Beschreibung: This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500 km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Beschreibung: Climate change is predicted to alter temperature, carbonate chemistry, and oxygen availability in the oceans, which will affect individuals, populations and ecosystems. We use the fossil record of benthic foraminifers to assess developmental impacts in response to environmental changes during the Paleocene Eocene Thermal Maximum (PETM). Using an unprecedented number of µ-Computer Tomography scans, we determine size of the proloculus (first chamber), number of chambers, and final size of two benthic foraminiferal species which survived the extinction at Sites 690 (Atlantic sector, Southern Ocean, paleodepth 1900m), 1210 (central equatorial Pacific, paleodepth 2100m), and 1135 (Indian Ocean sector, Southern Ocean, 600-1000m). The population at shallowest Site 1135 does not show a clear response to the PETM, whereas those at the other sites record reductions in diameter or proloculus size. Temperature was similar at all sites, thus not likely the reason for differences between sites. At Site 1210, small size coincided with higher chamber numbers during the peak event, and may have been caused by a combination of low carbonate ion concentrations and low food supply. Dwarfing at Site 690 occurred at lower chamber numbers, and may have been caused by decreasing carbonate saturation at sufficient food levels to reproduce. Proloculus size varied strongly between sites and through time, suggesting a large influence of environment on both microspheric and megalospheric forms without clear bimodality. The effect of the environmental changes during the PETM was more pronounced at deeper sites, possibly implicating carbonate saturation.

Beschreibung: Development plays an important part in shaping adult morphology and morphological disparity, yet its influence on evolutionary processes is seldom explored because of a lack of preservation of ontogenetic stages in the fossil record. By preserving their entire ontogenetic history within their test, and with the advent of high-resolution imaging techniques, planktic foraminifera allow us to investigate the influence of developmental constraints on disparity. Using Synchrotron radiation X-ray tomographic microscopy (SRXTM), we reconstruct the ontogenetic progression of seven species across several of the major morphotypic groups of planktic foraminifera, including morphotypes of a species exhibiting high phenotypic plasticity and closely related pseudo-cryptic sister-taxa. We show differences in growth patterns between the globigerinid species, which appear more tightly regulated within the framework of isometry from the neanic stage, and the globorotaliid species, whose adult stages present allometric trends. Morphological change through ontogeny results in a change in surface area to volume ratios. Different metabolic processes therefore dominate at different stages of ontogeny, changing the vulnerability of the organism to environmental influences over growth, from factors affecting diffusion rates in the juvenile to those affecting energy supply in the adult. These findings identify some of the parameters within which evolutionary mechanisms have to act.

Beschreibung: The Paleocene Eocene Thermal Maximum (PETM) is associated with major extinction events in the deep ocean, and significant paleogeographic and ecological changes in surface ocean and terrestrial environments. However, the impact of the associated environmental change on shelf biota is less well understood. Here we present a new PETM record of a low paleolatitude late Paleocene-earliest Eocene shallow-marine carbonate platform from Meghalaya, NE India (eastern Tethys). The biotic assemblage was distinctly different to other Tethyan PETM records dominated by larger benthic foraminifera and calcareous algae both in the Paleocene and Eocene. The record is lacking the ecological change from corals to larger foraminiferal assemblages and the Lockhartia dominance, characteristic of other sections in the Tethys. Limestone samples were collected at very high resolution of up to 10 cm from the carbonate successions outcropping in the Mawmluh Cement quarry (25°15.707' N; 91°42.626' E), East Khasi Hills, Meghalaya, NE India. Petrographic thin-sections were prepared from the limestone samples for the light and scanning electron microscopic analysis of the biotic components. In addition to LBF biostratigraphy, carbon isotope analysis was carried out for correlating the shallow benthic zones with the carbon isotope excursion (CIE) for developing a polished record of the PETM. An CIE of ~-3‰ (from 1.96 to -1.08 ‰) tied into the biostratigraphy places the PETM towards the upper part of the Lakadong Limestone from 25.0 to 30.5 m. A change in taxa and forms indicating deeper waters with a concurrent decrease in abundance of shallow water algae suggested a sea-level rise during the onset of the PETM. Oxygen isotope analysis indicated signs of diagenetic overprint in the studied succession.

Beschreibung: This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Beschreibung: Seventeen surface sediment samples from the North Atlantic Ocean off NE-Greenland between 76° and 81°N, and nine samples from the South Atlantic Ocean close to Bouvet Island between 48° and 55°S were taken with the aid of a Multiple Corer and investigated for their live (Rose Bengal stained) benthic foraminiferal content within the upper 15 cm of sediment. Preferentially endobenthic Melonis barleeanum, Melonis zaandami, and Bulimina aculeata as well as preferentially epibenthic Lobatula lobatula were counted from 1-cm-thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests. Live and dead specimens were counted and measured separately. The carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon (DIC) of simultaneously sampled bottom water. During a period of one month, one station off NE-Greenland was replicately sampled once every week and samples were processed as above. Live specimens of Lobatula lobatula are confined to the uppermost two centimeters of sediment. Live specimens of Melonis spp. are found down to 8 cm within the sediment but with a distinct sub-surface maximum between 2 and 5 cm. The down-core distribution of live Bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11-cm subbottom depth. The average stable carbon isotopic composition (d13C versus per mil PDB) of live Lobatula lobatula off NE-Greenland is by 0.4±0.1 per mil higher than the d13CDIC of the ambient bottom water at the time of sampling. There is evidence that this species calcify before the ice-free season, when bottom water d13CDIC is supposed to be higher. This would reconfirm the one-to-one relationship between d13C of ambient water DIC and cibicids, widely used by paleoceanographers. Live Melonis barleeanum show a negative offset from bottom water DIC of -1.7±0.6 per mil in the uppermost sediment and of -2.2±0.5 per mil in 3-4-cm subbottom depth. All d13C values of live Melonis spp. decrease within the upper four centimeters, regardless of the time of sampling and site investigated. The offset of live Bulimina aculeata from bottom water d13CDIC values of 8 stations rather constantly amounts to -0.6±0.1 per mil, no matter what subbottom depth the specimens are from. At one station however, where is strong indication of elevated organic carbon flux, the negative offset averaged over all sub-bottom depths increases to -1.5±0.2 per mil. Buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth. The recorded signal, however, depends on the organic carbon flux and reflects general but site-specific pore water d13CDIC values. If compared with epibenthic d13C values from the same site, not influenced by pore water and related phytodetritus layer effects, Buliminad13C values bear some potential as a paleoproductivity proxy. Specimens of Melonis spp. seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment. Although live specimens thus record a stratified pore water d13C signal, there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas.