Pelagic-Benthic Coupling in the Nordic Seas: The Role of Episodic Events

Abstract. The consequences of the following episodic phenomena for the pelagic-benthic coupling in the Nordic Seas are illustrated: (1) Advection of water masses between fjords and shelf environments, (2) freshwater run-off and vertical stability, (3) dynamics of the marginal ice zone in the central and northern Barents Sea and the Polar Ocean, (4) drift patterns of sinking particles along the North Norwegian coast, (5) advection of zooplankton into subarctic fjords and the southern Barents Sea, zooplankton overwintering and composition, and (6) transport of organic particulate matter from the Barents Sea shelf. It is shown that physical processes in the north-eastern North Atlantic and Polar Ocean can be strongly variable on time scales of days to decades. They have a significant influence on the dynamics of pelagic-benthic coupling. The physical oceanography influences the vertical and horizontal particle flux not only directly (mixing, advection, up- and down-welling), but also indirectly through its impact on the biota (for example radiation, wind, ice cover, freshwater run-off and overwintering, advection and retention of zooplankton). Understanding pelagic-benthic coupling at high latitudes depends even more on a best possible understanding of the physical oceanography and the time scales involved than elsewhere.     

Significance of vertical flux as a sink for surface water DMSP and as a source for the sediment surface in coastal zones of northern Europe

In April 1997 and 1998 the significance of sedimentation as a sink for epipelagic dimethylsulphoniopropionate (DMSP) production and as a source for marine sediments was reassessed using a newly designed sediment trap. The behaviour of the traps in immersion was monitored continuously and the collection efficiency was evaluated with ²³⁴Th measurements. Net DMS(P) fluxes were corrected for some physical and biological losses during the whole sedimentation process providing reliable estimates of gross DMSP fluxes. It is shown that daily losses by sedimentation account for between 0.1% and 16% of seawater particulate DMSP (DMSPp) standing stocks, and between 3% and 75% of daily DMSPp production. In the Malangen fjord we observed temporal increases of DMSP production and standing stocks which resulted also in increases of DMSP vertical fluxes and DMS(P) concentrations at the sediment surface. This result illustrates how tight the coupling can be between pelagos and benthos, and confirms that DMS(P) concentration in the sediment was a reliable diagnostic indicator of vertical export from overlying waters in Malangen fjord. In Ullsfjord, however, DMS(P) concentrations in the sediment were poorly indicators of Phaeocystis pouchetii export during the early stage of growth of a bloom. The high load of DMS(P) in Balsfjord's sediments could neither be attributed to local vertical sedimentation nor to short-term lateral advection of fresh DMSP-containing phytoplanktonic material, and provides indication that this tracer sometimes also can be misleading. The highest loads of DMS(P) in sediments and the fastest rates of sedimentation occurred in the Southern Bight of the North Sea.     

Rift kinematics preserved in deep-time erosional landscape below the northern North Sea

Our understanding of continental rifting is, in large parts, derived from the stratigraphic record. This record is, however, incomplete as it does not often capture the geomorphic and erosional signal of rifting. New 3D seismic reflection data reveal a Late Permian-Early Triassic landscape incised into the pre-rift basement of the northern North Sea. This landscape, which covers at least 542 km², preserves a drainage system bound by two major tectonic faults. A quantitative geomorphic analysis of the drainage system reveals 68 catchments, with channel steepness and knickpoint analysis of catchment-hosted palaeo-rivers showing that the landscape preserved a >2 Myr long period of transient tectonics. We interpret that this landscape records a punctuated uplift of the footwall of a major rift-related normal fault (Vette Fault) at the onset of rifting. The landscape was preserved by a combination of relatively rapid subsidence in the hangingwall of a younger fault (Øygarden Fault) and burial by post-incision sediments. As such, we show how and why erosional landscapes are preserved in the stratigraphic record, and how they can help us understand the tectono-stratigraphic evolution of ancient continental rifts.     

Diatom‐based reconstruction of summer sea‐surface salinity in the South China Sea over the last 15 000 years

We present a new reconstruction of summer sea‐surface salinity (SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea (SCS). The reconstructed diatom‐based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long‐term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20°N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ¹⁸O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea‐level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial‐scale oscillatory variations in summer SSS were superimposed on the long‐term trend. During the deglacial period (c. 12 000–9000 cal. a BP), the dominant periodicity was centred around 230–250 years, whereas a ～350‐year oscillation dominated in the period 2200–4500 cal. a BP. The balance of evidence suggests that these centennial‐scale changes in summer SSS may have been driven by solar‐induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship.     

