| 1. |
- Filipsson, Helena L., 1973, et al.
(författare)
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Climate variations, an overlooked factor influencing the recent marine environment. An example from Gullmar Fjord, Sweden, illustrated by benthic foraminifera and hydrographic data
- 2004
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Ingår i: Estuaries. - 0160-8347. ; 27:5, s. 867-881
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Tidskriftsartikel (refereegranskat)abstract
- Like most sill fjords, Gullmar Fjord on the Swedish west coast, is subject to periods of stagnation. Deep water is usually renewed annually, but since the late 1970s several low-oxygen events have been documented in the deepest part of the fjord. These events occurred during a time when the North Atlantic Oscillation (NAO) was in a highly positive phase. We investigated how the benthic environment, in the deepest part of the fjord, has varied during the 20th century, using benthic foraminifera. and an extensive history of instrumental hydrographic data. The foraminifera have undergone one major faunal change and two minor modifications during this time. The major faunal change occurred in the late 1970s to early 1980s, when the common Skagerrak-Kattegat fauna was replaced by one dominated by the opportunistic, low-oxygen-tolerant species, Stainforthia fusiformis. This major faunal change appears to be related to the severe low-oxygen event in 1979-1980. In the latter part of the 1990s the fauna changed again; the concentration of S. fusiformis was still high, but other low-oxygen-tolerant species also became important. This minor faunal modification occurred in connection with the 2-yr stagnation period between 1996 and 1998 when a low-oxygen event evolved, the most severe recorded in Gullmar Fjord. Between 1930 and 1980, there was little faunal variation, and a stable fjord environment is indicated. During this time, negative NAO indexes dominated and climate was more continental, with an increase in winds from the northeast and east. In connection with a climate transition indicated by the NAO index switching from positive to negative, a minor faunal change occurred in the late 1920s to early 1930s: the concentration of the Skagerrak-Kattegat fauna increased markedly in the fjord. The fauna characterizing the positive NAO phase between 1900 and the late 1920s is very different from the present positive NAO fauna. The foraminiferal record laid down between approximately 1914 and 2001 indicates that between 1930 and 1980 Gullmar Fjord was a stable fjord environment. During the last 20 yr, it experienced conditions that were more fluctuating and changing. For the most part, changes in the foraminiferal fauna are caused by changes in the deep-water renewal, their extent and frequency, which in turn are caused by climatic oscillations.
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| 2. |
- Lund-Hansen, LC, et al.
(författare)
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Vertical sediment fluxes and wave-induced sediment resuspension in a shallow-water coastal lagoon
- 1999
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Ingår i: ESTUARIES. - : ESTUARINE RES FEDERATION. - 0160-8347. ; 22:1, s. 39-46
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The present study describes variations in the vertical fluxes measured concurrently with sediment traps at both a shallow water (4 m) and a deeper water (7.5 m) position in a coastal lagoon in April 1995. A tripod equipped with five sediment traps (trap o
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| 3. |
- McQuoid, Melissa R., et al.
(författare)
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Environmental influence on the diatom and silicoflagellate assemblages in Koljo Fjord (Sweden) over the last two centuries
- 2003
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Ingår i: Estuaries. - 0160-8347. ; 26:4A, s. 927-937
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Tidskriftsartikel (refereegranskat)abstract
- Throughout the last century, the Swedish coasts have been exposed to climatic variation and human influence, and this has altered the biota in some areas. Diatoms and sillicoflagellates in a periodically-laminated sediment core from Koljo Fjord (Swedish west coast) were examined to assess recent changes in the microalgal community. The most notable changes in the plankton occurred at the beginning of a long period of water column stratification in the fjord that extended from 1930 to 1980. The planktonic flora changed from a community dominated by Bacterosira bathyomphala and Thalassionema nitzschioides during the 1800s to a community dominated by Detonula confervacea, T nitzschioides, and Thalassiosira spp. after 1930. Silicoflagellates were more abundant after 1940. Planktonic variations corresponded to oscillations in climate, hydrography, and weather, which determine water column stability in the fjord. The tychopelagic species, Paralia sulcata, was more abundant in unlaminated sections of the core, indicating preference for a vertically mixed water column. No direct effects of increased nutrient loading on the plankton could be established. Epiphytic diatoms show a period of decline from the 1950s to 1990s. This trend probably follows a shift in the macroalgal community, to less-suitable host species. To what extent this pattern has been influenced or reinforced by humans cannot be deter-mined at the present time. The results from Koljo Fjord, in particular the exploration of meteorological and physical oceanographic influences on algal dynamics, emphasize the importance of distinguishing between natural and human-induced changes in the environment.
