The possibility of applying absolute dating techniques to annual growth increments from the hard ... more The possibility of applying absolute dating techniques to annual growth increments from the hard parts of aquatic animals was examined. This was done using the theory of cross-dating, which was adopted from dendrochronological principles. Using two mollusc species as examples, the practical issues of the method were demonstrated. Empirical data were used to evaluate the different time series analysis techniques as follows. Biological growth trends were first captured from original time series using cubic splines. Dimensionless growth indices were obtained by extracting the observed growth values from the values of spline curves as ratios. The common growth signal among the index series was quantified visually and statistically. In statistical analysis, correlations between all possible pairs of indexed sample series and, alternatively, between sample series and master chronology (the average of all other remaining time series) were calculated. It was demonstrated that sample-master correlations were consistently higher than sample-sample correlations. Sclerochronologically cross-dated time series were proved to provide absolute dating of high-resolution proxy records that assessed environmental change in marine and freshwater settings. The wider applicability of the associated techniques is discussed, and it is suggested that use of the term 'sclerochronology' be restricted to refer only to material or studies for which careful cross-dating has been successfully applied.
Freshwater bivalves, Margaritifera margaritifera (Linnaeus) and Unio crassus (Philipsson), from r... more Freshwater bivalves, Margaritifera margaritifera (Linnaeus) and Unio crassus (Philipsson), from rivers in Sweden (79 specimens) and England (one specimen) were used to study the effects of human-induced pollution on shell growth . We analyzed variations in annual and daily shell growth rates of 80 specimens from unpolluted and polluted (pH b 5, oxygen depletion and eutrophication) localities. 35% of the variability in annual growth of shells from unpolluted rivers is explained by ambient temperature during June through August. Daily shell growth also co-varies with the temperature during the growth season (approximately April-October). Long-term trends in temperature and growth compare well to each other. A weak correlation was also found for shell growth and the summer North Atlantic Oscillation (NAO) index. However, all of these environmental signals are obscured in specimens from polluted settings. In settings with high human impact, shell growth does not co-vary with summer temperatures or the NAO. Results of our study suggest a judicious sampling strategy when shells are used for climate reconstructions. D
Zeitschrift Der Deutschen Gesellschaft Fur Geowissenschaften, 2005
ABSTRACT We present a revised, more robust summer (June–August) air temperature proxy record from... more ABSTRACT We present a revised, more robust summer (June–August) air temperature proxy record from variations in annual shell growth rates of the freshwater pearl mussel Margaritifera margaritifera (L.). Shell oxygen isotope profiles resemble the temperature range of about 7 to 8°C during the growing season and confirm the annual periodicity of shell formation. Based on similar growth patterns, 60 contemporaneous specimens (individual ages ranging from ten to 127 years) with overlapping life-spans were assembled to form a 216-year master chronology (AD 1777–1992). Age-detrended, standardized and pre-whitened annual growth rates and air temperature (river water temperature during summer closely coincides with air temperature) exhibit a significant positive correlation (R2 = 0.60, p <0.0001) and high running similarity confirming previous experimental findings. A linear growth-temperature model can reconstruct summer air temperature from annual shell growth increments with a precision error of better than ± 0.95°C (p <0.05) and verify dendrochronological reconstructions. Proxy (shells, trees) and available observational summer air temperature records from Scandinavia do not resemble the global surface temperature rise over the last 140 years. However, in Scandinavia, extremely cold summers occurred less frequently after ca. 1930 than before.Freshwater pearl mussels provide an independent measure for temperature changes in the pre-instrumental era capable of verifying and complementing other proxy archives.
It was generally assumed (e.g., Mutvei, 1967, 1975; Grégoire, 1984; Westermann, 1971, 1982, 1993,... more It was generally assumed (e.g., Mutvei, 1967, 1975; Grégoire, 1984; Westermann, 1971, 1982, 1993, 1996; Bandel, 1981; Obata et al., 1980; Tanabe, 1977, 1979; Hewitt et al., 1993; Kulicki, 1994; Hewitt, 1996) that the connecting ring in prosiphonate ammonoids, in which the septal necks are directed adorally, had similar structure and composition as that in the retrosiphonate Recent Nautilus, in which the septal necks are directed adapically, and in which the bathymetry is well known. Based on this assumption, Westermann (1971) calculated the mechanical strength of the ammonoid siphuncle against hydrostatic pressure (siphuncular strength index) from the siphuncular wall thickness, multiplied by 100 and divided by the siphuncle inner radius. This index was thought to indicate the maximum water depth where ammonoid shell imploded and, hence, the maximum habitat depth of the animal.
