Understanding Long-term Changes Research Articles

Regional ice flow piracy following the collapse of Midgaard Glacier in Southeast Greenland

Southeast Greenland contributes significantly to global sea level rise, with mass loss having increased by about 600% over the past 30 years due to enhanced melt and dynamic instabilities of marine-terminating glaciers. Accurate modelling of glacier dynamics is crucial to minimise uncertainties in predictions of future sea level rise, necessitating detailed reconstructions of long-term glacial histories. One key complexity in these models that is not well understood or documented is ice flow piracy, where ice is redirected between catchment basins, significantly influencing regional glacier dynamics and mass balance. Here, we document and characterise the collapse of Midgaard Glacier in Southeast Greenland using a multi-data approach, providing a 90-year record of the area’s complex glacial history. Initiated over 80 years ago, this collapse triggered catchment-scale dynamic changes in several neighbouring glaciers, impacting local glacial stability throughout the 20th century and into the present. Our analysis reveals that catchment-scale ice flow piracy can cause substantial disturbances in mass balance evolution and catchment reconfigurations, independent of climatic conditions. These findings underscore the importance of understanding long-term changes in complex glacier systems to make accurate predictions of future glacial mass loss and associated sea-level rise.

Early aerial expedition photos reveal 85 years of glacier growth and stability in East Antarctica

During the last few decades, several sectors in Antarctica have transitioned from glacial mass balance equilibrium to mass loss. In order to determine if recent trends exceed the scale of natural variability, long-term observations are vital. Here we explore the earliest, large-scale, aerial image archive of Antarctica to provide a unique record of 21 outlet glaciers along the coastline of East Antarctica since the 1930s. In Lützow-Holm Bay, our results reveal constant ice surface elevations since the 1930s, and indications of a weakening of local land-fast sea-ice conditions. Along the coastline of Kemp and Mac Robertson, and Ingrid Christensen Coast, we observe a long-term moderate thickening of the glaciers since 1937 and 1960 with periodic thinning and decadal variability. In all regions, the long-term changes in ice thickness correspond with the trends in snowfall since 1940. Our results demonstrate that the stability and growth in ice elevations observed in terrestrial basins over the past few decades are part of a trend spanning at least a century, and highlight the importance of understanding long-term changes when interpreting current dynamics.

Radiolarian assemblages related to the ocean–ice interaction around the East Antarctic coast

Abstract. The Southern Ocean plays a central role in Earth's climate, ecology, and biogeochemical cycles. Therefore, understanding long-term changes in Southern Ocean water masses in the geologic past is essential for assessing the role of the Southern Ocean in the climate system. Radiolarian fossils are a useful tool to reconstruct the water masses of the Southern Ocean. However, the radiolarian assemblages in the high latitudes of the Southern Ocean (south of the polar front (PF)) are still poorly understood. In this paper, we report the radiolarian assemblages in surface marine sediment and plankton tow samples collected from the high latitudes south of the PF. In the surface sediments, four factors (named F1–F4) of the radiolarian assemblages were identified using Q-mode factor analysis, which are related to different water masses and hydrological conditions. F1 is related to the surface waters south of the southern boundary (SB) of the Antarctic Circumpolar Current (ACC), which are cooled by melting sea ice and ice sheets. F2 is associated with water masses north of the SB. A comparison with the vertical distribution of the radiolarian assemblages in plankton tow samples indicates that characteristic species are associated with the Circumpolar Deep Water (CDW) and surface waters north of the SB. F3 is associated with modified Circumpolar Deep Water (mCDW). The radiolarian assemblage of F4 does not seem specifically related to any of the water mass here analyzed. However, the species in this assemblage are typically dwells within ice shelf and/or sea ice edge environments. Radiolarian assemblages here identified and associated with water masses, and ice edge environments are useful to reconstruct the environment south of the PF in the geologic past.

Birds on the edge: Spatial and temporal patterns in the bird community recorded at a conservation reserve on a bioregion woodland−grassland boundary in central Queensland

