Seasonal dynamics and decadal changes of benthic foraminiferal assemblages in the western Baltic Sea (NW Europe)

Living benthic foraminiferal assemblages were monitored between January and July 2004 in the Kiel Bight, Baltic Sea. Phytoplankton blooms and the deposition of organic detritus were depicted by fluorometer hydro casts and pigment concentrations in surface sediments. Three depositional pulses of organic matter were identified by high phytoplankton concentrations above the sea floor and elevated pigment concentrations in the surface sediment. The foraminiferal assemblage composition remained rather constant but the population density of Elphidium excavatum clavatum showed a two- to six-fold increase within a few days after organic detritus deposition. The foraminiferal assemblage composition was compared to earlier studies in this area. Elphidium excavatum, Ammotium cassis and E incertum dominated the living fauna in the 1960s and 1970s. The recent survey revealed a predominance of E. excavatum subspecies (more than 90% of the living assemblage). The average population densities were six times higher than in the 1970s. Data structure and model calculations suggested that E excavatum clavatum is able to reproduce rapidly, with high offspring numbers at elevated food supply. The diminution of A. cassis has occurred in Kiel Bight during the last ten years and was most likely induced by a period of low deep-water salinities in the early 1990s

Das marine Isotopenstadium 11 im östlichen Mittelmeer: größte Ähnlichkeit mit dem heutigen Tag?

