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The central Arctic Ocean is not isolated, but tightly connected to the northern Pacific and Atlantic Oceans. Advection of nutrient-, detritus- and plankton-rich waters into the Arctic Ocean forms lengthy contiguous domains that connect subarctic with the arctic biota, supporting both primary production and higher trophic level consumers. In turn, the Arctic influences the physical, chemical and biological oceanography of adjacent subarctic waters through southward fluxes. However, exports of biomass out of the Arctic Ocean into both the Pacific and Atlantic Oceans are thought to be far smaller than the northward influx. Thus, Arctic Ocean ecosystems are net biomass beneficiaries through advection. The biotic impact of Atlantic- and Pacific-origin taxa in arctic waters depends on the total supply of allochthonously-produced biomass, their ability to survive as adults and their (unsuccessful) reproduction in the new environment. Thus, advective transport can be thought of as trails of life and death in the Arctic Ocean. Through direct and indirect (mammal stomachs, models) observations this overview presents information about the advection and fate of zooplankton in the Arctic Ocean, now and in the future. The main zooplankton organisms subjected to advection into and inside the Arctic Ocean are (a) oceanic expatriates of boreal Atlantic and Pacific origin, (b) oceanic Arctic residents and (c) neritic Arctic expatriates. As compared to the Pacific gateway the advective supply of zooplankton biomass through the Atlantic gateways is 2–3 times higher. Advection characterises how the main planktonic organisms interact along the contiguous domains and shows how the subarctic production regimes fuel life in the Arctic Ocean. The main differences in the advective regimes through the Pacific and Atlantic gateways are presented. The Arctic Ocean is, at least in some regions, a net heterotrophic ocean that – during the foreseeable global warming trend – will more and more rely on an increasing local primary production while the advection of zooplankton, as revealed by models, will cease.

We assess inter-annual and spatial variability and pathways of carbon flow within lower trophic levels and between plankton and benthos. Simulations were performed of gross primary production over a 13-yr period (1995–2007) using a physical–biological coupled model (SINMOD). Model results are compared with interdisciplinary field research in the Northern Barents Sea, spanning a 3 yr period (2003–2005). Modelled productivity, presented for seven sub-regions around Spitsbergen, reveals that Atlantic influenced regions are highly productive and less influenced by inter-annual variability in comparison to seasonally ice-covered regions. In Atlantic Water influenced regions, the range of annual gross primary production is 106–134 g C m−2 yr−1, while seasonally ice-covered regions exhibit higher inter-annual variability but lower productivity (54–67 g C m−2 yr−1). We evaluate the pathways of primary production through the planktonic food web to the benthic compartment based on six stations from the field investigation representing different sub-regions and ecological scenarios. Comparing different ecological groups in terms of biomass and carbon turnover, we find that smaller planktonic organisms are major players in terms of carbon turnover (stations range 67–91%, average 77%), despite that larger groups often dominated in terms of biomass (stations range 22–72%, average 50%). Carbon budgets illustrated the importance of grazers for vertical flux regulation, as highest downward export coincided with lowest heterotroph consumption relative to autotroph biomass. Sediment carbon burial rates reflect longer time-scale (years), and these rates are relatively constant among the sampled field stations. Thus simulated patterns in annual productivity do not correspond with an increase in carbon burial in high-productivity regions. However, benthic biomass was higher in Atlantic Water influenced stations in good agreement with higher annual primary production and carbon export flux. While simulated primary production patterns in the sub-regions point to important physical drivers for productivity, field investigations provide important insights into the pathways of carbon flow and the relationships among lower trophic level groups. When combined, these approaches provide information on key ecological links to aid in evaluating the sensitivity of the Arctic Barents Sea ecosystem to longer term climatic variability.