The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in t... more The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in the gastropod Gibbula shell. Etching with Mutvei’s solution reveals that each tablet is composed of vertical crystalline columns that are structurally similar to the acicular crystallites in the outer spherulitic-prismatic layer of the shell wall. The columns are attached to each other to form numerous vertical crystalline lamellae, oriented parallel to the longitudinal axis of the tablet. It is still unknown whether or not the orientation of the vertical lamellae corresponds to that of the crystallographic a- or b-axis. The orientation of the crystalline lamellae in the adjacent tablets is parallel in some nacreous laminae, but random in other laminae. Similar large variation was found in the nacreous tablets of the gastropod and bivalve shells. The nucleation sites of the nacreous tablets are predominantly situated on the peripheral portion of the upper surface of the preceding tablet, both in the shell wall and septa. The “aragonite-nucleating proteins” in the central portion of the crystal imprints of the organic interlamellar sheets, described by several writers, have therefore a negative correlation with the nucleation sites of the nacreous tablets. Die Perlmutt-Tafeln in der Schale von Nautilus haben eine ähnliche kristalline Struktur wie jene in der Schale der Gastropode Gibbula. Anätzung mit Mutvei-Lösung zeigt, dass jede Tafel aus vertikalen kristallinen Säulen besteht, die strukturell den nadelförmigen Kristallen in der äußeren spherulitisch-prismatischen Lage der Schale ähneln. Die Säulen sind miteinander verbunden und bilden so zahlreiche, vertikale kristalline Lamellen, die parallel zu der Längsachse der Tafel angeordnet sind. Es ist noch unbekannt, ob die Orientation der vertikalen Lamellen der kristallographischen a- oder b-Achse entspricht. Die Orientation der kristallinen Lamellen in angrenzenden Tafeln ist parallel in einigen Perlmutt-Tafeln, aber zufällig in anderen. Eine ähnliche Variation wurde bei den Perlmutt-Tafeln der Schalen von Gastropoden und Bivalven beobachtet. Der Ursprungspunkt der Perlmutt-Tafeln liegt überwiegend im randlichen Bereich der Oberfläche der vorhergehenden Tafel, sowohl in der Wand der Schale, als auch in den Septen. Die „Aragonit-Ursprungs-Proteine" im zentralen Bereich der kristallinen Abdrücke auf den organischen interlamellären Lagen, die von verschiedenen Autoren beschrieben wurden, zeigen somit eine negative Korrelation mit dem Ursprungsort der Perlmutt-Tafeln.
The nacreous tablets in gastropods and the cephalopodNautilus are composed of three calcareous la... more The nacreous tablets in gastropods and the cephalopodNautilus are composed of three calcareous layers: a principal, thick, finely granular layer and two thin, coarse-granular layers, one covering the upper surface of the principal layer and another the lower surface of this layer. The granules on the surface layers inNautilus differ from those in gastropods by their much more elongated shape and larger size. The central portion of the nacreous tablet of gastropods andNautilus is more or less elevated forming the central elevation. The granules on this portion usually are larger, irregularly shaped and more crowded than on the main, peripheral portion of the tablet. The untreated, dry interlamellar organic sheets on upper surfaces of immature nacreous tablets are uncalcified and elastic. Narrow thicker parts of the sheet, the trabeculae, Surround large intertrabecular spaces where the sheet is thin. In places it can be observed that each calcareous granula on the surface layer of the nacreous tablet is situated within the intertrabecular space. The size, shape and distribution of the intertrabecular Spaces correspond those of the surface granules. No mineral bridges were observed between the consecutive nacreous tablets. Die Perlmutt-Tafeln in der Schale von Gastropoden und dem CephalopodenNautilus bestehen aus drei kalkigen Lagen, einer dicken, fein-granularen Hauptlage und zwei dünnen grob-granularen Lagen, von denen eine die äußere Oberfläche, die andere die innere Oberfläche der Hauptlage bedeckt. Die Körner der Decklagen beiNautilus unterscheiden sich von denen der Gastropoden durch ihre starke Verlängerung und Größe. Der zentrale Bereich der Perlmutt-Tafeln von Gastropoden undNautilus ist mehr oder weniger aufgewölbt und bildet die zentrale Wölbung. Normalerweise sind die Körner in diesem Bereich größer, unregelmäßig geformt und dichter gedrängt als im peripheren Bereich der Tafel. Die unbehandelten, trockenen interlamellaren organischen Lagen auf der äußeren Oberfläche von immaturen Perlmutt-Tafeln sind unverkalkt und elastisch. Schmale dickere Bereiche der Lagen, die Trabeculae, umgeben große intertrabeculäre Bereiche, in denen die Lagen dünn bleiben. An einigen Stellen zeigt sich, dass jedes kalkige Korn der Oberflächen-Lage einer Perlmutt-Tafel innerhalb des intertrabeculären Bereichs liegt. Größe, Form und Verteilung der intertrabeculären Räume entsprechen denen der Oberflächen-Körner. Zwischen aufeinander folgenden Perlmutt-Tafeln wurden keine Mineral-Brücken beobachtet.
