The Miocene epoch, spanning 23.03–5.33 Ma, was a dynamic climate of sustained, polar amplified warmth. Miocene atmospheric CO2 concentrations are typically reconstructed between 300 and 600 ppm and ...were potentially higher during the Miocene Climatic Optimum (16.75–14.5 Ma). With surface temperature reconstructions pointing to substantial midlatitude and polar warmth, it is unclear what processes maintained the much weaker‐than‐modern equator‐to‐pole temperature difference. Here, we synthesize several Miocene climate modeling efforts together with available terrestrial and ocean surface temperature reconstructions. We evaluate the range of model‐data agreement, highlight robust mechanisms operating across Miocene modeling efforts and regions where differences across experiments result in a large spread in warming responses. Prescribed CO2 is the primary factor controlling global warming across the ensemble. On average, elements other than CO2, such as Miocene paleogeography and ice sheets, raise global mean temperature by ∼2°C, with the spread in warming under a given CO2 concentration (due to a combination of the spread in imposed boundary conditions and climate feedback strengths) equivalent to ∼1.2 times a CO2 doubling. This study uses an ensemble of opportunity: models, boundary conditions, and reference data sets represent the state‐of‐art for the Miocene, but are inhomogeneous and not ideal for a formal intermodel comparison effort. Acknowledging this caveat, this study is nevertheless the first Miocene multi‐model, multi‐proxy comparison attempted so far. This study serves to take stock of the current progress toward simulating Miocene warmth while isolating remaining challenges that may be well served by community‐led efforts to coordinate modeling and data activities within a common analytical framework.
Plain Language Summary
As human activity continues to increase atmospheric carbon dioxide concentrations, scientists turn to warm intervals in Earth's history to develop insight into the behavior of the climate system under elevated carbon dioxide and temperature. One such interval is the Miocene epoch which has become increasingly relevant as reconstructions of Miocene atmospheric CO2 concentrations point to values ranging between current concentrations of ∼400 ppm and those projected for the end of this century under Shared Socioeconomic Pathways 3 and 4. In this study, we evaluate the surface warming patterns simulated by a range of different climate models configured with Miocene paleogeography and CO2 concentrations spanning 200–850 ppm. We also synthesize available Miocene surface temperature reconstructions. The primary factor controlling the amount of global warming seen across the Miocene simulations analyzed is the CO2 concentration that was prescribed within a given simulation. On average, Miocene elements other than CO2, such as Miocene paleogeography and ice sheets, raise global mean temperature by ∼2°C. While some Miocene simulations with high CO2 forcing overlap with the reconstructed global mean surface temperature estimates for their target Miocene interval, they still generally fail to capture the reconstructed pattern of warming.
Key Points
A synthesis of Miocene modeling efforts, and surface temperature reconstructions, is presented within a single analysis framework
Miocene global mean surface temperature estimates span ∼5.3°C–11.5°C higher than preindustrial, only ∼2°C is explained by non–CO2 boundary conditions in climate models
Some simulations overlap with reconstructed global mean surface temperature estimates but fail to capture the weak temperature gradient
The Miocene (23.03–5.33 Ma) is recognized as a period with close to modern‐day paleogeography, yet a much warmer climate. With large uncertainties in future hydroclimate projections, Miocene ...conditions illustrate a potential future analog for the Earth system. A recent opportunistic Miocene Model Intercomparison Project 1 (MioMIP1) focused on synthesizing published Miocene climate simulations and comparing them with available temperature reconstructions. Here, we build on this effort by analyzing the hydrological cycle response to Miocene forcings across early‐to‐middle (E2MMIO; 20.03–11.6 Ma) and middle‐to‐late Miocene (M2LMIO; 11.5–5.33 Ma) simulations with CO2 concentrations ranging from 200 to 850 ppm and providing a model‐data comparison against available precipitation reconstructions. We find global precipitation increases by ∼2.1 and 2.3% per degree of warming for E2MMIO and M2LMIO simulations, respectively. Models generally agree on a wetter than modern‐day tropics; mid and high‐latitude, however, do not agree on the sign of subtropical precipitation changes with warming. Global monsoon analysis suggests most monsoon regions, except the North American Monsoon, experience higher precipitation rates under warmer conditions. Model‐data comparison shows that mean annual precipitation is underestimated by the models regardless of CO2 concentration, particularly in the mid‐ to high‐latitudes. This suggests that the models may not be (a) resolving key processes driving the hydrological cycle response to Miocene boundary conditions and/or (b) other boundary conditions or processes not considered here are critical to reproducing Miocene hydroclimate. This study highlights the challenges in modeling and reconstructing the Miocene hydrological cycle and serves as a baseline for future coordinated MioMIP efforts.
