Henk Heijnis

Late Pleistocene vegetation and climate history of Lake Selina, western Tasmania

Analysis of pollen, NRM intensity of sediments, and dating of a 397 cm core from Lake Selina in western Tasmania provides a detailed record of vegetation and climate changes for the Last Interglacial–Last Glacial cycle. The vegetation record shows that cool temperate rainforest was present during Isotope Substage 5e and during the Holocene. Wet montane forest and subalpine shrublands dominated the early Last Glacial interstades; subalpine–alpine heathlands and herbfield the stadials. Stages 4–2 mainly had grassland, herbland and heath vegetation. There is close correlation between phases of maximum magnetic intensity in the sediments with pollen zones indicating presence of herbaceous vegetation. This suggests erosion of the catchment was greater in the absence of forest or woodland. Climate may have been slightly cooler than present during Substage 5e but the evidence is not definitive. Climate was colder at all times during the Last Glacial Stage until after ca. 14 kyr BP. Maximum temperature depression from present during Stage 2 was >3.5°C at Lake Selina, but probably as much as 6.5°C in the West Coast Range. Holocene climate was cool and wet. Comparison of the Lake Selina record, with others in western Tasmania and Victoria, indicate that variations in vegetation during the Last Interglacial–Last Glacial cycle were primarily responses to temperature changes in western Tasmania, and to precipitation changes, particularly summer drought, in western Victoria.

Late Quaternary sea-level highstands in the Tasman Sea: evidence from Lord Howe Island

Abstract Lord Howe Island, situated 600 km east of Australia, provides a unique opportunity to evaluate Late Quaternary highstands of sea level in the Tasman Sea. The mid-ocean island, which is the site of the southernmost coral reef, is composed of basalts of late Tertiary age, and calcarenites derived from bioclastic reefal carbonates. Both erosional and depositional evidence of Late Quaternary highstands of sea level is preserved. Uranium-series disequilibrium dating of coral clasts from a calcarenite beach facies at Neds Beach on the northeast of the island yielded a mean age of 136,000 yr B.P. Thermoluminescence dating of the quartz sand fraction from the same deposit, using fine-grained and coarse-grained methods, yielded ages of 138,000 and 116,000 yr B.P., respectively. These ages are interpreted to indicate that this beach unit, within which fossil bones and eggs of the extinct horned turtle, Meiolania , are found, formed during the Last Interglacial when the sea was 2–4 m above present. Benches and platforms developed on Tertiary basalt and on Late Pleistocene calcarenite on the more sheltered lagoonal shore on the west of the island indicate a sea level up to 1.5 m higher than present during the Holocene. Cemented boulder conglomerates (ca. 3000 yr B.P.) at North Head, and emergent mollusc-rich carbonate muds (ca. 900 yr B.P.) within an embayment fill at Old Settlement Beach, further support this interpretation. These palaeo-sea-level data from the Tasman Sea support previous estimates of the height of the Last Interglacial sea surface relative to eastern Australia, and supplement a growing body of evidence for a higher sea level in the region during the mid to late Holocene.

