Source Region Research Articles

Vegetation restoration effectiveness with main factors in the Beijing-Tianjin sandstorm source region during 2000–2020, China

The Beijing-Tianjin Sandstorm Source Region (BTSSR), a region with significant vegetation degradation in China, has been subjected to ecological engineering intended to curb vegetation browning. Nevertheless, few studies have used multisource data to quantitatively evaluate the vegetation restoration effectiveness in the BTSSR, and the relationship between ecological engineering and vegetation restoration effectiveness in this region from statistical evidence has received little attention so far. Here, we employed the comprehensive vegetation parameters to describe the vegetation restoration effectiveness, and examined the driving mechanism of natural and human factors in different sub regions. First, we evaluated the vegetation restoration effectiveness in the BTSSR using an index that combined Fractional Vegetation Coverage (FVC) and Net Primary Productivity (NPP). Our results showed that the vegetation restoration effectiveness has significantly increased over time. From 2000 to 2020, 60.9% of the area achieved significant vegetation restoration, and the area with higher vegetation restoration effectiveness was concentrated in the southern part of the study area. Then, we used the Geodetector Model to explore the main factors and their interactions affecting vegetation restoration effectiveness. We found that the vegetation restoration effectiveness in the entire area was dominated by annual precipitation, in the northern part of the study area was led by climate, and in the southern part of the study area was dominated by ecological engineering. We further demonstrated that the interaction between ecological engineering and climate, soil conditions, geographical background and socioeconomic had the synergistic effect on vegetation restoration effectiveness, and the interaction between ecological engineering and annual precipitation had the greatest impact. We recommend that the northern region of the BTSSR continue to build low-density wind and sand control forests, while the southern region needs to be strengthened to prevent soil erosion problems caused by the expansion of human activities.

Fermi Unassociated Sources in the MeerKAT Absorption Line Survey

Abstract Over 2000 γ-ray sources identified by the Large Area Telescope on NASA's Fermi Gamma-ray Space Telescope are considered unassociated, meaning that they have no known counterparts in any other frequency regime. We have carried out an image-based search for steep spectrum radio sources, with in-band spectral index < −1.4, within the error regions of Fermi unassociated sources using 1–1.4 GHz radio data from the MeerKAT Absorption Line Survey (MALS) data release. The first MALS data release with a median rms noise of 22–25 μJy and 735,649 sources is a significant advance over past image-based searches with improvements in sensitivity, resolution, and bandwidth. Steep spectrum candidates were identified using a combination of in-band spectral indices from MALS and existing radio surveys. We developed an optical and infrared source classification scheme in order to distinguish between Galactic pulsars and radio galaxies. In total, we identify nine pulsar candidates toward six Fermi sources that are worthy of follow-up for pulsation searches. We also report 41 steep spectrum radio galaxy candidates that may be of interest in searches for high-redshift radio galaxies. We show that MALS, due to its excellent continuum sensitivity, can detect 80% of the known pulsar population. This exhibits the promise of identifying exotic pulsar candidates with future image-based surveys with the Square Kilometre Array and its precursors.

The centimeter emission from planet-forming disks in Taurus

The last decade has witnessed remarkable advances in the characterization of the (sub-)millimeter emission from planet-forming disks. Conversely, the study of (sub-)centimeter emission has made more limited progress, to the point that only a few exceptional disk-bearing objects have been characterized in the centimeter regime. This work takes a broad view of the centimeter emission from a large sample with Karl G. Jansky Very Large Array (VLA) observations that is selected from previous Atacama Large (sub-)Millimeter Array (ALMA) surveys of more representative disks in brightness and extent . We report on the detection and characterization of flux at centimeter wavelengths from 21 sources in the Taurus star-forming region. Complemented by literature and archival data, the entire photometry from 0.85 mm to 6 cm is fit by a two-component model that determines the ubiquitous presence of free-free emission entangled with the dust emission. The flux density of the free-free emission is found to scale with the accretion rate but is independent of the outer-disk morphology depicted by ALMA. The dust emission at 2 cm is still appreciable and offers the possibility to extract an unprecedented large set of dust spectral indices in the centimeter regime. A pronounced change between the median millimeter indices (2.3) and centimeter indices (2.8) suggests that a large portion of the disk emission is optically thick up to 3 mm. The comparison of both indices and fluxes with the ALMA disk extent indicates that this portion can be as large as 40 au and suggests that the grain population within this disk region that emits the observed centimeter emission is similar in disks with different sizes and morphologies. All these results await confirmation and dedicated dust modeling once facilities such as next generation VLA (ngVLA) or Square Kilometre Array (SKA)-mid are able to resolve the centimeter emission from planet-forming disks and disentangle the various components.

