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| Titel |
Productivity response of calcareous nannoplankton to Eocene Thermal Maximum 2 (ETM2) |
| VerfasserIn |
M. Dedert, H. M. Stoll, D. Kroon, N. Shimizu, K. Kanamaru, P. Ziveri |
| 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 ; 8, no. 3 ; Nr. 8, no. 3 (2012-05-31), S.977-993 |
| Datensatznummer |
250005589
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| Publikation (Nr.) |
 copernicus.org/cp-8-977-2012.pdf |
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| Zusammenfassung |
| The Early Eocene Thermal Maximum 2 (ETM2) at ~53.7 Ma is one
of multiple hyperthermal events that followed the Paleocene-Eocene Thermal
Maximum (PETM, ~56 Ma). The negative carbon excursion and deep ocean
carbonate dissolution which occurred during the event imply that a
substantial amount (103 Gt) of carbon (C) was added to the
ocean-atmosphere system, consequently increasing atmospheric CO2(pCO2). This makes the
event relevant to the current scenario of anthropogenic CO2 additions and global change. Resulting changes in ocean stratification and
pH, as well as changes in exogenic cycles which supply nutrients to the
ocean, may have affected the productivity of marine phytoplankton,
especially calcifying phytoplankton. Changes in productivity, in turn, may
affect the rate of sequestration of excess CO2 in the deep
ocean and sediments. In order to reconstruct the productivity response by
calcareous nannoplankton to ETM2 in the South Atlantic (Site 1265) and
North Pacific (Site 1209), we employ the coccolith Sr/Ca productivity proxy
with analysis of well-preserved picked monogeneric populations by ion probe
supplemented by analysis of various size fractions of nannofossil sediments
by ICP-AES. The former technique of measuring Sr/Ca in selected nannofossil
populations using the ion probe circumvents possible contamination with
secondary calcite. Avoiding such contamination is important for an accurate
interpretation of the nannoplankton productivity record, since diagenetic
processes can bias the productivity signal, as we demonstrate for Sr/Ca
measurements in the fine (<20 μm) and other size fractions obtained from
bulk sediments from Site 1265. At this site, the paleoproductivity signal as
reconstructed from the Sr/Ca appears to be governed by cyclic changes,
possibly orbital forcing, resulting in a 20–30% variability in Sr/Ca in
dominant genera as obtained by ion probe. The ~13 to 21% increase
in Sr/Ca above the cyclic background conditions as measured by ion probe in
dominating genera may result from a slightly elevated productivity during
ETM2. This high productivity phase is probably the result of enhanced
nutrient supply either from land or from upwelling. The ion probe results
show that calcareous nannoplankton productivity was not reduced by
environmental conditions accompanying ETM2 at Site 1265, but imply an
overall sustained productivity and potentially a small productivity increase
during the extreme climatic conditions of ETM2 in this portion of the South
Atlantic. However, in the open oceanic setting of Site 1209, a significant
decrease in dominant genera Sr/Ca is observed, indicating
reduced productivity. |
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