Australian Monsoon Research Articles

Insights into the Australian mid-Holocene climate using downscaled climate models

Abstract. The mid-Holocene climate of Australia and the equatorial tropics of the Indonesian–Australian monsoon region is investigated using the Community Earth System Model (CESM) and the Weather Research and Forecasting (WRF) model. Each model is used to simulate the pre-industrial (1850) and the mid-Holocene (6000 years before 1950) climate. The results of these four simulations are compared to existing bioclimatic modelling of temperature and precipitation. The finer-resolution WRF simulations reduce the bias between the model and bioclimatic data results for three of the four variables available in the proxy data set. The model results show that temperatures over southern Australia at the mid-Holocene and in the pre-industrial period were similar, and temperatures were slightly warmer during the mid-Holocene over northern Australia and into the tropics compared to the pre-industrial. During the mid-Holocene, precipitation was generally reduced over northern Australia and in the Indonesian–Australian monsoon region, particularly during summertime. The results highlight the improved value of using finer-resolution models such as WRF to simulate the palaeoclimate.

Early Pleistocene Orbital‐Scale Variability in Australian Northwest Shelf Sediments

AbstractPaleoclimate proxy records from regions sensitive to humidity/aridity extremes provide crucial insights into the natural forcing mechanisms underlying long‐term climate variability in broader regions. One such area is Northwest Australia, where the Australian monsoon impacts its northernmost fringes, which are bordered by the Great Sandy Desert inland. Marine sediments from the Australian Northwest Shelf record fluvial run‐off and eolian dust input during the wet and dry seasons, respectively. The location is therefore ideal for investigating long‐term variability in the Australian monsoon and Northwest Australian dust flux over orbital timescales. However, there are few continuous, high‐resolution paleoclimate records from this region spanning the early Pleistocene, when strong ice‐climate feedbacks of the late Pleistocene did not yet dominate global climate. Here, we present geochemical and environmental magnetic proxy records that reveal %CaCO3 and dust‐flux variability between 2.9 and 1.6 million years (Myr) ago from International Ocean Discovery Program Expedition 356 Site U1464 on the Australian Northwest Shelf. We establish a new, orbitally‐tuned chronology for Site U1464, primarily based on ∼400 thousand year (kyr) eccentricity cyclicity in %CaCO3, and observe strong obliquity variability (41 and 54 kyr periodicities) but almost no precession signal in the dust‐flux records. We propose that the 41 kyr cycle in Northwest Australian dust flux could be a linear response to East Asian winter monsoon intensity and/or the summer inter‐tropical insolation gradient (SITIG), whereas the 54 kyr cyclicity might be a non‐linear response to obliquity amplitude modulation via the SITIG effect on the cross‐equatorial atmospheric circulations.

Detection of Dominant Rainfall Patterns in Indonesian Regions Using Empirical Orthogonal Function (EOF) and Its Relation with ENSO and IOD Events

Several studies indicate that Indonesia’s position on the equator, where winds from the northern and southern hemispheres converge, leads to year-round rainfall in Indonesia. Previous studies have also shown the presence of monsoon winds over Indonesia, which causes rain in Indonesia to follow the Asian and Australian monsoon wind patterns. Recently, variations in rainfall patterns and intensity in Indonesia have been highly volatile and difficult to predict. This study uses gridded data analysis of ocean-atmospheric rainfall for 69 years (1948–2016) to detect monsoonal, equatorial, and local signals and relate them to ENSO and IOD events. Rainfall analysis reveals that the first mode accounts for 38.57%, the second 13.92%, and the third 8.93% of the total variance. These results show that these variants are very variable, both in space and time. Monsoonal patterns were detected in the southern region of Indonesia, equatorial patterns in northern Sumatra and western Kalimantan, while local patterns were detected in Maluku and the Maluku Islands. Furthermore, the monsoonal and local rainfall patterns are strongly correlated (> 0.85) with local SST, but the equatorial rainfall pattern is weakly correlated (< 0.5) with local SST. Note that the equatorial pattern is associated with the Inter Tropical Convergence Zone (ITCZ) phase. The varied vector correlation map illustrates the asymmetric fluctuations in sea surface temperature and the simultaneous existence of winds coming from the west from the Indian Ocean and winds coming from the east from the Pacific Ocean during the period of heavy precipitation.

