Onset Of Paleocene-Eocene Thermal Maximum Research Articles

Accelerated light carbon sequestration following late Paleocene-early Eocene carbon cycle perturbations

Carbon releases into the climate system produce global warming and ocean acidification events that can be reversed eventually by carbon sequestration. However, the underlying controls on the timescales of carbon removal, and their dependence on the amplitude of the initial perturbation, are poorly understood. Here, we assess a series of late Paleocene-early Eocene (LPEE) carbon cycle perturbations (∼56-52 Ma) of different amplitudes to constrain carbon removal timescales. Carbon isotope excursions (CIEs) and sedimentation patterns for the largest event, the Paleocene-Eocene Thermal Maximum (PETM), allow identification of a light carbon injection that appeared ∼85 kyr after the PETM onset. This CIE may have been triggered by orbital forcing of long (∼400 kyr) and short (∼100 kyr) eccentricity maxima. The various LPEE light carbon injections were followed by exponential carbon removal trends with half-life (t1/2) estimates of ∼6-26 kyr. These values are smaller than background estimates for the modern carbon cycle (t1/2>100 kyr), which reveals accelerated light carbon sequestration. We find that one estimated t1/2 period coincided temporally with ocean acidification recovery in different locations with contrasting paleo-water depths. This pattern indicates enhanced chemical weathering following LPEE CIEs; however, chemical weathering timescales are an order of magnitude longer than the observed t1/2 estimates. This reveals that several carbon processes were optimized during LPEE CIE recovery. Similar t1/2 estimates are obtained for light carbon injections of different sizes, which suggests that carbon removal was optimized to conditions induced by the initial perturbation. Temperature controls on oxygen solubility may have accelerated the oceanic biological pump in proportion to each LPEE carbon injection. This process may have caused accelerated carbon sequestration during LPEE CIE recovery and produced the short carbon removal timescales identified by t1/2 estimates of LPEE carbon cycle perturbations.

A rapid sedimentary response to the Paleocene-Eocene Thermal Maximum hydrological change: New data from alluvial units of the Tremp-Graus Basin (Spanish Pyrenees)

A massive emission of light carbon about 56 Ma, recorded in marine and terrestrial sediments by a negative carbon isotope excursion (CIE), caused a short-lived (~170 kyr) global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). The onset and core of this event is represented in the south Pyrenean Tremp-Graus Basin by two successive alluvial units, the Claret Conglomerate (CC) and the Yellowish Soils, which represent laterally juxtaposed depositional environments. It is generally agreed that these units record a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM, but the timing of the sedimentary response to this hydrological change is a matter of debate. Some authors maintain that the CC was developed during the early, most intense phase of the carbon emission, others that its formation lagged by 16.5 ± 7.5 kyr behind the onset of the PETM. The latter claim was mainly based on the assumption that in two sections of this basin, Claret and Tendrui, the onset of the CIE occurs 3 and 8 m below the base of the CC, respectively. Here we show that in some zones between these two sections the CC was not deposited and the Yellowish Soil unit rests directly and conformably on the underlying Esplugafreda Formation. New δ 13 C org data from this intervening zone provide evidence that the onset of the CIE is situated just ~1 m below the Yellowish Soils. In adjacent sections the CC erosional base cuts down deeper than 5 m, thus removing or obscuring the chemostratigraphically-defined base of the PETM. A tentative estimate based on averaged sedimentation rates indicates that ~3.8 kyr, or less, may have elapsed from the onset of the CIE to the arrival of PETM alluvium into the Claret-Tendrui study area, less than half of the lowest estimate of previous authors. Since the study area was situated about 15 km from the source area, our new estimate supports a rapid response of the sedimentary system to the hydrological change at the onset of the PETM. • The PETM hydrological change is recorded in the Pyrenees by two alluvial units. • Between the PETM onset and the alluvial accumulation a lag of ~3.8 kyr is estimated. • The new data entail a rapid sedimentary response to the PETM hydrological change.

Paleocene/Eocene carbon feedbacks triggered by volcanic activity

The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.