Plain Language Summary
This study looks at Earth's hydrological cycle during the Miocene (23–5 million years ago). During this period, the Earth's climate was 3–7°C warmer than today, with carbon dioxide (CO2) estimates ranging between 400 and 850 ppm. Understanding how the hydrological cycle responded during warmer climate conditions can give us insight into what might happen as the Earth gets warmer. We analyzed a suite of Miocene paleoclimate simulations with different CO2 concentrations in the atmosphere and compared them against fossil plant data, which gives an estimate of the average annual rainfall during the period. We found that during the Miocene global rainfall increased by about 2.1%–2.3% for each degree of warming. The models agree that the tropics, mid‐ and high‐latitude, became wetter than they are today but have lower agreement on whether subtropical areas got wetter or drier as they warmed. Compared to proxies, models consistently underestimated how much rain fell in a year, especially in the mid‐ to high‐latitude. This illustrates the challenges in reconstructing the Miocene's hydrological cycle and suggests that the models might not fully capture the range of uncertainties associated with changes in the hydrological cycle due to warming or other factors that differentiated the Miocene.
Key Points
A multi‐model comparison of the hydrological cycle in early‐to‐middle and middle‐to‐late Miocene simulations is conducted
Models generally agree on wetter than modern tropics, middle and high latitudes, but not on the sign of subtropical precipitation changes
Model‐data comparison shows mean annual precipitation is underestimated by the models, particularly in the mid‐ to high‐latitudes
A functional beverages, with a high content in bioactive compounds, based on exotic fruits (mango juice, papaya juice and acai) mixed with orange juice, oat and sweetened with different ...concentrations (0, 1.25 and 2.5%w/v) of Stevia rebaudiana (Stevia) extracts, a natural source of non-caloric sweeteners (steviol glycosides) were formulated and studied. Ascorbic acid, total carotenoids, total phenolics, anthocyanins, total antioxidant capacity (TEAC and ORAC methods) and steviol glycosides were evaluated. Beverages sweetened with 1.25 and 2.5% (w/v) Stevia showed a significant increase (3-fold and 4-fold higher, respectively) in phenolic compounds as well as in antioxidant properties in comparison with the beverage without Stevia. The displayed results indicate the potential use of Stevia as an alternative non-caloric sweetener in the preparation of beverages based on fruit juice mixtures and oat, as it may provide good nutritional and physicochemical properties and also enhance the already existing beneficial effects of fruit juices. Synergistic interactions observed between phytochemicals and steviol glycosides in the complex food beverages when TEAC method was used suggest an improved solubility or stability of antioxidant compounds and hence, the combined antioxidant capacity measured by TEAC assay is potentiated in the complex food matrix.
The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled ...thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with
E
a=46.36
kJ/mol for aerobic degradation and
E
a=49.57
kJ/mol for anaerobic degradation.
The effect of heating on ascorbic acid in green asparagus during a simulated retort operation was investigated. The asparagus was heated in trays of ethylene-vinyl alcohol copolymer for selected time ...intervals at four temperatures ranging from 110 to 125 degrees C. It was found that the rate of degradation followed first-order kinetics. Kinetic parameters were obtained by using two least squares methods. The activation energy and z value were 35 kca1/mol and 20 degrees C, respectively.