The gross primary (GPP) and secondary production in the Arctic Basin, Eurasian shelves and the Barents Sea were investigated through the physically–biologically coupled, 3D SINMOD model with 20 km grid size. The model was applied in an experimental setting where a control run had atmospheric forcing from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. In order to test the effect of how retreating ice cover in the forthcoming century may affect the productivity through physical processes in the Arctic Ocean we added a latitude dependent air temperature starting at 1 °C at 40°N increasing to +2,+4,+6 and +8 °C at 90°N to the temperature forcing taken from ECMWF data. The model indicates that gross primary production (GPP) increases along the temperature gradient both in the Arctic Basin and along the Eurasian shelves from approximately 10 to 40 and 30 to 60 g C m −2 y −1 , respectively. In contrast, GPP in the Barents Sea was more or less constant (ca. 100 g C m −2 y −1 ). For secondary production (key mesozooplankton species Calanus finmarchicus and Calanus glacialis ) the results of the experimental runs are more complex. With an air temperature increase towards +8 °C secondary production of C. glacialis in the Barents Sea dropped from about 3.9 to 0.3 g C m −2 y −1 , while that of the Arctic Basin and Eurasian shelf increased from approximately −0.1 to 1.5 and 1.4 to 2.4 g C m −2 y −1 , respectively. Secondary production changes are unevenly distributed spatially during future warming with the most significant increases occurring along the Eurasian shelves and the Chukchi Sea. Reductions are predicted for the Kara Sea and northern Baffin Bay. During warming and among the key mesozooplankton species the distribution of C. finmarchicus is constrained to the Barents Sea and eastern Fram Strait while C. glacialis almost disappears from the northern Barents Sea, the western Fram Strait and northern Baffin Bay. In contrast, this typical Arctic species expands to the Arctic Basin and on and off the Eurasian shelf, in particular the Chukchi and East Siberian Seas.

We estimated primary and bacterial production, mineral nutrients, suspended chlorophyll a (Chl), particulate organic carbon (POC) and nitrogen (PON), abundance of planktonic organisms, mesozooplankton fecal pellet production, and the vertical flux of organic particles of the central Arctic Ocean (Amundsen basin, 89–88° N) during a 3 week quasi-Lagrangian ice drift experiment at the peak of the productive season (August 2001). A visual estimate of ≈15% ice-free surface, plus numerous melt ponds on ice sheets, supported a planktonic particulate primary production of 50–150 mg C m −2 d −1 (mean 93 mg C m −2 d −1 , n = 7), mostly confined to the upper 10 m of the nutrient replete water column. The surface mixed layer was separated from the rest of the water column by a strong halocline at 20 m depth. Phototrophic biomass was low, generally 0.03–0.3 mg Chl m −3 in the upper 20 m and −3 below, dominated by various flagellates, dinoflagellates and diatoms. Bacterial abundance (typically 3.7–5.3 × 10 5 , mean 4.1 × 10 5 cells ml −1 in the upper 20 m and 1.3–3.7 × 10 5 , mean 1.9 × 10 5 cells ml −1 below) and Chl concentrations were closely correlated ( r = 0.75). Mineral nutrients (3 μmol NO 3 l −1 , 0.45 μmol PO 4 l −1 , 4–5 μmol SiO 4 l −1 ) were probably not limiting the primary production in the upper layer. Suspended POC concentration was ∼30–105 (mean 53) mg C m −3 and PON ∼5.4–14.9 (mean 8.2) mg N m −3 with no clear vertical trend. The vertical flux of POC in the upper 30–100 m water column was ∼37–92 (mean 55) mg C m −2 d −1 without clear decrease with depth, and was quite similar at the six investigated stations. The mesozooplankton biomass (≈2 g DW m −2 , mostly in the upper 50 m water column) was dominated by adult females of the large calanoid copepods Calanus hyperboreus and Calanus glacialis (≈1.6 g DW m −2 ). The grazing of these copepods (estimated via fecal pellet production rates) was ≈15 mg C m −2 d −1 , being on the order of 3% and 20% of the expected food-saturated ingestion rates of C. hyperboreus and C. glacialis , respectively. The stage structure of these copepods, dominated by adult females, and their unsatisfied grazing capacity during peak productive period suggest allochthonous origin of these species from productive shelf areas, supported by their long life span and the prevailing surface currents in the Arctic Ocean. We propose that the grazing capacity of the expatriated mesozooplankton population would match the potential seasonal increase of primary production in the future decreased ice perspective, diminishing the likelihood of algal blooms.

