27 research outputs found
The benthic foraminiferal record of the Medieval Warm Period and the recent warming in the Gullmar Fjord, Swedish west coast
No full textA high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of Pb-210- and AMS C-14-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and delta C-13 values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak-Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences. (C) 2011 Elsevier B.V. All rights reserved
The Gonotrophic-Age Structure of a Population of the \u3ci\u3eSimulium Venustum\u3c/i\u3e Complex (Diptera: Simuliidae) in Algonquin Park, Ontario
No full textEight techniques for the determination of parity and gonotrophic age were assessed for the obligatorily anautogenous blackfly-species complex, Simulium venustum Say. All females could be age-graded by the presence or absence of dilatations on the ovarioles. However, multiple dilatations on a single ovariole were not found and the Polovodova method could not be used to determine the number of completed gonotrophic cycles. Most females could be age-graded by the appearance of the Malpighian tubules, which undergo morphological changes, probably as a result of a bloodmeal. In some cases, the size of the fat body, the presence of retained (relict), mature ova and the presence of meconium in the gut could be used as accessory age-grading criteria. Insemination status, the volume of the esophageal diverticulum, and the stage of development of the terminal ovarian follicles could not be used to age-grade females. The literature of age-grading in blackflies is reviewed, with special reference to the interpretability of the Polovodova method.
Seasonal changes in the gonotrophic-age structure of a population of the S. venustum complex in Algonquin Park, ON, Canada, were examined over two years. The maximal proportion of parous females in the population was 75 and 62% in the two years, respectively. There was weak evidence that parous females were more likely to host seek in the morning and nulliparous females in the afternoon. Parity declined in mid-season, due to the recruitment of newly emerged adults to the population
The benthic foraminiferal community in a naturally CO2-rich coastal habitat in the southwestern Baltic Sea
No full textIt is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwestern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chemistry and the ensuing response of the foraminiferal community with bi-monthly resolution in Flensburg Fjord. In comparison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sediment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 μatm. Nevertheless, in contrast to the bottom water, sediment pore water was slightly supersaturated with respect to calcite as consequence of higher alkalinity (AT) for the most time of the year. Foraminiferal assemblages were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated Ammotium cassis. The one year-cycle was characterized by seasonal community shifts. Our results revealed that there is no dynamic response of foraminiferal population density and diversity to elevated sediment pore water pCO2. Surprisingly, the fluctuations of sediment pore water undersaturation (Ωcalc) co-vary with the population densities of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying specimens were intact. Only Ammonia aomorienis showed dissolution and recalcification structures on the tests, especially at undersaturated conditions. Therefore, the benthic community is subjected to constantly high pCO2 and tolerates elevated levels as long as sediment pore water remains supersaturated. Model calculations inferred that increasing atmospheric CO2 concentrations will finally lead to a perennial undersaturation in sediment pore waters. Whereas benthic foraminifera indeed may cope with a high sediment pore water pCO2, the steady undersaturation of sediment pore waters would likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift may eventually lead to changes in the benthic foraminiferal communities in Flensburg Fjord, as well as in other regions experiencing naturally undersaturated Ωcalc levels
Biometry and dissolution features of the benthic foraminiferal species Ammonia aomoriensis at high pCO2
No full textCulturing experiments were performed with the benthic foraminifer Ammonia aomoriensis from Flensburg Fjord, western Baltic Sea. The experiments simulated a projected rise in atmospheric CO2 concentrations. We exposed specimens to 5 seawater pCO2 levels ranging from 618 µatm (pH 7.9) to 3130 µatm (pH 7.2) for 6 wk. Growth rates and mortality differed significantly among pCO2 treatments. The highest increase of mean test diameter (19%) was observed at 618 µatm. At partial pressures >1829 µatm, the mean test diameter was observed to decrease, by up to 22% at 3130 µatm. At pCO2 levels of 618 and 751 µatm, A. aomoriensis tests were found intact after the experiment. The outer chambers of specimens incubated at 929 and 1829 µatm were severely damaged by corrosion. Visual inspection of specimens incubated at 3130 µatm revealed wall dissolution of all outer chambers, only their inner organic lining stayed intact. Our results demonstrate that pCO2 values of ≥929 µatm in Baltic Sea waters cause reduced growth of A. aomoriensis and lead to shell dissolution. The bottom waters in Flensburg Fjord and adjacent areas regularly experience pCO2 levels in this range during summer and fall. Increasing atmospheric CO2 concentrations are likely to extend and intensify these periods of undersaturation. This may eventually slow down calcification in A. aomoriensis to the extent that net carbonate precipitation terminates. The possible disappearance of this species from the Baltic Sea and other areas prone to seasonal undersaturation would likely cause significant shifts in shallow-water benthic ecosystems in the near future
Multi-proxy study on two sediment cores in western and central Skagerrak
No full textWe present results from two sediment cores from the central (EMB046/20-3GC) and western (EMB046/10-4GC) Skagerrak. Both cores were dated by Hg pollution records and AMS 14C and analysed for palaeoproductivity proxies such as total organic carbon, δ13C, total planktonic foraminifera, benthic foraminifera (total assemblages as well as abundance of Brizalina skagerrakensis and other palaeoproductivity taxa) and palaeothermometers such as Mg/Ca and δ18O. Our results reveal two periods with changes in productivity in the Skagerrak region: i) a moderate productivity at ~ CE 900 – 1700 and ii) a high productivity at ~ CE 1700 – present