A long late-Quaternary record from Lake Poukawa, Hawke's Bay, New Zealand

Abstract The Lake Poukawa Basin is a large co-seismic depression located at 20 m above mean sea level in Hawke’s Bay in eastern North Island, New Zealand. We present a detailed environmental history of the basin for the last c. 60 ka based on analyses of the top 105 m of a 200-m core record. Dating control is provided by radiocarbon, optically stimulated luminescence (OSL) and U/Th disequilibrium ages. The chronology is supported by nine tephras of inferred age including marker tephras, Kawakawa (22 590±230 yr BP at −18.25 m core datum), Tahuna (c. 35–43 ka) at −33.1 m core datum, and Rotoehu (45–50 ka) at −39.1 m core datum. Disagreements between some of the older tephra ages and the numerical ages from the OSL and U/Th dating mean that more than one age model can be applied. Three major lithostratigraphic units are identified: a basal calcareous silt with lignitic peats between 105.28 and 98.58 m of marine oxygen isotope stage (MIS) 3 age; an extended sequence of detrital shelly sands and silts, between 98.58 and 8 m of MIS 3 and 2 age; and a Holocene peat unit (MIS 1) from 8 to 0 m. Alternatively, but less likely, the basal unit may represent stage MIS 5a and the detrital shelly sands would then contain an amalgam of MIS 4, 3, and 2 deposits. We propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3. This suggests the existence of mild conditions during an interstadial in central New Zealand at c. 55–50 ka when a podocarp–beech–broadleaf forest of near-interglacial affinity surrounded the basin. The interstadial is marked by both lake and peat formation in the basin. After 50 ka a thermal decline set in, though the climate remained moist initially. Under these conditions, the Poukawa Basin was rapidly infilled by alluvial fan deposits from the surrounding hills. The floor of the basin was occupied by grasses and sedges, responding to both the highly disturbed environment and swampy conditions in the basin. After the deposition of the Rotoehu Ash, effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor. The data suggest an apparent thermal decline of c. 6–7°C for much of MIS 2 and the latter half of MIS 3. The Holocene was marked by the establishment of fen and lake environments on the basin floor. Prior to human disturbance, podocarp–broadleaf forest surrounded the basin.

Signatures of natural catastrophic events and anthropogenic impact in an estuarine environment, New Zealand

The sedimentary record of known natural catastrophic events and anthropogenic activity in an estuarine environment is assessed using sedimentological, chemical and geochronological techniques. Shallow cores collected from intertidal and salt marsh sediments in Ahuriri Estuary, Hawkes Bay, reveal a variety of signatures of natural and human disturbance. Evidence for the 1931 Hawkes Bay earthquake, which resulted in an uplift of one to two metres in the Napier area, is given by a change from silt- to sand-dominated sediment in the lower estuary, which is consistent with a shift toward higher energy depositional conditions following uplift. However, based on physical properties of sediments, the 1931 uplift event does not appear to have caused major changes in depositional conditions in the upper estuary. Similarly, no changes were recorded at one site in the lower estuary, which seems to represent an area of low energy depositional environment. Although the 1960 Chilean tsunami resulted in structural damage in Napier, it did not produce any recognisable sedimentological and geochemical signature in the sedimentary record, suggesting that the study sites were possibly beyond the limit of sedimentation of the tsunami. Post-European settlement impact is mainly restricted to the lower estuary, where increased concentrations of Zn, Cr, Pb and Cu are attributed to industrial discharges. Evidence of agricultural runoff is shown by an increase in Cu concentrations within a fine-grained depositional environment that is distal from industrial sources in the town of Napier. Chemical data (Cl and S) suggest a change in the depositional environment in the upper estuary due to increased freshwater influx and/or decrease in seawater influence. Dating by 210Pb suggests that this occurred around the middle part of the 19th century, and might be attributed to river flooding in the region at that time.

Tephrostratigraphy and geochronology of a ca. 120 ka terrestrial record at Lake Poukawa, North Island, New Zealand

