SPRINGS, CORALS AND ACIDIFICATION EFFECTS

Coral  Credit:  NOAA

FROM: NATIONAL SCIENCE FOUNDATION

Natural Underwater Springs Show How Coral Reefs Respond to Ocean Acidification

Ocean acidification due to rising carbon dioxide levels reduces the density of coral skeletons, making coral reefs more vulnerable to disruption and erosion.


The results are from a study of corals growing where underwater springs naturally lower the pH of seawater. (The lower the pH, the more acidic.)

The findings are published today in the journal Proceedings of the National Academy of Sciences and are the first to show that corals are not able to fully acclimate to low pH conditions in nature.

"People have seen similar effects in laboratory experiments," said paper co-author Adina Paytan, a marine scientist at the University of California at Santa Cruz (UCSC).

"We looked in places where corals are exposed to low pH for their entire life span. The good news is that they don't just die. They are able to grow and calcify, but they are not producing robust structures."

With atmospheric carbon dioxide rising steadily, the oceans are absorbing more carbon dioxide, which lowers the pH of surface waters.

Ocean acidification refers to changes in seawater chemistry that move it closer to the acidic range of the pH scale, although seawater is not expected to become literally acidic.

"In our efforts to understand and predict ocean acidification and its long-term effects on marine chemistry and ecosystems, we must deal with a slow process that challenges our ability to detect change," said Don Rice, program director in the National Science Foundation's (NSF) Division of Ocean Sciences.

"This study shows that, with a little effort, we can find ocean sites where nature is already doing the experiments for us."

NSF funded the research through its Ocean Acidification Program, part of the agency's Science, Engineering and Education for Sustainability Investment.

The scientists studied coral reefs along the Caribbean coastline of Mexico's Yucatan Peninsula, where submarine springs lower the pH of the surrounding seawater in a natural setting.

The effect is similar to the widespread ocean acidification that's occurring as the oceans absorb increasing amounts of carbon dioxide from the atmosphere.

Led by first author Elizabeth Crook of UCSC, the researchers deployed instruments to monitor seawater chemistry around the springs and removed skeletal cores from colonies of Porites astreoides, an important Caribbean reef-building coral.

They performed CT scans of the cores in the lab of co-author Anne Cohen at the Woods Hole Oceanographic Institution in Woods Hole, Mass., to measure densities and determine annual calcification rates.

The results show that coral calcification rates decrease significantly along a natural gradient in seawater pH.

Ocean acidification lowers the concentration of carbonate ions in seawater, making it more difficult for corals to build their calcium carbonate skeletons.

"Carbonate ions are the building blocks corals need to grow skeletons," said Paytan.

"When the pH is lower, corals have to use more energy to accumulate these carbonate building blocks internally. As a result, the calcification rate is lower and they lay down less dense skeletons."

The reduced density of the coral skeletons makes them more vulnerable to mechanical erosion during storms, to organisms that bore into corals and to parrotfish, which sometimes feed on corals.

This could lead to a weakening of the reef framework and degradation of the coral reef ecosystem.

"There are likely to be major shifts in reef species and some loss of coral cover, but if ocean acidification is the only factor there won't be total destruction," Paytan said.

"We need to protect corals from other stressors, such as pollution and overfishing. If we can control those, the impact of ocean acidification might not be as bad."

In addition to Crook, Cohen and Paytan, co-authors of the paper include Mario Rebolledo-Vieyra and Laura Hernandez of the Centro de Investigacion Cientifica de Yucatan.

The research was also funded by UC-MEXUS.

-NSF-

SCIENTEST FIND THAT ARTIC WAS MUCH WARMER A FEW MILLION YEARS AGO

Artic Sun.  Credit:  U.S. Fish and Wildlife Serrvice.

FROM: NATIONAL SCIENCE FOUNDATION

Climate Record From Bottom of Russian Lake Shows Arctic Was Warmer Millions of Years Ago
The Arctic was very warm during a period roughly 3.5 to 2 million years ago--a time when research suggests that the level of carbon dioxide in the atmosphere was roughly comparable to today's--leading to the conclusion that relatively small fluctuations in carbon dioxide levels can have a major influence on Arctic climate, according to a new analysis of the longest terrestrial sediment core ever collected in the Arctic.

"One of our major findings is that the Arctic was very warm in the middle Pliocene and Early Pleistocene--roughly 3.6 to 2.2 million years ago--when others have suggested atmospheric carbon dioxide was not much higher than levels we see today," said Julie Brigham-Grette, of the University of Massachusetts Amherst.

