| 1. |
- Filipsson, Helena L., 1973, et al.
(författare)
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A 200-year environmental record of a low-oxygen fjord, Sweden, elucidated by benthic foraminifera, sediment characteristics and hydrographic data
- 2004
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Ingår i: Journal of Foraminiferal Research. - 0096-1191. ; 34:4, s. 277-293
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we have detailed the benthic environment of a sill fjord on the Swedish west coast, which is characterized by brackish conditions, intermittent water exchanges, and periodic low oxygen. We have used three important tools-benthic foraminifera, sediment characteristics, and historical records of hydrographic data. Periods of low oxygen have resulted in sequences of laminated sediments in the fjord. The foraminiferal fauna present in the fjord is of low diversity and low abundance, mostly Elphidium species-an assemblage that has dominated the foraminiferal fauna for at least 170 years. During this time period, however, there have been events when normal marine species have been introduced, or foraminiferal abundance and faunal diversity have suddenly increased. These events are linked to short sequences of homogenous sediments within the laminated sequences that, in turn, suggest more oxic conditions. Since the late 1940s, we have a more-or-less continuous salinity record from the fjord, the product of an instrumental monitoring program. This record has been used, together with the foraminiferal distribution and sediment characteristics, to reconstruct the salinity variations that occurred prior to the instrumental monitoring program. The salinity in the fjord has alternated between periods of low salinity (26-28.5%), which correspond with non-laminated sediments, and periods of higher salinity (>28.5%), corresponding with laminated sequences. Despite a general low abundance of foraminiferal fauna, there was a significantly higher diversity during deposition of laminated sequences than non-laminated sequences. In the deepest part of the record, corresponding to the late eighteenth and early nineteenth century, a different fauna occurs, where species in addition to Elphidium occur, suggesting generally higher salinities (29-31).
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| 2. |
- 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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| 3. |
- Filipsson, Helena L., 1973, et al.
(författare)
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Seasonal study of delta O-18 and delta C-13 in living (stained) benthic foraminifera from two Swedish fjords
- 2004
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Ingår i: Marine Micropaleontology. - : Elsevier BV. - 0377-8398. ; 53:1-2, s. 159-172
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Tidskriftsartikel (refereegranskat)abstract
- In a previous 16-month seasonal study on living (stained) benthic foraminifera from two fjords on the Swedish west coast, it was reported that foraminifera proliferated in response to phytodetritus input; the strongest response came from the opportunistic species Stainforthia fusiformis. In this study, our objective was to find out if that phytodetritus input resulted in a change in the carbon isotopic composition of the foraminiferal tests. We also wanted to examine if variations in salinity and temperature (due to seasonality or deep-water exchanges) were reflected in the delta(18)O values. From S. fusiformis that were obtained from the Havstens Fjord (20 m) and the Gullmar Fjord (119 m) during the 16-month study, we developed a time series of delta(18)O and delta(13)C. After the spring blooms in the Havstens and the Gullmar Fjord, decreases of about 0.2parts per thousand to 0.3parts per thousand in the foraminiferal delta(13)C values were noted; in the Gullmar Fjord after the autumn blooms, decreases of the same order were also noted. Comparing the Havstens and the Gullmar Fjord, we found a 1parts per thousand difference in both delta(13)C and delta(18)O; we attribute this to hydrographic differences between the two fjords. Using calculated values of delta(18)O, together with the measured ones, we noticed that S. fusiformis in the Gullmar Fjord seems to calcify close to equilibrium with respect to the oxygen isotopes. During autumn, water temperatures were relatively high in the Havstens Fjord, and foraminiferal abundance in the fjord was also high after a phytodetritus input; but, the measured delta(18)O values do not reflect these higher temperatures. This apparently contradictory combination of results might be explained by a varying delta(18)O composition of the water during the year, which counterbalances the temperature effect. (C) 2004 Published by Elsevier B.V.
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| 4. |
- Harland, Rex, et al.
(författare)
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A high-resolution dinoflagellate cyst record from latest Holocene sediments in Koljo Fjord, Sweden
- 2004
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Ingår i: Review of Palaeobotany and Palynology. - 0034-6667. ; 128:1-2, s. 119-141
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Tidskriftsartikel (refereegranskat)abstract
- A high-resolution dinoflagellate cyst record is detailed for the very latest Holocene sediments preserved in a silled fjord from western Sweden. Koljo Fjord is characterised by brackish water conditions together with intermittent deep-water renewal and oxygen depletion. The data provide information derived from the phytoplankton populations living in the surface waters, including possible changes to the nutrient availability and salinity regimes using an actualistic ecological approach. The cyst record provides evidence that the dinoflagellate populations within the surface waters of the fjord over the last 155 years or so have fluctuated markedly. The dinoflagellate cyst record from Core KG1A demonstrates a 10-fold increase in both total cyst numbers and Lingulodinium polyedrum since c. 1938, and a shift from assemblages with high Pentapharsodinium dalei to those with high L. polyedrum and Protoceratium reticulatum from about 1980. These fluctuations are singly and/or collectively indicative of possible cultural changes within the fjord; the effects of the North Atlantic Oscillation on both deep-water renewal and seasonality; nutrient enhancement (eutrophication?); and increased water column stability. (C) 2003 Elsevier B.V. All rights reserved.
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| 5. |
- Harland, Rex, et al.
(författare)
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The seasonal occurrence of dinoflagellate cysts in surface sediments from Koljo Fjord, west coast of Sweden - a note
- 2004
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Ingår i: Review of Palaeobotany and Palynology. - 0034-6667. ; 128:1-2, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- The opportunistic collection of the flocculent layer, over the spring to late summer seasons, has provided information on the seasonal dinoflagellate cyst sedimentation in Koljo Fjord, on the west coast of Sweden. The dinoflagellate cyst assemblages within the flocculent layer can be both diverse and contain many cysts. The cyst assemblages do not remain constant over time but demonstrate seasonality. Our very limited dataset of six samples suggests that the spring bloom is characterised by round, brown Protoperidinium cysts together with subsidiary Pentapharsodinium dalei and Protoperidinium conicum. The early summer assemblage differs in containing higher proportions of P. dalei with fewer round, brown Protoperidinium cysts together with relatively minor amounts of Lingulodinium polyedrum and Polykrikos schwartzii. The late summer cyst flora is co-dominated by Lingulodinium polyedrum and round, brown Protoperidinium cysts, together with minor amounts of P. dalei and Spiniferites spp. including Spiniferites bentorii. Cyst production within the different species occurs at times of the year when the surface water conditions within the fjord are suitable. This probably reflects, all or in part, the stability of the upper water column, the relative availability of nutrients and the overall phytoplankton productivity. (C) 2004 Elsevier B.V. All rights reserved.
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