Existing reconstructions of the winter North Atlantic Oscillation (WNAO) are based on terrestrial... more Existing reconstructions of the winter North Atlantic Oscillation (WNAO) are based on terrestrial proxies and historical documents. No direct high-resolution, long-term rec ords from marine settings are available for this major climate-dictating phenomenon, which severely affects a variety of economic aspects of our society. Here we present a 245 yr proxy WNAO index based on shells of the long-lived marine bivalve mollusk Arctica islandica</em>. Variations in annual rates of shell growth are positively correlated with WNAO-related changes in the food supply. Maximum amplitudes in frequency bands of 7 9 and 5 7 yr fall exactly within the range of instrumental and other proxy WNAO indices. These estimates were obtained for specimens collected live, 2000 km apart, in the central North Sea and on the Norwegian Shelf. Hence, the WNAO influences hydrographic regimes of large regions of the ocean. Our study demonstrates that A. islandica</em> can reliably reconstruct WNAO dynamics for time intervals and regions without instrumental records. Our new tool functions as a proxy for the WNAO index prior to the twentieth-century greenhouse forcing and has the potential to further validate other proxy-based WNAO records.
Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak ... more Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak (Swedish West Coast) were used to monitor local climate variations and the influence of human activities on the local environment. For this purpose, we analysed the growth, structure and chemical composition of these shells and compared them with shells collected from Kiel Bay, Norway and Iceland. The growth rate of the studied shells registers an NAO periodicity of ca 8 years. However, the observed signal is weak because of other environmental interferences that are either of natural or anthropogenic origin. For example, the oxygen isotope ratios show temperature fluctuation, but also the influx of low salinity water. Higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are related to human activities such as mining and industrial development. Our study indicates that in order to use Arctica shells as archives of climate change it is necessary to study the full range of environmental data that is recorded in the shells by using a multi element and isotope approach in combination with different analytical techniques including investigation of growth rates and shell structure.
Accretionary hard parts of many organisms provide excellent archives of past climate and environm... more Accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits. Variable growth rates function as environmental and physiological proxies, and growth increments as calendars. Recognition of growth structures is thus a prime necessity for sclerochronological studies. Here we present a new, handy, easyto-use and time-efficient technique that resolves annual and sub-annual growth structures in skeletons of a wide range of different organisms. Mutvei's solution simultaneously etches biogenic carbonates and calcium phosphates, fixates the soluble and insoluble organic matrices and fibers, and stains mucopolysaccharides. It produces a filigreed three-dimensional relief of etch-resistant ridges (growth lines) and etched depressions (growth increments) and stains skeletal growth structures in shadings of blue. Growth lines stand out as crisp, darker-blue stained lines. Reflected optical light microscopy (axial and oblique illumination) and scanning electron microscopy can be used to analyze the microgrowth structures. We demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves, a coral, a sclerosponge, a barnacle, gastropods, a cephalopod, a fish otolith and a whale's ear bone. This technique may be of interest for paleoclimatologists, geochemists and biologists. It can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars. D
Abstract: Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have rest... more Abstract: Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have restudied their siphuncular structure, first described some 20 years ago. The siphuncle is characterized by: (1) long and holochoanitic septal necks dorsally but short and recurved necks laterally and ventrally; (2) strongly expanded connecting rings laterally; (3) two calcified layers in each connecting ring, outer spherulitic-prismatic and inner compact, the latter perforated by numerous pore canals; and (4) highly oblique siphuncular segments. The strongly expanded lateral sides of the connecting rings, together with the highly oblique course of the siphuncular segments, considerably enlarged the surface area of the connecting rings in each chamber, thereby increasing the transport capacity of cameral liquid. Thus, from their first appearance, plectronocerid nautiloids had developed a siphuncle for the replacement of cameral liquid with gases, and this system had a better and a more sophisticated design than that seen in stratigraphically younger nautiloids. However, their small orthoconic or slightly cyrtoconic shells were not well adapted for jet-powered swimming.
