REPRESENTATIVES OF SOME DIAGNOSTIC AGGLUTINATED FORAMINIFERAL GENERA OF THE SUBCLASS MONOTHALAMANA (BATHYSIPHON, ORBULINELLOIDES, REPMANINA, MILIAMMINA, AGGLUTINELLA, DENTOSTOMENIA, AMMOMASSILINA, PSAMMOLINGULINA) IN THE TETHYS

The present study deals with the paleontology, stratigraphy, paleogeography and paleoenvironment of the sixteen representatives of the Paleogene agglutinated benthic foraminifer Monothalamana of eight genera: Bathysiphon Sars, Orbulinelloides Saidova, Repmanina Suleymanov, Miliammina Heron-Allen & Earland, Agglutinella El-Nakhal, Dentostomina Cushman, Ammomassilina Cushman, Psammolingulina Silvestri. One species Orbulinelloides kaminskii is believed here to be new. As a whole these faunae are rarely described in the micropaleontological literatures, that’s why this study is detected. The recorded species are distributed on both sides of the Northern Tethys (Hungary, France), Southern Tethys (Egypt, UAE, Pakistan), Pacific and Atlantic Ocean. It seems that the changes in paleoceanographic conditions should accentuate the benthic faunal changes. Some of the recorded species are mostly confined to that mention localities in the Atlantic and Pacific Ocean, Northern and Southern Tethys, and it was recorded by a few authors. The deeper water species have smooth tests, while the shallow water specimens are coarser grained. The number differences of the recorded species between the different localities in the Tethys may be due to one or more parameters: the deficiency of available literatures, differences in ecological or environmental conditions (depth, salinity, water temperature, dissolved oxygen, nutrient, land barrier) and not homogeneity in the generic or species concept according to different authors.

Oxygen Isotope Equilibrium of the Shallow-Water Benthic Foraminifer Hanzawaia nipponica Asano in Tosa Bay, Southwest Japan

Oxygen isotopic compositions (δ18O) of benthic foraminifer tests are widely used for reconstructing paleoceanographic changes, such as global ice volumes during glacial–interglacial cycles. Although deep-sea benthic foraminifers have been well characterized and are considered reliable indicators, little attention has been paid to the geochemistry of shallow-water benthic foraminifers. In this study we evaluated δ18O in the shallow-water benthic foraminifer Hanzawaia nipponica Asano, which lives in surface sediments on continental shelves and upper slopes under the influence of two warm currents, the Kuroshio and Tsushima currents, in the East China Sea, northwest Pacific, and southwestern Japan Sea. To evaluate oxygen isotope equilibrium, we analyzed δ18O of H. nipponica and ambient seawater on the continental shelf in Tosa Bay, southwest Japan. Seawater δ18O and salinity in Tosa Bay are similar to those of surface and subsurface waters in the Kuroshio region in the Okinawa Trough and the northwest Pacific. Vertical profiles of seawater δ18O show no variation with water depth (0–200 m) in Tosa Bay. However, tests of living H. nipponica (as determined by staining with Rose Bengal) and fossil (non-stained) H. nipponica, picked from samples of the top centimeter of seafloor sediment, yielded carbonate δ18O values that clearly increase with water depth, suggesting a temperature-dependent relationship. A comparison of carbonate δ18O values in living H. nipponica and those predicted on the basis of seawater δ18O and annual mean bottom temperature shows that H. nipponica tests are in oxygen isotopic equilibrium with ambient seawater. We determined the linear equations of δ18O–temperature relationship, and the slope of −5.26 (0.19‰°C−1) for living and −4.50 (0.22‰°C−1) for the fossil H. nipponica, respectively. The carbon isotopic compositions (δ13C) of H. nipponica also closely match seawater δ13C. Thus, we propose that the carbonate δ18O and δ13C of H. nipponica are useful proxies to reconstruct shallow-water paleoenvironmental changes in the northwest Pacific and its marginal seas.

Geochemical and micropaleontological evidence of the Messinian Salinity Crisis preconditioning phase in the West Alboran Basin

<p>The Messinian Salinity Crisis (MSC), still highly discussed within the scientific community, affected the Mediterranean Sea between 5.97 and 5.33 Ma and led to the deposition of huge evaporite accumulations both in its marginal and deep basins. During this profound palaeoecological change, the connections between the Atlantic Ocean and Mediterranean Basin were extremely reduced or even non-existing creating an environment where evaporation was dominant. However, the isolation from the global ocean was not a sudden change but most probably a stepwise process. At 7.17 Ma the first signs of restriction are visible in the sedimentological and micropaleontological records all over the Mediterranean.</p><p>Particularly, several Italian, Greek and Cypriot locations register a reduced deep water marine ventilation to the sea floor since 7.17 Ma ago as reflected in the higher abundance of benthic low oxygen foraminifer species, indicators of stressed conditions like Bolivinia spp., Bulimina aculeata, Uvigerina peregrina. In these locations, the start of the progressive Mediterranean isolation coincides with the beginning of a more regular occurrence or even the first appearance of sapropel levels which further confirms the increasingly adverse conditions and increasingly dysoxygenated bottom waters. On the other hand, apart from the first opal-rich deposits in the Sorbas basin (Southern Spain) and the Messadit section (North-East Morocco), evidence from the Western Mediterranean is lacking and no studies have focused so far on the 7.17 Ma event.</p><p>In this view, we conducted a detailed benthic foraminifer and stable isotope study of West Alboran Sea Site 976 before and after the 7.17 Ma event. This new record highlights the imprint that the early Atlantic-Mediterranean gateway restriction had on the Mediterranean sedimentological record, in a location proximal to the Messinian Gateways. Here, even if anoxic bottom water conditions were never reached, the benthic foraminifer association, paired with the benthic foraminifer carbon isotope record suggest a perturbation of the bottom water circulation and a decrease in bottom water oxygen levels starting ~7.17 Ma. In addition, a comparison of Western-Eastern Mediterranean records enabled us to make assumptions regarding the Mediterranean scale circulation before and after the 7.17 Ma event.</p>

Carbonic anhydrase is involved in calcification by the benthic foraminifer <i>Amphistegina lessonii</i>

Marine calcification is an important component of the global carbon cycle. The mechanism by which some organisms take up inorganic carbon for the production of their shells or skeletons, however, remains only partly known. Although foraminifera are responsible for a large part of the global calcium carbonate production, the process by which they concentrate inorganic carbon is debated. Some evidence suggests that seawater is taken up by vacuolization and participates relatively unaltered in the process of calcification, whereas other results suggest the involvement of transmembrane transport and the activity of enzymes like carbonic anhydrase. Here, we tested whether inorganic-carbon uptake relies on the activity of carbonic anhydrase using incubation experiments with the perforate, large benthic, symbiont-bearing foraminifer Amphistegina lessonii. Calcification rates, determined by the alkalinity anomaly method, showed that inhibition of carbonic anhydrase by acetazolamide (AZ) stopped most of the calcification process. Inhibition of photosynthesis either by 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) or by incubating the foraminifera in the dark also decreased calcification rates but to a lesser degree than with AZ. Results from this study show that carbonic anhydrase plays a key role in biomineralization of Amphistegina lessonii and indicates that calcification of those perforate, large benthic foraminifera might, to a certain extent, benefit from the extra dissolved inorganic carbon (DIC), which causes ocean acidification.