Recent  

The Mediterranean Sea turned repeatedly into an oxygen-deprived basin during the geological past, as evidenced by distinct sediment layers called sapropels. We use here records of the last sapropel S1 retrieved in front of the Nile River to explore the relationships between riverine input and seawater oxygenation. We decipher the seasonal cycle of fluvial input and seawater chemistry as well as the decisive influence of primary productivity on deoxygenation at millennial timescales.

To extend climate information back in time, we investigate the climate sensitivity of a δ¹⁸O network from tree rings, consisting of 26 European sites and covering the last 400 years. Our results suggest that the δ¹⁸O variability is associated with large-scale anomaly patterns that resemble those observed for the El Niño–Southern Oscillation. We conclude that the investigation of large-scale climate signals far beyond instrumental records can be done with a δ¹⁸O network derived from tree rings.

We present three new isotope-enabled simulations for the last millennium (850–1850 CE) and compare them to records from a global speleothem database. Offsets between the simulated and measured oxygen isotope ratios are fairly small. While modeled oxygen isotope ratios are more variable on decadal timescales, proxy records are more variable on (multi-)centennial timescales. This could be due to a lack of long-term variability in complex model simulations, but proxy biases cannot be excluded.

This study investigates the physical processes leading to the rare phenomenon of the sun appearing blue or green. The phenomenon is caused by anomalous scattering by, e.g., volcanic or forest fire aerosols. Unlike most other studies, our study includes a full treatment of the effect of Rayleigh scattering on the colour of the sun. We investigate different factors and revisit a historic example, i.e. the Canadian forest fires in 1950, that led to blue sun events in different European countries.

We present the first precipitation reconstructions for three sites along a latitudinal gradient in the Sikhote-Alin' mountains (Russian Far East). The reconstructions are based on Korean pine tree rings. We found that an important limiting factor for this species growth was precipitation during the spring-to-early-summer period. The periodicity found in our reconstructions suggests the influence of El Niño–Southern Oscillation and Pacific Dedacadal Oscillation on the region's climate.

There are controversies about whether poetry can be used as one of the evidence sources for past climate changes. We tried to discuss the reliability and validity of phenological records from poems of the Tang and Song dynasties (618–1279 CE) by analyzing their certainties and uncertainties. A standardized processing method for phenological records from poems is introduced. We hope that this study can provide a reference for the extraction and application of phenological records from poems.

How did cities respond to drought during the 17th century? This article studies the strategies followed by the city government of Barcelona during the severely dry period from 1620 to 1650. Beyond the efforts to expand urban water supply sources and to improve the maintenance of the system, the city government decided to compile knowledge about water infrastructure into a book and to restrict access to it. This management strategy aimed to increase the city's control over water.

The analysis of the dynamics of western central Mediterranean droughts for 850–2099 CE in the Community Earth System Model indicates that past Mediterranean droughts were driven by the internal variability. This internal variability is more important during the initial years of droughts. During the transition years, the longevity of droughts is defined by the land–atmosphere feedbacks. In the future, this land–atmosphere feedbacks are intensified, causing a constant dryness over the region.

The Last Interglacial period (LIG) is characterised by strong orbital forcing compared to the pre-industrial period (PI). This study compares the mean climate state of the LIG to the PI as simulated by the ACCESS-ESM1.5, with a focus on the southern hemispheric monsoons, which are shown to be consistently weakened. This is associated with cooler terrestrial conditions in austral summer due to decreased insolation, and greater pressure and subsidence over land from Hadley cell strengthening.

Using the temperature-dependent solubility of noble gases in ocean water, we reconstruct global mean ocean temperature (MOT) over the last 700 kyr using noble gas ratios in air enclosed in polar ice cores. Our record shows that glacial MOT was about 3 °C cooler compared to the Holocene. Interglacials before 450 kyr ago were characterized by about 1.5 °C lower MOT than the Holocene. In addition, some interglacials show transient maxima in ocean temperature related to changes in ocean circulation.

Uncertainties in climate proxy records are temporally autocorrelated. By deriving expressions for the power spectra of errors in proxy records, we can estimate appropriate uncertainties for any timescale, for example, for temporally smoothed records or for time slices. Here we outline and demonstrate this approach for climate proxies recovered from marine sediment cores.

Maps and fields of near-sea-surface temperature differences between the past and present can be used to visualize and quantify climate changes and perform simulations with climate models. We used a statistical method to map sparse and scattered data for the Last Glacial Maximum time period (23 000 to 19 000 years before present) to a regular grid. The estimated global and tropical cooling would imply an equilibrium climate sensitivity in the lower to middle part of the currently accepted range.

This paper focuses on the recovery of instrumental weather records available for Singapore and Malaysia (Straits Settlements) from the late 1780s to 1917. Taking a historical approach, the paper explores the types of records available, the circumstances of their production and their value to the scientific community.

This modeling study of the Last Glacial Maximum (LGM, ~ 21 000 years ago) ocean explores the biological and physical changes in the ocean needed to satisfy marine proxy records, with a focus on the carbon isotope ¹³C. We estimate that the LGM ocean may have been up to twice as efficient at sequestering carbon and nutrients at depth as compared to preindustrial times. Our work shows that both circulation and biogeochemical changes must have occurred between the LGM and preindustrial times.

This paper utilises a novel palaeoclimate archive from caves, cryogenic cave carbonates, which allow for precisely constraining permafrost thawing events in the past. Our study provides new insights into the climate of the Younger Dryas (12 800 to 11 700 years BP) in mid-Europe from the perspective of a high-elevation cave sensitive to permafrost development. We quantify seasonal temperature and precipitation changes by using a heat conduction model.

The similarity between indirect observations of past climates and information from climate simulations can increase our understanding of past climates. The further we look back, the more uncertain our indirect observations become. Here, we discuss the technical background for such a similarity-based approach to reconstruct past climates for up to the last 15 000 years. We highlight the potential and the problems.

At approximately 14 Ma, the East Antarctic Ice Sheet expanded to almost its current extent, but the role of CO₂ in this major climate transition is not entirely known. We show that atmospheric CO₂ might have varied on 400 kyr cycles linked to the eccentricity of the Earth’s orbit. The resulting change in weathering and ocean carbon cycle affected atmospheric CO₂ in a way that CO₂ rose after Antarctica glaciated, helping to stabilize the climate system on its way to the “ice-house” world.

A very high quality 160-year-long annually laminated (varved) sediment sequence of fluvial origin was recently discovered in an especially deep lake in Labrador. Each varve represents 1 hydrological year. A significant relation between varves' physical parameters (i.e., thickness and grain size extracted from each annual lamination) and river discharge instrumental observations provided the opportunity to develop regional discharge reconstructions beyond the instrumental period.

This study analyzes the impacts of changing vegetation and atmospheric dust concentrations over an area that is currently desert (the Sahara) to investigate their impacts on tropical cyclone activity during a warm climate state, the mid-Holocene. Our results suggest a significant change in Atlantic TC frequency, intensity and seasonality when considering the effects of a warmer climate in a greener world. They also highlight the importance of considering these factors in future climate studies.