Paleoclimatic Interpretation Research Articles

Palynology of Late Oligocene to Pliocene succession in Temana Field of Balingian Province, offshore Sarawak

Palynological records in Late Cenozoic succession from two Temana wells were reviewed and investigated for palynomorph assemblages, biostratigraphic correlation and age dating, as well as for paleoenvironment and paleoclimate interpretation. The data indicates abundant and diverse pollen and spores deposited in marginal marine with tidal influence setting. Three main palynomorph assemblages were identified from the Temana wells: (1) Zone-1 (dated as Late Oligocene), characterized by abundant Florschuetzia trilobata and dominant montane and seasonal elements such as Picea, Tsuga and Pinus, (2) Zone-2 (Early to Middle Miocene), dominated by Kerapah Casuarina-type pollen and characterized by increasing abundance of Rhizophoraceae mangrove pollen. Zone-2 can be further differentiated into Subzone-2a and Subzone-2b based on later appearance of Florschuetzia levipoli, and (3) Zone-3 (Late Miocene to Pliocene) occurring above a major angular unconformity is marked by a high percentage of the rainforest pollen Rubiaceae and a minor increase in seasonal elements. The interpreted paleoclimate inferred from temporal variations in hinterland-derived pollen shows cyclical pattern from seasonally dry climate in the Oligocene to warm and ever-wet climate, marked by the growth of Kerapah peat swamp during Early to Middle Miocene, and finally a prolong humid climate characterized by rainforest vegetation with minor intermittent seasonality since Late Miocene/Pliocene.

Isotopic Fractionation during Sublimation of Low Porosity Ice

The magnitude of isotopic fractionation during sublimation of ice remains poorly constrained. Field and laboratory studies that span decades have persistently shown conflicting results. A better understanding of fractionation during sublimation is needed to improve interpretation of alpine hydrology, glaciology, paleoclimate and planetary histories that rely on stable isotopic records stored in icy reservoirs. At the core of the problem is the question of whether sublimation occurs as a layer-by-layer process with no fractionation or whether diffusion within the ice and vapor-ice exchange generate fractionation. We present results from an experiment where we suspended ice spheres in temperatures ranging from -25 to -10 °C in an unsaturated atmosphere and used aRayleigh distillation model to estimate fractionation of the spheres. A small, yet statistically significant and repeatable, isotope fractionation (103lnα18O of ∼ −0.6 ‰ and 103lnα2H between −3.0 and − 4.0 ‰ or α = 0.999, α = 0.9940 to 0.9970, respectively) was found during the sublimation of ice. The results indicate the presence of fractionation yet the values are an order of magnitude smaller than would be predicted for equilibrium fractionation at this temperature. By assuming a porosity for the ice of 0.0005 % - which is typical for ice frozen under these conditions, we estimate an increase in diffusivity relative to solid ice consistent with the observed fractionation values. The results help to reconcile how fractionation estimates during sublimation could vary between experimental and observational studies where porosity is not controlled for and can vary substantially across a continuum from porous firn layers to low porosity ice deep in glaciers.

Revised OSL chronology of the Kisiljevo loess-palaeosol sequence: New insight into the dust flux in the eastern Carpathian Basin during MIS 3 - MIS1

This study presents a detailed investigation of the Kisiljevo loess-palaeosol sequence in north-eastern Serbia, offering a refined understanding of its paleoenvironmental dynamics. Contrasting our updated OSL chronology with a previous study, reveals discrepancies, particularly at 400 cm depth, where a considerable age underestimation is evident. While variations in sampling depth and methodology may contribute to some differences, the substantial deviation raises concern about the reliability of the earlier chronology. Our robust age-depth model constructed using Bayesian modelling, and the consistent increase in ages with depth suggest a potential underestimation in the uppermost layer of the earlier study, possibly due to partial bleaching or post-depositional mixing. The Bayesian age-depth model portrays a continuous sedimentation history from the later stages of Marine Isotope Stage 3 (MIS 3) to the present day. The patterns in the calculated Mass Accumulation Rates reveal distinctive peaks during MIS 3 and the middle of MIS 2, deviating from typical dust deposition models. The MIS 3 peaks in dustiness could be attributed to regional factors such as increased transportation rates, enhanced trapping efficiency, or elevated palaeowind intensity. This research not only enhances our understanding of the Kisiljevo LPS but also provides valuable insights into regional paleoenvironmental dynamics. The study emphasizes the importance of considering local geological variations in reconstructing past climates from sediment archives and sets the stage for further investigations into the factors influencing dust deposition in north-eastern Serbia. The MAR trends established here serve as a crucial reference for broader paleoclimatic interpretations in the Carpathian Basin.

