Cretaceous Austral Climate evolution - a benthic perspective

Austral Cretaceous Climate Evolution - Changes in the benthic realm during a Late Cretaceous climate crisis FWF Project J-4444 Affiliated institutions: University of Vienna (Austria), Università degli Studi di Milano (Italy) The Austrian Science Fund project "Austral Cretaceous Climate Evolution" investigated changes in bottom-water palaeoecosystems during the Late Cretaceous, with a focus on the Austral realm and the southern high latitudes. Despite their importance for understanding global ocean circulation patterns and palaeoclimate evolution, these regions are underrepresented in current palaeoclimate models. Project J-4444 analysed benthic foraminiferal assemblages from deep-sea drilling sites (IODP Sites U1512, U1513, and U1516), located off the southwest coast of Australia and in the Bight Basin, representing diverse palaeoenvironments (from marginal marine to bathyal settings). These sites, situated at a palaeolatitude of approximately 60S during the Late Cretaceous, provide an archive of environmental conditions and climate change in the southern hemisphere. Benthic foraminifera are highly sensitive archives of bottom-water conditions. Among the primary objectives was to track ecosystem responses during and after the Oceanic Anoxic Event 2 (OAE 2), a hyperthermal event characterised by massive carbon burial, long periods of global warming, widespread oxygen depletion, and carbon cycle disturbance around 94 million years ago. Geochemical data (including stable isotopes and elemental proxies) support the interpretation of changing oxygen levels and suggest bottom-water temperatures of up to 20C during the peak of OAE 2 at bathyal palaeowater depths. The data show a shift from diverse assemblages to communities dominated by oxygen-tolerant taxa, followed by the virtual disappearance of benthic foraminiferal fauna in seemingly oxygen-depleted intervals. Biostratigraphic data from foraminiferal assemblages document persistently warm conditions through most of the Late Cretaceous, with only a slight, gradual temperature decline. Only by the Santonian (~86 Ma) does a more persistent cooling trend become apparent in the southern high latitudes, with benthic and planktonic foraminifera indicating cooling of ~2C in bottom waters and ~5C at the surface. This work combined micropalaeontological and geochemical data to document ecosystem responses during phases of Cretaceous climate deterioration, highlighting how benthic communities were affected by long-term environmental change. Furthermore, new biostratigraphic data help refine the chronology of southern hemisphere climate evolution during the Late Cretaceous, a period of major tectonic reorganisation related to the breakup of the supercontinent Gondwana and episodes of intense volcanic activity. The information generated in this research effort is relevant for current discussions about ocean deoxygenation and long-term ecosystem stability and fragility in a warming climate.