Data for: A comparison of stomatal traits between contemporary and sub-fossil leaves of Melaleuca quinquenervia: do they reflect climate variation?

Stomatal traits have been shown to vary in predictable ways in response to environmental change in many species. As a consequence, stomatal traits in fossil leaves are sometimes used as proxies for past CO2 and climate. Here we investigate the influence of temperature, rainfall and CO2 on stomatal traits in Melaleuca quinquenervia. We use both modern and sub-fossil leaves to evaluate the effect of CO2, and modern leaves for climate variables. We found a significant negative relationship between stomatal size and density across both modern and sub-fossil leaves of M. quinquenervia. However, we were unable to find any relationship between stomatal traits and CO2 across a range from 260-380 ppm. Using the modern data set we were unable to find any robust relationships between stomatal traits and either evaporation or temperature. Apogeotropic roots account for the lack of stomatal anatomy correlation to evaporation in a region that experiences inundation. We conclude that stomatal size is a highly plastic trait in this species and changes do not necessarily reflect functional changes in the leaves

Ecology and climate sensitivity of a groundwater-fed lake on subtropical North Stradbroke Island (Minjerribah), Queensland, Australia over the last 7500 years

Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate

DataSheet1_Hydrological and Isotopic Variability of Perched Wetlands on North Stradbroke Island (Minjerribah), Australia: Implications for Understanding the Effects of Past and Future Climate Change.PDF

Over the first two decades of the 21st century, many wetlands in eastern Australia exhibited declining water levels, causing concern for communities and environmental managers and raising questions about the roles of climate change and other human activity in these water level declines. In this context we examine the causes of water level variability in four wetlands on North Stradbroke Island (Minjerribah), in the humid subtropics of south-eastern Queensland, Australia, using a combination of hydrological and water isotope monitoring and modelling. North Stradbroke Island has a high concentration of wetlands perched above the regional water table, with cultural and ecological significance, and value for palaeoclimate research. From 2015 to 2019, wetland water depths decreased markedly at all sites, coinciding with increases in oxygen isotope ratios in surface waters. The data indicate that climate, specifically a decrease in precipitation relative to evaporation, was responsible for those declining water levels, and that groundwater extraction did not play a critical role. At two of the sites—both palustrine wetlands—declining surface water levels led to intermittent connectivity with the local perched aquifers. At the other two sites, which are both shallow lakes, the surface waters were constantly fed by perched groundwater. The hydrology of the two lakes was modelled using simple mass balance. However, in order to accurately model lake level change, it was necessary to vary catchment runoff and lake outflow via groundwater through time, highlighting complexity in projecting future hydrological change in these lakes. The long term resilience of these lakes depends on a combination of rainfall regime and the balance between catchment runoff and groundwater throughflow, the future of which is highly uncertain. As a consequence, continued efforts to project future hydroclimate and to model the complex hydrology of subtropical wetlands are essential.</p

Fourier transform infrared spectroscopy as a tracer of organic matter sources in lake sediments

The source of sedimentary organic matter in lakes can help to elucidate climate and catchment variation and processes that reflect lake development. Common techniques for tracing sediment organic matter sources, such as the stable isotopes and elemental concentrations of C and N, can be too imprecise to identify the specific provenance of organic matter. By contrast, organic geochemical techniques such as gas or liquid chromatography and nuclear magnetic resonance provide detailed organic molecular characterisation but are both expensive and time consuming. Fourier Transform Infrared (FTIR) spectroscopy is a rapid, non-destructive, and well-established method for determining the constituents of lake sediments. However, the potential for identifying the sources of organic matter in lake sediments has not been fully explored. In this study, we assess the extent to which FTIR can be used to identify varying organic matter sources through analysis of modern autotrophs from Blue Lake, North Stradbroke Island, Australia. We investigated spectral processing techniques to identify the approach that could most accurately classify autotroph samples. Three autotroph groups (i.e algae, aquatic macrophytes, and terrestrial) were correctly classified 90% of the time. Processed spectra then became the basis of a model that used multivariate random forests to estimate sediment organic matter composition source from a sediment record from Blue Lake that spans the last 7500 years. FTIR-based estimates suggested that throughout the history of the lake, algae contributed the highest amount of organic matter to the sediment samples. These results allow a refinement of a previous study of C:N and δ13C from the same core and suggests that alterations in C:N and, particularly, δ13C reflect chemical changes in algae through time. This study demonstrates that FTIR spectroscopy is a promising tool to elucidate sources of sediment organic matter in lake sediments

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a considerable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary productivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates

Evaluation of PMIP2 and PMIP3 simulations of mid-Holocene climate in the Indo-Pacific, Australasian and Southern Ocean regions

