Search

Marine Isotope Stage 11 (MIS 11) from ∼424,000 to 374,000 yrs ago included one of the longest and warmest interglacials of the last 800,000 yrs, and is a potential analogue for the Holocene due to the similarity of Earth's orbital configuration at this time. The question of how the El Nino–Southern Oscillation (ENSO) responds to warmer background climates remains unanswered and is critical to understand how the ENSO system will evolve under the influence of anthropogenic warming. In this study, we present a 35 yr-long, high-resolution record of MIS 11 climate variability in the Western Pacific Warm Pool (WPWP) based on coupled measurements of skeletal Mg/Ca and δ18O in giant Tridacna gigas clams from Huon Peninsula, Papua New Guinea. The δ18O of modern T. gigas from Huon Peninsula faithfully records sea surface temperature, salinity/rainfall and regional ENSO variability. The geochemical integrity of the MIS 11 T. gigas for recording paleo-ENSO events was established through trace element screening, detailed petrography and SEM analysis. The fossil T. gigas δ18O record indicates that ENSO was operating during a 35-yr window in MIS 11, but with fewer events of shorter duration compared to those experienced during the last 100 yrs. The suppressed ENSO variability in the MIS 11 T. gigas record corresponds with a reduction in the amplitude of the average annual cycle in δ18O values. Distinctive changes in local insolation seasonality, and T. gigas δ18O, brought about by changes in Earth's orbit, provide an additional geochronological constraint on the timing of reef growth at Huon Peninsula to around 402 ka during the MIS 11.3 sub-stage (∼424–395 ka).

Estimates of regional erosion and sediment mixing from different sources in the Yangtse River system are presented, based on sand samples collected from major tributaries and the trunk stream, at 23 sites between western Sichuan and the Yangtse Delta. Mixing is estimated from concentrations of Mg, Ca, Sr, Ti, Mn and Fe, which are substantially higher in sand from major tributaries in the western Yangtse River catchment than from tributaries in the eastern catchment. Intermediate concentrations occur in sand from the Yangtse Delta, both for modern samples from the surface and for early Holocene samples from drill holes. Mixing ratios indicate that 35 ± 5% of sand in the delta came from eastern sources. A similar result was obtained using cosmogenic 10Be in quartz grains as a tracer of mixing. Regional erosion rate estimated from 10Be in sand grains from high mountain catchments of the western Yangtse River are mostly similar to rates based on sediment gauging but are sometimes higher, and range to over 700 m Ma− 1, while 10Be measured at upper Yangtse River tributaries on the northeast Tibetan plateau gave rates of 20–30 m Ma− 1. For the eastern catchments, 10Be measurements from quartz sand and sediment gauging both gave rates of 30–70 m Ma− 1. Eroding at this rate, the eastern catchments could not supply more than 20% of the sediment in the delta, in contrast with 35% estimated from geochemical fingerprints. The relative input from eastern sources may have been higher in Late Pleistocene times, under a different climatic regime, and reworking of Pleistocene deposits may still be in progress.

Since the end of the post-glacial sea level rise 6800 years ago, progradation of river mouths into estuaries has been a global phenomenon. The responses of upstream alluvial river reaches to this progradation have received little attention. Here, the links between river mouth progradation and Holocene valley aggradation are examined for the Macdonald and Tuross Rivers in south-eastern Australia. Optical and radiocarbon dating of floodplain sediments indicates that since the mid-Holocene sea level highstand 6800 years ago vertical floodplain aggradation along the two valleys has generally been consistent with the rate at which each river prograded into its estuary. This link between river mouth progradation and alluvial aggradation drove floodplain aggradation for many tens of kilometres upstream of the estuarine limits. Both rivers have abandoned their main Holocene floodplains over the last 2000 years and their channels have contracted. A regional shift to smaller floods is inferred to be responsible for this change, though a greater relative sea level fall experienced by the Macdonald River since the mid-Holocene sea level highstand appears to have been an additional influence upon floodplain evolution in this valley. Copyright © 2006 John Wiley & Sons, Ltd.