Climatic controls on water-mass chemistry in a Paleocene lacustrine setting, Subei Basin, eastern China

Abstract The Paleocene epoch was characterized by global climate fluctuations and major carbon-cycle perturbations. During the greenhouse climate that characterized the early Cenozoic, a short-lived late Paleocene global cooling event has been recognized from marine records. However, the response of the terrestrial system to this climate cooling event is poorly understood. Here, we present major- and trace-element analyses, iron speciation systematics, carbonate carbon isotope data, and mineralogical observations from lacustrine sediments in Member II of the Paleocene Funing Formation (E1f2), utilizing well-preserved drill core from the Subei Basin, eastern China. Both chemical (chemical index of alteration [CIA], Al/K ratios) and mineralogical (mineralogical index of alteration, clay/feldspar ratios) proxies yield consistent weathering and paleoclimatic interpretations, suggesting a transition from cool and arid climatic conditions to warmer and more humid climatic conditions. Correlation of carbon isotopes between the Subei Basin and deep-sea records implies that this terrestrial setting records the short-lived Paleocene climate cooling event. The combination of climate records and paleosalinity proxies (B/Ga and S/total organic carbon [TOC]) indicates a relatively high-salinity water column (brackish to saline) under cool and arid climatic conditions in the Subei Basin, suggesting that elevated salinity was likely produced via net-evaporative conditions, rather than marine incursions. A shift toward less saline brackish conditions up section reflects an increase in precipitation and freshwater runoff under warmer and more humid climatic conditions. Iron speciation and redox-sensitive trace-metal systematics reveal fluctuating redox conditions, from oxic through to anoxic ferruginous, but with the distinct development of better ventilated conditions as freshwater inputs increased under more humid conditions. Our findings demonstrate the sensitivity of terrestrial climate to the late Paleocene climate cooling event and further reveal the chemical response of a lacustrine setting to a cooling episode in a greenhouse world.

Proposed geo-educational activities at the Sidi Bouzid geosite, Safi Province, Marrakech-Safi region, Morocco

The Sidi Bouzid escarpment is one of the geosites that present high educational and tourism values in the Safi Province, extending for several kilometers along the Atlantic coast southwest of the city of Safi, Safi Province, Marrakech-Safi region, Morocco. It offers panoramic views over the town and the Atlantic Ocean, as well as a beautiful beach much frequented by holidaymakers. The sedimentary and paleontological information preserved in the rocks that form the escarpment makes a valuable contribution to paleobiogeographic and paleoclimatic interpretations and stratigraphic correlations on a regional and global scale. This paper focused on promoting and popularizing earth sciences among students at universities, research centers, colleges, schools, and the general public by developing an educational program adapted to the Sidi Bouzid geosite. Survey was employed to collect the data, the results of which was used to evaluate the effectiveness of the educational program. The results showed that the program had a significant impact on all visitor categories since it offered visitors a holistic view of how geological processes shaped the Earth, revealing the interconnections between many components of the Earth system (geosphere, hydrosphere, atmosphere, and biosphere).