Trend of Halmahera Eddy and Mindanao Eddy

Global warming, due to increasing greenhouse gases, has increased the frequency of El Niño Southern Oscillation events and influenced ocean dynamics. This research determined the trends of Mindanao Eddy’s and Halmahera Eddy’s over 28 years (1993–2020). The data used in this research consist of sea surface currents, surface wind, sea surface height, and NIŇO3.4 index. Determination of eddy currents was done using the Automated Eddies Detection method. The results showed that the Asian-Australian monsoon and El Niño Southern Oscillation events influence the characteristics of the Mindanao Eddy and Halmahera Eddy. During the Asian monsoon, the position of the Mindanao Eddy and Halmahera Eddy shifts southward, while during the Australian monsoon, it shifts northward. During El Niño, the position of the Mindanao Eddy turns eastward with a smaller diameter, but the position of the Halmahera Eddy does not shift. Conversely, during La Niña, the position of the Halmahera Eddy turns northwestward with a smaller diameter, while the position of the Mindanao Eddy remains unchanged. The shift of the Mindanao Eddy during the El Niño event is closely related to the weakening of the North Equatorial Current and the strengthening of the North Equatorial Countercurrent. On the other hand, the shift of the Halmahera Eddy during the La Niña event is related to the strengthening of the South Equatorial Current as a source of water masses for the New Guinea Coastal Current. The velocity of the Mindanao Eddy and Halmahera Eddy experienced an increasing trend in 1993-2020.

Rediscovery, systematics and conservation of an enigmatic freshwater crayfish (Parastacidae) from the Australian monsoon tropics

AbstractFreshwater wetlands are among the world's most valuable ecosystems, supporting diverse biota and critical ecological services, yet these habitats have suffered extensive and pervasive anthropogenic disturbance. Northern Australia represents a rare example of a relatively unmodified, vast wetland habitat. The freshwater crayfishes of the region are poorly documented, with one enigmatic species, the nutcracker yabby Cherax nucifraga, described from a single individual sampled opportunistically from the stomach of a predatory fish. Here we report on the rediscovery of C. nucifraga from a relatively limited distribution in semi‐permanent coastal freshwater wetlands. Field studies were conducted to inform natural resource management and conservation. Genome skimming to recover mitogenomes, 18S–28S and histone sequences demonstrated a sister relationship with two congeners from the tropics, and moderate molecular genetic substructure was apparent within C. nucifraga between mainland and Melville Island locations. Cherax nucifraga is characterised by the presence of a strawberry‐coloured soft patch on the outer margin of the claw, uniquely present in both mature males and females. Meristic and multivariate morphometric comparisons are made with the co‐occurring redclaw Cherax quadricarinatus and the allopatric whiteclaw yabby Cherax bicarinatus, with a summary of diagnostic traits developed into a visual guide and key. Programs to further understand ecology, threats and traditional ecological knowledge will help to inform the future conservation management of the species in the face of increasing development and environmental change to northern Australian coastal freshwater wetlands. Specific conservation actions include identifying and protecting refuge habitats and preventing incursions by other Cherax species.

Impacts of the Asian Australian Monsoon and Indo Pacific Sea Surface Temperature on Urban Climates in Major Indonesian Cities for Low Carbon Building Design

Impacts of the Asian Australian Monsoon and Indo Pacific Sea Surface Temperature on Urban Climates in Major Indonesian Cities for Low Carbon Building Design

Climatological Madden-Julian Oscillation during boreal spring leads to abrupt Australian monsoon retreat and Asian monsoon onsets

Abrupt monsoon onsets/retreats are indispensable targets for climate prediction and future projection, but the origins of their abruptness remain elusive. This study establishes the existence of three climatological Madden-Julian Oscillation (CMJO) episodes contributing to the rapid Australian summer monsoon retreat in mid-March, the South China Sea (or East Asian) summer monsoon onset in mid-May, and the Indian summer monsoon onset in early June. The CMJO displays a dynamically coherent convection-circulation structure resembling its transitionary counterpart, demonstrating its robustness as a convectively coupled circulation system and the tendency of the transient MJOs’ phase-lock to the annual cycle. The CMJO is inactive during the boreal winter due to destructive year-to-year modulations of El Niño-Southern Oscillation. We hypothesize that the interaction between atmospheric internal variability (MJO) and the insolation-forced slow annual cycle generates the sudden monsoon withdrawal/onset during the boreal spring. Understanding the factors determining the timing and location of the MJO’s phase-locking and its variability is vital for monsoon forecasting and climate projection.

