Accuracy and reproducibility of absolute nannoplankton abundances using the filtration technique in combination with a rotary sample splitter

The filtration technique is a widely applied method to calculate absolute coccolith abundances in paleoceanographic, paleoclimatic and ecological studies. Here, we have tested the accuracy and reproducibility of absolute coccolith abundance estimates obtained with the filtration method in combination with a rotary sample divider. The examination of two different filtration devices, a funnel and an in-line system, analysing a known number of microbeads per weight, revealed that counts obtained with funnel systems are up to Ø 18.6% too high. Repeated analyses (15×) of a fine-fraction sediment sample revealed a standard deviation of ±11.4% for the in-line system and ±15.2% for the funnel system, respectively. The comparison between three sub-samples (three splits of 1/30) showed a standard deviation of 4.6% for the in-line system and 9.9% for the funnel system, respectively. Therefore, we assume that the potential split error for the rotary splitter is ?4.6%.The comparison of our results with estimates for the same samples analysed with the random settling and the “spiking with microbeads and spraying method” (SMS method) reveal that only the data obtained with the SMS and in-line filter method are statistically equal. The results obtained with the settling method are too low, whilst the results obtained with funnel filtration are too high in terms of coccolith absolute abundances. Our results confirm that the filtration method, including sample splitting with a rotary splitter, is a suitable method for the analysis of absolute coccolith abundances. However, the use of different filtration devices appears to affect the accuracy and reproducibility of the results. Furthermore, the number of splitting steps should be as small as possible to avoid an increase of error due to error propagation. In order to increase the reliability of the filtration method, we suggest calibrating a filtration device with microbeads as a standard measure. The reported reproducibility of the various preparation techniques may help to compare data sets obtained with different methods. <br/

Mesozoic calcareous nannofossils - state of the art

Calcareous nannofossils originated in the Triassic, radiated in the Jurassic and became a dominant component of the marine biosphere from the earliest Jurassic onward. They can be considered as one of the most important "innoviations" of the Mesozoic oceans. Their basic morphology allows the differentiation of three different groups: coccoliths, nannoliths and calcispheres (= calcareous dinocysts). Only coccoliths and nannoliths are discussed in this article in some detail. occoliths and nannoliths have contributed greatly in the interpretation of Mesozoic marine systems through biostratigraphy and palaeoecology/palaeoceanography. Ever since the late 1960s both coccoliths and nannoliths have proven to be useful and reliable zonal markers for biostratigraphic schemes, allowing detailed zonations for the Jurassic and Cretaceous. Though affected by palaeobiogeographic provincialism, coccoliths and nannoliths have supplied many cosmopolitan biostratigraphic markers. These allow a global correlation of marine sedimentary units both from onshore sections in the classical European and North American areas and pelagic sequences recovered in the course of the DSDP/ODP drilling from the worl's oceans. Thus research on calcareous nannofossils covers both, regional and global aspects. Research in the last 15 years concentrated on palaeoecological aspects. Apart from dinoflagellates, coccolithophores were the most important primary producers in Mesozoic oceans. As such they heavily relied on autoecological factors such as light, nutrients and temperature. Variationes in the assemblage composition of these groups may thus be viewed as a key for understanding palaeoecological, palaeoceanographic and palaeoclimatic changes of the past. <br/

The heartbeat of the Oligocene climate system

A 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a pronounced “heartbeat” in the global carbon cycle and periodicity of glaciations. This heartbeat consists of 405,000-, 127,000-, and 96,000-year eccentricity cycles and 1.2-million-year obliquity cycles in periodically recurring glacial and carbon cycle events. That climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle, solar forcing, and glacial events. Box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass. The pronounced 405,000-year eccentricity cycle is amplified by the long residence time of carbon in the oceans

High resolution benthic foraminiferal stable isotope records from the late early Oligocene

The Oligocene (33.5-23.8 Ma) represents in many ways the “neglected middle child” of Cenozoic palaeoceanography – caught between the early Paleogene greenhouse and the well-developed Neogene icehouse. This situation is attributed to the view that the Oligocene marks a persistent interval of relative stasis in palaeoclimate and biotic turnover, reflected in deep-sea micropalaeontological communities by conservative body plans, confusing taxonomy and low biostratigraphic resolution. However, in some respects this interval represents the most interesting episode of the Cenozoic palaeoceanographic puzzle because it allows us to unravel the processes that lie behind the transition from a world free of large-scale continental icecaps and rapid eustatic sea-level oscillations to one dominated by these climatic changes. Here we present a high-resolution (~3 ka) epi- (Cibicidoides grimsdalei) and infaunal (Oridorsalis umbonatus) benthic foraminiferal stable isotope (oxygen, carbon) record of the late Early Oligocene equatorial Pacific (ODP Site 1218) between magnetochrons C11n.2n and C12n (29.9-31 Ma) in order to assess and quantify on astronomical timescales palaeoclimatic and palaeoceanographic changes

Early Maastrichtian stable isotopes: Changing deep water sources in the North Atlantic?

