Eocene Climate Change Research Articles

Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

AbstractUnderstanding current and future biodiversity responses to changing climate is pivotal as anthropogenic climate change continues. This understanding is complicated by the multitude of available metrics to quantify dynamics and by biased sampling protocols. Here, we investigate the impact of sampling protocol strategies using a data-rich fossil record to calculate effective diversity using Hill numbers for the first time on Paleogene planktonic foraminifera. We sample 22,830 individual tests, in two different size classes, across a 7 Myr time slice of the middle Eocene featuring a major transient warming event, the middle Eocene climatic optimum (MECO; ~40 Ma), at study sites in the midlatitude North Atlantic. Using generalized additive models, we investigate community responses to climatic fluctuations. After correcting for any effects of fossil fragmentation, we show a peak in generic diversity in the early and middle stages of the MECO as well as divergent trajectories between the typical size-selected community (>180 μm) and a broader assemblage, including smaller genera (>63 μm). Assemblages featuring smaller genera are more resilient to the climatic fluctuations of the MECO than those assemblages that feature only larger genera, maintaining their community structure at the reference Hill numbers for Shannon's and Simpson's indices. These results raise fundamental questions about how communities respond to climate excursions. In addition, our results emphasize the need to design studies with the aim of collecting the most inclusive data possible to allow detection of community changes and determine which species are likely to dominate future environments.

Late early to early middle Eocene climate and vegetation change at Tastakh Lake (northern Yakutia, eastern Siberia)

The late early – early middle Eocene climate and vegetation evolution in northern Yakutia (Eastern Siberia) is quantitatively studied in detail for the first time, based on a palaeobotanical record. Palaeobotanical data for this time interval were obtained from 16 palynofloras from continental sediments on the southern shore of Tastakh Lake (the left bank of Indigirka River). In this first integrative study, we applied the Coexistence Approach for quantification of palaeoclimate, the Plant Functional Type (PFT) approach and Integrated Plant Record (IPR) vegetation analysis to quantify palaeovegetation. Our investigation documents the persistence of warm temperate and, at times, nearly tropical climate conditions in the earlier part of the record and the subsequent onset of a cooling trend. Overall humid climate conditions prevailed throughout the late early – early middle Eocene. Our reconstruction indicates low temperature seasonality and relatively strong seasonality in precipitation. Vegetation data as reconstructed are in good agreement with the climate evolution. PFT diversity spectra indicate the prevalence of mixed evergreen-deciduous forests of warm temperate character. The IPR method suggests that the mixed mesophytic forest biome persisted throughout the studied sedimentary succession. The presence of mangroves in our late early Eocene records (at the base of the section) is largely in line with our climate reconstruction and possibly can be related to the Early Eocene Climatic Optimum (EECO) hyperthermal event.

Early‐Middle Eocene Hydroclimate Variations Recorded by Environmental Magnetism in the Linxia Basin, NE Tibetan Plateau

AbstractAlthough Neogene climate change reconstruction in central Asia is important for understanding global cooling, Asian monsoon evolution, and the Tibetan Plateau stepwise uplift during the Cenozoic, the paleoenvironmental evolution during the Paleogene in this region is still ambiguous due to a lack of corresponding continuous and complete terrestrial records with precise age constraints. Recently, a new fluvial sedimentary sequence with magnetostratigraphic ages spanning from ∼53 to 40 Ma was found in the Linxia Basin, NE Tibetan Plateau, thereby providing a window to understand Eocene climate change in the Asian interior. From this fluvial sedimentary sequence, we present early‐middle Eocene hydroclimate variations based on a combined method of rock magnetism and diffuse reflectance spectroscopy. Our results show magnetic enhancement of fluvial sediments at 51.7 Ma resulted from abundant single‐domain magnetite inputs from the surrounding mountains through strong erosion and transport in a relatively wet environment. Subsequently, at 47.6 Ma, magnetic weakening of floodplain sediments corresponds to an increase in hematite concentrations produced via low‐temperature oxidation in a prolonged dry environment. Comparisons of paleoclimatic proxies, such as organic geochemistry and rock magnetism from neighboring basins, tectonic deformation of the NE Tibetan Plateau, and sea level change in the Paratethys Sea suggest that the hydroclimate variation from relatively wet to dry climate in the early‐middle Eocene in this area was mainly controlled by global climatic change and probably superimposed by the uplift of the Tibetan Plateau.

Probing the Ecology and Climate of the Eocene Southern Ocean With Sand Tiger Sharks Striatolamia macrota.