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| 4. |
- Petersson, Mona, et al.
(författare)
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Vertical sediment fluxes and wave induced sediment resuspension in a shallow water coastal lagoon
- 1999
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Ingår i: Estuaries. - : Springer Science and Business Media LLC. - 1559-2723 .- 0160-8347. ; 22:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- The present study describes variations in the vertical fluxes measured concurrently with sediment traps at both a shallow water (4 m) and a deeper water (7.5 m) position in a coastal lagoon in April 1995. A tripod equipped with five sediment traps (trap openings at 0.35 m, 0.75 m, 1.05 m, 1.40 m, and 1.80 m above the seabed) was placed at the shallow water position. This tripod was deployed three times during the study period and deployment periods varied between 2 d and 5 d, The second sediment trap, placed at the deep water position in the central part of the lagoon, measured vertical flux for intervals of 12 h at 1.4 m above the seabed. The horizontal distance between the sediment traps was 8 km. The average maximum vertical flux at the shallow water position reached 27.9 g m(-2) d(-1) during a period of high, westerly wind speeds, and a maximum vertical flux of 16.9 g m(-2) d(-1) was reached at the deep water position during a period of high, easterly wind speeds. Both strong resuspension events were closely related to increased wave shear stress derived from surface waves. Maximum wave-induced resuspension rate was 10 times higher at the shallow water position and 3.8 times higher at the deep water position compared with the net sedimentation rate in the lagoon. Small resuspension events occurred at the shallow water position during periods of increased current shear stress. Estimations of conditions for transport of sediment between shallow water and deep water showed that particles must be resuspended to a height between 3 m and 4 m and that current speeds must be higher than about 0.1 m s(-1). An average sedimentation rate of 3.8 g m(-2) d(-1) was obtained at the shallow water position during a period without wave shear stress and low current shear stress. This rate measured by sediment traps is similar to a net sedimentation rate in the lagoon of 4.4 g m(-2) d(-1), which was determined by radiocarbon dating of a sediment core (Kristensen et al. 1995).
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| 5. |
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| 6. |
- Wulff, Angela, 1963, et al.
(författare)
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Effect of sediment load on the microbenthic community of a shallow-water sandy sediment
- 1997
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Ingår i: Estuaries. - 0160-8347. ; 20:3, s. 547-558
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic activities, such as construction work, dredging, and different kinds of recreation activities, can alter sediment loading in shallow coastal areas. The effect of increased load of fine sediment on the microbenthos (benthic microalgae, bacteria, and meiofauna) was studied in two experiments using undisturbed cores of a sandy sediment from a microtidal bay on the Swedish west coast. In each experiment, a total of 24 cores were incubated in an outdoor flow-through set-up. Twelve cores were treated with a 2.5-mm thick layer of autoclaved fine-grained, (silt) carbon-rich surface sediment. In the first experiment, estimates of the impact were based on measurements of chlorophyll alpha, biomass of microalgae, bacteria, and meiofauna, and bacterial production. The main purpose of the second experiment was to study the effect on sediment oxygen profiles using microsensors. Within a week, after being covered by fine sediment, benthic microalgae (particularly diatoms) had migrated upward and the oxygen profiles were restored at the sediment surface by photosynthesis. However, the oxygen-producing layer became thinner and the algal composition changed. Bacterial biomass was restored to the same level as in the sandy sediment. Meiofauna also appeared to move upward and the meiofaunal composition was reestablished. The results suggest that the microbenthic community of sandy sediment has an inherent capacity to recover after a moderate deposition of fine-particle sediment. Active upward migration of benthic diatoms appears to be a key mechanism for restoring the oxygenation of the sediment surface. The altered sediment type also implies changed species composition, and hence altered benthic trophic interactions, which may affect, for example, flatfish recruitment.
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