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  • Articles  (168)
  • diatoms  (62)
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  • hydrogen bonding  (34)
  • Springer  (168)
  • 2020-2023
  • 1995-1999  (168)
  • Geosciences  (168)
  • 1
    ISSN: 1572-8854
    Keywords: Crystal engineering ; hydrogen bonding ; acetonitrile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We report details of the synthesis and X-ray crystal structures of two new cocrystals that are sustained by the tetrahedral hydrogen bond donor [Mn(CO)3(μ3-OH)]4. [Mn(CO)3(μ3-OH)]4· 2(2,3,5,6-tetramethylpyrazine)·2H2O·2MeCN,a=21.503(3),b=12.674(1),c=17.318(2), β=102.15(2), C2/c,D calc=1.46 mg/m3,Z=4,4188 observed reflns,R f=0.047,R w=0.040; 1.[Mn(CO)3(μ3-OH)]4·4,4′-dipyridyl·2MeCn,a=16.942(6),b=12.395(2),c=18.790(6), β=114.88(3), C 2/c,D calc=1.60 mg/m3,Z=4,2430 observed reflns,R f=0.043,R w=0.051;2. 1 crystallizes as a 2-D grid, whereas2 forms 1-D strands. The hydrogen bond patterns exhibited by1 and2 are analyzed in the context of our earlier studies involving [Mn(CO)3(μ3-OH)]4 and other relevant literature.
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  • 2
    ISSN: 1572-8854
    Keywords: Tautomerism ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Crystals consisting of two distinct chemical entities, tautomers of each other, in exact 1∶1 ratio, have been obtained and their structure determined by X-ray analysis. The crystals of C9H11N3·C9H11N3 are monoclinic,P21/c,a=15.674(3),b=17.085(3),c=13.758(3)Å, β=90.78(2)°,Z=8. There are two hydroxylamine and two aminonitrone molecules in the asymmetric unit. Hydrogen bonds connect those molecules into chiral layers. Layers of opposite chirality alternate andthe crystal is centrosymmetric as a whole. Within those layers chains of tautomers joined by very strong O−H... O and strong N−H... N bonds can be recognized. Proton transfer along those chains with simultaneous rearrangement of π-bonds within the molecules would result in interconversion of tautomers and would affect chirality of the layer.
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  • 3
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    Journal of chemical crystallography 25 (1995), S. 569-571 
    ISSN: 1572-8854
    Keywords: PyrrolenineN-oxide ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2-Amino-5,5′-di(β-cyanoethyl)-1,2-pyrrolenineN-oxide monohydrate, C10H14N4O·H2O, crystallizes from MeCN in space group P212121 witha=7.0007(5),b=8.2998(6),c=20.8418(13) Å,V=1211.0(2) Å3,Z=4. The structure was refined toR=0.034 andR w=0.044 for 2325 observed reflections. The pyrrolenine ring adopts a nearly planar conformation, with maximum deviation from planarity 0.089(2) Å. The N−O distance is 1.345(2) Å. The water molecule bridges two pyrrolenine molecules via hydrogen bonds to theirN-oxide oxygen atoms, and also accepts a hydrogen bond from the NH2 group of another pyrrolenine molecule.
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  • 4
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    Journal of chemical crystallography 26 (1996), S. 747-752 
    ISSN: 1572-8854
    Keywords: Phosphine oxide ; quaternary ammonium ; water-soluble phosphine ; crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric triclinic space group $$P\bar 1$$ withZ=4. The crystallographic asymmetric unit contains two independent cations; interatomic distances within these include P=O=1.47(1) and 1.47(1) Å, P−C6H5=1.78(2)–1.81(1)Å and P−CH2CH2NMe3 +=1.80(1) and 1.81(1) Å. The phosphine oxide moiety is involved in intermolecular hydrogen bonding ()...H−C, with O...H≥2.42Å) and the iodide is involved in I...H−C contacts with I...H≥3.10Å.
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  • 5
    ISSN: 1572-8854
    Keywords: Structure ; thiosemicarbazide ; infrared ; nmr ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structures of three alkyl derivatives of thiosemicarbazide are described: anti,Z-4,4-dimethyl-3-thiosemicarbazide (1), syn,E,Z-2,4-dimethyl-3-thiosemicarbazide (2), and syn,E-1-cyclopentano-3-thiosemicarbazone (3). Crystal data: for 1: triclinic, P-1 (#2), a = 5.802(1)Å, b = 6.935(1)Å, c = 8.104(2)Å, α = 78.35(1)°, β = 82.13(1)°, γ = 70.71(1)°, and Z = 2; for 2: orthorhombic, Pbca (#61), a = 9.417(3)Å, b = 8.624(2)Å, c = 15.169(3)Å, and Z = 8; for 3: triclinic, P-1 (#2), a = 6.068(3)Å, b = 8.145(4)Å, c = 8.666(5)Å, α = 83.75(4)°, β = 86.16(5)°, γ = 74.07(4)°, and Z = 2. In general, molecules are linked by N–H···S hydrogen bonds with sulfurs accepting two or three hydrogen bonds. Structures 2 and 3, which adopt the syn conformation, form N–H···N intramolecular hydrogen bonds. The solid-state structures are consistent with their infrared and proton nuclear magnetic resonance spectra.
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  • 6
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    Journal of chemical crystallography 28 (1998), S. 931-933 
    ISSN: 1572-8854
    Keywords: Flavone ; hydrate ; hydrogen bonding ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The X-ray crystal structure of 7-hydroxyflavone monohydrate, C14H10O3 · H2O, is determined. The compound crystallizes in the monoclinic space group, P21/n with a = 3.801(3), b = 19.665(4), c = 16. 039(6), β = 93.69(3)°, and μ = 0.68 mm−1 for Z = 4. The phenyl ring of the flavone moiety is rotated 18.6(1)° out of the penzopyran plane, which is a typical value for flavones. In the crystal lattice, there are wide channels which are lined mainly by C–H groups. The water molecules enclosed in these channels are severely disordered.
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  • 7
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    Journal of chemical crystallography 28 (1998), S. 111-117 
    ISSN: 1572-8854
    Keywords: Di-hydroxymalonic acid ; hydrogen bonding ; crystal engineering ; supramolecular chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An examination of the crystal structures of di-hydroxy malonic acid 1 (P21/na = 5.384(2), b = 6.268(2), c = 14.354(8) Å, β = 103.57(3)°) and N-ethylbenzylammonium di-hydroxy hydrogenmalonate 2 (P212121 a = 13.373(2), b = 15.342(4), c = 18.741(4) Å,) has highlighted the influence of directional O–H···O interactions in the assembly of hydroxy-substituted dicarboxylic acids. The complementarity of carboxylic and hydroxy groups in 1 creates a very dense 3-D structure (D c = 1.919 g cm−3) through four O–H···O hydrogen bonds. In 2, the anions form infinite, spiraling chains created by head-to-tail O–H···O hydrogen bonds. Neighbouring chains are crosslinked into a complex 3-D anionic network with channels parallel to a and b. The cations are positioned within these channels and held in place via two N–H···O interactions.
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  • 8
    ISSN: 1572-8854
    Keywords: Cyclohexane ; alkyne ; hydrogen bonding ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The X-ray crystal structure of the title compound, C18H28O3, is determined. The hydrogen bond scheme does not follow considerations based on hierarchies of donor and acceptor strengths. The hydroxyl group of the molecule accepts only very weak C–H···O interactions.
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  • 9
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    Journal of chemical crystallography 28 (1998), S. 297-301 
    ISSN: 1572-8854
    Keywords: Crown ether ; hydrogen bonding ; alkylation ; biphenyl ; diols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The X-ray crystal structure of 2-hydroxy-2′-(1,4-bisoxo-6-hexanol)-1,1′-biphenyl, 3, is presented. This molecule crystallizes in the monoclinic space group P21/n (a = 9.440(2), b = 12.679(3), c = 11.679(3) Å β = 94.60(2)° V = 1382.5(5) Å3; Z = 4). One of the unique features of the X-ray structure of 3 is the intramolecular hydrogen bonding. The hydrogens of the phenolic and hydroxy groups occupies bridging positions via hydrogen bonding to an ether oxygen (O1) and a phenolic oxygen (O4), respectively. This hydrogen bonding does not affect the interplanar angle between phenyl rings (49.34°), which is in the range expected for ortho-disubstituted biphenyl compounds. The hydrogen bonding of this type explains why it is difficult to alkylate both phenoxy groups of 2,2′-biphenol with tetrahydropyranyl protected 2-(2′-chloroethoxy)ethanol.
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  • 10
    ISSN: 1572-8854
    Keywords: 2-Benzoyloxy-4-hydroxybenzaldehyde ; 2,4-dihydroxybenzaldehyde ; hydrogen bonding ; x-ray structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2,4-Dihydroxybenzaldehyde can be acylated at the 2 position if the more reactive 4 position is first protected as the methylmethoxy ether. Deprotection permits isolation of 2-benzoyloxy-4-hydroxybenzaldehyde. 2,4-Dihydroxybenzaldehyde, C7H6O3, crystallizes in P21/c, with a = 7.3762(6), b = 11.7455(9), c = 7.3149(6) Å, β = 90.533(2)°, Z = 4, and D X = 1.448 g cm−3. The individual molecules are characterized by an intramolecular hydrogen bond. The molecules form sheets with additional intermolecular hydrogen bonds. 2-Benzoyloxy-4-hydroxybenzaldehyde, C14H10O2, crystallizes in Pca21, with a = 24.2629(14), b = 3.8445(2), c = 12.3727(8) Å, Z = 4, and D X = 1.394 g cm−3. The molecules consist of two planar halves twisted by 51.63(5)° about the ester linkage. Intermolecular hydrogen bonding joins the molecules into ribbons approximately parallel to c.
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  • 11
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    Journal of chemical crystallography 29 (1999), S. 203-206 
    ISSN: 1572-8854
    Keywords: Manganese(III) ; Schiff base ; hydrogen bonding ; crystal structure ; Jahn-Teller distortion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The manganese complex, (Mn2(III)(salpa)2Cl2(H2O)2], has been prepared and its structure determined using x-ray crystallography. The dimer is a di-μ2-alkoxo complex which is a six-coordinate manganese dimer with unsupported alkoxide bridges and a rare example of a chloride- and water-containing manganese dimer. The complex crystallizes in the monoclinic space group P21/c with a = 9.315(5), b = 11.130(4), c = 11.637(5) Å, β = 104.33(3)°, V = 1169.0(9) Å3, and Z = 2. The structure comprises discrete binuclear clusters in which the metal atoms are bridged by two alkoxo oxygens of the salpa2− ligands. The Mn—O and Mn—N distances are in good agreement with those found for other manganese(III) Schiff base complexes. The Mn—Cl and Mn—O3 distances are 2.585(2) and 2.371(2) Å, respectively, and the Mn ··· Mn distance is 3.001(1) Å. In the crystal, there are two types of hydrogen bonding between the H2O molecule and the Cl atom with Cl ··· H(H2O) distance of 2.33(6) (intramolecule: −1 + x, y, −1 + z) and 2.68(6) Å (intermolecule: −1 + x, 0.5−y, −0.5 + z).
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  • 12
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    Journal of chemical crystallography 29 (1999), S. 725-727 
    ISSN: 1572-8854
    Keywords: 2-thiouracil derivatives ; crystal structure ; S-methyl-thiouracil ; hydrogen bonding ; structural methylation and metallation effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 2-S-Methylthiouracil crystallizes in the triclinic space group P $${\bar 1}$$ with unit cell dimensions a = 5.508(4), b = 7.175(3), c = 8.522(2) Å, α = 80.83(2), β = 80.43(3), γ = 76.86(3)°, and Z = 2. The molecule exists in the crystal in the lactam form and is essentially planar. The molecular packing consists of molecules linked in centrosymmetric hydrogen-bonded pairs. The effects of methylation and subsequent metallation on the 2-thiouracil structure are discussed.
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  • 13
    ISSN: 1572-8854
    Keywords: alkyne ; hydrogen bonding ; x-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In the x-ray crystal structure of the alkynol 5β-hydroxy-5α-ethynyl-10β-methyl-Δ1(9)-octalin-2-one [C13H16O2, Pbca, a = 10.244(7), b = 12.734(2), c = 17.125(2) Å, Z = 8], the hydroxyl and ethynyl groups are involved in a hydrogen bond arrangement C—C—H···O···H—O, which is supposed to be anticooperative, i.e., weaker than the sum of two isolated hydrogen bonds.
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  • 14
    ISSN: 1572-8854
    Keywords: Ruthenium(II) ; bipyridyl ; phenyldi(o-tolyl)phosphine ; solvate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2{PPh(o-tolyl)2}Cl+][ClO4 −] crystallized from a solution in dichloromethane as the dichloromethane-water solvate. The structure was refined toR=4.5% for those 2433 reflections with |F o|〉6σ(|F o|). The octahedral Ru(II) cation is associated with metal-ligand distances as follows: Ru−Cl=2.434(3)Å, Ru-PPh(o-tol)2=2.382(2)Å, and Ru−N=2.037(7)–2.088(7)Å. The structure is stabilized by a hydrogen-bonded CH2Cl2...ClO4 −...H2O channel which incorporates adventitious water of crystallization.
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  • 15
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    Journal of chemical crystallography 26 (1996), S. 483-487 
    ISSN: 1572-8854
    Keywords: Steroid conformation ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal structure of an orthorhombic polymorph of the title compound, crystallized by sublimation, has been determined. Dehydroepiandrosterone, C19H28O2, space groupP212121 witha=6.6408(4)b=11.4423(11)c=22.085(2)Å,V=1678.2(4)Å3,Z=4. The structure was refined toR=0.051 for 2645 observed reflections. The conformation of the molecule is similar to that found in other polymorphs and solvates, with a chair A ring, an 8β, 9α half-chair B ring, a chair C ring, and a 14α envelope D ring. Molecules are linked in chains by OH...O hydrogen bonds involving the carbonyl oxygen atom. The O...O distance is 2.855(3) Å, and the angle about H is 171(2)o.
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  • 16
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    Journal of chemical crystallography 26 (1996), S. 361-364 
    ISSN: 1572-8854
    Keywords: Crystal structure ; carboxylic acid ; phosphine oxide ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Diphenylphosphinylacetic acid crystallizes in the monoclinic space groupP2l/n with unit cell dimensionsa=5.6875(7),b=17.049(4),c=13.471(2) Å, β=93.36(1)° and Z=4. The molecular packing consists of hydrogen bonded chains arising from intermolecular interactions between a carboxylic acid hydroxyl group and an oxygen of an adjacent phosphine oxide moiety.
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  • 17
    ISSN: 1572-8854
    Keywords: Crystal structure ; bicyclononane ; triazene ; bis-triazene ; nitrile substituent ; nitro substituent ; trifluoromethyl substituent ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of a series of 3,7-bis(arylazo)-1,3,5,7-tetraazabicyclo[3.3.1] nonanes (1a–d) have been determined by single crystal X-ray diffraction analysis. All four compounds have the same feature, that the tetraazabicyclononane unit assumes a cage-like structure with the aryltriazene moieties lying parallel to one another so that the aryl rings are held together by π – π stacking. Crystal data: 1a C17H18N10O4, triclinic, space group P − 1, a = 9.8899(10), b = 13.0845(13), c = 16.458(2) Å, α = 94.095(2)°, β = 107.004(2)°, γ = 111.027(2)°, V = 1863.5(3) Å3 and Z = 4; 1b, C19H18F6N8, orthorhombic, space group Pbca, a = 15.3210(8), b = 10.9512(6), c = 24.5698(13) Å, V = 4122.4(4) Å3 and Z = 8; 1c C19H18N10, monoclinic, space group P21/n a = 6.3742(6), b = 13.7343(13), c = 21.542(2)Å, β = 97.738(2)°, V = 1868.8(3) Å3, and Z = 4; 1d, C19H18N10, monoclinic, space group P21/c, a = 18.205(2), b = 17.398(2), c = 12.784(12) Å, β = 109.480(2)°, V = 3818.0(6) Å3, and Z = 8.