Many explanations for Eocene climate change focus on the Southern Ocean—where tectonics influenced oceanic gateways, ocean circulation reduced heat transport, and greenhouse gas declines prompted glaciation. To date, few studies focus on marine vertebrates at high latitudes to discern paleoecological and paleoenvironmental impacts of this climate transition. The Tertiary Eocene La Meseta (TELM) Formation has a rich fossil assemblage to characterize these impacts; Striatolamia macrota, an extinct (†) sand tiger shark, is abundant throughout the La Meseta Formation. Body size is often tracked to characterize and integrate across multiple ecological dimensions. †S. macrota body size distributions indicate limited changes during TELMs 2–5 based on anterior tooth crown height (n = 450, mean = 19.6 ± 6.4 mm). Similarly, environmental conditions remained stable through this period based on δ18OPO4 values from tooth enameloid (n = 42; 21.5 ± 1.6‰), which corresponds to a mean temperature of 22.0 ± 4.0°C. Our preliminary ε Nd (n = 4) results indicate an early Drake Passage opening with Pacific inputs during TELM 2–3 (45–43 Ma) based on single unit variation with an overall radiogenic trend. Two possible hypotheses to explain these observations are (1) †S. macrota modified its migration behavior to ameliorate environmental changes related to the Drake Passage opening, or (2) the local climate change was small and gateway opening had little impact. While we cannot rule out an ecological explanation, a comparison with climate model results suggests that increased CO2 produces warm conditions that also parsimoniously explain the observations.

Eocene carbonate accumulation in the north-central Pacific Ocean: new insights from Ocean Drilling Program Site 1209, Shatsky Rise

Major climate transitions and perturbations in global carbon cycle are known to have occurred during the Eocene, between 56 and 34 million years ago (Ma). A series of carbon isotope excursions (CIEs) mark variations in the global carbon cycle and changes in climate through early Eocene. Paleocene-Eocene Thermal Maximum (PETM) ca. 56 Ma is the most pronounced and well documented of these events expressed as a clay rich layer in many deep-sea sections, resulting from widespread carbonate dissolution on the seafloor, which is in turn related to shoaling of the carbonate compensation depth (CCD) and lysocline. Other CIEs of early Eocene had similar response. However, response of these geologically ‘instantaneous’ hyperthermals differ from long-term warmth (multi-million-year time scale) of the Early Eocene Climate Optimum (EECO) in terms of sea-floor carbonate accumulation. Following the termination of EECO, earth's climate transitioned into long-term cooling. Pronounced fluctuations in CCD of equatorial Pacific are known to have occurred during middle-late Eocene as well, whose global extent and origin are still unresolved. Most proxy records either span the interval of early Eocene or document particular climatic events in Eocene, which significantly limits visualizing the long-term Eocene climate change and response of open marine carbonate preservation. The present study documents change in carbonate dissolution and carbonate mass accumulation rate through the entire Eocene (56–34 Ma) at ODP Site 1209 on Shatsky Rise, north-central Pacific and ties it to a stable carbon and oxygen isotope record. Our study determines the correlation between deep-sea carbonate dissolution and carbon cycling process during the dynamic climate regime of Eocene. A strong correlation between magnitude of CIEs and intensity of dissolution for early Eocene hyperthermal events appears to significantly weaken for multiple dissolution events in middle-late Eocene, thereby indicating fundamental difference in their causal mechanism.

The Early to Middle Eocene Transition: An Integrated Calcareous Nannofossil and Stable Isotope Record From the Northwest Atlantic Ocean (Integrated Ocean Drilling Program Site U1410)

AbstractThe early to middle Eocene is marked by prominent changes in calcareous nannofossil assemblages coinciding both with long‐term climate changes and modification of the North Atlantic deep ocean circulation. In order to assess the impact of Eocene climate change on surface water environmental conditions of the Northwest Atlantic, we developed calcareous nannoplankton assemblage data and bulk stable isotope records (δ18O and δ13C) across an early to middle Eocene interval (~52–43 Ma) at Integrated Ocean Drilling Program Site U1410 (Southeast Newfoundland Ridge, ~41°N). At this site, early Eocene sediments are pelagic nannofossil chalk, whereas middle Eocene deposits occur as clay‐rich drift sediments reflecting the progressive influence of northern‐sourced deep currents. Between the end of Early Eocene Climatic Optimum (EECO) and the Ypresian/Lutetian boundary, calcareous nannofossils switched from an assemblage mainly composed of warm‐water and oligotrophic taxa (Zygrhablithus,Discoaster,Sphenolithus,Coccolithus) to one dominated by the more temperate and eutrophic reticulofenestrids. The most prominent period of accelerated assemblage change occurred during a ~2‐Myr phase of relatively high bulk δ18O values possibly related to the post‐EECO cooling. Although the dominance of reticulofenestrids persisted unvaried throughout the middle Eocene interval, early Lutetian (~47.4 to 47 Ma) stable isotope records indicate a reversal in the paleoenvironmetal trends suggesting a potential restoration of warmer conditions. Importantly, our data indicate that the ~2‐Myr interval immediately following the EECO was crucial in establishing the modern calcareous nannofossil assemblage structure and also reveal that the establishment ofReticulofenestra‐dominated assemblage occurred prior to the onset of persistent deep current system in the Northwest Atlantic.

