Paleocene–Eocene Thermal Maximum Perturbation may Have Been Worst at the Middle Latitudes

A siliciclastic braid delta within a lower Paleogene carbonate platform (Ordesa-Monte Perdido National Park, southern Pyrenees, Spain): Record of the Paleocene–Eocene Thermal Maximum perturbation

Authors:

Pujalte et al

Abstract:

The La Pardina Formation is a siliciclastic-dominated unit up to 26 m thick intercalated within a 300 m thick Danian–lower Ilerdian succession of shallow marine carbonates in the southern Pyrenees. The unit is composed of four interdigitated facies, three of them of a coarse-grained siliciclastic character (Sf1, Sf2, Sf3), and the fourth one composed of bioclastic packstones with argillaceous matrix (calcareous facies, Cf). The siliciclastic facies make up the bulk of the La Pardina Formation in the Ordesa-Monte Perdido National Park, while the Cf is subordinate in the Park but widespread throughout the southern Pyrenees. Biostratigraphic and isotopic data suggest that the Cf pertains to the Paleocene–Eocene Thermal Maximum (PETM). No isotopic or biostratigraphic information could be obtained from the siliciclastic facies, but they are also assigned to the PETM because of their interfingering with the Cf. The siliciclastic facies were accumulated in a braid delta system fed by either a major river or by several minor rivers draining the Ebro Massif. The Sf3, Sf2 and Sf1 respectively represent the top-set, foreset and bottomset parts of the braid delta, whereas the Cf correspond to the prodelta. In proximal parts of the braid delta the Sf3 overlies a subaerial surface carved into upper Thanetian marine carbonates, a proof of a pre-PETM sea-level fall. In the remainder of the braid delta, the La Pardina Formation exhibits an overall thickening-coarsening-up trend that attests to rapid progradation. The development of the braid delta implies a dramatic increase in the influx of both coarse- and fine-grained siliciclastics, which temporarily halted a long-lasting period of carbonate-dominated sedimentation. This abrupt change demonstrates that the environmental impact caused by the intensification of the hydrological cycle during the PETM was particularly severe at middle latitudes.

An Isotopic Anomaly With Regards to CO2 Atmospheric Concentration for the PETM

Temperature and atmospheric CO2 concentration estimates through the PETM using triple oxygen isotope analysis of mammalian bioapatite

Authors:

Gehler et al

Abstract:

The Paleocene–Eocene Thermal Maximum (PETM) is a remarkable climatic and environmental event that occurred 56 Ma ago and has importance for understanding possible future climate change. The Paleocene–Eocene transition is marked by a rapid temperature rise contemporaneous with a large negative carbon isotope excursion (CIE). Both the temperature and the isotopic excursion are well-documented by terrestrial and marine proxies. The CIE was the result of a massive release of carbon into the atmosphere. However, the carbon source and quantities of CO2 and CH4 greenhouse gases that contributed to global warming are poorly constrained and highly debated. Here we combine an established oxygen isotope paleothermometer with a newly developed triple oxygen isotope paleo-CO2 barometer. We attempt to quantify the source of greenhouse gases released during the Paleocene–Eocene transition by analyzing bioapatite of terrestrial mammals. Our results are consistent with previous estimates of PETM temperature change and suggest that not only CO2 but also massive release of seabed methane was the driver for CIE and PETM.

Environmental dynamics during the Paleocene–Eocene thermal maximum of the Peri-Tethys Sea

Environmental dynamics during the Paleocene–Eocene thermal maximum (PETM) in the northeastern Peri-Tethys revealed by high-resolution micropalaeontological and geochemical studies of a Caucasian key section

Authors:

Shcherbinina et al

Abstract:

