Timothy T. Barrows

Sea-surface temperatures of the southwest Pacific Ocean during the Last Glacial Maximum

The southwest Pacific Ocean covers a broad range of surface-water conditions ranging from warm, salty water in the subtropical East Australian Current to fresher, cold water in the Circumpolar Current. Using a new database of planktonic foraminifera assemblages (AUSMAT-F2), we demonstrate that the modern analog technique can be used to accurately reconstruct the magnitude of sea-surfacetemperature (SST) in this region. We apply this technique to data from 29 deep-sea cores along a meridional transect of the southwest Pacific Ocean to estimate the magnitude of SST cooling during the Last Glacial Maximum. We find minimal cooling in the tropics (0°–2°C), moderate cooling in the subtropical midlatitudes (2°–6°C), and maximum cooling to the southeast of New Zealand (6°–10°C). The magnitude of cooling at the sea surface from the tropics to the temperate latitudes is found to generally be less than cooling at the surface of adjacent land masses.

Planktonic foraminifera from the eastern Indian Ocean: distribution and ecology in relation to the Western Pacific Warm Pool (WPWP)

Abstract Faunal assemblages, principal component (PCA), canonical correspondence (CCA), and factor analysis are applied to planktonic foraminifera from 57 core-top samples from the eastern Indian Ocean. The foraminiferal lysocline occurs at ∼2400 m north of 15°S where carbonate dissolution is induced by the Java upwelling system, and occurs deeper south of 15°S where carbonate dissolution is characteristic of the oligotrophic regions in the Indian Ocean. Dissolution effects, the February standing stock at the time of collection of the plankton-tow material, and different production rates explain the different foraminiferal assemblages found between plankton-tow and core-top samples. Core-top samples are differentiated by PCA into four groups — Upwelling, Western Pacific Warm Pool (WPWP), Transitional, and Southern — that are related to environmental variables (temperature, salinity and nutrients); all environmental variables follow a strong latitudinal component as indicated by the CCA analysis. Similarly, three assemblages are recognized by factor analysis: Factor 1 (dominated by Globigerinoides sacculifer , G. ruber , Globigerinita glutinata and Globorotalia cultrata ), factor 2 (dominated by Globigerina bulloides and Globorotalia inflata ) and factor 3 (dominated by Neogloboquadrina dutertrei ) explain more than 92% of the variance, and are related to sea-surface temperature, thermocline depth and nutrient levels. The seasonal influence of the Java upwelling system supplies nutrients, phyto- and zooplankton to the oligotrophic eastern Indian Ocean (factor 1). South of ∼24°S, a deep chlorophyll maximum, a deep euphotic zone, a deep thermocline, SSTs below ∼22°C, and brief upwelling pulses seem to explain factors 2 and 3. The ratio of G. sacculifer and N. dutertrei , two mutually excluding species, appears to indicate the southern boundary of the WPWP. This ratio is applied to core Fr10/95-11 to demonstrate past shifts of the southern boundary of the WPWP.

Palaeoceanography of the last glacial maximum in the eastern Indian Ocean: planktonic foraminiferal evidence

