Gerard J M Versteegh

Preservation of organic-walled dinoflagellate cysts in different oxygen regimes: a 10,000 year natural experiment

Abstract The occurrence of organic-walled dinoflagellate cysts in (fossil) sediments depends on several factors, including as the ecological preferences of the cyst-forming dinoflagellates, cyst production, transport and preservation. Although laboratory experiments have shown that several cyst species are sensitive to chemical treatment, no information about the selective preservation of dinoflagellate cyst species in natural environments has previously been presented. Here, we present data on the effects of oxygen availability in bottom sediments on a cyst assemblage from the ungraded Madeira Abyssal Plain f-turbidite of which only the upper layer has been oxidized. Based on differences in species composition between the oxidized and underlying, unoxidized layers of this turbidite, the influence of oxygen availability on the preservation of individual species has been estimated. Cyst species have been classified in ascending order of resistance to oxygen availability in sediments as: (1) highly sensitive (cysts formed by Protoperidinium species), (2) moderately sensitive (e.g. Spiniferites species), (3) moderately resistant (e.g. Impagidinium paradoxum and Nematosphaeropsis labyrinthus) and (4) resistant (e.g. Impagidinium aculeatum).

POSTDEPOSITIONAL OXIC DEGRADATION OF ALKENONES : IMPLICATIONS FOR THE MEASUREMENT OF PALAEO SEA SURFACE TEMPERATURES

Free and “bound” long-chain alkenones (C37∶2 and C37∶3) in oxidized and unoxidized sections of four organic matter-rich Pliocene and Miocene Madeira Abyssal Plain turbidites (one from Ocean Drilling Program site 951B and three from site 952A) were analyzed to determine the effect of severe post depositional oxidation on the value of U37k′. The profiles of both alkenones across the redox boundary show a preferential degradation of the C37∶3 compared to the C37∶2 compound. Because of the high initial U37k′ values and the way of calculating the U37k′ this degradation hardly influences the U37k′ profiles. However, for lower U37k′ values, measured selective degradation would increase U37k′ up to 0.17 units, equivalent to 5°C. For most of the U37k′ band-width, much smaller degradation already increases U37k′ beyond the analytical error (0.017 units). Consequently, for interpreting the U37k′ record in terms of past sea surface temperatures, selective degradation needs serious consideration.

Use of selective degradation to separate preservation from productivity

The assessment of diagenetic influences on the sedimentary record is problematic despite its crucial importance for accurate environmental reconstruction and understanding of biochemical cycles. We propose a general applicable method that uses differences in degradation rates of organic components to separate degradation and productivity. We demonstrate this method on a southeastern Atlantic sediment core covering the past 145 k.y. The new method solves discrepancies between existing organic matter, silica- and carbonate-based productivity reconstructions, and emphasizes the importance of bottom- and pore-water characteristics for transformation of the sedimentary record.

Resistant macromolecules of extant and fossil microalgae

The occurrence and composition of macromolecular resistant walls of microalgae and their fossil macromolecular counterparts are reviewed. To date, several algal groups have been identified to produce fossilizable biomacromolecules. Only two biosynthetic pathways seem to be responsible for this, of which the acetate/malate pathway used by Chlorophyta, Eustigmatophyta and Dinophyta is considered to lead to a series of closely related resistant biomacromolecules, called algaenans. Algaenans consist of a network of predominantly linear carbon chains. A different, as yet unidentified, pathway is used by the Dinophyta to produce the aromatic walls of their cysts. The poly‐ketide or acetogenic pathway may have been responsible for resorcinol‐based algae or bacteria‐derived microfossils of the acritarch Gloeocapsamorpha prisca, either through synthesis of the biomacromolecule or through a third pathway, the post‐mortem polymerization of its resorcinol lipids. The postmortem polymerization of lipids also appears to be responsible for the formation of fatty acid‐based macromolecules in Eocene dinoflagellate‐shaped remains from Pakistan. Finally, there is a clear need for elucidating the chemical differences between the biomacromolecules produced by the algae and their fossil analogs in the sediments. This notably applies to the release and condensation of aliphatic and aromatic moieties both at normal and at elevated temperature and pressure conditions.

Taraxerol and Rhizophora pollen as proxies for tracking past mangrove ecosystems

Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore. Analyses of mid-Pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity. This demonstrates the complex environmental response of the interaction between precession-related humidity cycles and obliquity-related sea-level changes on mangrove input.

U37K′ values for Isochrysis galbana as a function of culture temperature, light intensity and nutrient concentrations

Abstract The alkenone producing species Isochrysis galbana has been cultured at different temperatures, nutrient and light levels, to investigate effects of genetic and environmental variation on U37K′. The experiments show that: (1) the U37K′–temperature relationship of I. galbana differs significantly from such relationships established for other species, (2) U37K′ values are not significantly influenced by nitrogen limitation, (3) U37K′ values are influenced by phosphate and light limitation equivalent to temperature decreases of about 5–7°C at 16°C. Temperature thus is not the only variable capable of changing alkenone unsaturation and the model that alkenones play a role in membrane fluidity regulation alone, seems too simple.

