ALBERT

Description: A consistent chronostratigraphic framework is required to understand the effect of major paleoclimate perturbations on both marine and terrestrial ecosystems. Transient global warming events in the early Eocene, 56-54 Ma ago, show the impact of large scale carbon input into the ocean-atmosphere system. Here we provide the first time-scale synchronization of continental and marine deposits spanning the Paleocene-Eocene Thermal Maximum (PETM) and the interval just prior to the Eocene Thermal Maximum 2 (ETM-2). Cyclic variations in geochemical data come from continental drill cores of the Bighorn Basin Coring Project (BBCP, Wyoming, USA) and from marine deep-sea drilling deposits retrieved by the Ocean Drilling Program (ODP). Both are dominated by eccentricity modulated precession cycles used to construct a common cyclostratigraphic framework. Integration of age models results in a revised astrochronology for the PETM in deep-sea records that is now generally consistent with independent 3He age models. The duration of the PETM is estimated at ~200 kyr for the CIE and ~120 kyr for the associated pelagic clay layer. A common terrestrial and marine age model shows a concurrent major change in marine and terrestrial biotas ~200 kyr before ETM-2. In the Bighorn Basin, the change is referred to as Biohorizon B, and represents a period of significant mammalian turnover and immigration, separating the upper Haplomylus-Ectocion Range Zone from the Bunophorus Interval Zone and approximating the Wa-4-Wa-5 land mammal zone boundary. In sediments from ODP Site 1262 (Walvis Ridge), major changes in the biota at this time are documented by the radiation of a "2nd generation" of apical spine-bearing sphenoliths species (e.g., S. radians and S. editus), the emergence of T. orthostylus, and the marked decline of D. multiradiatus.

Description: Determining the timing and amplitude of tropical sea surface temperature (SST) change is an important part of solving the puzzle of the Plio-Pleistocene ice ages. Alkenone-based tropical SST records from the major ocean basins show coherent glacial-interglacial temperature changes of 1° to 3°C that align with (but slightly lead) global changes in ice volume and deep ocean temperature over the past 3.5 million years. Tropical temperatures became tightly coupled with benthic d18O and orbital forcing after 2.7 million years. We interpret the similarity of tropical SST changes, in dynamically dissimilar regions, to reflect "top-down" forcing through the atmosphere. The inception of a strong carbon dioxide-greenhouse gas feedback and amplification of orbital forcing at ~2.7 million years ago connected the fate of Northern Hemisphere ice sheets with global ocean temperatures since that time.

Description: Geochemical and Sr-Nd-Pb isotopic compositions of the detrital sediments from ODP Hole 1202B and Taiwan rivers were measured in this study, aiming to reveal changes in sediment provenance in the southern Okinawa Trough (SOT) since 28 ka, and to examine the weathering and sediment transport processes in response to monsoon climate variability. Large variations in Sr-Nd-Pb isotopic ratios at 11?9 ka suggest changes in detrital sediment provenance in the SOT from a dominance of the paleo-Changjiang (Yangtze River) and/or continental shelf sediment during the late deglaciation and to west Taiwan rivers since 9.5 ka. Volcanic rocks and eastern Taiwan sediments have not significantly contributed to the SOT. The large shift in sediment provenance during the early Holocene marks a major change in oceanic circulation, mainly caused by the intrusion of the Kuroshio Current into the trough. Clay mineral and geochemical proxies suggest that the Taiwan-derived sediments accumulated during the early-mid ?Holocene climate optimum? (ca. 9.5-4 ka) might be tightly related to the reworking of older altered sediments from terraces and floodplains, rather than having experienced more intense silicate weathering than in the late Holocene (~ 4-0 ka). Overall, silicate weathering in Taiwan was greatly inhibited by accelerating sediment production and transfer from land to ocean caused by monsoon intensification in Holocene. Our study illustrates that the radiogenic isotopic and geochemical compositions of fine-grained detrital sediments are sensitive tools for fingerprinting sediment sources and for reconstructing changes in oceanic currents and monsoon climate in river-dominated East Asian continental margin.