Foraminiferal response to environmental changes in Kiel Fjord, SW Baltic Sea
No full textThe living benthic foraminiferal assemblages in Kiel Fjord (SW Baltic Sea) were investigated in the years 2005 and 2006. The faunal studies were accomplished by geochemical analyses of surface sediments. In general, sediment pollution by copper, zinc, tin and lead is assessed as moderate in comparison with levels reported from other areas of the Baltic Sea. However, the inner Kiel Fjord is still exposed to a high load of metals and organic matter due to enhanced accumulation of fine-grained sediments in conjunction with potential pollution sources as shipyards, harbours and intensive traffic. The results of our survey show that the dominant environmental forcing of benthic foraminifera is nutrients availability coupled with human impact. A comparison with faunal data from the 1960s reveals apparent changes in species composition and population densities. The stress-tolerant species Ammonia beccarii invaded Kiel Fjord. Ammotium cassis had disappeared that reflects apparently the changes in salinity over the last 10 years. These changes in foraminiferal community and a significant increase of test abnormalities indicate an intensified environmental stress since the 1960s
Molecular identification of Ammonia and Elphidium species (Foraminifera, Rotaliida) from the Kiel Fjord (SW Baltic Sea) with rDNA sequences
No full textAmmonia and Elphidium collected in the Kiel
Fjord for the present study were first identified on morphological bases as Ammonia beccarii (Linne´, 1758) and Elphidium excavatum (Terquem, 1876). Phylogenetic analyses based on partial SSU rDNA and LSU rDNA sequences show that Ammonia specimens sampled in the Kiel Fjord belong to the phylotype T6, which has a disjunct distribution (Wadden and Baltic Seas/China and Japan) and has been identified as Ammonia aomoriensis (Asano, 1951). Partial SSU rDNA sequence analyses indicate that Elphidium specimens from the Kiel Fjord belong to the clade E. excavatum, confirming the morphological identification.
This clade can be further divided in three subclades. Kiel Fjord Elphidium belong to two of these subclades and were identified morphologically as the subspecies E. excavatum excavatum (Terquem, 1876) and E. e. clavatum Cushman, 1930
The Little Ice Age: evidence from a sediment record in Gullmar Fjord, Swedish west coast
No full textWe discuss the climatic and environmental changes during the last millennium in NE Europe based on a ca. 8-m long high-resolved and well-dated marine sediment record from the deepest basin of Gullmar Fjord (SW Sweden). According to the 210Pb- and 14C-datings, the record includes the period of the late Holocene characterised by anomalously cold summers and well-known as the Little Ice Age (LIA). Using benthic foraminiferal stratigraphy, lithology, bulk sediment geochemistry and stable carbon isotopes we reconstruct various phases of the cold period, identify its timing in the study area and discuss the land–sea interactions occurring during that time. The onset of the LIA is indicated by an increase in cold-water foraminiferal species Adercotryma glomerata at ~ 1350 AD The first phase of the LIA was characterised by a stormy climate and higher productivity, which is indicated by a foraminiferal unit of Nonionella iridea and Cassidulina laevigata. Maximum abundances of N. iridea probably mirror a short and abrupt warming event at ~ 1600 AD. It is likely that due to land use changes in the second part of the LIA there was an increased input of terrestrial organic matter to the fjord, which is indicated by lighter δ13C values and an increase of detritivorous and omnivorous species such as Textularia earlandi and Eggerelloides scaber. The climate deterioration during the climax of the LIA (1675–1704 AD), as suggested by the increase of agglutinated species, presence of Hyalinea balthica, and a decline of N. iridea may have driven the decline in primary productivity during this time period
The benthic foraminiferal record of the Medieval Warm Period and the recent warming in the Gullmar Fjord, Swedish west coast
No full textA high-resolution study of benthic foraminiferal assemblages was performed on a ca. eight metre long sediment core from Gullmar Fjord on the west coast of Sweden. The results of Pb-210- and AMS C-14-datings show that the record includes the two warmest climatic episodes of the last 1500 years: the Medieval Warm Period (MWP) and the recent warming of the 20th century. Both periods are known to be anomalously warm and associated with positive NAO winter indices. Benthic foraminiferal successions of both periods are compared in order to find faunal similarities and common denominators corresponding to past climate changes. During the MWP, Adercotryma glomerata, Cassidulina laevigata and Nonionella iridea dominated the assemblages. Judging from dominance of species sensitive to hypoxia and the highest faunal diversity for the last ca. 2400 years, the foraminiferal record of the MWP suggests an absence of severe low oxygen events. At the same time, faunas and delta C-13 values both point to high primary productivity and/or increased input of terrestrial organic carbon into the fjord system during the Medieval Warm Period. Comparison of the MWP and recent warming revealed different trends in the faunal record. The thin-shelled foraminifer N. iridea was characteristic of the MWP, but became absent during the second half of the 20th century. The recent Skagerrak-Kattegat fauna was rare or absent during the MWP but established in Gullmar Fjord at the end of the Little Ice Age or in the early 1900s. Also, there are striking differences in the faunal diversity and absolute abundances of foraminifera between both periods. Changes in primary productivity, higher precipitation resulting in intensified land runoff, different oxygen regimes or even changes in the fjord's trophic status are discussed as possible causes of these faunal differences. (C) 2011 Elsevier B.V. All rights reserved
