The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative ...importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.
The Middle Eocene Climatic Optimum (MECO) is an ~500 kyr interval of pronounced global warming from which the climate system recovered in <50 kyr. The deep‐sea sedimentary record can provide valuable ...insight on the marine ecosystem response to this protracted global warming event and consequently on the ecological changes during this time. Here we present new benthic foraminiferal assemblage data from Ocean Drilling Program Site 1051 in the subtropical North Atlantic, spanning the MECO and post‐MECO interval (41.1 to 39.5 Ma). We find little change in the species composition of benthic foraminiferal assemblages during the studied interval, suggesting that the rate of environmental change was gradual enough that these organisms were able to adapt. However, we identify two transient intervals associated with peak warming (higher‐productivity interval (HPI)‐1; 40.07–39.96 Ma) and shortly after the MECO (HPI‐2; 39.68–39.55 Ma), where benthic foraminiferal accumulation rates increase by an order of magnitude. These HPIs at Site 1051 appear to coincide with intervals of strengthened productivity in the Tethys, Southern Ocean, and South Atlantic, and we suggest that an intensified hydrological cycle during the climatic warmth of the MECO was responsible for eutrophication of marine shelf and slope environments.
Key Points
Two higher‐productivity intervals (HPIs) at peak MECO and shortly after the MECO
HPIs attributed to strengthened hydrological cycle and enhanced runoff
HPIs appear to correlate with similar events in other ocean basins
The Middle Eocene Climatic Optimum (MECO) was a ~650kyr long interval of pronounced warmth superimposed on the long-term Eocene cooling trend. We investigate benthic foraminiferal assemblage and ...fossil fish tooth cerium anomaly variability from Ocean Drilling Program (ODP) Site 738 in the Indian sector of the Southern Ocean (Southern Kerguelen Plateau) to assess changes in bottom water chemistry and effects on benthic foraminiferal ecosystems. The studied section spans 41.9 to 38.4Ma, encompassing the MECO as well as extensive Pre-MECO and Post-MECO intervals. We report a marked faunal turnover at 40.4Ma, 200kyrs after the onset of the MECO at ~40.6Ma, from an assemblage dominated by epifaunal benthic foraminifera to an infaunal-dominated assemblage. The infaunal domination persisted until the termination of the MECO at 39.95Ma. Thereafter, the Pre-MECO assemblage returned. This change is attributed to an increase in export productivity associated with the warming, possibly caused by an increase in continental runoff or the influence of a more eutrophic surface water mass. Superimposed on the change in tropic state the Ce/Ce* record shows a positive excursion during the 100kyrs long MECO peak warming at around 40.05Ma, indicative of a decrease in bottom-water oxygen content. Synchronously, infaunal benthic foraminifera drop briefly in abundance. Hence, we suggest that the peak warming is associated with bottom water oxygen depletion potentially caused by elevated productivity and/or a transient influence of an older, oxygen-depleted water mass.
•We investigate benthic foraminiferal assemblages and Ce/Ce* in the Southern Ocean.•Benthic foraminifera show a significant faunal turnover across the MECO warming.•This shift is interpreted as an increase in productivity from 40.40 to 39.95Ma.•Our data suggest an interval of bottom-water oxygen depletion at peak MECO warming.•Oxygen depletion is proposed to reflect influence of a North pacific water mass.
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