Drivers of the end-Permian hyperthermal: system failure?
Professor Lee Kump, Pennsylvania State University, USA
In the context of the archetypal hyperthermal (the PETM), the end-Permian event presents an extreme comparison. Unlike the relatively benign effects of the PETM on the biota (apologies to the benthic foraminifera), the end-Permian event was the largest mass extinction of animals in Earth history. Yet the two events left similar records in the carbon isotope composition of limestones, reflecting potentially quite similar carbon cycle perturbations, both likely triggered by volcanism. Why was one a mass killer and the other not?
Despite the similar isotope record, there are differences: the end-Permian event occurred at the culmination of Paleozoic-long environmental trends reflected in the sedimentological, isotopic, and geochemical records, reflecting maxima or minima in sea level, continentality, weathering rates, hydrothermal activity, and tectonic uplift. Moreover, the seafloor at the time may have been largely free of the blanket of acid-absorbing calcium carbonate that has existed to varying extents and thicknesses since the Jurassic. Thus, the pre-existing conditions for these two disturbances differ substantially.
While the carbon isotope records are strikingly similar in magnitude and rate of change, they may have resulted from quite different rates of carbon injection: negative carbon isotope anomalies are the consequence essentially of the product of the rate of carbon addition and its isotopic composition: the same perturbation can result from slower addition of a source depleted in the heavy isotope (methane or volatilized organic matter addition triggered by a small volcanic addition) or a faster addition of carbon from a heavier source (e.g., the volcanism itself). Thus the more acute response in the end-Permian may indicate that much of the carbon addition was magma-sourced. Needed is a second proxy, e.g., the B isotope proxy of pH as being applied to the PETM, to constrain the source and rate of C addition. However, more voluminous release of CO2 and consequent warming could have overwhelmed the ocean uptake, seafloor carbonate dissolution, and silicate weathering feedbacks that more effectively damped the PETM perturbation.
The styles of volcanism potentially differed substantially, with greater subaerial eruption and injection of toxic materials into the atmosphere during the end-Permian Siberian Traps event.
Clearly the duration of C cycle disruption, the scale of biotic impact and delay of recover, and the persistence and extent of anoxia distinguish the end-Permian from the PETM. Whether the difference was in the rate and duration of C addition or in the pre-existing conditions remains to be determined.
Orbital forcing of Early Eocene hyperthermals
Professor Lucas Lourens, Utrecht University, the Netherlands
The Paleocene-Eocene Thermal Maximum (PETM) is the first of a series of punctuated global warming events, termed hyperthermals, that mark the hot climate conditions of the early Eocene (~56 to ~48 million years ago). The occurrence of these hyperthermals are generally explained by the rapid increase in greenhouse gas forcing (carbon dioxide and methane) as portrayed by distinct negative carbon isotope excursions in both marine and terrestrial realms. So far, approximately 20 hyperthermals were identified based on the positive covariance between oxygen and carbon isotope excursions in high-resolution deep sea benthic foraminiferal records derived in particular from the sedimentary successions of the Walvis Ridge in the southern Atlantic ocean that were drilled during Ocean Drilling Program leg 208 in 2003. Despite that the origin of the carbon released during these events is still highly debated, their regular occurrence points towards a perturbation in the global carbon cycle and associated global temperatures on dominantly eccentricity-paced (i.e. 405 and 95-125 kyr) time scales.
Volcanic causes for past hothouse climates
Dr Henrik H. Svensen, Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Norway
Mass extinctions and transient climate events commonly coincide in time with the formation of Large igneous provinces (LIPs). Classic examples include the end-Permian event which coincides with the Siberian Traps, the end-Triassic with the Central Atlantic Magmatic Event (CAMP), the Toarcian with the Karoo LIP, and the Palaeocene-Eocene Thermal Maximum (PETM) with the North Atlantic Igneous Province. The emplacement of igneous sills into sedimentary basins, and the associated contact metamorphism of the host sedimentary rocks, has emerged as a major player in the understanding of the link between LIPs and past climatic change. This presentation stresses that for these processes to have an environment impact, the gases need to be transferred to the surface and atmosphere on a very short timescale, which is borne out by dating of the sill complexes in question. We have identified a range of different pipe structures that acted as gas transport channels during the end-Permian, the Toarcian, and the PETM, and present a classification and detailed overview of the key parameters governing their formation. This talk shows that the potential for degassing of greenhouse gases, aerosols, and ozone destructive gases in sedimentary basins affected by volcanism is substantial, and can explain the triggering of both transient climatic events and mass extinctions.
