A new study by scientists at the University of Toronto and the University of California, Santa Cruz suggests that changes in world ocean chemistry is one potential cause of the cooling trend of the past 45 million years.
In an article in the July 20 issue of the journal Science, Ulrich Wortmann, geoscientist at the University of Toronto, and Adina Paytan, research professor at UCSC's Institute of Marine Sciences, point to the collision between India and Eurasia approximately 50 million years ago as a trigger of one interval of rapid change. This collision enhanced dissolution of the most extensive belt of water-soluble gypsum on Earth, stretching from modern-day Oman to Pakistan, and well into Western India – remnants of which are exposed in the Zagros Mountains in Iran.
“Seawater chemistry is characterized by long phases of stability, which are interrupted by short intervals of rapid change,” Wortmann said. “We’ve established a new framework that helps us better interpret evolutionary trends and climate change over long periods of time. The study focuses on the past 130 million years, but similar interactions have likely occurred through the past 500 million years.”
The study, which relies heavily on ocean floor core samples collected by the scientific drillship JOIDES Resolution, suggest that the dissolution or creation of such massive gyspum deposits will change the sulfate content of the ocean, and that this will affect the amount of sulfate aerosols in the atmosphere – and thus climate.
“We propose that times of high sulfate concentrations in ocean water correlate with global cooling, just as times of low concentration correspond with greenhouse periods. When India and Eurasia collided, it caused dissolution of ancient salt deposits, which resulted in drastic changes in seawater chemistry,” said Paytan. “This may have led to the demise of the Eocene epoch – the warmest period of the modern-day Cenozoic era – and the transition from a greenhouse to icehouse climate, culminating in the beginning of the rapid expansion of the Antarctic ice sheet.”
The researchers combined data of past seawater sulfur composition that Paytan assembled in 2004, with Wortmann’s recent discovery of the strong link between marine sulfate concentrations and carbon and phosphorus cycling. They were able to explain the seawater sulfate isotope record as a result of massive changes to the accumulation and weathering of gyspum – the mineral form of hydrated calcium sulfate.
“While it has been known for a long time that gyspum deposits can be formed and destroyed rapidly, the effect of these processes on seawater chemistry has been overlooked,” says Wortmann. “The idea represents a paradigm shift in our understanding of how ocean chemistry changes over time and how these changes are linked to climate.”
The paper, titled “Rapid Variability of Seawater Chemistry over the Past 130 Million Years,” appears in the July 20, 2012 issue of the journal Science. Data used in the research were collected through the Integrated Ocean Drilling Program (IODP), an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring and monitoring the subseafloor.
Two lead agencies support the IODP: the National Science Foundation and Japan's Ministry of Education, Culture, Sports, Science and Technology.
Additional program support comes from the European Consortium for Ocean Research Drilling, the Australia-New Zealand IODP Consortium, India's Ministry of Earth Sciences, the People's Republic of China's Ministry of Science and Technology, and the Korea Institute of Geoscience and Mineral Resources.