Monitoring the changes in occurrence and abundance of wildlife communities over time is important for more effective and targeted management and understanding long-term changes due to local and global environmental influences. In this study, we report on the first systematic bird survey carried out on Edgbaston Reserve, a protected area on the boundary of tropical and semi-arid bioregions in north-central Queensland. We systematically sampled the bird fauna at 24 sites over five surveys between 2018 and 2020, using a combination of 2-ha area searches and timed nocturnal censuses. We examined variation in composition and species abundance across the surveys using multivariate, regression and non-parametric analyses. A total of 6201 bird records comprising 123 species was collected. Forty-six species exhibited significant variation in abundance across the six sampled habitat types (Ironbark, Gidgee and Escarpment woodlands, Springs, Spinifex grasslands and Mitchell Grass Downs). Species composition also varied significantly across habitats and surveys, and there were clear differences in the Spinifex and Mitchell grass bird communities compared with those in the woodlands. Twenty species were recorded in only one of the five surveys, and 17 species were recorded in significantly higher abundance in some survey years, associated with an influx of granivores and nomadic and migratory species. The location of the property on the boundary of woodlands and more arid grasslands that contain springs, and the contrasting mix of eastern- and western-distributed birds, suggests that the continued monitoring of the avifauna provides an important opportunity to investigate long-term trends, linked to environmental change and annual management, to assist the preservation of this important bird community situated on the edge of two bioregions.

Automated extraction of map symbology from nineteenth century topographical maps by convolutional neural networks for understanding long-term changes in the extent and distribution of wetlands

Automated extraction of map symbology from nineteenth century topographical maps by convolutional neural networks for understanding long-term changes in the extent and distribution of wetlands

Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft

Abstract. We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 km, inferred from ionospheric data, for which there is a global network of ground-based stations. Measurements of thermospheric composition via ground-based instrumentation are challenging to make, and so details about this important region of the upper atmosphere are currently sparse. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the “G” factor, a function of ion production rate and loss rates via ion–atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the G factor obtained from ionograms recorded at Kwajalein (9∘ N, 167.2∘ E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between G and the molecular-to-atomic composition ratio, with a gradient of 2.55±0.40. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be 4.75±0.4. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of 4.20±0.8. This relationship has potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding long-term change and the efficacy of the upper atmosphere on satellite drag.

Repeat photography and urban change

Repeat photography—the practice of rephotographing the same locations at different moments in time—is an under-utilised method for interpreting urban change. Despite this, it has the potential to give new empirical and theoretical meanings to our understanding of the ways in which major forces of change shape cities and their urban landscapes. The purpose of this article is to give a visual dimension to understanding long-term change in Toronto, Canada, since the 1960s. It will use historic images taken by streetcar enthusiasts as a starting point. Rather than studying these trolleys themselves, it is everything around them that is of interest for this study. As streetcar systems were disappearing or contracting after World War II, dedicated and passionate enthusiasts visited Toronto, which retained the largest streetcar network in North America, to ride and photograph them. Their images give us unique insights into the ordinary city in ways that few other genres do. To analyse long-term patterns of change, these historic images have been rephotographed over the past few years and show how trends such as deindustrialisation, financialisation, and gentrification are made visible in the urban landscape. In this article, I also echo assertions by Elvin Wyly and others that photographs are a useful part of critical constructive analysis of the city.

Eruption frequency patterns through time for the current (1999–2018) activity cycle at Volcán de Fuego derived from remote sensing data: Evidence for an accelerating cycle of explosive paroxysms and potential implications of eruptive activity

Volcán de Fuego is a stratovolcano in Guatemala that has produced over 50 VEI ≥ 2 eruptions since 1524. After two decades of quiescence, in 1999 Fuego entered a new period of eruptive activity that continues until the present day, characterized by persistent Strombolian activity interspersed with occasional “paroxysmal” eruptions of greater magnitude, the most recent of which occurred in 2018. The land surrounding Fuego accommodates tens of thousands of people, so greater understanding of its eruptive behaviour has important implications for hazard assessment. Nevertheless, there is relatively little literature that studies recent (since 1999) activity of Fuego in detail.Using time-series analysis of remote sensing thermal data during the period 2000–2018 combined with recent bulletin reports, we present evidence for a new eruptive regime beginning in 2015. We find that this regime is defined by a greater frequency of paroxysmal eruptions than in previous years and is characterized by the following sequence of events: (i) effusion of lava flows and increase in summit explosive activity, followed by (ii) an intense eruptive phase lasting 24–48 h, producing a sustained eruptive column, continuous explosions, and occasional pyroclastic flows, followed by (iii) decrease in explosive activity. We discuss various models that explain this increase in paroxysmal frequency, and consider its implications for hazard assessment at Fuego. We advocate the pairing of remote sensing data with monitoring reports for understanding long-term changes in behaviour of poorly-instrumented volcanoes. The results that we present here provide a standard for informed assessment of future episodes of unrest and paroxysmal eruptions of Fuego.