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  • 18
    ISSN: 1572-8854
    Keywords: M(acac)3 derivatives ; isomorphous ; β-diketonate ligands ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The molecular structures of Al(tfac)3 (1), Co(tfac)3 (2) (H-tfac = 1,1,1-trifluoroacetylacetone) and Cu(H2O)(fod)2 (3) (H-fod = 1,1,1,2,2,3,3-hepta-fluoro-7,7-dimethyloctane-4,6-dione) have been determined. The metal coordination spheres in compounds 1 and 2 are essentially the same as the respective M(acac)3 derivatives. Despite the isomorphous nature of the structures of compounds 1 and 2, the identity of the nearest intermolecular van der Waals contacts are altered by minor changes in the metal coordination sphere. The geometry about copper in compound 3 is close to that of an ideal square bipyramid with the β-diketonate ligands occupying the basal plane. The water ligand in each molecule of compound 3 is hydrogen bonded to an oxygen of a β-diketonate ligand on an adjacent molecule resulting in the formation of dimers, which form rods along the y-axis due to weak C–F···Cu interactions. Crystal data: (1) orthorhombic, Pca21, a = 14.949(3), b = 19.806(4), c = 13.624(3) Å, V = 4033(1) Å3, and Z = 8, and (2) orthorhombic, Pca21, a = 14.930(3), b = 19.620(4), c = 13.540(3) Å, V = 3966(1) Å3, and Z = 8,; (3) monoclinic, P21/c, a = 12.447(3), b = 10.486(2) c = 21.980(4) Å, β = 102.65(3)°, V = 2799(1) Å3, and Z = 4.
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  • 19
    ISSN: 1572-8854
    Keywords: 1,10-Phenanthroline ; bis-phenanthrolineprotium ; adduct ; crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Herzog's reported bis-1,10-phenanthrolineammonium perchlorate, [(phen)2(NH4)](ClO4) is in fact the known 2:1 adduct of l,10-phenanthroline (phen) with perchloric acid, [(phen)2H](CIO4). Its crystal structure, mode of formation, and properties are described. The compound crystallizes in the triclinic space group with $$P\bar 1$$ , a = 7.2510(8), b = 13.120(2), c = 22.083(12) Å, α = 77.4550(12), β = 84.45(2), γ = 82.204(14)°, V = 2026.7(6) Å3, Z = 4, and D c = 1.510 g cm−3. It contains cationic columns of alternating 1,10-phenanthroline and its conjugate acid.
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  • 20
    ISSN: 1572-8854
    Keywords: 3-Amino-1,2,4-triazole ; hydrogen bonding ; x-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 3-Amino-1,2,4-triazolium (3-AT) 5-nitrofuran-2-carboxylate has been prepared and its x-ray crystal structure reported (a = 12.363(3) Å, b = 12.5720(10) Å, c = 12.8550(10) Å, Pbca, orthorhombic, Z = 8, and D c = 1.604 mg m−3). The solid-state packing of this organic acid-base salt consists of a three-dimensional hydrogen-bonded network which exhibits a cage-like repeat unit involving both the N(2)–H and N(4)–H sites of 3-AT. A review of five such structures reveals that in all cases the carboxylate groups interact with either of these sites [and the N(31)H2] and form a R 2 2(8) graph set interaction. Analysis of all 3-AT complexes which form this interaction reveals that the hydrogen-bonding distances between the non-hydrogen atoms are not equal [av. 2.712(5) Å and 2.897(5) Å], with the shorter distance being the interaction between the heterocyclic nitrogen and the corresponding carboxylate oxygen. Furthermore, a review of the interactive modes of all 3-AT adducts has been undertaken.
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  • 21
    ISSN: 1572-8854
    Keywords: Melaminium dinitramide and melaminium nitrate ; melaminium salts ; dinitramide salt ; hydrogen bonding ; X-ray structure ; energetic materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two energetic salts of the melaminium cation have been prepared and structurally characterized from room temperature X-ray single crystal diffraction data. Melaminium dinitramide (I), triclinic, P1¯, a = 6.6861(11), b = 6.9638(16), c = 10.447(2) Å , α = 99.07(3), β = 98.30(3), γ = 108.50(3)°, V = 445.6(2) Å3, and Z = 2. Melaminium nitrate (II), monoclinic, P21/c, a = 3.5789(7), b = 20.466(4), c = 10.060(2) Å, β = 94.01(2)°, V = 735.0(3) Å3, and Z = 4. The crystal structures of both salts show distinct monoprotonated melaminium cations and dinitramide- or nitrate anions, respectively. Efficient packing in the solid state is achieved by extensive hydrogen bonding between two-dimensional zigzag ribbons of the melaminium cations and the respective anions resulting in high densities of the solid state structures of 1.74 (I) and 1.71 g/cm3 (II).
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  • 22
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    Journal of chemical crystallography 29 (1999), S. 99-102 
    ISSN: 1572-8854
    Keywords: Isoflavone ; natural compound ; Dalbergia spinosa ; X-ray crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The X-ray crystal structure of the plant isoflavone dalspinin from Dalbergia spinosa is determined. The compound, C17H12O7, is monoclinic in P21/n with a = 3.970(1), b = 23.607(5), c = 14.633(3) Å, β = 94.46(3)°, V = 1367.2(5) Å3, D calc = 1.595 g cm−1 and Z = 4. The molecular structure is characterized by a short intramolecular O–H···O=C hydrogen bond, and a large tilt angle of the two rigid ring systems with respect to each other. The intermolecular interactions in the crystal are discussed.
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  • 23
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    Journal of chemical crystallography 28 (1998), S. 581-584 
    ISSN: 1572-8854
    Keywords: Cyclohexane ; alkyne ; hydrogen bonding ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In the X-ray crystal structure of the alkynol 5β-hydroxy-5α-(prop-2-ynyl)-10β-methyl-Δ1(9)-octalin-2-one [C14H18O2, Pca2 1, a = 13.559(1), b = 7.960(2), c = 21.748(3) Å], the hydroxyl and propynyl groups form a hydrogen bond chain C---C-H⋯O-H⋯O which is supposed to be a cooperative arrangement. Quantum chemical calculations estimate cooperativity enhancement within the array to be 0.4 kcal/mol, which is only a small (but recognizable) effect.
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  • 24
    ISSN: 1572-8854
    Keywords: 1,4,10,13-Tetraoxa-7,16-diazacyclooctadecane ; 2,5-pyridinedicarboxylic acid ; 2,2′-dithiosalicylic acid ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 1:2:2 complex of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with 2,5-pyridinedicarboxylic acid and water (1) and its 1:1:1.75 complex with 2,2′-dithiosalicylic acid and water (2) have been obtained and characterized by x-ray diffraction. C26H40N4O14 (1), triclinic, $$P\bar 1$$ , a = 9.574(1) Å, b = 9.632(1) Å, c = 9.723(1) Å, α = 112.70(1)°, β = 91.07(1)°, γ = 115.45(1)°, V = 728.35(13) Å3, Z = 1. C26H39.5N2O9.75S2 (2), M = 600.22, triclinic, $$P\bar 1$$ , a = 10.492(1) Å, b = 10.945(1) Å, c = 14.535(2) Å, α = 102.74(1)°, β = 109.08(1)°, γ = 90.68(1)°, V = 1532.2(3) Å3, Z = 2. In complex 1, both N-atoms of the macrocyclic ring are protonated. The following types of H-bonding have been found: (1) between protonated aza groups of the macrocycle and ionized carboxylic groups; (2) between the protonated aza groups and N-atoms of the pyridine nuclei (D–A distance slightly exceeds 3 Å); (3) between water molecules and C=O groups of the non-ionized carboxylic groups; and (4) between the nonionized and ionized groups of the carboxylic acid. The above interactions give rise to the formation of a developed supramolecular network in the crystals of 1. In complex 2, despite the presence of several types of hydrogen bonds involving the aza crown, 2,2′-dithiosalicylic acid and water, the aromatic anions are H-bound only to the two other components, and not to each other. The H-bonds found in complex 2 are between (1) one of the protonated aza groups and water, (2) protonated aza groups and O-atoms of the ionized carboxylic groups, (3) water molecule and carboxylic O-atom, (4) water molecule and sulfur atom, and (5) water molecule and O-atom of diaza-18-crown-6.
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  • 25
    ISSN: 1572-8854
    Keywords: silver ; pyridinecarboxylate ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Silver(I) complexes of 6-methyl-2-pyridinecarboxylic acid (HL) have been prepared, and the crystal structure of [Ag(L)(LH)] has been determined from X-ray diffraction data. This complex crystallizes in the monoclinic space group P21/n, with a = 13.4055(13), b = 7.1012(7), c = 15.588(2) Å, β = 112.779(2)°, and Z = 4. Anionic [AgL2]− units are linked together by protons in approximately symmetrical linear O—H—O hydrogen bonds involving uncoordinated carboxylate oxygen atoms, to give polymeric chains. The most significant intermolecular interaction between adjacent parallel chains is offset ring stacking of pairs of aromatic rings with a perpendicular distance of 3.27 Å. The Ag coordination geometry is highly distorted tetrahedral, from two pyridine N atoms and two carboxylate O atoms, each ligand forming a five-membered chelate ring.
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  • 26
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    Journal of chemical crystallography 29 (1999), S. 1235-1237 
    ISSN: 1572-8854
    Keywords: multiple phenyl interactions ; hydrogen bonding ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The x-ray crystal structure of 3,3,3-triphenylpropionic acid is determined [space group triclinic P-1 (No. 2) with a = 9.789(8), b = 9.946(8), c = 10.058(7) Å, α = 65.71(6), β = 63.77(5), γ = 85.37(6)°, and D calc = 1.264 g cm−1 for Z = 2]. The molecules form molecular columns which are organized by alternate carboxylic acid dimers and sixfold phenyl embraces.
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  • 27
    ISSN: 1572-8854
    Keywords: Thiosemicarbazone ; 2-benzoylpyridine ; N4-substituted ; hydrogen bonding
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    Topics: Geosciences , Physics
    Notes: Abstract 2-Benzoylpyridine N4-methyl-N4-phenylthiosemicarbazone, HBz4MePh, monoclinic,P2(1)/n a=9.141(2),b=18.507(4),c=11.401(2) Å, β=110.58(3)o,V=1805.6(9) Å3,Z=4, μ=1.655 mm−1. HBz4MePh crystallizes in a hydrogen bonded Z isomeric conformation with respect to the C7−N2 bond. The intramolecular hydrogen bond is between N3−H...N1, and the S atom isZ to the azomethine nitrogne, N2.
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  • 28
    ISSN: 1572-8854
    Keywords: Betaine ; 4-dimethylaminopyridinioacetate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystalline dihydrate and hydrochloride trihydrate of a new betaine, namely, L·2H2O (1) and [L2H]Cl·3H2O(2) (L=p-Me2NC5H4N+CH2CO2), have been synthesized and characterized by X-ray crystallography. Molecule L in compound1 [space groupPbcn, witha=15.732(3),b=7.894(2),c=18.304(4) Å, andZ=8] possesses approximateC s symmetry. The formation of hydrogen bonds by water molecules bridging neighboring carboxy oxygen atoms leads to an infinite two-dimensional network composed of a packing of two different kinds of 12-membered rings. In compound2 [space group PT witha=7.341(2),b=9.543(2),c=17.010(4) Å, α=82.43(2)°, δ=80.34(2)°, λ=74.05(2)°, andZ=2], the carboxylate groups of a pair of betaine molecules are bridged by a proton to form a dimeric cation L2H+ with a very strong asymmetric hydrogen bond of length 2.464(7) Å. The crystal structure features a hydrogen-bonded corrugated ribbon comprising an alternate arrangement of edge-sharing centrosymmetric (H2O)4(Cl−)2 and (H2O)4 rings running parallel to thea axis.
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  • 29
    ISSN: 1572-8854
    Keywords: Bidentate ligand ; crystal structure ; pyrazolyl group ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound lies on a site of C2 symmetry, with the two planar pyrazolyl moieties oriented at 86.1° to one another. The hydrogen atoms were located and refined.
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  • 30
    ISSN: 1572-8854
    Keywords: Pyrazolyl group ; crystal structure ; bidentate ligand ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound consists of two planar pyrazolyl fragments oriented at 73.0° to each other and linked to a common carbon atom. All hydrogen atoms were located unambiguously and their positions were refined.
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  • 31
    ISSN: 1572-8854
    Keywords: Crystal structure ; triazene ; bis-triazene ; nitrile substituent ; methoxy substituent ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of 1,2-bis-{1-(2-cyanophenyl)-3-methyltriazen-3-yl-}ethane (1) and 1,2-bis-{1-(2-methoxyphenyl)-3-methyltriazen-3-yl-}ethane (2) have been determined by single crystal X-ray diffraction analysis. Bis-triazene (1) exists as the “staggered” conformation in the solid state, with an anti-anti configuration around the N2–N3 bond of the triazene units, whereas 2 assumes a “gauche” conformation with the syn-syn configuration in the triazene units. Crystal data: 1 C18H18N8, triclinic, space group P −1, a = 6.108(2), b = 8.118(3), c = 9.600(4)Å, α = 101.37(7)°, β = 96.47(7)°, γ = 102.71(5)°, V = 449.1(3)Å3, Z = 2; 2 C18H24N6O2, monoclinic, space group P 21/n, a = 13.119(5), b = 7.745(2), c = 19.201(2)Å, β = 96.47(7)°, V = 1910.3(9)Å3, Z = 4.
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  • 32
    ISSN: 1572-8854
    Keywords: 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane ; 2,6-dihydroxyanthraquinone ; hydrogen bonding ; ribbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 1:2:2 complex of diaza crown ether 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, anthraflavic acid (2,6-dihydroxyanthraquinone) and water has been synthesized. The crystal is triclinic, P1, with a = 7.705(2), b = 10.871(2), c = 11.540(2) Å, α = 100.40(2), β = 91.38(2), γ = 98.01(2)°, Z = 1, and Dcalc = 1.375 mg m−3. The main feature of the crystal structure is the formation of a supramolecular sheet by hydrogen bonding of the anthraflavic monoanions, not only head-to-tail through the hydroxyl oxygens, but sideways through the quinone oxygens. This complex represents an intermediate case between total transfer of protons of a hydroxy-guest to crown N-atoms, and no transfer.
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  • 33
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    Journal of chemical crystallography 29 (1999), S. 355-358 
    ISSN: 1572-8854
    Keywords: Quinestrol ; sex steroid ; alkyne ; crystal structure ; solvent inclusion ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The X-ray crystal structure of the synthetic sex steroid quinestrol (3-O-cyclopentyl-17α-ethynylestradiol) as crystallized from ethanolic solution is determined. The asymmetric unit contains two steroid and one ethanol molecules. The conformation of the two steroid molecules differs in the orientation of the cyclopentane ring. The cocrystallized ethanol molecule facilitates formation of cooperative O—H···O hydrogen bonding. The title compound crystallizes in the monoclinic space group P21, with a = 13.950(6), b = 6.5945(8), c = 25.403(8) Å, β = 104.78(4)°, and D calc = 1.136 g cm−1 for Z = 4.
