Regions Of High Productivity Research Articles

Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective

A strong oxygen minimum zone (OMZ) currently exists at upper intermediate water depths on the northern Japanese margin, NW Pacific. The OMZ results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters. We investigated late Quaternary history (last 34 kyr) of ocean floor oxygenation and the OMZ using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off Shimokita Peninsula and Tokachi, northern Japan, at water depths between 975 and 1363 m. These cores are well located within the present‐day OMZ, a region of high surface water productivity, and in close proximity to the source region of North Pacific Intermediate Water. Late Quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments. Foraminiferal assemblages are interpreted to represent three main groups representing oxic, suboxic, and dysoxic conditions. Assemblage changes in all three cores and hence in bottom water oxygenation coincided with late Quaternary climatic episodes, similar to that known for the southern California margin. These episodes, in turn, are correlated with orbital and millennial climate episodes in the Greenland ice core including the last glacial episode, Bølling‐Ållerød (B/A), Younger Dryas, Preboreal (earliest Holocene), early Holocene, and late Holocene. The lowest oxygen conditions, marked by dysoxic taxa and laminated sediments in one core, occurred during the B/A and the Preboreal intervals. Suboxic taxa dominated mainly during the last glacial, the Younger Dryas, and most of the Holocene. Dysoxic conditions during the B/A and Preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern Pacific. Remarkable similarities are evident in the late Quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern Japan and southern California. The oscillations in OMZ strength, reflected by these faunal changes, were widespread and apparently synchronous over wide areas of the North Pacific, reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late Quaternary climate change on millennial and orbital timescales.

Atmospheric Occurrence and Deposition of Polycyclic Aromatic Hydrocarbons in the Northeast Tropical and Subtropical Atlantic Ocean

Atmospheric transport and deposition of polycyclic aromatic hydrocarbons (PAHs) over tropical oceans has not yet been studied even though tropical oceans account for 35% of the global oceans. Here we show the results from measurements of gas- and aerosol-phase PAHs and dry deposition samples in the NE tropical Atlantic Ocean atmosphere, a region between 26 degrees and 21 degrees N, off shore of the Saharan desert. The results show that PAHs concentrations are high at the coastal ocean (15-20 ng m(-3) for sum of 27 gas-phase individual PAHs) and decrease by a factor of 2-3 at open ocean (26 degrees W). The spatial variability observed is consistent with dilution, reaction, and deposition during transport. Atmospheric dry deposition velocities ranged between 0.1 and 0.3 cm s(-1) with higher deposition velocities for the more volatile PAHs. Outbreaks of Saharan Dust significantly increase the deposition rates of PAHs. The occurrence and deposition of PAHs in tropical regions is complex and results from the interplay of a number of processes, such as wind speed, aerosol loads, important sources from West Africa, processes controlling the diurnal variability, and sequestration driven by high primary productivity regions. The measured average atmospheric residence times of gas- and aerosol-phase PAHs are 3.7 and 3.5 days, respectively.

From production networks to geographical economics

Although standard economics textbooks are seldom interested in production networks, modern economies are more and more based upon supplier/customer interactions. One can consider entire sectors of the economy as generalised supply chains. We will take this view in the present paper and study under which conditions local failures to produce or simply to deliver can result in avalanches of shortage and bankruptcies and in localisation of the economic activity. We will show that a large class of models exhibit scale free distributions of production and wealth among firms and that regions of high production are localised.

Dissolution of calcium carbonate: observations and model results in the subpolar North Atlantic

Abstract. We investigate the significance of in situ dissolution of calcium carbonate above its saturation horizons using observations from the open subpolar North Atlantic [sNA] and to a lesser extent a 3-D biogeochemical model. The sNA is particularly well suited for observation-based detections of in situ, i.e. shallow-depth CaCO3 dissolution [SDCCD] as it is a region of high CaCO3 production, deep CaCO3 saturation horizons, and precisely-defined pre-formed alkalinity. Based on the analysis of a comprehensive alkalinity data set we find that SDCCD does not appear to be a significant process in the open sNA. The results from the model support the observational findings by indicating that there is not a significant need of SDCCD to explain observed patterns of alkalinity in the North Atlantic. Instead our investigation points to the importance of mixing processes for the redistribution of alkalinity from dissolution of CaCO3 from below its saturation horizons. However, mixing has recently been neglected for a number of studies that called for SDCCD in the sNA and on global scale.