Within the framework of the physical forcing, we describe and quantify the key ecosystem components and basic food web structure of the Barents Sea. Emphasis is given to the energy flow through the ecosystem from an end-to-end perspective, i.e. from bacteria, through phytoplankton and zooplankton to fish, mammals and birds. Primary production in the Barents is on average 93 g C m−2 y−1, but interannually highly variable (±19%), responding to climate variability and change (e.g. variations in Atlantic Water inflow, the position of the ice edge and low-pressure pathways). The traditional focus upon large phytoplankton cells in polar regions seems less adequate in the Barents, as the cell carbon in the pelagic is most often dominated by small cells that are entangled in an efficient microbial loop that appears to be well coupled to the grazing food web. Primary production in the ice-covered waters of the Barents is clearly dominated by planktonic algae and the supply of ice biota by local production or advection is small. The pelagic–benthic coupling is strong, in particular in the marginal ice zone. In total 80% of the harvestable production is channelled through the deep-water communities and benthos. 19% of the harvestable production is grazed by the dominating copepods Calanus finmarchicus and C. glacialis in Atlantic or Arctic Water, respectively. These two species, in addition to capelin (Mallotus villosus) and herring (Clupea harengus), are the keystone organisms in the Barents that create the basis for the rich assemblage of higher trophic level organisms, facilitating one of the worlds largest fisheries (capelin, cod, shrimps, seals and whales). Less than 1% of the harvestable production is channelled through the most dominating higher trophic levels such as cod, harp seals, minke whales and sea birds. Atlantic cod, seals, whales, birds and man compete for harvestable energy with similar shares. Climate variability and change, differences in recruitment, variable resource availability, harvesting restrictions and management schemes will influence the resource exploitation between these competitors, that basically depend upon the efficient energy transfer from primary production to highly successful, lipid-rich zooplankton and pelagic fishes.

Perhaps more than in any other ocean, our understanding of the continental shelves of the Arctic Mediterranean is decidedly disciplinary, regional and fractured, and this shortcoming must be addressed if we are to face and prepare for climate change. A fundamental flaw is that while excellent process studies exist, and while recent ship-based expeditions have added greatly to our collective body of knowledge, an integrated and fully pan-Arctic perspective on the structure and function of food webs on Arctic shelves is lacking. Based on the collective overviews given in Progress in Oceanography xx, xx–xx, we attempt to address this issue. To build a perspective that inter-connects the various shelf regions we suggest three unifying typologies affecting food webs that will hopefully allow inter-comparison of regional investigations. The first is for shelf geography, wherein shelves are classified according to their role in the Arctic throughflow. The second is for ice climate, wherein the various ice regimes are examined for their specific impacts on food web dynamics. The third is for stratification where it is argued that the source of buoyancy, thermal or haline, impacts production and the vertical carbon flux. We then address the connection between physical habitat and biota on pan-Arctic (and global climate) scales. This discussion begins with the recognition that the Arctic Ocean is integral to the World Ocean via its thermohaline (“estuarine”) exchanges with the Atlantic and Pacific. As such the Arctic and its shelves act as a double estuary, wherein incoming waters become both lighter (positive estuary), by mixing with freshwater sources, and heavier (negative estuary) by cooling and brine release. Shelves are central to such transformations. This complex interconnectivity coupling of the Arctic Ocean to its sub-Arctic (and more productive) neighbors demands that food webs be considered through a macroecological view that includes an ecology of advection. We argue that the macroecological view is required if we are to understand and model food webs under forcing along climate gradients. To aid this effort we introduce the concept of contiguous domains, wherein physical habitats are joined by common features that will allow inter-comparisons of existing and future food webs over large scales and climatic gradients. Finally, we speculate on the range of possible futures for Arctic shelves based on the palaeo-record.

Vertical distribution of faecal pellets (FP), their sedimentation and the production rates of FP by mesozooplankton were studied during a cruise on and off the Iberian shelf in August 1998. The cruise was divided into two legs, each of them a short-term Lagrangian drift experiment. FP were collected with water bottles, with drifting sediment traps and during experiments carried out onboard the ship. The pellets were enumerated and their biovolumes and carbon contents (FPC) were calculated. The standing stock of FP in the upper 50 m was on average three times higher during the first on-shelf experiment than during the second off-shelf experiment. There were large diurnal variations, but no clear pattern emerged between day and night sampling. The vertical export of FPC from the upper, productive layer was on average one order of magnitude greater on the shelf (range 6–160 mg.m−2.d−1) compared to the off-shelf experiment (range 1–30 mg.m−2.d−1). FPC sedimentation explained ∼20% of the total POC export from the euphotic layer on the shelf, but