Calcium isotope composition ofMorozovellaover the late Paleocene–early Eocene

AbstractOcean acidification (OA) during the Paleocene-Eocene thermal maximum (PETM) likely caused a biocalcification crisis. The calcium isotope composition (δ44/40Ca) of primary carbonate producers may be sensitive to OA. To test this hypothesis, we constructed the first high-resolution, high-precision planktic foraminiferal δ44/40Ca records before and across the PETM. The records employ specimens of Morozovella spp. collected from Ocean Drilling Program Sites 1209 (Shatsky Rise, Pacific Ocean) and 1263 (Walvis Ridge, Atlantic Ocean). At Site 1209, δ44/40Ca values start at −1.33‰ during the Upper Paleocene and increase to a peak of −1.15‰ immediately before the negative carbon isotope excursion (CIE) that marks the PETM onset. Values remain elevated through the PETM interval and decrease into the earliest Eocene. A shorter-term record for Site 1263 shows a similar trend, although δ44/40Ca values are on average 0.22‰ lower and decrease shortly after the CIE onset. The trends support neither diagenetic overprinting, authigenic carbonate additions, nor changes in the δ44/40Ca value of seawater. Rather, they are consistent with a kinetic isotope effect, whereby calcite δ44/40Ca values inversely correlate with precipitation rate. Geologically rapid Ca isotope shifts appear to reflect the response of Morozovella to globally forced changes in the local carbonate geochemistry of seawater. All data combined suggest that the PETM-OA event occurred near the peak of a gradual reduction in seawater carbonate ion concentrations during a time of elevated atmospheric pCO2, potentially driven by North Atlantic igneous province emplacement.

Constraining the magnitude of the carbon isotope excursion during the Paleocene-Eocene thermal maximum using larger benthic foraminifera

The Paleocene-Eocene thermal maximum (PETM) was an extraordinary pulse of global warming that left an indelible mark on the Earth approximately 56 Ma ago. This warming event is associated with an addition of large amounts of 13C-depleted carbon into the atmosphere-ocean system, but the magnitude of the negative carbon isotope excursion (CIE) signaling the PETM onset and often used to estimate mass of the released carbon is still debated. Here we gauge the CIE magnitude through the use of secondary ion mass spectrometry (SIMS) to perform in situ δ13C measurements within individual larger benthic foraminifera preserved in a tropical shallow-marine limestone section at Tingri, south Tibet. This SIMS-based δ13C record yields a CIE (Δ~7‰) comparable in magnitude to that registered by some terrestrial PETM records but larger than the ~4‰ CIE returned by surface-dwelling planktonic foraminifera in deep-sea records. We posit that the CIE magnitude in the surface ocean and atmosphere was ~7‰, and that previous ~4‰ estimates are attenuated by incomplete preservation and/or diagenetic overprinting. Mass balance calculations indicate that the released carbon mass during the CIE would not exceed 28,000 petagrams, given that the carbon was sourced from organic matter, permafrost, thermogenic methane, methane hydrate, or any of their combinations. Our study demonstrates that δ13C records from some shallow-marine carbonate sections can avoid strong diagenetic alteration, preserving primary signals of deep-time carbon perturbations.

Environmental and Geomorphological Changes on the Eastern North American Continental Shelf Across the Paleocene‐Eocene Boundary

AbstractForaminiferal evidence from two sites in southern Maryland, eastern United States, reveals a series of rapid environmental changes on the continental shelf during the onset of the Paleocene‐Eocene Thermal Maximum (PETM). Benthic and planktic foraminifer assemblages from the South Dover Bridge and Mattawoman Creek‐Billingsley Road coreholes in the central Salisbury Embayment record changing latest Paleocene and earliest Eocene environmental conditions that began prior to the carbon isotope excursion that marks the beginning of the PETM. The foraminiferal response reflects increases in productivity in the bottom water, a minor dissolution event, and sea surface warming in the latest Paleocene. Relative sea level changes, a sudden change in sedimentary regime, and a decrease in bottom water oxygenation occurred in this region across the PETM onset. While South Dover Bridge assemblages support a rise in sea level across the PETM onset, Mattawoman Creek‐Billingsley Road assemblages record a reduction in water depth interpreted as delta progradation and possible tectonic activity. Transitional carbon isotope values are recorded in these delta sediments. We present an initial bathymetric reconstruction of the Salisbury Embayment showing the physical effects of the carbon isotope excursion onset on shelf morphology and highlight the importance of understanding coastal zone processes when examining shelf sediments.

