Distribution of Patterned Ground and Surficial Deposits on a Debris-covered Glacier Surface in Mullins Valley and Upper Beacon Valley, Antarctica

Beacon Valley is located in the western Dry Valleys, Antarctica, adjacent to the East Antarctic Ice Sheet (EAIS). The surficial material on the floor of Beacon Valley is segmented into large polygonal landforms separated by trenches. Buried beneath the polygons and surficial material is massive ground ice. One hypothesis is that the buried ice in upper Beacon Valley is glacier ice originating from local debris-covered glaciers. The networks of polygons and trenches form as the buried ice undergoes thermal contraction and sublimation. Contraction cracks that penetrate the surficial material and buried ice in Beacon Valley contain Late Miocene age volcanic ashes. The ashes postdate the buried ice. The preservation of such old ice implies a continuous extreme polar condition in Beacon Valley since late Miocene time. An alternative explanation is that the buried ice in Beacon Valley is modem ground ice that formed from percolation of melted, wind-blown snow that subsequently froze within the sediment mantle. Polygonal landforms would result from the seasonal freeze-thaw of the modem ground ice and surficial material. Continual freeze-thaw action, or cryoturbation, would create a mass of coalesced, modern ice lenses covered with older sediment. The buried ice in this case could be young, and hence could not be used to imply stable climatic conditions in Beacon Valley since the late Miocene. Polygons cover the surface of a debris-covered glacier that fills part of upper Beacon Valley and Mullins Valley. A survey of the debris-covered glacier surface indicates that polygons mature with distance from the equilibrium line. The polygon morphology highlights the transport path of the buried ice in upper Beacon Valley, which can be sourced to the cirque (accumulation zone) at the head of Mullins Valley. The buried ice in upper Beacon Valley is part of a coherent, massive ice body of glacial origin. A gray diamicton is draped over the buried ice. It has textural and weathering characteristics akin to englacial, buried ice sediment. This diamicton is classified as a till that formed from sublimation of buried ice. The sublimation till (28% sand, 69% gravel, and 3% mud) is sorted by narrow contraction cracks in the buried ice that results in sand wedge deposits (83% sand, 11% gravel, and 6% mud). The grain-sizes that comprise sublimation till and sand wedges indicate that sediment is initially derived from sublimation of the buried ice. Deep polygon trenches develop over thermal contraction cracks in the buried ice, and create traps for wind-blown sediment (reworked sublimation till, sand wedge sediment and volcanic ash.) The tops of some contraction cracks were void of sediment, indicative of a sediment starvation. In this case, any primary volcanic ashfall could descend directly into active sand wedges. As sublimation occurs, sand wedges containing volcanic ash can slump over the sublimation till and buried ice. The stratigraphy of massive weathered sand, with stringers of volcanic ash, resting on sublimation till and buried ice is widespread in upper Beacon Valley. Because the contraction cracks and sand wedges are secondary to the buried ice, the ashes contained in them can afford a minimum age for the buried ice. This study supports the concept of the ash chronology previously used (Sugden et al., 1995) to date the buried ice at late Miocene age, and argues for persistent polar conditions in Beacon Valley since that time

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Wiggle-match radiocarbon dating of the Taupo eruption

The Taupo eruption deposit is an isochronous marker bed that spans much of New Zealand’s North Island and pre-dates human arrival. Holdaway et al. (2018, Nature Comms 9, 4110) propose that the current Taupo eruption date is inaccurate and that the eruption occurred “…decades to two centuries…” after the published wiggle-match estimate of 232 ± 10 CE (2 s.d.) derived from a tanekaha (Phyllocladus trichomanoides) tree at the Pureora buried forest site (Hogg et al. 2012, The Holocene 22, 439-449). Holdaway et al. (2018) propose that trees growing at Pureora (and other near-source areas) that were killed and buried by the climactic ignimbrite event were affected by ¹⁴C-depleted (magmatic) CO₂. Holdaway et al.'s (2018) proposal utilises a wide range of published ¹⁴C data, but their work results in assertions that are implausible. Four parts to their hypothesis are considered here

