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Ocean–atmosphere climatic interactions, such as those resulting from El Niño Southern Oscillation (ENSO) are known to influence sea level, sea surface temperature, air temperature, and rainfall in the western Pacific region, through to the north-west Australian Ningaloo coast. Mangroves are ecologically important refuges for biodiversity and a rich store of blue carbon. Locations such as the study site (Mangrove Bay, a World Heritage Site within Ningaloo Marine Park and Cape Range National Park) are at the aridity range-limit which means trees are small in stature, forests small in area, and are potentially susceptible to climate variability such as ENSO that brings lower sea level and higher temperature. Here we explore the relationship between mangrove dieback, and canopy condition with climatic variables and the Southern Oscillation Index (SOI)—a measure of ENSO intensity, through remote sensing classification of Landsat satellite missions across a 29 year period at a north-west Australian site. We find that the SOI, and seasonal mean minimum temperature are strongly correlated to mangrove green canopy (as indicator of live canopy) area. This understanding of climate variations and mangrove temporal heterogeneity (patterns of abundance and condition) highlights the sensitivity and dynamics of this mangrove forest and recommends further research in other arid and semi-arid tropical regions at mangrove range-limits to ascertain the extent of this relationship.

Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. Here we present a near annual resolution reconstruction of climate developed from a speleothem that spans the Eemian [Marine Isotope Stage 5e (MIS 5e)] from 117,500 to 123,500 years BP—the most recent period in the Earth’s history when temperatures were similar to those of today. Using 25 Mg, 88Sr, and 137Ba as proxies, we show the first indication of solar and teleconnection cyclic forcing of Eemian climate in southeast Australia, a region at present often affected by severe drought and bushfires. We find evidence for multi-centennial dry periods interpreted as mega-droughts, and highlight the importance of understanding the causes of these in the context of a rapidly warming world, where temperatures are now, or projected to exceed those of the Eemian.

Snowmelt from the seasonal snowpack in the Australian Alps is a significant source of water for irrigated agriculture, electricity generation, and environmental flows in the Murray–Darling Basin. Previous studies have reported negative decadal to multidecadal trends in maximum snow depth, snow season duration, and snow-covered area. Here, we characterise the energy balance of this marginal maritime snowpack for the first time. Turbulent fluxes measured using the eddy covariance and bulk aerodynamic methods are compared; discrepancies are attributed to the differing assumptions of the methods and characteristics of the measurement site. We examine the variability of the individual energy balance components and the drivers of snowmelt, and we find that incoming longwave radiation is the dominant control on snowmelt, providing more than 80% of the total energy to the snowpack over the season. During a midwinter rain-on-snow event, the advected rain heat flux provided 8% of the daily total, with the incoming longwave flux still accounting for almost 80%. The ground heat flux contributes a small proportion of the seasonal total but increases in patchy or intermittent snow cover. Comparing these results with those of studies in other maritime locations, we find that the turbulent fluxes are likely to make a proportionally higher contribution to the energy balance due to the short Australian snow season, underpinning the sensitivity of this environment to climate variability and change. These results extend the limited body of knowledge on highly marginal snowpacks and may be relevant to other regions with no direct measurements of the energy balance.

Annual resolution reconstructions of alpine temperatures are rare, particularly for the Southern Hemisphere, while no snow cover reconstructions exist. These records are essential to place in context the impact of anthropogenic global warming against historical major natural climate events such as the Roman Warm Period (RWP), Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Here we show for a marginal alpine region of Australia using a carbon isotope speleothem reconstruction, warming over the past five decades has experienced equivalent magnitude of temperature change and snow cover decline to the RWP and MCA. The current rate of warming is unmatched for the past 2000 years and seasonal snow cover is at a minimum. On scales of several decades, mean maximum temperatures have undergone considerable change ≈ ± 0.8 °C highlighting local scale susceptibility to rapid temperature change, evidence of which is often masked in regional to hemisphere scale temperature reconstructions.

Resolving the hydrological processes that form speleothems and the palaeo-climate archives that they contain is difficult. Typical approaches to hydrological investigation are not suited to karst landscapes, geophysics are seldom applied, drip monitoring and modelling have limitations, and ignoring potential hydrological impacts can result in a proxy record that does not reflect the external environment. We aim to understand the processes and controls that have created a palaeo-climate proxy record preserved in a speleothem (JC001) in the “Grotto of Oddities”, part of the Jersey Cave at the Yarrangobilly Caves, Australia, to infer the likely nature and resolution of this record. Electrical Resistivity Tomography (ERT), traditional surveying, and drip discharge monitoring (April 2013 to February 2015) were used to investigate the structure and hydrology of the epikarst overlying the “Grotto of Oddities”. Data collected through these methods were then used to construct a physically informed and parsimonious drip hydrology model. Geophysics showed that changes in hillslope above the “Grotto of Oddities” are collocated with a region of low resistivity which forms an epikarstic reservoir acting to supply enhanced discharge to the speleothem. Drip monitoring showed hysteretic behaviour with a distinct threshold response, and a simple drip classification indicated that the speleothem associated with the drip has the potential to record palaeo-seasonality or an annual-decadal signal. Discharge modelling indicated discharge was comprised of quick and slow flow, and that discharge is probably perennial. These multi-method results together indicate that the speleothem likely represents a palaeo-climate record of a length and resolution unprecedented for non-glacial areas of the Southern Hemisphere and for Australia in particular, and will significantly enhance current knowledge of the climate of southeast Australia. While ERT methods have previously been applied in the karst landscape, to our knowledge, this represents the first application of these multiple methods in combination as an approach to assess the fidelity of a speleothem, based on an understanding of the hydrological processes for palaeo-climate reconstruction.

