Interpreting coral reef microbialites is challenging as they are difficult to date and usually do not contain fossils of the organisms that produce them - they are precipitates caused by those organisms. Despite their potential as significant environmental archives, even basic understanding of key issues are lacking, including growth rates and the meaning of the laminae. Also, knowledge on the microbial consortia responsible for the precipitation is usually hampered by preservation.
Here, an exceptional preservation of morphological bioindicators is opening the unique opportunity to combine indirect with direct evidence of microbial activity. IODP 389 (Hawaiian Drowned Reefs) targeted drowned Pleistocene reefs around the Island of Hawai’i. The microbialites present in those reefs represent an untapped archive to untangle nutrient from alkalinity influence on coral reef ecosystems.
This project focuses on microbialites formed during MIS 7-1 and aims to (1) unravel the information yielded by the exceptionally well-preserved bioindicators, (2) advance the understanding of the laminae and growth rates of microbialites (chronology of the inherent environmental archive), and (3) test the environmental archive against humidity-aridity dynamics and pCO2 – marine alkalinity dynamics associated with glacial interglacial cycles.
For more information on IODP 389 see:
https://www.ecord.org/expedition389/
For more information on the microbialites studied here see:
Contacts 
Project flyer for download