A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. marga... more A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. margarifitera, Sweden) Abstract Variations in annual shell growth of the freshwater pearl mussel Margritifera margritifera (L.) were utilized to reconstruct summer (June-August) air temperatures for each year over the period AD 1777-1993. Our study is based on 60 live-collected specimens with overlapping life-spans from six different Swedish rivers. Individual age-detrended and standardized chronologies ranging from 10 to 127 years in length were strung together to form one master chronology (AD 1777-1993) and three regional mean chronologies (Stensele, Uppsala, and Karlshamn). Standardized annual growth rates and air temperature (river water covaries with water temperature) exhibit a significant positive correlation and high running similarity confirming previous experimental findings. Up to 55% in the variability of annual shell growth is explained by temperature changes. From north to south this correlation slightly decreases. We establish a growth-temperature model capable of reconstructing summer air temperature from annual shell growth increments with a precision error of 70.6-0.9 C (2SD). The validity of the model was tested against instrumentally determined air temperatures and proxy temperatures derived from tree rings.
In most of the European countries there are general efforts to improve the environmental conditio... more In most of the European countries there are general efforts to improve the environmental conditions necessary for the regeneration of existing populations of the freshwater pearl mussel, Margaritifera margaritifera. In order to create sustainable conservation strategies it is important to have a scientific background for the biology of this species.
The possibility of applying absolute dating techniques to annual growth increments from the hard ... more The possibility of applying absolute dating techniques to annual growth increments from the hard parts of aquatic animals was examined. This was done using the theory of cross-dating, which was adopted from dendrochronological principles. Using two mollusc species as examples, the practical issues of the method were demonstrated. Empirical data were used to evaluate the different time series analysis techniques as follows. Biological growth trends were first captured from original time series using cubic splines. Dimensionless growth indices were obtained by extracting the observed growth values from the values of spline curves as ratios. The common growth signal among the index series was quantified visually and statistically. In statistical analysis, correlations between all possible pairs of indexed sample series and, alternatively, between sample series and master chronology (the average of all other remaining time series) were calculated. It was demonstrated that sample-master correlations were consistently higher than sample-sample correlations. Sclerochronologically cross-dated time series were proved to provide absolute dating of high-resolution proxy records that assessed environmental change in marine and freshwater settings. The wider applicability of the associated techniques is discussed, and it is suggested that use of the term 'sclerochronology' be restricted to refer only to material or studies for which careful cross-dating has been successfully applied.