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  • 34
    ISSN: 1432-0819
    Keywords: Calc-alkaline volcanism ; Geochemistry ; Isotopic study ; Petrology ; Magmatic evolution ; Aegean Arc ; Nisyros volcano
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Nisyros island is a calc-alkaline volcano, built up during the last 100 ka. The first cycle of its subaerial history includes the cone-building activity with three phases, each characterized by a similar sequence: (1) effusive and explosive activity fed by basaltic andesitic and andesitic magmas; and (2) effusive andextrusive activity fed by dacitic and rhyolitic magmas. The second eruptive cycle includes the caldera-forming explosive activity with two phases, each consisting of the sequence: (1) rhyolitic phreatomagmatic eruptions triggering a central caldera collapse; and (2) extrusion of dacitic-rhyolitic domes and lava flows. The rocks of this cycle are characteized by the presence of mafic enclaves with different petrographic and chemical features which testify to mixing-mingling processes between variously evolved magmas. Jumps in the degree of evolution are present in the stratigraphic series, accompanied by changes in the porphyritic index. This index ranges from 60% to about 5% and correlates with several teochemical parameters, including a negative correlation with Sr isotope ratios (0.703384–0.705120). The latter increase from basaltic andesites to intermediate rocks, but then slightly decrease in the most evolved volcanic rocks. The petrographic, geochemical and isotopic characteristics can be largely explained by processes occurring in a convecting, crystallizing and assimilating magma chamber, where crystal sorting, retention, resorption and accumulation take place. A group of crystal-rich basaltic andesites with high Sr and compatible element contents and low incompatible elements and Sr isotope ratios probably resulted from the accumulation of plagioclase and pyroxene in an andesitic liquid. Re-entrainment of plagioclase crystals in the crystallizing magma may have been responsible for the lower 87Sr/86Sr in the most evolved rocks. The gaps in the degree of evolution with time are interpreted as due to liquid segregation from a crystal mush once critical crystallinity was reached. At that stage convection halted, and a less dense, less porphyritic, more evolved magma separated from a denser crystal-rich magma portion. The differences in incompatible element enrichment of pre-and post-caldera dacites and the chemical variation in the post-caldera dome sequence are the result of hybridization of post-caldera dome magmas with more mafic magmas, as represented by the enclave compositions. The occurrence of the quenched, more mafic magmas in the two post-caldera units suggests that renewed intrusion of mafic magma took place after each collapse event.
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  • 35
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    Bulletin of volcanology 60 (1998), S. 224-238 
    ISSN: 1432-0819
    Keywords: Key words Fe ; Ti oxides ; Tephrostratigraphy ; Geochemistry ; Geothermometry ; Taupo volcanic zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Grain-specific analyses of Fe–Ti oxides and estimates of eruption temperature (T) and oxygen fugacity (fO2) have been used to fingerprint rhyolitic fall and flow deposits that are important for tephrostratigraphic studies in and around the Taupo volcanic zone of North Island, New Zealand. The analysed Fe–Ti oxides commonly occur in the rims of orthopyroxene crystals and appear to reflect equilibrium immediately prior to eruption because of geochemical correlation with the co-existing glass phase. The composition of the spinel phase is particularly diagnostic of eruptive centre for post-65 ka events and can be used to distinguish many tephra beds from the same volcano. The 29 different units examined were erupted over a wide range in T (690–990°C) and Δ log fO2 (–0.1 to 2.0). These parameters are closely related to the mafic mineral assemblage, with hydrous mineral-bearing units displaying higher fO2. Such trends are superimposed on larger differences in fO2 that are related to eruptive centre. At any given temperature, all post-65 ka Okataina centre tephra have higher fO2 values than post-65 ka Taupo centre tephra. This provides a useful criterion for identifying the volcanic source. There are no temporal T and fO2 trends in the tephra record; over intervals 〉20 ka, however, tephra sequences from Taupo centre form characteristic T-fO2 buffer trends mirroring the glass chemistry. Individual eruptive events display uniform spinel and rhombohedral phase compositions and thus narrow ranges in T (± 〈20°C) and log fO2 (± 〈0.5), allowing these features to identify individual magma batches. These criteria can help distinguish tephra deposits of similar bulk or glass composition that originated from the same volcano. Distal fall deposits record the same T-fO2 conditions as the proximal ignimbrite and enable distal–proximal correlation. Lateral and vertical compositional and T-fO2 variability displayed in large volume (〉100 km3) ignimbrites, such as the Oruanui, Rotoiti and Ongatiti, is similar to that found in a single pumice clast and thus mainly reflects analytical error; however, thermal gradients of ca. 50°C may occur in some units.
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  • 36
    ISSN: 1437-3262
    Keywords: Bohemian Massif ; Variscan ; Geochemistry ; Garnet pyroxenite ; Eclogite ; Lithosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract High-temperature, high-pressure eclogite and garnet pyroxenite occur as lenses in garnet peridotite bodies of the Gföhl nappe in the Bohemian Massif. The high-pressure assemblages formed in the mantle and are important for allowing investigations of mantle compositions and processes. Eclogite is distinguished from garnet pyroxenite on the basis of elemental composition, with mg number 〈80, Na2O 〉 0.75 wt.%, Cr2O3 〈 0.15 wt.% and Ni 〈 400 ppm. Considerable scatter in two-element variation diagrams and the common modal layering of some eclogite bodies indicate the importance of crystal accumulation in eclogite and garnet pyroxenite petrogenesis. A wide range in isotopic composition of clinopyroxene separates [εNd, +5.4 to −6.0; (87Sr/86Sr)i, 0.70314–0.71445; δ18OSMOW, 3.8–5.8%o] requires that subducted oceanic crust is a component in some melts from which eclogite and garnet pyroxenite crystallized. Variscan Sm-Nd ages were obtained for garnet-clinopyroxene pairs from Dobešovice eclogite (338 Ma), Úhrov eclogite (344 Ma) and Nové Dvory garnet pyroxenite (343 Ma). Gföhl eclogite and garnet pyroxenite formed by high-pressure crystal accumulation (±trapped melt) from transient melts in the lithosphere, and the source of such melts was subducted, hydrothermally altered oceanic crust, including subducted sediments. Much of the chemical variation in the eclogites can be explained by simple fractional crystallization, whereas variation in the pyroxenites indicates fractional crystallization accompanied by some assimilation of the peridotite host.
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  • 37
    ISSN: 1437-3262
    Keywords: Key words Plate tectonics ; Geochemistry ; Trace fossils ; Late Precambrian ; Eocambrian stratigraphy and magmatism ; Gravity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Stratigraphic correlations and tectonic analysis suggest that the Puncoviscana fold belt of northwestern Argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the Rodinia supercontinent (at ∼800 Ma). Several lines of evidences point to an initial lithosphere rupture, possibly induced by a rising mantle plume. The earliest synrift igneous products are represented by ultra-potassic dykes and alkaline lava flows of high LREE/HREE and low Zr/Nb–Y/Nb ratios. The dyke emplacements and the initiation of rifting were probably synchronous. They pass laterally and upwards (middle part of the Puncoviscana succession) into basalts of alkaline transitional character (OIB-like source). The distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts; thus, they are thought to represent a magmatism associated with the rift and rift-drift transition stage. During this stage of rifting probably true oceanic crust was formed. The upper part of the Puncoviscana sequence, Late Precambrian/Lower Cambrian in age, comprises a thick and monotonous sequence of pillow lavas, massive basaltic flows and minor volcanic breccias and hyaloclastites. These lavas exhibit MORB trace element characteristics with high FeOt and TiO2, low K2O and P2O5, flat light REE spectra, little or no depletion in Nb and Ta. This volcanism consists of the major and latest effusive episode from the Puncoviscana basin which was slightly modified by subduction processes. The geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages. In the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin. In contrast, the second stage shows the effects of a completed Wilson cycle including a primitive volcanic arc which continued until the accreted Cuyania-Arequipa-Belen-Antofalla (CABA) terrane against the proto-Gondwana western borderland of the Amazonian shield (∼535 Ma).
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  • 38
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    International journal of earth sciences 84 (1995), S. 164-174 
    ISSN: 1437-3262
    Keywords: Geochemistry ; Granite ; source material South-west Sweden ; Eutectic melting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Granites, among them three generations of microline-rich granites, intruded repeatedly between 1600 and 900 Ma in the South-western Swedish Gneiss Complex. The deformed and metamorphosed Gösta and Sundsta granites are medium-grained, pale greyish red rocks belonging to the oldest generation of microclinerich granites. Biotite dominates over hornblende. Allanite, titanite, apatite and zircon are important accessory minerals. The granites are metaluminous and syeno- to monzogranitic in composition. SiO2 varies between 70.4 and 78.7% and K2O/Na2O between 0.86 and 2.32. Na and K are poorly correlated with the other major elements. The rocks are low in MgO (〈 0.9%) and FeO (〈 3.6%). They are characterized by high Rb/Sr, Ba/Sr and Ba/Rb ratios. The ratio Nb/Ta is almost constant (≈ 12) and the ratio Al/Ga decreases slightly with increasing SiO2 content. The Gösta granite has small, negative Eu anomalies, differentiated light and almost flat heavy rare earth element patterns. It intruded into continental crust approximately 1560 Ma ago. It is argued that the granites formed from continental rocks by pseudoeutectic partial melting at a fairly shallow depth. The source is older than the dominant country rock.
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  • 39
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    International journal of earth sciences 84 (1995), S. 213-219 
    ISSN: 1437-3262
    Keywords: Sediments ; Varves ; Tephra layers ; Radiocarbon dating ; Geochemistry ; Palaeomagnetics Volcanism ; Holocene ; Westeifel (Germany)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A minerogeniclayer occurs in early postglacial organic sediments from five maar lakes (West Eifel Volcanic Field, Germany). The mineralogy and stratigraphic position of this tephra suggests that it is related to the youngest German volcano, Ulmener Maar, nearby. Radiocarbon dating of wood from the base of the Ulmener Maar Tephra at two locations provide ages in agreement with an accelerator mass spectrometer 14C date for the minerogenic layer from sediments of Lake Holzmaar situated 13 km south-west of Ulmener Maar. The mean radiocarbon age is 9 560 years BP. Dating by varve chronology provides an age of 10017 years VT (varve time in years before 1950) or 10 895 years corrected VT. Based on palynology the Ulmener Maar Tephra was deposited at the end of the Preboreal. High values of natural remnant magnetization intensity, typical of pyroclastic material, confirm that this minerogenic layer differs in composition from other clastic deposits of the sedimentary record. Geochemical analyses reveal increased values of total trace elements for the Laacher See Tephra and Ulmener Maar Tephra. An isopach map based on thickness variations of the Ulmener Maar Tephra at five investigated maar lakes indicates that the tephra was mainly transported to the south west.
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  • 40
    ISSN: 1437-3262
    Keywords: L. Palaeozoic volcanics ; Amphibolites ; Geochemistry ; Petrogenesis ; Crustal contamination ; Palaeotectonic environment ; Orlica-Śnieżnik dome, Bohemian massif
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Orthoamphibolites within and marginal to the Orlica-Śnieżnik dome in the eastern Bohemian massif are associated with a series of Proterozoic-Lower Palaeozoic supracrustal meta-sediments of the Stronie, Nové Město and Staré Město formations. Massive and variably foliated amphibolites range from common epidote-plagioclase-blue-green/green hornblende varieties to assemblages with diopside, garnet and brown amphibole. All the amphibolites have a basaltic composition and are divided into three main chemical groups which are intimately associated in the field: main series tholeiites, low-Ti tholeiites and alkali basalts. All groups exhibit a common enrichment in LIL elements+Nb+Ta (relative to high-field-strength elements) which reflects contamination by upper continental crust and/or pelagic sediment compositions. The gross chemistry of the tholeiitesapproaches that for MORB, although the geological environment and nature of crustal contamination suggests that the basaltic precursors were probably emplaced in a rifted ensialic basinal environment. If the amphibolites are representative of an early phase of the Lower Palaeozoic fragmentation of Gondwanaland, then rifting did not fully develop ocean crust. The wider significance of the chemical interpretation implies that some of the variation from Variscan Proterozoic-Palaeozoic metabasite suites that is ascribed to a complex of different eruptive settings could be accounted for by variable contamination and/or source composition.
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  • 41
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    International journal of earth sciences 84 (1995), S. 506-519 
    ISSN: 1437-3262
    Keywords: Peraluminous granite ; Rare-metal granite ; Western Bohemia ; Oberpfalz ; Geochemistry ; Cordierite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Rozvadov Pluton is a complex of mainly Variscan granitoid rocks situated near the Bohemian-Bavarian border between Bärnau, Tachov, Rozvadov and Waidhaus, 25 km ESE of the KTB site. Five mappable units can be distinguished, which intruded as folows: (1) slightly deformed leucocratic meta-aplite/metapegmatite dykes with garnet and tourmaline; (2) a complex of cordierite-bearing granitoids, which have been divided into three facies (a) biotite granite with cordierite (at the margin of the complex), (b) biotite-cordierite granite and (c) cordierite tonalite (in the centre of the complex; (3) fine-grained biotite granite of the Rozvadov type with associated pegmatite bodies; (4) two-mica Bärnau granite; and (5) geochemically specialized albite-zinnwaldite-topaz granite (Krížový kámen/Kreuzstein granite) with indications of Sn-Nb-Ta mineralization and associated phosphorus-rich pegmatite cupolas. Rare earth element data suggest that meta-aplite/pegmatite dykes are the result of a batch partial melting process, whereas the compositional variation of the other rock types was mainly controlled by fractional crystallization. The genesis of the cordierite granitoid suite is best explained in terms of a batch melting of metapelitic source followed by crystallization of a cordierite-rich cumulate and K-feldspar enriched melt. The leucocratic pluton constituents — the meta-aplites and the Bärnau and Křížový kámen granites are rich in phosphorus (0.5–0.8%). The main carriers of phosphorus are alkali feldspars, especially K-feldspar (up to 0.8% P2O5). The presence of P-rich leucocratic granites is one of the features distinguishing the Variscan granitoids within the Moldanubian zone from the nearly contemporaneous granitoids in the Saxothuringian zone.
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  • 42
    ISSN: 1437-3262
    Keywords: Key words Oman ; Chromite ; Paleogeography ; Geochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  In Oman, the convergence between Arabia and Eurasia resulted in the Late Cretaceous overthrusting of oceanic crust and mantle lithosphere onto the Arabian continental margin. During this compressional event, a part of the continental plate was subducted to a depth of more than 60 km (0.5 GPa, 250–350  °C to more than 2.0 GPa, 550  °C) resulting in progressive metamorphism of the continental margin sediments, well exposed in the Saih Hatat tectonic window, northeastern Oman Mountains. We attempt to constrain the possibility of one continuous history of extension (starting along the east Arabian continental margin in the Permian) that was followed by one continuous history of convergence starting at 90 Ma near a dead oceanic ridge. This compression resulted in the observed progressive metamorphism by ophiolite overthrusting onto the continental margin. Constraining arguments are the palaeogeographic setting before ophiolite obduction of the As Sifah units and the Hawasina Complex near Ghurba. Detrital chromites in the Triassic–Cretaceous metasediments of the Hawasina Complex are compared with magmatic Semail chromites, and the whole-rock chemistry of these metasediments and associated metabasites are investigated. In contrast to former hypotheses, differences in the chemical composition between detrital and magmatic chromites, and the probable origin of all detrital chromites in the Hawasina Basin from Permian age oceanic rocks, suggest that the high-pressure metamorphic sediments of As Sifah can be considered as part of the basal deposits of the Hawasina Basin.
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  • 43
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    Journal of paleolimnology 13 (1995), S. 51-63 
    ISSN: 1573-0417
    Keywords: acidification ; England ; Holocene ; Lake District ; paleolimnology ; testate amoebae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Tests of testate amoebae extracted from samples of bottom sediments from 33 tarns in the English Lake District reveal a relationship between their distribution and physical-chemical parameters of the tarn waters.Nebela and several species ofDifflugia appear to prefer more acidic conditions, i.e., pH less than 6.2, while others such asCentropyxis, Lesquereusia and some species ofCyclopyxis andDifflugia are more common in lakes with pH's above that value. Using these data, and inferring rates of sedimentation from the densities of tests found in a 6-m core, a paleolimnological history for the past 11 000 years is presented for Ullswater (English Lake District). The record of testate amoebae, beginning shortly after deglaciation, depicts an uneven increase in acidity and a history of episodes of rapid and slow deposition that correlate reasonably well with paleoclimatological changes and anthropogenic alterations in the catchment.