Gypsy-Travellers/Roma and Social Integration: Childhood, Habitus and the "We-I Balance"

Norbert Elias provides a very useful theoretical framework for understanding long-term changes in childhood-adulthood relations at the societal level. Key processes central to this theorization include: the increasing separation of the social worlds of children and adults; the increasing distance between childhood and adulthood; the partial defunctionalisation of the family; the civilizing of parents; changes in the we-I balance towards the I; and the gradual conversion of social constraints into self-restraints. Yet variable trajectories are under-developed in Elias' work: the differing nature of these interrelated social processes for different outsider groups in society were not systematically addressed by him. However, this paper argues that Elias's theories on childhood do provide us with a very useful conceptual framework from which to understand these variable trajectories. It applies his theories on childhood and individualization to Gypsy-Traveller/Roma groups in Europe. The paper argues that the above processes differ markedly for many groups and, coupled with the existence of a very strong group orientation and long-term stigmatisation, are central to accounting for their relative lack of social integration. That is, differing processes of childhood and family socialisation are crucial in explaining how Gypsy-Traveller/Roma groups have maintained their own group identity and cultural continuity under intense pressures to assimilation and conformity.

A re-evaluated Canadian ozonesonde record: measurements of the vertical distribution of ozone over Canada from 1966 to 2013

Abstract. In Canada routine ozone soundings have been carried at Resolute Bay since 1966, making this record the longest in the world. Similar measurements started in the 1970s at three other sites, and the network was expanded in stages to 10 sites by 2003. This important record for understanding long-term changes in tropospheric and stratospheric ozone has been re-evaluated as part of the SPARC/IO3C/IGACO-O3/NDACC (SI2N) initiative. The Brewer–Mast sonde, used in the Canadian network until 1980, is different in construction from the electrochemical concentration cell (ECC) sonde, and the ECC sonde itself has also undergone a variety of minor design changes over the period 1980–2013. Corrections have been made for the estimated effects of these changes to produce a more homogeneous data set. The effect of the corrections is generally modest. However, the overall result is entirely positive: the comparison with co-located total ozone spectrometers is improved, in terms of both bias and standard deviation, and trends in the bias have been reduced or eliminated. An uncertainty analysis (including the additional uncertainty from the corrections, where appropriate) has also been conducted, and the altitude-dependent estimated uncertainty is included with each revised profile. The resulting time series show negative trends in the lower stratosphere of up to 5 % decade−1 for the period 1966–2013. Most of this decline occurred before 1997, and linear trends for the more recent period are generally not significant. The time series also show large variations from year to year. Some of these anomalies can be related to cold winters (in the Arctic stratosphere) or changes in the Brewer–Dobson circulation, which may thereby be influencing trends. In the troposphere, trends for the 48-year period are small and for the most part not significant. This suggests that ozone levels in the free troposphere over Canada have not changed significantly in nearly 50 years.

In ‘splendid isolation'. A comparative perspective on the historiographies of the ‘material renaissance' and the ‘consumer revolution'

Richard Goldthwaite's pioneering work on the material culture of the Italian Renaissance offered many clues for better understanding long-term changes and continuities in European patterns of consumption during the early modern period. Yet the large historiographical body on the subject of the ‘material renaissance’ has largely ignored or rejected these, and has more often than not studied the field in a sort of ‘splendid isolation’. This article presents a review of some of the most important contributions to this field, and attempts to link them to the ongoing debates on early modern consumer change in the social and economic history outside of Italy.

A satellite-based snow cover climatology (1985–2011) for the European Alps derived from AVHRR data

Abstract. Seasonal snow cover is of great environmental and socio-economic importance for the European Alps. Therefore a high priority has been assigned to quantifying its temporal and spatial variability. Complementary to land-based monitoring networks, optical satellite observations can be used to derive spatially comprehensive information on snow cover extent. For understanding long-term changes in alpine snow cover extent, the data acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensors mounted onboard the National Oceanic and Atmospheric Association (NOAA) and Meteorological Operational satellite (MetOp) platforms offer a unique source of information. In this paper, we present the first space-borne 1 km snow extent climatology for the Alpine region derived from AVHRR data over the period 1985–2011. The objective of this study is twofold: first, to generate a new set of cloud-free satellite snow products using a specific cloud gap-filling technique and second, to examine the spatiotemporal distribution of snow cover in the European Alps over the last 27 yr from the satellite perspective. For this purpose, snow parameters such as snow onset day, snow cover duration (SCD), melt-out date and the snow cover area percentage (SCA) were employed to analyze spatiotemporal variability of snow cover over the course of three decades. On the regional scale, significant trends were found toward a shorter SCD at lower elevations in the south-east and south-west. However, our results do not show any significant trends in the monthly mean SCA over the last 27 yr. This is in agreement with other research findings and may indicate a deceleration of the decreasing snow trend in the Alpine region. Furthermore, such data may provide spatially and temporally homogeneous snow information for comprehensive use in related research fields (i.e., hydrologic and economic applications) or can serve as a reference for climate models.

