Stable carbon and oxygen isotope ratios and age model of ODP Hole 182-1127B

The aim of this study was to evaluate the potential of constructing an oxygen and carbon isotope stratigraphy for the late Pleistocene succession from Hole 1127B drilled on the Great Australian Bight. Stable isotope analyses were performed on bulk- and fine-fraction (<38 µm) sediment samples. The oxygen isotope variations are generally smaller in magnitude than expected from global pelagic records. This is most likely due to the neriticly dominated sediment composition. Correlation of the oxygen isotope data with carbonate mineralogy and downhole logging data shows simultaneous variations and trends, which are particularly evident in the mid-Pleistocene sediments. Correlation of the oxygen isotope data with the classic SPECMAP curve is used to evaluate the stratigraphic potential of the Site 1127 sediments. This study indicates that an isotope stratigraphy based on planktonic and benthic foraminifers is needed to fully evaluate the response of cool-water carbonates deposited in a margin setting to global ice-volume fluctuations and, hence, the associated sea level variations.

Stable isotope record and distribution of foraminifera in sediment core GeoB3004-1

Fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon-driven organic matter fluxes in the deep western Arabian Sea during the last 190 kyr. Times of maximum surface production coincide with periods of intensified SW monsoon as shown by the abundance of Globigerina bulloides and enhanced carbonate corrosion. Benthic ecosystem variability in the deep Arabian Sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation. Deepening of the base of the oxygen minimum zone (OMZ) below 1800 m water depth is strongly coherent on the precessional band but lags proxies of SW monsoon strength by 4 to 6 kyr. The "out-of-phase" relationship between OMZ deepening and maximum SW monsoon strength is explained by temporal changes in the advection of oxygen-rich deepwater masses of North Atlantic and Antarctic origin. This process affected the remineralization and burial efficiency of organic matter in the deep Arabian Sea, resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation.

Planktic foraminiferal sieve size specific d13C and d18O values and maximum test diameter from ODP sites 171-1051 and 120-748

Many genera of modern planktic foraminifera are adapted to nutrient-poor (oligotrophic) surface waters by hosting photosynthetic symbionts, but it is unknown how they will respond to future changes in ocean temperature and acidity. Here we show that ca. 40 Ma, some fossil photosymbiont-bearing planktic foraminifera were temporarily 'bleached' of their symbionts coincident with transient global warming during the Middle Eocene Climatic Optimum (MECO). At Ocean Drilling Program (ODP) Sites 748 and 1051 (Southern Ocean and mid-latitude North Atlantic, respectively), the typically positive relationship between the size of photosymbiont-bearing planktic foraminifer tests and their carbon isotope ratios (d13C) was temporarily reduced for ~100 k.y. during the peak of the MECO. At the same time, the typically photosymbiont-bearing planktic foraminifera Acarinina suffered transient reductions in test size and relative abundance, indicating ecological stress. The coincidence of minimum d18O values and reduction in test size-d13C gradients suggests a link between increased sea-surface temperatures and bleaching during the MECO, although changes in pH and nutrient availability may also have played a role. Our findings show that host-photosymbiont interactions are not constant through geological time, with implications for both the evolution of trophic strategies in marine plankton and the reliability of geochemical proxy records generated from symbiont-bearing planktic foraminifera.

Age determination and age tie-points of sediment cores from the Timor Sea

The evolution of the Australian monsoon in relation to high-latitude temperature fluctuations over the last termination remains highly enigmatic. Here we integrate high-resolution riverine runoff and dust proxy data from X-ray fluorescence scanner measurements in four well-dated sediment cores, forming a NE-SW transect across the Timor Sea. Our records reveal that the development of the Australian monsoon closely followed the deglacial warming history of Antarctica. A minimum in riverine runoff documents dry conditions throughout the region during the Antarctic Cold Reversal (15-12.9 ka). Massive intensification of the monsoon coincided with Southern Hemisphere warming and intensified greenhouse forcing over Australia during the atmospheric CO2 rise at 12.9-10 ka. We relate the earlier onset of the monsoon in the Timor Strait (13.4 ka) to regional changes in landmass exposure during deglacial sea-level rise. A return to dryer conditions occurred between 8.1 and 7.3 ka following the early Holocene runoff maximum.