Das Marine Isotopen Stadium 11 (MIS 11, ca. 400 ka vor Heute), gilt als einer der Zeitabschnitte, der dem heutigen Interglazial im Bezug auf die orbitalen Parameter am nächsten kommt. Dies wurde oft als Anlass genommen, das Klima im MIS 11 zu untersuchen um daraus Rückschlüsse auf aktuelle und zukünftige Klimatrends zu ziehen. Die orbitalen Parameter während MIS 11 und die heutigen sind jedoch nicht exakt identisch, so dass aktuell intensiv diskutiert wird, in wie weit die beiden Stadien überhaupt tatsächlich direkt vergleichbar sind. Die vorliegende Studie zeigt die erste detaillierte Untersuchung von MIS 11 im östlichen Mittelmeer. Hochauflösende Datensätze wurden für verschiedene paläoklimatologische Proxies an zwei marinen Sedimentkernen, GeoTü-SL96 (32°46’N, 19°12’E, 1399 m, größere Syrte) und ODP Site 964 (36°16’N, 17°45’E, 3658 m, östlich von Sizilien) erstellt. Ein zuverlässiges Altersmodel wurde mithilfe stabiler Isotopen, der Sapropele und Änderungen in der Foraminiferenfauna entwickelt. Die Meeresoberflächentemperaturen wurden anhand von Transferfunktionen auf Basis von Faunenzusammensetzungen planktischer Foraminiferen an 404 Proben rekonstruiert und durch Alkenon Messungen an einem der Kerne ergänzt. Beide Kerne zeigen typische Warmzeitverhältnisse im MIS 11 erst nach der Sapropelbildung, welche mit dem zweiten Insolationsmaximum nach Termination V zusammenfällt. Im Gegensatz dazu liegt im MIS 1 Abschnitt beider Kerne jeweils ein deutlich ausgeprägter Sapropel vor. Die verschiedenen Tiefen aus denen die beiden Kerne kommen erklären dieses Phänomen: in MIS 11 muss die Grenzschicht zwischen sauerstoffreichem und sauerstoffarmen Wassern tiefer gelegen haben als zur Zeit der Bildung des Sapropels in MIS 1. Zusätzlich dazu zeigen die sehr leichten Isotopenwerte in ODP Site 964 im entsprechenden Zeitabschnitt einen extrem erhöhten Eintrag von Frischwasser durch vermehrte Monsunaktivität und/oder einer Öffnung zum schwarzen Meer. Der Abgleich der beiden Sapropele von MIS 11 und MIS 1 lässt eine scheinbar verzögerte Reaktion des pelagischen Systems auf das Ende der Kaltzeit erkennen. Der Zeitraum im MIS 11 vor dem Sapropel ist gekennzeichnet durch glaziale planktonische Foraminiferenvergesellschaftungen und kältere Alkenon Temperaturen. Benthische Foraminiferenhäufigkeiten und Ba/Ca Verhältnisse lassen zudem eine hohe Produktivität für den entsprechenden Zeitraum vermuten. Das wahrscheinlichste Szenario für die verzögerte Reaktion, die in starkem Kontrast zu den globalen Entwicklungen und auf Pollen basierenden Ergebnissen aus der Mittelmeerregion steht, ist hohe Produktivität im Winter mit relativ kühlen und feuchten Bedingungen, angetrieben von erhöhtem Eintrag terrestrischen Materials, wodurch sich eine glaziale Vergesellschaftung planktonischer Foraminiferen halten konnte und die Alkenone bis zur Bildung des MIS 11 Sapropels das Signal der kalten Jahreshälfte widerspiegeln. Die Vergesellschaftungen planktonischer Foraminiferen zeigen im weiteren Verlauf von MIS 11 drei auffällige Phasen, die mit Faunen in verschiedenen jüngeren Sapropelen verglichen werden können. Da diese drei Phasen mit Insolationsmaxima und niedrigen Ba/Ca und Fe/Al Verhältnissen im Sediment zusammenfallen, scheinen sie mit orbital gesteuerten Saisonalitätsmaxima und starker Stratifizierung der Wassersäule und niedriger Produktivität, und daher fehlender Sapropele, zusammenzuhängen. Zusätzlich dazu bleiben die Vergesellschaftungen planktonischer Foraminiferen im späteren MIS 11 dominiert von der tropischen/subtropischen Art G. ruber, mit Höchstwerten im späten MIS 11/frühen MIS 10. Dieses Muster lässt sich erklären durch außergewöhnlich hohe Temperaturen während dieses Zeitabschnittes, kombiniert mit sehr niedriger Produktivität. Während der Bearbeitung der Proben fielen Unregelmäßigkeiten in Form und Größe von G. ruber auf und führten zu der Definition von vier verschiedenen Morphotypen innerhalb dieser Art. Die Häufigkeiten dieser Morphotypen variieren deutlich zwischen Glazialen und Interglazialen und in drei dieser Morphotypen konnten signifikante Unterschiede in den stabilen Isotopenverhältnissen festgestellt werden. Da diese systematisch sind und oft mehr als 1 ‰ betragen, ist ein besseres Verständnis der Morphotypen von großer Bedeutung für die Interpretation von allen auf G. ruber basierenden paläozeanografischen Proxies. Die scheinbar verzögerte Reaktion des Systems im frühen MIS 11 im Verhältnis zu globalen Entwicklungen erschweren einen Abgleich von MIS 11 und MIS 1 bezüglich des Endes der jeweiligen Kaltzeit. Das Ausmaß der Ähnlichkeit der orbitalen Parameter beider Zeitabschnitte war definitiv zu gering um absolut vergleichbare klimatische Entwicklungen hervorzurufen. Der auf Sapropelen beruhende Abgleich beider Interglaziale legt eine deutliche Asymmetrie zwischen beiden Zeitabschnitten offen und stellt die abnormal lange Dauer von MIS 11 als nicht unbedingt repräsentativ für das heutige Interglazial