Differentiating the Acceleration Mechanisms in the Slow and Alfvénic Slow Solar Wind

Abstract In the corona, plasma is accelerated to hundreds of kilometers per second and heated to temperatures hundreds of times hotter than the Sun's surface before it escapes to form the solar wind. Decades of space-based experiments have shown that the energization process does not stop after it escapes. Instead, the solar wind continues to accelerate, and it cools far more slowly than a freely expanding adiabatic gas. Recent work suggests that fast solar wind requires additional momentum beyond what can be provided by the observed thermal pressure gradients alone, whereas it is sufficient for the slowest wind. The additional acceleration for fast wind can be provided through an Alfvén wave pressure gradient. Beyond this fast/slow categorization, however, a subset of slow solar wind exhibits high Alfvénicity that suggests that Alfvén waves could play a larger role in its acceleration compared to conventional slow wind outflows. Through a well-timed conjunction between Solar Orbiter and Parker Solar Probe (PSP), we trace the energetics of slow wind to compare with a neighboring Alfvénic slow solar wind stream. An analysis that integrates remote and heliospheric properties and modeling of the two distinct solar wind streams finds that Alfvénic slow solar wind behaves like fast wind, where a wave pressure gradient is required to reconcile its full acceleration, while non-Alfvénic slow wind can be driven by its nonadiabatic electron and proton thermal pressure gradients. Derived coronal conditions of the source region indicate good model compatibility, but extended coronal observations are required to effectively trace solar wind energetics below PSP's orbit.

Transforming US agriculture for carbon removal with enhanced weathering.

Enhanced weathering (EW) with agriculture uses crushed silicate rocks to drive carbon dioxide removal (CDR)1,2. If widely adopted on farmlands, it could help achieve net-zero emissions by 20502-4. Here we show, with a detailed US state-specific carbon cycle analysis constrained by resource provision, that EW deployed on agricultural land could sequester 0.16-0.30 GtCO2 yr-1 by 2050, rising to 0.25-0.49 GtCO2 yr-1 by 2070. Geochemical assessment of rivers and oceans suggests effective transport of dissolved products from EW from soils, offering CDR on intergenerational timescales. Our analysis further indicates that EW may temporarily help lower ground-level ozone and concentrations of secondary aerosols in agricultural regions. Geospatially mapped CDR costs show heterogeneity across the USA, reflecting a combination of cropland distance from basalt source regions, timing of EW deployment and evolving CDR rates. CDR costs are highest in the first two decades before declining to about US$100-150 tCO2-1 by 2050, including for states that contribute most to total national CDR. Although EW cannot be a substitute for emission reductions, our assessment strengthens the case for EW as an overlooked practical innovation for helping the USA meet net-zero 2050 goals5,6. Public awareness of EW and equity impacts of EW deployment across the USA require further exploration7,8 and we note that mobilizing an EW industry at the necessary scale could take decades.