Investigating speleothem magnetism as a proxy for dust mobilization and rainfall

Commonly used speleothem-based paleoclimate proxies such as δ18O, δ13C, and trace element ratios are capable of high temporal resolution, but their interpretations are often ambiguous due to the conflated effects of multiple forcings. This complexity motivates the development of targeted proxies that can track specific local hydrological conditions. To this end, the concentration of ferromagnetic Fe-oxide particles in speleothem laminae has been suggested as a potential tracer for local precipitation. Here we use the quantum diamond microscope (QDM) to obtain a sub-annual resolution time series of ferromagnetic content in a Brazilian speleothem from a well-ventilated cave environment covering the period between 1913 and 2016 CE. This high resolution allows us to quantify the correlation between speleothem magnetic properties and an instrumental precipitation record for the first time. We find that ferromagnetic content in the central column displays a modest but significant negative correlation with rainfall (R2=0.35;p=0.0027), while magnetism in the speleothem flanks shows a weaker, statistically insignificant relationship. Rock magnetic analyses of the speleothem further reveal ultrafine, pedogenic grains to be the dominant ferromagnetic carriers. Combining QDM and electron microprobe data, we show that these pedogenic grains were likely developed in surface soils and delivered into the cave as part of airborne, 10–200 μm silicate-carbonate soil agglomerates. Our results show that speleothem magnetism holds strong potential as a targeted proxy for paleorainfall and demonstrate a method for identifying the mechanism of magnetic enhancement, which sets the necessary foundation for any paleoclimatic interpretations.

Millennial-scale paleoclimate changes recorded in Holocene ferromanganese crusts with oscillatory micro-bands: insights from mineralogical and chemical variations in hydrogenetic ferromanganese crusts of the Magellan Seamounts

Abstract This study investigates the hydrogenetic ferromanganese crust (HFMC) from the Magellan Seamounts in the northwest Pacific Ocean, focusing on its mineralogy, crystal chemistry, and paleoclimatic records. Given that ferromanganese is composed of poorly crystalline MnOx phases, such as vernadite, structural determination using conventional X-ray diffraction (XRD) methods is challenging and has very limited effectiveness. Therefore, synchrotron-based pair-distribution function (PDF) analysis of total X-ray scattering and high-resolution electron microscopy techniques were employed to characterize the structures and compositions of HFMC. The results from the synchrotron XRD and transmission electron microscopy (TEM) reveal that the studied HFMC consists primarily of poorly crystalline Fe-bearing vernadite. The chemical analysis of the HFMC layers indicates that the rare-earth elements (REE) and P were preferentially adsorbed on the Fe-rich vernadite, whereas platinum-group elements (PGE), Co, and Ni were enriched in the Mn-rich vernadite. The top layers of the HFMC display fine-scale compositional variations (cycle of ~1600 y) that signify millennial-scale paleoclimate oscillations during the Middle-Late Pleistocene and Holocene periods linked to the glacial termination event that occurred ~126,000 y ago. This millennial-scale oscillation correlates with sea-level variations influenced by the expansion and contraction of ice sheets, offering a crucial signal for understanding the paleoclimatic interpretation throughout the glacial periods. To fully decipher the fine-scale paleoclimate signals and assist in forecasting future climatic conditions, a more extensive examination of ferromanganese crusts from diverse depths, sources, and locations is necessitated.

Late Miocene paleoecology and paleoclimate in the central High Plains of North America reconstructed from paleopedological, ichnological, and stable isotope analyses of the Ogallala Formation in western Kansas, USA