dar.Marine Isotope Stage 11 (MIS 11) is known to be the closest analogue to the Holocene (MIS 1) in terms of Earth’s orbital configuration during the last 400,000 years. This has often been used as an argument to investigate climate trends of MIS 11, reconstructed from natural geological archives in order to evaluate current and future climate developments. However, the orbital configuration during MIS 11 was not exactly identical to that of MIS 1 and the comparability of climate trends during both interglacials is currently hotly debated. In this study, the first high resolution palaeoclimatic investigation of MIS 11 is presented here for the Eastern Mediterranean Sea, known to yield an especially sensitive climate archive. High-resolution, continuous multi-proxy palaeoclimatic data have been generated from two sediment cores of this region (ODP Site 964: 36°16’N, 17°45’E, 3658 m; GeoTü-SL96 32°46’N, 19°12’E, 1399 m). The records have been tied to an absolute time scale using an age model based on stable oxygen isotopes, planktonic faunal abundance events and sapropel formations. As a proxy of surface water conditions, assemblage compositions of planktonic foraminifera were determined in 404 samples and supplemented with alkenone unsaturation ratios in one of the cores. The new MIS 11 data indicate that MIS 11 sapropel formation and onset of interglacial conditions in both cores correlated with the second insolation peak after Termination V. In contrast, the MIS 1 sapropel S1 coincides with the first insolation peak after Termination I. In contrast, both cores show a significant sapropel layer in MIS 1, indicating a different depth for the oxycline during MIS 11. In addition, the size of the oxygen isotopic peak at ODP Site 964 is larger than in the Holocene at the same site, indicating enhanced monsoonal activity and/or Black Sea discharge during MIS 11, despite a weaker insolation forcing. The alignment of MIS 11 sapropel to the second insolation maximum of MIS 11 reveals an apparently delayed response of the pelagic system to deglaciation. Benthic foraminifera concentrations and Ba/Ca ratios in the sediment furthermore suggest high productivity for the pre-sapropel interval. The most likely scenario to explain the apparent delayed response, in stark contrast with global trends and pollen evidence from the Mediterranean region, is high winter productivity during relatively cool and wet interglacial conditions in early MIS 11, fuelled by enhanced influx of terrigenous material, leading to the persistence of glacial planktonic foraminifera assemblages and alkenones representing the cold season signal until the development of the MIS 11 sapropel. Within the later part of MIS 11, planktonic foraminifera assemblage compositions show three conspicuous phases. The assemblages occurring during these phases resemble faunas known from later sapropels. As they coincide with insolation maxima and low Ba/Ca and Fe/Al values in the sediment, they appear to be controlled by orbitally driven maxima in seasonality and stratification with low productivity and thus no sapropel formation. In addition, the planktonic foraminifera assemblages throughout late MIS 11 remain dominated by the warm-water indicator G. ruber, reaching an absolute maximum in late MIS 11 and the first half of MIS 10 (~ 80 %). This pattern can be explained by unusually warm temperatures during the late phase of MIS 11, which is consistent with alkenone data, combined with extremely low productivity, as indicated by benthic foraminifera concentrations. During sample preparation, anomalies in shape and size of G. ruber were identified, which led to the definition of four different morphotypes within this species, in accordance with literature. Abundances of the morphotypes significantly change between glacials and interglacials, and in three of the morphotypes of G. ruber, significant offsets in stable isotope composition were found. Since the isotope shifts among the three G. ruber morphotypes are systematic and often exceed 1 ‰, their understanding is essential for the interpretation of all G. ruber – based proxy records for palaeoceanographic reconstructions. The apparent delayed reaction of MIS 11 pelagic ecosystem in the Mediterranean region to global trends, resulting in a sapropel formation coinciding with the second insolation peak of the interglacial period, makes it difficult to align MIS 11 and MIS 1 with respect to the deglaciation. The degree of orbital analogy between MIS 11 and MIS 1 was clearly insufficient to force analogous climatic trends during the two interglacials that could be used to predict the future development of the Holocene without human impact. The alignment of the two interglacial periods based on sapropel formation as proposed here identifies a significant asymmetry between the two interglacials and highlights the anomalous length of MIS 11 as not necessarily representative of the course of the current interglacial

