Evolution of the deep-sea ecosystem during early Eocene transient warming events: stable- isotope and foraminiferal evidence

Tijdens het laat Paleoceen – vroeg Eoceen (60-50 Ma) onderging de aarde de warmste omstandigheden van het Cenozoïcum. Vooral op hoge en gematigde breedten waren de temperaturen veel hoger dan vandaag. Bovenop deze warme basissituatie beïnvloedde een felle en kortstondige opwarming (“hyperthermaal”) van de aarde, bekend als het Paleoceen-Eoceen thermische maximum (55 Ma), de ontwikkeling van de biogeosfeer op dramatische wijze.

Recente studies tonen aan dat er tijdens het late Paleoceen en vroege Eoceen een reeks van secundaire hyperthermalen plaatsvonden. De twee bekendste staan bekend als Elmo en X-event. De gevolgen op korte- en lange termijn van deze hyperthermalen voor de ontwikkeling van de mariene biosfeer zijn vooralsnog nauwelijks gekend.

In samenwerking met diverse partners in binnen- en buitenland worden momenteel de vroeg-Eocene hyperthermalen onderzocht in opeenvolgingen van de continentale rand, met name in de ondiepe randbekkens langs de Tethys en de Atlantische Oceaan. In het huidige onderzoeksvoorstel wordt het bathymetrisch bereik van de shelf uitgebreid naar de diepzee (gebaseerd op DSDP en ODP materiaal). Op deze manier wordt getracht een vollediger beeld te verkrijgen van de gevolgen van snelle opwarming en circulatieveranderingen van de oceanen voor het hele dieptespectrum van mariene benthische ecosystemen.

Our overall objective is to evaluate the short- and long-term responses of the marine biosphere to the sequence of transient climatic perturbations of the early Eocene. These hyperthermals provide insight into the dynamics and interactions of the biogeosphere in an extreme climate state: the early Paleogene (super) greenhouse. Although the basic state of this greenhouse world differs in several fundamental aspects from the present day situation (e.g. continent distribution, mountain chains, CO2 concentrations), such research is also relevant to the current global warming debate in that it reveals how robust/sensitive the biosphere and the earth system react to rapid global warming. For instance, we could recently demonstrate that coral reefs completely disappeared from the tropical Tethys in response to global warming during the PETM, in order to give way to carbonate ramps dominated by larger foraminifera (Scheibner & Speijer 2008). Time will only tell whether this is also a near future scenario.

More specifically, our central goal is to understand the response of epicontinental and deep-sea benthic ecosystems as reflected by faunal and isotopic records. If hyperthermals are a recurrent aspect of the early Paleogene greenhouse, we anticipate to find systematic faunal responses within the different depth zones of trhe oceans. For instance, in deep-sea environments it was suggested that the blooming of Aragonia and other infaunal morphotypes reflects enhanced food fluxes and/or weakened seafloor ventilation during hyperthermals (Thomas et al. 2000), whereas the combination of thin-shelled Nuttallides and Abyssammina is indicative of corrosive bottom waters during hyperthermals (Lourens et al. 2005; Röhl et al. 2005). If such faunal charaterisations would prove to be correct, it wuld be possible to identify hyperthermals independently of isotopic data, which is particularly useful in cases when diagenesis has overprinted primary geochemical signals. By studying the non-catastrophic ETM-2/3, we aim to assess the sensitivity of early Eocene benthic communities to changes in temperature, circulation-stratification, pH, and Corg flux to the sea floor. This will provide a reference frame to which the catastrophic to semi-catastrophic consequences of the PETM to benthic life can be scaled (are there any permanent changes? What is the rate of change?). By expanding from our earlier and current studies on marginal seas (Steurbaut et al. 2003; Stassen et al. 2009) and intergrating the deep sea record, we obtain a bathymatric continuum, from 0 to 2500 m depth in the low to middle latitides. From this overview we will be able to distinguish between local turnovers, biofacial shifts, migration patterns and extinctions at the seafloor and to couple these to surface processes.

Publications

  • D’haenens, S., Bornemann, A., Roose, K., Claeys, P. & Speijer, R., 2012. Stable isotope paleoecology (δ13C and δ18O) of early Eocene Zeauvigerina aegyptiaca from the North Atlantic (DSDP Site 401). Austrian Journal of Earth Sciences, 105 (1): 179-188.
  • D’haenens, S., Bornemann, A., Stassen, P. & Speijer, R., 2012. Multiple early Eocene benthic foraminiferal assemblage and δ13C fluctuations at DSDP Site 401 (Bay of Biscay – NE Atlantic). Marine Micropaleontology, 88-89: 15-35.
Internal member(s)
Other member(s)
R. Speijer (coordinator, KU Leuven)
P. Claeys (co-promoter, VUB)
S. D’haenens (Ku Leuven)
P. Stassen (KU Leuven)
J. Yans (FUNDP Namur)
P. Schulte (Universität Erlangen, Germany)
C. Schreibner (Univ. Bremen, Germany)
A. Bornemann (Univ. Leipzig, Germany)
S. Galeotti (Univ. Urbino, Italy)
A.M. Morsi (Univ. Cairo, Egypt)
M. Petrizzo (Univ. Milano, Italy)
E. Thomas (Yale, USA)
Funding
FSR-Vlaanderen Research Project G.0422
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