Phosphorus transitions driven by cyclone biparjoy linked middle east North Africa (MENA) and Indian Thar Desert dust storm pathways in Asia’s largest grassland

Phosphorus (P) is an important nutrient for terrestrial ecosystems like grassland and plays a critical role in influencing primary productivity and hence ecosystem dynamics. The deposition of airborne dust, particularly from arid and semiarid regions, has been recognised as a significant source of phosphorus input in distant ecosystems. The study area, the Banni grassland, is a semiarid ecosystem with a unique geological history that has experienced degradation for various natural and anthropogenic reasons. It is located in the arid tract of western India. Soil samples were collected from 10 × 10 km grid locations in the grassland before, 48 h after, and 20 days after a cyclonic storm, Biparjoy, which hit the region in June 2023. Statistical analyses (Shapiro‒Wilk normality and Kruskal–Wallis H test) were performed on the data to assess the differences in phosphorus concentrations in terms of PAC (Phosphorus Activation Coefficient) among the phases. To examine the long-range transport of dust-borne phosphorus and its subsequent deposition in the target grassland, we employed an interdisciplinary approach that integrated satellite imagery and ground-based measurements. Spatial and temporal variations in dust emissions were assessed using satellite remote sensing data, while ground truthing was performed for phosphorus content analysis using standard protocols. The aerosol data from MERRA-2 for the past 40 years were used to examine the relationships between aerosol concentrations and wind direction and speed. Our findings revealed that the Middle East, North Africa, and Thar Desert significantly contributed to phosphorus deposition in the target grassland during specific seasons. The SW cyclone ‘Biparjoy’, which followed the same track of aerosol loading (MENA), made landfall in this zone (June 16, 2023) and affected the P depositional patterns. The pre-cyclone, post-cyclone and 20 DAC (days after cyclone) had AP values of 15.15, 22.54 and 24.06, respectively. However, the TP values were 45.81 ± SE = 1.73, 60.95 ± SE = 1.39 and 61.98 ± SE = 1.40, respectively. The highest TP values were in phase 3 (20 DAC phase) (61.89 ± SE = 1.40). Similarly, the transformation of locked forms of P to bioavailable forms was coincidental with higher PSM (Phosphate Solubilising Microorganisms) in soil samples. Dust storms and other atmospheric circulation patterns were found to play pivotal roles in facilitating the long-range transport of phosphorus-laden dust particles from these source regions to the target grassland. Ultimately, our research contributes to the broader understanding of global nutrient cycling and land‒air interactions, enabling informed decision-making for the conservation and sustainable management of terrestrial ecosystems.

Significant greening in the western Tibetan Plateau and surroundings occurred after the 1970s

Vegetation greening on the Tibetan Plateau (TP) has profoundly changed the connection between terrestrial ecosystems and regional carbon, water, and energy cycling, but existing research on vegetation greenness can only be traced back to the 1980s, because of the scarcity of long-term remote sensing data. Here we present an ice-core record of pollen accumulation rates with a 3-year resolution during 1935–2012 AD for the western TP. Based on backward trajectory and wind data, we identified the pollen source region and transport mechanisms. We found that the 3-year total pollen accumulation rate (TPAR3a) is a good indicator of vegetation coverage of the source region, and our data showed that the greening of the western TP and surroundings began as early as 1935 AD, mostly due to regional warming and moistening. The greening trend became more significant after the 1970s, which is mostly related to the significant increase in temperature.

Observations and Numerical Modelling of the Sumatra Tsunami of 28 March 2005

On 28 March 2005, a major Mw 8.6 earthquake occurred near Nias and Simeulueislands, in the vicinity of northwestern Sumatra (Indonesia). The earthquake generated a significant tsunami. Although it was not as destructive as the 2004 Sumatra tsunami, the 2005 event was of sufficient strength to be recorded by tide gauges throughout the entire Indian Ocean. We selected 12 records for analysis, most from open-ocean islands but also some from continental stations. The maximum wave heights were measured at Salalah (Oman) (87 cm), Colombo (Sri Lanka), Pointe La Rue (Seychelles) and Rodrigues Island (53–54 cm). The dominant wave periods, estimated from frequency–time (f-t) diagrams, were 60–66 min, 40–48 min, and 20 min, which we assume are associated with the 2005 tsunami source. From the same stations, we calculated the mean ratio of the 2004 to 2005 tsunami heights as 5.11 ± 0.60, with the maximum and minimum heights to the west and south of the source region as 9.0 and 2.49, respectively. We also used these data to estimate the mean energy index, E0 = 65 cm2, for the 2005 tsunami, which was 16 times smaller than for the 2004 event. The USGS seismic solution was used to construct a numerical model of the 2005 tsunami and to simulate the tsunami waveforms for all 12 tide gauge stations. The results of the numerical computations were in general agreement with the observations and enabled us to map the spatial wave field of the event. To estimate the influence of location and orientation of the source area on the propagating tsunami waves, we undertook a set of additional numerical experiments and found that this influence is substantial and that these factors explain some of the differences between the physical properties of the 2004 and 2005 events.

