Northwest Australia Research Articles

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.

Early-stage intracontinental rifting in the Neoproterozoic Centralian Superbasin: Systematic U–Pb and Lu–Hf isotopes in detrital and inherited zircons from the Yeneena Basin, northwest Australia

Detrital zircons from different lithostratigraphic units of Supersequence 1 across the Neoproterozoic northwest Officer and Yeneena basins were investigated using LA-ICPMS U−Pb and Lu − Hf isotope analyses to understand the source of detritus and potential links to regional tectono-magmatic events, as well as the crustal evolution of the sedimentary sources terranes. All data show that Proterozoic detritus dominate the age spectra of samples from the Yeneena Basin and northwest Officer Basin, with signatures varying in the heights of peaks rather than the presence or absence of age groups in different formations. The Archean and Proterozoic ages overlap with known magmatic events in the Pilbara Craton, Fortescue Basin, Rudall Province, Capricorn Orogen, Musgrave Province, Madura Province, and the Coompana Province suggesting these terranes are possible sources of the detritus. The detrital zircon population of the samples have main age peaks in the range 1300 to 1000 Ma, suggesting magmatic rocks of the Rudall and Musgrave provinces are the main sources of detrital zircons, which can be differentiated by Hf signature. The distal Musgrave Province persistently dominates the provenance of detritus in the northwestern Officer and Yeneena basins, while detritus from the proximal Rudall Province contributes to a lesser extent. This suggests that the distal Musgrave Province remained emergent during the evolution of the northwestern Officer Basin and the Yeneena Basin, whereas the proximal Rudall Province potentially became buried by the accumulating sedimentary rocks and contributed less detrital zircons. The 833.6 ± 1.4 Ma maximum depositional age obtained in this study for the sedimentary rocks of the northwestern Officer and Yeneena basins point to the approximate time of the start of basins development. The extensional event in this age period is related to emplacement and extrusion of the ca. 830 Ma Willouran Large Igneous Province (LIP). The Duke gabbro sills observed in the Yeneena Basin are part of this LIP, which extends from the Adelaide Rift Complex, through the Musgrave Province, central–northwest Officer Basin and into the Yeneena Basin. The sediment source terranes suggest a southeast–northwest oriented depositional system between central and Western Australia, possibly because of intracontinental rifting related to widespread mafic–ultramafic magmatic events that could include the earlier Ngaanyatjarra Rift formed by the 1090–1040 Ma Warakurna LIP as well as the ca. 830 Ma Willouran LIP, synchronous with the breakup of Rodinia in the mid-Neoproterozoic.

Healing country together: A seagrass restoration case study from Gathaagudu (Shark Bay)

Ecological restoration is a key part of the global solution to help repair damaged ecosystems and moderate climate change. However, there are enormous challenges to contemporary restoration. Solutions that integrate western science and traditional ecological knowledge offer great opportunities to overcome these challenges. Partnerships with Indigenous Ranger programs can assist with solutions to some of the age-old restoration challenges. Managing and caring for a living and dynamic Country is at the heart of wellbeing for all Indigenous Peoples. The act of participating in restoration activities On Country assists with connecting to Country, healing people and Country. We describe the development of a successful partnership between western science and Indigenous traditional knowledge via a collaborative Malgana Aboriginal Corporation Ranger program that included On Country workshop-based knowledge sharing in north-west Western Australia, with a focus on seagrass restoration. Field-based restoration workshops helped people reconnect with Country through two-way knowledge sharing. Additional benefits of the partnership included education and preservation of Malgana language, educating western scientists and general public about Malgana culture, and adapting and field trialling seagrass restoration methods for Gathaagudu. Restoration can be successfully implemented through partnerships that share western science and traditional ecological knowledge.