Abstract A 198-m-long core was obtained from Lake Poukawa, Hawkes Bay, New Zealand for paleoclimatic analysis. A chronology extending back to ca. 120 ka has been developed using a combination of tephrostratigraphy, radiocarbon, optical, and U–Th disequilbrium dating. The core contains a new record of tephra beds, including temporal intervals poorly recorded elsewhere, and revises the dispersal for some known events. Thirty macroscopic tephra beds were identified, comprising 20 rhyolites with compositions consistent with previously studied tephra from Taupo and Okataina calderas, and 10 andesites–dacites compositionally similar to Tongariro and Egmont centre eruptions. Electron microprobe data provides evidence for a total of 24 rhyolite eruptions amongst the 20 macroscopic beds. Four widespread rhyolitic marker beds: Whakatane (4.6 ka), Kawakawa (22.6 ka), Tahuna (ca. 43 ka), and Rotoehu (ca. 50 ka) provide temporal constraints for the upper 40 m of the core. The occurrence of Opepe (9 ka) and Okaia (23 ka) tephra beds in this core extends their known dispersal to southern North Island. A previously unrecognised and chemically distinct rhyolite tephra (ca. 35 ka) was also found in the sequence. Twelve rhyolitic tephra occur in the interval 50–120 ka, a period in which the timing and nature of volcanic events is poorly understood at proximal sites of the Taupo Volcanic Zone. The Lake Poukawa core provides evidence for widely dispersed tephra-producing eruptions from Egmont volcano and Tongariro centre back to about 120 ka. The tephra are glassy, unlike many proximal deposits, and can be geochemically fingerprinted, thus providing an opportunity to develop a framework for eruptions not assessable in proximal localities. The pre-50 ka, high-K Egmont tephra are compositionally similar to younger (post-30 ka) proximal pyroclastics, but differ from contemporaneous low- and medium-K rocks that characterise the proximal ring-plain of the volcano. An average Holocene peat accumulate rate of 1.5 m/ka and an average post-50 ka sedimentation rate of 0.78 m/ka are implied from the ages of interbedded tephra. However, the depositional history of the core is complex because tephra at a depth of 40 m, and optical and U–Th disequilbrium ages at ca. 103 m are the same age within analytical uncertainties. This implies either rapid alluvial sedimentation or unrecognised problems in the dating methods. U–Th disequilbrium ages, together with paleoecological information, suggest that a peat interval at 143–146 m depth formed during the last interglacial maximum (oxygen isotope substage 5e).

The contributions of uranium/thorium and marine palynology to the dating of the Lake Wangoom pollen record, western plains of Victoria, Australia

Abstract An extended pollen record from Lake Wangoom provides clear evidence for two climatic cycles incorporating three major effective precipitation peaks. The existing radiocarbon dates and age estimates derived from uranium/thorium dating and correlation with the pollen sequence from an isotopically-dated marine record presented here provide conflicting chronologies for these cycles. The radiocarbon dates indicate the youngest and middle precipitation peaks correspond, respectively, to the Holocene and the last major interstadial (oxygen isotope stage 3). By extrapolation, the oldest peak correlates most closely with substage 5c. Uranium/thorium disequilibrium dates suggest both the middle and oldest precipitation peaks occur within the isotope stage 5 complex, the middle phase corresponding with an interstadial and the oldest with the height of the Last Interglacial. The most reliable chronology, at least for the later cycle, is considered to be provided by comparison with the pollen record from a marine core with an oxygen isotope sequence from offshore Victoria. This record indicates that the last time precipitation levels attained those of the Holocene was during the Last Interglacial period and suggests that the Wangoom record extends back to the penultimate interglacial of isotope stage 7.

Land Use and Lake Sedimentation on the New England Tablelands of New South Wales, Australia

Lead-210 methods have been used to establish a chronology of sedimentation extending back almost 80 years in Black Mountain Lagoon near Guyra on the New England Tablelands of north-eastern New South Wales, Australia. Estimates of the direct atmospheric fallout of unsupported 210Pb and historical records of the pattern of phosphorus input to the lake provide support for the 210Pb chronology. The sediments in the lake record an episode of disturbance which took place prior to c .1916, but after c .1790-1860. Since then, however, the site-specific rate of minerogenic sedimentation has been maintained at a relatively low and constant level of 0.93 kg m-2 a-1. [Note: the following symbols are used in this paper: a = year (annum), and d min-1 g-1 = radioactivity (spontaneous nuclear disintegrations per minute per gram of material).] This is despite major shifts in land use and intensification of agriculture, despite the occurrence of significant floods and droughts, and in the absence until recent times of the ...