Australian Summer Monsoon Bursts: A Moist Static Energy Budget Perspective

AbstractThe Australian monsoon's wet season is associated with sequences of wet and dry conditions known as bursts and breaks, which usually have timescales of a week or two. There are several hypotheses for the physical processes involved in monsoon bursts, ranging from the effects of the Madden‐Julian Oscillation to extratropical influences. We analyze rainfall bursts in Northern Australia using a moist static energy (MSE) budget framework. We separate the bursts into three types and further separate them into pre‐monsoon, active monsoon, and post‐monsoon. We then apply ERA5 data to calculate the MSE budget for each burst and construct composite bursts for each of the three types. We find that the horizontal advection of MSE over the tropical northern Australian convergence zone is the most critical term in the budget for the day‐to‐day precipitation variation. MSE‐related gross moist stability analysis reveals that each type has distinct characteristics. The burst type associated with active monsoon bursts displays convective growth and decay patterns both before and after the precipitation peak, which is typical of oceanic convection. A low‐rainfall burst type, which is often seen before monsoon onset, is linked to coastal convection and has minimal rainfall decay after the burst. Finally, a sustained high‐rainfall burst type, mostly observed at the end or after the monsoon retreat, has growth characteristics similar to the typical monsoon burst but does not decay, maintaining very high rainfall for at least a week due to a rearrangement of the circulation and local thermodynamic structure of the atmosphere.

A strange negative Indian Ocean Dipole (IOD) in 2022

The Indian Ocean Dipole (IOD) is a prominent pattern of climatic mode in the Indian Ocean that contributes to the changes in Rainfall pattern, Sea Surface Temperature (SST), and Surface Salinity (SSS) in the Indian Ocean. Recently in the scenario of Climate Change, this IOD may experience shifting in the phases development that link to the Indo-Pacific teleconnection. Here, we analyse the changes of negative IOD patterns in 2022 through the SST, SSS, rainfall pattern, and surface current system. This study showed the negative IOD was initiated earlier and coincided with the Asian monsoon during May 2022. The IOD is faster ended in October 2022 when the Australian Monsoon was generated. The Rainfall pattern at the Eastern Indian Ocean (EIO) and the Indonesian Archipelago experienced an intensive pattern from May up to December 2022. During the negative IOD phases, the precipitation at the EIO is more concentrated in Java and less precipitation in Sumatra. The warmer SST and fresh surface salinity in the Indonesian Archipelago are wider following the Pacific SST. This reveals the Indo-Pacific teleconnection is stronger during 2022 via the surface ocean patterns and the coincidence of stronger westerly wind and easterly wind in the maritime continent.

Pacific‐Driven Salinity Variability in the Timor Passage Since 1777

AbstractSalinity in the Indonesian seas integrates regional oceanographic and atmospheric processes, such as Indonesian Throughflow (ITF) and monsoon rainfall. Here we present a multicentury (1777–1983) δ18O coral record from Nightcliff Reef, located in the Timor Passage off the coast of northern Australia, which we use to infer local salinity change. We show that Australian monsoon rainfall and ITF influence salinity at the study site. These reconstructed salinity changes in the Timor Passage correlate with changes in Pacific sea surface temperature (SST) modes, including the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). While environmental stress creates challenging conditions for coral growth, this record particularly tracks the central Pacific signature of ENSO‐driven interannual variability, in agreement with reconstructions of rainfall across northern Australia. The strength of interannual variance in the record follows fluctuations in other local ENSO‐sensitive rainfall reconstructions, demonstrating a strong regional ENSO signature. However, this regional pattern differs from variance in composite ENSO reconstructions, suggesting that the multi‐site nature of these reconstructions may create biases. Salinity variability on decadal and longer time scales occurs throughout the record. Some of these oscillations are consistent with other ITF‐sensitive coral records. Our new salinity record adds a strongly Pacific‐sensitive record to the existing suite of regional paleoclimate reconstructions. Relationships among these records highlight the complexity of salinity in the Indonesian seas and the controls on its variability.

