Linking Arctic sea‐ice and atmospheric circulation anomalies on interannual and decadal timescales

Abstract

The relationship between Arctic sea‐ice concentration anomalies, particularly those associated with the “Great Salinity Anomaly” of 1968–1982, and atmospheric circulation anomalies north of 45°N is investigated. Empirical orthogonal function (EOF) analyses are performed on winter Arctic ice concentration from 1954 to 1990, sea level pressure and 500‐hPa heights from 1947 to 1994, and 850‐hPa temperatures from 1963 to 1994. Variability on both interannual and decadal timescales is apparent in the time series of the leading winter EOFs of all variables. The first EOF of winter sea‐ice concentration was found to characterize the patterns of ice variability associated with the Great Salinity Anomaly in the northern North Atlantic from 1968–82. Spatial maps of temporal correlation coefficients between the time series of the first EOF of winter sea‐ice concentration and the winter atmospheric anomaly fields are calculated at lags of 0 and ±7 year. Maximum correlations were found to exist when the time‐series of this ice EOF 1 leads the atmospheric anomaly fields by one year. A particularly interesting result is the connection between the presence of ice anomalies in the Greenland and Barents Seas and subsequent pressure anomalies of the same sign over the Irminger Basin and the Canadian Arctic. The main emphasis of the paper is to identify connections between Arctic sea‐ice and atmospheric circulation anomalies at interannual time‐scales.     

A necessary voice: Climate change and lived experiences of youth in Rigolet,Nunatsiavut, Canada

Globally, youth voices and their experiences, observations, and perceptions about climatic and environmental change and variability are relatively absent in the published literature to date. To address this gap, the goal of this research was to explore the observations and perceptions of climate change held by youth (12–25 years old) in the Inuit community of Rigolet, Nunatsiavut, Canada. Twenty in-depth interviews were conducted with youth in Rigolet to gather data about climatic and environmental changes young people have observed, and the subsequent impacts of these changes on their lives, culture, and community. Youth reported observing and experiencing climatic and environmental changes throughout their lives, with reported impacts falling within five main themes: changing travel conditions and access to hunting; challenges to Inuit culture; a concern for Elder and senior well-being; strong climate-related emotional responses; and youth-identified potential adaptation strategies. More broadly, this research demonstrated that young people have valuable knowledge and perspectives to offer. In particular, researchers, community leaders, and policy makers are encouraged to meaningfully engage youth as crucial stakeholders in future climate change work, research, dialogue, and policy.     

Synoptic Controls on Boundary-Layer Characteristics

We report the characteristics of the three-dimensional, time evolving, atmospheric boundary layer that develops beneath an idealised, dry, baroclinic weather system. The boundary-layer structure is forced by thermal advection associated with the weather system. Large positive heat fluxes behind the cold front drive a vigorous convective boundary layer, whereas moderate negative heat fluxes in the warm sector between the cold and warm fronts generate shallow, stably stratified or neutral boundary layers. The forcing of the boundary-layer structure is quantified by forming an Eulerian mass budget integrated over the depth of the boundary layer. The mass budget indicates that tropospheric air is entrained into the boundary layer both in the vicinity of the high-pressure centre, and behind the cold front. It is then transported horizontally within the boundary layer and converges towards the cyclone’s warm sector, whence it is ventilated out into the troposphere. This cycling of air is likely to be important for the ventilation of pollution out of the boundary layer, and for the transformation of the properties of large-scale air masses.     

The socio-environmental data explorer (SEDE): a social media–enhanced decision support system to explore risk perception to hazard events

ABSTRACT

Social media are increasingly recognized as a useful data source for understanding social response to hazard events in real time and in post-event analysis. This article establishes social media–enhanced decision support systems (SME-DSS) as a synergistic integration of social media and decision support systems (DSSs) to provide structured access to native, near real-time data from a large and diverse population to assess social response to social, environmental, and technological risk and hazard events. We introduce a prototype SME-DSS entitled socio-environmental data explorer (SEDE) to explore the opportunities and challenges of leveraging social media for decision support. We use a winter storm during 25–28 January 2015 that accumulated record amounts of snow along the East Coast of the United States as a case study to evaluate SEDE in helping assess social response to environmental risk and hazard events as well as evaluate social media as a theoretical component within the social amplification of risk framework (SARF) that serves as a theoretical foundation for SME-DSS.     

Fluvial geomorphic features of the Lower Mississippi alluvial valley

The Lower Mississippi Valley (LMV) has been one of the most intensively studied alluvial valleys in the world in terms of it's geological and geomorphic framework and history. A brief outline of the history of the major geological and geomorphological investigations of the LMV is provided. The results of these investigations are discussed in terms of the fluvial geomorphic framework of the valley and the apparent significant changes in the regime of the Mississippi River during the Late Wisconsinan and Holocene stages.