Origin and evolution of the Holocene magmatic system at Sakurajima volcano, Japan

Abstract Sakurajima volcano has developed since 26 ka through post-caldera magmatic activity at the Aira caldera (formed at 30 ka) and is one of the most active volcanoes in Japan. In this study, new petrological and geochemical analyses were conducted on proximal volcanic products to understand the origin and evolution of the magmatic system during the Holocene. The volcanic products have andesitic and dacitic compositions (58–69 wt.% SiO2), and relatively older products (9–1.6 ka) and younger products (<1.3 ka) are characterised by having lower and higher P2O5 contents, respectively (low- and high-P2O5 groups, respectively). The low-P2O5 group products had lower TiO2 and Y contents, higher 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios, and lower 143Nd/144Nd ratios than the high-P2O5 group products. It is suggested that the low-P2O5 group magmas were produced by the partial melting of lower crustal materials, and the compositional variations primarily reflected the variation in the degree of melting, with some contribution from mixing with mafic magmas. In contrast, the high-P2O5 group magmas were produced by mixing mafic and felsic magmas in varying proportions. The mafic end-member magmas evolved from mantle-derived primitive magmas with some contribution from crustal assimilation. The felsic end-member magmas were produced by fractional crystallisation following the melting of lower crustal materials with higher melting degrees than those of the low-P2O5 group magmas. In summary, the geochemical evolution of Holocene magmatic activity at Sakurajima was essentially controlled by intermittent discharges of partial melts from the lower crustal source region with increasing melting degrees. The remnants of the voluminous Aira rhyolitic magmas from caldera-forming eruptions were not involved in the Holocene magmatic system. Lower crustal source materials that produced the Aira rhyolites were also not involved. The lower crustal melting region, which was the main source of Holocene magmatism at Sakurajima, may have already existed at ~100 ka, well before the caldera-forming eruption at 30 ka.

Cross-validation of methods for quantifying the contribution of local (urban) and regional sources to PM2.5 pollution: application in the Eastern Mediterranean (Cyprus).

A comprehensive (1-year-long) daily-resolved filter-based PM2.5 chemical speciation database was built over Cyprus (Eastern Mediterranean), encompassing various sites with different typologies (urban traffic, urban background and regional background). Such experimental strategy was designed and implemented with the view to quantify the contribution of local (Cypriot cities) versus regional (Eastern Mediterranean & Middle East) pollution sources on fine PM levels in Cyprus using the “Lenschow” approach (Lenschow et al., 2001). On an annual basis, fine PM fraction originated mainly from regional sources (53–61 %), while during winter a totally different pattern was observed, with local PM sources being the dominant ones (up to 70 %) due to enhanced biomass burning for domestic heating and unfavorable meteorological conditions enhancing stagnation and accumulation of air pollution close to the ground. At that period, the urban PM2.5 was found to be predominantly made of carbonaceous species (> 70 %). Dust from local sources unexpectedly dominated the summertime local PM2.5 (37–47 %).The results derived from “Lenschow” approach were quantitatively compared against an independent PM source apportionment approach using Positive Matrix Factorization (US EPA PMF 5.0) to assess more-local versus more-regional PM sources. We show here that both approaches applied over Cyprus have led to consistently similar results, further cross-validating the robustness of the two techniques. The influence of regional hotspots was further confirmed by using the Potential Source Contribution Function (PSCF) model which pinpointed the Middle East as the main source region of fine PM pollution affecting Cyprus.