This study uses the "simplified patterns of temperature and effective precipitation" approach from the Australian component of the international palaeoclimate synthesis effort (INTegration of Ice core, MArine and TErrestrial records - OZ-INTIMATE) to compare atmosphere-ocean general circulation model (AOGCM) simulations and proxy reconstructions. The approach is used in order to identify important properties (e.g. circulation and precipitation) of past climatic states from the models and proxies, which is a primary objective of the Southern Hemisphere Assessment of PalaeoEnvironment (SHAPE) initiative. The AOGCM data are taken from the Paleoclimate Modelling Intercomparison Project (PMIP) mid-Holocene (ca. 6000 years before present, 6 ka) and pre-industrial control (ca. 1750 CE, 0 ka) experiments. The synthesis presented here shows that the models and proxies agree on the differences in climate state for 6 ka relative to 0 ka, when they are insolation driven. The largest uncertainty between the models and the proxies occurs over the Indo-Pacific Warm Pool (IPWP). The analysis shows that the lower temperatures in the Pacific at around 6 ka in the models may be the result of an enhancement of an existing systematic error. It is therefore difficult to decipher which one of the proxies and/or the models is correct. This study also shows that a reduction in the Equator-to-pole temperature difference in the Southern Hemisphere causes the mid-latitude westerly wind strength to reduce in the models; however, the simulated rainfall actually increases over the southern temperate zone of Australia as a result of higher convective precipitation. Such a mechanism (increased convection) may be useful for resolving disparities between different regional proxy records and model simulations. Finally, after assessing the available datasets (model and proxy), opportunities for better model-proxy integrated research are discussed

Calcium and strontium isotope systematics in the lagoon-estuarine environments of South Australia: Implications for water source mixing, carbonate fluxes and fish migration

This study uses Ca and Sr isotopes (δ44/40Ca and87Sr/86Sr), coupled with elemental ratios, to better understand the water source apportionment and carbonate output in the Coorong, Lower Lakes and Murray Mouth Estuary, which represents the terminus of Australia's longest river system. The geochemistry of waters in the Coorong (i.e., North and South Lagoon) can be explained by mixing of three major components, including: (i) the Southern Ocean seawater, (ii) local freshwaters, and (iii) hypersaline lagoon waters, the latter significantly modified by ongoing evaporation and carbonate formation. The Sr and Ca isotope composition of the North Lagoon is indistinguishable from that of the Southern Ocean (i.e., normal salinity of ∼35 PSU), with the exception of transient freshwater input events that can temporarily lower the salinity to brackish levels. Interestingly, our results from the hypersaline South Lagoon (salinity up to ∼120 PSU) confirmed that the latter is highly evaporated brackish water (with ≥40% contribution from continent-derived waters), which has been additionally modified by in-situ carbonate precipitation. Importantly, our Ca isotope and elemental constraints showed that about 15-17% of the dissolved Ca2+in the South Lagoon has been removed as CaCO3(primarily as aragonite). This in turn has implications for the local carbonate cycle and blue carbon studies, suggesting that the South Lagoon acts as a net sink for the dissolved inorganic carbon (DIC). Ca isotope data from the otoliths of smallmouth hardyhead fish species (Atherinosoma microstoma) collected in the Coorong indicate that δ44/40Ca is primarily controlled by biological processes (i.e., kinetic isotope fractionation effects related to growth rate), rather than by the Ca isotope composition of local lagoon waters. As to87Sr/86Sr in otoliths, the latter confirmed the importance of continent-derived water sources in the Coorong, recorded over the life span of the fish. Overall, with suitable fossil carbonate archives (e.g., bivalve shells, foraminifera), our calibration of87Sr/86Sr and δ44/40Ca in the modern hydrological system, with respect to a large salinity gradient (ranging from fresh to hypersaline, i.e., 0 to ∼120 PSU), implies potential future applications of these isotope tracers in carbonate-producing coastal systems, which include (i) tracing and apportioning different water sources, (ii) quantifying local carbonate outputs, and (iii) reconstructing paleo-salinity changes

The application of pollen radiocarbon dating and Bayesian age-depth modeling for developing robust geochronological frameworks of wetland archives

Wetland sediments are valuable archives of environmental change but can be challenging to date. Terrestrial macrofossils are often sparse, resulting in radiocarbon (14C) dating of less desirable organic fractions. An alternative approach for capturing changes in atmospheric 14C is the use of terrestrial microfossils. We 14C date pollen microfossils from two Australian wetland sediment sequences and compare these to ages from other sediment fractions (n = 56). For the Holocene Lake Werri Berri record, pollen 14C ages are consistent with 14C ages on bulk sediment and humic acids (n = 14), whilst Stable Polycyclic Aromatic Carbon (SPAC) 14C ages (n = 4) are significantly younger. For Welsby Lagoon, pollen concentrate 14C ages (n = 21) provide a stratigraphically coherent sequence back to 50 ka BP. 14C ages from humic acid and >100 μm fractions (n = 13) are inconsistent, and often substantially younger than pollen ages. Our comparison of Bayesian age-depth models, developed in Oxcal, Bacon and Undatable, highlight the strengths and weaknesses of the different programs for straightforward and more complex chrono-stratigraphic records. All models display broad similarities but differences in modeled age-uncertainty, particularly when age constraints are sparse. Intensive dating of wetland sequences improves the identification of outliers and generation of robust age models, regardless of program used.</p

Comparing interglacials in eastern Australia: A multi-proxy investigation of a new sedimentary record

The widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using C and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment δ C values (−34 to −26‰) suggests that C vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0–1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20–40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low δ C and δ N values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5–10%), is relatively higher in δ C and δ N, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using C-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in δ C, δ N and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e–d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one. 14 13 13 15 13 15 13 13 15

OCTOPUS Database v.2.2: Sedimentary Charcoal Records Sahul & NZ

An open database of sedimentary charcoal and black carbon records from Australia, New Guinea, and New Zealand. The data uses the WGS84/Pseudo-Mercator (EPSG: 3857) projected coordinate reference system. Sample metadata is comprehensive and includes bibliographic, contextual, and sample preparation and measurement related information