The late Miocene was a critical time in the development of the North American Great Plains marked by paleoclimate-driven biotic change, including faunal turnovers and the spread of C4 dominated grasslands. The large volume of sediment shed from the Rocky Mountain region during this time preserves a record of these transitions, which can be informed by previously undescribed paleosol and trace fossil properties from the Ogallala Formation of the central High Plains. The purpose of this paper is to reconstruct paleoenvironments, paleoclimate, and paleoecology from outcrops of the Ogallala Formation in western Kansas by integrating paleopedology, ichnology, and stable isotope geochemistry. Eleven lithofacies are recognized in the study area, mostly massive to crudely stratified, fine-to coarse-grained sandstone and pebbly gravel with stratigraphically uncommon fine-grained lithofacies restricted to thinly bedded intervals or lens-shaped geometries within the sand-dominated strata. These host five pedotypes: 1) calcic Vertisols developed on overbank fines, 2) Entisols developed on braid bar gravels, 3) Entisols developed on volcaniclastic sediment lenses, 4) calcic Inceptisols developed on coarse sandy channel fills, and 5) calcareous Mollisols developed on fine sandy bedforms and channel fills. We recognize ten ichnogenera within paleosols, including burrows attributed to ants, bees, beetles or hemipterans, vinegarroon-like arthropods, fossorial reptiles, seed caching mammals, and large carnivorous mammals. Organic carbon stable isotopes indicate that the flora consisted entirely of C3 plants, and paleosols and trace-fossil evidence suggest a tree-limited savanna environment with patches of unvegetated soil. Paleoclimate proxies from paleosol and trace fossil properties indicate mean annual air temperatures between 8 °C and 20 °C with seasonal differences of up to 14 °C between mean monthly temperatures of the warmest and coolest months. Mean annual precipitation was likely between 250 mm and 460 mm with a seasonal difference of up to 250 mm between mean monthly precipitation of the driest and wettest months. While hymenopteran tracemakers were active, soil surface temperatures reached at least 30 °C and moisture content was between 10% and 20%. With timing of deposition constrained biostratigraphically to the Barstovian through Hemphillian, our paleoclimate interpretations are most consistent with the period of relative climate stability after Middle Miocene Climate Transition cooling and before Late Miocene Cooling (∼13.8 Ma–7 Ma). The trace-fossil assemblage reveals previously unknown biodiversity among soil arthropods, as well as important trophic connections between the belowground and aboveground components of the terrestrial food web.

Decoupled local climate and chemical weathering intensity of fine-grained siliciclastic sediments from a paleo-megalake: An example from the Qaidam basin, northern Tibetan Plateau

Clay mineralogy and elemental geochemistry of lacustrine sedimentary records have been widely used in paleo-weathering and paleo-climate studies. However, different paleo-climatic interpretations may be produced via analyses on siliciclastic sediments and other sedimentary components (e.g., authigenic minerals and organic materials), especially for megalake systems. To test this hypothesis, we focus on late Cenozoic lacustrine fine-grained deposits from the northwestern Qaidam basin and combine clay mineralogical and geochemical data (including neodymium isotope) to interpret sediment provenance, reconstruct paleo-weathering history and characterize sediment-climate feedback processes. Provenance analysis results show that the lacustrine siliciclastic sediments were derived from lithologically similar sources that provided dominant felsic parent-rocks. The kaolinite/illite ratio, illite chemistry index, Chemical Index of Alteration (CIA) values are low and demonstrate overwhelmingly mild-moderate chemical weathering intensity, seemingly matching well with the middle–late Miocene regional arid climate. However, these weathering intensity index values are also highly fluctuant and display increasing trends during ~13.4–12 Ma and ~8.8–8.4 Ma. The reconstructed paleo-weathering history is discrepant with local intensified aridity conditions documented by previously published sedimentary carbonate oxygen isotope, evaporite mineral, biomarker and sporopollen data. Given the occurrence of a middle–late Miocene megalake in the Qaidam basin, the intense exhumation at ~13–12 Ma and the ~9 to ~7 Ma intensified East Asian summer monsoon precipitation in northeastern Tibet regions, we suggest that the lacustrine fine-grained siliciclastic compositions and corresponding weathering records were likely influenced by tectonic and climatic changes in far regions to the east. The observed clay mineralogical and geochemical variations reflect weathering conditions involving sediment sources and transport pathways, not merely the depositional areas. Our findings verify the possible differences in paleo-climate reconstruction results from different lacustrine sediment indicators. This study emphasizes the importance of a sediment source-to-sink perspective for paleo-climate study based on siliciclastic materials in megalake systems.

