Climatic variability during the last interglacial inferred from geochemical proxies in the Lake El'gygytgyn sediment record

The Last Interglacial Period (LIP) is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios. Despite this, there is still debate over the nature, duration and frequency of climatic changes during this period. One particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives, especially within the Arctic, a key region for global climate change research. In this paper, geochemical records from Lake El'gygytgyn, north-eastern Russia, are used to infer past climatic changes during the LIP from within the high Arctic. With a sampling resolution of ~20–~90 years, these records offer the potential for detailed, high-resolution palaeoclimate reconstruction. This study shows that the LIP commenced in central Chukotka ~129 thousand years ago (ka), with the warmest climatic conditions occurring between ~128 and 127 ka before being interrupted by a short-lived cold reversal. Mild climatic conditions then persisted until ~122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation. A further climatic deterioration at ~118 ka marks the return to glacial conditions. This study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions, thus providing the potential to identify signals related to environmental change within the catchment. We also demonstrate the importance of considering how changes in sedimentation rate influence proxy records, in order to develop robust palaeoenvironmental reconstructions.

Last interglacial temperature evolution — a model inter-comparison

There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG). This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter temperatures. Secondly, for the Atlantic region, the Southern Ocean and the North Pacific, possible changes in the characteristics of the Atlantic meridional overturning circulation are crucial. Thirdly, the presence of remnant continental ice from the preceding glacial has shown to be important when determining the timing of maximum LIG warmth in the Northern Hemisphere. Finally, the results reveal that changes in the monsoon regime exert a strong control on the evolution of LIG temperatures over parts of Africa and India. By listing these inter-model differences, we provide a starting point for future proxy-data studies and the sensitivity experiments needed to constrain the climate simulations and to further enhance our understanding of the temperature evolution of the LIG period.

Annual layering in the NGRIP ice core during the Eemian

The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core, annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 11 mm for all three sections, which, to first order, confirms the modeled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core, provided sufficiently highly-resolved profiles become available.

NGRIP CH4 concentration from 120 to 10 kyr before present and its relation to a δ15N temperature reconstruction from the same ice core

During the last glacial cycle, Greenland temperature showed many rapid temperature variations, the so-called Dansgaard–Oeschger (DO) events. The past atmospheric methane concentration closely followed these temperature variations, which implies that the warmings recorded in Greenland were probably hemispheric in extent. Here we substantially extend and complete the North Greenland Ice Core Project (NGRIP) methane record from the Preboreal Holocene (PB) back to the end of the last interglacial period with a mean time resolution of 54 yr. We relate the amplitudes of the methane increases associated with DO events to the amplitudes of the local Greenland NGRIP temperature increases derived from stable nitrogen isotope (δ15N) measurements, which have been performed along the same ice core (Kindler et al., 2014). We find the ratio to oscillate between 5 parts per billion (ppb) per °C and 18 ppb °C−1 with the approximate frequency of the precessional cycle. A remarkably high ratio of 25.5 ppb °C−1 is reached during the transition from the Younger Dryas (YD) to the PB. Analysis of the timing of the fast methane and temperature increases reveals significant lags of the methane increases relative to NGRIP temperature for DO events 5, 9, 10, 11, 13, 15, 19, and 20. These events generally have small methane increase rates and we hypothesize that the lag is caused by pronounced northward displacement of the source regions from stadial to interstadial. We further show that the relative interpolar concentration difference (rIPD) of methane is about 4.5% for the stadials between DO events 18 and 20, which is in the same order as in the stadials before and after DO event 2 around the Last Glacial Maximum. The rIPD of methane remains relatively stable throughout the full last glacial, with a tendency for elevated values during interstadial compared to stadial periods.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

We present successful 81 Kr-Kr radiometric dating of ancient polarice. Krypton was extracted from the air bubbles in four∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81 Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean abso-lute age offset of 6±2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85 Kr and 39 Ar analyses that show the samples to be free of modern air contamination and (ii)air content measurements that show the ice did not experience gas loss. We estimate the error in the 81 Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81 Kr dating of ice cores is a future possibility.