Palaeoceanographic conditions in the eastern Indian Ocean for the last30 kyr are documented by means of planktonic foraminiferal analyses of 10 gravity cores. Quantitative foraminiferal analysis (%), Q-mode factor analysis, the modern analog technique (MAT) and oxygen-isotope analyses are used. A conspicuous increase during the last glacial maximum (LGM) of foraminiferal fragmentation resulting from a more productive Java upwelling system and=or a more corrosive Antarctic Intermediate Water (AAIW) was found at intermediate water depths (1000 m). Contrasting Q-mode factors based on foraminifera between today and the LGM suggest changes in the thermocline depth, sea-surface temperature (SST), upwelling, and the strength of both the Australasian Mediterranean Water (AAMW) and the Indian Central Water (ICW). The decrease in the percentage abundance of shallow-dwelling and symbiont-bearing planktonic foraminifera, the increase in percentage of the upwelling-related species Globorotalia cultrata and Neogloboquadrina dutertrei , and factor 3 (dominated by Globorotalia tumida and Globigerinella siphonifera) suggest a stronger Java upwelling system during the LGM. A steeper, steric latitudinal gradient (in the presence of a weak Leeuwin Current), and a geostrophic flow similar to today’s is postulated for the LGM, and this must have prevented upwelling offshore Western Australia. Today’s AAMW‐ICW sharp front was weaker during the LGM when the AAMW was saltier, cooler, and nutrient richer and more similar to the ICW. During the LGM, a more gentle SST latitudinal gradient over the16 to23oS region contrasts with today’s steeper conditions at the AAMW‐ICW Front. Also, for the LGM, a nutrient-rich ICW may explain previously documented increases in mass accumulation rates of CaCO3, organic carbon and benthonic foraminifera in a region where the nutricline was deep and within the lower euphotic zone.

Holocene hydrologic variability in temperate southeastern Australia: An example from Lake George, New South Wales

Lake George is one of the largest freshwater lakes in Australia when full, and provides one of the most complete records of Quaternary sedimentation in the southeastern part of the continent. The lake is currently ephemeral, but sediments within the basin preserve evidence of multiple permanent and dry lake conditions in the past. We present an optically stimulated luminescence (OSL) chronology of recent lake shoreline sediments in order to reconstruct Holocene hydrologic variability at Lake George, providing past climatic context for the presently ephemeral lake conditions. The OSL chronology indicates three distinct periods of permanent lake conditions up to 15—18 m depth over the Holocene period, at approximately 10—8, 6—2.4 and 0.7—0.3 ka, with lower lake levels occurring in between those events. There appears to be a trend towards lake regression over this period despite relatively recent high lake levels. The chronology is broadly synchronous with comparable records of Holocene climatic variability across southeastern Australia. We also investigate the intrinsic luminescence characteristics of different sediment types as diagnostic tools, but these appear not to be appropriate in this context or form.

Advances in Quaternary studies in Tasmania

Abstract The last 35 years have seen rapid advances in our knowledge of climate change during the Quaternary Period in Tasmania. Extensive mapping and new dating studies, particularly since the advent of exposure dating, have revealed that maximum ice advance occurred 1 Ma ago and later advances were less extensive. Ice advances occurred several times during the last 100 ka, not only during the Last Glacial Maximum. Deglaciation was rapid after 18 ka and complete by 14 ka. Ice strongly affected limestone and produced extensive glaciokarst with deranged surface drainage. Glacial sediment plugged conduits to underground passages partially filled with glaciofluvial gravels. Periglacial erosion, and human impact since late oxygen isotope stage (OIS) 3, enhanced sediment influxes. New pollen records, particularly from Lake Selina, provide a 125 ka vegetation and climate record representative of the Southern Hemisphere. Finally, stable isotope studies of speleothem growth have revealed wide swings in climate. The climate was warm and moist during OIS 5e and early in OIS 1. Climate was cold and dry during OIS 5d and 4, and prevented speleothem growth during OIS 3 and OIS 2.

A White Nile megalake during the last interglacial period

The eastern Sahara Desert of Africa is one of the most climatically sensitive areas on Earth, varying from lake-studded savannah woodland to hyperarid desert over the course of a glacial-interglacial cycle. In currently semiarid Sudan, there is widespread evidence that a very large freshwater lake once filled the White Nile River valley. Here we present the first quantitative estimate for the dimensions of the lake and a direct age for the emplacement of its shoreline. Using a profile dating approach with the cosmogenic nuclide 10 Be, we estimate an exposure age of 109 ± 8 ka for this megalake, indicating that it probably formed during the last interglacial period. This age is supported by optically stimulated luminescence dating of Blue Nile paleochannels associated with the lake. Using a high-resolution digital elevation model, we estimate that the lake was more than 45,000 km 2 in area, making it comparable to the largest freshwater lakes on Earth today. We attribute the lake9s existence to seasonal flood pulses as a result of local damming of the White Nile by a more southern position of the Blue Nile and greatly increased precipitation associated with an enhanced monsoon.