Impact of Monthly Age Model on Coral Paleothermometer Fidelity: Insights From the Northern South China Sea

AbstractThe strontium‐to‐calcium (Sr/Ca) ratio of coral is widely used as a paleothermometer for tropical sea surface temperature (SST) at subannual resolutions. The fidelity of Sr/Ca‐derived SST estimates largely depends on the properties of the monthly age model selected. Here, we develop a revised monthly age model for coral Sr/Ca estimation from the northern South China Sea based on specific tie points and evaluate the impacts of different age models on SST reconstruction. Our results indicate that our revised monthly age model reduces conversion errors by up to nearly 20%–30% relative to previously reported values, thereby improving the precision of seasonal SST estimates and enabling better paleoclimate interpretations, such as El Niño–Southern Oscillation variability. The revised monthly age model provides a generalized approach for developing more robust seasonal resolution Sr/Ca–SST reconstructions in other regions.

“Cold-Dry” and “Cold-Wet” Events in the Late Holocene, Southern Russian Far East

Two late Holocene cold events were described for the Southern Russian Far East: 2800–2600 year BP and the Little Ice Age (LIA) (~1300–1850 CE). The synthesis is based on multi-proxy records on profile “the mainland (Primorye)-islands (Sakhalin-Kurils)”. Main archives are sediments of small lakes and peat bogs that recorded the high-resolution environmental changes. The temporal resolution of reconstructions here is up to 26–40 years. During the cold event of 2800–2600 year BP, the humidity decreased sharply, there were long-term dry seasons without strong floods, and buried soil formed on floodplains. The LIA was wet in the mainland and the Kurils, with frequent strong floods, but was drier in Sakhalin. The cooling was characterized by sharp temperature fluctuations where high moisture conditions alternated with short-term drier periods. The shift in geographical position and intensity of the main centers of atmospheric action caused a paleoclimatic interpretation of these events (Aleutian Low, Siberian and North Pacific Highs, the summer Okhotsk anticyclone and the Far East depression). Changes in the North Pacific oscillations played an important role in the alternation of cold-dry and cold-wet periods. Anomalies in the intensity of El Niño and the monsoon system led to changes in tropical and extratropical cyclone trajectories and cyclogenesis in general.

Terrain methods on spectral analysis for paleoclimate interpretations: A novel visualization technique using python

Spectral analysis techniques are valuable tools at the disposal of paleoclimate scientists in their research of cyclical phenomena potentially responsible for past climatic fluctuations. Advances in computing and an increased availability of climate time series have helped to consolidate this approach. Yet the visual representation of spectral analysis results has not improved at the same pace. Time-frequency analysis aims to identify periodic signals that vary over time using 2-D color graphs, depicting spectral bands theoretically discernible from the image background. The paleoclimate literature is full of examples such as the continuous wavelet analysis, the evolutionary fast Fourier transform (FFT) spectrogram, or even the more recent synchrosqueezing transform. Our approach is based on the stack of non-evolutive (assuming stationary behaviour) spectral analysis results from thousands of fixed interval time series, previously split from a longer and unevenly spaced (irregular sampling) paleoclimate time series. As illustrative examples, the targeted time series are derived from the LR04 Global Pliocene-Pleistocene Benthic δ18O stack and from the 65 °N summer insolation for the last 5.3 Myr, by means of the Lomb-Scargle periodogram technique. Enhanced and clearer visualization is achieved through the novel incorporation of the terrain analysis techniques: slope, hillshading and color mapping, and posterior blending of the individual images, using Python code. The result consists of a high resolution graphical output, allowing for better qualitative and quantitative interpretations of the obtained cyclicity, as the code incorporates the import of the achieved confidence levels from the spectral technique and the option to obscure the pixels under a certain threshold value. The application of terrain analysis techniques on visualization of spectral analysis results has the purpose of improving previous graphical representations of paleoclimate time-series, especially those time-frequency aspects of the involved phenomena. New developments of our approach may be applied to time-frequency analysis directly, supporting present and future paleoclimate studies.

