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The calcareous nannoplankton response to short-lived episodes of global warming during the Early Eocene greenhouse world: inferences from the Cicogna section (Italy).
No full textShort-lived episodes of warming in the greenhouse world: a late Palaeocene and early Eocene record from the Cicogna section, Italy.
No full textECOLOGICAL AND EVOLUTIONARY RESPONSE OF TETHYAN PLANKTONIC FORAMINIFERA TO THE MIDDLE EOCENE CLIMATIC OPTIMUM (MECO) FROM THE ALANO SECTION (NE ITALY)
No full textThe enigmatic middle Eocene climatic optimum (MECO) is a transient (~500 kyr) warming event that significantly interrupted at ~40 Ma the long-term cooling through the middle and late Eocene, eventually resulting in establishment of permanent Antarctic ice-sheet. This event is still poorly known and data on the biotic response are so far scarce. Here we present a detailed planktonic foraminiferal analysis of the MECO interval from a marginal basin of the central-western Tethys (Alano section, northeastern Italy). The expanded and continuous Alano section provides an excellent record of this event and offers an appealing opportunity to better understand the role of climate upon calcareous plankton evolution. A sapropel-like interval, characterized by excursions in both the carbon and oxygen bulk-carbonate isotope records, represents the lithological expression of the post-MECO event in the study area and follows the δ18O negative shift, interpreted as representing the MECO warming.
High-resolution quantitative analysis performed on both >38 μm and >63 μm fractions reveals pronounced and complex changes in planktonic foraminiferal assemblages indicating a strong environmental perturbation that parallels the variations of the stable isotope curves corresponding to the MECO and post-MECO interval. These changes consist primarily in a marked increase in abundance of the relatively eutrophic subbotinids and of the small, low-oxygen tolerant Streptochilus, Chiloguembelina and Pseudohastigerina. At the same time, the arrival of the abundant opportunist eutrophic Jenkinsina and Pseudoglobigerinella bolivariana, typical species of very high-productivity areas, also occurs. The pronounced shift from oligotrophic to more eutrophic, opportunist, low-oxygen tolerant planktonic foraminiferal assemblages suggests increased nutrient input and surface ocean productivity in response to the environmental perturbation associated with the MECO. Particularly critical environmental conditions have been reached during the deposition of the sapropel-like beds as testified by the presence of common giant and/or odd morphotypes. This is interpreted as evidence of transient alteration in the ocean chemistry.
The enhanced surface water productivity inferred by planktonic foraminiferal assemblages at the onset of the event should have resulted in heavier δ13C values. The recorded lightening of the carbon stable isotope preceding the maximum warmth therefore represents a robust indication that it derives principally by a conspicuous increase of pCO2. The increased productivity of surface waters, also supported by geochemical data, may have acted as mechanism for pCO2 reduction and returned the climate system to the general Eocene cooling trend. The oxygen-depleted deep waters and the organic carbon burial following the peak of the MECO event represent the local response to the MECO warming and suggest that high sequestration of organic matter, if representing a widespread response to this event, might have contributed to the decrease of pCO2 as well. Though the true mechanisms are still obscure, several lines of evidence indicate a potential pressure on planktonic foraminiferal evolution during the MECO event including permanent changes besides transient and ecologically controlled variations
Ecological and evolutionary response of Tethyan planktonic foraminifera to the Middle Eocene Climatic Optimum (Alano di Piave section, NE Italy).
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The magneto-bio-chemostratigraphy of the Torrente Cicogna section (Italy): a record of Late Paleocene-Early Eocene climate
No full textOrganic carbon burial following the Middle Eocene Climatic Optimum (MEC0): a mechanism for global cooling?
No full textSapropel-like sediments at the Middle Eocene Climatic Optimum in the central-western Tethys (Alano di Piave section): the biotic record.
No full textChanges in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: clues from the central-western Tethys (Alano section, NE Italy).
No full textWe present a study focused on changes in calcareous nannofossil assemblages of the Alano section during the
Middle Eocene Climatic Optimum (MECO). This warming event is characterized by a prominent perturbation
both in oxygen and carbon stable isotopes around the Chron C18r–C18n transition (ca. 40 Ma) and lasting ca.
500–600 kyr. Semi-quantitative analyses on calcareous nannofossil assemblages have been carried out. Our
results show that the MECO interval coincides with a significant shift in the relative abundance of calcareous
nannofossil taxa, suggesting a relationship between biotic changes and stable isotope shifts. Paleoecological
studies at species level and/or based on morphometric criteria (i.e., small placoliths) sometimes show the
opposite behavior between changes observed at the genus level and those observed at lower taxonomic
levels. For instance, a taxon thought to be better adapted to oligotrophic/warm waters, e.g. Sphenolithus,
shows a prominent decrease if analyzed at genus level, but an increase was instead recorded for S. spiniger.
Moreover, taxa preferentially thriving in eutrophic/cold waters, as for instance small reticulofenestrids,
increase remarkably in abundance during this warming phase, while medium–large placoliths do not show
any significant trend. An increase in reworked, mainly Cretaceous, specimens is also observed during the
MECO. These lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea
surface waters suggesting that an enhanced nutrient availability could have driven the make-up of the
calcareous nannofossil assemblages. The increase in reworking may indicate an increase in terrigenous input,
due to increased chemical weathering likely produced by an enhanced hydrological cycle
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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