The Oceans

Toxic Ocean Conditions During Major Extinction 93.9 Million Years Ago Quantified: Doesn't Take Much Sulfide to Impact Ocean Life

Oxygen in the atmosphere and ocean rose dramatically about 600 million years ago, coinciding with the first proliferation of animal life. Since then, numerous short lived biotic events -- typically marked by significant climatic perturbations -- took place when oxygen concentrations in the ocean dipped episodically.

Science News,

28 October, 2013

The most studied and extensive of these events occurred 93.9 million years ago. By looking at the chemistry of rocks deposited during that time period, specifically coupled carbon and sulfur isotope data, a research team led by University of California, Riverside biogeochemists reports that oxygen-free and hydrogen sulfide-rich waters extended across roughly five percent of the global ocean during this major climatic perturbation -- far more than the modern ocean's 0.1 percent but much less than previous estimates for this event.

The research suggests that previous estimates of oxygen-free and hydrogen sulfide-rich conditions, or "euxinia," were too high. Nevertheless, the limited and localized euxinia were still sufficiently widespread to have dramatic effect on the entire ocean's chemistry and thus biological activity.

"These conditions must have impacted nutrient availability in the ocean and ultimately the spatial and temporal distribution of marine life," said team member Jeremy D. Owens, a former UC Riverside graduate student, who is now a postdoctoral scientist at the Woods Hole Oceanographic Institution. "Under low-oxygen environments, many biologically important metals and other nutrients are removed from seawater and deposited in the sediments on the seafloor, making them less available for life to flourish."

"What makes this discovery particularly noteworthy is that we mapped out a landscape of bioessential elements in the ocean that was far more perturbed than we expected, and the impacts on life were big," said Timothy W. Lyons, a professor of biogeochemistry at UCR, Owens's former advisor and the principal investigator on the research project.

Study results appear online this week in the Proceedings of the National Academy of Sciences.

Across the event 93.9 million years ago, a major biological extinction in the marine realm has already been documented. Also associated with this event are high levels of carbon dioxide in the atmosphere, which are linked to elevated ocean and atmospheric temperatures. Associated consequences include likely enhanced global rainfall and weathering of the continents, which further shifted the chemistry of the ocean.

"Our work shows that even though only a small portion of the ocean contained toxic and metal-scavenging hydrogen sulfide, it was sufficiently large so that changes to the ocean's chemistry and biology were likely profound," Owens said. "What this says is that only portions of the ocean need to contain sulfide to greatly impact biota."

For their analysis, the researchers collected seafloor mud samples, now rock, from multiple localities in England and Italy. They then performed chemical extraction on the samples to analyze the sulfur isotope compositions in order to estimate the chemistry of the global ocean.

According to the researchers, the importance of their study is elevated by the large amount of previous work on the same interval and thus the extensive availability of supporting data and samples. Yet despite all this past research, the team was able to make a fundamental discovery about the global conditions in the ancient ocean and their impacts on life.

"Today, we are facing rising carbon dioxide contents in the atmosphere through human activities, and the amount of oxygen in the ocean may drop correspondingly in the face of rising seawater temperatures," Lyons said. "Oxygen is less soluble in warmer water, and there are already suggestions of such decreases. In the face of these concerns, our findings from the warm, oxygen-poor ancient ocean may be a warning shot about yet another possible perturbation to marine ecology in the future."

Acidification of oceans threatens to change entire marine ecosystem

Ocean acidification due to excessive release of carbon dioxide into the atmosphere is threatening to produce large-scale changes to the marine ecosystem affecting all levels of the food chain, a University of B.C. marine biologist warned Friday

Vancouver Sun,

25 October 2013

Chris Harley, associate professor in the department of zoology, warned that ocean acidification also carries serious financial implications by making it more difficult for species such as oysters, clams, and sea urchins to build shells and skeletons from calcium carbonate. Acidic water is expected to result in thinner, slower-growing shells, and reduced abundance. Larvae can be especially vulnerable to acidity.

“The aquaculture industry is deeply concerned,” Harley said. “They are trying to find out, basically, how they can avoid going out of business.”

While there is potential for, say, commercial oyster growers to reduce acidity for larvae in land-based facilities, the greater marine environment doesn’t have that luxury. “For wild populations, you can’t just take part of their lifecycle and babysit it,” he said.

A total of 10,000 tonnes of oysters, clams, scallops and mussels worth $21.7 million were harvested in B.C. in 2010. The sea urchin fishery was worth another $9 million, based on a harvest of 2,300 tonnes.

Lab studies at the University of B.C. also show that acidic water can impair the ability of salmon to grow and smell properly, which has implications for their ability to find native spawning streams. Research in Australia’s coral reefs has found that acidity can erode a fish’s ability to sniff out their best habitat and to avoid predators.

Development of small creatures such as pteropods — free-swimming snails that are food for salmon — will also be stunted by acidity.

Harley was speaking in an interview at the conclusion of a week-long meeting on ocean acidification involving some 20 scientists and research students from Canada, the U.S., Scandinavia, Australia, Italy, Great Britain, and Hong Kong.

Harley said that research into ocean acidification is only about a decade old, which is why it is important to bring researchers together from different parts of the world to share findings and better understand the big picture.

“We know the impacts are going to be really widespread. The last big unknown is whether species will be able to adapt.”

Coral reefs in tropical waters also stand to be severely impacted, which he described as a pending “biodiversity catastrophe.”

On the other hand, kelp and seaweed, including those found on the B.C. coast, may benefit from increased carbon dioxide through enhanced photosynthesis. They will also benefit from a decline in grazers such as urchins and snails. “If they become less abundant or smaller, they’ll eat less kelp and that’s a win-win for the kelp.”

Purple sea stars also grow faster under acidic conditions. “That good for them, but it’s bad for the mussels, which are their favourite food,” Harley noted.

Average pH levels in the oceans have dropped form 8.2 to 8.1 and are “headed to 7.8 or below by the end of this century,” he said.

While part of the equation involves the upwelling of naturally acidic waters from the deep ocean, researchers believe that the major driver is carbon dioxide released from burning fossil fuels.

While the issue is global in scale, there are steps that can be taken locally to lessen the impact such as by reducing fertilizer runoff from farms and protecting biodiversity through measures such as marine protected areas.

“Every little bit helps. The more we can transition from fossil fuels, the better off we’ll be.”