An independent constraint on the duration of the Paleocene-Eocene CIE onset from cosmic spherule abundances
Professor Morgan Schaller, Earth and Environmental Sciences, Rensselaer Polytechnic Institute, USA
The P-E boundary hyperthermal event is considered a geologic analog to our current warming. However, the rate of carbon release associated with the onset of the P-E event has not been adequately determined by an independent empirical means from an expanded section. Modeling efforts have attempted to address the duration of the onset, but the resultant estimates are only as reliable as the available input records, the majority of which come from slow sedimentation localities in the open ocean. Here we place an independent empirical constraint on sedimentation rates from two P-E shelf localities on the Atlantic Coastal plain (Wilson Lake-B and IODP Leg 174AX at Millville) by determining the abundance of cosmic spherules in the Vincentown Fm. and overlying Marlboro Clay, the base of which is coincident with the onset of the carbon isotope excursion (CIE) that defines the P-E boundary. Because the flux of cosmic dust to Earth’s surface is known and is relatively constant on short timescales, the accumulation of extraterrestrial material in sediments can provide surprisingly precise estimates of bulk sedimentation rates. Exploiting this known flux, we use the cosmic spherule abundance in the upper Vincentown at Wilson Lake to establish the baseline sedimentation rate as ~1.6 cm/kyr. Against this backdrop, we find a sharp ~70-fold increase in sediment accumulation rate in the lower Marlboro, concomitant with the base of the clay. We note that our rates for the Marlboro are only ~4-5-fold higher than previously published estimates based on foraminifera accumulation. At this sedimentation rate, the duration of the 3‰ 13Cbulk onset recorded at Wilson Lake spans less than 0.35 kyr. The same exercise applied to micrometeorite counts from Millville yields a comparable result, making the CIE onset recorded there less than ~0.3 kyr. The remarkable agreement between the two sites is a testament to the robustness of the method. Preliminary counts from open ocean sites show a decrease in sedimentation rates through the onset of the event, opposite of what is observed on the shelves but in agreement with previous estimates based on extra-terrestrial 3He. These sedimentation rate determinations based on cosmic spherule accumulation are objective and reproducible, and the only noteworthy source of uncertainty is in the flux of extraterrestrial material to the planetary surface. These expanded shelf sections afford a level of resolution unfamiliar in the deep ocean and demonstrate that the onset of the carbon isotope excursion was at least centennial-scale at these sites. Future modeling efforts should account for these observations.
Constraining the rate of PETM onset
Professor Sandra Kirtland Turner, University of California, Riverside, USA
It is the rate of current and projected future warming that makes anthropogenic climate change particularly challenging for natural ecosystems. In attempts to use episodes of climatic change in the geologic past as analogs for the future, therefore, timescale is key. The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) has been suggested as the best, most recent example of rapid carbon release and warming. The PETM is characterized by a geologically abrupt negative carbon isotope excursion, global warming, and ocean acidification, all of which point to massive carbon release to the atmosphere and/or oceans. Yet the duration of the onset, here defined as the time interval between pre-PETM and minimum carbon isotope values, remains highly debated. Estimates have ranged from decadal to tens of thousands of years. The difficulty of utilizing traditional methods for age determination to constrain rapid events, combined with poor preservation of the PETM onset in many geologic sections, is responsible for the large discrepancy between estimates. Here the results from the Earth System Model cGENIE are used to look for fingerprints of carbon release rate within the atmosphere, oceans, and sediments that may be preserved in the geologic record. These experiments focus on identifying spatial patterns in the propagation timescale for carbon isotopic and temperature anomalies through the ocean. Applied to existing PETM datasets, these estimates support an onset for the PETM of between two to five thousand years.