A Simulation Model of Fission–Fusion Dynamics and Long-Term Settlement Change

Archaeological analyses often detect abrupt changes over time in the hierarchy of settlement sizes and the spatial distribution of residential units. These transformations have been explained looking at a variety of possible causes, from climatic changes to the sudden release of slowly cumulating political tensions. While many of these models offer plausible explanations for specific historical contexts, a broad-breadth model is desirable if cross-cultural analysis is sought. This paper tackles this problem by starting from the theoretical proposition that human groups are characterised by a non-linear relationship between size and per-capita fitness. Increasing group size has beneficial effects, but once a certain threshold is exceeded, negative frequency dependence will start to predominate leading to a decline in the per-capita fitness. Such a relationship can potentially have long-term implications in the spatial structure of human settlements if individuals have the possibility to modify their fitness through group fission–fusion dynamics. I will illustrate the equilibrium properties of these dynamics by means of an abstract agent-based simulation and discuss its implication for understanding long-term changes in human settlement pattern. Results suggest that changes in settlement pattern can originate from internal dynamics alone if the system is highly integrated and interconnected.

Marine denitrification rates determined from a global 3-D inverse model

Abstract. A major impediment to understanding long-term changes in the marine nitrogen (N) cycle is the persistent uncertainty about the rates, distribution, and sensitivity of its largest fluxes in the modern ocean. We use a global ocean circulation model to obtain the first 3-D estimate of marine denitrification rates that is maximally consistent with available observations of nitrate deficits and the nitrogen isotopic ratio of oceanic nitrate. We find a global rate of marine denitrification in suboxic waters and sediments of 120–240 Tg N yr−1, which is lower than many other recent estimates. The difference stems from the ability to represent the 3-D spatial structure of suboxic zones, where denitrification rates of 50–77 Tg N yr−1 result in up to 50% depletion of nitrate. This depletion reduces the effect of local isotopic enrichment on the rest of the ocean, allowing the N isotope ratio of oceanic nitrate to be achieved with a sedimentary denitrification rate about 1.3–2.3 times that of suboxic zones. This balance of N losses between sediments and suboxic zones is shown to obey a simple relationship between isotope fractionation and the degree of nitrate consumption in the core of the suboxic zones. The global denitrification rates derived here suggest that the marine nitrogen budget is likely close to balanced.

Generation of a novel 1 km NDVI data set over Canada, the northern United States, and Greenland based on historical AVHRR data

Time series of the Normalized Difference Vegetation Index (NDVI) derived from satellite observations provide important information on the state of terrestrial vegetation over a wide range of spatiotemporal scales. For understanding long-term changes in terrestrial ecosystems (post-1981), data collected by the Advanced Very High Resolution Radiometer (AVHRR) on board the satellites of National Oceanic and Atmospheric Administration (NOAA) series is a unique source of information. In this paper, we describe a new processing methodology for a comprehensive AVHRR data set at 1km spatial resolution acquired over Canada, the northern United States and Greenland post-1981. The methodology incorporates a pre-processing algorithm, Canadian AVHRR Processing System (CAPS), recently developed by the Canada Centre of Remote Sensing (CCRS), which enables highly accurate geolocation and ortho-rectification at efficiency rates of >90%. Once image navigation is completed, our approach consists of five key steps: first, two clear-sky composites for each 10day interval are generated from the forward or backward scattering hemisphere; second, AVHRR Channel 1 and 2 reflectances are normalized to the AVHRR/3 on board NOAA-17 to account for differences in the spectral response function among the AVHRR sensors; third, atmospheric correction is performed using the Simplified Method for Atmospheric correction (SMAC) algorithm, using standard meteorological data sets (water vapor, surface level air pressure, ozone); fourth, NDVI is calculated based on atmospherically corrected Channel 1 and 2 reflectances; and finally, the NDVI is adjusted for directional effects based on the Ross-Thick Li-Sparse Bidirectional Reflectance Distribution Function (BRDF) model. The processed NDVI data are compared to an equivalent spatially and temporally overlapping MODIS NDVI data set from 2001 to 2005 for validation. Results at continental scale indicate that time series of MODIS and AVHRR were similar for a wide range of biomes and generalized ecoregions. Analysis stratified by land cover indicated that the correlation was strongest for homogeneous land cover types, such as cropland, when compared to structurally more diverse classes, such as deciduous broadleaf forests. The comparison of the NDVI at the local scale at seven sites of the Fluxnet Canada Research Network resulted in the correlation coefficient r=0.95. Given confidence in the processing approach, this NDVI data set can be a valuable source of information for climate and vegetation-related studies over Canada and the northern United States.