The 2.1 Ga old Francevillian biota: biogenicity, taphonomy and biodiversity.

The Paleoproterozoic Era witnessed crucial steps in the evolution of Earths surface environments following the first appreciable rise of free atmospheric oxygen concentrations ∼2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rod-shaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

The use of dinoflagellate cysts to separate human-induced from natural variability in the trophic state of the Po River discharge plume over the last two centuries.

To obtain insight into the natural and/or human-induced changes in the trophic state of the distal portion of the Po River discharge plume over the last two centuries, high temporal resolution dinoflagellate cyst records were established at three sites. Cyst production rates appear to reflect the natural variability in the rivers discharge, whereas cyst associations reflect the trophic state of the upper waters, which in turn can be related to agricultural development. The increased abundances of Lingulodinium machaerophorum and Stelladinium stellatum found as early as 1890 and 1920 correspond to the beginning of the industrial revolution in Italy and the first chemical production and dispersion of ammonia throughout Europe. After 1955, the increased abundances of these species and of Polykrikos schwartzii, Brigantedinium spp. and Pentapharsodinium dalei correspond to agriculturally induced alterations of the hypertrophic conditions. A slight improvement in water quality can be observed from 1987 onward.

Variations in calcareous dinoflagellate associations from the Maastrichtian to Middle Eocene of the western South Atlantic Ocean (São Paulo Plateau, DSDP Leg 39, Site 356)

Abstract Calcareous dinoflagellates often dominate the dinoflagellate cyst assemblage in Cretaceous to Recent oceanic sediments. However, their distribution in Paleogene sediments has scarcely been studied. The investigation of samples from DSDP Site 356 for their calcareous dinoflagellate content revealed 35 mainly long-ranging taxa. The associations and characteristic wall types (pithonelloid, oblique, radial, tangential) fluctuate quantitatively and qualitatively in distinct stratigraphic patterns. Significant shifts, primarily at the K/T boundary and the Paleocene/Eocene boundary, reflect changes in environmental conditions. Certain dinoflagellates forming calcareous cysts, such as Operculodinella operculata, were well adapted to the relatively rapid change of environmental conditions at the K/T boundary, thus blooming to dominate the carbonate flux to the ocean floor. In contrast to the stable Paleocene associations, Eocene calcareous dinoflagellates show fluctuations in relative abundances. These fluctuations can possibly be attributed to redeposition related to increased seaward transport of specimens, due to strengthened western boundary currents. The flora includes two new genera, one new species, and two new forms: Retesphaera diadema Hildebrand-Habel, Willems et Versteegh, gen. et. sp. nov., Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Sphaerodinella? tuberosa forma elongata Hildebrand-Habel, Willems et Versteegh, comb. et forma nov., Sphaerodinella? tuberosa forma variospinosa Hildebrand-Habel, Willems et Versteegh, comb. et forma nov. Three new combinations are proposed: Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Operculodinella operculata (Bramlette et Martini, 1964) Hildebrand-Habel, Willems et Versteegh, comb. nov., and Sphaerodinella? tuberosa (Kamptner, 1963) Hildebrand-Habel, Willems et Versteegh, comb. nov. The genus Operculodinella Kienel, 1994 is emended.

Temperature and productivity influences on U37K′ and their possible relation to solar forcing of the Mediterranean winter

To assess the extent and nature of human-induced climate change, we need to understand natural climate variability. This heavily relies on proxy-based climate reconstructions, calling for excellent understanding of the conditions represented by the proxies. Here we report on an alkenone-based (U37K′) sea surface temperature (SST) proxy record originating from south Italian marine sediments, and covering 1305 A.D. to 1979 A.D. with a 3.87 year resolution. The shallow-water cores, extracted from the Gallipoli terrace in the Gulf of Taranto, were dated by the Torino group with high accuracy over the last two millennia, using radiometric and tephroanalysis methods. On the basis of comparison with historical and satellite-derived climate and productivity data, we propose that U37K′ reflects mainly SST of the cooler part of the year and is modified by variation in magnitude and timing of peak alkenone production on the seasonal temperature cycle. Comparison of the U37K′ record with the record of atmospheric Δ14C, a proxy for solar energy variability, shows a high correlation (r = −0.73) for the period between 1420 A.D. and before human interference with the Δ14C record by combustion of fossil carbon and the release of radioactive isotopes by nuclear tests. This suggests a centennial-scale solar forcing. We propose that wind-induced mixing resulting from Mediterranean climate dynamics plays a crucial role in translating solar activity to alkenone productivity and SST during the cooler part of the year.