Application of Ni, Cu and Fe isotopes as indicators of ore genesis - New insights from the epigenetic-hydrothermal Rajapalot Au[sbnd]Co prospect, Finnish Lapland

Application of stable transition metal isotopes as indicators of ore genesis is becoming more popular, yet the fractionation mechanisms and isotopic distribution in these unconventional systems remain poorly understood. In this study, we present an analysis of sulphide Ni, Cu and Fe isotopes measured from solution using multicollector ICP-MS. The data were collected from the dominant sulphide phases in the Raja prospect within the epigenetic-hydrothermal Rajapalot AuCo deposit, Finnish Lapland. Our main goal was to gain new information on the systematics and behaviour of the isotopes in high-temperature ore-forming environments, with implications for ore genesis. The Raja prospect is hosted by a Paleoproterozoic volcanic-sedimentary sequence and was formed by multi-stage hydrothermal processes during the Svecofennian orogeny. Pyrite shows significant variation in δ56Fe (-2.08 to +3.29 ‰), including the heaviest iron isotopes thus far observed in natural pyrite. The δ56Fe values in pyrrhotite vary less (-0.74 to +0.80 ‰) but are unusually heavy compared to those of magmatic pyrrhotite. δ56Fe in chalcopyrite ranges from +0.10 to +1.45 ‰, δ60Ni in pyrrhotite from -1.03 to +0.18 ‰, and δ65Cu in chalcopyrite from -0.30 to +0.23 ‰. The δ56Fe values in co-existing sulphide phases suggest both equilibrium and kinetic fractionation effects. The extreme Fe fractionation in pyrite implies that kinetic fractionation played a major role in the precipitation of isotopically light pyrite. Moreover, inheritance of low δ56Fe values from a pyrrhotite precursor is likely. The heavy Fe isotopic composition of some of the pyrrhotite and pyrite is probably the result of preferential leaching of light isotopes by late hydrothermal fluids.Systematic correlations between the composition of the examined isotope systems, Co and Au concentrations, and textural features link the sulphide isotopes to multi-stage ore formation. Gradual trends in the isotope compositions suggest Rayleigh fractionation. Early Co deposition is attributed to isotopically heavy fluid, probably derived from a sedimentary formation with abundant iron oxides. The isotopically lighter Au mineralising fluids point to a separate fluid source, probably involving evolved granites. The late hydrothermal Au-carrying fluids overprinted the early Co mineralisation forming AuCo enriched zones. Our study highlights the potential of multiple isotope systematics in sulphides as a useful diagnostic tool for tracing mineralisation processes in and source regions of hydrothermal Au and Co.

Analysis of runoff and sediment evolution and attribution in the source regions of the Yangtze and Yellow Rivers

Analysis of runoff and sediment evolution and attribution in the source regions of the Yangtze and Yellow Rivers

Atmospheric emissions of microplastics entrained with dust from potential source regions

Atmospheric emissions of microplastics entrained with dust from potential source regions

Global impacts of land use on terrestrial carbon emissions since 1850.

Since the Industrial Revolution, significant changes in global land-use patterns have occurred, which have disrupted terrestrial carbon emissions. However, the disturbance processes, change trends, and distribution patterns are not clear. Therefore, the changes in terrestrial carbon emissions (Eluc) caused by land-use change (LUC) since 1850 were analyzed in this study. The results showed that, owing to the sharp decrease in forestland (-13.39%; 84.26×105km2) and significant increases in built-up land (+1360.4%; 7.21×105km2), cropland (+175.8%; 130.88×105km2), and grassland (+162.6%; 239.73×105km2), the global Eluc increased from 0.42 Pg C in 1850 to 11.05 Pg C in 2018, with an average annual increase of approximately 3.42 Pg C yr-1, while the average annual carbon emissions after the 21st century reached 9.65 Pg C yr-1. Among them, direct Eluc increased by approximately 0.80 Pg C yr-1 and indirect Eluc increased by 2.62 Pg C yr-1. In addition, from 1850 to 2018, global Eluc was approximately 578.26 Pg C, with North America, Europe, and Asia being the largest regional sources. Our results highlight the changing trend and distribution pattern of global terrestrial carbon emissions under the influence of LUC since the Industrial Revolution and provide a scientific basis for regional and sectoral formulation of low-carbon emission-reduction policies and planning of low-carbon land-use patterns.