Long-distance human migration across the Pacific Ocean occurred during the late Holocene and originated almost entirely in the west. As prevailing tradewinds blow from the east, the mechanisms of prehistoric seafaring have been debated since the sixteenth century. Inadequacies in propositions of accidental or opportunistic drifting on occasional westerlies were exposed by early computer simulation. Experimental voyaging in large, fast, weatherly (windward-sailing) double-canoes, together with computer simulation incorporating canoe performance data and modern, averaged, wind conditions, has supported the traditional notion of intentional passage-making in a widely accepted hypothesis of upwind migration by strategic voyaging. The critical assumption that maritime technology and sailing conditions were effectively the same prehistorically as in the historical and modern records is, however, open to question. We propose here that maritime technology during the late-Holocene migrations did not permit windward sailing, and show that the episodic pattern of initial island colonization, which is disclosed in recent archaeological data, matches periods of reversal in wind direction toward westerlies, as inferred from the millennial-scale history of ENSO (El Niño-Southern Oscillation).

Samples of plankton, surface sediments and Holocene deposits from the South Alligator River, an energetic macrotidal river in northern Australia, are examinedto evaluate the usefulness of estuarine foraminifers for palaeoenvironmental interpretation of sediments deposited in tropical macrotidal conditions. Although marine and estuarine foraminifers in the estuarine channel are mixed by strong tidal currents, there are significant trends along the 80-km length of the tidal river. The relative proportions of marine andporcellaneous taxa d ecrease upstream from the mouth, but hyaline taxa andthose with brackish affinities increase upstream. Foraminifers in intertidal sediments have distinctly different assemblages in the uppermost intertidal, mid-tidal (mangrove), lower intertidal and subtidal zones. In addition to the effects of tidal mixing, preserved thanatacoenoses are affected by selective dissolution and/or pyritisation within the sediment bodies. Despite the effects of adverse taphonomic factors, foraminiferal assemblages preserved in drill cores provide an accurate guide to original depositional environments (intertidal/subtidal; brackish estuarine/coastal marine), in mid-Holocene sediments in the South Alligator area. Foraminifers are found to improve the precision of previous palaeoenvironmental reconstructions made on the basis of sedimentary facies and pollen analyses. r 2001 Elsevier Science LtdandINQUA. All rights reserved .

Eighty-eight conventional radiocarbon age measurements of corals, collected from Holocene transgressive reefs at Huon Peninsula have been published previously, but, except for 29 dates from a 52 m drillhole, the data have not been systematically analysed. From these data, we show that post-glacial reef growth tracked rising sea level (‘keep-up’ growth) at Huon Peninsula, from −70 m at 11,200 yr BP. The Holocene reef emerged about 6300 yr BP in the southeast of the region, where uplift rate is highest (3.3 m ka-1), and at about 5950 yr BP in the northwest, where uplift rate is 1.9 m ka-1. The uplift process is dominated by metre-scale coseismic uplift events; the difference in timing of reef emergence between northwest and southeast, is related to differences in the stepwise uplift of the two regions. Although uplift is stepwise, the uplift-corrected age–height data from the dated corals fall within a tight envelope, which represents a well defined eustatic sea level curve for the calibrated age interval from 7000 to 13,000 yr BP.

The eustatic component of relative sea-level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles. This has been quantified for the period since the Last Glacial Maximum by correcting observed sea-level change for the glacio-hydro-isostatic contributions using realistic ice distribution and earth models. During the Last Glacial Maximum (LGM) the eustatic sea level was 125±5 m lower than the present day, equivalent to a land-based ice volume of (4.6–4.9)×107 km3. Evidence for a non-uniform rise in eustatic sea level from the LGM to the end of the deglaciation is examined. The initial rate of rise from ca. 21 to 17 ka was relatively slow with an average rate of ca. 6 m ka−1, followed by an average rate of ca. 10 m ka−1 for the next 10 ka. Significant departures from these average rates may have occurred at the time of the Younger Dryas and possibly also around 14 ka. Most of the decay of the large ice sheets was completed by 7 ka, but 3–5 m of water has been added to the oceans since that time.

Skeletal Sr/Ca and 18 O/ 16 O ratios in corals from the Great Barrier Reef, Australia, indicate that the tropical ocean surface ∼5350 years ago was 1°C warmer and enriched in 18 O by 0.5 per mil relative to modern seawater. The results suggest that the temperature increase enhanced the evaporative enrichment of 18 O in seawater. Transport of part of the additional atmospheric water vapor to extratropical latitudes may have sustained the 18 O/ 16 O anomaly. The reduced glacial-Holocene shift in seawater 18 O/ 16 O ratio produced by the mid-Holocene 18 O enrichment may help to reconcile the different temperature histories for the last deglaciation given by coral Sr/Ca thermometry and foraminiferal oxygen-isotope records.