A physicochemical analysis was made of the different types of horchata de chufa sold in Spain. The analytical methods for the determination of total fat, total solids, ash, reducing sugars, starch ...and protein were adapted for these low-acid vegetable beverages. The contents found were: fat, 0.91-3.40 g per 100 g; total solids, 13.61-22.06 g per 100 g; ash, 0.079-0.298 g per 100 g; protein, 0.294-0.742 g per 100 g; starch, not detected-7.45 g per 100 ml; reducing sugars, 11.13-17.86 g per 100 ml; pH, 6.37-7.56; density, 1.039-1.067 g mlE-1. The fat content of all the sterilised horchatas was below the minimum value specified in the regulations
E' stata condotta un'analisi chimico-fisica sui differenti tipi di horchata de chufa commercializzati in Spagna. I metodi analitici per la determinazione dei grassi totali, dei solidi totali, delle ceneri, degli zuccheri riducenti, dell'amido e delle proteine sono stati adattati a questa bevanda vegetale. La composizione riscontrata è la seguente: grassi, 0,91-3,40 g%; solidi totali, 13,61-22,06 g%; ceneri, 0,079-0,298 g%; proteine, 0,294-0,742 g%; amido, non riscontrato -7,45 g%; zuccheri riducenti, 11,13-17,86 g%; pH, 6,37-7,56; densità, 1,039-1,067. Il contenuto in grassi di tutte le horchata sterilizzate è risultato al di sotto del minimo previsto dalla legge
The Middle Miocene Climate Transition was characterized by major Antarctic ice sheet expansion and global cooling during the interval ∼ 15–13 Ma. Here we present two sets of boundary conditions for ...global general circulation models characterizing the periods before (Middle Miocene Climatic Optimum; MMCO) and after (Middle Miocene Glaciation; MMG) the transition. These boundary conditions include Middle Miocene global topography, bathymetry, and vegetation. Additionally, Antarctic ice volume and geometry, sea level, and atmospheric CO2 concentration estimates for the MMCO and the MMG are reviewed. The MMCO and MMG boundary conditions have been successfully applied to the Community Climate System Model version 3 (CCSM3) to provide evidence of their suitability for global climate modeling. The boundary-condition files are available for use as input in a wide variety of global climate models and constitute a valuable tool for modeling studies with a focus on the Middle Miocene.
The growing interest in new functional foods with special characteristics and health properties has led to the development of new beverages based on fruit juice–skim milk mixtures. The proliferation ...of ready-to-drink beverages has caused the market to focus its interest on these products. Commercial conventionally pasteurized or sterilized beverages based on a mixture of fruit juice and skim milk were evaluated nutritionally for their concentrations of vitamin C, vitamin A and phenolic compounds and their total antioxidant capacity, taking the influence of physicochemical parameters into account. The main contribution to the total antioxidant capacity (TEAC, trolox equivalent antioxidant capacity) was provided by vitamin C, followed by phenolic compounds, in accordance with a mathematical equation obtained from the data: TEAC
=
−0.184
+
0.009
∗
vitamin A
+
0.011
∗
phenolic compounds
+
0.058
∗
vitamin C. The
R-squared value was 86.88%. Citrus fruits, such as lemons or oranges, were the fruits associated with the greatest antioxidant capacity in the samples analysed.
Liquid chromatography (LC) was the method of choice for quantification of carotenoids (including geometrical isomers) to evaluate the effects of high-intensity pulsed electric field (HIPEF), a ...nonthermal preservation method, with different parameters (electric field intensities and treatment times), on an orange−carrot juice mixture (80:20, v/v). In parallel, a conventional heat treatment (98 °C, 21 s) was applied to the juice. HIPEF processing generally caused a significant increase in the concentrations of the carotenoids identified as treatment time increased. HIPEF treatment at 25 and 30 kV/cm provided a vitamin A concentration higher than that found in the pasteurized juice. Keywords: Carotenoid; high-intensity pulsed electric field; heat treatment; orange−carrot juice
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