Freshwater bivalves, Margaritifera margaritifera (Linnaeus) and Unio crassus (Philipsson), from r... more Freshwater bivalves, Margaritifera margaritifera (Linnaeus) and Unio crassus (Philipsson), from rivers in Sweden (79 specimens) and England (one specimen) were used to study the effects of human-induced pollution on shell growth . We analyzed variations in annual and daily shell growth rates of 80 specimens from unpolluted and polluted (pH b 5, oxygen depletion and eutrophication) localities. 35% of the variability in annual growth of shells from unpolluted rivers is explained by ambient temperature during June through August. Daily shell growth also co-varies with the temperature during the growth season (approximately April-October). Long-term trends in temperature and growth compare well to each other. A weak correlation was also found for shell growth and the summer North Atlantic Oscillation (NAO) index. However, all of these environmental signals are obscured in specimens from polluted settings. In settings with high human impact, shell growth does not co-vary with summer temperatures or the NAO. Results of our study suggest a judicious sampling strategy when shells are used for climate reconstructions. D
Zeitschrift Der Deutschen Gesellschaft Fur Geowissenschaften, 2005
ABSTRACT We present a revised, more robust summer (June–August) air temperature proxy record from... more ABSTRACT We present a revised, more robust summer (June–August) air temperature proxy record from variations in annual shell growth rates of the freshwater pearl mussel Margaritifera margaritifera (L.). Shell oxygen isotope profiles resemble the temperature range of about 7 to 8°C during the growing season and confirm the annual periodicity of shell formation. Based on similar growth patterns, 60 contemporaneous specimens (individual ages ranging from ten to 127 years) with overlapping life-spans were assembled to form a 216-year master chronology (AD 1777–1992). Age-detrended, standardized and pre-whitened annual growth rates and air temperature (river water temperature during summer closely coincides with air temperature) exhibit a significant positive correlation (R2 = 0.60, p &lt;0.0001) and high running similarity confirming previous experimental findings. A linear growth-temperature model can reconstruct summer air temperature from annual shell growth increments with a precision error of better than ± 0.95°C (p &lt;0.05) and verify dendrochronological reconstructions. Proxy (shells, trees) and available observational summer air temperature records from Scandinavia do not resemble the global surface temperature rise over the last 140 years. However, in Scandinavia, extremely cold summers occurred less frequently after ca. 1930 than before.Freshwater pearl mussels provide an independent measure for temperature changes in the pre-instrumental era capable of verifying and complementing other proxy archives.
It was generally assumed (e.g., Mutvei, 1967, 1975; Grégoire, 1984; Westermann, 1971, 1982, 1993,... more It was generally assumed (e.g., Mutvei, 1967, 1975; Grégoire, 1984; Westermann, 1971, 1982, 1993, 1996; Bandel, 1981; Obata et al., 1980; Tanabe, 1977, 1979; Hewitt et al., 1993; Kulicki, 1994; Hewitt, 1996) that the connecting ring in prosiphonate ammonoids, in which the septal necks are directed adorally, had similar structure and composition as that in the retrosiphonate Recent Nautilus, in which the septal necks are directed adapically, and in which the bathymetry is well known. Based on this assumption, Westermann (1971) calculated the mechanical strength of the ammonoid siphuncle against hydrostatic pressure (siphuncular strength index) from the siphuncular wall thickness, multiplied by 100 and divided by the siphuncle inner radius. This index was thought to indicate the maximum water depth where ammonoid shell imploded and, hence, the maximum habitat depth of the animal.
The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in t... more The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in the gastropod Gibbula shell. Etching with Mutvei’s solution reveals that each tablet is composed of vertical crystalline columns that are structurally similar to the acicular crystallites in the outer spherulitic-prismatic layer of the shell wall. The columns are attached to each other to form numerous vertical crystalline lamellae, oriented parallel to the longitudinal axis of the tablet. It is still unknown whether or not the orientation of the vertical lamellae corresponds to that of the crystallographic a- or b-axis. The orientation of the crystalline lamellae in the adjacent tablets is parallel in some nacreous laminae, but random in other laminae. Similar large variation was found in the nacreous tablets of the gastropod and bivalve shells. The nucleation sites of the nacreous tablets are predominantly situated on the peripheral portion of the upper surface of the preceding tablet, both in the shell wall and septa. The “aragonite-nucleating proteins” in the central portion of the crystal imprints of the organic interlamellar sheets, described by several writers, have therefore a negative correlation with the nucleation sites of the nacreous tablets. Die Perlmutt-Tafeln in der Schale von Nautilus haben eine ähnliche kristalline Struktur wie jene in der Schale der Gastropode Gibbula. Anätzung mit Mutvei-Lösung zeigt, dass jede Tafel aus vertikalen kristallinen Säulen besteht, die strukturell den nadelförmigen Kristallen in der äußeren spherulitisch-prismatischen Lage der Schale ähneln. Die Säulen sind miteinander verbunden und bilden so zahlreiche, vertikale kristalline Lamellen, die parallel zu der Längsachse der Tafel angeordnet sind. Es ist noch unbekannt, ob die Orientation der vertikalen Lamellen der kristallographischen a- oder b-Achse entspricht. Die Orientation der kristallinen Lamellen in angrenzenden Tafeln ist parallel in einigen Perlmutt-Tafeln, aber zufällig in anderen. Eine ähnliche Variation wurde bei den Perlmutt-Tafeln der Schalen von Gastropoden und Bivalven beobachtet. Der Ursprungspunkt der Perlmutt-Tafeln liegt überwiegend im randlichen Bereich der Oberfläche der vorhergehenden Tafel, sowohl in der Wand der Schale, als auch in den Septen. Die „Aragonit-Ursprungs-Proteine" im zentralen Bereich der kristallinen Abdrücke auf den organischen interlamellären Lagen, die von verschiedenen Autoren beschrieben wurden, zeigen somit eine negative Korrelation mit dem Ursprungsort der Perlmutt-Tafeln.