Seasonal cycles in biogenic production and export in Northern Bay of Bengal sediment traps

Sediment traps in the northern and north central Bay of Bengal are characterized by highly seasonal fluxes and unusually high efficiency of organic carbon export. However, the mechanism for high export production remains under debate. To evaluate the relationships between production in the photic zone and export processes responsible for the fluxes into the traps, over an annual cycle we examine a series of indicators of production regime set in surface waters. These indicators include communities of planktic foraminifera and coccolithophores, stable isotopic chemistry of foraminifera and coccoliths, and the Sr/Ca ratios in coccoliths. Coccolith and foraminiferal assemblages confirm that the Bay of Bengal is a region of high productivity. Coccolithophore communities are dominated to an unusually high degree (90%) by the lower photic zone dweller Florisphaera profunda, a species adapted to high-nutrient and low-light conditions typical of stratified waters like those induced by the strong halocline in the Bay of Bengal. Cyclonic eddy pumping and strong winds during the southwest monsoon (SWM) increase the relative abundance of upwelling indicator species like foraminifera Globigerina bulloides and the upper photic coccolithophores Globigerina oceanica and Emiliania huxleyi. However, while upwelling and eddy pumping do coincide with high opal and coccolith export, in both traps peak organic carbon export precedes the onset of eddy pumping and upwelling indicators. These data suggest an alternate mode of production in the Bay of Bengal, which is not driven by upwelling but rather high production deeper in the water column, probably by taxa adapted to lower light levels. In both traps, the pulses of organic carbon export coincide with elevated fluxes of planktonic foraminifera, which likely reflect increased primary production. Consequently, while major export pulses of organic carbon coincide with pulses of lithogenic export, the pulses of organic carbon export are not likely to reflect simple scavenging of suspended organic carbon by lithogenic pulses. Rather, they reflect increased organic carbon production. Nonetheless, some seasonal changes increase in coccolith export efficiency during the SWM are suggested by coccolith Sr/Ca ratios. In the northern trap, coccolith carbonate export is decoupled from the main pulse of organic carbon export. Consequently, ballasting of organic carbon aggregates by coccolith carbonate does not play a major role in the seasonal cycle of organic carbon export from the photic zone to shallow (800-m) traps.

Reduced sea ice concentrations in the Arctic Ocean during the last interglacial period revealed by sediment cores off northern Greenland

We present a record encompassing marine isotope stages 7‐1 from a hitherto unexplored and heavily ice‐covered area of the Arctic Ocean, the Lomonosov Ridge off the northern Greenland‐Canada continental margin, using nannofossil and benthic foraminifera stratigraphy. Planktic foraminifera assemblages are used as a key paleoceanographic proxy, and a surprisingly large variability is found for an interior Arctic Ocean site. Abundant small (63–125 μm) subpolar Turborotalita quinqueloba occur in two sections, possibly representing substages 5e (last interglacial) and 5a (warm interstadial). However, the present‐day circulation pattern and the very distant location of high productive regions cannot explain such high abundances of subpolar specimens in the interior, perennially sea ice–covered Arctic Ocean. Hence our proxy record indicates that last interglacial sea ice concentrations were reduced off some areas of northern Greenland‐Canada. Whether this was part of a larger regional pattern or it represents the influence of polynya areas with locally increased productivity remains to be solved. With respect to glacial conditions, increased ice‐rafted debris (IRD) deposition in the area appears to be associated with glacial stages 6, 4, and late 3. Stage 2 sediments (including the Last Glacial Maximum) are condensed with a sparse IRD content only.

