Description: A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205±0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by ∼2.3°C for the combined proxy data (foraminifera Mg∕Ca and alkenones), or by ∼3.2–3.4°C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.

Description: Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

Description: Published

Description: 1383–1387

Description: 5A. Ricerche polari e paleoclima

Description: JCR Journal

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Beasley, C., Kender, S., Giosan, L., Bolton, C. T., Anand, P., Leng, M. J., Nilsson-Kerr, K., Ullmann, C. V., Hesselbo, S. P., & Littler, K. Evidence of a South Asian proto-monsoon during the Oligocene-Miocene transition. Paleoceanography and Paleoclimatology, 36(9), (2021): e2021PA004278, https://doi.org/10.1029/2021PA004278.

Description: The geological history of the South Asian monsoon (SAM) before the Pleistocene is not well-constrained, primarily due to a lack of available continuous sediment archives. Previous studies have noted an intensification of SAM precipitation and atmospheric circulation during the middle Miocene (∼14 Ma), but no records are available to test how the monsoon changed prior to this. In order to improve our understanding of monsoonal evolution, geochemical and sedimentological data were generated for the Oligocene-early Miocene (30–20 Ma) from Indian National Gas Hydrate Expedition 01 Site NGHP-01-01A in the eastern Arabian Sea, at 2,674 m water depth. We find the initial glaciation phase (23.7–23.0 Ma) of the Oligocene-Miocene transition (OMT) to be associated with an increase in water column ventilation and water mass mixing, suggesting an increase in winter monsoon type atmospheric circulation, possibly driven by a relative southward shift of the intertropical convergence zone. During the latter part of the OMT, or “deglaciation” phase (23.0–22.7 Ma), a long-term decrease in Mn (suggestive of deoxygenation), increase in Ti/Ca and dissolution of the biogenic carbonate fraction suggest an intensification of a proto-summer SAM system, characterized by the formation of an oxygen minimum zone in the eastern Arabian Sea and a relative increase of terrigenous material delivered by runoff to the site. With no evidence at this site for an active SAM prior to the OMT we suggest that changes in orbital parameters, as well as possibly changing Tethyan/Himalayan tectonics, caused this step change in the proto-monsoon system at this intermediate-depth site.

Description: This research forms part of a PhD study funded by the Natural Environment Research Council (NERC) Centre for Doctoral Training in Oil & Gas (grant number NE/M00578X/1) awarded to C. Beasley, and was also supported by a NERC National Environmental Isotope Facility Steering Committee grant (IP-1865-1118) awarded to S. Kender. L. Giosan acknowledges funding from USSP and WHOI and thanks colleagues from the NGHP-01 expedition. C. Ullmann acknowledges funding via NERC grant NE/N018508/1.

Description: Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 〉  800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼  50  Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 ×  CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.

Description: The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than present day. As such, study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to 10 evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model-model and model-data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene-Eocene thermal maximum and early Eocene climatic optimum. A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and 15 coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate "atlas" will be used to constrain and evaluate climate models for the three selected time intervals, and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.

Description: Much of our understanding of Earth’s past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states—Hothouse, Warmhouse, Coolhouse, Icehouse—are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

Description: Highlights • We present LGC record of the Pb isotope composition Labrador Sea seawater. • These data can be used to track Laurentide Ice Sheet extent over Hudson Bay. • LIS retreat during the PGM was relatively fast compared to the LGM • The LIS first advanced significantly over Hudson Bay during MIS 4. • Our record does not support significant LIS retreat during MIS 3. Understanding the history of continental ice-sheet growth on North America, and in particular that of the Laurentide Ice Sheet (LIS), is important for palaeoclimate and sea-level reconstructions. Information on ice-sheet extent pre-dating the Last Glacial Maximum (LGM) is heavily reliant, though, on the outputs of numerical models underpinned by scant geological data. Important aspects of LIS history that remain unresolved include the timing of its collapse during Termination 2, the first time that it expanded significantly during the Last Glacial Cycle, and whether its volume was significantly reduced during marine isotope stage (MIS) 3. To address these issues and more, we present authigenic iron-manganese (Fe–Mn) oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning the past ∼130 kyr from northwest North Atlantic Labrador Sea, IODP Site U1302/3. We use these new data to track chemical weathering intensity and solute flux to the Labrador Sea associated with LIS extent on the adjacent highly radiogenic (high Pb isotope composition) North American Superior Province (SP) craton since the Penultimate Glacial Maximum (PGM). Our new records show that relatively high (radiogenic) values characterise warm marine isotope stages (MIS) 5, 3 and 1 and the lowest (most unradiogenic) values occurred during cold stages MIS 6, 4 and 2. The radiogenic Pb isotope excursion associated with Termination 2 is short-lived relative to the one documented for Termination 1, suggesting that LIS retreat during the PGM was relatively fast compared to the LGM and that its collapse during the last interglacial occurred ∼125 ka. Highly radiogenic inputs to the Labrador Sea during MIS 5d-a, ∼116–71 ka, most likely reflect a spin-up in Labrador Current vigour, incipient glaciation and renewed glacial erosion of high grounds of the eastern SP craton by localised wet-based ice-caps. A large decrease in Pb isotope values towards unradiogenic LGM-like compositions between ∼75–65 ka across the MIS 5/4 transition likely reflects a slow-down in Labrador Current vigour, an increase in subaerial deposition of aeolian dust and a significant advance of the LIS across Hudson Bay caused a strong reduction or even abandonment of Pb sourcing from the SP. The relatively radiogenic Pb isotope composition of bottom-waters bathing our study site during MIS 3, 57–29 ka, is unlikely to support a recently proposed major reduction in LIS extent for this time. Instead, we argue these values are better explained by southern Greenland Ice Sheet retreat, increased chemical weathering of the Ketelidian Mobile Belt and subsequent Pb runoff from Greenland.

Description: Three disaggregation methods, i.e. Calgon, acetic acid and electric pulse fragmentation (EPF), have been applied to a range of heavily lithified, carbonate-rich sedimentary rock samples of Paleogene age. Samples are predominantly from the carbonate-rich, shallow water domain (〈 250m palaeo-water depth) of Tanzania, Malta and the United Arab Emirates (Paleogene Tethys Ocean). The effectiveness and efficiency of each method has been compared, in addition to the preservation of the resultant liberated microfossil material (primarily larger foraminifera; LF). Of the three methods, the most efficient and effective was EPF, which liberated the largest number of LF in a very short processing time and resulted in the best preservation. Samples with calcitic, silicic, and clay matrices and cements were successfully disaggregated using EPF. In this study, recovered microfossils were largely 〉 500 μm, suggesting this technique may be more appropriate for liberating larger microfossils (e.g. LFs); however, we discuss nuances to the method that would allow for more effective recovery of smaller microfossil specimens. The more traditional acetic acid method was also able to disaggregate a number of the samples; however, preservation of the LF was compromised. We suggest a best-practice methodology for implementing EPF in micropalaeontological studies.