Middle Eocene to Late Oligocene Antarctic glaciation/deglaciation and Southern Ocean productivity

Abstract

During the Eocene-Oligocene transition, Earth cooled significantly from a greenhouse to an icehouse climate. Nannofossil assemblages from Southern Ocean sites enable evaluation of paleoceanographic changes and, hence, of the oceanic response to Antarctic ice sheet evolution during the Eocene and Oligocene. A combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes. A cooling trend, started in the Middle Eocene, was interrupted by warming during the Middle Eocene Climatic optimum and by short cooling episodes. The cooling episode at 39.6 Ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from~39.1 to~36.2 Ma. We suggest that oligotrophic conditions were associated with increased water mass stratification, low nutrient contents, and high efficiency of the oceanic biological pump that, in turn, promoted sequestration of carbon from surface waters, which favored cooling. After 36.2 Ma, we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance. This turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient Antarctic ice sheet and/or to iron delivery to the sea surface. Eutrophic conditions were maintained throughout the Oligocene, which was characterized by a nannofossil assemblage shift toward cool conditions at the Eocene-Oligocene transition. Finally, a warm nannofossil assemblage in the Late Oligocene indicates a warming phase.

Meridional Contrasts in Productivity Changes Driven by the Opening of Drake Passage

“…Although there are reasonable explanations to these discrepancies (Erhardt et al, ; Moore et al, ), this observation highlights the complexity associated with reconstructing paleoproductivity from proxy signals (Anderson & Delaney, ). In the high latitudes, many records show significant enhancement of the paleoproductivity during the EOT event (e.g., Diester‐Haass & Zahn, ; Plancq et al, ; Salamy & Zachos, ; Villa et al, ) or during the latest Eocene (Diekmann et al, ; Egan et al, ; Villa et al, ). In particular, during the latter, it has been argued that pulses of tectonic opening of DP (Scher & Martin, ) may play a role in the transition from oligotrophic to eutrophic nannofossils taxa (Villa et al, ) or an increase in diatom abundance (Egan et al, ).…”

Palaeogene climate evolution in the Paris Basin from oxygen stable isotope (δ 18 O) compositions of marine molluscs

“…However, the Palaeogene corresponds to the transition from an ice-free world to an icehouse period (Zachos et al 2001), which implies that a different global δ 18 O w should be considered depending on the period under study. Great controversy exists about the age of the first ice-sheets on Earth during the Palaeogene (Lear et al 2000;Tripati et al 2005;Burgess et al 2008;Dawber et al 2011;Villa et al 2014), but a consensus seems to have been adopted for the Middle Eocene. Here, we have chosen to consider the work of Lear et al (2000) for the Eocene and Oligocene and that of Bohaty et al (2012) for the Eocene-Oligocene boundary.…”

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

“…Eutrophication could have been stimulated by sea surface iron fertilization produced by addition of iron-rich aeolian dust to surface waters. This promoted enhanced organic carbon export to deeper waters and burial on the seafloor, which stimulated increased magnetotactic biomineralization (e.g., Villa et al, 2014). The iron needed for biomineralization by magnetotactic bacteria is likely to have been provided by diagenetic iron reduction that released Fe 3+ from the most reactive iron-bearing minerals, including hydrous ferric oxide and lepidocrocite (Poulton et al, 2004).…”