The Synthesized Hot Ion Plasmoid Experiment at GDT

The Synthesised Hot Ion Plasmoid (SHIP) experiment is in progress at the GDT facility of the Budker Institute (Novosibirsk). It is aimed at the investigation of plasmas in the region of high neutron production in a GDT based fusion neutron source proposed by the Budker Institute. This paper presents the recent results obtained in the experiments with SHIP. The results of numerical simulations are compared with the experimental results.The average value of fast ion density was two times greater than density of unperturbed streaming plasma and three times greater than the warm ion density in the presence of NBI. Fast ion confinement was determined only by Coulomb collisions and charge - exchange of fast ions on neutral beams. No evidence of MHD or micro instabilities was observed. Ambipolar plugging was demonstrated in the SHIP experiment. Further experiments with upgraded Neutral Beam system are started.

Calcareous dinoflagellate cyst distributions in surface sediments from upwelling areas off NW Africa, and their relationships with environmental parameters of the upper water column

Only very few studies have focussed on the spatial distribution and ecology of calcareous dinoflagellate cysts (dinocysts) in upwelling areas. Here, distributions of individual calcareous dinocyst species in surface sediment samples from the coastal upwelling zone off NW Africa and their relationships with known environmental parameters of the (sub-)surface waters have been analysed in order to enhance our knowledge on their modern distribution patterns and to determine the ecological significance and palaeoenvironmental reconstruction potential of each calcareous dinocyst species within this exemplary high-productivity region. In addition to calculating relative cyst abundances, well-constrained sedimentation rates have allowed the calculation of dinocyst accumulation rates (cysts cm − 2 ka − 1 ) for most of the surface sample positions, thus providing a much more accurate estimation of actual calcareous dinocyst production in the upper water column than could be warranted in similar studies so far. Distinct differences in the geographic distribution patterns of nine species were observed. In general, high accumulation rates of calcareous dinocysts were found around and south of 29°N and offshore the westernmost Canary Island La Palma, with slightly lower accumulation rates in the upwelling-influenced areas off Cape Yubi and in the upwelling filament area off Cape Ghir. Multivariate ordination techniques were applied in order to compare the cyst accumulation rates of individual species with physical parameters (temperature, salinity, density, mixed layer depth) and the trophic state (nitrate, phosphate and chlorophyll concentrations) of the overlying (sub-)surface waters. All species were found to relate significantly to one or more of the environmental parameters, partly confirming previous results on cyst ecology but also providing new information which will be useful for future palaeoenvironmental reconstructions within upwelling areas.

Nutrient irrigation of the North Atlantic

The North Atlantic, as all major oceans, has a remarkable duality in primary production, manifested by the existence of well-defined high and low mean primary production regions. The largest region is the North Atlantic Subtropical Gyre (NASTG), an anticyclone characterized by bowl shaped isopycnals and low production. The NASTG is surrounded at its margins by smaller cyclonic high-production regions, where these isopycnals approach the sea surface. The most extensive cyclonic regions are those at the latitudinal extremes, i.e. the subpolar and tropical oceans, though smaller ones do occur at the zonal boundaries. In this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western/northwestern and eastern/southeastern boundaries of the NASTG, with the objective of investigating the importance of upward epipycnal advection of nutrient-rich subsurface layers (irrigation) in maintaining high primary production in the euphotic layers. In the North Atlantic Subpolar Gyre (NASPG) irrigation implies intergyre exchange caused by the outcropping extension of the Gulf Stream (GS), following the formation of the deep winter mixed-layer. In the eastern boundary of the NASTG irrigation is attained through a permanent upwelling cell, which feeds the Canary Upwelling Current (CUC). In the southeastern corner irrigation occurs in fall, when the Guinea Dome (GD) is reinforced, and in winter, when the CUC reaches its southernmost extension. Other characteristics of the north/south extension of the GS/CUC are the seasonal nutrient replenishing of subsurface layers (spring restratification of NASPG and winter relaxation of the GD) and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers. Off the Mid-Atlantic Bight the GS transports a total of about 700 kmol s −1 of nitrate, with almost 100 kmol s −1 carried in the surface ( σ θ < 26.8) layers and some 350 kmol s −1 in the intermediate (26.8 < σ θ < 27.5) layers. A box model suggests that north of Cape Hatteras most surface and upper-thermocline nitrates are used to sustain the high levels of primary production in the NASPG. Off Cape Blanc there is winter along-shore convergence of order 10 kmol s −1 of nitrate in the near-surface layers (possibly larger in summer), with only a small fraction used to sustain local primary production in the coastal upwelling band and the remainder carried to the interior ocean. Nutrients and biomass exported from these cyclonic regions may account for the concentration levels observed within the NASTG.