Up to six regressive terraces occur on the Holocene raised reef tract and up to 15 occur on late Pleistocene raised reef tracts along 40 km of coastline at Huon Peninsula, Papua New Guinea. We suggest that the regressive terraces represent repeated episodic uplift caused by great earthquakes. Ages of Holocene coseismic uplift events are established by radiocarbon dating; the late Pleistocene events are bracketed by U series ages of the raised reef tracts on which they occur. The mean recurrence interval of great earthquakes that caused the uplift events is 970 to 1165 years in the Holocene and probably the same in the late Pleistocene; the interval ranged from about 200 to 1900 years. The uplift rate increases parallel to the coast from northwest to southeast, and the amplitude of coseismic uplifts generally increases similarly, although some events produced uplift with little shore-parallel tilting. The mean amplitude of coseismic uplifts throughout the study area is ∼3 m in for both Holocene and late Pleistocene sequences. Large, late Quaternary landslides are numerous, and some probably were triggered by the great earthquakes that caused coseismic uplift. There appears to be no continuum between historical large earthquakes at Huon Peninsula of magnitudes >7 that produced no or only minor uplift, and the great earthquakes represented by meter-scale coseismic uplifts and very large landslides. Two tectonic subregions are recognized, which were uplifted together by some Holocene events but not by others. There is no surface trace of Holocene faulting between the subregions, and a buried fault is thought to separate them.

High-precision measurements of SrCa ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ234U(t) values of 145 ± 2, similar to modern seawater. The SrCa coral records provide 5–6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Nino-Southern Oscillation) events. Mean annual SrCa temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ∼ 2–3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (∼ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ∼ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ∼ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

A flight of coral terraces, up to ca. 1, 000 m above sea level, is well preserved on the northern coast of the Huon Peninsula, Papua New Guinea, and records the sea level and tectonic history since ca. 300 ka. The region is located near the boundary between the Western Pacific and Australian plates. The uplift rate since the last interglacial maximum (oxygen isotope stage 5e) ranges from 0.7 m/ka at the northwest end of the coast, and up to 3.5 m/ka towards the southeast end. Late Quaternary paleoseismicity is estimated from subdivided Holocene and late Pleistocene terraces, each of which records meter-scale coseismic uplift events.The study area covers about 40 km of coast. Holocene coral terraces, up to 25 m above sea level, are divided into seven levels at maximum, four to five at most sites. The highest Holocene terrace is a reef crest representing former sea level of the culmination of the sea level rise at ca. 6-6.6 ka BP. The lower terraces are regressive terraces, which record successive intermittent uplift events, probably caused by great earthquakes. Timing of the Holocene uplift events is ca. 2.5, 3.8, 4.4-5.1, and 5.4 ka BP at Kwambu-Kilasairo area on the northwestern coast, and at ca. 0.8, 1.4, 1.8, 2.5, 3.9 and 5.4 ka BP at Kanomi-Nanda area to Hubegong on the central and southern coast. Difference in the timing of the uplift events implies that there are at least two tectonic suregions on this coast.Similar small regressive terraces are also recognized from the detailed profiles of late Pleistocene terraces. For example, in the central and southern part of the study area, 15-7 extra steps occur between transgressive terrace IIIa (ca. 52 ka) and terrace II (ca. 38 ka). Thus, we infer that repeated meter-scale uplift events have occurred at least since ca. 52 ka. The apparent interval of uplift events, about 1-1.5 ka, resembles to that for Holocene.Such a meter-scale uplift with ka-scale recurrence intervals records a different earthquake deformation cycle from the centimeter-scale uplift associated with the 1992 May earthquake (M= 7.2 : Pandolfi et al., 1994). Such a small event with shorter recurrence interval is apparently not expressed geomorphologically as in the form of regressive terrace.

Late Quaternary stratigraphy of a 50 km2 catchment on the south-eastern highlands of Australia reveals processes and history of denudation, and helps resolve a long-standing debate about factors controlling episodic valley aggradation and degradation during Holocene times. Valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels, promoting aggradation for periods of several thousand years, with most incoming sediment being trapped in swampy meadows. Much of the sediment was reworked from late Pleistocene alluvial fan and valley fill deposits, and primary hillslope erosion was minor during the Holocene. Differing sedimentation patterns between the Late Pleistocene, Holocene and Post-European settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change. Within the Holocene, however, valley fill stratigraphy is controlled by massive, episodic gully erosion terminating aggradation. Gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply. Whether the thresholds are exceeded because of climatic change, autonomous change or extreme events cannot yet be determined. Overall, the Holocene history represents continuing complex response to events of the Late Pleistocene, and does not support the K-cycle concept, which has strongly influenced late Quaternary geomorphology in Australia.