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  • 44
    ISSN: 1573-0417
    Keywords: paleolimnology ; lake levels ; biogenic silica ; organic matter ; isotopes ; North Dakota
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract An 84 cm sediment core collected from the center of Devils Lake, North Dakota, was analyzed at 1-cm intervals for,210Pb,137Cs, sediment conductivity, the concentrations of, biogenic silica, total organic carbon, carbon to nitrogen ratio, and the carbon and nitrogen isotopic composition of the organic fraction. Variations in210Pb activities in the upper 20 centimeters indicate that sediment accumulations rates in Devils Lake are not constant, and that accumulation rates were highest during periods of high lake level. The mean sedimentation accumulation rate was calculated as 0.24 cm−1 yr. The137Cs profile is characterized by near-surface maximum concentrations, possibly the result of redistribution of137Cs during salinity excursions. Biogenic silica is strongly correlated to lake level in Devils Lake. Periods of low lake level (characterized by high sediment conductivity) correspond to low biogenic silica concentrations. The trends in biogenic silica are attributed to variations in diatom productivity in the lake and to variations in sediment accumulation rates. Based on biogenic silica content and the composition of organic matter in the sediment (total organic carbon, carbon:nitrogen ratio and the δ13C and δ15N composition of total organic matter), paleobiologic conditions of Devils Lake during low lake stands were characterized by, (1) decreased primary productivity, (2) decreased input of detrital organic matter, and (3) increased nitrogen availability. During the 350 years of sediment accumulation represented by the 84-cm sediment core Devils Lake has experienced two periods of sustained high lake level; one between about 130 and 170 years ago (1820 to 1860 A.D.) and the second between 270 and 310 years ago (1680 to 1720 A.D.). Devils Lake experienced a period of intense drying about 260 years ago (1720 A.D.).
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  • 45
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    Journal of paleolimnology 15 (1996), S. 237-243 
    ISSN: 1573-0417
    Keywords: reservoir ; diatom ; core ; sediments ; hydrology ; paleolimnology ; eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A 43 cm by 5 cm diameter sediment core sample was obtained from Ford Lake reservoir in Washtenaw County, Michigan, and sectioned at 1 cm intervals. The purpose of this study was to determine whether diatom communities in this reservoir have undergone quantifiable changes in abundance and composition since its creation. Thirty-one cm of this core appeared to represent material deposited since the creation of the reservoir based on changes in diatom abundance, the physical composition of the sediment and the change in biogenic SiO2 concentration. Fortyseven species of diatoms were identified total concentrations of diatom remains varied from 1×104 g-1 to 1×107 g-1. Prior to the establishment of the reservoir, the diatom flora was dominated by benthic taxa. Benthic diatoms were numerous throughout the entire core, but eutrophic taxa (e.g., Aulacoseira italica, Aulacoseira granulata, Stephanodiscus niagarae, Fragilaria crotonensis) dominated much of the core after the reservoir's creation. Total diatom density increased about tenfold in the about the first 10–15 years after the reservoir's creation before declining markedly.
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  • 46
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    Journal of paleolimnology 14 (1995), S. 69-82 
    ISSN: 1573-0417
    Keywords: Russia ; Lake Baikal ; paleolimnology ; diatoms ; stomatocysts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Examination of surficial sediments at 16 stations shows minor, but consistent differences in the numbers and kinds of siliceous microfossils deposited in different regions of Lake Baikal. There is a general north-south decreasing trend in total microfossil abundance on a weight basis. Endemic plankton diatom species are the most abundant component of assemblages at all stations. Chrysophyte cysts are present at all stations, but most forms are more abundant at northern stations. Non-endemic plankton diatom species are most abundant at southern stations. Small numbers of benthic diatoms and sponge spicules are found in all samples. Although low numbers are present in offshore sediments, the benthic diatom flora is very diverse. Principal components analysis confirms primary north-south abundance trends and suggests further differentiation by station location and depth.
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  • 47
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    Journal of paleolimnology 14 (1995), S. 113-122 
    ISSN: 1573-0417
    Keywords: Cladocera remains ; paleolimnology ; climate ; pollution ; human impact ; Italy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We use Cladocera remains in the sediments to reconstruct the longterm history of Lake Orta, a lake which experienced severe pollution from copper and ammonium sulphate, and started to recover during the last 15 years. Both human and natural impacts were detected over almost 400 years. Pollution was manifested by a dramatic decrease in the number of remains, in the planktonic/littoral (P/L) ratio, and in chydorid species diversity. Most species, even those most tolerant to stress, disappeared. The recolonization of biota was initially sustained by one species of chydorid,Chydorus sphaericus, which had a three-fold increase at the beginning of the 1980s, when studies on plankton recorded the development of a pelagic population. This fact, and the appearance in the sediments ofAlona quadrangularis, attest to the development of filamentous algae which was reported in studies on the plankton. The colonization of the lake by pelagic species came only in the last twelve years and was manifested also as a stabilization of the P/L ratio. Two other periods of disturbance were detected in the sediments: the first, at the end of the 19th century, was related to the introduction of exotic fish species; the second occurred during the second half of the 17th century. This event probably cannot be ascribed to human impact, but may be related to a decrease in temperature in that period (the Maunder Minimum).
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  • 48
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    Journal of paleolimnology 14 (1995), S. 185-223 
    ISSN: 1573-0417
    Keywords: taphonomy ; representativity ; diatoms ; acidification ; liming ; sediment traps
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    Topics: Biology , Geosciences
    Notes: Abstract The representative quality of fossil diatom assemblages in the recent sediment of a lake is compared with its contemporary diatom flora. In April 1986 experimental liming of the catchment of a small acidified lake, Loch Fleet (Galloway, U.K.), produced immediate changes in water quality. Lakewater pH rose from a mean of approximately 4.5 to 6.5, and in the two year period following liming a consistently higher pH was maintained. The marked response of diatom species to changing water quality provided a means of tracing events from living communities to the fossil assemblages. Diatom periphyton and plankton were sampled during a 20 month period and archived material was used to characterise earlier diatom communities. A comparison is made between living diatom communities and diatom assemblages collected by sediment traps and from sediment cores taken during the same period. Following liming, the diatom communities were found to respond within days or weeks to the changes in water quality. There is an initial change from acidobiontic communities, dominated byTabellaria quadriseptata, to dominance by the acidophilous speciesEunotia incisa andPeronia fibula. However, in the epipsammic community the acidobiontic speciesTabellaria binalis fo.elliptica remains abundant after liming. Approximately one year after liming the abundances of species such asAchnanthes minutissima andBrachysira vitrea increase in the epilithon, epiphyton and epibryon, whilst in the epipsammonT. binalis fo.elliptica is replaced by smallEunotia spp. andAchnanthes altaica. During the latter part of 1987 and in 1988, despite a stable pH, fluctuating patterns of species abundances are seen in the epilithon, epiphyton and epibryon whilst the species composition of the epipsammon remains relatively stable. Spring blooms of the planktonic speciesSynedra acus andAsterionella formosa occur during 1988 and 1989 respectively. Sediment trapping, which began in April 1987, records shifts in species composition corresponding with those seen in the epilithon, epiphyton and epibryon and with the blooms of planktonic species. The signal from the smaller, and probably less easily transportable, epipsammic community is not so clearly discernible. Although the fundamental record of the sediment traps is one from living diatom communities, the appearance of taxa ‘extinct’ during the post-liming period reflects a low, but significant level of sediment resuspension. In contrast to the rapid response of living communities and their record in sediment traps, sediment cores do not begin to reflect changes in diatom composition until about 14 months after the initial liming. The first appearance of circumneutral taxa in significant abundance occurs only approximately 17 months after liming. The delayed reaction of sediment assemblages cannot be attributed principally to a slow rate of transport from the littoral to the profundal zone. Time-averaging processes within the sediment appear to be the main cause of the lag in core response. In contrast, blooms of planktonic species are quickly reflected in the stratigraphy of cores, but indicate that a considerable degree of downward mixing occurs. Comparison of the time trajectories of whole species assemblages in living communities, sediment traps and core surface sediments shows that the direction of change is similar in all three, but that the magnitude of change is attenuated in sediment assemblages.
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  • 49
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    Journal of paleolimnology 15 (1996), S. 19-45 
    ISSN: 1573-0417
    Keywords: diatoms ; grain-size analysis ; lake-level changes ; Lake Michigan ; paleolimnology
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    Topics: Biology , Geosciences
    Notes: Abstract Paleolimnological investigations of a marginal lake in the Lake Michigan basin revealed signals of long-term lake-level changes primarily controlled by climatic forces. Multiple analyses identified concurrent signals in sediment chemistry, grain size, and the microfossil record. Coarse-grained sediments, benthic diatoms, and nutrient response species increased as lake levels rose or fell. Finer sediments and higher percentages of taxa associated with stable thermocline conditions occurred during high-lake periods. Sedimentary evidence revealed corresponding strong high-lake signals c. 2500–2200, 1800–1500, 1170–730, and 500–280 BP. Low-lake periods occurred c. 1500–1170 and 700–500 B.P. An additional signal of lake-level decline was apparent beginning c. 280 BP but was interrupted by anthropogenic effects. Evidence of extreme low-lake levels (c. 1400–1300 BP), and signals for a medieval warming period (1030–910 BP) and the Maunder minimum (370–325 BP) indicate occurrence of short-lived dry climatic conditions.
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  • 50
    ISSN: 1573-0417
    Keywords: diatoms ; high arctic ; Ellesmere Island ; laminated sediments ; rheophilous ; river input ; marine isolation
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    Notes: Abstract Diatoms preserved in the sediments of Lake C2 (82°50′ N, 76°00′ W), a high arctic meromictic lake, track changes in the lake's salinity which have occurred as the basin was isolated from the sea. An assemblage dominated by marine taxa, such as Chaetoceros species, Nitzschia cylindrus and Diploneis spp., was replaced by a Cyclotella kuetzingiana var. planetophora dominated freshwater flora. A brief brackish period separates the two assemblages. Relatively little floristic change occurred within either the marine or freshwater periods, indicating rather stable environmental conditions, except that rheophilous diatoms fluctuated in relative abundance during the lacustrine phase, perhaps tracking past changes in discharge from inflowing streams. These may reflect periods of warmer, wetter environmental conditions.
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  • 51
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    Journal of paleolimnology 16 (1996), S. 323-354 
    ISSN: 1573-0417
    Keywords: diatoms ; chrysophytes ; pollen ; charcoal ; hemlock decline ; Holocene ; Massachusetts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We examined the stratigraphic record of North Pond, a small, oligotrophic lake in western Massachusetts, U.S.A. to describe late and post-glacial watershed-lake interactions. In particular we investigated the effects of two similar vegetation changes in the watershed on lake biogeochemistry. There was a transient (about 100 years) decline in hemlock ca. 7500 yr B.P. that has not been recorded in other pollen stratigraphies in the northeast. The second event was the classical hemlock decline that occurred ca. 4800 yr B.P. and lasted about 2000 years. This decline occurred throughout the range of hemlock and is thought to have been caused by a pathogen. As the climate began to warm ca. 10 000 yr B.P., a spruce dominated boreal woodland was established in the watershed. Sediment chemistry data showed that as soils became more acidic, the lake also acidified as evidenced by diatom-inferred (DI) pH. Hemlock was established in the watershed by about 8000 yr B.P. This was accompanied by a slight decrease in DI pH. The transient hemlock decline ca. 7500 yr B.P. was associated with an increase in sedimentary charcoal particles, that suggested fire was responsible for its demise. The diatom stratigraphy indicated a brief, slight, increase in productivity and alkalinity and a brief decrease in lakewater dissolved organic carbon concentrations. Aquatic microfossil data indicated a decrease in the area of the littoral zone ca. 7500 yr B.P. Following the transient decline the lake became more acidic. There were only brief, subtle changes associated with the classical hemlock decline, including a slight decline in DI pH. Although the two disturbances involved a similar vegetation shift, the timing and mechanisms of the disturbances had a greater impact on lake biogeochemistry.
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  • 52
    ISSN: 1573-0417
    Keywords: colonization ; evolution ; lakes ; Norway ; deglaciation ; land uplift ; invertebrates ; Chironomidae ; Porifera ; Bryozoa ; diatoms ; Charophyta ; tsunami
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Invertebrate colonization of lakes following the uplift of land from the sea was studied in four lakes, currently situated between 39 and 24 m a.s.l., on the central Norwegian coast. The lakes were isolated from the sea between 9500 and 7700 years B.P. Animal and algal remains picked from core samples showed that the first colonizers preserved as fossils were usually members of the Chironomidae, Daphnidae/Chydoridae, Acarina, Porifera (Ephydatia mülleri and Spongilla lacustris), Bryozoa (Cristatella mucedo and Plumatella spp.) and Charophyta (Chara sp.). Of the chironomids, the genus Chironomus was present in the oldest lacustrine layers of all four lakes, but other genera recorded at the marine/lacustrine boundary were Dicrotendipes, Procladius (?), Einfeldia, Microtendipes, and Glyptotendipes. Remains of the caddis fly family Limnephilidae were also present in the earliest lacustrine sediments in Kvennavatnet and Kvernavatnet. The oldest invertebrate fauna is typical for mesotrophic lakes. However, chironomids and mites have been present in this area from at least about 10 500 years B.P. A diverse chironomid community was established between 300 and 800 years after isolation from the sea at Kvernavatnet on the island of Hitra, while only between 80 and 120 years passed before a comparably diverse community developed at Kvennavatnet on the mainland coast. A similar development of the invertebrate fauna occurred in Kvennavatnet, Kvernavatnet and Storkuvatnet. However, Litjvatnet deviates greatly from the ‘normal’ pattern because a tsunami disturbed the bottom sediments and fauna. The tsunami, a gigantic sea wave, was caused by a submarine slide from the Norwegian continental slope. It reached Litjvatnet, today located 24 m a.s.l., but was not traced in Storkuvatnet at 30 m a.s.l. This event happened about 7200 years B.P.
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  • 53
    ISSN: 1573-0417
    Keywords: geochemistry ; Guatemala ; Holocene ; lakesediment ; Maya ; magnetic susceptibility ; paleolimnology ; pollen ; stable isotopes
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    Notes: Abstract We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS 14C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to ∼9000 14C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by ∼9000 14C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (∼9000 to ∼6800 14C yr BP), pollen data suggest moist conditions, but high δ 18O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in δ 18O values and associated change in ostracod species at ∼6800 14C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning ∼5780 14C yr BP may indicate early human disturbance. By ∼2800 14C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning ∼1100 to 1000 14C yr BP, following the collapse of Classic Maya civilization.
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  • 54
    ISSN: 1573-0417
    Keywords: Lake Baikal ; Russia ; paleolimnology ; diatoms ; chrysophyte cysts ; climate change
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    Notes: Abstract Siliceous microfossil assemblage succession was analyzed in a 100 m sediment core from Lake Baikal, Siberia. The core was recovered from the lake's central basin at a water depth of 365 m. Microfossil abundance varied greatly within the intervals sampled, ranging from samples devoid of siliceous microfossils to samples with up to 3.49 × 1011 microfossils g-1 sediment. Fluctuations in abundance appear to reflect trends in the marine δ18O record, with peak microfossil levels generally representing climate optima. Microfossil taxa present in sampled intervals changed considerably with core depth. Within each sample a small number of endemic diatom species dominated the assemblage. Changes in dominant endemic taxa between sampled intervals ranged from extirpation of some taxa, to shifts in quantitative abundance. Differences in microfossil composition and the association of variations in abundance with climate fluctuations suggest rapid speciation in response to major climatic excursions.
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  • 55
    ISSN: 1573-0417
    Keywords: magnetism ; diatoms ; radioisotopes ; erosion ; laminae ; chronology
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    Notes: Abstract Two frozen cores from Blelham Tarn were subsampled and measured using mineral magnetic, loss-on-ignition (LOI), radiometric, granulometric and diatom analyses. A detailed chronology was established using varves, radioisotopes and diatoms. This has enabled an accurately dated reconstruction of sedimentation over the past forty years. Despite a large increase in lake productivity, evidence suggests that the observed exponential increase in sedimentation rates can be attributed to erosion within the catchment. The predominant sediment source has been identified as surface soil. A comparison between the trend of accelerated sedimentation and the record of increased sheep stocking density for the area within which the most of the catchment lies, as well as observations of contemporary surface processes within the catchment, both suggest that much of the recent erosion is a direct response to increased pressure from sheep grazing.