Search for Phobos and Deimos gas/dust tori using in situ observations from Mars Global Surveyor MAG/ER

More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible signatures of solar wind interaction with dust or gas escaping from the moons. A total of 1246 solar wind disturbance events were identified and their distribution was examined relative to Phobos, the Phobos orbit, and the Deimos orbit. We find that the spatial distribution of solar wind perturbations does not increase near or downstream of Phobos, Phobos’ orbit, or Deimos’ orbit, which would have been expected if there is significant outgassing or dust escape from the martian moons. Of the 1246 magnetic field perturbation events found in the MGS data set, 11 events were found within 2000 km of the Phobos orbit, while three events were found within 2000 km of the Deimos orbit. These events were analyzed in detail and found to likely have other causes than outgassing/dust escape from the martian moons. Thus we conclude that the amount of gas/dust escaping the martian moons is not significant enough to induce detectable magnetic field perturbations in the solar wind. In essence we have not found any clear evidence in the MGS magnetic field data for outgassing or dust escape from the martian moons.     

Trace Elements in Sediments and Mussels – Spatial Distribution,Chemical Partitioning,and Risk Assessment

Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.     

A carbon budget for the Barents Sea

The first carbon budget constructed for the Barents Sea to study the fluxes of carbon into, out of, and within the region is presented. The budget is based on modelled volume flows, measured dissolved inorganic carbon (DIC) concentration, and literature values for dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations. The results of the budget show that ～5600±660×10⁶ t C yr^?1 is exchanged through the boundaries of the Barents Sea. If a 40% uncertainty in the volume flows is included in the error calculation it resulted in a total uncertainty of ±1600×10⁶ t C yr^?1. The largest part of the total budget flux consists of DIC advection (～95% of the inflow and ～97% of the outflow). The other sources and sinks are, in order of importance, advection of organic carbon (DOC+POC; ～3% of both in- and outflow), total uptake of atmospheric CO₂ (～1% of the inflow), river and land sources (～0.2% of the inflow), and burial of organic carbon in the sediments (～0.2% of the outflow). The Barents Sea is a net exporter of carbon to the Arctic Ocean; the net DIC export is ～2500±660×10⁶ t C yr^?1 of which ～1700±650×10⁶ t C yr^?1 (～70%) is in subsurface water masses and thus sequestered from the atmosphere. The net total organic carbon export to the Arctic Ocean is ～80±20×10⁶ t C yr^?1. Shelf pumping in the Barents Sea results in an uptake of ～22±11×10⁶ t C yr^?1 from the atmosphere which is exported out of the area in the dense modified Atlantic Waters. The main part of this carbon was channelled through export production (～16±10×10⁶ t C yr^?1).     

Bayesian lithology/fluid inversion—comparison of two algorithms

Algorithms for inversion of seismic prestack AVO data into lithology-fluid classes in a vertical profile are evaluated. The inversion is defined in a Bayesian setting where the prior model for the lithology-fluid classes is a Markov chain, and the likelihood model relates seismic data and elastic material properties to these classes. The likelihood model is approximated such that the posterior model can be calculated recursively using the extremely efficient forward–backward algorithm. The impact of the approximation in the likelihood model is evaluated empirically by comparing results from the approximate approach with results generated from the exact posterior model. The exact posterior is assessed by sampling using a sophisticated Markov chain Monte Carlo simulation algorithm. The simulation algorithm is iterative, and it requires considerable computer resources. Seven realistic evaluation models are defined, from which synthetic seismic data are generated. Using identical seismic data, the approximate marginal posterior is calculated and the exact marginal posterior is assessed. It is concluded that the approximate likelihood model preserves 50% to 90% of the information content in the exact likelihood model.     

Governing cities through participation—a Foucauldian analysis of CityPlan Vancouver

In 1995 Vancouver City Council approved new policy guidelines for future urban development that departed from the traditional model of suburban growth, instead prioritizing urban intensification. Theoretically guided by the Foucauldian governmentality approach, I argue in this paper that this shift towards intensification can be understood through an analysis of Vancouver’s extensive participatory planning process known as CityPlan. Created as an answer to conflicts around the intensification of historically evolved urban neighbourhoods, CityPlan Vancouver exemplifies a specific form of urban governance that has been understudied in geography and participation research: a governance consisting of conducting the conduct of citizens through participatory processes. The paper examines this “governing through participation” by carrying out a microanalysis of the problematizations, rationalities, and technologies of CityPlan. Such an analysis differs significantly from an evaluation of participatory planning processes against normative ideals, and thus enriches critical research on participation in urban governance.     

Food webs and carbon flux in the Barents Sea

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.