Recent  

This research contributes to efforts solving research questions related to the history of ice sheet decay in the Northern Hemisphere. The East Siberian continental margin sediments provide ideal material for identifying the mineralogical signature of ice sheet derived material. Heavy mineral analysis from marine glacial sediments from the De Long Trough and Lomonosov Ridge was used in interpreting the activity of the East Siberian Ice Sheet in the Arctic region.

We examined annually resolved stable carbon and hydrogen isotope ratios of wood lignin methoxy groups of beech trees growing in temperate, low elevation environments. Here, carbon isotope ratios reveal highest correlations with regional summer temperatures while hydrogen isotope ratios correlate more strongly with large-scale temperature changes. By combining the dual isotope ratios of wood lignin methoxy groups, a proxy for regional- to subcontinental-scale temperature patterns can be applied.

Algae preserved in seafloor sediments have allowed us to reconstruct how Antarctic sea ice has varied between cold and warm time periods in the last 130 000 years. The patterns and timings of sea-ice increase and decrease vary between different parts of the Southern Ocean. Sea ice is most sensitive to changing climate at the external edges of Southern Ocean gyres (large areas of rotating ocean currents).

The WACSWAIN project (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) investigates the fate of the West Antarctic Ice Sheet during the last warm period on Earth (115 000–130 000 years before present). Within this framework an ice core was recently drilled at Skytrain Ice Rise. In this study we present a stratigraphic chronology of that ice core based on absolute age markers and annual layer counting for the last 2000 years.

We present sedimentary redox-sensitive trace metal records from five sediment cores retrieved from the SW Indian Ocean. These records are indicative of oxygen-depleted conditions during cold periods and enhanced oxygenation during interstadials. Our results thus suggest that deep-ocean oxygenation changes were mainly controlled by ocean ventilation and that a generally more sluggish circulation contributed to sequestering remineralized carbon away from the atmosphere during glacial periods.

We provide high-resolution Cd / Ca records of benthic foraminifera on two cores from the northern Indian Ocean since the last deglaciation. We reconstructed intermediate Cd_w records based on Cd / Ca. Combined with benthic foraminiferal assemblages, we show that intermediate Cd_w during the last deglaciation was mainly influenced by the ventilation of intermediate–bottom water masses. Thereafter during the Holocene surface productivity is the main forcing factor related to monsoon precipitation.

Applying yearly drought and flood records from historical documents and precipitation data in the period of instrumental measurements, this study constructs a time series of extreme droughts and floods in the Hanjiang River Basin from 1426–2017 and analyzes the temporal and spatial characteristics of the extreme drought and flood event variations.

Despite its importance in the global climate, our knowledge of Antarctic sea-ice changes throughout the last glacial–interglacial cycle is extremely limited. As part of the Cycles of Sea Ice Dynamics in the Earth system (C-SIDE) Working Group, we review marine- and ice-core-based sea-ice proxies to provide insights into their applicability and limitations. By compiling published records, we provide information on Antarctic sea-ice dynamics over the past 130 000 years.

Changes in the Southern Hemisphere westerly winds are drivers of recent environmental changes in West Antarctica. However, our understanding of this relationship is limited by short and sparse observational records. Here we present the first regional wind study based on the novel use of diatoms preserved in Antarctic ice cores. Our results demonstrate that diatom abundance is the optimal record for reconstructing wind strength variability over the Southern Hemisphere westerly wind belt.

We have digitized and analyzed meteorological variables (temperature, direction of the movement of the clouds, and cloud cover), which were noted by Louis Morin in the period 1665–1713 in Paris. This time period is characterized by cold winters and autumns and moderate springs and summers. A low frequency of westerlies in the winter months leads to a cooling. Morin's measurements seem to be trustworthy. Only cloud cover in quantitative terms should be taken with caution.

Our high-resolution loess Ca/Ti record displays millennial monsoon oscillations that persist over the last 650 kyr. Wavelet results indicate the ice volume and GHG co-modulation at the 100 kyr band and GHG and local insolation forcing at the precession band for the magnitude of millennial monsoon variability of loess Ca/Ti. The inferred mechanism calls on dynamic linkages to variability in AMOC. At the precession band, combined effects of GHG and insolation lead to increased extreme rainfall.

Using climate model simulations, we find that SE Asian tropical climate was strongly seasonal under Late Glacial conditions. During Northern Hemisphere winters, it was highly arid in this region that is today humid year-round. The seasonal aridity was driven by orbital forcing and stronger East Asian winter monsoon. A breakdown of deep convection caused a reorganized Walker Circulation and a mean state resembling El Niño conditions.

We collected and standardized the output of five isotope-enabled simulations for the last millennium and assess differences and similarities to records from a global speleothem database. Modeled isotope variations mostly arise from temperature differences. While lower-resolution speleothems do not capture extreme changes to the extent of models, they show higher variability on multi-decadal timescales. As no model excels in all comparisons, we advise a multi-model approach where possible.

A double volcanic eruption in 536 and 540 CE caused one of the coldest decades during the last 2000 years. We analyzed new climate model simulations from that period and found a cooling of up to 2°C and a sea-ice extent up to 200 km further south. Complex interactions between sea ice and ocean circulation lead to a reduction in the northward ocean heat transport, which makes the sea ice extend further south; this in turn leads to a surface cooling up to 20 years after the eruptions.