The sedimentary record of the Paleocene–Eocene Thermal Maximum (PETM) in the wide epeiric sea of the NE Peri-Tethys contains a sapropelitic bed (SBD) characterized by a specific microfossil assemblage and negative oxygen and carbon isotope excursions (CIE). New results obtained from a high-resolution sampling of this interval in the Kheu section, central Caucasus, allows us to explore the succession, interrelationships and consequences of global and regional palaeoenvironmental events during the PETM. The CIE apparently lasted twice as long as the SBD accumulation period; thus, the SBD represents a response to the early and most dramatic phase of the PETM related to rapid transgression and greatly enhanced eutrophication of the basin. The lithological architecture of the SBD represents four bands, each of which consists of a dark, low-calcareous TOC-rich clay and relatively paler calcareous clays. The highest TOC concentrations are found in the lower and upper bands of the SBD; however, the lower band mostly consists of basinal organic matter, while the upper band represents mixed, basinal and terrestrial, organic matter. Pre-PETM events include the initial evolution of the Rhomboaster nannofossil lineage with the early first appearance of a short-arm species, relatively reduced calcareous plankton productivity, changes in the ratios of dinocyst ecological groups, and minor fluctuations in δ13C and δ18O. The onset of the CIE corresponds to the base of the SBD, which exhibits a dramatic decrease in total nannofossil abundance and an increase in total dinoflagellate abundance, the occurrence of “excursion taxa” of nannofossils (rhomboasters, asymmetric discoasters) and dinocysts (Axiodinium augustum, Epelidinium pechoricum), and significant variations in the species ratios of both nannoplankton and dinoflagellate communities, with widespread dominance of warm-water and eutrophic species. Above the SBD but during the late phase of CIE, the nannofossil abundance and species composition show a slight recovery, but most Paleocene taxa become extinct during the CIE recovery. Apectodinium spp. significantly decrease in abundance above the SBD, but rare specimens of Ax. augustum persist higher in the section after the end of the CIE. Thus, the major extinction of the Paleocene nannofossil taxa occurs after the termination of the most critical conditions during the CIE recovery phase, while the dinocyst “excursion taxa” survive even later.

Ocean Warming, NOT Acidification, Impacts Calicified Plankton (coccolithophore) Growth

Ocean warming, not acidification, controlled coccolithophore response during past greenhouse climate change

Authors:

Gibbs et al

Abstract:

Current carbon dioxide emissions are an assumed threat to oceanic calcifying plankton (coccolithophores) not just due to rising sea-surface temperatures, but also because of ocean acidification (OA). This assessment is based on single species culture experiments that are now revealing complex, synergistic, and adaptive responses to such environmental change. Despite this complexity, there is still a widespread perception that coccolithophore calcification will be inhibited by OA. These plankton have an excellent fossil record, and so we can test for the impact of OA during geological carbon cycle events, providing the added advantages of exploring entire communities across real-world major climate perturbation and recovery. Here we target fossil coccolithophore groups (holococcoliths and braarudosphaerids) expected to exhibit greatest sensitivity to acidification because of their reliance on extracellular calcification. Across the Paleocene-Eocene Thermal Maximum (56 Ma) rapid warming event, the biogeography and abundance of these extracellular calcifiers shifted dramatically, disappearing entirely from low latitudes to become limited to cooler, lower saturation-state areas. By comparing these range shift data with the environmental parameters from an Earth system model, we show that the principal control on these range retractions was temperature, with survival maintained in high-latitude refugia, despite more adverse ocean chemistry conditions. Deleterious effects of OA were only evidenced when twinned with elevated temperatures.

Middle Eocene Climatic Optimum's Ocean Productivity Spiked Because of Increased Eolian Iron Fertilization

Environmental magnetic implications of magnetofossil occurrence during the Middle Eocene Climatic Optimum (MECO) in pelagic sediments from the equatorial Indian Ocean

Authors:

Savian et al

Abstract:

Magnetic properties of pelagic marine sediments that record the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma provide information about major environmental changes. The main variations observed during this transient warming event reflect a bacterial magnetofossil signal, but the cause of the linkage between bacterial production and climate remains unclear. We present an environmental magnetic study of middle Eocene deep-sea sediments from the northern edge of Madingley Rise (Ocean Drilling Program Hole 711A, equatorial Indian Ocean) to investigate the origin of the increased magnetic mineral concentration concomitant with subchron C18n.2n, which corresponds to the MECO interval in ODP Hole 711A. This magnetic mineral peak also coincides with a change in lithofacies from calcareous nannofossils to radiolarian ooze, and a slight increase in clay concentration. Magnetite is the main magnetic mineral in the MECO sediments, which occurs as magnetically non-interacting single domain biogenic particles. The increased magnetic mineral concentration across the MECO event is likely to have been caused by increased eolian iron fertilization. This is interpreted to have given rise to increased surface ocean productivity, where increased delivery of iron and nutrients to the seafloor enhanced magnetotactic bacterial populations during the MECO event.

New Evidence Eocene Paleogene Carbon dioxide Levels Were 1260 ppm

Eocene atmospheric CO2 from the nahcolite proxy

Authors:

Jagniecki et al

Abstract:

Estimates of the atmospheric concentration of CO2, [CO2]atm, for the "hothouse" climate of the early Eocene climatic optimum (EECO) vary for different proxies. Extensive beds of the mineral nahcolite (NaHCO3) in evaporite deposits of the Green River Formation, Piceance Creek Basin, Colorado, USA, previously established [CO2]atm for the EECO to be greater than 1125 ppm by volume (ppm). Here, we present experimental data that revise the sodium carbonate mineral equilibria as a function of [CO2] and temperature. Co-precipitation of nahcolite and halite (NaCl) now establishes a well-constrained lower [CO2]atm limit of 680 ppm for the EECO. Paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for [CO2]atm in the EECO from the nahcolite proxy of ∼1260 ppm. These data support a causal connection between elevated [CO2]atm and early Eocene global warmth, but at significantly lower [CO2]atm than previously thought, which suggests that ancient climates on Earth may have been more sensitive to a doubling of [CO2]atm than is currently assumed.

Evidence of Increased Weathering, Volcanism During Paleocene-Eocene Thermal Maximum

Evidence for weathering and volcanism during the PETM from Arctic Ocean and Peri-Tethys osmium isotope records

Authors:

Dickson et al

Abstract:

Sudden global warming during the Paleocene–Eocene Thermal Maximum (PETM, 55.9 Ma) occurred because of the rapid release of several thousand gigatonnes of isotopically light carbon into the oceans and atmosphere; however, the cause of this release is not well understood. Some studies have linked carbon injection to volcanic activity associated with the North Atlantic Igneous Province (NAIP), while others have emphasised carbon cycle feedbacks associated with orbital forcing. This study presents the osmium isotope compositions of mudrocks that were deposited during the PETM at four locations (one from the Arctic Ocean, and three from the Peri-Tethys). The Os-isotope records all exhibit a shift of similar magnitude towards relatively radiogenic values across the PETM. This observation confirms that there was a transient, global increase in the flux of radiogenic Os from the weathering of continental rocks in response to elevated temperatures at that time. The tectonic effects of NAIP volcanic emplacement near the onset of the PETM is recorded by anomalously radiogenic Os-isotope compositions of PETM-age Arctic Ocean samples, which indicate an interval of hydrographic restriction that can be linked tectonic uplift due to hotspot volcanism in the North Atlantic seaway. The Peri-Tethys data also document a transient, higher flux of unradiogenic osmium into the ocean near the beginning of the PETM, most likely from the weathering of young mafic rocks associated with the NAIP. These observations support the hypothesis that volcanism played a major role in triggering the cascade of environmental changes during the PETM, and highlight the influence of paleogeography on the Os isotope characteristics of marine water masses.

Alluvial response to the Paleocene–Eocene Thermal Maximum

Alluvial response to the Paleocene–Eocene Thermal Maximum climatic event, Polecat Bench, Wyoming (U.S.A.)