Temporal Scaling of Carbon Emission and Accumulation Rates: Modern Anthropogenic Emissions Compared to Estimates of PETM Onset Accumulation

AbstractThe Paleocene‐Eocene thermal maximum (PETM) was caused by a massive release of carbon to the atmosphere. This is a benchmark global greenhouse warming event that raised temperatures to their warmest since extinction of the dinosaurs. Rates of carbon emission today can be compared to those during onset of the PETM in two ways: (1) projection of long‐term PETM rates for comparison on an annual time scale and (2) projection of short‐term modern rates for comparison on a PETM time scale. Both require temporal scaling and extrapolation for comparison on the same time scale. PETM rates are few and projection to a short time scale is poorly constrained. Modern rates are many, and projection to a longer PETM time scale is tightly constrained—modern rates are some 9–10 times higher than those during onset of the PETM. If the present trend of anthropogenic emissions continues, we can expect to reach a PETM‐scale accumulation of atmospheric carbon in as few as 140 to 259 years (about 5 to 10 human generations).

Calcareous nannofossils of the Paleocene–Eocene transition in four sections from Egypt

A detailed analysis of calcareous nannofossil assemblages was carried out across the Paleocene-Eocene transition in four outcrops in Egypt (the Gebel Matulla, Markha, El-Quss Abu Said, and Gebel Duwi sections) that span the Discoaster multiradiatus (NP9) to Discoaster binodosus (NP11) zones. The Paleocene-Eocene (P/E) boundary is placed in the lower part of the Esna Shale Formation based on the LOs of the Calcareous Nannofossil Excursion Taxa (CNET or RD) that define the base of NP9b. The studied sections are considered complete and document the Paleocene-Eocene Thermal Maximum (PETM). The occurrences of long-armed and asymmetrical discoasters (e.g., D. araneus, D. anartios) and rhomboasters (e.g., R. intermedia, R. bitrifidia, and R. spineus) are characteristic of the PETM interval. A sharp decrease in the diversification of Fasciculithus is noted at the onset of PETM. The abundance of Zygrhablithus bijugatus increases and corresponds with the dramatic decline in the oligotrophic Fasciculithus above the Paleocene/Eocene boundary and appears to be a significant global event. The Discoaster, Fasciculithus, and Rhomboaster species reflect relatively warm and, probably, oligotrophic surface waters. A minor hiatus in most of the studied sections near the upper part of Zone NP10 has been recorded in many parts of the world and reflects a global sea level drop.

Paleocene–Eocene palaeoenvironmental conditions of the main phosphorite deposits (Chouabine Formation) in the Gafsa Basin, Tunisia

A detailed sedimentary section of the marine Chouabine Formation in the palaeogeographic Gafsa Basin, south-western Tunisia, was investigated in order to characterize environmental and depositional conditions focusing on the interval that spans the Paleocene–Eocene transition. We did stable isotope analyses of bulk sediments. Both phosphorite and carbonate yielded relatively similar isotopic compositions; while marls show observable trends, with negative shifts in both δ13Cinorg and δ18O values at the Paleocene–Eocene transition.The diversity of the calcareous microfossils is low. The presence of few environmentally tolerant small benthic foraminifera and the absence of planktic forms indicate a restricted palaeoenvironment subject to variation in salinity and temperature. The ostracod fauna is more diverse and is rather comparable to Paleocene and PETM (Paleocene–Eocene thermal maximum) assemblages in northwest Tunisia. While all these microfossils demonstrate various diagenetic features (i.e., phosphatization, secondary mineral overgrowths and infills), the different groups retain distinct stable isotopic compositions, suggesting partial preservation of signatures derived from their respective ecological niches.Few organic-rich layers below the negative δ13C shift yielded dinoflagellate assemblages with the common forms of Adnatosphaeridium sp., Operculodinium sp., Spiniferites spp. and Thalassiphora sp. The rare presences of Apectodinium-complex agree with depositional age prior to the PETM.The combined data emphasize that most of the Chouabine Formation in the Gafsa Basin was deposited during the late Paleocene. The most negative isotopic values from marls are believed to represent the onset of PETM or pre-PETM record, and the related perturbation of the carbon cycle in shallow water deposits in Tunisia.