Bauxitic insect pupal cases from northern Australia

Within the Weipa bauxite deposit of northern Queensland, Australia, are rare ovoid structures averaging 49 × 30 mm in size and of a similar composition to the surrounding bauxite. Comprised of a thin shell with an opening near one end, these structures encase ordinary bauxitic pisolitha and are referred to as ovate compound pisoliths. A small proportion of them are completely hollow and have no apparent opening into their chamber. Similar calcareous structures are found along the west coast of Eyre Peninsula, South Australia. These calcareous structures are interpreted to have been constructed by the larval stage of the weevil Leptopius duponti, for protection during pupation. The calcareous structures have a similar size and shape to bauxitic pisoliths, suggesting that ovate compound pisoliths may have been constructed by a similar organism, possibly belonging to the genus Leptopius.

The Glaciation of the South-East Asian Equatorial Region

Abstract This chapter presents estimates of likely glaciation extents across equatorial southeast Asia based on the Shuttle Radar Topography Mission digital elevation model and also discusses new evidence for multiple glaciations. Mt. Kinabalu in Malaysia has an area of 19.3 km 2 higher than 3000 m above sea level (asl) but maximum glacier extent is closer to 5.5 km 2 . At least 3000 km 2 of Papua, Indonesia, and 400 km 2 of Papua New Guinea (PNG) rise above 3600 m asl. These areas represent rough glaciation extents because the late Pleistocene glacial snowline was broadly at 3600 m asl. On Mt Giluwe, PNG, small frontal moraines overlie large down-valley lateral moraines indicating a recent advance of relatively thick ice over an older glacial landscape. The small moraines appear to date to Marine Isotope Stages (MIS) 4 and 2. The large downvalley moraines on Mt. Giluwe are old with boulder exposure ages that date to MIS 6-7. North of Mount Trikora, Papua, cross-cutting moraines suggest at least two major glacial advances. Five boulders spread across an up-valley moraine have cosmogenic exposure ages that postdate the last glaciation. Boulders on downvalley moraines exhibit a range of older exposure ages, four dating to the last glaciations.

Flank-Collapse on Ta’u Island, Samoan Archipelago: Timing and Hazard Implications

A discrepancy between the cartographic depiction of Ta’u Island, Samoan archipelago, in 1849 and its present geomorphology, leads to the impression that a massive collapse involving an estimated 30 km3 occurred on the island’s southern flank less than 170 years ago. It is likely that this flank-collapse, whenever it occurred, generated a tsunami with regional impacts. Here we apply exposure dating to the remnant landslide scarp using the cosmogenic nuclide 36Cl, to show that the flank-collapse occurred 22.4 ± 1.8 ka during the last glacial maximum (LGM). The collapse may have been triggered due to volcanic-related processes, but it is also possible that climatic-eustatic sea-level during the LGM may have played a role in influencing failure of the flank. We confirm that the initial cartographic depiction of Ta’u in 1849 was incorrect, and that this prehistoric landslide-tsunami was not a societal hazard at the time of its occurrence. This is because the Samoan and surrounding Island Nations were only inhabited about 3 ka or so. Nevertheless, we suggest that geomorphic features similar to the Ta’u flank-collapse on analogous islands and seamounts in the Pacific likely represent signatures of landslide-tsunamis in the past. We conclude that there is a need to identify and date other such features in the Pacific, in order to further improve our spatial and geochronological understanding of these events. There is also a need to identify flank features that have not yet failed, and assess the likely mechanisms that could potentially trigger failure. By doing this, we can start assessing with more confidence the hazard potential of similar flank-collapses in future—a risk that is presently under-represented.