Paleoenvironmental response of midlatitudinal wetlands to Paleocene–early Eocene climate change (Schöningen lignite deposits, Germany)

Abstract. The early Paleogene is marked by multiple negative carbon isotope excursions (CIEs) that reflect massive short-term carbon cycle perturbations that coincide with significant warming during a high-pCO2 world, affecting both marine and terrestrial ecosystems. Records of such hyperthermals from the marine–terrestrial interface (e.g., estuarine swamps and mire deposits) are therefore of great interest as their present-day counterparts are highly vulnerable to future climate and sea level change. Here, we assess paleoenvironmental changes of midlatitudinal late Paleocene–early Eocene peat mire records along the paleo-North Sea coast. We provide carbon isotope data of bulk organic matter (δ13CTOC), organic carbon content (%TOC), and palynological data from an extensive peat mire deposited at a midlatitudinal (ca. 41∘ N) coastal site (Schöningen, Germany). The δ13CTOC data show a carbon isotope excursion of −1.3 ‰ (mean decrease in δ13CTOC; −1.7 ‰ at the onset of CIE) coeval with a conspicuous Apectodinium acme. Due to the exceptionally large stratigraphic thickness of the CIE at Schöningen (10 m of section) we established a detailed palynological record that indicates only minor changes in paleovegetation leading into and during this event. Instead, paleovegetation changes mostly follow natural successions in response to changes along the marine–terrestrial interface. The available age constraints for the Schöningen Formation hamper a solid assignment of the detected CIE to a particular hyperthermal such as the Paleocene–Eocene Thermal Maximum (PETM) or any succeeding hyperthermal event such as the Eocene Thermal Maximum 2 (ETM2). Compared to other nearby peat mire records (Cobham, UK; Vasterival, F) it appears that wetland deposits around the Paleogene North Sea have a consistent CIE magnitude of ca. −1.3 ‰ in δ13CTOC. Moreover, the Schöningen record shares major characteristics with the Cobham Lignite PETM record, including evidence for increased fire activity prior to the CIE, minor plant species change during the hyperthermal, a reduced CIE in δ13CTOC, and drowning of the mire (marine ingressions) during much of the Schöningen CIE event. This suggests that either the Schöningen CIE reflects the PETM or that early Paleogene hyperthermals similarly affected paleoenvironmental conditions of a major segment of the paleo-North Sea coast.

Sedimentological and mineralogical records from drill core SKD1 in the Jianghan Basin, Central China, and their implications for late Cretaceous–early Eocene climate change

The Jianghan Basin, Central China, contains a thick, continuous sequence of early Cenozoic evaporite-bearing deposits that provide a wealth of information about early Cenozoic climate change and evaporites accumulation in East Asia. However, the paleoclimatic history of the basin and its effect on the evaporites are largely unknown. We obtained a deep drill core (SKD1, 2346.5 m long) from the late Cretaceous to early Eocene evaporite-bearing deposits in the Jianghan Basin. Detailed analyses of the lithofacies, mineralogy and geochemistry of the core indicate that salinization and deepening of the lake occurred (corresponding to the Yuyang Formation to the lower Xingouzui Formation), followed by desalting and shallowing (corresponding to the upper Xingouzui Formation). Reconstruction of the spatiotemporal evolution of the evaporites in the Jiangling depression suggests a transition from semi-arid conditions in the late Cretaceous to extremely arid conditions in the initial stage of the Eocene. The climate then became semi-humid during the deposition of the upper Xingouzui Formation, indicating a monsoon or monsoon-like climate in East Asia during the early Eocene. The southward migration of the depocenter of the Jiangling depression, coupled with a warm and extremely arid climate, resulted in the precipitation of evaporites during the accumulation of the upper Shashi Formation and the lower Xingouzui Formation. These results indicate great potential for identifying potash resources within the subsag in the southern Jiangling depression.