Ecosystem regimes and responses in a coupled ancient lake system from MIS 5b to present: the diatom record of lakes Ohrid and Prespa

We reconstruct the aquatic ecosystem interactions since the last interglacial period in the oldest, most diverse, hydrologically connected European lake system, by using palaeolimnological diatom and selected geochemistry data from Lake Ohrid “DEEP site” core and equivalent data from Lake Prespa core, Co1215. Driven by climate forcing, the lakes experienced two adaptive cycles during the last 92 ka: "interglacial and interstadial" and "glacial" cycle. The short-term ecosystems reorganizations, e.g. regime shifts within these cycles substantially differ between the lakes, as evident from the inferred amplitudes of variation. The deeper Lake Ohrid shifted between ultra oligo- and oligotrophic regimes in contrast to the much shallower Lake Prespa, which shifted from a deeper, (oligo-) mesotrophic to a shallower, eutrophic lake and vice versa. Due to the high level of ecosystem stability (e.g. trophic state, lake level), Lake Ohrid appears relatively resistant to external forcing, such as climate and environmental change. Recovering in a relatively short time from major climate change, Lake Prespa is a resilient ecosystem. At the DEEP site, the decoupling between the lakes' response to climate change is marked in the prolonged and gradual changes during the MIS 5/4 and 2/1 transitions. These response differences and the lakes' different physical and chemical properties may limit the influence of Lake Prespa on Lake Ohrid. Regime shifts of Lake Ohrid due to potential hydrological change in Lake Prespa are not evident in the data presented here. Moreover, a complete collapse of the ecosystems functionality and loss of their diatom communities did not happen in either lake for the period presented in the study.

The response of atmospheric nitrous oxide to climate variations during the last glacial period

Detailed insight into natural variations of the greenhouse gas nitrous oxide (N2O) in response to changes in the Earth's climate system is provided by new measurements along the ice core of the North Greenland Ice Core Project (NGRIP). The presented record reaches from the early Holocene back into the previous interglacial with a mean time resolution of about 75 years. Between 11 and 120 kyr BP, atmospheric N2O concentrations react substantially to the last glacial-interglacial transition (Termination 1) and millennial time scale climate variations of the last glacial period. For long-lasting Dansgaard/Oeschger (DO) events, the N2O increase precedes Greenland temperature change by several hundred years with an increase rate of about 0.8-1.3 ppbv/century, which accelerates to about 3.8-10.7 ppbv/century at the time of the rapid warming in Greenland. Within each bundle of DO events, the new record further reveals particularly low N2O concentrations at the approximate time of Heinrich events. This suggests that the response of marine and/or terrestrial N2O emissions on a global scale are different for stadials with and without Heinrich events.

Psychogenic aphonia: no fixation even after a lengthy period of aphonia

Although psychogenic aphonia is considered to be a conversion disorder, aphonic patients are primarily treated symptomatically. This is because it is considered of overriding importance to elicit a voice quickly to avoid fixation of the aphonia. The aim of this study was to show that, for patients exhibiting the symptom of voicelessness, not eliciting the voice immediately will not lead to a permanent aphonia.

On the way to light the dark: a retrospective inquiry into the registered cases of domestic violence towards women over a six year period with a semi-quantitative analysis of the corresponding forensic documentation

Domestic violence victims are increasingly identified at emergency departments (ED). Studies report a prevalence of 6-30%; women are more frequently affected and to a more serious extent than men. Studies have shown that without screening domestic violence victims are often not recognised. The primary aim of the study is to collect data descriptive of domestic violence victims and to show whether medical documentation meets the requirements of forensic medicine.

Period prevalence and risk factors for postoperative short-term wound complications in vulvar cancer: a cross-sectional study

Although clinicians recognize that postoperative wound management in patients with vulvar cancer (VC) is challenging, the prevalence and risk factors for different types of short-term wound complications (WCs) remain unclear. The aims of this study were: (1) to determine the period prevalence of postoperative short-term WCs and (2) to identify risk factors associated with short-term WCs in patients with VC.