Noble gas tracing of groundwater/coalbed methane interaction in the San Juan Basin, USA

The San Juan Basin natural gas field, located in northwestern New Mexico and southwestern Colorado in the USA, is a case-type coalbed methane system. Groundwater is thought to play a key role in both biogenic methane generation and the CO 2 sequestration potential of coalbed systems. We show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas. We collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control. Stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin, and the underpressured low producing region as having a significant admix of thermogenic coal gas. 3He/ 4He ratios increase from 0.0836R a at the basin margin to 0.318R a towards the center, indicating a clear but small mantle He signature in all gases. Coherent fractionation of water-derived 20Ne/ 36Ar and crustal 4He/ 40Ar* are explained by a simple Rayleigh fractionation model of open system groundwater degassing. Low 20Ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater-associated gas by desorbed coalbed methane. This Rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well. The quantified water volumes in both underpressured and overpressured zones range from 1.7 × 10 3 m 3 to 4.2 × 10 5 m 3, with no clear distinction between over- and underpressured production zones. These results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds. There is no requirement of continuous groundwater flow for renewing the microbes or nutrient components. We furthermore observe strong mass related isotopic fractionation of 20Ne/ 22Ne and 38Ar/ 36Ar isotopic ratios. This can be explained by a noble gas concentration gradient in the groundwater during gas production, which causes diffusive partial re-equilibration of the noble gas isotopes. It is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air-derived noble gases can occur when such concentration gradients are established during gas production. Excess air-derived Xe and Kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if Xe and Kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form CH 4.

Ocean circulation and exchanges through the northern Bering Sea—1979–2001 model results

Abstract We have developed and run a model with sufficiently high resolution (∼9 km and 45 levels) and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern Bering Sea. This is potentially important for quantification of long-term mean and time-dependent ocean circulation, and water mass and property exchanges between the Pacific and Arctic Oceans. Over a 23 year interval (1979–2001), mean transport through Bering Strait is estimated to be 0.65 Sv. Comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short-term atmospheric forcing. One of such events occurred during the winter of 2000–2001 with reversed oceanic flow in some areas and much reduced sea-ice cover. Analyses of eddy kinetic energy fields identify some high biological productivity regions of the Chirikov Basin coincident with persistent high energy (up to 2700 cm 2 s −2 in the surface layer and up to 2600 cm 2 s −2 at mid-depth) throughout the annual cycle. Model output in the Bering Strait region is validated against several time series of moored observations of water mass properties. Comparison with shipboard observations of near-bottom salinity from late winter through autumn indicates that the model reasonably represents the major water-mass properties in the region. The modeled vertical water-column structure in the northern Bering Sea allows increased understanding of the mechanisms of water transformation and transport northward through Bering Strait into the Chukchi and Beaufort Seas. We conclude that the long-term model results for the northern Bering Sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short-term and/or cover only a small geographic region.