A High‐Fidelity Benthic Stable Isotope Record of Late Cretaceous–Early Eocene Climate Change and Carbon‐Cycling

AbstractThe Late Cretaceous–Early Paleogene is the most recent period in Earth history that experienced sustained global greenhouse warmth on multimillion year timescales. Yet, knowledge of ambient climate conditions and the complex interplay between various forcing mechanisms are still poorly constrained. Here we present a 14.75 million‐year‐long, high‐resolution, orbitally tuned record of paired climate change and carbon‐cycling for this enigmatic period (~67–52 Ma), which we compare to an up‐to‐date compilation of atmospheric pCO2 records. Our climate and carbon‐cycling records, which are the highest resolution stratigraphically complete records to be constructed from a single marine site in the Atlantic Ocean, feature all major transient warming events (termed “hyperthermals”) known from this time period. We identify eccentricity as the dominant pacemaker of climate and the carbon cycle throughout the Late Maastrichtian to Early Eocene, through the modulation of precession. On average, changes in the carbon cycle lagged changes in climate by ~23,000 years at the long eccentricity (405,000‐year) band, and by ~3,000–4,500 years at the short eccentricity (100,000‐year) band, suggesting that light carbon was released as a positive feedback to warming induced by orbital forcing. Our new record places all known hyperthermals of the Late Maastrichtian–Early Eocene into temporal context with regards to evolving ambient climate of the time. We constrain potential carbon cycle influences of Large Igneous Province volcanism associated with the Deccan Traps and North Atlantic Igneous Province, as well as the sensitivity of climate and the carbon‐cycle to the 2.4 million‐year‐long eccentricity cycle.

Sedimentary and geochemical evidence of Eocene climate change in the Xining Basin, northeastern Tibetan Plateau

The northeastern Tibetan Plateau began to grow during the Eocene and it is important to understand the climatic history of Asia during this period of so-called ‘doubthouse’ conditions. However, despite major advances in the last few decades, the evolutionary history and possible mechanisms of Eocene climate change in the northeastern Tibetan Plateau remain unclear. The Xining Basin in the northeastern Tibetan Plateau contains a continuous sequence of Early to Late Eocene non-marine sediments which provides the opportunity to resolve long-term climate changes during this period. In this study, we report the results of analyses of lithofacies, sediment color and geochemistry of bulk samples collected from the Xijigou section of the Xining Basin. An abrupt lithofacies change between the Early (~52–40 Ma) and Late Eocene (~40–34 Ma) indicates a change in the depositional environment from a shallow lake to a playa lake in response to a significant climatic shift. During ~52–40 Ma, higher values of sediment redness ( a *), redness/lightness ( a */ L *) and higher modified Chemical Index of Weathering (CIW′) indicate a relatively warm and humid climate, while from ~40–34 Ma the lower values of a *, a */ L * and lower CIW′ imply sub-humid to semi-arid climatic conditions. The paleoclimatic records indicate a long-term (~52–34 Ma) trend of decreasing chemical weathering, consistent with global climate change. An abrupt sharp excursion of the proxy records during ~42–40 Ma suggests a relatively brief warm interval, corresponding to the Middle Eocene Climatic Optimum (MECO). We suggest that global cooling substantially reduced humidity in inner Asia, resulting in sub-humid to semi-arid climatic conditions after 40 Ma in the Xining Basin, which may have been responsible for the long-term trend of decreasing chemical weathering during the Eocene.

Baltic amber impact on historical biogeography and palaeoclimate research: oriental rove beetle Dysanabatium found in the Eocene of Europe (Coleoptera, Staphylinidae, Paederinae)

AbstractBaltic amber is a rich source of fossilized organisms and a valuable tool for evolutionary, biogeographical and palaeoenvironmental research. Because it is found in several deposits around the Baltic Sea, the exact area of origin, age in the Eocene and palaeoenvironment of the amber forest form a subject for ongoing discussion. Furthermore, there is a puzzling connection between Eocene climate change and the co‐occurrence of thermophilic and temperate insect taxa in Baltic amber, sometimes even in the same inclusions. We revisit these issues through a new piece of evidence: the rare South‐East Asian rove beetle genus Dysanabatium (11 extant species) found to be abundant in Baltic amber. We describe four new extinct species of Dysanabatium based on 13 specimens from 8 amber pieces collected in Denmark, Poland, Ukraine and Russia. These species are Dysanabatium kechrimparense sp. nov., D. aenaum sp. nov., D. damgaardi sp. nov. and D. johannesi sp. nov. The occurrence of one species, D. kechrimparense sp. nov., in the amber from all countries, as well as its co‐occurrence with D. damgaardi sp. nov. in one amber piece from Russia, suggest a possible common origin of Baltic amber from all these deposits. Dysanabatium adds to a plethora of fossil species congeneric with extant species restricted to South‐East Asia, which points to the warm and equable climate of the north European Eocene amber forest.