Ion geochemistry of a coastal ice wedge in northwestern Canada: Contributions from marine aerosols and implications for ice‐wedge paleoclimate interpretations

AbstractIce wedges are a characteristic ground ice feature in permafrost regions that form primarily from the meltwater of the seasonal snowpack. Ice‐wedge oxygen and hydrogen stable isotopes have been used in winter paleotemperature reconstructions; however, until recently, the ion geochemistry of ice wedges has rarely been analyzed as a potential paleoclimate proxy. This potential is greatest for ice wedges located in coastal regions, where marine aerosols are the dominant contributor to snowpack impurities. Here, we evaluate the source and integrity of ionic concentrations of a coastal ice wedge in the northwestern Canadian Arctic (Beaufort Sea coast) to evaluate the use of ice wedges as a marine aerosol archive. Comparison to a regionally comparable snowpack reveals remarkably similar ionic concentrations for Cl−, Na+, Br−, SO42−, Ca2+, and Mg2+, with a Cl−/Na+ ratio similar to bulk seawater (1.80 vs. 1.79 in seawater), suggesting that marine aerosols, probably from sea salt aerosol production during blowing snow events over sea ice as indicated by depleted SO42− values relative to Na+, are probably the dominant contributor to ion concentrations. A previously established linear age model for the ice wedge is used to develop a continuous ion record spanning ~4,600 to ~700 yr b2k. Cl− and Na+ concentrations reveal a strong and continuous increase in concentrations over the late Holocene, thought to be driven by reduced distance‐to‐coast of up to 1 km as a result of coastal erosion. This study presents a novel interpretation of ice‐wedge geochemical data and represents the first Holocene ice‐wedge ion record.

Trace element composition of modern planktic foraminifera from an oxygen minimum zone: Potential proxies for an enigmatic environment

Oxygen limited marine environments, such as oxygen minimum zones, are of profound importance for global nutrient cycling and vertical habitat availability. While it is understood that the extent and intensity of oxygen minimum zones are responsive to climate, the limited suite of viable proxies for low oxygen pelagic environments continues to pose a real barrier for paleoclimate interpretations. Here we investigate the proxy potential of an array of trace element (Mg, Mn, Zn, and Sr) to Ca ratios from the shells of Globorotaloides hexagonus, a planktic foraminifer endemic to tropical through temperate oxygen minimum zones. A species-specific relationship between Mg/Ca and temperature is proposed for quantitative reconstruction of oxygen minimum zone paleotemperatures. Both Mn/Ca and Zn/Ca ratios vary with oxygen concentration and could be useful for reconstructing G. hexagonus habitat where the primary signal can be d\istinguished from diagenetic overprinting. Finally, a robust correlation between Sr/Ca ratios and dissolved oxygen demonstrates a role for Sr as an indicator of oxygen minimum zone intensity, potentially via foraminiferal growth rate. The analysis of these relatively conventional trace element ratios in the shells of an oxygen minimum zone species has tremendous potential to facilitate multiproxy reconstructions from this enigmatic environment.

Non-spherical microparticle shape in Antarctica during the last glacial period affects dust volume-related metrics

