Paleocene/Eocene carbon feedbacks triggered by volcanic activity.
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ABSTRACT:
SUBMITTER: Kender S
PROVIDER: S-EPMC8408262 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The Paleocene-Eocene Thermal Maximum (PETM) (55.6 Mya) was a geologically rapid carbon-release event that is considered the closest natural analog to anthropogenic CO2 emissions. Recent work has used boron-based proxies in planktic foraminifera to characterize the extent of surface-ocean acidification that occurred during the event. However, seawater acidity alone provides an incomplete constraint on the nature and source of carbon release. Here, we apply previously undescribed culture calibrations for the B/Ca proxy in planktic foraminifera and use them to calculate relative changes in seawater-dissolved inorganic carbon (DIC) concentration, surmising that Pacific surface-ocean DIC increased by [Formula: see text] µmol/kg during the peak-PETM. Making reasonable assumptions for the pre-PETM oceanic DIC inventory, we provide a fully data-driven estimate of the PETM carbon source. Our reconstruction yields a mean source carbon δ13C of -10‰ and a mean increase in the oceanic C inventory of +14,900 petagrams of carbon (PgC), pointing to volcanic CO2 emissions as the main carbon source responsible for PETM warming.
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Project description:A negative carbon isotope excursion recorded in terrestrial and marine archives reflects massive carbon emissions into the exogenic carbon reservoir during the Paleocene-Eocene Thermal Maximum. Yet, discrepancies in carbon isotope excursion estimates from different sample types lead to substantial uncertainties in the source, scale, and timing of carbon emissions. Here we show that membrane lipids of marine planktonic archaea reliably record both the carbon isotope excursion and surface ocean warming during the Paleocene-Eocene Thermal Maximum. Novel records of the isotopic composition of crenarchaeol constrain the global carbon isotope excursion magnitude to -4.0 ± 0.4‰, consistent with emission of >3000 Pg C from methane hydrate dissociation or >4400 Pg C for scenarios involving emissions from geothermal heating or oxidation of sedimentary organic matter. A pre-onset excursion in the isotopic composition of crenarchaeol and ocean temperature highlights the susceptibility of the late Paleocene carbon cycle to perturbations and suggests that climate instability preceded the Paleocene-Eocene Thermal Maximum.
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Project description:The Palaeocene-Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.
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Project description:The Paleocene-Eocene Thermal Maximum (PETM, 55.8 Ma), an abrupt global warming event linked to a transient increase in pCO2, was comparable in rate and magnitude to modern anthropogenic climate change. Here we use plant fossils from the Bighorn Basin of Wyoming to document the combined effects of temperature and pCO2 on insect herbivory. We examined 5,062 fossil leaves from five sites positioned before, during, and after the PETM (59-55.2 Ma). The amount and diversity of insect damage on angiosperm leaves, as well as the relative abundance of specialized damage, correlate with rising and falling temperature. All reach distinct maxima during the PETM, and every PETM plant species is extensively damaged and colonized by specialized herbivores. Our study suggests that increased insect herbivory is likely to be a net long-term effect of anthropogenic pCO2 increase and warming temperatures.
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Project description:New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene-Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear.
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Project description:We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 microm long and hexaoctahedral prisms up to 1.4 microm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability--a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming--drove diversification of magnetite-forming organisms, likely including eukaryotes.
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Project description:Soil organisms, as recorded by trace fossils in paleosols of the Willwood Formation, Wyoming, show significant body-size reductions and increased abundances during the Paleocene-Eocene Thermal Maximum (PETM). Paleobotanical, paleopedologic, and oxygen isotope studies indicate high temperatures during the PETM and sharp declines in precipitation compared with late Paleocene estimates. Insect and oligochaete burrows increase in abundance during the PETM, suggesting longer periods of soil development and improved drainage conditions. Crayfish burrows and molluscan body fossils, abundant below and above the PETM interval, are significantly less abundant during the PETM, likely because of drier floodplain conditions and lower water tables. Burrow diameters of the most abundant ichnofossils are 30-46% smaller within the PETM interval. As burrow size is a proxy for body size, significant reductions in burrow diameter suggest that their tracemakers were smaller bodied. Smaller body sizes may have resulted from higher subsurface temperatures, lower soil moisture conditions, or nutritionally deficient vegetation in the high-CO(2) atmosphere inferred for the PETM. Smaller soil fauna co-occur with dwarf mammal taxa during the PETM; thus, a common forcing mechanism may have selected for small size in both above- and below-ground terrestrial communities. We predict that soil fauna have already shown reductions in size over the last 150 years of increased atmospheric CO(2) and surface temperatures or that they will exhibit this pattern over the next century. We retrodict also that soil fauna across the Permian-Triassic and Triassic-Jurassic boundary events show significant size decreases because of similar forcing mechanisms driven by rapid global warming.
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Project description:The Paleocene-Eocene Thermal Maximum (PETM; 56 Ma) is one of our best geological analogs for understanding climate dynamics in a "greenhouse" world. However, proxy data representing the event are only available from select marine and terrestrial sedimentary sequences that are unevenly distributed across Earth's surface, limiting our view of the spatial patterns of climate change. Here, we use paleoclimate data assimilation (DA) to combine climate model and proxy information and create a spatially complete reconstruction of the PETM and the climate state that precedes it ("PETM-DA"). Our data-constrained results support strong polar amplification, which in the absence of an extensive cryosphere, is related to temperature feedbacks and loss of seasonal snow on land. The response of the hydrological cycle to PETM warming consists of a narrowing of the Intertropical Convergence Zone, off-equatorial drying, and an intensification of seasonal monsoons and winter storm tracks. Many of these features are also seen in simulations of future climate change under increasing anthropogenic emissions. Since the PETM-DA yields a spatially complete estimate of surface air temperature, it yields a rigorous estimate of global mean temperature change (5.6 ∘C; 5.4 ∘C to 5.9 ∘C, 95% CI) that can be used to calculate equilibrium climate sensitivity (ECS). We find that PETM ECS was 6.5 ∘C (5.7 ∘C to 7.4 ∘C, 95% CI), which is much higher than the present-day range. This supports the view that climate sensitivity increases substantially when greenhouse gas concentrations are high.
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