Paleoclimatic research using coral records

Measuring a core on board the Evohe in Kiribati, July 2003. Photo by J. Cole.

I've maintained an active program in coral paleoclimate work since I was a graduate student and have worked on coral records from throughout the tropics. Corals are uniquely valuable sources of information on tropical climate variability: their skeletons preserve geochemical records of environmental change through the isotopic ratios and elements that they incorporate, and they can be analyzed at seasonal resolution and dated to the year. In most of the tropical oceans, instrumental climate records don't predate the mid-20th century. Thus coral records can provide histories of climate change and variability that give new insight into the behavior of important components of the Earth's climate system.

I have a longstanding interest in applying coral paleoclimatology to expand our understanding of El Niño/Southern Oscillation (ENSO) and Pacific decadal variability. ENSO is one of the most influential climate systems on Earth: it orchestrates temperature and rainfall variations throughout the Pacific and its bordering continents as well as in Africa, India, and the Caribbean, and it influences atmospheric composition, storminess, fire frequency, agriculture, and ecosystem processes in many regions. Understanding how this system has behaved in the past and how it has responded to past and present changes in global climate is clearly relevant for anticipating its future behavior. I have worked at many sites in the tropical Pacific (Kiribati, Marquesas, New Guinea, Galapagos) to expand the history of ENSO and Pacific decadal variability using coral records, using mainly records developed from from modern colonies.

I have also been working in the western Indian Ocean since 1995 on developing coral records of regional climate and environmental processes along the East African coast. This region feels the impact of ENSO through regional warming and rainfall, but also experiences its own set of climate processes, as well as regional environmental disturbances relevant to reef health. All of our Indian and Pacific records show a long-term trend towards warmer-wetter conditions, consistent with observed global warming.

Finally, I have worked in the Caribbean along the coast of Venezuela, where regional upwelling and temperature changes are linked to the large-scale behavior of the tropical Atlantic. The tropical Atlantic "dipole" system orchestrates rainfall in the African Sahel and Brazil's Nordeste as well as tropical storm frequency. The goal in this region is to characterize the variability of this system and explore the linkages between oceanic and continental rainfall variability. This project also links to climate variability on longer time scales, through comparison with varved sediment records from the Cariaco Basin.

Current projects include

• using coral Sr/Ca to quantify changes in the zonal SST gradient across the Pacific (funded by NOAA Climate Program Office; doctoral work of Diane Thompson)
• exploring records in fossil corals for Holocene and deglacial changes in Pacific variability (partly funded by IODP)
• using coral Ba/Ca as a tracer of sedimentation on East African reefs (ISPE interdisciplinary faculty research grant)
• synthesis of Indo-Pacific records, with a focus on decadal-multidecadal variability

Crew of the Kiribati coring expedition on board the Evohe, July 2003.

(Above and below) Drilling and laying out coral cores on Onotoa, Kiribati, July 2003. Photos by R. Grace.

Collaborating faculty: Mike Evans, Warren Beck (UA); Sandy Tudhope (Edinburgh)

Students and staff: Toby Ault (PhD candidate), Diane Thompson (incoming PhD candidate 2008), and Heidi Barnett (lab manager), Guleed Ali (undergraduate McNair fellow)

For relevant papers, see publication list.

See this NOAA site for more on coral paleoclimatology.