Authors:

Kraus et al

Abstract:

The stratigraphic interval spanning the Paleocene–Eocene Thermal Maximum in the northern Bighorn Basin, Wyoming shows changes in the alluvial record that can be tied to a high resolution climate record. The complexity and stratigraphic spacing of paleosols change through the study section. Comparison to the climate record, reconstructed from paleosols, indicates the changes correspond to Paleocene–Eocene Thermal Maximum climatic fluctuations. In particular, the middle of the section contains thick, welded paleosols and thin avulsion deposits that link to times of well-drained floodplains and lower mean annual precipitation. Stratigraphic intervals below and above the main part of the Paleocene–Eocene Thermal Maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation. These strata contain thinner paleosols and thick avulsion deposits.

Differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the Paleocene–Eocene Thermal Maximum. Welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the Paleocene–Eocene Thermal Maximum. Intervals with widely spaced paleosols indicate more rapid accretion. We hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield. Because precipitation was reduced, much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin. Welded paleosols formed because of diminished sediment supply to the basin. With a return to wetter conditions during the recovery phase of the Paleocene–Eocene Thermal Maximum, upstream water flux increased, stored sediment moved to the basin, and vertically spaced, thinner paleosols developed. The results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change.

Why the Atlantic Ocean was More Acidified During the Paleocene Eocene Thermal Maximum

Around 55 million years ago, an abrupt global warming event triggered a highly corrosive deep-water current through the North Atlantic Ocean. The current's origin puzzled scientists for a decade, but an international team of researchers has now discovered how it formed and the findings may have implications for the carbon dioxide emission sensitivity of today's climate.

The researchers explored the acidification of the ocean that occurred during a period known as the Paleocene Eocene Thermal Maximum (PETM), when the Earth warmed 9 degree Fahrenheit in response to a rapid rise in carbon dioxide in the atmosphere and subsequently one of the largest-ever mass extinctions occurred in the deep ocean. They report their findings in today's (May 11) issue of Nature Geoscience.

This period closely resembles the scenario of global warming today.

"There has been a longstanding mystery about why ocean acidification caused by rising atmospheric carbon dioxide during the PETM was so much worse in the Atlantic compared to the rest of the world's oceans," said lead author Kaitlin Alexander, ARC Centre of Excellence for Climate System Science, University of New South Wales, Australia. "Our research suggests the shape of the ocean basins and changes to ocean currents played a key role in this difference. Understanding how this event occurred may help other researchers to better estimate the sensitivity of our climate to increasing carbon dioxide."

To get their results the researchers recreated the ocean basins and land masses of 55 million years ago in a global climate model.

During that time a ridge on the ocean floor existed between the North and South Atlantic that separated the deep water in the North Atlantic from the rest of the world's oceans. The ridge was like a giant bathtub on the ocean floor.

The simulations showed this ridge became filled with extremely corrosive water from the Arctic Ocean, which mixed with dense salty water from the Tethys Ocean and sank to the seafloor, where it accumulated. The sediment in this area indicates the water was so corrosive that it dissolved all the calcium carbonate produced by organisms that settled on the ocean floor.

When the Earth warmed as a result of a rapid increase in atmospheric carbon dioxide, it eventually warmed this corrosive bottom water. As this water warmed it became less dense and denser water sinking from above replaced it. The corrosive deep water was pushed up and spilled over the edge of the giant "bathtub" and flowed into the South Atlantic.

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Four Phases of the Paleocene–Eocene Thermal Maximum Recovered From Egypt

New geochemical constraints on the Paleocene–Eocene thermal maximum: Dababiya GSSP, Egypt

Authors:

Khozyem et al

Abstract:

The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of carbonate and organic matter across the globe, suggesting massive release of 13C-depleted carbon dioxide into the ocean and atmosphere over a very short time interval (probably less than 20ky). We report a geochemical and mineralogical study of 106 samples spanning the most expanded PETM at the Dababiya Global Stratotype Standard section and Point (GSSP) near Luxor, Egypt. The field and laboratory observations reveal that the deposition occurred in a submarine channel extended laterally about 200 m with the deepest part (~ 0.88 m) at the designated GSSP, although all bio-zones are present. Stable isotope records of both carbonate and organic carbon show decreases starting 0.6 m below the Paleocene-Eocene boundary (PEB) and culminating at the erosion surface. A persistent shift in δ15Norg values to near zero reflects a gradual increase in bacterial activity. High Ti, K and Zr and low Si contents at the PEB coincide with increased kaolinite contents, which suggests intense chemical weathering under more humid conditions at the PETM onset. Two negative Ce-anomalies indicate intervals of anoxic conditions during the lower and middle PETM (base and top of zone E1). The first anoxic event is represented by a negative Ce-anomaly, high V/C rand V/V + Ni ratios, negative Mn* and an abundance of idiomorphic pyrite crystals that indicate anoxic to euxinic conditions. The anoxic event (middle PETM) is marked by high U, Mo, V, Fe and abundant small sized (2–5 μm) pyrite framboids, increased Cu, Ni, and Cd at the same level suggesting anoxic conditions linked to high surface water productivity. Above this interval, oxic conditions returned as indicated by the precipitation of phosphorus and barium. These data reveal an expanded PETM interval marked by intense weathering as a crucial parameter during the recovery phase.

Heavy Extinction on a Pacfic Guyot Paleocene–Eocene Thermal Maximum

No place to retreat: Heavy extinction and delayed recovery on a Pacific guyot during the Paleocene–Eocene Thermal Maximum

Authors:

Yamaguchi et al

Abstract:

Modern global change threatens alpine ecosystems by forcing species to migrate to higher elevations and potentially eliminating alpine habitat altogether. Here we show that an analogous restriction of suitable habitat operates on submarine mountains. During the Paleocene–Eocene Thermal Maximum (PETM, ca. 55.96 Ma), ostracodes underwent local extinction on the crest of Allison Guyot in the central Pacific Ocean, which lost 64% of its ostracode species richness (14 species reduced to three species) and as much as 94% of ostracode abundance for ∼1.1 m.y., before recolonization rebuilt biodiversity and abundance over the next 200 k.y. Biotic changes may reflect an increase in current speeds, acidification, and a decrease in food supply owing to a temperature-driven increase in metabolic rates. Notably, continental margin ostracodes also underwent extinction during the PETM (25%–38% loss) but, unlike Allison Guyot faunas, could quickly repopulate the continental slope. The absence of refugia for isolated seamounts prolonged the reduction in biodiversity initiated by the PETM, a pattern that may be expected for modern seamount faunas in an era of future global change.

Royal Tyrrell Museum Lecture Series: Mammals During the PETM

Evidence of Seasonal Change in Eocene Paleogene Paleoclimate

Stable isotope patterns found in early Eocene equid tooth rows of North America: Implications for reproductive behavior and paleoclimate

Authors:

D'Ambrosia et al

Abstract:

Reproductive behaviors of early Eocene equids were likely different from their modern-day counterparts as a result of their small body size and warmer global temperatures. To better understand the paleoenvironment and ecology of these early horses, teeth of Protorohippus montanum jaws from a single stratigraphic locality in early Eocene sedimentary deposits of Wyoming were sampled for oxygen and carbon isotope analysis. These enamel data along with an inferred body mass of ~ 7.5 kg suggests that adult teeth formed over a matter of months, with the final tooth erupting at ~ 1.3 years of age. Thus, average isotopic values from each tooth likely represent environmental conditions from a single season. Results indicate two isotopic patterns. In the case of isotopic “pattern A,” the second forming molars (m/2s) have significantly lower isotopic ratios compared to other teeth within the jaw. This suggests the first forming molars (m/1s) formed during a cooling fall season, followed by formation of the m/2s during the cooler winter. In the case of isotopic “pattern B,” results suggest that m/1s formed during a warming spring season, while the m/2s formed during the following warmer summer season. Isotopic ratios of m/1s may represent an individual's birth season (or in utero season, depending on timing of initial formation), implying that early equids experienced at least two birth seasons per year. These results suggest that temperatures and reduced seasonality of the early Eocene played a strong role in early equid birth cycles. Lastly, the mean and variance in carbon and oxygen isotope ratios was not significantly different across tooth positions of all jaws when all individuals were grouped together, regardless of their pattern assignment. Such results indicate that isotopic data from fourth premolars, first molars, second molars, and third molars can be combined for purposes of temporal reconstructions of paleoclimate, thus increasing the potential sample sizes for these types of studies.