A 47,000 year archaeological and palaeoenvironmental record from Juukan 2 rockshelter on the western Hamersley Plateau of the Pilbara region, Western Australia

Archaeological and palaeoenvironmental investigations at Juukan 2 rockshelter have yielded new information on the ancient Aboriginal occupation of the Pilbara uplands in northwest Australia. Using multiple lines of evidence, including lithic, faunal, pollen, ancient DNA, radiocarbon dating, optically stimulated luminescence, and Bayesian chronological modelling, we show that Aboriginal people occupied the western Hamersley Plateau as early as 47,000 years ago (47 ka). Late Pleistocene populations utilised a diverse range of tool technologies, including bone points, grindstones, and flaked stone artefacts. Palaeoclimatic conditions at Juukan 2 rockshelter varied greatly over the past 47 ka, with repeated site visits by people, including during the peak hyper-arid phase of the Last Glacial Maximum (LGM) c. 21 ± 2 ka. Ancient starch analyses of the ground stone artefacts show the processing of Ipomoea (Bush Potato) from around 42 ka to the present day. Pronounced increases in the discard of stone artefacts and bone in the last 3500 years are interpreted to be the result of increased frequency of site use. A braided hair fragment dated to this period has demonstrated genetic links between the earlier rockshelter occupants and contemporary Puutu Kunti Kurrama and Pinikura peoples, who have maintained strong cultural connections to the area.

Trees to remember: culturally modified boab trees in the face of climate change

ABSTRACT Culturally modified trees (CMTs) are a unique form of archaeology and cultural heritage. There are several factors affecting the survival of culturally modified trees in Australia, and these will all likely be exacerbated by climate change. Boab trees (Adansonia gregorii), which are endemic to northwest Australia, have been subject to modification by Indigenous people both prior to and following the settlement of the Kimberley region by European and Anglo-Australians. Many of the potential impacts of climate change on boab tree survival are yet to be determined, but a range of new threats are emerging as potential endangerment. Through the insights of Indigenous knowledge, this paper discusses one particularly significant boab tree in Nyikina Country and how its demise may be linked to erroneous human actions in the recent past. This provides a unique perspective on how the complexities of climate change may be conceptualised through living knowledge and experience.

The magma plumbing system of the Northern Carnarvon Basin, offshore Australia: multiscale controls on basin-wide magma emplacement, and implications for petroleum exploration

Abstract The Northern Carnarvon Basin (NCB) located on Australia's North West Shelf hosts an extensive (∼40 000 km 2 ) intrusive igneous complex related to Mesozoic rifting and break-up. Using an extensive suite of modern 3D seismic reflection surveys, we have mapped this intrusive system across the NCB. We identify three predominant intrusion morphologies: stacked sheets of large interconnected sill intrusions (up to ∼170 km long) and smaller (8–30 km long) isolated, strata concordant intrusions, which often interact with normal faults emplaced into deltaic sedimentary rocks, and variably sized (10–40 km long) saucer-shaped intrusions emplaced into marine shales, spread across seven zones (geographically constrained groups of intrusions of a specific morphology). We consider the zones’ margin-parallel orientation, suggesting control by subcrustal extensional processes during rifting, and the variation in intrusion morphology between these zones, suggesting a dominant control by host rock mechanical properties. We integrate previous work with our observations, constraining emplacement to between the Kimmeridgian and Valanginian, coinciding with key phases of margin evolution. Finally, we assess the impact of this intrusive complex on local petroleum systems. There is likely little to no adverse impact on source rock maturation or reservoir contamination by CO 2 , but there is a spatial dissociation between the location of groups of intrusions and the gas fields, particularly in the Exmouth Plateau. This suggests that migrating hydrocarbons may be blocked, baffled and/or redirected by emplaced igneous rocks.

Developing plant functional groups to identify changes in functional composition and diversity in a dryland river experiencing artificially sustained flows

