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| Titel |
Climate variability and ocean fertility during the Aptian Stage |
| VerfasserIn |
C. Bottini, E. Erba, D. Tiraboschi, Hugh C. Jenkyns, S. Schouten, J. S. Sinninghe Damsté |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 3 ; Nr. 11, no. 3 (2015-03-05), S.383-402 |
| Datensatznummer |
250117206
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| Publikation (Nr.) |
 copernicus.org/cp-11-383-2015.pdf |
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| Zusammenfassung |
| Several studies have been conducted to reconstruct temperature variations
across the Aptian Stage, particularly during early Aptian Oceanic Anoxic
Event (OAE) 1a. There is a general consensus that a major warming
characterized OAE 1a, although some studies have provided evidence for
transient "cold snaps" or cooler intervals during the event. The climatic
conditions for the middle–late Aptian are less constrained, and a complete
record through the Aptian is not available. Here we present a reconstruction
of surface-water palaeotemperature and fertility based on calcareous
nannofossil records from the Cismon and Piobbico cores (Tethys) and DSDP
Site 463 (Pacific Ocean). The data, integrated with oxygen-isotope and
TEX86 records, provide a detailed picture of climatic and ocean
fertility changes during the Aptian Stage, which are discussed in relation to
the direct/indirect role of volcanism. Warm temperatures characterized the
pre-OAE 1a interval, followed by a maximum warming (of
~ 1.5–2 °C) during the early phase of anoxia under intense
volcanic activity of the Ontong Java Plateau (OJP). A short-lived cooling
episode interrupted the major warming, following a rapid increase in
weathering rates. Nannofossils indicate that mesotrophic conditions were
reached when temperatures were at their highest and OJP volcanism most
intense, thus suggesting that continental runoff, together with increased
input of hydrothermal metals, increased nutrient supply to the oceans. The
latter part of OAE 1a was characterized by cooling events, probably promoted
by CO2 sequestration during burial of organic matter. In this phase,
high productivity was probably maintained by N2-fixing cyanobacteria,
while nannofossil taxa indicating higher fertility were rare. The end of
anoxia coincided with the cessation of volcanism and a pronounced cooling.
The mid-Aptian was characterized by highest surface-water fertility and
progressively decreasing temperatures, probably resulting from intense
continental weathering drawing down pCO2. The lowest temperatures,
combined with low fertility, were reached in the middle–late Aptian across
the interval characterized by blooming of Nannoconus truittii. The
prolonged cooling was followed by significant warming across the
Aptian–Albian boundary. The data presented suggest that OJP activity played
a direct role in inducing global warming during the early Aptian, whereas
other mechanisms (weathering, deposition of organic matter) acted as feedback
processes, favouring temporary cooler interludes. |
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