Brigham-Grette is a National Science Foundation- (NSF) funded researcher on the sediment core project and a lead author of a new paper published this week in the journal Science that describes the results.

She added that "this could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier climate models."

The data come from the analysis of a continuous cylinder of sediments collected by NSF-funded researchers from the bottom of ice-covered Lake El'gygytgyn, pronounced El-Guh-Git-Kin, the oldest deep lake in the northeast Russian Arctic, located 100 kilometers (62 miles) north of the Arctic Circle. The drilling was an international project.

Drilling took place in the early months of 2009. The Earth Sciences and Polar Programs divisions of NSF's Geosciences Directorate funded the drilling and analysis.

Analysis of the sediment core provides "an exceptional window into environmental dynamics" never before possible, noted Brigham-Grette.

"While existing geologic records from the Arctic contain important hints about this time period, what we are presenting is the most continuous archive of information about past climate change from the entire Arctic borderlands," she said. "Like reading a detective novel, we can go back in time and reconstruct how the Arctic evolved with only a few pages missing here and there."

Results of the core analysis, according to Brigham-Grette, have "major implications for understanding how the Arctic transitioned from a forested landscape without ice sheets to the ice- and snow-covered land we know today."

"Lake E," as it is often called, was formed 3.6 million years ago when a meteorite, perhaps a kilometer in diameter, hit the Earth and blasted out an 18-kilometer (11-mile) wide crater. The lake bottom has been accumulating layers of sediment ever since the initial impact.

The lake also is situated in one of the few areas of the Arctic that was not eroded by continental ice sheets during ice ages. So a thick, continuous sediment record was left remarkably undisturbed. Cores from Lake E reach back in geologic time nearly 25 times farther than Greenland ice cores that span only the past 140,000 years.

Important to the story are the fossil pollen found in the core, including Douglas fir and hemlock, clearly not found in this part of the Arctic today. The pollen allows the reconstruction of the vegetation living around the lake in the past, which in turn paints a picture of past temperatures and precipitation.


"We show that this exceptional warmth well north of the Arctic Circle occurred throughout both warm and cold orbital cycles and coincides with a long interval of 1.2 million years when other researchers from the ANDRILL project have shown the West Antarctic Ice Sheet did not exist," the authors point out.

Hence both poles share some common history, but the pace of change differed.

Along with Brigham-Grette, her co-authors Martin Melles of the University of Cologne, Germany, and Pavel Minyuk of Russia's Northeast Interdisciplinary Scientific Research Institute, Magadan, led research teams on the project. Robert DeConto, also at the University of Massachusetts, led the climate-modeling efforts. These data were compared with ecosystem reconstructions performed by collaborators at University of Berlin and University of Cologne.

The Lake E cores provide a terrestrial perspective on the stepped pacing of several portions of the climate system through the transition from a warm, forested Arctic to the first occurrence of land ice, Brigham-Grette says, and the eventual onset of major glacial-interglacial cycles.

"It is very impressive that summer temperatures during warm intervals even as late as 2.2 million years ago were always warmer than in our pre-Industrial reconstructions," she added.

Minyuk notes that they also observed a major drop in Arctic precipitation at around the same time large Northern Hemispheric ice sheets first expanded and ocean conditions changed in the North Pacific. This has major implications for understanding what drove the onset of the ice ages.

The sediment core also reveals that even during the first major "cold snap" to show up in the record 3.3 million years ago, temperatures in the western Arctic were similar to recent averages of the past 12,000 years. "Most importantly, conditions were not 'glacial,' raising new questions as to the timing of the first appearance of ice sheets in the Northern Hemisphere," the authors add.

This week's paper is the second article published in Science by these authors using data from the Lake E project. Their first in July 2012 covered the period from the present to 2.8 million years ago, while the current work addresses the record from 2.2 to 3.6 million years.

"This latest paper completes our goal of providing an overview of new knowledge of the evolution of Arctic change across the Western borderlands back to 3.6 million years and places this record into a global context with comparisons to records in the Pacific, the Atlantic and Antarctica," Melles points out.

The Lake E paleoclimate reconstructions and climate modeling are consistent with estimates made by other research groups that support the idea that Earth's climate sensitivity to carbon dioxide may well be higher than suggested by the 2007 report of the Intergovernmental Panel on Climate Change.

-NSF-