Late Quaternary climate change record from two long sediment cores from Guaymas Basin, Gulf of California

AbstractModern Guaymas Basin (Gulf of California, Mexico) is a region of high diatom productivity where exceptional preservation factors maintain biannually alternating sediment deposition as annual varves. New sediment cores from Guaymas Basin (MD02‐2512 and MD02‐2515) present the opportunity to construct climate records from below the last glacial period. A low‐resolution age model has been constructed from oxygen isotope analysis, correlation with other dated short piston cores from Guaymas Basin and an estimate of sedimentation rate. MD02‐2512 from eastern Guaymas Basin has an age range from the Holocene to late marine isotope stage 6 (MIS 6); MD02‐2515 from western Guaymas Basin has an age range from ∼8000 to 40 000 yr. Shipboard analyses of colour reflectance, magnetic susceptibility and sediment density are combined with continuous X‐ray fluorescence scans to reconstruct a picture of glacial climate in the Gulf of California. Eastern Guaymas Basin is affected by glacial sea level fall, which results in a drastic change in productivity rates and sediment type. The laminated record of MIS 5 allows comparison with the Holocene, showing a similarity of sedimentation patterns during deglaciation and a series of very rapid variations just prior to the last glaciation. In western Guaymas Basin there are a series of Younger Dryas‐like events during the glacial, typified by low productivity and high terrigenous input. Long‐term climate and productivity changes appear to be caused by the southward displacement of the Subtropical High pressure zone. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Evaluation of six relations of the kinetics of uptake by phytoplankton in multi-nutrient environment using JGOFS experimental results

Abstract The inhibitory effect of ammonium on nitrate uptake, which has received a fair amount of attention, is an example of phytoplankton uptake kinetics in a multi-nutrient environment with nutrient interaction. We examine six relations [Wroblewski, 1977. Journal of Marine Research 35, 357–394; O’Neill et al., 1989. Ecological Modelling 46, 147–163; Walsh and Dugdale, 1971. Deep-Sea Research 22, 201–236; Jamart et al., 1977. Deep-Sea Research 31, 21–37; Frost and Franzen, 1992. Marine Ecology Progress Series 83, 291–303; Yajnik and Sharada, 2003. Current Science 85(8), 1180–1189] governing the uptake of nitrate and ammonium by phytoplankton in the context of the nitrogen dynamics experiments of McCarthy et al. [1999. Nitrogen dynamics during the Arabian Sea northeast monsoon. Deep- Sea Research II 46 (8–9), 1623–1664] in the Indian Ocean. One of the relations [Yajnik and Sharada, 2003. Current Science 85(8), 1180–1189], which is based on the properties of similarity and hyperbolicity, is shown to represent the experimental observations more accurately than others. We then examine the consequences of selection of one of these kinetic relations on 3D simulations of the Indian Ocean ecosystem. The 3D simulations are based on the biological model of Fasham et al. [1990. Journal Marine Research 48, 591–639] coupled to a physical oceanographic model Saramiento et al. [1993. Global Biogeochemical Cycles 7 (2), 417–450] and are performed for three relations [Wroblewski, 1977. Journal of Marine Research 35, 357–394; O’Neill et al., 1989. Ecological Modelling 46, 147–163; Yajnik and Sharada, 2003. Current Science 85(8), 1180–1189]. The values of kinetic parameters are determined from the experiments of McCarthy et al. [1999. Deep- Sea Research II 46 (8–9), 1623–1664]. The spatial variation of annual average primary productivity, especially in the regions of high primary productivity in the northern Indian Ocean, is found to agree most favourably with SeaWiFS data for the relation [Yajnik and Sharada, 2003. Current Science 85(8), 1180–1189] based on similarity and hyperbolicity. The distribution of particle export ratios also appears to be close to present expectations.

Iodine oxide in the Dead Sea Valley: Evidence for inorganic sources of boundary layer IO

The importance of iodine oxide (IO) in tropospheric boundary layer chemistry has been well established in the last decade. Iodine‐containing radicals have been detected in regions of high biological productivity. To date, most explanations assume biogenic precursors (e.g., emission of iodocarbons). In a 2 week field campaign at the Dead Sea, Israel, IO was found to exceed the detection limit (0.3–2 parts per trillion (ppt)) almost daily, with peak levels topping 10 ppt. Macro algae are nonexistent because of the water's high salinity. The Dead Sea's microbiology is discussed in detail, and organic sources of iodine oxide are found to be of minor importance. Thus the site can be treated as a unique place for the investigation of inorganic sources of IO. Such processes have recently been included in model studies. Our study focuses on the first direct evidence for inorganic sources of reactive boundary layer iodine. Heterogeneous iodine release induced by photolysis, liquid phase ozone reactions, or catalytic HOX interactions are discussed as well as NOx chemistry.