Radioactive contamination transported to Western Europe with Saharan dust.

The Reggane region, where the first French atmospheric nuclear tests were conducted in the 1960s in Southern Algeria, is located in one of the most active dust source regions responsible for recurrent massive Saharan dust events reaching Western Europe and affecting air quality. After a major outbreak in March 2022, a citizen participative science campaign was launched to study the radioactivity born by the dust. One hundred ten deposit samples were collected from six countries in Western Europe with 53 demonstrated as scientifically representative. Geochemical and mineralogical sample analyses combined with satellite observations and back trajectory calculations confirmed an origin from South Algeria, including the Reggane site. Plutonium isotopic signatures, a unique nuclear bomb fingerprint, remained in the range of the global fallout signatures largely dominated by US and former USSR nuclear tests, significantly different from French fallout signatures. Radioactive contamination detected in all samples did not, however, present a risk to public health in terms of radioactivity exposure.

Characteristics of the IBEX Ribbon and Their Implications for a Source Region Outside the Heliopause

Abstract This paper presents a comprehensive exploration of the Interstellar Boundary Explorer energetic neutral atom (ENA) ribbon, focusing on its spatial and temporal variations over 14 yr. Methodological advancements, including a refined map modeling procedure and a new ribbon separation technique with appropriate error propagation, enable a detailed investigation of the ribbon’s features. Utilizing statistically robust metrics, this study reveals details of the ribbon across energy and time. Key findings include energy- and time-dependent variations in flux, angular radius, ribbon profile width, and higher moments. By applying these metrics, we reveal new complexity to the evolution of the ribbon over time, highlighting the nuanced relationship between it and the solar wind. Furthermore, the study examines for the first time the ribbon as it passes through the starboard/heliotail region (LonEC 120°–180°), revealing properties distinct from other portions of the ribbon. The analysis uncovers an anticorrelation between ribbon width and flux, which provides quantitative support for a multisource ribbon created by a combination of solar wind neutrals that generate a spatiall narrow ribbon component and heliosheath neutrals giving rise to a broad component. Finally, differences in the temporal evolution of the ENA flux at different energies provide additional support that the location of the ribbon source region is beyond the heliopause.

Quasi-weekly oscillation of regional PM2.5 transport over China driven by the synoptic-scale disturbance of the East Asian winter monsoon circulation

Abstract. Regional PM2.5 transport is an important cause of atmospheric environment change. However, the variations in regional PM2.5 transport on a synoptic scale with meteorological drivers have been incomprehensively understood. Therefore, this study is targeted at the quasi-weekly oscillation (QWO) of regional PM2.5 transport over central and eastern China (CEC) with the influence of synoptic-scale disturbance of the East Asian winter monsoon (EAWM) circulation. By constructing the data of daily PM2.5 transport flux in CEC in the winters of 2015–2019, we utilize the extended empirical orthogonal function (EEOF) decomposition and other statistical methods to extract the moving spatial distribution of regional PM2.5 transport over CEC, recognizing the QWO in regional PM2.5 transport with the spatial–temporal variations over CEC. The source–receptor relationship in regional transport of PM2.5 is identified with the 2 d lag effect of the North China Plain, as the upwind source region, on the PM2.5 pollution change in the Twain-Hu Basin, as the downwind receptor region in central China. The QWO of regional PM2.5 transport over CEC is regulated by the synoptic-scale disturbance of the EAWM circulation with the periodic activities of the Siberian high. These findings provide new insights into the understanding of regional PM2.5 transport with the source–receptor relationship and the meteorological mechanism in atmospheric environment change.

Projected changes in moisture sources and sinks affecting the US East Coast and the Caribbean Sea.