We propose that the observed short-term stable isotope fluctuations reflect changes in high- and low-latitude intermediate to deep water sources, based on a high-resolution stable isotope record of planktic and benthic foraminifera from the Early Maastrichtian (71.3 to 69.6 Ma) of Blake Nose (DSDP Site 390A, North Atlantic). Sources of these waters may have been the low-latitude eastern Tethys and high-latitude North Atlantic. Changes in intermediate to deep water sources were probably steered by eccentricity-controlled insolation fluctuations. Lower insolation favored the formation of high-latitude deep waters due to positive feedback mechanisms resulting in high-latitude cooling. This led to a displacement of low-latitude deep waters at Blake Nose. Higher insolation reduced intermediate to deep-water formation in high latitudes, yielding a more northern flow of low-latitude deep waters. <br/

Short-term environmental changes in the Cretaceous Tethyan Ocean: micropaleontological evidence from the Early Albian Oceanic Anoxic Event 1b

To better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils, palynomorphs and benthic foraminifera from the Early Albian Oceanic Anoxic Event 1b black shale (OAE 1b) in the Vocontian Basin (SE France). We propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity-driven temperature changes represents the driving factor of OAE 1b formation in low latitudes. With the onset of OAE 1b, increasingly warm and humid conditions, stronger winds and enhanced terrestrial input led to higher surface water productivity. Therefore, increased productivity is an important factor for OAE 1b formation in the Vocontian Basin. However, monsoonally forced productivity changes are a regional climate signal only. The supraregional occurrence of the OAE 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions, leading to enhanced preservation of organic matter.<br/

Absence of major vegetation and palaeoatmospheric pCO2 changes associated with oceanic anoxic event 1a (Early Aptian, SE France)

The deposition of organic-rich sediments during the late Early Aptian Oceanic Anoxic Event (OAE) 1a has been interpreted to result in a major decrease of palaeoatmospheric CO2 concentrations, accompanied by significant changes in the terrestrial flora. In order to test this hypothesis, the OAE 1a interval in the Vocontian Basin (SE France) has been studied with a combined approach including stable carbon isotopes, organic geochemistry and palynology. To estimate changes in palaeoatmospheric CO2 levels across the OAE 1a, the 13C composition of presumed algal biomarkers (low molecular weight n-alkanes, steranes) and of bulk carbonate carbon are used. Our results yield estimated Early Aptian carbon dioxide partial pressure (pCO2) values three to four times the preindustrial level and only a moderate drop across the black shale event. This moderate drop in pCO2 is supported by palynological results. The frequency patterns of climate-sensitive sporomorphs (incl. pteridophyte spores, bisaccate pollen and Classopollis spp.) display only minor fluctuations throughout the studied section and indicate relatively stable patterns of terrestrial vegetation during and after formation of the OAE 1a black shale. The occurrence of a characteristic Early Aptian carbon isotope pattern across the OAE 1a interval permits accurate chemostratigraphic correlation with the well-studied Livello Selli interval of the Cismon record (N Italy). The contemporaneous formation of individual black shale layers at both sites indicates that transient episodes of dysoxic–anoxic bottom waters prevailed over large areas in the W Tethys Ocean independent of depositional setting. Comparison of the palynological data from the two locations displays significant differences in the frequency patterns of bisaccate pollen. The contrasting pollen spectra are interpreted to reflect prominent changes in the palaeoceanographic current patterns and/or selective sorting due to sea-level rise rather than latitudinal shifts of the major floral belts

High-resolution carbon isotope records of the Aptian to Lower Albian from SE France and the Mazagan Plateau (DSDP Site 545): a stratigraphic tool for paleoceanographic and paleobiologic reconstruction

High-resolution carbon isotope stratigraphy is established for the Aptian to Lower Albian of the Vocontian Basin (SE France), and correlated to the carbon isotope record of the Mazagan Plateau (DSDP Site 545). The carbon isotope stratigraphy of the Vocontian Basin is proposed as a standard reference curve for the Aptian to Lower Albian, due to the completeness and high temporal resolution of the stratigraphic succession, the good biostratigraphical time control, and the frequent occurrence of regional to global black shale horizons including Oceanic Anoxic Events 1a (OAE 1a) of the Lower Aptian and OAE 1b of the Lower Albian. The carbon isotope record appears better suited for long-distance short-term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types. However, the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography, and to correlate regional to global black shale horizons in different marine environments. This combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species. Based on the demonstrated diachroneity of important biostratigraphic markers of the Aptian/Albian boundary, the globally observed break point between the end of the uppermost Aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13C values, is an alternative criterion. The distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the Aptian to Lower Albian

Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France)

Calcareous nannoplankton, palynomorph, benthic foraminifera, and oxygen isotope records from the supraregionally distributed Niveau Paquier (Early Albian age, Oceanic Anoxic Event 1b) and regionally distributed Niveau Kilian (Late Aptian age) black shales in the Vocontian Basin (SE France) exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid-Cretaceous low latitudes. To quantify surface water productivity and temperature changes, nutrient and temperature indices based on calcareous nannofossils were developed. The nutrient index strongly varies in the precessional band, whereas variations of the temperature index reflect eccentricity. Since polar ice caps were not present during the mid-Cretaceous, these variations probably result from feedback mechanisms within a monsoonal climate system of the mid-Cretaceous low latitudes involving warm/humid and cool/dry cycles. A model is proposed that explains the formation of mid-Cretaceous black shales through monsoonally driven changes in temperature and evaporation/precipitation patterns. The Lower Albian Niveau Paquier, which has a supraregional distribution, formed under extremely warm and humid conditions when monsoonal intensity was strongest. Bottom water ventilation in the Vocontian Basin was diminished, probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes. Surface water productivity in the Vocontian Basin was controlled by the strength of monsoonal winds. The Upper Aptian Niveau Kilian, which has a regional distribution only, formed under a less warm and humid climate than the Niveau Paquier. Low-latitude deep water formation was reduced to a lesser extent and/or on regional scale only. The threshold for the formation of a supraregional black shale was not reached. The intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale. At least in the Vocontian Basin, the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity. <br/