The McArthur River drains from a semiarid, sandstone catchment into a shallow embayment behind the Sir Edward Pellew Group of islands in the southwestern Gulf of Carpentaria. It has built a broad Holocene delta, presently with two active distributaries and several abandoned, mangrove-lined, former distributaries. Augering indicates that much of the delta is underlain by shelly sands which contain distinct shell beds in their position of growth. These are interpreted as delta front deposits, and the elevation of the landwardmost beds above high tide level implies emergence of 1–2 m over the last 4000 years. This relative sea-level fall appears to have been a major cause of rapid mid-Holocene delta progradation. The eastern margin of the delta has undergone little net progradation over the last 2000 years, though there has been accretion of small mangrove-covered islands to the northwest of the delta. Distributaries have migrated across the upper deltaic plain by lateral migration, leaving nested sequences of fluvial ridges. In the lower deltaic plain, channel migration appears to have occurred mainly by avulsion; former distributaries have been infilled with fluvial sands and are now tidally dominated.

The estuarine plain of the macrotidal Daly River, in monsoonal northern Australia, is underlain by extensive mid-Holocene mangrove swamp sediments which accumulated during the last stages of Post-glacial sea-level rise. Sediment yield from the catchment is too low to account for the volume which accumulated during sea-level rise, and onshore transport is invoked. This is supported by radiocarbon ages and facies analysis of the transgressive sediment tract beneath the maximum flooding surface (MFS), and of the tract of vertical sedimentation which extends from the MFS to the surface of estuarine/fluvial transition (the EFT). The EFT occurred about 5000 to 6000 BP throughout the estuarine plain. A contrasting situation exists in the lowland Holocene basin of the microtidal Sepik and Ramu rivers in Papua New Guinea, which derive sediment from highly tectonic catchments. A tectonic basin, which was a shallow brackish inland sea after Post-glacial transgression, is separated by a low divide from a deltaic plain. Progradation of the deltaic plain commenced about 3500 BP after regressive sedimentation eclipsed the inland sea in the tectonic basin. Contrasting organic facies, mangrove in the Daly and freshwater swamp deposits in the Sepik-Ramu, highlight differences between facies models of the two systems. Differences between fluvio-tidal regimes are reflected by the EFT, which is synchronous in the Daly and diachronous in the Sepik-Ramu, and possibly by the MFS which is diachronous in the Daly and may be synchronous in the Sepik-Ramu.

The march of environmental changes in eastern Australia, from the Last Interglacial to the Holocene, is reviewed. Palynologic evidence suggests that forest composition fluctuated substantially during Oxygen Isotope (OI) Substages 5a to 5e, but physical evidence for this period is as yet poorly defined. During OI Stage 3 and possibly part of 4, inland lakes were larger and the hydrologic balance was wetter than at any time since. Conditions were coldest, and dune activity was maximal throughout the continent, during OI Stage 2, but driest conditions as judged from lake levels occurred at the termination of the Pleistocene, when temperatures were rising rapidly. Lags between changes of boundary conditions and responses of natural systems are clearly seen in Holocene behaviour of coasts and reefs, and the effects of extreme events rather than climatic changes are seen in some sedimentary sequences. Establishment of the chronology of deposits older than about 35 ka, and forging links between the terrestrial and deep-sea records, are major challenges for future research.

Swadling et al. (1988) suggest that an inland sea, open to the north, was formed in the Sepik-Ramu lowlands by rising sea level in the late Pleistocene. This sea was infilled during the later Holocene. They also imply that these geographical changes would have significantly affected the human and ecologie prehistory of the region, although without documenting any detail. We report here evidence for existence of the inland sea and for its history of recession towards the current Sepik River mouth. We also report evidence of unusually early use of pottery at sites on former shorelines east of the lower Ramu River and of a 5000-year-old Tridacna shell adze found in alluvium about 300 km from the Sepik mouth.

Previous studies of Holocene sea level in north Queensland have been based on a variety of sea-level related deposits, with interpretations of mid-Holocene levels ranging from near zero up to 4 m above Present. We report data from 8 carefully controlled new sites, located from the Palm Group northwards and extending into the Gulf of Carpentaria. Field evidence is from coral reef flats and prograded coastal deposits. The highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago. The results of this and of certain previous studies are reduced to a common reference surface, or isobase, which varies systematically in elevation across the region. The isobase correlates strongly with predicted hydro-isostatic deformation caused by postglacial sea-level rise.

Isostatic response of the Earth to changes in Quaternary Times of ice and water loads is partly elastic, and partly involves viscous mantle flow. The relaxation spectrum of the Earth, critical for estimation of the mantle flow component, is estimated from published determinations of Fennoscandian and Laurentide rebound, and of the nontidal acceleration of the Earth's rotation. The spectrum is consistent with an asthenosphere viscosity around 1021P, and a viscosity around 1023P below 400 km depth. Calculation of relaxation effects is done by convoluting the load history with the response function in spherical harmonics for global effects, and in rectangular or cylindrical transforms for smaller regional effects. Broad-scale deformation of the globe, resulting from the last deglaciation and sea level rise, is calculated to have involved an average depression of ocean basins of about 8 m, and mean upward movement of continents of about 16 m, relative to the center of the Earth, in the last 7000 yr. Deflection in the ocean margin “hinge zone” varies with continental shelf geometry and rigidity of the underlying lithosphere: predictions are made for different model cases. The computational methods is checked by predicting Fennoscandian and Laurentide postglacial warping, from published estimates of icecap histories, with good results. The depth variations of shorelines formed around 17,000 BP (e.g., North America, 90–130 m; Australia, 130–170 m), are largely explainable in terms of combined elastic and relaxation isostasy. Differences between Holocene eustatic records from oceanic islands (Micronesia, Bermuda), and continental coasts (eastern North America, Australia), are largely but not entirely explained in the same terms.

these upon human prehistory often are discussed in the reports of archaeological studies from tropical coastal and island sites. However, it often happens that the exact pattern of change of one factor or another is not known for a particular site, and results from sites elsewhere are extrapolated, or are called on as analogies. Holocene sea level variations are a good example, particularly because some confusion exists about the nature of such

Post-glacial sea-level curves are expected to differ between different parts of the world, as a result of global isostatic changes1 or perhaps other forms of geoidal changes2. I report here results from the inner part of the northern Great Barrier Reef which seem to show a pattern of smoothly falling sea level during the past 6,000 yr. The results are consistent with stratigraphical results from prograded mangrove coasts on the nearby north Queensland mainland. The region is remote from the tectonically active margin of the south-west Pacific Ocean, and the results contribute to the global data set relevant to isostatic changes being assembled by the International Sea Level project (IGCP Project No. 61). They also provide a baseline relevant to Holocene coral reef growth in the inner Great Barrier Reef.

A major discrepancy between the Late Quaternary sea level changes derived from raised coral reef terraces at the Huon Peninsula in Papua New Guinea and from oxygen isotopes in deep sea cores is resolved. The two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka (ka = 1000 yr before present), but between 70 and 30 ka the isotopic sea levels are 20–40 m lower than the Huon Peninsula sea levels derived in earlier studies. New, high precision U-series age measurements and revised stratigraphic data for Huon Peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic δ18O data. Using the sea level and deep sea isotopic data, oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from Greenland ice cores. The record of ice volume changes through the last glacial cycle now appears to be reasonably complete.

At the tectonically rising terraced coast of Huon Peninsula, Papua New Guinea, a Holocene reef is emerging by as much as 12 m. A clean seacliff section 8 m high provides detailed evidence of the relationship between reef development and early Holocene sea-level changes, relative to the rising coast. The section shows a shallow-water reef-crest facies that grew steadily upward while relative sea level rose approximately 7 m. Reef growth terminated with emplacement of a fluvial gravel cap, which was followed by emergence. Twelve C 14 dates and six Th 230 /U 234 dates put the base of the cliff section at 8200 C 14 yr B.P. and the crest at 6600 C 14 yr B.P. Four Th 230 /U 234 dates from near the base average 9,400 yr old, but C 14 ages from the same samples average 7,600 yr old; the cause of the discrepancy is not known. Uplift of the section is known from previous studies of the Pleistocene reefs in the area to be approximately 1.9 m/1,000 yr. If uplift has been at a uniform rate, then the position of sea level at 6,000 C 14 yr ago (around northeast Papua New Guinea) was about −4 m; 8,000 yr ago it was about −14 m. Mean upward growth rate of the reef was 4.7 m/1,000 yr, and the maximum rate was about 8 m/1,000 yr.