The LMV occupies the broad deep synclinal trough of the Mississippi Embayment which extends from Cairo, Illinois, to the Gulf of Mexico in a slightly sinuous north-south trend. The embayment is filled with a north to south thickening wedge of non-marine and marine sediment ranging in age from Jurassic to Holocene. The major landscapes of the LMV may be considered in four regions: (1) a narrow active meander belt in a broad valley of Late Pleistocene valley train in the northern third; (2) a wide mosaic of interwoven Holocene meander belts in the middle third; (3) a relatively narrow valley of the Atchafalaya Basin bounded on each side by narrow meander belts in the upper part of the lower third; and (4) the broad distributary wedge of the deltaic plain in the southernmost region of the valley. The valley trains vary in age and landform with the oldest occurring as slightly dissected low ridges and the youngest as broad flats separated by shallow interwoven former braided channels. Meander belts formed throughout the Holocene are comprised of low natural levee ridges flanking abandoned courses and bordered by crescent-shaped oxbow lakes and ridge and swale topography. In the middle third of the valley, meander belts are separated by expansive backswamps of very little relief. The deltaic plain is also exceptionally flat, interrupted by the low natural levee ridges of the abandoned deltaic distributaries.

The floodplain of the LMV is a complex mosaic of fluvial features and landscapes within the four landscape regions. Included in this mosaic are abandoned channels and courses, lateral accretion topography of ridges and swales, natural levees, crevasses and crevasse channels, distributary channels, backswamps and rimswamps, alluvial fans and aprons, valley trains (braided stream terraces), lakes and lacustrine deltas, terraces, and the alluvial valley bluff.

Changes in the hydraulic regime of the Lower Mississippi River (LMR) since the Late Pleistocene have played a major role in the development of the landscape of the valley. The most important regime change was the diminishment of the influence of Wisconsinan glaciation in the upper Midwest and the resultant evolution of the Mississippi River from a broad braided outwash channel to a more narrow but sinuous meandering channel at the end of the Pleistocene. During the Holocene, the Mississippi River undoubtedly responded to major climatic changes, rising sea level, tributary stream influence, and possibly tectonism, diapirism, and subsidence through the growth and evolution, and abandonment of it's meander belts and deltas.     

Macro‐ and micro‐sedimentology of a modern melt‐out till – Matanuska Glacier,Alaska, USA

The macro‐ and micro‐sedimentology of a supraglacial melt‐out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open‐work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore‐water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris‐rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt‐out till require in situ melting of a stagnant, debris‐rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice‐marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore‐water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre‐modern supraglacial melt‐out tills may be more common than previously thought.     

Millennial timescale resolution of rhyolite magma recharge at Tarawera volcano: insights from quartz chemistry and melt inclusions

Most rhyolite eruption episodes of Tarawera volcano have emitted several physiochemically distinct magma batches (∼1–10 km³). These episodes were separated on a millennial timescale. The magma batches were relatively homogeneous in temperature and composition at pumice scale (>4 cm), but experienced isolated crystallisation histories. At the sub-cm scale, matrix glasses have trace element compositions (Sr, Ba, Rb) that vary by factors up to 2.5, indicating incomplete mixing of separate melts. Some quartz-hosted melt inclusions are depleted in compatible trace elements (Sr, Ti, Ba) compared to enclosing matrix glasses. This could reflect re-melting of felsic crystals deeper in the crystal pile. Individual quartz crystals display a variety of cathodoluminescence brightness and Ti zoning patterns including rapid changes in melt chemistry and/or temperature (∼50–100°C), and point to multi-cycle crystallisation histories. The Tarawera magma system consisted of a crystal-rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Carbonate stable isotope signals in the 1-Ma sedimentary record of the HDP-04 drill core from Lake Hovsgol, NW Mongolia