Land use and climate changes are driving significant shifts in the magnitude and persistence of dryland stream surface flows. The impact of these shifts on ecological functioning is largely unknown, particularly where streams have become wetter rather than drier. This study investigated relationships between hydrologic regime (including surface water persistence, differences in groundwater depth and altered flooding dynamics) with plant traits and riverine vegetation functional composition. Our study system was a previously ephemeral creek in semi-arid northwest Australia that has received groundwater discharge from nearby mining operations for >15 years; surface flows are now persistent for ∼27 km downstream of the discharge point. We aimed to (i) identify plant functional groups (FGs) associated with the creek and adjacent floodplain; and (ii) assess their distribution across hydrological gradients to predict shifts in ecological functioning in response to changing flow regimes. Seven FGs were identified using hierarchical clustering of 40 woody perennial plant species based on morphometric, phenological and physiologic traits. We then investigated how FG abundance (projective foliar cover), functional composition, and functional and taxonomic richness varied along a 14 km gradient from persistent to ephemeral flows, varying groundwater depths, and distances from the stream channel. Dominant FGs were (i) drought avoidant mesic trees that are fluvial stress tolerant, or (ii) drought tolerant xeric tall shrubs that are fluvial stress intolerant. The drought avoidant mesic tree FG was associated with shallow groundwater but exhibited lower cover in riparian areas closer to the discharge (persistent surface flows). However, there were more FGs and higher species richness closer to the discharge point, particularly on the floodplain. Our findings demonstrate that quantifying FG distribution and diversity is a significant step in both assessing the impacts of mine water discharge on riverine ecosystems and for planning for post-mining restoration.

Leeuwin current dynamics in the SE Indian Ocean and implications for regional surface hydrography since the latest Miocene: Results from ODP Site 763A

This study examines the relationship between the ocean circulation dynamics in the eastern Indian Ocean and climate variability in Northwest (NW) Australia over the last 6.1 million years. The vertical water column of the southeastern Indian Ocean was analyzed using planktic foraminifera assemblages, and oxygen and carbon isotope ratios of surface and subsurface dwelling foraminifera from Ocean Drilling Program (ODP) Site 763A. The X-ray fluorescence data of bulk sediment from ODP Site 763A was also used to understand variability in relative humidity and aridity in NW Australia associated with surface ocean warming. The findings suggest a pronounced change in surface oceanography and climate in the region from 5.4 to 5 Ma, indicating a weak Leeuwin Current (LC) and reduction in mixed layer thickness. Subsequently, between 5.0 and 3.6 Ma, a strongly stratified water column with a thick mixed layer and deep thermocline emerged owing to the intensified Indonesian Throughflow (ITF). This led to a strengthened LC and diminished surface productivity, corresponding to a wet phase in NW Australia. The closure of the Indonesian Seaway during the Middle Pliocene (3.6–3.2 Ma) restricted the flow of West Pacific Warm Water into the Indian Ocean, weakened the LC and intensified the dry phase in NW Australia. Significant shifts in planktic foraminifera abundances are observed in the early Pleistocene (2.6–1.2 Ma) perhaps linked to major changes in surface ocean circulation. During the Mid-Pleistocene Transition (1.2–0.6 Ma), the West Australian Current exerted a significant influence over Site 763A.

Flatback futures—evaluating conservation interventions to reduce threats to an endemic Australian turtle

Australia’s endemic flatback turtle Natator depressus is the focus of a long-term conservation program aimed at securing the persistence of healthy populations in the northwest of Australia into the future. Primary threats to flatback turtles include (1) sea level rise, (2) predation from introduced species, (3) temperature increases, (4) onshore and nearshore light, (5) marine debris, and (6) modification to beaches. Population declines resulting from these threats have been reported or are anticipated, and a range of intervention options are possible that may limit their negative impact. Following methods previously developed and applied to iconic marine species and habitats, we generated a range of intervention options, and asked experts to prioritise those actions using an intervention prioritisation tool (IPT) and the public to prioritise based on social acceptability assessment (SAS). The IPT allows different conservation interventions to be assessed based on their economic cost, implementation feasibility, social acceptability, and perceived effectiveness in maintaining or increasing future turtle populations while simultaneously accounting for expert confidence in their assessment. Results generated by the IPT and SAS can be explored further to resolve uncertainty, a process that can help managers and experts alike in their decision-making process associated with flatback conservation. While this paper is focused on interventions relating to flatback turtles, we propose that our IPT can be applied in different settings to enable consideration of interventions for a range of threatened species and habitats to guide research and conservation investment decisions by managers.