Meteorological data rescue: citizen science lessons learned from Southern Weather Discovery

Daily weather reconstructions (called "reanalyses") can help improve our understanding of meteorology and long-term climate changes. Adding undigitized historical weather observations to the datasets that underpin reanalyses is desirable; however, time requirements to capture those data from a range of archives is usually limited. Southern Weather Discovery is a citizen science data rescue project that recovered tabulated handwritten meteorological observations from ship log books and land-based stations spanning New Zealand, the Southern Ocean, and Antarctica. We describe the Zooniverse-hosted Southern Weather Discovery campaign, highlight promotion tactics, and replicate keying levels needed to obtain 100% complete transcribed datasets with minimal type 1 and type 2 transcription errors. Rescued weather observations can augment optical character recognition (OCR) text recognition libraries. Closer links between citizen science data rescue and OCR-based scientific data capture will accelerate weather reconstruction improvements, which can be harnessed to mitigate impacts on communities and infrastructure from weather extremes

Unlocking pre-1850 instrumental meteorological records: a global inventory

A global inventory of early instrumental meteorological measurements is compiled. It comprises thousands of series, many of which have not been digitized, pointing to the potential of weather data rescue. Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data”. They have played an important role in climate research as they allow daily-to-decadal variability and changes of temperature, pressure, and precipitation, including extremes, to be addressed. Early instrumental data can also help place 21st century climatic changes into a historical context such as to define pre-industrial climate and its variability. Until recently, the focus was on long, high-quality series, while the large number of shorter series (which together also cover long periods) received little to no attention. The shift in climate and climate impact research from mean climate characteristics towards weather variability and extremes, as well as the success of historical reanalyses which make use of short series, generates a need for locating and exploring further early instrumental measurements. However, information on early instrumental series has never been electronically compiled on a global scale. Here we attempt a worldwide compilation of metadata on early instrumental meteorological records prior to 1850 (1890 for Africa and the Arctic). Our global inventory comprises information on several thousand records, about half of which have not yet been digitized (not even as monthly means), and only approximately 20% of which have made it to global repositories. The inventory will help to prioritize data rescue efforts and can be used to analyze the potential feasibility of historical weather data products. The inventory will be maintained as a living document and is a first, critical, step towards the systematic rescue and re-evaluation of these highly valuable early records. Additions to the inventory are welcomed

A global multiproxy database for temperature reconstructions of the Common Era

Source at https://doi.org/10.1038/sdata.2017.88 .Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python

Unlocking pre-1850 instrumental meteorological records

A global inventory of early instrumental meteorological measurements is compiled that comprises thousands of mostly nondigitized series, pointing to the potential or weather data rescu

Environmental, Physiological and Biochemical Processes Determining the Oxygen Isotope Ratio of Tree-Ring Cellulose

AbstractAnalysis of the oxygen isotope ratioof tree-ring cellulose (δ18Ocell) is a promising tool for reconstructingpast climatic variations and their influence on terrestrial ecosystems, but control mechanisms of δ18Ocell are multi-faceted, involving a number of fractionation steps along the oxygen transfer pathway from precipitation water to the site of cellulose formation. The goal of the current chapter is to provide an overview of the current knowledge concerning fractionation mechanisms related to δ18Ocell. The review is organized by using the currently widely-used δ18Ocell model as a reference context, and is focused on three main determinants of δ18Ocell: source water isotope ratio (δ18Osw), leaf water isotope enrichment (Δ18Olw), and biochemical fractionations downstream of Δ18Olw. For each component, we summarize environmental, physiological, and/or biochemical processes underlying 18O fractionations, and provide explanations of how these processes are critically relevant for linking δ18Ocell to climatic factors in real-world scenarios. We identify knowledge gaps in mechanistic controls of δ18Ocell, and highlight opportunities for more research to improve upon the existing model.</jats:p