Color Infrared Photography Is Not a Good Predictor of Macro Invertebrate Abundance on Mudflats Used by Shorebirds

The applicability of color infrared photography to indirectly predict prey abundance for shorebirds was tested by measuring the chlorophyll concentrations of primary producers on the mudflat surface at eleven migratory stopover sites of shorebirds in Georgia Strait, British Columbia during southward migration in July and August 2002. Many shorebirds are associated with regions of high coastal zone productivity, which may contribute to high prey abundance. Chlorophyll levels of primary producers contribute to the red tones of an infrared photograph. The hue of an infrared photograph was positively related to the chlorophyll concentration of the sediment surface across all sites. However, invertebrate density was not strongly related to surficial sediment chlorophyll concentration or photograph hue. The color infrared photography method is useful to quickly assess the surficial sediment concentration of the phytobenthos, but of low value to estimate invertebrate prey densities.

First Results from SHIP Experiment

At present, the GDT facility is being upgraded. The first stage of the upgrade is the Synthesised Hot Ion Plasmoid (SHIP) experiment. It aims, on the one hand, at the investigation of plasmas which are expected to appear in the region of high neutron production in a GDT based fusion neutron source proposed by the Budker Institute and, on the other hand, at the investigation of plasmas the parameters of which have never been achieved before in axisymmetric magnetic mirrors.The experiment is performed in a small mirror section which is installed at the end of one side of GDT. The magnetic field on axis is in the range of 0.5-2.0 Tesla and the mirror ratio is 1.2-1.4. The mirror is filled with background plasma streaming in from the central cell. This plasma component is maxwellised and has an electron temperature of about 100 eV. Two neutral beam injectors perpendicularly inject a total current of about 50 Atom Amperes of deuterium neutrals with an energy of 20 keV as a pulse with a duration of about 1 ms. Ionisation of the beams generates the high-energy ion component. The device has been equipped with several diagnostic methods which are successfully used in GDT experiments.The paper presents first results of plasma parameter measurements in SHIP experiment.

Illustrating the importance of particulate organic matter to pelagic microbial abundance and community structure—an Arctic case study

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 40:217-227 (2005) - doi:10.3354/ame040217 Illustrating the importance of particulate organic matter to pelagic microbial abundance and community structure—an Arctic case study Lisa R. Hodges1,2, Nasreen Bano1, James T. Hollibaugh1, Patricia L. Yager1,* 1Department of Marine Sciences, University of Georgia, 220 Marine Sciences Building, Athens, Georgia 30602-3636, USA2Present address: Centers for Disease Control & Prevention, 1600 Clifton Road, Mail-Stop C16, Atlanta, Georgia 30333, USA *Corresponding author. Email: pyager@uga.edu ABSTRACT: The pelagic bacterial community composition of the summertime Chukchi Sea (coastal Alaskan Arctic) was investigated under varying particle concentrations. Free-living and wholecommunity assemblages were compared using PCR-amplified 16S rDNA with denaturing gradient gel electrophoresis (PCR/DGGE) alongside traditional geochemical and microbial inventories. Algal blooms were characterized by increased microbial abundance, decreased species richness, and decreased similarity between free-living and whole-community bacterial assemblages. Bacterial and viral abundance correlated positively with a bloom index identified by principle components analysis that included particulate organic carbon and nitrogen, total organic carbon, and chlorophyll a, but not dissolved organic carbon or inorganic nutrients. The species richness of the free-living community correlated negatively with microbial abundance; differences between free-living and whole-community assemblages correlated positively with viral abundance. Algal blooms may therefore increase microbial abundance while stimulating a succession of the bacterial assemblage to fewer free-living species and more specialized particle-associated bacteria. Such community-level shifts are very likely to impact the fate of carbon in high production and export regions like the coastal Arctic. We speculate about the importance of viral lysis to such a succession. KEY WORDS: Bacterioplankton · Virioplankton · Bacterial community composition · Particleassociated bacteria · Free-living bacteria · Psychrophiles · Arctic · Carbon fluxes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 40, No. 3. Online publication date: October 18, 2005 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2005 Inter-Research.