Detection of Traveling Ionospheric Disturbances Triggered by 2022 Tonga Volcanic Eruptions Through CubeSats Coherent GNSS‐Reflectometry Measurement

AbstractWe present two case studies of traveling ionospheric disturbances (TIDs) triggered by the 2022 Tonga volcanic eruption observed by low‐cost CubeSat‐based global navigation satellite system reflectometry (GNSS‐R) measurements. The GNSS‐R data used in this work are from Spire Global CubeSats. Our analysis shows that coherent GNSS signals reflected over the ocean can be used to derive precise ionospheric total electron content (TEC) measurements. The first case shows clear TID structures with a TEC disturbance magnitude of ∼1 TEC unit (TECu) and horizontal wavelength of ∼330 km over Northwest Australia on the day of Tonga volcanic eruption. The second case shows the TIDs with ∼0.05 TECu disturbance magnitude and horizontal wavelength of ∼240 km over East Russia the day after the eruption. The second case is likely a TIDs propagated outward from Tonga for the second time after it traversed around the Earth. The GNSS‐R observed TID may be associated with the incident or reflection signal ray path. In this paper, the appropriate ray path was identified using simultaneous observations from ground receiver networks in the areas of both ray paths.

Resilience to periodic disturbances and the long-term genetic stability in Acropora coral

Climate change is restructuring natural ecosystems. The direct impacts of these events on biodiversity and community structure are widely documented, but the impacts on the genetic variation of populations remains largely unknown. We monitored populations of Acropora coral on a remote coral reef system in northwest Australia for two decades and through multiple cycles of impact and recovery. We combined these demographic data with a temporal genetic dataset of a common broadcast spawning corymbose Acropora to explore the spatial and temporal patterns of connectivity underlying recovery. Our data show that broad-scale dispersal and post-recruitment survival drive recovery from recurrent disturbances, including mass bleaching and mortality. Consequently, genetic diversity and associated patterns of connectivity are maintained through time in the broader metapopulation. The results highlight an inherent resilience in these globally threatened species of coral and showcase their ability to cope with multiple disturbances, given enough time to recover is permitted.

Environmental DNA metabarcoding for the detection of the silverlip pearl oyster (Pinctada maxima) offshore of Eighty Mile Beach in northwest Australia

Effective fishery management relies on accurate knowledge of the spatial distribution of stocks of target species to efficiently focus fishing efforts. However, the distribution and abundance of species such as the silverlip pearl oyster (Pinctada maxima) can be difficult to determine with traditional survey methods since populations are patchy, often occur in low densities, and individuals can be quite cryptic, living partially buried in sediment. Environmental DNA is increasingly used to survey marine species and has proven to be particularly useful in detecting rare or elusive organisms. Here, we compared the presence of silverlip pearl oysters detected via eDNA metabarcoding to traditional towed video surveys offshore of Eighty Mile Beach, northwest Australia. Seawater samples were collected at the end of towed video transects and sites were categorised into shallow (<40 m depth) or deep (40 m +) groups. We applied an oyster-specific 16S metabarcoding assay as well as a universal 18S assay to identify potential indicator taxa associated with the presence of pearl oysters. Using the 16S assay, we detected silverlip pearl oysters at three of the 12 sites sampled, and found that eDNA records generally matched towed video transect data, with both survey methods detecting the target species predominantly in inshore waters at depths <40 m. Our results indicate that metabarcoding of seawater eDNA can be applied to detect cryptic species of commercial importance but highlight limitations around detecting organisms at very low abundances.

Incorporating uncertainty in Indigenous sea Country monitoring with Bayesian statistics: Towards more informed decision-making.

Partnerships in marine monitoring combining Traditional Ecological Knowledge and western science are developing globally to improve our understanding of temporal changes in ecological communities that better inform coastal management practices. A fuller communication between scientists and Indigenous partners about the limitations of monitoring results to identify change is essential to the impact of monitoring datasets on decision-making. Here we present a 5-year co-developed case study from a fish monitoring partnership in northwest Australia showing how uncertainty estimated by Bayesian models can be incorporated into monitoring management indicators. Our simulation approach revealed there was high uncertainty in detecting immediate change over the following monitoring year when translated to health performance indicators. Incorporating credibility estimates into health assessments added substantial information to monitoring trends, provided a deeper understanding of monitoring limitations and highlighted the importance of carefully selecting the way we evaluate management performance indicators.