The benthic foraminiferal response to the 2004 spring bloom in the western Baltic Sea

The diatom spring bloom and response of the benthic foraminifera was monitored between January and July 2004 in the Kiel Bight, western Baltic Sea. Phytoplankton production, the deposition of organic detritus, and feeding of Elphidium excavatum clavatum and Reophax dentaliniformis were monitored by pigment concentrations and pigment composition in water samples, surface sediments, and foraminiferal protoplasm. The population dynamics of the dominant species, Elphidium e. clavatum, was assessed by using their size distributions. The main spring bloom was triggered by a sudden rise in the three-day average insolation to above 170 W m(-2) d(-1) and took place during late February. Chlorophyll a concentrations in the protoplasm of Elphidium e. clavatum followed those in the surface water. The chlorophyll a / fucoxanthin ratio was the same as in bacillariophycean diatoms suggesting a "bloom-feeding" behaviour of Elphidium e. clavatum. Alternatively, the pigment composition in Reophax dentaliniformis only occasionally mirrored that of diatoms, indicating prochlorophycean and cyanophycean algae as this species' preferred food source. The size distributions and the abundances of living Elphidium e. clavatum revealed two reproduction events, which were 17 days apart. Both events coincided with an increase in sedimentary chlorophyll a concentrations. The reproduction was preceded by growth and feeding of adult specimens and it was followed by distinct growth phases of young specimens, which lasted a few days only. One reproductive cycle covered the spring bloom and produced many more offspring than the subsequent cycle. The light carbon isotopic signal from diatoms was only transiently recorded in foraminiferal calcite and with a low offset during the spring bloom. The oxygen isotopic composition of foraminiferal calcite mirrors seasonal delta(18)O-seawater-salinity relationships rather than temperature

The Northernmost Occurrence of the Tropical-Subtropical Brittle Star <i>Ophiocoma</i> (Echinodermata, Ophiuroidea) from a Late Cretaceous Rocky Shore in Southern Sweden

In spite of considerable progress during the last few years, the fossil record of the ophiuroids, or brittle stars, is still poorly known, especially with respect to taxa restricted to specific environments. Here, we describe new ophiuroid fossils collected from an Upper Cretaceous rocky shore in Ivö Klack, southern Sweden, consisting of fully disarticulated skeletal remains retrieved from the sediments deposited between boulders and hummocks. The fossils are identified as a new species of the extant ophiocomid genus Ophiocoma. In a critical revision of the ophiocomid fossil record, we show that all fossils previously assigned to the Ophiocomidae belong to other families. Thus, the fossil record of the Ophiocomidae is currently restricted to the new species described herein, and Amphiura? gigantiformis from the Miocene of Austria which, in fact, is a species of Ophiocoma. Since recent species of Ophiocoma exclusively occur in tropical to subtropical shallow subtidal environments, our discovery of a fossil Ophiocoma species in the rocky shore sediments of Ivö therefore conforms with the previously assumed subtropical palaeotemperatures prevailing in southern Sweden during the Late Cretaceous. Most notably, it represents the northernmost occurrence of an ophiocomid recorded to date

A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean

Numberger-Thuy, Lea D., Thuy, Ben (2020): A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean. Zootaxa 4820 (1): 19-30, DOI: https://doi.org/10.11646/zootaxa.4820.1.

A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands

A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids

New Brittle Stars (Echinodermata, Ophiuroidea) from the Oligocene of the Mainz Basin, Germany

The fossil record of the Ophiuroidea is still patchy, especially in the Cenozoic. Only four species have been described from the entire Oligocene, which is in stark contrast to the present-day diversity counting more than 2000 species. Here, we describe two new species of ophiuroid, Ophiura tankardi sp. nov. and Ophiodoris niersteinensis sp. nov., from the Lower Oligocene of the Mainz Basin. The species are based on microfossils extracted from the sieving residues of bulk sediment samples from a flush drill in Nierstein, Rhineland-Palatinate. The new species belong to extant genera and add to the poor Oligocene fossil record of the class. Based on present-day distributions, the occurrence of Ophiodoris suggests deep sublittoral to shallow bathyal palaeodepths for the Nierstein area of the Mainz Basin