Methane and environmental change during the Paleocene-Eocene thermal maximum (PETM): Modeling the PETM onset as a two-stage event

An atmospheric CH4 box model coupled to a global carbon cycle box model is used to constrain the carbon emission associated with the PETM and assess the role of CH4 during this event. A range of atmospheric and oceanic emission scenarios representing different amounts, rates, and isotopic signatures of emitted carbon are used to model the PETM onset. The first 3 kyr of the onset, a pre-isotope excursion stage, is simulated by the atmospheric release of 900 to 1100 Pg C CH4 with a delta C-13 of -22 to - 30 %. For a global average warming of 3 deg C, a release of CO2 to the ocean and CH4 to the atmosphere totalling 900 to 1400 Pg C, with a delta C-13 of -50 to -60%, simulates the subsequent 1 -kyr isotope excursion stage. To explain the observations, the carbon must have been released over at most 500 years. The first stage results cannot be associated with any known PETM hypothesis. However, the second stage results are consistent with a methane hydrate source. More than a single source of carbon is required to explain the PETM onset.

Palynological evidence of vegetation dynamics in response to palaeoenvironmental change across the onset of the Paleocene‐Eocene Thermal Maximum at Cobham, Southern England

A high‐resolution palynological study is undertaken through the Cobham Lignite Bed (Cobham, Kent, UK) to investigate vegetation response to the rapid climate warming at the onset of the Paleocene‐Eocene thermal maximum (PETM). The lower laminated lignite records negative carbon isotope (δ 13C) excursions (CIE) (marking the PETM onset) in bulk organic material, n‐alkanes and, uniquely, also in hopanes. The upper blocky lignite represents an estimated 4–12 kya after PETM onset. Raw and rarefied palynomorph species richness measures are higher in the PETM but the difference is not statistically significant. Only five (of 24) common taxa have last appearance or major shifts in percentage occurrence close to the PETM onset. One of these, a triporate eudicot, occurs only in the maximum negative CIE sample and the immediately underlying sample, the former at very high percentages, an interesting feature of PETM onset. The palynomorph composition of Late Paleocene samples is significantly different from PETM samples. In the late Paleocene there is a close association of high abundances of Cicatricosisporites (Schizaeaceae) fern spores with microscopic and mesoscopic charcoal representing a low diversity fire prone fern and woody angiosperm community. By contrast, the PETM vegetation is characterised by the loss of ferns and cessation of fires, an increase in wetland plants (including cupressaceous conifers) and a more varied flowering plant community with palms and eudicots. These palynofloras thus indicate little response in plant species across the PETM onset but a major change in vegetation composition, linked to a switch in fire regime.

Calcareous plankton evolution and the Paleocene/Eocene thermal maximum event: New evidence from Tanzania

The biotic response of calcareous microplankton at the Paleocene/Eocene thermal maximum (PETM) climate event principally comprised poleward migrations, the appearance of excursion taxa and elevated turnover in calcareous nannoplankton. Here we examine whether this relatively muted evolutionary signal may be due to the quality of the stratigraphic and fossil record by analysing exceptionally well preserved microfossils from an expanded, hemipelagic PETM section in southern Tanzania (TDP Site 14). Both nannofossils and planktonic foraminifera show major abundance declines at the onset of the PETM that are not explained by dilution or dissolution. The PETM onset is also marked by the extinction of eight nannofossil species, possibly as many as 12, and the intra-PETM assemblages are quite distinct from background, and dominated by Coccolithus including the excursion taxon C. bownii. This biotic response is not clearly biased in favour of particular ecological groups, although the nannofossil excursion taxa were all warm-water favouring, and there was a net diversity loss within cool-water-favouring eutrophic groups. A shift from Toweius- to Coccolithus-dominated assemblages is suggestive of increased oligotrophy, although the presence of abundant Gladiolithus indicates upper photic zone oligotrophy throughout the time interval represented by the TDP Site 14 section. The significant plankton assemblage shifts, diversity decline and possible reduction of calcareous plankton production and/or export suggest the rapid onset of highly disruptive environmental change at the PETM onset. This change must have included rapid temperature increase, and heat stress may have played a role in shaping the PETM assemblage compositions, causing a limited number of extinctions and favouring taxa from warmer areas of the groups' ecological range. However, the muted evolutionary response in these plankton groups indicates that they were highly resilient to this environmental change and through adaptation to the new conditions (e.g. the excursion taxa), but probably principally through range shifts (i.e. migration) or simply the ability to acclimatize, the vast majority of the biodiversity survived and thrived again once conditions returned to normal.