Climate Driver Influences on Prediction of the Australian Fire Behaviour Index

Fire danger poses a pressing threat to ecosystems and societies worldwide. Adequate preparation and forewarning can help reduce these threats, but these rely on accurate prediction of extreme fire danger. With the knowledge that climatic conditions contribute heavily to overall fire danger, this study evaluates the skill with which episodes of extreme fire danger in Australia can be predicted from the activity of large-scale climate driver patterns. An extremal dependence index for extreme events is used to depict the historical predictive skill of the Australian Bureau of Meteorology’s subseasonal climate prediction system in replicating known relationships between the probability of top-decile fire danger and climate driver states at a lead time of 2–3 weeks. Results demonstrate that the El Niño Southern Oscillation, Southern Annular Mode, persistent modes of atmospheric blocking, Indian Ocean Dipole and Madden-Julian Oscillation are all key for contributing to predictability of fire danger forecasts in different regions during critical fire danger periods. Northwest Australia is found to be particularly predictable, with the highest mean index differences (&gt;0.50) when certain climate drivers are active, compared with the climatological index mean. This integrated approach offers a valuable resource for decision-making in fire-prone regions, providing greater confidence to users relying on fire danger outlooks for key management decisions, such as those involved in the sectors of national park and forest estate management, agriculture, emergency services, health and energy. Furthermore, the results highlight strengths and weaknesses in both the Australian Fire Danger Rating System and the operational climate model, contributing additional information for improving and refining future iterations of these systems.

Social acceptability of conservation interventions for flatback turtles: comparing expert and public perceptions

Sea turtles are facing significant threats, including anthropogenic warming, predation from feral animals, and sea level rise. While a range of intervention options are available, resource constraints and increasing time pressures means managers face the difficult task of prioritising options. To achieve successful conservation outcomes, managers are increasingly seeking to understand the social acceptability, as well as biological plausibility and economic feasibility, of these intervention options. Previous studies have used expert opinion as predictors of social acceptability, given their technical knowledge and experience implementing the interventions; however, the assumption that the social acceptability of interventions is the same for both the general public and experts is largely untested. We tested this assumption using surveys to assess the social acceptability of 24 interventions proposed for a population of flatback turtles Natator depressus in northwest Australia. Survey responses were collected from community members (residents) and experts (resource managers and researchers). Experts were asked to provide their own opinion of acceptability and how they perceived community members would rate intervention options. In general, residents ranked interventions that directly intervene with human behaviour or the environment as more acceptable than those that directly target turtles, while experts tended to favour direct turtle interventions. Experts incorrectly predicted that the community would not be influenced by the target of the intervention. Our findings highlight the importance of understanding social acceptability of interventions before implementation to inform management decisions and engagement and communication strategies, particularly when interventions might be controversial or restrict human behaviour directly.

Connecting Land and Sea Vertical Datums: A Data Evaluation for Developing Australia’s AUSHYDROID Model

Land and sea vertical datums have traditionally been separate reference levels, due to the different methodologies and observations used in their derivations. However, the need for a seamless connection of these datums has become important due to a wide range of applications in the coastal zone. This study evaluates existing methods, oceanographic and geodetic models and observations for the development of an operational model of coastal heights called AUSHYDROID. We use a complex study area in north west Australia to gain a new insight into how accurately the separation between the lowest astronomical tide (LAT) and a reference ellipsoid can be estimated from existing models, which could form the basis of a national AUSHYDROID model for Australia. Our results are the first attempt to use this combination of existing data in this location, suggesting that ellipsoidal heights of LAT can be estimated to an accuracy of ∼0.2 m at the coast, with the combination of DTU18MSS and FES2014b having the lowest RMS of 0.125 m. However, in some complex coastline areas such as bays and estuaries, the differences increase to >0.5 m so that additional tide gauge observations with GNSS levelling connections and improved models are needed in these regions.