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  • 56
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    Journal of paleolimnology 18 (1997), S. 261-268 
    ISSN: 1573-0417
    Keywords: diatoms ; microfossil concentrations ; methods ; paleolimnology ; West Okoboji Lake ; Iowa
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    Notes: Abstract The diatom concentration of a uniform lake sediment sample was estimated in 15 laboratories. Whilst 21 of 35 estimates were between 13 and 19 × 107 valves g-1, values ranged from 8.2 × 106 to 2.0 × 109 valves g-1. However, counts from replicate sediment digestions, replicate slide preparations from a single digested slurry, and multiple counts from an individual slide all yielded internally consistent results, with acceptably low coefficients of variation (±4.5–6.3%). Without greater efforts towards harmonization, for example by calibrating techniques to a standard of known concentration, reported diatom concentration values, as well as derived data such as diatom accumulation rates, are not directly comparable between most laboratories. This sharply contrasts the strong reproducibility of diatom relative frequency data. A calibration exercise, using the Eucalyptus pollen spike technique to estimate a known concentration of Lycopodium spores, demonstrates that this method performs best when approximately equal proportions of microfossils and introduced markers are counted.
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  • 57
    ISSN: 1573-0417
    Keywords: palaeolimnology ; diatoms ; meromixis ; lakeontogeny ; human disturbance
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Three meromictic lakes in the World Heritage Area of south-west Tasmania possess unusual microbiological communities. Their meromixis is maintained by periodic incursions of brackish water from the nearby Gordon River which, in its lower reaches, is a salt-wedge estuary. In 1977 the construction of a dam in the middle reaches of the river restricted penetration of the salt-wedge and meromixis rapidly declined in all three lakes. A palaeolimnological study was carried out on one of the lakes, Lake Fidler, firstly to determine the history of meromixis and its associated microbiological communities, and secondly to assess whether the recent and rapid decline of meromixis is inconsistent with natural rates of development of the Gordon River meromictic lakes. One part of this study included the analysis of the stratigraphy of fossil diatoms from a 17-metre sediment core dating back 8000 yrs. Detrended Correspondence Analysis and Analog Matching were used to compare diatom species assemblages in core samples with diatom samples from a reference dataset consisting of a selection of lake and river sites in the lower Gordon River valley. Five distinct stratigraphic zones were identified in the core. These zones indicated specific stages in the development of the Gordon River lakes from river backwaters to ectogenically-maintained meromictic lakes which will, finally, become terrestrialised by encroaching rainforest. The onset of a stratified water column was identified by the emergence of a dominant freshwater algal flora which suggested that the lake had developed a mixolimnion and become meromictic ca. 2070 ± 50 14C yrs ago. In the context of this long history of meromixis, the rapid demise in meromictic stability following construction of the dam is judged to be inconsistent with natural rates of development. The palaeolimnological studies, of which this paper is one part, prompt recommendations for a management strategy to prevent the further decay of these meromictic lakes in the World Heritage Area.
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  • 58
    ISSN: 1573-0417
    Keywords: drought ; diatoms ; paleoclimate ; Northern Great Plains ; paleosalinity ; Medieval Warm Period ; Little Ice Age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom assemblages preserved in sediment cores from closed-basin lakes can provide high-resolution records of past hydrologic and climatic conditions, including long-term patterns in the intensity, duration, and frequency of droughts. At Moon Lake, a closed-basin lake in eastern North Dakota, a comparison of diatom-inferred salinity and the precipitation-based Bhalme-Mooley Drought Index (BMDI) over the last 100 years was highly significant, suggesting that the diatom record contains a sensitive archive of past climatic conditions. A sub-decadal record of inferred salinity for the past 2300 years indicates that extreme droughts of greater intensity than those during the 1930s 'Dust Bowl' were more frequent prior to A.D. 1200. This high frequency of extreme droughts persisted for centuries and was most pronounced from A.D. 200–370, A.D. 700–850 and A.D. 1000–1200. A pronounced shift to generally wetter conditions with less severe droughts of shorter duration occured at A.D. 1200. This abrupt change coincided with the end of the 'Medieval Warm Period' (A.D. 1000–1200) and the onset of the 'Little Ice Age' (A.D. 1300–1850).
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  • 59
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    Journal of paleolimnology 19 (1998), S. 297-307 
    ISSN: 1573-0417
    Keywords: eutrophication ; algae ; bluegreen akinetes ; non-siliceousmicro fossils ; diatoms ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Although the phytoplankton and protozoan assemblages of Lake Winnipeg are quite variable both, spatial and temporally, knowledge of their current distribution and ecology enables them to be used as indicators providing unique information concerning past and recent ecosystem conditions. Many of the main taxa have been similar throughout history although there have been dramatic changes in their abundance. Lake Winnipeg is currently very responsive to the climatic conditions in its drainage basin and it appears, historically, to have been a diatom-bluegreen algal lake with Tintinnids and thecate amoeba forming significant components of the protozoan community. A wide variety of microfossil remains have been used to infer past conditions in this large prairie lake. Microfossils reported from the long core 103 (8 m) taken from the north basin of LakeWinnipeg and short core Namao 7a taken from the south basin of the lake in August 1994 indicate that the lake has experienced several changes over its history. Diatom assemblages, low throughout the core 103 below 50 cm, except for a peak around 300–400 cm are virtually absent below 690–800 cm (Lake Agassiz). Stephanodiscus and Aulacoseira are the two major pelagic diatom genera represented throughout the lake's history. Species changes occur near the top of the core indicate increased anthropogenic eutrophication. Shallow water littoral taxa were never abundant at either coring sites. The presence of planktic cyanoprokaryote (cyanophyte, cyanobacteria, bluegreen algae) remains (akinetes) from 600 cm depth and the progressive increase in abundance from 400 cm to through the top 100 cm of the core indicates increasing phosphorus levels, warming summer temperatures and increasing summer nitrogen limitation in the lake. Nitrogen fixing bluegreens (especially Anabaena and Aphanizomenon akinetes) and the diatoms (Aulacoseira ambigua, A. granulata, A. islandica, S. binderanus, and S. niagarae) were abundant in the upper sediments and changes after 100 cm can be interpreted as the effects of human impact. These taxa indicative of increase eutrophication, in addition to S. agassizensis, Melosira varians and Cyclostephanos dubius, are representative of present day plankton. The short core Namao 7a was dated by Pb210 and the fossil remains also show a rise in the Aulacoseira (particularly A. granulata and A. ambigua) and bluegreen akinetes in the last 40 years as was seen in the upper sediments of the 103 core. There was an interesting peak in chrysophyte cysts during the 1930's which corresponds nicely with climatic conditions during this period. The fires accompaning the hot dry period in the mid 70's can be seen in the dramatic rise in charcoal during this period. Multiple types of micro fossils remains provides several useful tools for interpreting past lacustrine conditions.
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  • 60
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    Journal of paleolimnology 19 (1998), S. 399-416 
    ISSN: 1573-0417
    Keywords: saline lakes ; paleolimnology ; paleoclimate ; diatoms ; transfer functions ; Spain ; CCA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom-salinity transfer functions for interpretation of palaeosalinity and palaeoclimate change have been developed successfully for parts of North America and North and East Africa, but there is a need for data-sets in other saline lake regions of the world. A data-set of 74 modern diatom samples and associated water chemistry data is described from Spain. The influence of conductivity and other environmental variables on diatom distribution is explored using canonical correspondence analysis (CCA) and partial CCAs. A transfer function is derived for conductivity (70 samples) whose apparent predictive ability is high (apparent r2 = 0.91). Performance under jackknifing is poor due to the heterogeneous nature of the data-set and poor coverage of the freshwater end of the salinity gradient. There is a lack of suitable low-salinity sites in Spain, and the accuracy of estimated salinity optima and tolerance ranges may be improved by merging this data-set with those of other regions. The Spanish transfer function has strong affinities with the African data-set and contributes important ecological data for diatom taxa which are absent or poorly represented in the modern flora of African lakes, and for which, in fossil material, there were previously no good modern analogues.
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  • 61
    ISSN: 1573-0417
    Keywords: Pliocene ; Oklahoma ; Pyrgophorus hibbardi ; paleolimnology ; stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The basal portion of the Ogallala Formation (=‘Laverne Formation’) (Lower Pliocene) Beaver County, Oklahoma, contains an interesting assemblage of non-marine fossil molluscs that include both spinose and non-spinose forms of the aquatic gastropod species Pyrgophorus hibbardi. The origin and paleolimnological significance of the spinose morph has been a source of much conjecture that has influenced environmental reconstructions of this assemblage. In one hypothesis the spinose forms of P. hibbardi are assumed to be associated with brackish water conditions by analogy with some populations of a related hydrobiid Potamopyrgus jenkinsi. To test the hypothesis that the spinose forms lived under different water conditions than the non-spinose morphs, we analyzed 10 specimens each of the two varieties for stable oxygen and carbon isotope ratios in the shell aragonite. The mean isotope ratios for the smooth and spinose morphs show no significant difference (oxygen: t = 0.28, df = 18, P (T ≤ t) 0.78 n.s.; carbon: t = 0.96, df = 18, P (T ≤ t) 0.35 n.s). We conclude that the lack of a statistically significant difference between the means of the oxygen and carbon isotope values for the smooth and spinose morphs suggests that the two forms lived in waters having similar isotope signatures. The considerable range in oxygen isotope values recorded by both morphs of P. hibbardi, including values as high as 5–6‰, suggest that both morphs were associated with waters which were periodically evaporatively enriched in 18O.
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  • 62
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    Journal of paleolimnology 20 (1998), S. 253-265 
    ISSN: 1573-0417
    Keywords: Late Quaternary ; diatoms ; climate change ; vegetation change ; shallow ; subalpine ; Crowfoot Lake ; Alberta ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The late Quaternary diatom record from subalpine Crowfoot Lake, Banff National Park, Alberta (lat. 51° 61′N; long. 116° 31′W) has been analyzed. Results are related to independently inferred vegetation and climate changes. No diatoms were found in the basal diamict that predates 11330 14C yr BP. Very few occur until ca. 10 10014 C yr BP probably due to the short time between de-glaciation and an advance of the Crowfoot Glacier during the ‘Younger Dryas Chron’. Initial pioneering species were characteristic of alkaline water and calcareous organic sediments. They appeared as sediments became organic and laminated suggesting increasing water clarity, and as the Pinus-dominated forest expanded and the climate warmed. After ca. 9060 14C yr BP diatom numbers increased rapidly, reaching a maximum prior to the Mazama tephra; they remained high until ca. 3500 14C yr BP. The period between ca. 9060 and 3500 14C yr saw timberline elevation increase and the dominance of xerophytic taxa. These are consistent with early to mid-Holocene warmth and aridity. Diatom productivity reflects the warm climate and presumably longer ice-free season, a stable catchment and transparent water. Decreases in diatom productivity coincide with a vegetation change with reduction of xerophytic taxa and the appearance of a closed Picea-Abies forest, hence a cooler, wetter climate at ca. 4100 to 3500 14C yr BP. The diatom numbers during the Neoglacial were of the same magnitude as prior to ca. 9060 14C yr BP. Small species of Fragilaria (overwhelmingly Fragilaria construens v. venter) became extremely dominant during the period of high diatom productivity, and remained so thereafter. Recovery of the lake appears to have been rapid after deposition of the Mazama tephra. Maximum occurrence of Cyclotella radiosa occurred ca. 8000 14C yr BP during the warm early Holocene and may reflect this warmer climate, a longer ice-free season than presently, perhaps less turbid water, or it may reflect a subtly higher nutrient status of the lake water. The diatom record of Crowfoot Lake has responded with sensitivity, particularly in terms of productivity, to the Holocene vegetation and climate changes.
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  • 63
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    Journal of paleolimnology 20 (1998), S. 57-69 
    ISSN: 1573-0417
    Keywords: Kushu Lake ; diatoms ; sulfur ; threshold ; sea-level change ; salinity ; coastal paleoenvironments ; Japan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom assemblages and sulfur content in sediments were analyzed to clarify changes in the sedimentary environment of Kushu Lake, a coastal lake on Rebun Island in Hokkaido, Japan. Salinity variations were assessed by means of a diatom-based index of paleosalinity and the sedimentary sulfur content. This paper discusses the Holocene development of the lake, in relation to Holocene relative sea-level change. For paleoenvironmental interpretation of the lake development, the rationale of the threshold method (Anundsen et al., 1994) was applied. At ca. 8000 yr BP, a coastal embayment (paleo-Kushu Bay) resulted from marine ingression. The threshold elevation at the mouth of the paleo-Kushu Bay kept pace with the rising sea-level, resulting in its enclosure at the culmination of Holocene marine transgression (ca. 6500–5000 yr BP). From predicted relative sea-level at ca. 6000 yr BP for Rebun Island (Nakada et al., 1991), the threshold may have been at least above –3 to –5 m altitude. A freshwater lake environment with strongly anoxic bottom conditions may have occurred from ca. 5500 to 5100 yr BP. After an important episode of marine ingression, the lake was isolated completely from the open sea at ca. 4900 yr BP. The diatom record suggests that the maximum lacustrine extent occurred at ca. 4900–3100 yr BP. Thereafter, water depth decreased at the lake margins. In Kushu Lake, the threshold elevation, due to a build-up of a coastal barrier, prevents us from determining the amplitude of sea-level changes, even though the age of isolation contacts corresponds to periods of regression and climatic deterioration. In spite of isostatic subsidence, the effective protection provided by the well-developed barrier did not allow registration of any relative sea-level fluctuations since its isolation.
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  • 64
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    Journal of paleolimnology 20 (1998), S. 107-117 
    ISSN: 1573-0417
    Keywords: Lake Baikal ; pollution history ; trace metals ; carbonaceous particles ; magnetic minerals ; diatoms ; turbidites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Recent environmental change research in Lake Baikal is introduced together with an overview of several interrelated papers published concurrently in this issue of Journal of Paleolimnology. Five themes are tackled by analysis of recent Baikal sediment cores, dating, geochemistry, particulate pollutants, magnetism and diatoms. The concurrent papers focus on the first four themes in some detail and summary results of diatom analysis (from Mackay et al., 1998) are given here. Taken together these studies provide a time-space framework for recent environmental change in Lake Baikal not previously available. There are significant shifts in species composition of the endemic planktonic diatom assemblages in uppermost sediments collected from throughout the lake. However, these changes usually precede the sediment record of low level but widespread contamination by industrial products. The most clear sign of industrial contamination is the presence of particles from fossil fuel combustion in sediment post dating the 1930s. Although evidence for widespread biostratigraphic changes by pollution is lacking, radionuclide, diatom, lithostratigraphic and magnetic stratigraphies indicate two main features, (i) it is possible to make stratigraphic correlations within and between basins using recent sediment cores, (ii) that turbidite deposits, from several to tens of cm thick, are frequently encountered in recent sediments. Turbidite deposits occur in 210Pb dated and pre-210Pb sediment core sections and are undoubtedly a major macro-disturbance feature in many deep water locations in Lake Baikal. If profiles are to be used as direct proxy records of climate variability, then screening of cores for turbidites is a pre-requisite for quality assurance in future paleoenvironmental studies. On-going international research including Swiss, Russian and British joint paleoenvironmental studies on the distribution and biological formation of recent sediments will hopefully lead to better interpretation of Holocene and pre-Holocene sediment records in Lake Baikal.
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  • 65
    ISSN: 1573-0417
    Keywords: bulk geochemistry ; Holocene ; lacustrine sediments ; paleoenvironments ; paleolimnology ; statistical methods
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    Notes: Abstract The paper involves detailed geochemical and mineralogical analysis of lacustrine sediments from a 95 cm core profile collected in the closed lake basin of the Laguna de Gallocanta, central Iberian Chain. The environmental and depositional changes are confirmed by: (1) variations in concentrations of SiO2, CaO and P2O5, (2) Fe2O3:MnO-ratios, (3) ς(CaO,MgO):SiO2-ratio, (4) statistical relationship of silica and phosphate content to metallic oxide content, (5) the Mg:Ca-ratio of protodolomites in relation to the position of the diffraction angle of dolomite's major diffraction peak (dol100, and (6) changes in mineralogical composition. Three sedimentary units were identifyed and characterized by their mineralogical and geochemical composition. The deposition of the underlying strata (section 1) occurred under sub-arid conditions. The environment changed to sub-humid conditions during deposition of the sediments in section 2 (post Middle Ages). Increasing aridity influenced the accumulation of the upper sediments (section 3). It is also proven that mineralogical analyses of lacustrine sediments allows mostly conclusions on the limnic environments during deposition. In contrast to this, geochemical features of lacustrine sediments indicate weathering and soil forming processes during deposition and the overall geomorphological system.
