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Supplemental material, sj-docx-1-hol-10.1177_09596836221095981 for Aboriginal earth mounds of the Calperum Floodplain (Murray Darling Basin, South Australia): New radiocarbon dates, sediment analyses and syntheses, and implications for behavioural change by Robert Jones, Amy Roberts, Craig Westell, Ian Moffat, Geraldine Jacobsen and Rachel Rudd in The Holocene

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 2.4m sediment core with a basal age of 7.5cal 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 4.2cal 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.

Climate change is affecting the distribution of species and the functioning of ecosystems. For species that are slow growing and poorly dispersed, climate change can force a lag between the distributions of species and the geographic distributions of their climatic envelopes, exposing species to the risk of extinction. Climate also governs the resilience of species and ecosystems to disturbance, such as wildfire. Here we use species distribution modelling and palaeoecology to assess and test the impact of vegetation–climate disequilibrium on the resilience of an endangered fire‐sensitive rainforest community to fires. First, we modelled the probability of occurrence of Athrotaxis spp. and Nothofagus gunnii rainforest in Tasmania (hereon “montane rainforest”) as a function of climate. We then analysed three pollen and charcoal records spanning the last 7,500 cal year BP from within both high (n = 1) and low (n = 2) probability of occurrence areas. Our study indicates that climatic change between 3,000 and 4,000 cal year BP induced a disequilibrium between montane rainforests and climate that drove a loss of resilience of these communities. Current and future climate change are likely to shift the geographic distribution of the climatic envelopes of this plant community further, suggesting that current high‐resilience locations will face a reduction in resilience. Coupled with the forecast of increasing fire activity in southern temperate regions, this heralds a significant threat to this and other slow growing, poorly dispersed and fire sensitive forest systems that are common in the southern mid to high latitudes.

Increased export production (EP) in the Subantarctic Zone (SAZ) of the Southern Ocean due to iron fertilisation has been proposed as a key mechanism for explaining carbon drawdown during the last glacial maximum (LGM). This work reconstructs marine EP since the LGM at four sites around New Zealand. For the first time in this region, 230-Thorium-normalised fluxes of biogenic opal, carbonate, excess barium, and organic carbon are presented. In Subtropical Waters and the SAZ, these flux variations show that EP has not changed markedly since the LGM. The only exception is a site currently north of the subtropical front. Here we suggest the subtropical front shifted over the core site between 18 and 12ka, driving increased EP. To understand why EP remained mostly low and constant elsewhere, lithogenic fluxes at the four sites were measured to investigate changes in dust deposition. At all sites, lithogenic fluxes were greater during the LGM compared to the Holocene. The positive temporal correlation between the Antarctic dust record and lithogenic flux at a site in the Tasman Sea shows that regionally, increased dust deposition contributed to the high glacial lithogenic fluxes. Additionally, it is inferred that lithogenic material from erosion and glacier melting deposited on the Campbell Plateau during the deglaciation (18–12ka). From these observations, it is proposed that even though increased glacial dust deposition may have relieved iron limitation within the SAZ around New Zealand, the availability of silicic acid limited diatom growth and thus any resultant increase in carbon export during the LGM. Therefore, silicic acid concentrations have remained low since the LGM. This result suggests that both silicic acid and iron co-limit EP in the SAZ around New Zealand, consistent with modern process studies.

International audience

To investigate changes in oxygenation at intermediate depths in the southwest Pacific between the Last Glacial Maximum (LGM) and the Holocene, redox sensitive elements uranium and rhenium were measured in 12 sediment cores located on the Campbell and Challenger plateaux offshore from New Zealand. The core sites are currently bathed by Subantarctic Mode Water (SAMW), Antarctic Intermediate Water (AAIW) and Upper Circumpolar Deep Water (UCDW). The sedimentary distributions of authigenic uranium and rhenium reveal reduced oxygen content at intermediate depths (800–1500 m) during the LGM compared to the Holocene. In contrast, data from deeper waters (≥1500 m) indicate higher oxygen content during the LGM compared to the Holocene. These data, together with variations in benthic foraminiferal δ13C, are consistent with a shallower AAIW–UCDW boundary over the Campbell Plateau during the LGM. Whilst AAIW continued to bathe the intermediate depths (≤1500 m) of the Challenger Plateau during the LGM, the data suggest that the AAIW at these core sites contained less oxygen compared to the Holocene. These results are at odds with the general notion that AAIW was better oxygenated and expanded deeper during the LGM due to stronger westerlies and colder temperatures. These findings may be explained by an important change in AAIW formation and circulation.