Bog burst in the eastern Netherlands triggered by the 2.8 kyr BP climate event

The nature and cause of the so-called 2.8 kyr BP event have been a subject of much debate. Peat sequences have provided much of the evidence for this event, but the process link between climate and peatland response is not well understood. Multiproxy, high-resolution analysis of a core from Bargerveen in the eastern Netherlands based on pollen, non-pollen palynomorphs, testate amoebae and geochemistry identified an abrupt shift from relatively dry to extremely wet conditions. Radiocarbon-based wiggle-match dating (WMD) and biostratigraphy based on the pollen record show that this shift in local hydrology occurred around 2800 cal. yr BP. We interpret an erosional hiatus lasting up to 950 years immediately prior to this, as the effect of a bog burst after excessive rainfall. This phenomenon was not limited to our sampling location but occurred over a large part of the former Bargerveen. Peat at the hiatus contains microfossils that reflect temporary eutrophication as a consequence of local fires and secondary decomposition because of increased drainage after the erosion event. Our data show how detailed multiproxy analyses can elucidate the past response of peatlands to changing climate and suggest that the climatic change in northwest Europe at this time caused major non-linear disruption to these ecosystems.

Use of 210Pb and 137Cs to simultaneously constrain ages and sources of post-dam sediments in the Cordeaux reservoir, Sydney, Australia

Environmental radionuclides can be employed as tracers of sediment movement and delivery to water bodies such as lakes and reservoirs. The chronologies of sediments that have accumulated in the Cordeaux reservoir in Sydney, Australia, were determined by the rate of change of (210)Pb(ex) with depth and indicate slow accretion in the reservoir. The ratio of enrichment of radionuclides in sediment cores to (210)Pb(ex) and (137)Cs concentrations in a reference soil sample within the Cordeaux catchment indicates that the dominant source of sediment in the Cordeaux reservoir is surface erosion (detachment and removal of sediment at depths less than 30 cm). However, in the Kembla Creek arm of the reservoir a mixture of sources was detected and includes sheet and rill erosion together with sub-soil contributions. Implications for the utility of these radionuclide sedimentation assessments, especially where samples are limited, are that well-constrained chronologies and sources of soil erosion are facilitated.

Determining the history and sources of contaminants in the Tamar Estuary, Tasmania, Australia, using 210Pb dating and stable Pb isotope analyses

Environmental Context. Dating estuary sediments provides insights into the materials entering the estuary and can pinpoint when the contamination occurred. Heavy metal contamination is a known health risk but attributing it to a source can be contentious. For a sample sourced downstream of a city and a mining region, lead-210 dating and stable lead isotope analyses uncovered the sources of lead inputs. These methods quantified the extent that upstream mining activities and, for the first time, the extent that non-mining inputs (vehicles, industry) contributed to the estuarys pollution. Abstract. 210Pb dating and heavy metal analyses (Cd, Cu, Pb, Zn) have been combined to establish an historical profile of pollutant levels in sediments in the Tamar Estuary (Tasmania, Australia) over the past century. Heavy metal profiles through the core show a strong correlation with mining activities and industrialization during the past century, reflecting catchment disturbance in one of Australias earliest settled areas. A source apportionment of Pb in the sediment core using stable Pb isotope ratios (204Pb, 206Pb, 207Pb, 208Pb) shows that mine pollution has been contributing 10-25 mg kg-1 to Tamar Estuary sediments since the start of mining in the early 1890s, whilst non-mining inputs were not significant until post-1930 and became increasingly significant post-World War II. Since the 1950s-1960s, non-mining anthropogenic Pb inputs have become as significant as Pb from mining activities, although there does appear to be a decline in non-mining inputs during the past 20 years, which is consistent with findings elsewhere where reductions in atmospheric Pb levels have been observed and are attributed to the phasing-out of leaded gasoline. The source apportionment does, however, suggest that Pb from mine pollution at Storys and Aberfoyle Creeks continues to impact upon upper Tamar Estuary sediment quality.