We investigate the sensitivity of the glacial Alpine hydro-climate to northern hemispheric and local ice-sheet changes. We perform sensitivity simulations of up to 2 km horizontal resolution over the Alps for glacial periods. The findings demonstrate that northern hemispheric and local ice-sheet topography are important role in regulating the Alpine hydro-climate and permits a better understanding of the Alpine precipitation patterns at glacial times.

Projects are underway to drill ice cores in Antarctica reaching 1.5 Myr back in time. Dating such cores will be challenging. One method is to match records from the new core against datasets from existing marine sediment cores. Here we explore the options for doing this and assess how well the ice and marine records match over the existing 800 000-year time period. We are able to recommend a strategy for using marine data to place an age scale on the new ice cores.

We wanted to take an in-depth look at how climate events affected the economy of early modern Poland. We focused on analysing all available sources of a fiscal nature for this period. In addition, we analysed available materials on the export of primary agricultural products. Our results have shown that the economic system in Poland at that time coped effectively with periodic droughts, and it was only the great drought of 1540 that significantly shook the state's economy.

Atmospheric circulation in the supercontinent of Pangaea is thought to have been significantly different from today. We present the spatial distribution of palaeowind directions recorded in Lower Jurassic aeolian sandstones in the western US. This reveals the development of longitudinal dunes formed by a combination of westerly, northwesterly, and northeasterly palaeowinds. The reconstructed palaeowind pattern at ~19–27°N is consistent with the model-generated surface wind pattern in Pangaea.

The Southern Annular Mode (SAM) is a major mode of climate variability. Proxy-based SAM reconstructions show changes that last millennium climate simulations do not reproduce. We test the SAM's sensitivity to solar forcing using simulations with a range of solar values and transient last millennium simulations with large-amplitude solar variations. We find that solar forcing can alter the SAM and that strong solar forcing transient simulations better match proxy-based reconstructions.

We assess the climatic and societal impact of the 852/3 CE Alaska Mount Churchill eruption using environmental reconstructions, historical records and climate simulations. The eruption is associated with significant Northern Hemisphere summer cooling, despite having only a moderate sulfate-based climate forcing potential; however, evidence of a widespread societal response is lacking. We discuss the difficulties of confirming volcanic impacts of a single eruption even when it is precisely dated.

Salinity is an important and integrative measure of changes to the water cycle steered by changes to the balance between rainfall and evaporation and by vertical and horizontal movements of water parcels by ocean currents. However, salinity measurements in our oceans are extremely sparse. To fill this gap, we have developed a 334-year coral record of seawater oxygen isotopes that reflects salinity changes in the globally important Agulhas Current system and reveals its main oceanic drivers.

Termination V (TV, ~ 404–433 kyr BP) marks a transition in the climate system towards amplified glacial–interglacial cycles. While the associated atmospheric CO₂ changes are mostly attributed to the Southern Ocean, little is known about the terrestrial biosphere contribution to the carbon cycle. This study provides the first (model- and pollen-based) reconstruction of global forests highlighting the potential role of temperate and boreal forests in atmospheric CO₂ sequestration during TV.

This comprehensive inventory of quantitative documentary evidence related to climate extending back to 1400 CE promotes the first ever global perspective on documentary climate records. It lays the foundation for incorporating documentary evidence from archives of societies into global-scale climate reconstructions, complementing (early) instrumental measurements and natural climate proxies. Documentary records are particularly relevant in seasons and regions poorly covered by natural proxies.

The mid-Pliocene (MP; ∼3.0 Ma) had CO₂ levels similar to today and average temperatures ∼3°C warmer. At terrestrial high latitudes, MP temperatures from climate models are much lower than those reconstructed from data. This mismatch occurs in the winter but not the summer. The winter model–data mismatch likely has multiple causes. One novel cause is that the MP climate may be outside the modern sample, and errors could occur when using information from the modern era to reconstruct climate.

Terrestrial materials in marine environments record source information and help us understand how climate and ocean impact sediment compositions. Here, we use evidence on the Ninetyeast Ridge to analyze the relationship between terrestrial material supplementation and climatic change. We find that the ITCZ controlled the rainfall in the Burman source area and that closer connections occurred between the Northern–Southern Hemisphere in the eastern Indian Ocean during the late LGM.

The geochemistry preserved in polar ice can provide detailed histories of Earth’s climate over millennia. Here we use the stable isotope ratios of ice from many Antarctic ice cores to reconstruct temperature variability of Antarctica and the midlatitude Southern Hemisphere over tens of thousands of years. We improve upon existing methods to estimate temperature from the geochemical measurements and investigate the patterns of climate change in the past.

Previous studies of Paleogene greenhouse climates identified short-lived global warming events, termed hyperthermals, that provide insights into global warming scenarios. Within the same time period, we have identified a short-lived cooling event in the late Paleocene, which we term a hypothermal, that has potential to provide novel insights into the feedback mechanisms at work in a greenhouse climate.

In layer counted proxy records each measurement is accompanied by a timestamp typically measured by counting periodic layers. Knowledge of the uncertainty of this timestamp is important for a rigorous propagation to further analyses. By assuming a Bayesian regression model to the layer increments we express the dating uncertainty by the posterior distribution, from which chronologies can be sampled efficiently. We apply our framework to dating abrupt warming transitions during the last glacial.