A 3-dimensional (3-D) primitive equation model coupled to a biological model was used to study the effects of physics on the productivity and carbon export along the Iberian coast during the upwelling season (May–September). Open boundaries for this model were generated with a basin scale model covering major parts of the North Atlantic and nested in two steps into models with grid resolutions of 10 and 3.3km, respectively. The ecosystem model consists of eight state variables (nitrate, ammonium, silicate, diatoms, flagellates, meso- and microzooplankton, fast and slow sinking detritus) and assumes that nitrogen and silicate are the potential limiting nutrients. The primitive equation models produced coastal upwelling that injects nutrients into the euphotic zone in response to northerly wind forcing. Filaments were formed when the upwelling favourable wind peaked in July/August. High primary production was found on the shelf and in the core of the upwelling filaments. The simulations used atmospheric input from 1998 allowing comparison with a Lagrangian experiment in August 1998. The ecological model, having the same structure as a model been applied on boreal shelves, gave good simulations of the carbon flux on and off the Iberian margin. However, some stocks and rates of carbon were not well validated with the data from the field investigation. The simulated net export of carbon from May to September across the 400km long, 200m isobath is estimated to be 4.4×10 11 gC or 6.3mgC m −2 .s −1 .

Lagrangian experiments with short-term, drifting sediment traps were conducted during a cruise on RRS Charles Darwin to the NW coast of Spain to study the vertical flux and composition of settling biogenic matter. The cruise was split into two legs corresponding to (i) a period of increased production following an upwelling event on the continental shelf (3–10 August 1998) and (ii) an evolution of a cold water filament originating from the upwelled water off the shelf (14–19 August). The export of particulate organic carbon (POC) from the upper layer (0–60m) on the shelf was 90–240mgC.m−2.d−1 and off the shelf was 60–180mgC.m−2.d−1. Off shelf the POC flux at 200m was 50–60mg.m−2.d−1. A modest sedimentation of diatoms (15–30mgC.m−2.d−1) after the upwelling was associated with increased vertical flux of chlorophyll a (1.8–2.1mg.m−2.d−1) and a decrease of the POC:PON molar ratio of the settled material from 9 to 6.4. Most of the pico-, nano-, and microplankton in the settled material were flagellates; diatoms were significant during the on shelf and dinoflagellates during the off shelf leg. Off shelf, the exponential attenuation of POC flux indicated a strong retention capacity of the plankton community between 40 and 75m. POC:PON ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased, suggesting a novel, flagellate and aggregate mediated particulate flux in these waters. Export of POC from the euphotic layer comprised 14–26% of the integrated primary production per day during the on shelf leg and 25–42% during the off shelf leg, which characterises the importance of sedimentation in the organic carbon budget of these waters.

To analyse and quantify the seasonal particulate vertical flux of faecal pellets and microplankton in the oligotrophic Cretan Sea, sediment traps were deployed at 200 m and 1500 m depth on the shelf north of Crete. Microscopical analysis revealed numerous zooplankton faecal pellets and intact cells of foraminifera and phaeodarian radiolarians, but few phytoplankton cells among the sedimented material. The greatest share among the identified particles was comprised by small (30–65 μm) and medium (80–200 μm) sized elliptical faecal pellets. A maximum flux of large (250–400 μm) and medium sized elliptical pellets was recorded during March to May at 200 m, but in general faecal pellet flux was rather uniform and increased at depth. On a seasonal basis the estimated carbon flux from identifiable particles was calculated to 0.175 and 0.303 mg C m−2 d−1 at 200 m and 1500 m depth, respectively. This was only about 6% of the vertical POC flux. The relative contribution of faecal pellets decreased from 93% to 84% of the carbon content of the identified sedimenting particles at 200 m and 1500 m depth, respectively. The increased faecal pellet flux recorded at 200 m depth during spring may probably reflect changes in the balance between the ‘classical’ grazing and microbial food web in the euphotic zone, followed by significant retention during periods when the microbial food web dominates. However, the vertical flux at depth, receives only a small contribution directly from the surface layer production at the investigation site. Vertical flux at depth reflects advective transport of biogenic matter across the shelf and slope, as well as resuspension and faecal pellets from a deep-dwelling zooplankton community. Signals of direct and rapid deposition of surface water appear buffered and greatly modified by mid- and deep-water zooplankton communities on the Cretan Sea shelf.