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doi:10.2204/iodp.sp.325.2009

Abstract

The history of sea level and sea-surface temperature variation associated with the last deglaciation is of prime interest to understanding the dynamics of large ice sheets and their effects on Earth's isostasy. So far, the only sea level record that encompasses the whole deglaciation is based on offshore drilling of Barbados coral reefs. The Barbados coral reefs overlie an active subduction zone, implying that the apparent sea level record may be biased by tectonic movements. Furthermore, Barbados is located in a region close to the former ice sheets, implying that the sea level record might have been affected by hydro-isostatic mechanisms.

Integrated Ocean Drilling Program (IODP) Proposal 519 was designed to establish the course and effects of the last deglaciation in reef settings that developed in tectonically inactive areas located far away from glaciated regions. Two complementing expeditions were envisaged, one offshore Tahiti (French Polynesia) and the other on the Great Barrier Reef (offshore northeast Australia). The first of these, IODP Expedition 310 (Tahiti Sea Level), was successfully completed in 2005 and 2006 and recovered a near-complete record of sea level change during the last deglaciation.

IODP Expedition 325 proposes to core at several offshore sites along transects on the Great Barrier Reef using a dynamically positioned drilling vessel. The first objective will be to reconstruct the deglaciation curve for the period 20,000 to 10,000 calendar years before present (cal. y BP) in order to establish the minimum sea level during the Last Glacial Maximum and to assess the validity, timing, and amplitude of meltwater pulses (so-called 19 ka MWP, MWP-1A, and MWP-1B events; ca. 19,000, 13,800, and 11,300 cal. y BP), which are thought to have disturbed the general thermohaline oceanic circulation and, hence, global climate. Secondly, we aim to establish the sea-surface temperature variation accompanying the transgression at each transect. These data will allow us to examine the impact of sea level changes on reef growth, geometry, and biological makeup, especially during reef drowning events, and will help improve the modeling of reef development. The third major objective will be to identify and establish patterns of short-term paleoclimatic changes that are thought to have punctuated the transitional period between present-day climatic conditions following the Last Glacial Maximum. It is proposed to quantify the variations of sea-surface temperatures based on high-resolution isotopic and trace element analyses on massive coral colonies. When possible, we will try to identify specific climatic phenomena such as El Nino-Southern Oscillation in the time frame prior to 10,000 cal. y BP.

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