The nacreous tablets in gastropods and the cephalopodNautilus are composed of three calcareous la... more The nacreous tablets in gastropods and the cephalopodNautilus are composed of three calcareous layers: a principal, thick, finely granular layer and two thin, coarse-granular layers, one covering the upper surface of the principal layer and another the lower surface of this layer. The granules on the surface layers inNautilus differ from those in gastropods by their much more elongated shape and larger size. The central portion of the nacreous tablet of gastropods andNautilus is more or less elevated forming the central elevation. The granules on this portion usually are larger, irregularly shaped and more crowded than on the main, peripheral portion of the tablet. The untreated, dry interlamellar organic sheets on upper surfaces of immature nacreous tablets are uncalcified and elastic. Narrow thicker parts of the sheet, the trabeculae, Surround large intertrabecular spaces where the sheet is thin. In places it can be observed that each calcareous granula on the surface layer of the nacreous tablet is situated within the intertrabecular space. The size, shape and distribution of the intertrabecular Spaces correspond those of the surface granules. No mineral bridges were observed between the consecutive nacreous tablets. Die Perlmutt-Tafeln in der Schale von Gastropoden und dem CephalopodenNautilus bestehen aus drei kalkigen Lagen, einer dicken, fein-granularen Hauptlage und zwei dünnen grob-granularen Lagen, von denen eine die äußere Oberfläche, die andere die innere Oberfläche der Hauptlage bedeckt. Die Körner der Decklagen beiNautilus unterscheiden sich von denen der Gastropoden durch ihre starke Verlängerung und Größe. Der zentrale Bereich der Perlmutt-Tafeln von Gastropoden undNautilus ist mehr oder weniger aufgewölbt und bildet die zentrale Wölbung. Normalerweise sind die Körner in diesem Bereich größer, unregelmäßig geformt und dichter gedrängt als im peripheren Bereich der Tafel. Die unbehandelten, trockenen interlamellaren organischen Lagen auf der äußeren Oberfläche von immaturen Perlmutt-Tafeln sind unverkalkt und elastisch. Schmale dickere Bereiche der Lagen, die Trabeculae, umgeben große intertrabeculäre Bereiche, in denen die Lagen dünn bleiben. An einigen Stellen zeigt sich, dass jedes kalkige Korn der Oberflächen-Lage einer Perlmutt-Tafel innerhalb des intertrabeculären Bereichs liegt. Größe, Form und Verteilung der intertrabeculären Räume entsprechen denen der Oberflächen-Körner. Zwischen aufeinander folgenden Perlmutt-Tafeln wurden keine Mineral-Brücken beobachtet.
Existing reconstructions of the winter North Atlantic Oscillation (WNAO) are based on terrestrial... more Existing reconstructions of the winter North Atlantic Oscillation (WNAO) are based on terrestrial proxies and historical documents. No direct high-resolution, long-term rec ords from marine settings are available for this major climate-dictating phenomenon, which severely affects a variety of economic aspects of our society. Here we present a 245 yr proxy WNAO index based on shells of the long-lived marine bivalve mollusk Arctica islandica</em>. Variations in annual rates of shell growth are positively correlated with WNAO-related changes in the food supply. Maximum amplitudes in frequency bands of 7 9 and 5 7 yr fall exactly within the range of instrumental and other proxy WNAO indices. These estimates were obtained for specimens collected live, 2000 km apart, in the central North Sea and on the Norwegian Shelf. Hence, the WNAO influences hydrographic regimes of large regions of the ocean. Our study demonstrates that A. islandica</em> can reliably reconstruct WNAO dynamics for time intervals and regions without instrumental records. Our new tool functions as a proxy for the WNAO index prior to the twentieth-century greenhouse forcing and has the potential to further validate other proxy-based WNAO records.
Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak ... more Shells of Arctica islandica collected between 1884 and 2004 from Öresund, Kattegat and Skagerrak (Swedish West Coast) were used to monitor local climate variations and the influence of human activities on the local environment. For this purpose, we analysed the growth, structure and chemical composition of these shells and compared them with shells collected from Kiel Bay, Norway and Iceland. The growth rate of the studied shells registers an NAO periodicity of ca 8 years. However, the observed signal is weak because of other environmental interferences that are either of natural or anthropogenic origin. For example, the oxygen isotope ratios show temperature fluctuation, but also the influx of low salinity water. Higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are related to human activities such as mining and industrial development. Our study indicates that in order to use Arctica shells as archives of climate change it is necessary to study the full range of environmental data that is recorded in the shells by using a multi element and isotope approach in combination with different analytical techniques including investigation of growth rates and shell structure.
Accretionary hard parts of many organisms provide excellent archives of past climate and environm... more Accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits. Variable growth rates function as environmental and physiological proxies, and growth increments as calendars. Recognition of growth structures is thus a prime necessity for sclerochronological studies. Here we present a new, handy, easyto-use and time-efficient technique that resolves annual and sub-annual growth structures in skeletons of a wide range of different organisms. Mutvei's solution simultaneously etches biogenic carbonates and calcium phosphates, fixates the soluble and insoluble organic matrices and fibers, and stains mucopolysaccharides. It produces a filigreed three-dimensional relief of etch-resistant ridges (growth lines) and etched depressions (growth increments) and stains skeletal growth structures in shadings of blue. Growth lines stand out as crisp, darker-blue stained lines. Reflected optical light microscopy (axial and oblique illumination) and scanning electron microscopy can be used to analyze the microgrowth structures. We demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves, a coral, a sclerosponge, a barnacle, gastropods, a cephalopod, a fish otolith and a whale's ear bone. This technique may be of interest for paleoclimatologists, geochemists and biologists. It can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars. D
Abstract: Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have rest... more Abstract: Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have restudied their siphuncular structure, first described some 20 years ago. The siphuncle is characterized by: (1) long and holochoanitic septal necks dorsally but short and recurved necks laterally and ventrally; (2) strongly expanded connecting rings laterally; (3) two calcified layers in each connecting ring, outer spherulitic-prismatic and inner compact, the latter perforated by numerous pore canals; and (4) highly oblique siphuncular segments. The strongly expanded lateral sides of the connecting rings, together with the highly oblique course of the siphuncular segments, considerably enlarged the surface area of the connecting rings in each chamber, thereby increasing the transport capacity of cameral liquid. Thus, from their first appearance, plectronocerid nautiloids had developed a siphuncle for the replacement of cameral liquid with gases, and this system had a better and a more sophisticated design than that seen in stratigraphically younger nautiloids. However, their small orthoconic or slightly cyrtoconic shells were not well adapted for jet-powered swimming.
A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. marga... more A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. margarifitera, Sweden) Abstract Variations in annual shell growth of the freshwater pearl mussel Margritifera margritifera (L.) were utilized to reconstruct summer (June-August) air temperatures for each year over the period AD 1777-1993. Our study is based on 60 live-collected specimens with overlapping life-spans from six different Swedish rivers. Individual age-detrended and standardized chronologies ranging from 10 to 127 years in length were strung together to form one master chronology (AD 1777-1993) and three regional mean chronologies (Stensele, Uppsala, and Karlshamn). Standardized annual growth rates and air temperature (river water covaries with water temperature) exhibit a significant positive correlation and high running similarity confirming previous experimental findings. Up to 55% in the variability of annual shell growth is explained by temperature changes. From north to south this correlation slightly decreases. We establish a growth-temperature model capable of reconstructing summer air temperature from annual shell growth increments with a precision error of 70.6-0.9 C (2SD). The validity of the model was tested against instrumentally determined air temperatures and proxy temperatures derived from tree rings.
In most of the European countries there are general efforts to improve the environmental conditio... more In most of the European countries there are general efforts to improve the environmental conditions necessary for the regeneration of existing populations of the freshwater pearl mussel, Margaritifera margaritifera. In order to create sustainable conservation strategies it is important to have a scientific background for the biology of this species.
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Papers by Elena Dunca