Project II.1: Towards an astronomically calibrated time scale for the Paleogene (Diederik Liebrand supervised by Heiko Pälike / Ursula Röhl / Thomas Westerhold)

Objective: Two logical and integrated main objectives have been identified for this task: 1) Extending the astronomical time calibration of geological time and paleoclimatic events from the Oligocene into the late and middle Eocene; 2) Cross-calibrate cyclostratigraphies with absolute radiometric ages for the early Paleogene which as of yet cannot be linked to the Neogene-Oligocene-late Eocene calibration with confidence; constrain ages of long-term 2.4 Myr cycles, and provide absolute durations of magnetochrons in the early Paleogene, all in direct collaboration with Project IV.

Background: This task is the next logical step of constructing a fully calibrated astronomical time scale for the Paleogene, thus extending the Neogene calibration, and better understanding the complex workings of the "climate machine" that operates between the astronomical forcing and the recorded climatic response. The Paleogene represents the most recent time during which atmospheric pCO2 levels approached those predicted by the IPCC for the year 2100. An astronomically calibrated deep-sea record of the entire Oligocene was recently published from a single site (Pälike et al., 2006), without the complications that arise from multi-site compilations. Existing tuning efforts for the earlier parts of the Paleogene are still confined mostly to floating fragments of geological time, though progress is currently being made on the Paleocene (Lourens et al., 2005; Westerhold et al., 2007).

Research strategy and methodology: Objective 1): We will select high-quality existing and new data sets to provide the first full orbital calibration from the late Eocene into the early Oligocene, thereby linking the existing good chronology from the Neogene and Oligocene with fragmentary data sets in the earlier parts of the Eocene. New datasets will result from the Ocean Drilling Expedition "Pacific Equatorial Age Transect" (March-June 2008, with H. Pälike co-PI and co-chief), which specifically aims to bridge the crucial Eocene-Oligocene Transition. Work will exploit the signature of the stable 405 kyr eccentricity cycle from existing and new astronomical solutions (Task IV.1) in climate proxy records (stable oxygen and carbon isotopes, high-resolution physical property data). Objective 2): A detailed cyclostratigraphy will be developed for the early Paleogene and placed into the correct framework of long-term astronomical cycle patterns of 405-kyr eccentricity, and the 1.2 Myr and 2,4 Myr amplitude modulations, using detailed radiometric ash-layer dating. The strong interaction with tasks II.2 and III.3 is critical here and typifies the integrated approach of GTSnext, with strong multi-disciplinary tasks.

Feasibility: Existing sediment archives from multiple IODP Sites (Expeditions 171B, 177, 199, 207, 208) as well as established land sections in (Massignano, Venetian Alps) and the USA will be used to systematically assess and establish the detailed correlation between astronomical forcing and Earth System Response. While these datasets can fulfil the objectives, the results will be much strengthened by new sediment cores firmly scheduled to be taken in March-June 2008 on the first expedition of the new IODP phase (http://iodp.tamu.edu/scienceops/expeditions/). For Objective 2), previous work has demonstrated the feasibility of sections for cyclostratigraphic work, and the main emphasis will be to generate new data for projects II.2 and II.3. Recent preliminary work has demonstrated the presence of dateable ash layers in the envisioned sections.

Innovative aspects and relevance: An extension of the fully calibrated timescale into the Eocene will for the first time allow progress on understanding how and why the Earth transitioned from a greenhouse world into an icehouse world, providing exciting new constraints for astronomers and modellers. By linking existing fragmentary records from the Eocene and Paleocene with the younger Neogene, we will also test existing astronomical models, and chart the evolution of the chaotic behaviour of the solar system (currently the 2.4 Myr cycle diverges for different models in the early Paleogene).

Link with other projects: Project II.1 is strongly linked to projects I.1, II.2, II.3 and IV.1. Beyond the scope of the call, results from this task will be of direct benefit for the paleoceanographic community by providing detailed new constraints on the duration and age of paleoclimatic events, and the astronomical community by providing new constraints on astronomical parameters such as long-term amplitude modulation patterns in astronomical cycles.