This study uses a combination of the FLEXPART Lagrangian dispersion model with the Weather Research and Forecasting (WRF) mesoscale Eulerian model (FLEXPART-WRF) to analyze the expected mid- to late-century changes in the moisture sources and sinks of the North American East Coast (ENA) and the Gulf of Mexico (GM), as well as their most relevant abrupt moisture transport events-atmospheric rivers (ARs) and low-level jets of the Great Plains (GPLLJ) and the Caribbean (CLLJ). Both the ENA and GM are expected to increase in importance as moisture source regions over the century, both overall and in their contributions to the ARs and both LLJs. A notable increase in the intensity of the GPLLJ and CLLJ moisture sources is also observed. All of these behaviors are neither spatially nor temporally homogeneous and need to be analyzed in a seasonal context. Likewise, the most relevant signs of change are practically all observed by the end of the century. Other noteworthy behaviors are also observed, including an increase in humidity associated with landfalling atmospheric river events in the winter months, or a notable latitudinal shift of the CLLJ's area of influence. These findings are best understood within the context of an observed increase in both continental precipitation and sea surfacetemperature.

Composition of pre-Carboniferous siliciclastic rocks in Tasmania

Twelve hundred whole-rock compositions of the Proterozoic and Paleozoic rocks of Tasmania were compiled from a range of published and unpublished sources. We used these data to establish a chemostratigraphic evolution of the island and to resolve several problems in Tasmanian geology. Six chemostratigraphic mega-sequences were defined for Tasmania. The major events that separate these sequences are the onset of continental rifting (ca 700 Ma), arc–continent collision (ca 515 Ma), post-collisional volcanism (506 Ma) and then the return to continental conditions (500 Ma). Within this large-scale classification, we recognised smaller-scale changes in provenance. Within the Mesoproterozoic, there is a trend to more mafic rocks in the source region, which is interrupted by a short period where granites were prominent in the provenance. The Mesoproterozoic rocks of King Island have a subtly different provenance from the shallow water siliciclastic rocks of the Rocky Cape Group. The distribution of Cr across Tasmania can be attributed to two different events. First, the primitive basalts associated with Cryogenian continental rifting introduced a Cr signature associated with high TiO2. The ophiolite obduction event in the Cambrian produced a second Cr enrichment event dominated by chromite from supra-subduction-zone peridotite. These two events can be differentiated by the composition of the sedimentary rocks but are more clearly defined by the composition of detrital spinels. Within the East Tasmanian terrane, a trend to less weathered sources reflects the influx of young volcanic detritus at the end of the Silurian.

Multi-spacecraft observations of the decay phase of solar energetic particle events

The parameters of solar energetic particle (SEP) event profiles such as the onset time and peak time have been researched extensively to obtain information on the acceleration and transport of SEPs. The corotation of particle-filled magnetic flux tubes with the Sun is generally thought to play a minor role in determining intensity profiles. However recent simulations have suggested that corotation affects the SEP decay phases and depends on the location of the observer with respect to the active region associated with the event. We aim to determine whether signatures of corotation are present in observations of the decay phases of SEP events, and we study the dependence of the parameters of the decay phase on the properties of the flares and coronal mass ejections associated with the events. We analysed multi-spacecraft observations of SEP intensity profiles from 11 events between 2020 and 2022 using data from Solar Orbiter, PSP, STEREO-A, and SOHO. We determined the decay-time constant, τ, in three energy channels; electrons ∼1 MeV, protons ∼25 MeV, and protons ∼60 MeV. We studied the dependence of τ on the longitudinal separation, Δ ϕ, between the source of the active region and the spacecraft magnetic footpoint on the Sun. Individual events show a tendency for the decay-time constant to decrease with increasing Δ ϕ. This agrees with test particle simulations. The magnitude of the event as measured through the intensity of the associated flare and SEP peak flux affects the measured τ values and likely is the cause of the observed large inter-event variability together with the varying solar wind and the conditions in the interplanetary magnetic field. We conclude that corotation affects decay phase of an SEP event and should be included in future simulations and interpretations of these events.