Abstract. Knowledge of microparticle geometry is essential for accurate calculation of ice core volume-related dust metrics (mass, flux, and particle size distributions) and subsequent paleoclimate interpretations, yet particle shape data remain sparse in Antarctica. Here we present 41 discrete particle shape measurements, volume calculations, and calibrated continuous particle time series spanning 50–16 ka from the South Pole Ice Core (SPC14) to assess particle shape characteristics and variability. We used FlowCAM, a dynamic particle imaging instrument, to measure aspect ratios (width divided by length) of microparticles. We then compared those results to Coulter counter measurements on the same set of samples as well as high-resolution laser-based (Abakus) data collected from SPC14 during continuous flow analysis. The 41 discrete samples were collected during three periods of millennial-scale climate variability: Heinrich Stadial 1 (18–16 ka, n=6; ∼250 years per sample), the Last Glacial Maximum (LGM) (27–18 ka, n=19; ∼460 years per sample), and during both Heinrich Stadial 4 (42–36 ka, n=8; ∼620 years per sample) and Heinrich Stadial 5 (50–46 ka, n=8; ∼440 years per sample). Using FlowCAM measurements, we calculated different particle size distributions (PSDs) for spherical and ellipsoidal volume estimates. Our calculated volumes were then compared to published Abakus calibration techniques. We found that Abakus-derived PSDs calculated assuming ellipsoidal, rather than spherical, particle shapes provide a more accurate representation of PSDs measured by Coulter counter, reducing Abakus to Coulter counter flux and mass ratios from 1.82 (spherical assumption) to 0.79 and 1.20 (ellipsoidal assumptions; 1 being a perfect match). Coarser particles (>5.0 µm diameter) show greater variation in measured aspect ratios than finer particles (<5.0 µm). While fine particle volumes can be accurately estimated using the spherical assumption, applying the same assumption to coarse particles has a large effect on inferred particle volumes. Temporally, coarse and fine particle aspect ratios do not significantly change within or among the three time periods (p value >0.05), suggesting that long-range transport of dust is likely dominated by clay minerals and other elongated minerals.

Polish Palaeobotany: 750 Million Years of Plant History as Revealed in a Century of Studies. Mesozoic Terrestrial Palynology and Flora Reconstruction

Palynological studies of the Mesozoic era in Poland began in the 1950s. These investigations developed in many directions, including stratigraphy, systematics of spores and pollen grains and their botanical affinities, as well as paleoecological and paleoclimatic interpretations. In this study, we provide an overview of the most important achievements in Mesozoic terrestrial palynology in Poland.

Correspondence Among Mid‐Latitude Glacier Equilibrium Line Altitudes, Atmospheric Temperatures, and Westerly Wind Fields

AbstractMountain glaciers are highly sensitive to climate change. However, the extent to which glaciers capture regional to hemisphere‐scale atmospheric processes remains uncertain, hindering paleoclimatic interpretations derived from moraine‐based glacier reconstructions. Here, we evaluate how mid‐latitude glacier systems monitor climate by comparing climate reanalysis products with glacier annual equilibrium line altitude (ELA) elevations from the antipodal Southern Alps of New Zealand and European Alps. We find significant regional and hemispheric correlations between glacier annual ELA and summer tropospheric temperatures. Annual ELA also exhibit positive correlations with the latitude of the westerly jets in both hemispheres. These results indicate that westerly wind‐belt latitude modulates the proportion of cold versus warm air masses influencing these glacier systems. These results highlight the sensitivity of mid‐latitude glaciers to atmospheric temperatures and circulation, with implications for interpreting moraine‐based paleoclimate reconstructions. Combined impacts of ongoing tropospheric warming and poleward‐shifting westerlies will likely accelerate recession of mid‐latitude glaciers.

How Hot Is Too Hot? Disentangling Mid‐Cretaceous Hothouse Paleoclimate From Diagenesis

AbstractThe North American Newark Canyon Formation (NCF; ∼113–98 Ma) presents an opportunity to examine how terrestrial carbonate facies reflect different aspects of paleoclimate during one of the hottest periods of Earth's history. The lower NCF type section preserves heterogeneous palustrine facies and the upper NCF preserves lacustrine deposits. We combined carbonate facies analysis with δ13C, δ18O, and Δ47 data sets to assess which carbonate facies preserve stable isotope signals that are most representative of climatic conditions. Palustrine facies record the heterogeneity of the original wetland environment in which they formed. Using the pelmicrite facies that formed in deeper wetlands, we interpret a lower temperature zone (35–40°C) to reflect warm season water temperatures. In contrast, a mottled micrite facies which formed in shallower wetlands records hotter temperatures (36–68°C). These hotter temperatures reflect radiatively heated “bare‐skin” temperatures that occurred in a shallow depositional setting. The lower lacustrine unit has been secondarily altered by hydrothermal fluids while the upper lacustrine unit likely preserves primary temperatures and δ18Owater of catchment‐integrated precipitation. Resultantly, the palustrine pelmicrite and lacustrine micrite are the facies most likely to reflect ambient climate conditions, and therefore, are the best facies to use for paleoclimate interpretations. Average warm season water temperatures of 41.1 ± 3.6°C and 37.8 ± 2.5°C are preserved by the palustrine pelmicrite (∼113–112 Ma) and lacustrine micrite (∼112–103 Ma), respectively. These data support previous interpretations of the mid‐Cretaceous as a hothouse climate and demonstrate the importance of characterizing facies for identifying the data most representative of past climates.