Evidence of Transient Drying During Paleocene-Eocene Thermal Maximum in Wyoming, North America

MANGANESE-BEARING RHIZOCRETIONS IN THE WILLWOOD FORMATION, WYOMING, U.S.A.: IMPLICATIONS FOR PALEOCLIMATE DURING THE PALEOCENE–EOCENE THERMAL MAXIMUM

Authors:

Woody et al

Abstract:

Changes in the stratigraphic distribution of manganese (Mn)-bearing columnar structures interpreted as rhizocretions indicate a shift in paleohydrological conditions in the Bighorn Basin during the Paleocene–Eocene Thermal Maximum (PETM). While most studies agree that significant warming occurred during the PETM, interpretations differ as to the effects of warming on the paleohydrologic regime. The columns consist of sand and silt cemented by calcite that also contains black, Mn-bearing nodules. The rhizocretions are typically vertically oriented and range from a few cm to over 50 cm in diameter and up to 75 cm tall. They are interpreted to have formed in the rhizospheres of relatively large root systems. The rhizocretions are restricted to intervals, showing only weak paleopedogenic development, that are interpreted as crevasse-splay or avulsion deposits. While such deposits are present throughout the study section at Polecat Bench in the northern Bighorn Basin, Wyoming, the Mn-bearing rhizocretions are found only below and above the PETM interval and within the initial carbon isotope excursion (CIE) marking the onset of the PETM. The abundance of black, Mn-rich nodules (less than 1 cm in diameter) in the rhizocretions and presence of other pedogenic features indicate that the soils in which the plants were growing underwent seasonal flooding and repeated redox alternations. Their distribution in similar host deposits throughout the study interval, except for the main body of the PETM, supports climate as the driving factor in preservation of the Mn-bearing rhizocretions. The Mn-bearing rhizocretions support recent studies that suggest transient drying in northern Wyoming during the PETM.

Evidence of Hypoxic Upper Ocean Waters During the Paleocene-Eocene Thermal Maximum (PETM)

I/Ca evidence for upper ocean deoxygenation during the Paleocene-Eocene Thermal Maximum (PETM)

Authors:

Zhou et al

Abstract:

Anthropogenic global warming affects marine ecosystems in complex ways, and declining ocean oxygenation is a growing concern. Forecasting the geographical and bathymetric extent, rate and intensity of future deoxygenation and its effects on oceanic biota, however, remains highly challenging because of the complex feedbacks in the earth-ocean-biota system. Information on past global warming events such as the Paleocene Eocene Thermal Maximum (PETM, ~55.5 Ma), a potential analog for present and future global warming, may help in such forecasting. Documenting past ocean deoxygenation, however, is hampered by the lack of sensitive proxies for past oceanic oxygen levels throughout the water column. As yet no evidence has been presented for pervasive deoxygenation in the upper water column through expansion of Oxygen Minimum Zones (OMZs). We apply a novel proxy for paleo-redox conditions, the iodine to calcium ratio (I/Ca) in bulk coarse fraction sediment and planktic foraminiferal tests from pelagic sites in different oceans, and compared our reconstruction with modeled oxygen levels. The reconstructed iodate gradients indicate that deoxygenation occurred in the upper water column in the Atlantic, Indian Oceans, and possibly the Pacific Ocean as well during the PETM, due to vertical and potentially lateral expansion of OMZs.