Seasonal Variation of Rainfall in Indonesia under Normal Conditions without ENSO and IOD Events from 1981-2021

This study explores the seasonal rainfall variation in Indonesia under normal conditions, excluding the influence of El-Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events. Monthly rainfall data is sourced from the CHIRPS dataset, and wind and atmospheric movement data are obtained from the ECMWF ERA-5 dataset. Identification of normal conditions relies on the ONI and DMI indices. Results reveal that the seasonal rainfall patterns during these normal conditions align with previous studies encompassing all atmospheric conditions. Indonesia typically witnesses one or two peaks in rainfall annually, notably in December-January-February (DJF), May-June (MJ), and March-April-May (MAM), consistent with established rainfall zone classifications in earlier research. A nuanced discrepancy emerges in the timing of the May-June peak, previously noted in June-July. The congruence in peak rainfall patterns during normal conditions, as observed in prior comprehensive research, implies a negligible influence of ENSO and IOD on the timing of seasonal rainfall peaks. Although ENSO and IOD may impact the amplitude of seasonal variation, particularly in Indonesia's eastern and western regions, they do not alter the temporal occurrence of rainfall peaks. Consequently, the timing of rainfall peaks in Indonesia predominantly reflects the combined influence of the Asian and Australian monsoons.

Characteristics of atmospheric variables over the southern coast of West Java in the presence of Australian Monsoon and MRG waves

The characteristics of atmospheric variables over the southern coast of West Java in the presence of Australian Monsoon (AUM) and Mixed Rossby-Gravity (MRG) waves were investigated by conducting a dedicated radiosonde observation campaign from 26 to 29 September 2022 at Pameungpeuk Station (107.7°E, 7.6°S). The vertical profiles of pressure, temperature, relative humidity, and wind in the presence of the AUM and MRG waves were obtained and analyzed. The Global Navigation Satellite System - Radio Occultation (GNSS-RO) and the latest ECMWF climate reanalysis (ERA5) data were used to identify the MRG waves features using Hovmöller, space-time spectral, and wavelet analyses. Furthermore, spatial and time-series analyses were performed to study the wave propagation. The results showed the characteristics of atmospheric variables over Pameungpeuk Station in the presence of the AUM and MRG waves. We found that the presence of AUM significantly reduced the relative humidity, particularly in the region from 2 to 10 km altitude, and enhanced the average wind speed during the campaign compared to the wet season. Moreover, we found the reduction of low-level pressure, the enhancement of temperature and relative humidity in the mid-troposphere, and the weakening of the easterly and southerly winds during the dry phase approaching the wet phase of the MRG waves over the southern coast of West Java following the wave structure and propagation.

Variability of the Indonesian Throughflow and Australian monsoon across the mid Pleistocene transition (IODP 363, Site U1483)

The Mid-Pleistocene Transition (MPT) between ∼1200 and ∼800 ka was associated with a major shift in global climate and was marked by a change in glacial/interglacial periodicity from ∼41 to ∼100 kyr that resulted in higher-amplitude sea-level variations and intensified glacial cooling. The sensitivity of the Indonesian Throughflow (ITF), and the Asian-Australian Monsoon dynamics to changing MPT climate remains controversial, although its understanding is important to constrain future climate projections. In this study, we analyzed radiolarian assemblages in core top samples retrieved during the RV Sonne Expedition 257 and in downcore samples from International Ocean Discovery Program (IODP) Site U1483 to estimate the variability in regional sea surface temperatures (SSTs), and to explore ITF dynamics in relation to glacio-eustatic sea-level variations and tropical monsoon strength during the MPT. Our results suggest that tropical monsoon strength and glacio-eustatic sea-level change influenced SST variations at Site U1483. Comparisons with SST data from the mid latitudes off Northwest Australia and the South China Sea suggest that SST variations at Site U1483 and in the ITF outflow into the Timor Sea are highly dependent on prevailing climate changes in the source region of the ITF, rather than on southern hemisphere. atmospheric circulation. In addition, comparisons of radiolarian abundances with X-ray fluorescence-scanning elemental data indicate that until ∼980 ka radiolarian productivity was higher during strong interglacial summer monsoons, likely because of the riverine runoff generated by monsoonal precipitation. However, at ∼980 ka pronounced winter monsoon cooling was associated with a re-organization of radiolarian production patterns in the Timor Sea.

Fire regime shapes butterfly communities through changes in nectar resources in an Australian tropical savanna