Influence of Planting Date on Sunflower Stem Weevil (Coleoptera: Curculionidae) Larval Density and Parasitism in Oilseed and Confection Sunflower in Western Kansas

The sunflower stem weevil infests stalks of cultivated sunflower and can cause lodging resulting in loss of the head prior to harvest. Our objective was to determine whether altered planting periods could reduce weevil densities in confection and oilseed sunflower in the central High Plains production region. We evaluated impact of planting date by measuring larval density within sunflower stalks, larval parasitoid species present, and parasitization rates. Trials were conducted at Colby, KS from 1999 to 2001, with plots seeded in four planting periods. Results, although inconsistent over years and between the two sunflower types, showed that later planting dates reduced weevil density in stalks. Weevil numbers in stalks from the first seeding period until the last had decreased by 10% to 50%. The third planting date in each year coincided with cumulative degree-days (581) for the predicted emergence of 90% of adult sunflower stem weevils. Yields were not reduced as planting was delayed. Fewer weevils were observed in oilseed than in confection hybrids. Lower densities of sunflower stem weevils in the stalk can reduce losses from lodged plants. Seven hymenopteran parasitoid species were reared from sunflower stem weevil larvae. Nealiolus curculionis (Fitch) and Neocatolaccus tylodermae (Ashmead) were the most common species. Parasitization rates were low, but wasps actively attacked the weevil throughout the growing season. Research showed that delaying planting until after the early and later May planting periods reduced weevil densities in western Kansas.

Trade, migration and regional unemployment

A by now large literature in regional economics has greatly improved our understanding of the determinants of the observed spatial disparities in productivity. However, this literature neglects what seems to be a robust and persistent fact accompanying regional productivity differences: high productivity regions also have lower unemployment than low productivity regions. In this paper, we set out a model in the New Economic Geography (NEG)/job search tradition to explore the theoretical determinants of this fact. We find that the same forces producing regional agglomeration and productivity differences also generate persistent unemployment disparities. Moreover, we highlight a contrast between the short-run and long-run effects of migration on regional unemployment. In particular, migration from the periphery to the core may reduce unemployment disparities in the short-run, but exacerbates them in the long-run.

Satellite and hydrographic observations of the Bering Sea ‘Green Belt’

Abstract Green Belt is the aptly named region of high productivity occurring principally along and above the shelf-slope boundary in the Bering Sea. TOPEX altimeter measurements of sea-surface topography, SeaWiFS imagery of chlorophyll a concentration, and shipboard measurements of salinity and fluorescence are used to describe the surface structure of the Green Belt and its relationship to the Bering Slope Current eddy field during the 2000, 2001, and 2002 spring blooms. During spring 2000, high surface chlorophyll a concentrations (>10 mg m −3 ) were observed within a ∼200-km wide band adjacent to and seaward of the shelf break in the northwest Bering Sea. This high concentration chlorophyll band was associated with an anticyclonic eddy group that propagated along isobaths above the continental slope and entrained chlorophyll from the shelf-slope front. During spring 2001, anticyclonic eddies in the northwest Bering Sea had propagated off-slope prior to the onset of the spring bloom and were too far from the shelf-slope front to entrain frontal chlorophyll during the bloom. A second chlorophyll front associated with the leading edge of the off-slope eddies was observed. Between these two fronts was a region of relatively low chlorophyll a concentration (∼1 mg m −3 ). The eddy field during the 2002 spring bloom was observed to propagate northwestward adjacent to the shelf-break and entrain chlorophyll from the shelf-slope region in a manner similar to what was observed during the 2000 spring bloom. These observations suggest that eddies are important, if not the principal, agents that cause variability in the distribution of chlorophyll during the spring bloom in the central Bering Sea.