Washover fans typically form due to barrier overwash or breaching and coastal inundation and generally represent geomorphological and depositional evidence of intense storms. Few studies have investigated the chronostratigraphy of washover fans in order to infer magnitude/frequency patterns of extreme-wave events over longer time scales. Here we present new data on the chronostratigraphy of late Holocene washover fans in the Exmouth Gulf (Western Australia) by using ground penetrating radar and unmanned aerial vehicle (UAV) survey techniques, as well as geomorphological, sedimentological and chronological investigations. This study aims to (i) provide a detailed characterization of the washover fans' geomorphology and stratigraphical architecture; (ii) document depositional processes involved in their formation; (iii) establish a chronostratigraphy based on optically stimulated luminescence (OSL); and (iv) understand the significance of the washover fans for recording past tropical cyclone (TC) activity. The fans consist of multiple sequences of sand, shell debris and coral rubble comprising depositional units related to TC-induced inundation. The units are separated by palaeosurfaces with incipient soil formation, formed during periods of reduced depositional activity. In combination with the interpretation of a UAV-based high-resolution digital surface model, multiple phases of reactivation are inferred. OSL results allow the establishment of a local long-term TC record and suggest storm-induced deposition at ∼170, ∼360, ∼850 and ∼1300 years ago. Further units were dated to ∼1950, ∼2300, and ∼2850 years ago. The chronology of TC events is consistent with other work relating TC activity with El Nino Southern Oscillation (ENSO) and sea surface temperature (SST) patterns, corroborating the regional palaeotempestological relevance of this unique geomorphological record.

Secondary dryland salinity is a global land degradation issue. Because drylands are often less-developed, less-well instrumented and less-well understood, we often adapt and impose an understanding from different hydro-geomorphological settings. Dryland catchments are likely to exhibit some functional qualities of wet and hydrologically-connected landscapes, but also those more typical of flat and arid rangelands, smooth plainlands and deserts, where flow (dis)connectivity is an important feature. The functional hydrological mechanisms used to conceptualise causes of dryland salinity, originate from wet and more hydrologically-connected landscapes. They are then imposed with adjustments for rainfall and streamflow quantity to describe how hillslope-recharge processes interact with groundwater to cause dryland salinity. The pervasive understanding concludes that low flow yield from the end-of-catchment gauging stations indicates that land clearing alters water balance in favour of increased infiltration and rising groundwater that bring salts to the surface, causing land degradation from dryland salinity. This paper presents data from an intra-catchment surface flow gauging network run for six years and a surface water–groundwater interaction site to assess the adequacy of our conceptual understanding of secondary dryland salinity in environments with low gradients and runoff yield. The aim is to (re)conceptualise pathways of water and salt redistribution in dryland landscapes, to investigate the role that surface water flows and connectivity plays in land degradation from salinity in low-gradient drylands. Based on the long-term end-of-catchment gauge, average annual runoff yield is only 0.14 % of rainfall. The internal gauging network operated from 2007–2012 found pulses of internal water (also mobilising salt) in years when no flow was recorded at the catchment outlet. Data from a surface water–groundwater interaction site shows top-down recharge of surface water early in the water year, that transitions to a bottom-up system of discharge later in the water year. This connection provides a mechanism for the vertical diffusion of salts to the surface waters, followed by evapo-concentration and downstream export when depression storage thresholds are exceeded. Intervention in this landscape by constructing a broad-based channel to address these processes, resulted in a 25 % increase in flow volume and a 20 % reduction in salinity, by allowing the lower catchment to more effectively support bypassing of the storages in the lower landscape that would otherwise retain water and allow salt to accumulate. Results from this study suggests catchment internal redistribution of relatively fresh runoff onto the valley floor is a major contributor to development of secondary dryland salinity. Seasonally inundated areas are subject to significant transmission losses and drive processes of vertical salt mobility. These surface flow and connectivity processes are not acting in isolation to cause secondary salinity, but are also interact with groundwater systems responding to land clearing and processes recognised in the more conventional understanding of hillslope recharge and groundwater discharge. The study landscape appears to have three functional hydrological components: upland, hillslope flow landscapes that generate fresh runoff; valley floor fill landscapes with high transmission losses and poor flow connectivity controlled by the micro-topography that promotes surface–groundwater connection and salt movement; and the downstream flood landscapes, where flows are recorded only when internal storages (fill landscapes) are exceeded. This work highlights the role of surface water processes as a contributor to land degradation by dryland salinity in low-gradient landscapes.

Frost research to improve genetics or management solutions requires a robust experimental design that minimizes the effects of all other variables that can cause plant damage except for the treatment (frost). Controlled environment facilities cannot faithfully replicate field radiative frost processes, but field studies are limited by the reliability of field methods to exclude frost. An effective field frost exclusion method needs to prevent frost damage while not impacting growing microclimate or yield, and be automatic, modular, mobile, and affordable. In this study, we designed an effective prototype treatment with these features for field frost research that uses diesel heating. The effectiveness of the plot heater to provide an unfrosted control is evaluated by monitoring canopy temperature (CT) and air temperature during frost events, showing that these remain above zero in the heated plots when ambient temperature drops below zero. We find that the plot heater method can prevent potential frost damage at the plot-scale, while not appearing to have an impact on either plant development or yield components. This offers a potential new tool for frost field crop researchers to incorporate a plot-scale control into their experimental design.