AbstractFire‐dependent savanna provides key habitat for butterflies globally, but we know little about how fire regimes, including fire frequency and season, affect them. These impacts are likely to be primarily indirect, through changes in overall habitat structure, the abundance of larval host plants, and/or the provision of nectar resources for adults. We examined the relationships among fire regime, butterfly abundance and diversity, and vegetation structure and floral resources within a long‐term fire experiment near Darwin in the Australian monsoon tropics. We surveyed butterflies and floral resources throughout the 2019–2020 wet season in three replicate plots of each of six experimental treatments that had been operating for 15 years. All plots subject to fire had been burned in the previous dry season. We observed 24 butterfly species and 280 individuals representing all five butterfly families found in Northern Australia. Butterfly abundance was highest under early dry‐season (June) fire regimes (mean = 11.9 individuals per plot survey) compared with a late dry‐season (October) regime (mean = 6.7) and in the long‐term absence of fire (mean = 5.3), and this was correlated with the abundance of floral resources. The distribution of butterflies was also highly associated with floral resources within plots regardless of fire treatment. Butterfly species richness was significantly higher in early dry‐season (mean = 6.8) compared with unburned (mean = 3.3) plots but did not differ between early and late dry‐season (mean = 4.7) plots. Butterfly and floral diversity were similar across all early dry‐season fire treatments regardless of whether they had been burned every 1, 2, 3, or 5 years. Our finding that early dry‐season burning promotes butterfly diversity and abundance by increasing the supply of nectar resources has important implications for biodiversity management more broadly, given that nectar is a critical resource for many animal taxa.

Revision of Litoria rothii (Anura: Pelodryadidae) from northern Australia.

Litoria rothii is a widespread pelodryadid frog with a charismatic laughing advertisement call, distributed across the Australian Monsoon Tropics and southern New Guinea. Given its large distribution spanning well-known biogeographic barriers, variation in male advertisement calls and the prevalence of unresolved species complexes in the Australian frog fauna, we examine the genetic, morphological and acoustic diversity in the species from across its range. Our analyses reveal the presence of a previously unrecognised species in western parts of the range of L. rothii sensu lato, which we describe herein as a new species. Litoria ridibunda sp. nov. is distinguished from L. rothii on the basis of paraphyly of nuclear gene trees with L. everetti from Indonesia, colour patterns on the posterior thigh and male advertisement calls. Compared to L. rothii, the new species has a less contrasting pattern on the posterior thigh and a male advertisement call with a greater number of notes per call and a greater call duration. In particular, the magnitude of call differences between the species is highest where the ranges of the two species are in proximity in north-western Queensland. Our study further emphasises the undiagnosed diversity that remains in Australian frogs, even in relatively large, charismatic, frequently encountered species that often share human dwellings.

The Utilization of Seasonal Variation of Ocean Wave Characteristics Identification in Monitoring the Chlorophyll-a Distribution in South Sulawesi

South Sulawesi is one of Indonesia’s provinces with various forms of waters around its territory, such as the sea, strait, the Spermonde archipelago, and bay. This geographical condition makes it interesting to examine what phenomena can affect the characteristics and variability of ocean waves in each type to increase efficiency and effectiveness in carrying out activities in the waters, especially fishing. By utilizing the BMKG Ina-Waves wave model and NASA’s Aqua MODIS satellite image, the characteristics and variations of ocean waves and the level of fertility of the waters around South Sulawesi Province can be seen. Based on the climatological analysis of wind, ocean waves, and the distribution of chlorophyll-a in this study, the results showed that the Asian and Australian monsoon phenomena greatly influenced these three parameters. The monsoon winds increase the average wave height and affect the distribution of chlorophyll-a concentrations in the waters of South Sulawesi and its surroundings. Efficiency and effectiveness of fishing at sea are carried out during the transition season in the coastal waters of South Sulawesi so that the risk of sea accidents can be minimized.

Aridification of Northwest Australia and Nutrient Decline in the Timor Sea During the 40 Kyr World

AbstractStudying tropical hydroclimate and productivity change in the past is critical for understanding global climate dynamics. Northwest Australia is an ideal location for investigating Australian monsoon dynamics, the variability of the Indonesian Throughflow (ITF), and their impact on past productivity and Pacific warm pool evolution, which remain poorly understood during the 40 kyr world in the mid‐early Pleistocene. In this study, we present multi‐proxy records from International Ocean Discovery Program (IODP) Site U1483 in the Timor Sea spanning the last 2,000 ka, including orbitally‐resolved records from the 40 kyr world between 2,000 and 1,300 ka. Our results suggest that northwest Australia underwent a step of increased aridification and that productivity in the Timor Sea declined during the transition from ∼1,700 to ∼1,400 ka. We attribute this aridification to the reduced moisture supply to this region caused by the ITF restriction and warm pool contraction. We ascribe the declined productivity to a decrease in the nutrient supply of the Pacific source water associated with global nutrient redistribution. At orbital timescale, multiple mechanisms, including sea level changes, monsoon, and the Intertropical Convergence Zone (ITCZ) dynamics, and variations in the ITF and Walker circulation could have controlled variations of productivity and terrigenous input in the Timor Sea during the 40 kyr world. Our bulk nitrogen and benthic carbon isotope records suggest a strong coupling to biogeochemical changes in the Pacific during this period. This research contributes to a better understanding of tropical hydroclimate and productivity changes during the 40 kyr world.