Site fidelity of migratory shorebirds facing habitat deterioration: insights from satellite tracking and mark-resighting

BackgroundSite fidelity, the tendency to return to a previously visited site, is commonly observed in migratory birds. This behaviour would be advantageous if birds returning to the same site, benefit from their previous knowledge about local resources. However, when habitat quality declines at a site over time, birds with lower site fidelity might benefit from a tendency to move to sites with better habitats. As a first step towards understanding the influence of site fidelity on how animals cope with habitat deterioration, here we describe site fidelity variation in two species of sympatric migratory shorebirds (Bar-tailed Godwits Limosa lapponica and Great Knots Calidris tenuirostris). Both species are being impacted by the rapid loss and deterioration of intertidal habitats in the Yellow Sea where they fuel up during their annual long-distance migrations.MethodsUsing satellite tracking and mark-resighting data, we measured site fidelity in the non-breeding (austral summer) and migration periods, during which both species live and co-occur in Northwest Australia and the Yellow Sea, respectively.ResultsSite fidelity was generally high in both species, with the majority of individuals using only one site during the non-breeding season and revisiting the same sites during migration. Nevertheless, Great Knots did exhibit lower site fidelity than Bar-tailed Godwits in both Northwest Australia and the Yellow Sea across data types.ConclusionsGreat Knots encountered substantial habitat deterioration just before and during our study period but show the same rate of decline in population size and individual survival as the less habitat-impacted Bar-tailed Godwits. This suggests that the lower site fidelity of Great Knots might have helped them to cope with the habitat changes. Future studies on movement patterns and their consequences under different environmental conditions by individuals with different degrees of site fidelity could help broaden our understanding of how species might react to, and recover from, local habitat deterioration.

Exposure of marine megafauna to cumulative anthropogenic threats in north-west Australia

As the use of coastal and offshore environments expands, there is a need to better understand the exposure of marine megafauna to anthropogenic activities that potentially threaten their populations. Individual satellite telemetry studies are often hampered by small sample sizes, providing limited information on spatiotemporal distributions of migratory animals and their relationships to anthropogenic threats. We addressed this issue by synthesising satellite tracking data from 484 individuals of three taxonomic groups and six species; three marine turtle, two whale and one shark. The spatial overlap between taxa distributions and multiple anthropogenic activities was assessed as a proxy for the cumulative exposure of these taxa to anthropogenic threats (coastal modification, vessel strike, underwater noise, oil spill, bycatch, entanglement, and artificial light) across an area totalling 2,205,740 km2 off north-western Australia. Core exposure areas (top 50% of the distribution) encompassed ecologically important sites for all taxa, such as the Ningaloo and Pilbara regions, migratory routes for whales and sharks in offshore waters beyond Ningaloo Reef, and marine turtle nesting beaches at Barrow Island and Cape Lambert. Although areas of high exposure represented &amp;lt;14% of taxa distributions, we showed that no taxa occurred in the absence of threats and that even areas with existing spatial protections are experiencing high levels of exposure. Importantly, we developed a robust approach for documenting the potential exposure of marine species to a range of human activities at appropriate spatial scales to inform conservation management.

Mid‐level dry air intrusions over the southern Maritime Continent

AbstractPatterns in extreme precipitation across the Maritime Continent in southeast Asia are known to be modulated by many processes, from large‐scale modes of variability such as the Madden–Julian oscillation, to finer‐scale mechanisms such as the diurnal cycle. Transient mid‐level dry air intrusions are an example of a feature not extensively studied over the Maritime Continent, which has the potential to influence rainfall patterns. Here, we show that these dry air intrusions originate from upper level disturbances along the subtropical jet. Mid‐level cyclonic circulation anomalies northwest of Australia from December to February (DJF) intensify westerlies in the southern Maritime Continent, advecting dry air eastward. In contrast, mid‐level anticyclonic circulation anomalies northwest of Australia from June to August (JJA) intensify southern Maritime Continent easterlies, advecting dry air westward. The resultant transport direction of associated air parcels is also dependent on the seasonal low‐level monsoon circulation. Dry air intrusions are important in influencing low‐level wind and rainfall patterns, suppressing rainfall over seas near the southern Maritime Continent in both seasons, as well as over southern Maritime Continent islands in DJF and the Indian Ocean in JJA. In both seasons there is enhanced rainfall to the east of the intrusion, where there is moist return flow to the extratropics. This study highlights the importance of synoptic‐scale extratropical features in influencing meteorological patterns in the Tropics.

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.