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  • 66
    ISSN: 1573-0417
    Keywords: fire ; disturbance ; paleoecology ; paleolimnology ; pollen ; chrystophytes ; charcoal ; Chile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A 1600 year paleoecological record of environmental change is developed from a small lake in the Nothofagus forest of southern Chile (45.5°S, 72°W). High resolution fossil pollen, charcoal, sedimentological, and chrysophycean stomatocyst analyses are used to investigate the impacts of natural and anthropogenic disturbances on terrestrial and lacustrine environments. Chronological control is based on a combination of 210Pb and 14C dating. Temporal resolution during the past 150–200 yr is ca. 8 yr/sample. The macroscopic charcoal record correlates very closely with historical and dendroecological records of 20th century anthropogenic burning in this region. The chrysophyte stratigraphy indicates that this burning had immediate impacts on the lake itself, while the pollen record provides evidence for a succession of vegetation changes lagging slightly behind the disturbance. These palynological changes are very similar to the pollen signal of European disturbance in northeastern North America. Pre-European shifts in chrysophyte assemblages may be due to the influence of earthquake activity on the lake, though there is no corroborative evidence in the pollen or charcoal records. This study demonstrates that high resolution paleoecological methods can be used to help bridge the temporal gap between traditional ecological and paleoecological studies of environmental change in the temperate forests of southern South America.
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  • 67
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    Journal of paleolimnology 13 (1995), S. 79-83 
    ISSN: 1573-0417
    Keywords: chrysophytes ; cysts ; Stomatocysts ; diatoms ; periphyton ; Arctic ; Ellesmere Island ; Paleolimnology
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    Notes: Abstract In a survey of 35 high arctic ponds, chrysophycean cysts were relatively more common in moss periphyton and epilithon habitats, than in surface sediment samples. The highest percentages of cysts relative to diatoms were found in the semi-aquatic mosses. Although chrysophytes are generally considered to be planktonic, periphytic taxa may be common in high latitudes. The ratio of diatom frustules to chrysophyte cysts in arctic sediment cores may be tracking different environmental variables than paleolimnologists may intuitively expect based on observations from more temperate regions.
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  • 68
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    Journal of paleolimnology 13 (1995), S. 107-118 
    ISSN: 1573-0417
    Keywords: 210Pb ; sediments ; cores ; paleolimnology ; lakes ; sediment focusing ; sampling
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    Topics: Biology , Geosciences
    Notes: Abstract In this paper we test the utility of the mud deposition boundary depth (mud DBD) theory (Rowanet al. 1992) as a means of maximizing sampling efficiency in paleolimnological investigations, particularly those that apply to210Pb dating. The mud DBD is defined by the relationship between near bottom wave velocity and particle threshold velocity, with wave and particle threshold theory simplified to terms of exposure and depth. Mud DBD theory can be used to define the depositional zone in lakes, and within the depositional zone defined by the mud DBD: 1) there is a high probability of obtaining a representative core, 2) variation in mass sediment accumulation rate (MSAR) is not correlated with water depth, and 3) variation in MSAR is considerably reduced from the whole lake average. This suggests that mud DBD theory can account for the effects of sediment focusing, and that the mud DBD defined depositional zone is the zone to which fine-grained sediments are focused. Finally, we have shown that to optimize sampling effort, 5 to 10 cores within the depositional zone are necessary for a reasonably precise estimate of the mean mass sediment accumulation rate. In addition, the use of mud DBD theory prior to sampling can dramatically reduce the cost associated with analyzing large numbers of cores for210Pb.
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  • 69
    ISSN: 1573-0417
    Keywords: diatoms ; eutrophication ; lake management ; paleolimnology ; British Columbia ; lakes ; phosphorus ; training sets
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    Notes: Abstract Eighteen lakes were added to a published training set of 46 British Columbia (BC) lakes in order to expand the original range of total phosphorus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and environmental variables. Specific conductivity and [TP] each explained significant (P≤0.05) directions of variance in the distribution of the diatoms. The relationship between diatom assemblages and [TP] was sufficiently strong to warrant the development of a weighted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages. The relationship between observed and inferred [TP] was not improved by the addition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with TP concentrations greater than 85 µg 1−1, so we document the development of a model containing lakes with TP≤85 µg 1−1. The updated model uses 59 training lakes and covers a range of species optima from 6 to 41.9 µg 1−1 TP, and a total of 150 diatom taxa. The updated inference model provided a more realistic reconstruction of the anthropogenic history of a highly eutrophic BC lake. The model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status.
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  • 70
    ISSN: 1573-0417
    Keywords: Younger Dryas ; pollen ; diatoms ; varves ; laminated sediment ; Laacher See Tephra ; Holzmaar ; rates of change ; sequence splitting ; variance partitioning ; redundancy analysis
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract A high-resolution pollen and diatom stratigraphy has been studied from late-glacial annually laminated sediments of Holzmaar (425 m a.s.l., Germany). The sediment sequence studied comprises 475 varves and includes two environmental perturbations of different type and duration: the short, abrupt deposition of the late Allerød tephra layer of the Laacher See volcano (LST, 11 000 yr B.P.), and the more gradual onset of the 'Younger Dryas climatic cooling. Numerical analyses involving (partial) redundancy analyses in connection with Monte Carlo permutation tests suggest that the deposition of 78 mm of Laacher See Tephra had a statistically significant effect on the pollen stratigraphy (percentage and accumulation rates), most probably because of the proximity of the site to the volcano. The diatom accumulation rates also show a statistically significant change, whereas the diatom percentage data do not change significantly. The between-sample rates-of-change in both biostratigraphies are higher at and just after the LST event than at the transition to the Younger Dryas biozone. Sequence splitting of pollen and diatom accumulation rate data also shows a clustering of significant splits at the LST event. A close correlation between changes in the pollen and diatom percentage data for the investigated time-interval suggests a common underlying climatic signal, whereas the accumulation rates of both biostratigraphies behave more individualistically and show more short-term variability due, in part, to the inherent noise in the two data sets. Variance partitioning shows that the local pollen and diatom assemblage zones explain much of the variance in the data-sets. Statistical modelling using redundancy analysis shows that the changes in the diatom assemblages are best predicted by the Younger Dryas biozone and the main changes in the pollen stratigraphy (as represented by the first PCA axis of the pollen data). The results suggest that the biostratigraphies studied at Holzmaar reflect generally stable systems which were disturbed by the deposition of the Laacher See Tephra. After a phase of recovery both systems again reached a new phase of stability prior to the long-term Younger Dryas climatic deterioration that perturbed the assemblages again. The very close and statistically significant parallelism between the major stratigraphical patterns in the pollen and diatom percentage data highlights the responses of the two biological systems to environmental perturbations at different temporal scales.
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  • 71
    ISSN: 1573-0417
    Keywords: chlorophyll ; diatoms ; myxoxanthophyll ; oscillaxanthin ; sediments ; eutrophication ; England ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Cyanobacterial carotenoids and diatom remains have been analyzed in recent sediments from the Windermere South Basin (WSB) to study the trophic evolution experienced by the lake. Dates in the top 30 cm were specifically established through radionuclide (210Pb and137Cs) analyses. Diatom stratigraphy shows dominance of the centric diatomsCyclotella comensis andC. radiosa and several benthic taxa in the early postglacial. This indicates oligotrophy in the WSB during that period. This assemblage was replaced by another dominated by the diatomAsterionella formosa in the 1870's, as has been established from the210Pb dating. From that date onwards, the lake underwent a progression towards eutrophy, indicated by the progressive increase inAulacoseira subarctica (c. 1930's),Fragilaria crotonensis (c. 1943), and more recently, of the centricsStephanodiscus parvus (c. 1971) andCyclotella meneghiniana (1988). Carotenoid stratigraphy reveals the differences between different sections of the core. Oscillaxanthin and myxoxanthophyll had very low records in the early and medium parts of the core, but increased fromc. 1950's, showing peaks atc. 1967, 1979 and 1987. Some of these peaks indicated a differential abundance ofOscillatoria, and are matched to those observed directly during the ongoing monitoring of the phytoplankton of the lake. The coincidence between the historic appearance of diatoms associated with nutrient-rich waters and the enhanced carotenoid occurrence suggest a common response to phosphorus enrichment, and that the progressive change towards eutrophy has been accentuated during the last twenty-five years.
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  • 72
    ISSN: 1573-0417
    Keywords: diatoms ; temperature ; climatic change ; paleoclimate proxies ; canonical correspondence analysis ; weighted-averaging ; Yukon ; Northwest Territories
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    Topics: Biology , Geosciences
    Notes: Abstract We identified, enumerated, and interpreted the diatom assemblages preserved in the surface sediments of 59 lakes located between Whitehorse in the Yukon and Tuktoyaktuk in the Northwest Territories (Canada). The lakes are distributed along a latitudinal gradient that includes several ecoclimatic zones. It also spans large gradients in limnological variables. Thus, the study lakes are ideal for environmental calibration of modern diatom assemblages. Canonical correspondence analysis, with forward selection and Monte Carlo permutation tests, showed that maximum lake depth and summer surface-water temperature were the two environmental variables that accounted for most of the variance in the diatom data. The concentrations of sodium and calcium were also important explanatory variables. Using weighted-averaging regression and calibration techniques, we developed a predictive statistical model to infer lake surface-water temperature, and we evaluated the feasibility of using diatoms as paleoclimate proxies. This model may be used to derive paleotemperature inferences from fossil diatom assemblages at appropriate sites in the western Canadian Arctic.
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  • 73
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    Journal of paleolimnology 16 (1996), S. 205-215 
    ISSN: 1573-0417
    Keywords: fjords ; stratification ; meromixis ; paleolimnology ; Arctic ; Ellesmere Island
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The middle arm of Taconite Inlet shows many features in common with high-Arctic fjords and coastal meromictic lakes. The surface mixed layer is fresh, and a relatively constant 5.5 m deep, indicating a layer of ice of approximately the same thickness blocks communication with the Arctic Ocean. Below the primary halocline to a depth of 85 m, at least partial communication with the Arctic Ocean exists as indicated by the oxygen, salinity and thermal structures. A sill is probably found between 40 and 85 m depth, reducing circulation below it and contributing to the oxycline. For a long but undetermined period prior to the separation of lakes C1, and C2 from the middle arm of Taconite Inlet, the surface water of the inlet was probably strongly brackish to marine suggesting that the entrance to Taconite Inlet was not blocked by an ice shelf at the time of separation. The deep water of these future lakes probably became isolated from the general estuarine circulation and began to develop some of their present limnological features prior to actual separation of the surface waters of the lakes from the inlet.
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  • 74
    ISSN: 1573-0417
    Keywords: Stable isotopes ; strontium isotopes ; hydrology ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Reconnaissance δ18O,, δD, and δ87Sr data for fifteen lakes in the Western Lakes Region of the Sand Hills of Nebraska indicate dynamic hydrologic systems. The rather narrow range of δ87Sr from lake water (1.1 to 2.1) and groundwater (0.9 to 1.7) indicates that the groundwater is generally unradiogenic. Groundwater residence times and relatively unradiogenic volcanic ash within the dune sediments control the δ87Sr values. Based on the mutual variations of δ18O and δD, the lakes can be divided into three groups. In Group 1, both δ18O and δD values increase from spring to fall. The δ18O and δD values in Group 2 decreased from spring to fall. Group 3 are ephemeral lakes that went dry some time during 1992. The data and isotopic modeling show that variations in the ratio of evaporation relative to groundwater inflow, local humidity conditions, and the δa has substantial influence on the isotopic composition. In addition, isotopic behavior in ephemeral lakes can be rather unusual because of the changing activities of water and mineral precipitation and redissolution. The annual and interannual isotopic variability of these lakes which is reflected in the paleonvironmental indicators may be the rule rather than the exception in these types of systems.
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  • 75
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    Journal of paleolimnology 17 (1997), S. 155-171 
    ISSN: 1573-0417
    Keywords: Mexico ; palaeoclimate ; sediments ; diatoms ; pollen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Northern Mexico lies close to the present day boundary between mid-latitude (Westerly) and tropical (monsoonal) sources of moisture. Studies from the adjacent southwest USA have shown major changes in lake levels and vegetation distributions over the late Quaternary which have been interpreted in terms of significant variations in the relative strengths and positions of these climate systems. Palaeoclimatic data from this area have, however, left a number of unresolved questions which can only be answered by extending work into northern Mexico, closer to the major source of summer (monsoonal) rain, the Gulf of Mexico. Studies of palaeolake sediments from a series of hydrologically closed lake basins across a range of altitudes (1280 to 2200 m a.s.l.) in northern Chihuahua are in progress using geochemical, mineral magnetic, diatom and plant microfossil analyses. Preliminary results are presented from the Alta Babícora and Encinillas basins. The sites provide records of lacustrine deposition between 〉11 000 and about 2500 yr BP. The diatom record from Babíora provides clear evidence for a deep water lake in this basin in the late glacial which persisted into the early Holocene. A dry episode coinciding with the timing of the Younger Dryas is recorded in Alta Babícora. Conditions wetter than present are indicated up to at least 7000 yr BP.
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  • 76
    ISSN: 1573-0417
    Keywords: diatoms ; lotic diatoms ; varves ; paleolimnology ; turbidities ; high arctic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Both habitat preferences and community associations for some of the most prominent pennate taxa in our profile were established using samples from the modern lake and its watershed. Habitat preferences were used to establish a simple indicator for the relative contribution of lotic communities in this lake (Lotic Index) and indicator taxa for both littoral (Achnanthes spp. and Cymbella spp.) and lotic (Hannaea arcus and Meridion circulare) communities. When profiled, the Lotic Index showed a clear positive relationship to sedimentation rate as recorded in the varves, while profiles of littoral indicator taxa show the opposite trends. It seems likely that the patterns we observed in the Lotic Index are related to changes in runoff. Apparently, there was a period of declining runoff beginning ca. two centuries ago and ending in the late 1800's. This was followed by increasing runoff lasting until the middle of the 20th century. A brief minimum occurred in ca. 1970 followed by a recovery by ca. 1980. A strong positive relationship was also found between the dates of major turbidites, exceptionally thick varves and the concentration of valves in the sediment. It is possible that many of the thicker varves in the profiles contain littoral material transported to the site of deposition by turbid interflows and underflows. For this reason, the concentration of valves in the sediment in our cores appears to be a proxy for sediment deposition from turbidity currents.
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  • 77
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    Journal of paleolimnology 18 (1997), S. 249-260 
    ISSN: 1573-0417
    Keywords: Quaternary ; paleoclimates ; paleolimnology ; ostracodes ; Wisconsin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Ostracodes document a series of late Quaternary climatic and limnologic changes within the Lake Winnebago basin of east-central Wisconsin. Using a 14 C, 137Cs, and 210Pb-based geochronology, Lake Winnebago ostracode abundances were compared to regional patterns of ostracode biogeography and the paleontological, sedimentological, and geochemical records of Elk Lake (Clearwater County), Minnesota, in order to interpret past temperature and hydrochemical changes in Lake Winnebago. Lake Winnebago sediments contain five major ostracode species, Candona ohioensis, Candona rawsoni, Cytherissa lacustris, Limnocythere verrucosa, and Physocypria pustulosa. In combination with sedimentology and geochronology, variations in the abundances of these species allow the late Quaternary record of the Lake Winnebago basin to be subdivided into five major climatic intervals: (1) glacial to post-glacial (15.5–11.0 ka), (2) cold and variable immediate post-glacial (11.0–10.4 ka), (3) warmer and wet early Holocene (10.4–7.8 ka), (4) warm but not particularly dry middle Holocene (7.8–4.2 ka), and (5) warm and moist late Holocene (4.2 ka-present).
