Shock to the (Eco)system

Thanks to a new instrument, Scripps Institution of Oceanography at UC San Diego graduate student Celli Hull can scan through thousands of years of ancient mud in hopes of gaining a long-term view of how marine ecosystems reacted to a mass extinction 65 million years ago.

Hull scanned sediment cores in a search for traces of barium and titanium using a new Avaatech core scanner located in the Scripps geological collection facility, one of only three in the United States, purchased with the help of a private donor. The information could help researchers observe changes in the ocean’s primary productivity during the Cretaceous-Tertiary mass extinction, which was caused by a 13-kilometer (eight-mile)-wide meteorite that left a 250-kilometer (155-mile) -wide crater in the Yucatan peninsula that exterminated the dinosaurs.

“One of the primary motivations for this research is the desire to understand how oceanic ecosystems recover from really big disturbances,” said Hull, a graduate student working in the lab of Scripps paleoceanographer Richard Norris.  “In the modern ocean, humans are a really big disturbance, and this research can help us understand the time scales and mechanisms of recovery on evolutionary time scales.”
 

The ratio of barium to titanium is used by scientists to estimate the amount of sinking organic matter on the seafloor before, during, and after the event. This sophisticated tool allowed Hull to obtain thousands of measurements across the Cretaceous-Tertiary boundary and more than seven million years after the event.

Hull scanned cores from two sites, Shatsky Rise located in the equatorial North Pacific at the time and Maud Rise located in the Weddell Sea near Antarctica. Her results show that these two sites appear to have been relatively resilient to the mass extinction as compared to other sites in the Atlantic and Indian oceans.

After the ancient mass extinction, the oceans were devoid of many species, including more than 80 percent of open-ocean organisms.  As a result, the remaining species over millions of years created new ecosystems that scientists say functioned in fundamentally different ways.

“The parallel to today's oceans is that we are emptying the seas of many of the major players that used to top the oceanic food web,” said Hull.  This along with climate change impacts such as ocean acidification exacerbates the negative effects on today’s ecosystems. According to Hull, “Relative to the time these ecosystems have been around, our effect is really rapid.”
 

Norris hopes this new instrument along with the new three-dimensional X-ray scanner, will open up new interdisciplinary study opportunities at Scripps, such as studies on the effects the climate system has on fish population and other marine communities.

The new facility promotes its open door to the broader research community, said Norris, who plans to incorporate it into a classroom study of the use of leaded gasoline by looking for traces of lead in pine tree cores.

“We had it in mind for geosciences and climate studies but it has the potential to do lots of other things,” he said.

--Annie Reisewitz