Kjell Nordberg

Viability of phytoplankton resting stages in the sediments of a coastal Swedish fjord

Viable diatom and dinoflagellate resting stages were recovered from sediments in Koljö Fjord on the west coast of Sweden. To determine the maximum survival time of buried resting stages, samples from sediment depths down to 50 cm were incubated at temperatures of 3, 10 and 18 °C. Sediment cores were dated by 210Pb and the age of samples containing viable resting stages was determined using the constant rate of supply model. Dilution cultures of surface sediments allowed semiquantitative estimates of the potential seed bank. Dinoflagellate cysts from species such as Diplopsalis sp., Gymnodinium nolleri, Oblea rotunda and Protoceratium reticulatum were viable down to 15 cm depth, or 37 years old. Spores and resting cells of the diatoms Chaetoceros spp., Detonula confervacea and Skeletonema costatum were viable to over 40 cm depth, and may have been buried for many decades. The seed bank of living resting stages in surficial sediments was found to be rich (c. 57000 diatom resting stages g−1 wet weight and c. 200 dinoflagellate cysts g−1 wet weight), and the percentage of viable resting stages was higher for spore- and cyst-forming species. The oxygen-deficient sediments in Koljö Fjord appear to be a natural conservator of cell viability, a condition not easily simulated in laboratory studies. These results are ecologically important since spores and cysts are a repository of genetic material able to repopulate waters if resuspended and exposed to suitable light, temperature and nutrients.

Decreasing oxygen concentrations in the Gullmar Fjord, Sweden, as confirmed by benthic foraminifera, and the possible association with NAO

The deep Gullmar Fjord on the Swedish west coast may be subject to a trend of decreasing oxygen content of the bottom-water. Due to a non-uniform frequency of oxygen measurements before and after 1980, and small differences in the minimum concentrations, it is difficult to assess with certainty if this is true or not. We have used benthic foraminifera from three ultra-high resolution sediment records to try to find out if such a trend exists. The sediment records comprise the time between 1930 and 1996, with an almost year-based temporal resolution. The foraminiferal records show a significant change in faunal composition during the mid-1970s when it altered from a common Skagerrak fauna to an assemblage characterized by an opportunistic, low oxygen tolerant species; Stainforthia fusiformis. This species is an indicator of low oxygen environments of many Scandinavian fjords. The timing of this faunal change coincides with one of the first recorded severe low oxygen events in the Gullmar Fjord in the winter of 1973/1974. The change suggests that the Gullmar Fjord has actually been subject to a decrease in bottom-water oxygen concentrations. The reason for this change is not clear but here, for the first time, we present sediment records that suggest that there is a causal relation between variations in the North Atlantic Oscillation (NAO) indices and the marine environment. In the early 1970s the NAO-indices altered from a mainly negative phase towards a mainly positive period which is still ongoing. Positive NAO-indices (winter values) in the Skagerrak region are generally marked by westerly winds which normally prevent the exchange of bottom-water in the fjords, i.e., the oxygenation of the sea floor and the supply of oxygen to benthic life.

LIVING (STAINED) BENTHIC FORAMINIFERAL RESPONSE TO PRIMARY PRODUCTION AND HYDROGRAPHY IN THE DEEPEST PART OF THE GULLMAR FJORD, SWEDISH WEST COAST, WITH COMPARISONS TO HÖGLUND’S 1927 MATERIAL

Living (stained) benthic foraminifera were studied in the deepest part (116 m) of the classical marine study area, the Gullmar Fjord on the Swedish west coast. This is a silled fjord with a strongly stratified water column where stagnant conditions temporarily develop in the deeper parts. The aim of this study is to determine how the living foraminiferal assemblage develops with seasonal variations in bottom water hydrography and primary production in the surface water. From August 1993 to December 1994, monthly hydrographic and oxygen measurements were made. Parallel undisturbed sediment cores were taken using a Multiple-corer. Foraminifera from the >63 μm fraction were stained with Rose Bengal to separate living from dead specimens. Monthly values of the surface water chlorophyll a content were also available and give a measure of the primary production. During spring 1994 the dominant foraminiferal species, Stainforthia fusiformis, multiplied its population size by seven times during one month as a consequence of food input from the spring phytoplankton bloom. The abundance of this species correlates positively with the surface water chlorophyll a content. Populations of several other species also increased during the spring of 1994. A deep-water inflow in February 1994 may have triggered reproduction of several foraminiferal species, recognized as a temporary population decline. We also compared our results with Hoglund’s (1947) foraminiferal study, performed in the same area in the summer of 1927. We found that a major alteration trending towards a more opportunistic low oxygen tolerant fauna has occurred since then.