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  • 78
    ISSN: 1573-0417
    Keywords: arctic ; lake sediments ; varves ; Devon Island ; bacteria ; diatoms ; paleoclimate
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Sediments from a 3 ha lake (75 °34.34′N, 89 °18.55′W) from the coastal region of northern Devon Island, Nunavut, Canada, contain discrete laminations in the deepest part of the basin. The laminations are varves as indicated by the correspondence between counts and thickness measurements of the couplets and 210Pb dating. A 14 cm core representing 150 years of sedimentation contained laminated couplets consisting of a lighter inorganic layer with a higher percentage of calcium and magnesium, alternating with fine darker bands, typically more cohesive, and comprising higher proportions of silica and carbon. A reddish oxidation zone with higher iron and aluminum frequently separates the laminations. The dark layer represents a biogenic component deposited in summer and is made cohesive by bacterial filaments among the other particles. The light inorganic layer represents clastic deposition from allochthonous sources. Deposition rates were relatively consistent through the core with an increase in varve thickness in the 1950s. Diatom concentrations in the sediments increased by two orders of magnitude in this century, with major increases in the 1920s and 1950s. The increase in varve thickness and diatom abundance coincides with an increase in summer melt percentage in an ice core from the Devon Island Ice Cap (Koerner, 1977). The relatively high sedimentation rate (0.15 cm yr-1) coupled with the consistency of deposition makes this lake a significant indicator for recent climate changes of the Canadian Arctic Archipelago.
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  • 79
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    Journal of paleolimnology 19 (1998), S. 309-328 
    ISSN: 1573-0417
    Keywords: agglutinated rhizopods ; testate amoebae ; thecamoebians ; Lake Winnipeg ; paleolimnology ; Holocene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Holocene sediments in Lake Winnipeg are expressed in the lower Lake Agassiz sequence which is unconformably overlain by the Lake Winnipeg sequence. Nine sites, covering the North and South basins and the connecting Narrows, were selected for analysis of Holocene changes in thecamoebian faunae. Only the Lake Winnipeg sequence contains thecamoebians. This study indicates that biologic productivity and consequently the type of organic material in the sediments is the main control on thecamoebian taxa in Lake Winnipeg. Other factors controlling the distribution of thecamoebians are water chemistry and turbidity. Inorganic sediment geochemistry and water temperature do not appear to significantly influence the thecamoebian fauna of Lake Winnipeg. Variations in the abundance of key thecamoebian species along a north-south transect divide Lake Winnipeg into three distinct areas. The North Basin has remained relatively unchanged since the retreat of Lake Agassiz as indicated by the domination of Difflugia manicata throughout its history. This species appears to prefer Cyanophyta and diatoms as its food source. In the Narrows harsh conditions created by turbid waters and lack of algal food taxa result in Centropyxis aculeata replacing Difflugia manicata as the dominant species. In the South Basin three thecamoebian assemblages are recognized. Cucurbitella tricuspis, indicative of eutrophic conditions, dominates the most recent sediments of the South Basin. The underlying sediments are characterized by Difflugia globulus. In Lake Winnipeg this species is not a cold climate (arctic) indicator as suggested elsewhere but instead seems to prefer sediments containing green and yellow-green algal material. A Centropyxis-Arcella Assemblage occurs only at the base of the southernmost core where it is indicative of an early phase of hyposaline conditions as developed in shallow pools during the southward transgression of Lake Winnipeg. This study illustrates the usefulness of thecamoebians as paleolimnological indicators. Environmental changes are more significant in the restricted South Basin resulting in distinct thecamoebian assemblages. In contrast, the North Basin provided a stable environment throughout the late Holocene reflected in only subtle faunal changes.
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  • 80
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    Journal of paleolimnology 20 (1998), S. 91-98 
    ISSN: 1573-0417
    Keywords: opal-A ; biogenic silica ; lake levels ; Allerød ; Weichselian Late-glacial ; paleolimnology ; Belgium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Macroscopic opal-A concretions were observed in lake marl deposited in a small Flemish lake (Belgium) during the Allerød biozone of the Weichselian Late-glacial (ca. 12–11 ka BP). The silica from these concretions was derived within the profile, by the leaching of siliceous microfossils – mainly diatom frustules. Formation of the concretions probably resulted from pH- and/or evaporation related precipitation of the silica at a lower stratigraphic level, presumably corresponding more or less to a former low position of the groundwater table. The presence of these concretions is probably related to alternatingly wet and dry local conditions during the middle and later part of the Allerød.
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  • 81
    ISSN: 1573-0417
    Keywords: diatoms ; Carolina bays ; paleolimnology ; calibration set ; non-metric multidimensional scaling ; weighted averaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Inferences of past climate from the fossil record in lakes rely on the accurate quantification of a relationship of fossilizing organisms to their environment. Whereas the relationship of diatoms to water chemistry parameters has been modeled in many systems, few studies adequately address the relationship of diatoms to physical properties, such as water depth or hydrology, that may be more directly tied to climate. We examined the composition of modern diatoms in surface sediments of 75 isolated ponds (mostly Carolina bays) of the Atlantic Coastal Plain to: (1) assess the influence of physical and chemical variables on the distribution of diatoms among ponds of the region, and (2) develop a model that predicts hydroperiod (a measure of pond permanence) from diatom assemblages. We constructed two hydroperiod calibration models: the first infers hydroperiod from the weighted-average optima and tolerances of taxa along the hydroperiod gradient, the second bases inferences on the hydroperiod estimates of compositionally similar samples. Both approaches incorporate a-priori and post-hoc tests of assumptions often inherent in the construction of transfer functions. Diatom assemblage composition had strong, approximately linear relationships to hydroperiod, water depth, and calcium concentration in non-metric multidimensional ordination space; effects of other variables, including pH, were non-linear or ambiguous. Overall, the assemblages reflected the dilute, acidic chemical characteristics of bays. The assemblages contained differing abundances of euterrestrial, benthic and planktonic taxa, depending on a pond's susceptibility to drying. A weighted-averaging regression model based on taxon-specific hydroperiod optima generated adequate, unbiased hydroperiod inferences from diatom species composition (r2 = 0.81). This model may be used to infer past drought episodes from fossil diatom assemblages at appropriate sites on the Atlantic Coastal Plain.
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  • 82
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    Journal of paleolimnology 20 (1998), S. 47-55 
    ISSN: 1573-0417
    Keywords: diatoms ; spatial variability ; canonical correspondence analysis ; lake eutrophication ; transfer functions ; phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom analyses were undertaken of sediment cores covering a range of water depths in a small eutrophic lake (Lough Augher, Co. Tyrone, N. Ireland). The significance of between-core variability in diatom relative frequency stratigraphy was assessed by Canonical Correspondence Analysis (CCA) where the ordination axes were constrained to external environmental variables (sediment depth, core location coordinates, water depth, effective fetch, distance-from-shore and distance-from-inflow). After the removal of the effect of sediment age by partialling it out, the resultant first two axes from the partial-CCA were significantly correlated with water depth and distance-from-shore, indicating non-uniform diatom stratigraphies across the lake. Despite this variability, all cores show the same succession of species and, therefore, record the eutrophication of the lake. Diatom-inferred total phosphorus (DI-TP) was inferred for six cores using weighted averaging regression and calibration. Apart from considerable differences of DI-TP in surficial sediment samples, there was good between-core repeatability of DI-TP profiles. These data support the use of DI-TP for establishing background nutrient concentrations for lakes, and associated implications for lake restoration schemes using single cores. Comparisons of DI-TP profiles and total diatom accumulation rate data for the individual cores indicate that diatom production peaked prior to the maximum TP concentrations in the lake.
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  • 83
    ISSN: 1573-0417
    Keywords: Lake Baikal ; pollution history ; trace metals ; carbonaceous particles ; magnetic minerals ; diatoms ; turbidites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Results of lithostratigraphic and mineral magnetic analysis of two surficial sediment cores (21 cm and 45 cm in length) collected from the Southern basin of Lake Baikal at a water depth of 1390 m, are presented. The sediments have been measured for a wide range of mineral magnetic parameters in order to assess their value in the identification of turbidite layers. Particle size and geochemical data are also presented and these explain some of the down core variations in magnetic mineralogy. It is suggested that changes in the particle size frequency distributions down core may be related to fossil diatom shells. One of the cores has been dated using 210Pb. The sediment cores were cross-correlated using low frequency magnetic susceptibility (χf) and these cores can also be correlated with a nearby core collected earlier in 1992. Changes in the magnetic parameters of χlf, IRMs and HIRM210 suggest that there are significant changes in the concentration of ferrimagnetic minerals in the sediment cores, indicating changing sediment sources and/or increasing concentrations of spheroidal carbonaceous particles and the dissolution of minerals through reduction below the oxidised layer within the sediment core.
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  • 84
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    Journal of paleolimnology 20 (1998), S. 205-215 
    ISSN: 1573-0417
    Keywords: subarctic lakes ; diatoms ; paleolimnology ; climate change ; Cyclotella ; Finnish Lapland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms were analysed from a 30-cm long sediment core obtained from remote subarctic Lake Saanaärvi (69°03′N, 20°52′E) in order to trace possible changes in the lake. Diatom assemblages were relatively constant throughout the core, except in the top 4–5 cm (approx 1850 A.D.) where relative frequencies of Aulacoseira italica subsp. subarctica, A. lirata var. biseriata, Cyclotella comensis and C. glomerata increased markedly. No significant trends were observed in the weighted averaging (WA) reconstructed pH values. Several hypotheses, including (i) airborne pollution, (ii) climatic change, and (iii) catchment disturbances have been put forth to explain the recent changes in diatom assemblages. The diatom change coincides with a marked increase in mean annual temperature that has been documented in the area since the termination of the Little Ice Age. Our evidence favours climate change as the main causative mechanism for the observed diatom compositional changes, although other explanations cannot be ruled out.
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  • 85
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    Journal of paleolimnology 20 (1998), S. 267-276 
    ISSN: 1573-0417
    Keywords: diatoms ; lake depth ; Sylvania Wilderness Area ; Upper Peninsula of Michigan ; hemlock ; mid-Holocene warm period
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Transects of surface sediment samples were taken in 4 lakes from the Sylvania Wilderness Area, Upper Peninsula of Michigan. These surface samples were compared with diatom samples from a core taken in the Northwest basin of Crooked Lake, also from the Sylvania Wilderness Area. Weighted Averaging calibration was used to reconstruct lake depths in Crooked Lake using the diatom microfossils from the core and the surface samples to infer past lake depth. During the early Holocene the lake was dominated by planktonic species and diatom-inferred water depth was large – approx. 13 m. At about 6700 BP inferred water depth was 2 m and samples were dominated by Fragilaria construens var. venter – a species characteristic of shallow parts of the surface sample transects. From 6700 to 5000 BP reconstructed water level was at its shallowest. From 5000 to 3000 BP it increased. This rise in water level was marked by increasing abundances of Aulacoseira ambigua and occurred at the same time increasing percentages of hemlock pollen indicate increasing available moisture. Modern water depth was reached about 3000 BP. The water level changes at Crooked Lake are consistent with regional climate changes in the Upper Midwest during the Holocene. The lake was shallowest during the mid-Holocene warm period documented by other investigators. It deepened as the Midwestern climate became cooler and wetter during the late Holocene.
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  • 86
    ISSN: 1573-0417
    Keywords: diatoms ; sediment cores ; industrial pollution ; copper ; teratology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom remains were analysed in two short sediment cores from a subalpine Italian lake (Lake Orta), known for its major industrial pollution dating from the late 1920s, which has only recently been stopped. Copper was recognised as the main toxic agent for diatoms during the first 30 years of pollution (peak value: 100 μg l-1 in the late 1950s). A diatom community similar to other deep subalpine lakes existed in the past, and was disrupted by the pollution events. Acute and long-term effects of Cu contamination were tracked by changes in three distinct groups of species around the sharp boundary corresponding to the onset of the pollution. These groups were respectively composed of: (1) Species quickly extirpated by the discharge, mostly belonging to Fragilaria and Cyclotella and never reappearing; (2) Species apparently not affected, or not immediately affected, by the pollution, showing no definite trends with time. Synedra species, with various deformities, were conspicuous among these; (3) Species with accumulation rates increasing with time irrespective of pollution, mostly belonging to Achnanthes. Properties and tolerances of these groups (e.g. Synedra and Achnanthes) are discussed in detail.
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  • 87
    ISSN: 1573-0417
    Keywords: chironomid ; Holocene ; paleoclimate ; paleolimnology ; treeline ; lake sediment ; British Columbia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Analysis of the distributions of chironomid (midge) and other dipteran subfossils from two high elevation lake sediment cores in the Cascade Mountains reveals changes in midge communities and inferred climate since the late-glacial. Cabin Lake and 3M Pond are located near treeline in the subalpine Engelmann Spruce/Subalpine Fir biogeoclimatic zone of British Columbia. In Cabin Lake, chironomid head capsule assemblages depict a typical late-glacial community, and three distinct Holocene communities. In Cabin Lake, the late-glacial community is composed of cold-stenothermous taxa dominated by Stictochironomus, Mesocricotopus, Heterotrissocladius, Parakiefferiella nigra, Protanypus and Paracladius, whereas warm water midges are absent or rare, indicating cold conditions. A late-glacial chironomid community was not found in 3M Pond. In both lakes the early Holocene is dominated by a diverse warm-adapted assemblage, corresponding to the warm climatic conditions of the xerothermic period. Cabin Lake's mid-Holocene zone records a decrease in relative abundance of the warm water types and is accompanied by an increase in cold-stenotherms. At 3M Pond this period shows a dramatic loss in diversity of warm-adapted taxa, as the temperate genus Dicrotendipes dominates. This zone corresponds to Hebda's (1995) mesothermic period. Further cooling in the late Holocene (to modern conditions) is inferred from continued reduction of warm water midges and persistence (at Cabin Lake) or appearance (at 3M Pond) of a cold-stenothermal community. This late Holocene cooling is similar in timing to Neoglacial advances in the Coast, Cascade, and Rocky Mountains of southern British Columbia. Similarities in the timing of chironomid and vegetation community changes at these high elevation sites, along with the more rapid response time of the Chironomidae, support the sensitivity of midges to postglacial climatic change at high elevation sites.
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  • 88
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    Journal of paleolimnology 20 (1998), S. 353-368 
    ISSN: 1573-0417
    Keywords: Argentina ; Holocene ; paleolimnology ; diatom assemblages ; paleoclimatology ; paleoenvironments ; brackish water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We present a climatic reconstruction of Holocene lacustrine episodes in the Salinas del Bebedero basin (Argentina), based on geological and diatom information. Morphological, sedimentological and diatom evidence between 11600 ± 140 yr BP and 325 ± 95 yr BP, allowed us to interpret the paleoenvironments of the basin. Episodes of high energy (sandy levels) are linked to large inflow of meltwater through the Desaguadero River, related to development of glaciers on the Andes. This inflow is characterized by peaks of relative abundance of the brackish water diatom Cyclotella choctawatcheeana Prasad. The values of C. choctawatcheeana decrease in deposits of low energy (clay levels), where it co-dominates with oligohalobous Fragilaria and Epithemia spp. To the last two peaks of large inflow of meltwater, radiocarbon dates corrected to sidereal ages, are AD 1280/1420 and AD 1443/1656. These ages agree with two cold episodes clearly recorded in dendrological studies from the Patagonian Andes and were correlated to the Little Ice Age. Thus, older Holocene episodes of large inflow of water to the basin were correlated with the Neoglacial Advances defined by Mercer (1976) for the Andes.
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  • 89
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    Journal of paleolimnology 20 (1998), S. 381-407 
    ISSN: 1573-0417
    Keywords: paleolimnology ; ostracode ; paleoecology ; Great Salt Lake ; Pliocene ; Pleistocene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract This study summarizes the results of micropaleontological, sedimentological, and isotope geochemical analyses of cuttings from five deep wells drilled in the Great Salt Lake (Utah, USA). Spanning the last 5.0 million yrs, our environmental history of the Great Salt Lake distinguishes four intervals based on paleobiological and sedimentological characteristics, using a previously developed tephrochronology for age control. For most of its history, the Great Salt Lake Basin has been occupied by a mixture of marsh, shallow lacustrine and sand flat conditions. In contrast, open lake conditions, typical of the Bonneville cycles and the modern Great Salt Lake apparently have only dominated the basin for the past 0.6-0.8 Ma. The two main structural basins in the study area (the North and South Basins) experienced different lacustrine histories. Large but frequently saline lakes occupied the North Basin after about 0.6 Ma. In the South Basin, ephemeral, saline lacustrine conditions started at 2.1 Ma and developed to full lacustrine conditions at 0.3 Ma. Our paleoenvironmental interpretations are broadly consistent with the aquatic palynological records from the same wells, as well as with the prior core- and outcrop-based lines of evidence. However, the differences in lake history between the North and South Basin have not been previously recognized.