Interpretação paleoclimática com base na análise da fisionomia foliar de duas floras pleistocênicas, Formação Rio Claro, São Paulo, Brasil

Paleoclimatic interpretation based on the analysis of the leaf physiognomy of two Pleistocene floras, Rio Claro Formation, São Paulo, Brazil. The Jaguariúna and Jazigo Vargem Grande do Sul fossil floras are well-preserved records of an ancestor of one of the phytophysiognomies of the Atlantic Forest, the oldest belt of tropical forest in the world. These fossil floras are associated with the Rio Claro Formation, one of the most important sedimentary records of the Pleistocene from the São Paulo State Peripheral Depression, Brazil. The main physiognomic characteristics–type of margins and leaf area – of the angiosperm leaves from these floras allowed us to carry out the reconstruction of the mean annual temperature (MAT) and the mean annual precipitation (MAP) for the moment of their deposition. The different equations used to reconstruct the MAT and the MAP are based on univariate methods known as Leaf Margin Analysis and Leaf Area Analysis. These equations indicated that the warm and humid subtropical/tropical climate under which the Jaguariúna fossil flora developed was characterized by a MAT of 22.1–22.8°C and a MAP of 566–831 mm, and also that the warm and humid subtropical climate under which the Jazigo Vargem Grande do Sul fossil flora developed was characterized by a MAT of 24.6–25.1°C and a MAP of 747–961 mm. These values indicate that, at the moment of deposition of the fossil floras of Jaguariúna and Jazigo Vargem Grande do Sul, conditions were warmer and less humid than the current ones. Therefore, it is possible to infer that these floras developed in a smaller climatic cycle, the interglacial period, during which the Rio Claro Formation was deposited. Keywords: Atlantic Forest, Pleistocene, physiognomic characteristics, angiosperm leaves, climatic cycle, interglacial period.

Determining key upstream convection and rainout zones affecting δ18O in water vapor and precipitation based on 10-year continuous observations in the East Asian Monsoon region

An increasing number of studies have recognized the crucial impact of upstream convective activities and rainout processes on the stable isotopic composition of precipitation (δ18Op) and water vapor (δ18Ov) at mid and low latitudes. However, it is difficult to precisely identify the upstream convection and rainout zones using the common method based on the spatial distribution of time-lagged temporal correlation. Using a 10-year continuous high-resolution δ18Ov and δ18Op dataset at Nanjing (southeast China), the longest record of this kind, we develop an improved time-lagged correlation method for Key Upstream Convection Zones Identification (KUCZI). Utilizing this method, we find that summer δ18Ov and δ18Op at Nanjing are primarily controlled by the convective activities and rainout processes along the moisture transport pathway from the Maritime Continent (MC), via the Indo-China Peninsula and South China Sea (ICP_SCS), to Southeast China (SEC), particularly over SEC. Contrary to the conclusion of many existing studies, there is a possibility that the Indian Ocean is not a major convection zone affecting δ18Op and δ18Ov at Nanjing. Our results indicate that we may need to reconsider the role of the Indian Ocean on the paleoclimate interpretation of stalagmite δ18O records in the East Asian Monsoon (EAM) region.