Oxygen and carbon stable isotope ratios in carbonates from the HDP-04 drill core from Lake Hovsgol, NW Mongolia, show an overall covariant relationship suggesting that for the most of the past 1 Ma Hovsgol remained a closed-basin lake. Carbonate δ¹⁸O ratio is responsive to regional climate change: a ca. +1.5‰ basinwide δ¹⁸O shift has occurred with the onset of Bølling–Allerød warming (sensu lato), followed by a ca. 0.8‰ depletion during the Younger Dryas. The post-glacial δ¹⁸O shift of the same magnitude is recorded in bulk carbonates, shells of two ostracod species and in wet-sieved fine fraction <63 μm. Associated with the lake-level rise and correlative with the post-glacial warming in the northern hemisphere, the observed δ¹⁸O shift is nevertheless positive. This argues against changes in local temperature and hydrology as key driving mechanisms. Most likely, Lake Hovsgol δ¹⁸O reflects a climate-driven shift in the composition of regional precipitation. Tied into a distinct lithologic succession, the radiocarbon-dated late glacial δ¹⁸O shift apparently represents a ‘template’ of the lake's response to glacial–interglacial transitions: a similar pattern of parallel changes in lithology and carbonate stable isotope composition is observed in at least 10 more intervals in the 1-Ma record, including the MIS 20/MIS19 transition at the Brunhes/Matuyama paleomagnetic reversal boundary. The comparison of carbon stable isotope ratios of untreated and in vacuo roasted bulk sediment with those of detrital carbonates suggests that clastic input of carbonates by lake tributaries does not affect the geochemistry of bulk carbonates in the HDP-04 section. The profiles of bulk carbonate δ¹⁸O and δ¹³C in the Pleistocene section of the HDP-04 drill core suggest at ca. 15.4 ka, at ca. 100 m below today's level, Lake Hovsgol still stood relatively high as compared with prior extended periods of time during late Matuyama and early Brunhes. Isotopically heavy δ¹⁸O and δ¹³C ratios during the mid–late Brunhes, particularly, in carbonate crusts and oolites, are suggestive of past episodes of dramatic evaporative ¹⁸O-enrichment of lake waters. Despite the expectation of muted amplitudes of temperature- and precipitation-related isotope signals, the sedimentary record from the sensitive ‘water gauge’ basin of Lake Hovsgol has high potential for providing important constraints on past hydrologic evolution of continental interior Asia during the Pleistocene.     

A wind tunnel study of the flow field within and around open-top chambers used for air pollution studies

The EPA Meteorological Wind Tunnel was used to examine the flow field in and around models of open-top field-plant growth chambers used to assess the effects of pollutant gases on plant growth. Baffles designed to reduce the ingress of ambient air into the chamber through the open top were tested; the mean flow and turbulence in the simulated boundary layer with and without the chambers were compared (the chamber was operated with and without the pollutant flow system on); and the effects of surrounding chambers on the concentration field were measured. Results showed that a baffle with a reduced opening vertically above the test area maintained the highest uniform concentration in the test area. The major differences between the three (no chamber and the chamber with flow on and off) mean velocity profiles occurred below z/h = 2.0 (h is chamber height) and at z/h ≤ 4.2. The three Reynolds stress profiles were similar above z/h = 2.0. Downwind of the chamber, the Reynolds stresses in the on-mode were greater than those in the off-mode above z/h = 1.1. The reverse was true below that point. Both longitudinal and vertical intensities above and downwind of the chamber were greater with the mixture flow system on rather than off, below about z/h < 1.5. Lateral variations in the mean wind indicated that the mean velocity was greater with the mixture flow system on except near the centerline where the reverse was true. The concentrations in the downwind wake resembled those for a cube. The location of a cylinder within a regular array had some effect on its internal gas concentration. Locations near the upwind and downwind edges of the array were associated with lower concentrations, although for all locations the highest internal values were always found at the lowest portion of the upwind wall. With active cylinders downwind, the gas plume emitted from a source cylinder at the windward edge of the array was forced 0.5 h higher and the centerline meandered laterally when compared with the single-cylinder case. A cylinder located at z/h = 1.0 downwind from a source cylinder received approximately 3%; of the concentration input to the source, or roughly 10%; of the actual concentration within the source cylinder.     

A paleointensity study of Cretaceous volcanic rocks from the Western Cordillera,Colombia

The Cretaceous Normal Superchron is a period of great interest to investigate global scale variations of the geomagnetic field. Long periods of single polarity are still a matter of debate: up to now there are two contradicting theories, which try to relate geomagnetic field intensity and reversal rate. We aim to shed light on the geomagnetic field strength during the Cretaceous Normal Superchron because data are still scarce and of dissimilar quality. To obtain reliable, absolute paleointensity determinations we investigate volcanic rocks from the Western Cordillera of Colombia. Several age determinations allow relating the samples to an age of about 92.5 Ma. To characterize the samples, we investigate rock magnetic properties and determine the characteristic remanent magnetization behavior. To determine paleointensities, we use a multimethod approach: first, we apply the classic Thellier-Coe protocol, and then, the relatively new multispecimen method. Rock magnetic measurements indicate magnetite as the main ferrimagnetic mineral, a stable magnetization revealed by reversible and nearly reversible thermomagnetic curves, and grain sizes that are either in the pseudosingle domain range or a mixture of single and multidomain grains. Alternating field and thermal demagnetization are rather complex, although we observe a few vector diagrams with a single, essentially uni-vectorial component with a small viscous overprint. Paleointensity determination with the Thellier-Coe protocol was unsuccessful, while with the multispecimen protocol we obtained four successful determinations out of 20. The failure of the Thellier-Coe protocol can be attributed to multidomain grains, which were observed during demagnetization and in rock magnetic experiments, and to the inhomogeneity of the volcanic rocks. Our multispecimen paleointensity determinations support low field strength at around 90 Ma during the Cretaceous Normal Superchron.