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  • 90
    ISSN: 1573-0417
    Keywords: Lake cores ; Easter Island culture ; South America ; diatoms ; cladocerans ; ostracods ; chrysophytes ; magnetic properties ; palaeopigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We reconstruct aspects of the history of Easter Island over the last 4-5 centuries based on the study of a core from Rano Raraku Lake, situated in the crater that contains the quarry of the island's giant statues or moai. We use microfossils of plants and animals to identify five zones. The last three of these are separated by waves of immigration from South America and from the subantarctic. We argue that the first or South American wave, dated to the second half of the 14th century, may represent a visit by South American Indians. Magnetic information, pollen, diatoms, chrysophyte stomatocysts and fossil plant pigments reveal a synchronism between the South American contact and the cessation of moai quarrying. We therefore suggest that Amerindians contributed to the cultural collapse of the island. The second or subantarctic wave may reflect an early European visit to the island, possibly by Cpt. James Cook in 1774, or by Jacob Roggeveen in 1722.
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  • 91
    ISSN: 1573-0417
    Keywords: ostracodes ; environmental change ; Holocene ; northern Great Plains ; Saskatchewan ; paleolimnology ; Canada
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Holocene paleoenvironments of Harris Lake, southwestern Saskatchewan, are reconstructed from the ostracode stratigraphy of a 10.4 m sediment core. Twenty three taxa, representing nine genera, were identified and counted from 113 samples. At each depth, a theoretical faunal assemblage was derived from the raw counts. The mean and variance of chemical, climatic and physical variables were inferred from modern analogues of the fossil assemblages, using existing autecological data from 6720 sites, mostly in western Canada. These data suggest four paleoenvironments: an early-Holocene (9240–6400 years BP) variable climate supporting aspen parkland vegetation; the warm dry hypsithermal (6400–4500 years BP); a short transitional period of ameliorating climate and expanding subboreal forest (4500–3600 years BP); and the present environment since 3600 years BP. A change in regional climate with the draining of Glacial Lake Agassiz (ca. 8500 years BP) and landsliding in the watershed (ca. 4000 years BP) caused relatively rapid environmental change. The ostracode record generally corroborates the interpretations of other proxy data previously published for Harris Lake. Most of the discrepancy involves the timing and severity of maximum Holocene warmth and aridity. Peak aridity interpreted from the pollen data is earlier than in the other proxy records. Both the diatoms and ostracodes indicate highest paleosalinity between ca. 6500 and 5000 years BP, but maximum salinity in the diatom record occurs between ca. 6000–5700 years BP, whereas the ostracode-inferred salinity is relatively low at this time and peaks later at ca. 5000 years. Neither of these reconstructions suggests the short episodes of hypersalinity interpreted from the mineralogy.
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  • 92
    ISSN: 1573-0417
    Keywords: lake sediments ; near infrared (NIR) spectroscopy ; sediment characteristics ; loss-on-ignition ; paleolimnology ; northern Sweden
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Near-infrared (NIR) spectral data were obtained from 165 surface sediment samples from a northern Swedish humic, mesotrophic lake (0.5 km2). The NIR spectra, together with data on water depth and loss-on-ignition (LOI), allow an evaluation of the source of spatial variance in sediment characteristics. The results show that water depth and organic matter (LOI) account for 20 and 16%, respectively, of the variance in the NIR-absorbance data. More importantly, the spatial variance in the spectral data suggest that NIR analysis of lake sediments mainly reflect sediment properties that cannot simply be explained by depth or amount of organic matter. The influence of inlets and land-use (e.g. clear-cutting) on sediment characteristics was more pronounced in the spectral data than would be expected from the LOI data. This is explained by differences in the chemical composition of the organic matter, as revealed by NIR spectroscopy, rather than in the amount of organic matter or depth-related sedimentation properties (e.g. particle size or density). This initial attempt to characterise sediment properties using NIR suggests that NIR analysis might become a valuable complementary tool to traditional sediment characterisation.
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  • 93
    ISSN: 1573-0417
    Keywords: diatoms ; biogenic silica ; pigments ; biomass ; trophic state changes ; eutrophication ; Lake Constance ; Germany
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract In Lake Constance, phosphorus concentrations and the seasonal development of phytoplankton communities in water samples from the pelagic zone were regularly recorded since the 1950's. Before the 1950's, there were occasional investigations of plankton communities since 1896. We compared these data with the sedimentary record in two sediment cores. Then, the eutrophication history of Lake Constance was inferred from diatoms. The record of biogenic silica in the cores is discussed with respect to diatom biomass increase. Diatom assemblages in the sediment cores precisely reflected the pelagic diatom development for the period 1971--1992. Both sediment cores and the water samples have a high interannual variability of diatom assemblages. Below a sediment depth of 27 cm (AD 1920), more than 50% of the diatoms were partly corroded, and we limited the reconstruction of trophic state changes to the interval of 1920--1993. Oligotrophic conditions of Lake Constance were indicated by the dominance of various Cyclotella taxa from 1920 to 1940. Since 1939/1940, increasing abundance of it Tabellaria fenestrata showed oligotrophic to mesotrophic conditions. Between 1953 and 1956, increasing Stephanodiscus hantzschii and disappearing Cyclotella indicated advanced eutrophication and total phosphorus values ranged between 8--10 mg m-3 during turnover in late winter. Further eutrophication was shown by disappearing T. fenestrata and increasing S. minutulus in 1963. Maximum TP concentrations of 87 mg m-3 occurred in 1979/80 and was accompanied by increasing abundances of Aulacoseira granulata. From 1986 to 1992, reoccurrence of Tabellaria fenestrata and Cyclotella indicate some recovery of Lake Constance. Biogenic silica and diatom abundances were similar among cores but indicate a 3--4 fold increase of diatom biomass only. This was far below the estimate of biomass increase from sedimentary pigment data (25 fold) and the estimate of phytoplankton data from the literature (70 fold).
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  • 94
    ISSN: 1573-0417
    Keywords: Florida ; geochemistry ; 210Pb dating ; macrophytes ; nutrients ; paleolimnology ; sediments ; shallow lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We retrieved four sediment cores from shallow, eutrophic, macrophyte-dominated Orange Lake (A = 51.4 km2, zmax 〈5 m, zmean 〈 2 m), north-central Florida, USA. The 210Pb-dated profiles were used to evaluate spatial and temporal patterns of bulk sediment and nutrient accumulation in the limnetic zone and to infer historical changes in lake trophic state. Bulk density, organic matter, total carbon, total nitrogen, total phosphorus and non-apatite inorganic phosphorus (NAIP) concentrations displayed stratigraphic similarities among three of four cores, as did accumulation rates of bulk sediment, organic matter and nutrients. Accumulation rates were slower at the fourth site. Nutrients showed generally increasing rates of accumulation since the turn of the century. Percentages of periphytic diatom taxa increased progressively in the cores after ~ 1930. Diatom-inferred limnetic total P trends were similar among profiles. Eutrophic conditions were inferred for the period prior to the turn of the century. The lake was hypereutrophic in the early decades of the 1900s, but inferred limnetic total P values declined after ~ 1930. Declining inferred limnetic total P trends for the last 60--70 years were accompanied by concomitant increases in accumulation rates of total P and NAIP on the lake bottom. Several lines of evidence suggest that after ~ 1930, phosphorus entering Orange Lake was increasingly utilized by submersed macrophytes. Paleolimnological records from Orange Lake highlight the importance of using multiple sediment variables to infer past trophic state and suggest that aquatic macrophytes can play a role in regulating water-column nutrient concentrations in shallow, warm-temperate lakes.
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  • 95
    ISSN: 1573-0417
    Keywords: acidification ; chrysophytes ; Adirondack Park ; Big Moose Lake ; New York ; acidic deposition ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A 40-cm sediment core from Big Moose Lake (Adirondack Mountains, New York, U.S.A.) was analyzed for recent changes in chrysophyte composition of chrysophyte species to assess if legislated reductions of sulphur emissions have resulted in changes in biological composition and inferred lakewater pH in this lake. This core, taken in September 1994, had a record of stratigraphic changes in chrysophyte assemblages remarkably similar to those in 210Pb-dated sediment cores taken in 1983 and 1988. Abrupt changes in chrysophyte stratigraphy were used to date the newest sediment core by stratigraphic correlation. We observed relatively constant composition of chrysophyte species and inferred-pH values in post-1970 sediments, which suggests that there has been little change in lakewater pH values despite the reductions in sulfate deposition since 1970 in the Adirondacks. These results are consistent with recent monitoring measurements in the Adirondacks. Further research is necessary to ascertain the applicability of these findings to other lakes in the Adirondacks and to determine the reasons for the lack of recovery.
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  • 96
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    Journal of paleolimnology 21 (1999), S. 235-255 
    ISSN: 1573-0417
    Keywords: saline lake ; groundwater inputs ; geochemical modelling ; closed-basin lake ; paleolimnology ; Great Plains ; paleohydrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sediment cores from Chappice Lake, a hypersaline, groundwater-fed lake in southeastern Alberta, have been used in previous studies to reconstruct Holocene climate using lake levels as a source for proxy climate data. This assumes that the lake is fed by a shallow groundwater system sensitive to changes in climate. In this study we use the dynamics and chemistry of groundwater entering the lake to test this hypothesis. Groundwater inputs calculated from historical records using a simple water budget were highest during periods when the precipitation deficit was high. Over specific time intervals, the expected relationship between lake volumes and climate were not always found. Feedback loops between lake levels and groundwater input, and time lags within the system are the mechanisms proposed to explain these discrepancies. Field measurements suggest discharge of a local surficial groundwater system. Slug tests reveal a high conductivity system (K = 10-5 m/s) surrounding the lake. Hydraulic heads measured in standpipe, multilevel and minipiezometers installed around Chappice Lake show that the lake is situated in a closed hydraulic head contour. Hydraulic heads and water table elevations show strong annual fluctuations corresponding to seasonal changes in recharge. Horizontal hydraulic gradients measured in areas of groundwater springs indicate a strong horizontal component of flow towards the lake. Vertical hydraulic gradients are low and indicate the upward flow of water consistent with the discharge of a shallow, surfical groundwater system. Groundwater sampled from deposits surrounding Chappice Lake and springs feeding the lake have compositions similar to both shallow surficial aquifers and bedrock aquifers suggesting that the lake may be receiving inputs from both sources. However, evaporation simulations using PHRQPITZ, show that the evaporation of water typical of bedrock aquifers result in a mineral assemblage and brine composition different from that found at Chappice Lake. This suggests that discharge of a regional groundwater system can be eliminated as a dominant source over the lake's history. Evaporation simulations suggest that evaporation of groundwater from shallow surficial deposits can best explain the present mineral assemblage and brine chemistry and were likely the dominant source of water to the lake. Bedrock and shallow surficial groundwater sources have different chemistries and isotopic compositions. In hydrogeological settings such as Chappice Lake where more than one source may contribute to the lake, the relative importance of the different sources may change with changes in climate. If the source water composition to the lake changes, identifying changes in climate or hydrology based on changes in the composition of the lake preserved in sediment core will be made more difficult. This may complicate paleoclimate and paleohydrological reconstructions that rely on mineralogical and isotopic data.
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  • 97
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    Journal of paleolimnology 21 (1999), S. 263-269 
    ISSN: 1573-0417
    Keywords: clay ; flocculation ; meromixis ; lakes ; laminae ; Tasmania ; lake Fidler ; paleolimnology ; estuaries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sediments of Lake Fidler, a meromictic lake in south-west Tasmania, contain distinctive laminae. In order to determine their composition and formation, these laminae were studied using a combination of X- ray analysis, scanning electron microscopy, X-ray diffraction and vibrational spectrometry. Results indicated that the laminae were composed of clay originating from the adjacent Gordon River estuary. The clay was also found as part of the general sediment matrix of the core. The evidence indicates that the laminae are formed during incursions of brackish water from the adjacent Gordon River estuary into Lake Fidler which cause the flocculation of clay minerals in the water column. These clay minerals then sink rapidly to the sediments to form laminae. Although the formation of these laminae pre-dates meromixis, their mode of formation corroborates the theory that meromixis is maintained ectogenically by periodic inflows of brackish water replenishing monimolimnetic salts.
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  • 98
    ISSN: 1573-0417
    Keywords: pollen ; diatoms ; algae ; ostracods ; stable isotopes ; palaeolimnology ; Holocene ; Morocco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Pollen, geochemical and sedimentological data from Sidi Ali, a montane Moroccan lake, provide a 7000 yr record of changes in climate, catchment vegetation and soil erosion intensity. Diatoms, non-silicious algae, macrophyte fossils and ostracods from the same core record the dynamics of the lake ecosystem. Oxygen isotope and trace-element ratios of benthic ostracods appear to be relatively insensitive to climatic variation in this open lake with low water-residence time, but diatom plankton / periphyton (P/L) ratios show lake-level variations that are probably climate controlled. At least two superimposed processes are recorded, but at different timescales: catchment vegetation and soils show long-term changes due to climate and human impact, whereas P/L ratios suggest century-scale oscillations in lake depth. The timing of changes in algal and macrophyte productivity and carbon cycling within the lake broadly corresponds to changes in terrestrial vegetation, suggesting either that lake nutrient status is linked to catchment vegetation and soils, or that both were influenced by climate. The lack of a sensitive and independent (non-biological) climate proxy makes it more difficult to assess the lake's ecological response to short-term climate variation. Overall, the lake's evolution has been influenced both by catchment-mediated nutrient flux and by changes in water balance, thus having characteristics in common with both temperate and arid zone lakes.
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  • 99
    Electronic Resource
    Electronic Resource
    Springer
    Journal of paleolimnology 22 (1999), S. 1-15 
    ISSN: 1573-0417
    Keywords: diatoms ; lake sediments ; acidification ; pH ; alkalinity ; colour ; regional estimates ; northern Sweden
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Changes in lake-water pH, alkalinity and colour were inferred from diatoms in surface sediment samples and sediment samples from pre-industrial times from 118 northern Swedish lakes. This palaeolimnological study does not support the hypothesis that there is a large-scale modern acidification in the two northernmost counties of Sweden; pH had decreased significantly in eight lakes, while five had a significant increase. Partial least-squares regression of changes in water chemistry in relation to catchment characteristics was performed to evaluate the causes of the acidity status. Furthermore, temporal trends were assessed from long sediment cores from five acidic lakes. The results suggest that the presently acid lakes have faced a long-term acidification trend over several thousand years due to soil-forming processes and vegetation development. However, due to the acid sensitivity of the region, future acidification trends in northern Swedish lakes should be carefully observed and assessed.
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Journal of paleolimnology 22 (1999), S. 71-80 
    ISSN: 1573-0417
    Keywords: circulation model ; diatoms ; Baltic Sea ; shoreline displacement ; palaeosalinity ; laminated sediments ; palaeoproductivity ; anoxia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract During the last retreat of the Laurentide Ice Sheet in North America, many proglacial lakes formed as continental drainage was impounded against the southern and western ice margin. Lake Agassiz was the largest of these lakes. The bathymetry of Lake Agassiz at the Herman and Upper Campbell beach levels – formed at about 11.5–11.0 ka and 9.9–9.5 ka, respectively – was computer modelled in this study by first collecting data for the isostatically-deformed paleowater planes of the two lake levels (derived from isobase lines constructed from beach elevations), and then subtracting these from the modern topography of the former lake floor. Pixels with dimensions of 1/30 × 1/30 of a degree were used in the model. Using these data, the area and volume of the lake were also calculated: at the Herman level these were ∼152 500 km2 and ∼13 100 km3 respectively; at the Upper Campbell level these were ∼350 400 km2 and ∼38 700 km3. Contour maps showing the paleobathymetry of both periods in the lake's history were also constructed. Determining the paleobathymetry and volume of Lake Agassiz is an important step in understanding the impact that the lake had on its surrounding environment and on the rivers, lakes, and oceans into which it flowed.
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