Taxonomic revision of Australian <i>Erythrophleum</i> (Fabaceae: Caesalpinioideae) including description of two new species

The genus <i>Erythrophleum</i> Afzel ex R.Br. is revised for Australia and three species are recognised, all previously included in <i>E. chlorostachys</i> (F.Muell.) Baill. <i>Erythrophleum arenarium</i> R.L.Barrett & M.D.Barrett is described as a new species to accommodate populations from desert sands of the Great Sandy Desert and Dampier Botanical Districts in north-western Australia, parapatric to the remaining species. <i>Erythrophleum pubescens</i> R.L.Barrett & M.D.Barrett is described as a new species spanning tropical Australia, and is sympatric with <i>E. chlorostachys sensu stricto</i> in the Northern Territory and adjacent areas of Western Australia and Queensland. Morphological examination has shown these three taxa to be consistently distinct across their respective ranges. Analyses of the nuclear ribosomal <i>ITS1</i> region recovered three well-supported clades corresponding to the three morphologically defined species, and <i>ITS1</i> has utility as a marker to separate sterile specimens. <i>Erythrophleum pubescens</i> is widespread in the Australian Monsoon Tropics, from the coast of Western Australia, near Derby, to Cape York Peninsula in northern Queensland. <i>Erythrophleum chlorostachys</i> is also widespread, from the eastern Kimberley Region, in Western Australia, to the Gulf of Carpentaria, in northern Queensland. A lectotype is chosen for <i>Laboucheria chlorostachya</i> F.Muell. Full descriptions, illustrations of key features and identification keys are provided for the three Australian species. A summary of the significant utilisation of <i>Erythrophleum</i> species is presented.

Divergent rainforest tree microbiomes between phases of the monsoon cycle, host plants and tissues.

The Australian Monsoon Tropics (AMT) contain some of the most biodiverse forests on the continent. Little is known about the dynamics of rainforest plant microbiomes in general, and there have been no community-level studies on Australian rainforest endophytes, their seasonality, tissue and host specificity. We tested whether community composition of tropical tree endophytes (fungi and bacteria) differs: (i) at different points during a monsoon cycle, (ii) between leaf and stem tissues, (iii) between forest microclimates (gully/ridge), and between (iv) host plant species, and (v) host plant clade, using amplicon sequencing of the bacterial 16S and fungal ITS2 gene regions. Results indicated that the composition of rainforest plant microbiomes differs between wet and dry seasons, which may be explained by physiological shifts in host plants due to annual climate fluctuations from mesic to xeric. Endophyte microbiomes differed between leaves and stems. Distinct fungal communities were associated with host species and clades, with some trees enriched in a number of fungal taxa compared to host plants in other clades. Diversity of bacterial endophytes in plant stems increased in the dry season. We conclude that the microbiomes of tropical plants are responsive to monsoonal climate variation, are highly compartmentalised between plant tissues, and may be partly shaped by the relatedness of their host plants.

A new species of trapezitine skipper (Lepidoptera: Hesperiidae) from the Kimberley in the Australian Monsoon Tropics

A new species of skipper butterfly, Toxidia aurantia Braby, sp. nov., is illustrated, diagnosed and described from the northern Kimberley of Western Australia. A molecular phylogeny based on one mitochondrial (COX1 barcode fragment) and four nuclear genes (EF1-a, RSB2, RSB5, Wingless) for nearly all members of Toxidia Mabille, 1891 and its sister genus Timoconia Strand, 1909 according to the Maximum Likelihood optimality criterion, indicated that the new species belongs in the Toxidia xanthomera species-group (formerly classified in the genus Neohesperilla Waterhouse & Lyell, 1914) and is most closely related to T. crocea (Miskin, 1889). These two taxa are sister to T. xiphiphora (Lower, 1911). Toxidia aurantia Braby, sp. nov. is currently known from only a limited area on the mainland in the Admiralty Gulf near the Osborn Islands and Borda Island, WA. The discovery of this new species contributes to the emerging picture that the northern Kimberley is likely an area of high species richness for butterflies and day-flying moths within the Australian Monsoon Tropics.