The Paleocene–Eocene Thermal Maximum as recorded by Tethyan planktonic foraminifera in the Forada section (northern Italy)

The Forada section in the Venetian Pre-Alps of northern Italy represents an expanded record of the Paleocene–Eocene Thermal Maximum (PETM) at a depositional paleodepth of about 1 km ± 0.5 km. High-resolution planktonic foraminiferal analysis of this section, in a time interval of approximately 1.3 Myr across the Paleocene/Eocene boundary, reveals striking faunal changes that allow the identification of eight phases (a–h). The late Paleocene was represented by stable, warm and oligotrophic surface water conditions (phase a). Unstable environmental conditions start well before the onset of PETM (ca. 150 kyr, phase b) and involved a change towards eutrophy, as marked by the increase of Subbotina and the concomitant decrease of Morozovella. This step is also characterized by enhanced fragmentation and dissolution. The interval corresponding to the main body of the carbon isotope excursion (CIE) is characterized by a marked increase of Acarinina, though with some differences in the species composition and relative abundance, both in high-and low-latitudes, particularly in the Tethyan area. Forada is no exception to this pattern. However, at Forada, two prominent peaks in abundance of acarininids are recorded ca. 30 kyr prior to the onset of the CIE, thus suggesting an increase in temperature heralding the onset of the PETM (phase c). Interestingly, the lower peak in abundance of Acarinina just precedes the 1‰ carbon isotope negative shift occurring below the onset of the main CIE. The basalmost Eocene, corresponding to the lower part of CIE curve, is represented by intense planktonic foraminiferal dissolution, implying an extraordinary rise of the CCD. This interval has an estimated duration of about 16 kyr (phase d). The dominance of acarininids in the lower part of the CIE (phase e, f; ca. 14 and 22.5 kyr) is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the Forada depositional environment at that time. These acarininids include at Forada also the temporally constrained Acarinina sibaiyaensis and A. africana. The morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the Cretaceous anoxic events, suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the PETM. The recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups (e.g., biserials, globanomalinids, igorinids, planorotalids and pseudohastigerinids), occurring in the middle part of the CIE (ca. 30 kyr after the onset of the PETM), indicates an initial environmental recovery (phase g). A new stable state is definitely reached in the upper part of the Forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late Paleocene conditions (phase h). However, the perturbation during the PETM produced significant changes in the ocean geochemistry that endured after the PETM event, as testified by the prominent high carbonate dissolution characterizing the marly levels, and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages. These striking oscillations were not present in the latest Paleocene.

Paleocene-Eocene Thermal Maximum and the Opening of the Northeast Atlantic

The Paleocene-Eocene thermal maximum (PETM) has been attributed to a sudden release of carbon dioxide and/or methane. 40Ar/39Ar age determinations show that the Danish Ash-17 deposit, which overlies the PETM by about 450,000 years in the Atlantic, and the Skraenterne Formation Tuff, representing the end of 1 +/- 0.5 million years of massive volcanism in East Greenland, are coeval. The relative age of Danish Ash-17 thus places the PETM onset after the beginning of massive flood basalt volcanism at 56.1 +/- 0.4 million years ago but within error of the estimated continental breakup time of 55.5 +/- 0.3 million years ago, marked by the eruption of mid-ocean ridge basalt-like flows. These correlations support the view that the PETM was triggered by greenhouse gas release during magma interaction with basin-filling carbon-rich sedimentary rocks proximal to the embryonic plate boundary between Greenland and Europe.

Deep-Sea Temperature and Circulation Changes at the Paleocene-Eocene Thermal Maximum

A rapid increase in greenhouse gas levels is thought to have fueled global warming at the Paleocene-Eocene Thermal Maximum (PETM). Foraminiferal magnesium/calcium ratios indicate that bottom waters warmed by 4 degrees to 5 degrees C, similar to tropical and subtropical surface ocean waters, implying no amplification of warming in high-latitude regions of deep-water formation under ice-free conditions. Intermediate waters warmed before the carbon isotope excursion, in association with downwelling in the North Pacific and reduced Southern Ocean convection, supporting changing circulation as the trigger for methane hydrate release. A switch to deep convection in the North Pacific at the PETM onset could have amplified and sustained warming.