Climate variability and the Icelandic marine ecosystem     

Olafur S. Astthorsson  Astthor Gislason  Steingrimur Jonsson   《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2456

This paper describes the main features of the Icelandic marine ecosystem and its response to climate variations during the 20th century. The physical oceanographic character and faunal composition in the southern and western parts of the Icelandic marine ecosystem are different from those in the northern and the eastern areas. The former areas are more or less continuously bathed by warm and saline Atlantic water while the latter are more variable and influenced by Atlantic, Arctic and even Polar water masses to different degrees. Mean annual primary production is higher in the Atlantic water than in the more variable waters north and east of Iceland, and higher closer to land than farther offshore. Similarly, zooplankton production is generally higher in the Atlantic water than in the waters north and east of Iceland. The main spawning grounds of most of the exploited fish stocks are in the Atlantic water south of the country while nursery grounds are off the north coast. In the recent years the total catch of fish and invertebrates has been in the range of 1.6–2.4 million ton. Capelin (Mallotus villosus) is the most important pelagic stock and cod (Gadus morhua) is by far the most important demersal fish stock. Whales are an important component of the Icelandic marine ecosystem, and Icelandic waters are an important habitat for some of the largest seabird populations in the Northeast Atlantic.In the waters to the north and east of Iceland, available information suggests the existence of a simple bottom-up controlled food chain from phytoplankton through Calanus, capelin and to cod. Less is known about the structure of the more complex southern part of the ecosystem. The Icelandic marine ecosystem is highly sensitive to climate variations as demonstrated by abundance and distribution changes of many species during the warm period in the 1930s, the cold period in the late 1960s and warming observed during the recent years. Some of these are highlighted in the paper.  相似文献   

Current-depth refraction of water waves     

Ivar G. Jonsson  John D. Wang   《Ocean Engineering》1980,7(1):153-171

Surface gravity waves propagating on large-scale currents over a gently sloping sea bed are considered. Assuming irrotational flow a general proof is given of the existence of a mean energy level, leading directly to the current wave set-down. The complete set of conservation equations describing combined current-depth refraction is presented and solved in two special ssituations. Also a case with a rotational current is considered. Dissipation is neglected.  相似文献   

Power resource estimate of ocean surface waves     

Ivar G. Jonsson 《Ocean Engineering》1977,4(4-5):211-212

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Toxic effects of decomposing red algae on littoral organisms   总被引：2，自引：0，他引：2  

Britta Eklund  Andreas P. Svensson  Conny Jonsson  Torleif Malm   《Estuarine, Coastal and Shelf Science》2005,62(4):621-626

Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l⁻¹ dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe.  相似文献   

Influence of humidity on the aerosol scattering coefficient and its effect on the upwelling radiance during ACE‐2     

S. Gassó  D. A. Hegg  D. S. Covert  D. Collins  K. J. Noone  E. Öström  B. Schmid  P. B. Russell  J. M. Livingston  P. A. Durkee  H. Jonsson 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):546-567

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Clear‐sky closure studies of lower tropospheric aerosol and water vapor during ACE‐2 using airborne sunphotometer, airborne in‐situ, space‐borne, and ground‐based measurements     

Beat Schmid  John M. Livingston  Philip B. Russell  Philip A. Durkee  Haflidi H. Jonsson  Donald R. Collins  Richard C. Flagan  John H. Seinfeld  Santiago Gassó  Dean A. Hegg  Elisabeth Öström  Kevin J. Noone  Ellsworth J. Welton  Kenneth J. Voss  Howard R. Gordon  Paola Formenti  Meinrat O. Andreae 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):568-593

We report on clear‐sky column closure experiments (CLEARCOLUMN) performed in the Canary Islands during the second Aerosol Characterization Experiment (ACE‐2) in June/July 1997. We present CLEARCOLUMN results obtained by combining airborne sunphotometer and in‐situ (optical particle counter, nephelometer, and absorption photometer) measurements taken aboard the Pelican aircraft, space‐borne NOAA/AVHRR data and ground‐based lidar and sunphotometer measurements. During both days discussed here, vertical profiles flown in cloud‐free air masses revealed 3 distinctly different layers: a marine boundary layer (MBL) with varying pollution levels, an elevated dust layer, and a very clean layer between the MBL and the dust layer. A key result of this study is the achievement of closure between extinction or layer aerosol optical depth (AOD) computed from continuous in‐situ aerosol size‐distributions and composition and those measured with the airborne sunphotometer. In the dust, the agreement in layer AOD (λ=380–1060 nm) is 3–8%. In the MBL there is a tendency for the in‐situ results to be slightly lower than the sunphotometer measurements (10–17% at λ=525 nm), but these differences are within the combined error bars of the measurements and computations.  相似文献   

Accuracy of asymptotic series for the kinematics of high solitary waves     

Ivar G. Jonsson  Pernille Thorup  Henriette T. Tama&#x;auskas 《Ocean Engineering》2000,27(5)

The accuracy of several asymptotic series expansions for wave speed and particle velocity under the crest of a solitary wave (on a fluid at rest) up to maximum height is investigated. The very accurate numerical results of Williams (1985) are the measure for our comparisons. The results are based on a scaling of calculated properties of long periodic waves to the case of solitary waves.For wave speeds the classical Boussinesq–Rayleigh expression gives good agreement up to a relative wave height of, say, 0.3. An asymptotic fourth-order expression based on Fenton (1990) can be used up to a relative wave height of 0.7, whereas the corresponding fifth-order expression is slightly less accurate.The Eulerian particle velocity profile under the wave crest is examined using a cnoidal wave expression from Fenton (1990) in the limit of the solitary wave. For low waves a `consistent' (i.e. properly truncated) fifth-order expression and an `inconsistent' ditto both coincide with Williams' results. Beginning at medium high waves, the consistent expression surprisingly exhibits oscillations in the velocity profile, and the oscillations become stronger as the wave gets higher. The inconsistent expression, however, yields the same shape as Williams' profile, but is displaced parallel to this, resulting in slightly larger velocities. For high waves also the inconsistent expression begins to differ in shape from Williams' profile, and asymptotic theory fails. Only for low waves `lowest order theory' gives acceptable results. We show analytically that for the highest wave the particle velocity profile has a horizontal tangent at the water surface; this is corroborated by Williams' numerical results.We also study the particle velocity at the wave crest as a function of wave height. It is shown that the variation has a vertical tangent for the highest wave. Two fifth-order asymptotic series for this velocity, based on the wave speed through the Bernoulli equation, show very good agreement with Williams up to a relative wave height of about 0.6.It is finally shown that it is possible to produce very accurate rational-function approximations to Williams' results for the wave speed as well as for the particle velocity at the wave crest.  相似文献   

A note on the economics of Swedish Baltic Sea fisheries     

Staffan Waldo  Anton Paulrud  Anna Jonsson 《Marine Policy》2010

The cod stocks in the Baltic Sea are important not only for fisheries but for the entire ecosystem utilized by numerous stakeholders around the coast. All such activities have economic values. In this note the economics of the Swedish Baltic Sea cod fishery is estimated in relation to the sector's interaction with other users of the Baltic Sea ecosystem. The results show a negative resource rent for the fishery, € −5 million without public expenses (subsidies and administrative costs), and € −13 million including public expenses. The interactions between the fisheries and tourism, seal population, carbon dioxide emissions, recreational fishing, and discards are discussed, and when monetary estimates are available these are related to the estimated resource rent.  相似文献