic climate change on ecosystems,pointing out a critical lack of reliable baseline data on AO ecosys-tems. Vaquer-Sunyer et al. (2010) and Kritzberg et al. (2010) exam-ine the response of phytoplankton and bacteria to warming andpredict that respiration rates in the AO will increase far more rap-idly than primary production. A warmer AO will thus contributeCO2 to the atmosphere rather than being a region of net CO2 up-take. Tremblay and Gagnon (2009) found no relation between inci-dent solar radiation and cumulative production, but rather thatannual primary production per unit area in the SIZ is controlledby nitrate supply.

A picture of today’s AO is gradually emerging and predictions ofhow it will develop in the near future are being made (seeSection 4.3). But providing adequate answers concerning how theAO will function and what consequences change will have in theforeseeable future requires additional support, attention, and ded-ication than presently given. During the 4th International PolarYear, it became increasingly obvious that we need to prepare foran unprecedented era in the AO. Commercial activities will becomeever more attractive as sea ice retreats. With today’s resources(ships, research stations, funding) scientists are unable to providevalid answers to evolving questions about operating safely andsustainably in the AO. At the same time, climate is a global, not aregional issue, making changes in the Arctic of worldwide signifi-cance. To understand and minimize negative impacts of humanactivities, we need continued monitoring, more studies of ecosys-tem processes, more modelling, and more interdisciplinaryresearch.

Many of the projects presented here have contributed to a pilotphase of what could be a long-term commitment to pan-Arctic re-search, hopefully supported by a supporting Arctic Observing (andAnalysis) System. To make progress in comprehending marine Arc-tic ecosystems we need to fill the geographic and seasonal gaps,extend existing time series and commence new ones in critical re-gions. However, the most significant advances will come throughunderstanding and quantifying the large-scale regulation of pan-Arctic ecosystems and the function of the SIZ and MIZ. Pan-Arcticecosystem research requires careful coordination as well as in-creased resources. Our chances of comprehending Arctic marineecosystems in an era of rapid climate change will be enhanced

by communication between national and international research ef-forts and increased support from the strong research nations of theNorthern Hemisphere.

Acknowledgements

The stimulating atmosphere at the science session Arctic marineecosystems in an era of rapid climate change of the Arctic Frontiersconference in 2009 (www.arctic-frontiers.com) inspired theassembly this second volume on pan-Arctic marine ecosystems.The contributions published here benefited significantly from theextensive comments and suggestions of many referees. My heart-felt gratitude goes to them and to all authors for sharing theirbroad knowledge of marine Arctic ecosystems and for their signif-icant contributions to pan-Arctic awareness. Thanks go to JanetHolmén for language support and to Dag Slagstad, Eva Leu and,in particular, Frøydis Strand for assistance with the figures. Thecover picture was created by Manuel Elviro Vidal.

The Norwegian Research Council’s Norklima and IPY pro-grammes supported some of the scientists involved. This researchis also a contribution to the Arctic Tipping Points project (www.eu-atp.org, http://www.eu-atp.org) funded by FP7 of the EuropeanUnion (Contract #226248). This is the third volume containing pro-ceedings from the ARCTic marine ecOSystem research network,ARCTOS (www.arctosresearch.net), a northern-Norwegian networkthat emphasizes interdisciplinary approaches to addressing large-scale and pan-Arctic questions in marine Arctic oceanography.The ARCTOS network extends its sincere thanks to the faculties,companies and agencies that have encouraged publication of thesereports, in particular Statoil (SAARP programme: http://saarp.arctosresearch.net/) for research support and financial assistancewith the printing and distribution of this volume.

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Paul WassmannInstitute of Arctic and Marine Biology, Faculty for Biosciences,

Fisheries and Economy, University of Tromsø,N-9037 Tromsø, Norway

E-mail address: [email protected]

http://dx.doi.org/10.1029/2003GB002134

http://dx.doi.org/10.1029/2003JC001823

http://dx.doi.org/10.1029/2004GL020860

http://dx.doi.org/10.1029/2007GL029703

http://dx.doi.org/10.1007/s00300-010-0788-

http://interstat.statjournals.net/YEAR/2009/abstracts/0905003.php

http://interstat.statjournals.net/YEAR/2009/abstracts/0905003.php

http://dx.doi.org/10.1007/s00300-010-0839-3

http://dx.doi.org/10.1007/s00300-010-0839-3

http://dx.doi.org/10.1007/s00300-010-0839-3

http://dx.doi.org/10.1038/443043a

http://dx.doi.org/10.1029/2008JC005000

mailto:[email protected]

arctic marine ecosystems in an era of rapid climate change

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