Application of New Precipitation and Reconstructed Streamflow Products to Streamflow Trend Attribution in Northern Eurasia

Abstract River runoff to the Arctic Ocean has increased over the last century, primarily during the winter and spring and primarily from the major Eurasian rivers. Some recent studies have suggested that the additional runoff is due to increased northward transport of atmospheric moisture (and associated increased precipitation), but other studies show inconsistencies in long-term runoff and precipitation trends, perhaps partly due to biases in the observational datasets. Through trend analysis of precipitation, temperature, and streamflow data, the authors investigate the extent to which Eurasian Arctic river discharge changes are attributable to precipitation and temperature changes as well as to reservoir construction and operation between the years of 1936 and 2000. Two new datasets are applied: a gridded precipitation product, in which the low-frequency variability is constrained to match that of long-term bias-corrected precipitation station data, and a reconstructed streamflow product, in which the effects of reservoirs have been minimized using a physically based reservoir model. It is found that reservoir operations have primarily affected streamflow seasonality, increasing winter discharge and decreasing summer discharge. To understand the influences of climate on streamflow changes, the authors hypothesize three cases that would cause precipitation trends to be inconsistent with streamflow trends: first, for the coldest basins in northeastern Siberia, streamflow should be sensitive to warming primarily as a result of the melting of excess ground ice, and for these basins positive streamflow trends may exceed precipitation trends in magnitude; second, evapotranspiration (ET) in the warmer regions of western Siberia and European Russia is sensitive to warming and increased precipitation, therefore observed precipitation trends may exceed streamflow trends; and third, streamflow from the central Siberian basins should respond to both effects. It is found that, in general, these hypotheses hold true. In the coldest basins, streamflow trends diverged from precipitation trends starting in the 1950s to 1960s, and this divergence accelerated thereafter. In the warmest basins, precipitation trends consistently exceeded streamflow trends, suggesting that increased precipitation contributed to increases in both ET and streamflow. In the central basins, permafrost degradation and ET effects appear to be contributing to long-term streamflow trends in varying degrees for each basin. The results herein suggest that the extent and state of the permafrost underlying a basin is a complicating factor in understanding long-term changes in Eurasian Arctic river discharge.

Revisiting Schramm's Radiotown: Media Displacement and Saturation

In 1959 Wilbur Schramm collected data on the media use behavior of children in what he believed was the last remaining town in North America to have radio as its only electronic mass media, and he concluded the primary impact of new media was the displacement of incumbent media. This research returns to Schramm's “Radiotown” for two follow-up studies to assess the validity of displacement as a mechanism for understanding long-term changes in media use. The first study is a qualitative data collection among a convenience sample (n = 28) of the now-adult participants of the 1959 study. The second study quantitatively tests the conclusions of the first study among the youth of Radiotown (n = 263). Among both adults and youth, radio remains a primary mass media device, with adults using more radio now than in 1959. Three principles of media use are proposed: the ubiquity of mass media devices in the household, the proximity of media devices, and the constancy of media use. Implications for the displacement hypothesis are discussed.

Antarctica's role in understanding long-term change in the upper atmosphere

Within the global context, Antarctica has a key role to play in understanding long-term change in the upper atmosphere, both because of its isolation from the rest of the world and because of its unique geophysical attributes. Antarctic upper atmosphere data can provide global change observations regarding the mesosphere, thermosphere, ionosphere, plasmasphere and magnetosphere. It will not only provide trend estimates but, just as importantly, it will define the background variability which exists in the upper atmosphere and against which these trends must be resolved. Upper atmospheric change can be driven both from within the Earth's near environment primarily through changing atmospheric composition, dynamics or geomagnetic field, or it can be driven externally, predominantly by the Sun. Recent observations are discussed in the light of increasing interest in global change issues and sun-weather relationships.

System analysis techniques applied to the Forrester world model—Part III: Correlation and spectral analysis

Correlation analysis reveals some of the inherent properties of the world system. Natural resources and capital investment form an independent subsystem and are unaffected by other state variables. Population is stable and will not increase unless forced to do so by capital investment. Spectral analysis is not particularly revealing except for the fact that a large amplitude occurs around ƒ = ƒ 0. This indicates a very inertial system and the need for more study to aid in understanding long-term changes in world behavior.