Dispersal of thermophilic beetles across the intercontinental Arctic forest belt during the early Eocene

Massive biotic change occurred during the Eocene as the climate shifted from warm and equable to seasonal and latitudinally stratified. Mild winter temperatures across Arctic intercontinental land bridges permitted dispersal of frost-intolerant groups until the Eocene-Oligocene boundary, while trans-Arctic dispersal in thermophilic groups may have been limited to the early Eocene, especially during short-lived hyperthermals. Some of these lineages are now disjunct between continents of the northern hemisphere. Although Eocene climate change may have been one of the most important drivers of these ancient patterns in modern animal and plant distributions, its particular events are rarely implicated or correlated with group-specific climatic requirements. Here we explored the climatic and geological drivers of a particularly striking Neotropical-Oriental disjunct distribution in the rove beetle Bolitogyrus, a suspected Eocene relict. We integrated evidence from Eocene fossils, distributional and climate data, paleoclimate, paleogeography, and phylogenetic divergence dating to show that intercontinental dispersal of Bolitogyrus ceased in the early Eocene, consistent with the termination of conditions required by thermophilic lineages. These results provide new insight into the poorly known and short-lived Arctic forest community of the Early Eocene and its surviving lineages.

Penguin response to the Eocene climate and ecosystem change in the northern Antarctic Peninsula region

Eocene Antarctic penguins are known solely from the La Meseta Formation (Seymour Island, James Ross Basin). They are most numerous and taxonomically diverse (at least ten species present) within strata formed at the end of this epoch, which is concomitant with a significant cooling trend and biotic turnover prior to the onset of glaciation. Moreover, all newly appeared taxa were small-bodied, and most probably evolved in situ. Interestingly, some chemical proxies suggest enhanced nutrient upwelling events that coincided with obvious changes in the record of La Meseta penguins.

Fossil hydrothermal systems tracking Eocene climate change in Antarctica: Comment and Reply

It is an outstanding property of hydrogen and oxygen isotopes in surface fresh waters to be directly climate related. Since actual traces of ancient waters, such as in fluid inclusions, are often lost or difficult to read, the pressure to use substitute information is intense. [Dallai et al. (2001

Fossil hydrothermal systems tracking Eocene climate change in Antarctica

During the Cenozoic, alkaline magmatism related to rifting in the Ross Sea embayment affected the basement of northern Victoria Land, Antarctica. Shallow intrusions supplied the necessary heat to cause groundwater circulation through permeable rocks, producing local hydrothermal systems. In the granitoid country rocks of the two adjacent areas of Mt. Monteagle and Mt. McGee, the biotite δD values range from −69‰ to −141‰ and from −66‰ to −183‰, respectively, and K-feldspars show δ 18 O values as low as 3.7‰ and 4.4‰. These values result from isotope exchange between igneous minerals and hydrothermal fluids with a dominant meteoric water component. Geological and tectonic histories of the two areas show marked similarities; therefore, different δ 18 O and δD values of hydrothermally altered rocks may be interpreted in terms of different isotopic composition of the waters feeding the hydrothermal systems. The isotopic shift of these meteoric waters indicates that climate change occurred in the time span between the 42 Ma intrusion of Mt. Monteagle and the 38 Ma intrusion of Mt. McGee, thus suggesting a cooling episode in the Ross Sea region during late Eocene time.

Paleocene—Eocene climate change in southwestern Wyoming: Isotopic records from paleosol carbonates and freshwater bivalves

Paleocene—Eocene climate change in southwestern Wyoming: Isotopic records from paleosol carbonates and freshwater bivalves

Can increasing carbon dioxide cause climate change?

The realistic physical functioning of the greenhouse effect is reviewed, and the role of dynamic transport and water vapor is identified. Model errors and uncertainties are quantitatively compared with the forcing due to doubling CO2, and they are shown to be too large for reliable model evaluations of climate sensitivities. The possibility of directly measuring climate sensitivity is reviewed. A direct approach using satellite data to relate changes in globally averaged radiative flux changes at the top of the atmosphere to naturally occurring changes in global mean temperature is described. Indirect approaches to evaluating climate sensitivity involving the response to volcanic eruptions and Eocene climate change are also described. Finally, it is explained how, in principle, a climate that is insensitive to gross radiative forcing as produced by doubling CO2 might still be able to undergo major changes of the sort associated with ice ages and equable climates.