Temperature was Very Important for Warm Water Carbon Cycling in Eocene Oceans

Temperature-dependent remineralization and carbon cycling in the warm Eocene oceans

Authors:

John et al

Abstract:

Metabolic rates in heterotrophic bacteria are more sensitive to temperature than rates of primary production (e.g., López-Urrutia et al., 2006; Regaudie-de-Gioux and Duarte, 2012). Consequently, faster bacterial respiration rates in a warmer ocean may result in more efficient remineralization of sinking organic matter higher in the water column, with implications for carbon and nutrient cycling during warm climate states. This is supported by a series of reconstructed δ13CDIC: depth profiles based on well-preserved planktonic foraminifera assemblages from Tanzania from the warm Eocene epoch (55.5–33.7 Ma) when global surface and deep ocean temperatures exceeded those of the modern day (John et al., 2013). These results indicate relatively sharp δ13CDIC gradients in the upper water column which supports the hypothesis that high metabolic rates in warm Eocene oceans led to more efficient recycling of organic matter and reduced burial rates of organic carbon (Olivarez Lyle and Lyle, 2006). Shallower remineralization depths would also cause an upward displacement and intensification of the oxygen minimum zone which is consistent with evidence for a pelagic ecosystem that was focused in a narrow depth range near the surface during the warm early and middle Eocene. Here we use the Earth System model, cGENIE, that incorporates a new temperature dependence of remineralization rates to illustrate the potential effects of temperature on particulate organic carbon fluxes and hence vertical δ13CDIC gradients. Modeled δ13CDIC vertical profiles off the coast of Tanzania for the Eocene agree well with the reconstructed δ13CDIC profiles, supporting our interpretations based on temperature-dependent remineralization.

How Much Atmospheric Carbon is Necessary to Create the Paleocene-Eocene Thermal Maximum?

The Paleocene-Eocene Thermal Maximum: How much carbon is enough?

Authors:

Meissner et al

Abstract:

The Paleocene-Eocene Thermal Maximum (PETM), ~55.53 million years before present, was an abrupt warming event that involved profound changes in the carbon cycle and led to major perturbations of marine and terrestrial ecosystems. The PETM was triggered by the release of a massive amount of carbon, and thus the event provides an analogue for future climate and environmental changes given current anthropogenic CO2 emissions. Previous attempts to constrain the amount of carbon released have produced widely diverging results, between 2000 and 10000 gigatonnes carbon (GtC). Here we use the UVic Earth System Climate Model in conjunction with a recently published compilation of PETM temperatures [14] to constrain the initial atmospheric CO2 concentration as well as the total mass of carbon released during the event. Thirty-six simulations were initialized with varying ocean alkalinity, river runoff, and ocean sediment cover. Simulating various combinations of pre-PETM CO2 levels (840, 1680, and 2520 ppm) and total carbon releases (3000, 4500, 7000, and 10000 GtC), we find that both the 840 ppm plus 7000 GtC and 1680 ppm plus 7000–10000 GtC scenarios agree best with temperature reconstructions. Bottom waters outside the Arctic and North Atlantic Oceans remain well oxygenated in all of our simulations. While the recovery time and rates are highly dependent on ocean alkalinity and sediment cover, the maximum temperature anomaly, used here to constrain the amount of carbon released, is less dependent on this slow acting feedback.

Enhanced Primary & Bacterial Productivity During Paleocene-Eocene Thermal Maximum

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

Authors:

Savian et al

Abstract:

Earth's climate experienced a warming event known as the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma, which was an abrupt reversal of a long-term Eocene cooling trend. This event is characterized in the deep Southern, Atlantic, Pacific and Indian Oceans by a distinct negative δ18O excursion over 500 kyr. We report results of high-resolution paleontological, geochemical, and rock magnetic investigations of the Neo-Tethyan Monte Cagnero (MCA) section (northeastern Apennines, Italy), which can be correlated on the basis of magneto- and biostratigraphic results to the MECO event recorded in deep-sea sections. In the MCA section, an interval with a relative increase in eutrophic nannofossil taxa (and decreased abundances of oligotrophic taxa) spans the culmination of the MECO warming and its aftermath and coincides with a positive carbon isotope excursion, and a peak in magnetite and hematite/goethite concentration. The magnetite peak reflects the appearance of putative magnetofossils, while the hematite/goethite apex is attributed to an enhanced detrital mineral contribution, likely as aeolian dust transported from the continent adjacent to the Neo-Tethys Ocean during a drier, more seasonal climate during the peak MECO warming. Based on our new geochemical, paleontological and magnetic records, the MECO warming peak and its immediate aftermath are interpreted as a period of high primary productivity. Sea-surface iron fertilization is inferred to have stimulated high phytoplankton productivity, increasing organic carbon export to the seafloor and promoting enhanced biomineralization of magnetotactic bacteria, which are preserved as putative magnetofossils during the warmest periods of the MECO event in the MCA section. Together with previous studies, our work reinforces the connection between hyperthermal climatic events and the occurrence (or increased abundance) of putative magnetofossils in the sedimentary record.

More Contrarian Data: Cool Equitorial Temperatures From Early Eocene Paleogene India

Cool equatorial terrestrial temperatures and the South Asian monsoon in the Early Eocene: Evidence from the Gurha Mine, Rajasthan, India

Authors:

Shukla et al

Abstract:

Early Eocene (~ 55–52 Ma) laminated lacustrine sediments overlying lignites in the Gurha Mine (27.87398°N, 72.86709°E), Rajasthan, India, yield a diversity of fossil leaves, flowers, fruits, seeds and insects. CLAMP (multivariate foliar physiognomic) analysis of two horizons separated by an estimated several tens of thousands of years of deposition indicates cool equatorial (~ 10°N) temperatures and a pronounced monsoon signature. A lower assemblage consisting of 54 leaf morphotypes and an upper assemblage of 57 leaf forms yielded mean annual temperatures (MAT) of 24.7 and 23.9 °C, respectively. The uncertainty (± 2.82 °C) means these temperature regimes are identical despite few similarities in the morphotypes between the two assemblages.The mean annual range of temperature (MART) was approximately 9.7 °C for both assemblages. When corrected for evapotranspirational cooling these temperature regimes are similar to those experienced today at 10°N on the west coast of India and surprisingly cool for the tropics at a time of extreme global warmth. Growth was year round. The tropical to paratropical fossil floras also suggest a moist regime (80% annual relative humidity) and high mean annual precipitation of ~ 1800 mm for both assemblages but with a pronounced wet/dry seasonality indicative of a pronounced monsoonal regime. The lower assemblage has a stronger monsoon index (11.8) than the upper assemblage (8.8). The two assemblages seem to have been deposited less than 100 ka apart. This suggests that not only a pronounced South Asian monsoon existed when India and Asia first made contact, but also a variation in monsoon strength existed that cannot be ascribed to tectonic drivers.

Tropical Sea Surface Temperatures may Have Exceeded 40 C During Paleocene–Eocene Thermal Maximum

Extreme warming of tropical waters during the Paleocene–Eocene Thermal Maximum

Authors:

Aze et al

Abstract:

The Paleocene–Eocene Thermal Maximum (PETM), ca. 56 Ma, was a major global environmental perturbation attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. Geochemical records of tropical sea-surface temperatures (SSTs) from the PETM are rare and are typically affected by post-depositional diagenesis. To circumvent this issue, we have analyzed oxygen isotope ratios (δ18O) of single specimens of exceptionally well-preserved planktonic foraminifera from the PETM in Tanzania (∼19°S paleolatitude), which yield extremely low δ18O, down to less than –5‰. After accounting for changes in seawater chemistry and pH, we estimate from the foraminifer δ18O that tropical SSTs rose by greater than 3 °C during the PETM and may have exceeded 40 °C. Calcareous plankton are absent from a large part of the Tanzania PETM record; extreme environmental change may have temporarily caused foraminiferal exclusion.