Benthic foraminifera and their response to hydrography, periodic hypoxic conditions and primary production in the Koljö fjord on the Swedish west coast

Abstract The Koljo fjord on the Swedish west coast is a silled fjord characterised by strong stratification and stagnant bottom water, with periodically occurring hypoxic or anoxic conditions. In the Koljo fjord, renewal of the deep water generally occurs during winter. This study investigates how living benthic foraminifera react to hydrographic variations, periodic oxygen deficiency and variations in primary production. A series of monthly hydrographic measurements was made from August 1993 to December 1994, combined with sediment sampling along a (12–43 m) depth transect at five different sites. Monthly values of surface chlorophyll-a were available. Two periods of hypoxia to anoxia with one intervening period of oxic conditions, together with two autumn phytoplankton blooms and a spring phytoplankton bloom, made it possible to achieve the aims of this study. Below the pycnocline, three foraminiferal species: Elphidium excavatum clavatum , Elphidium incertum and Elphidium magellanicum represented more than 95% of the fauna. When oxygen content was very low, the foraminiferal fauna decreased but did not die out completely. A deep-water inflow in January 1994 caused the oxygen content to rise, but the foraminiferal population did not start to grow until three months later when the spring phytoplankton bloom sedimented out. Under oxic conditions, food availability seemed to limit the foraminiferal population. In itself, a very high organic content in the sediments does not seem to be a suitable food source; it is more likely that fresh phytoplankton is a potent food for these foraminifera. Reproduction of E. excavatum clavatum and E. incertum seems to have been triggered by increased food supply and sudden fluctuations in hydrographic variables. These foraminifera appear to grow from juvenile to adult in less than a month.

Climate, hydrographic variations and marine benthic hypoxia in Koljö Fjord, Sweden

Abstract Since the late 1970s, Scandinavian waters have been extensively investigated for human-induced marine pollution, especially marine eutrophication, oxygen deficiency in bottom waters and subsequent benthic mortality. The most serious oxygen deficiencies are noted in the sill fjords along the Swedish west coast, in southern Norway and in large areas of the southern Kattegat and Baltic Sea. One of these sill fjords, Koljo Fjord, is located on the Swedish west coast. This fjord is characterised by frequently occurring episodes of hypoxia/anoxia which last for months or even years. Sediments are laminated and the fjord is generally regarded as seriously affected by human-induced eutrophication. We detail the environmental development of a well-documented fjord by combining high resolution sediment records with long hydrographical and meteorological instrumental data, and we present ultra high-resolution sediment information together with long-term instrumental records of air-temperatures, NAO indices and hydrography from Koljo Fjord. These data show, in contrast to the current opinion focusing on anthropogenic eutrophication, that natural causes are the most important factors controlling the marine environment in this sparsely populated area. Natural variables concerned are fjord physiography, weather and hydrography (including the macro-nutrients DIN and PO 4 -P), sediment laminations and organic carbon. Interactions between fjord physiography, weather and hydrography regulate the possibility for water exchange and deep-water renewals. The present study points to the importance of natural causes for the environmental status of sill basins and semi-enclosed areas along the west coast of Sweden.

The seasonal occurrence of dinoflagellate cysts in surface sediments from Koljö Fjord, west coast of Sweden – a note

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.

A high-resolution dinoflagellate cyst record from latest Holocene sediments in Koljö Fjord, Sweden

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.

Climate variations, an overlooked factor influencing the recent marine environment. An example from Gullmar Fjord, Sweden, illustrated by benthic foraminifera and hydrographic data

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 ofS. 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-oxygenevent 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.

Upwelling along the Swedish west coast during the 20th century

Abstract A time series of geostrophic winds from 1892 until present is used to force a simple upwelling model. The model is tuned against a long time series (1930–1989) of daily hydrographic observations at Borno station inside Gullmar fjord at the Swedish west coast. It is shown that a large part of the short-term variability at Borno is controlled by upwelling events that can be predicted from the model. Statistical properties of upwelling events for the entire forcing period are presented as well as time series of upwelling and downwelling. Distinctive feature of the upwelling in the time series are: a declining trend between the late 1890s and 1920, an increasing trend between 1920 and 1940s and another declining trend between 1950s and 1990. After 1990 no trend is obvious. Another feature is that upwelling during summer (May–September) is much less intense after 1963. The up/downwelling is related in a qualitative way to the North Atlantic oscillation index during January–April but there is no correlation during summer. Some possible effects on the coastal marine environment due to long-term changes of the upwelling intensity are discussed.

A 200-YEAR ENVIRONMENTAL RECORD OF A LOW-OXYGEN FJORD, SWEDEN, ELUCIDATED BY BENTHIC FORAMINIFERA, SEDIMENT CHARACTERISTICS AND HYDROGRAPHIC DATA

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).