Chemical changes in the Pacific over 55 million years

5th September 2012 - 11:32

Coloured scanning electron micrograph of a fossil planktonic foraminifera from drill cores in the equatorial Pacific Ocean

Bridget Wade examining microscopic fossils onboard the JOIDES Resolution

Sediment cores recovered from the equatorial Pacific Ocean

Bridget Wade co-authors an article published in Nature "A Cenozoic record of the equatorial Pacific carbonate compensation depth". The study provides a detailed picture of changes in the chemistry of the Pacific Ocean through the last 55 million years.

Dr. Wade was part of an international team of scientists on Integrated Ocean Drilling Program Expedition 320/321. Eight sites were drilled in the equatorial Pacific Ocean in 2009 by the drilling vessel JOIDES Resolution. During the expedition the scientists collected more than 6 km of sediment core, in water depths greater than 4 km.

Dr. Wade’s expertise is in microfossils (planktonic foraminifera). These microplankton live in the surface waters of the ocean and make their shells out of calcium carbonate. When these organisms die they sink to the sea floor. The depth in the ocean at which carbonate dissolves entirely, known as the carbonate compensation depth (or CCD) is today about 4.5 km in the Pacific Ocean, but has changed through time.

During times of warm climate the CCD was shallow, but deepened during colder climate intervals. The study shows that in the Eocene (55 to 34 million years ago) when global temperatures were much warmer than today, the CCD was 3.3 to 3.6 km, but fluctuated dramatically up and down by 200-900 m. The study also reveals other excursions that have taken place during the last 20 million years. The new record is important for understanding long term changes in the global carbon cycle and how climate has influenced the chemistry of the deep ocean.