The effect of pH on the uptake of zinc and cadmium in marine phytoplankton: Possible role of weak complexes

In natural samples from the New Jersey coast and the Gulf of Alaska, zinc (Zn) and cadmium (Cd) uptake rates by phytoplankton decreased on average about 30% as pH was decreased from 8.5 to 7.9 or 7.7, and the partial pressure of carbon dioxide (PCO₂) increased accordingly. The underlying mechanism was explored with the model species, Thalassiosira weissflogii and Emiliania huxleyi, using ethylenediaminetetraacetic acid (EDTA), desferrioxamine B, phytochelatin, and cysteine as complexing agents. Experiments with single complexing agents did not reproduce the effect of pH seen in field samples, ruling out two possible mechanisms: a direct effect on the uptake machinery or down-regulation of uptake at high PCO₂. Zn and Cd bioavailability must thus somehow decrease at low pH in natural seawater, which is counterintuitive since the protonation of complexing agents at low pH should increase the total free concentration of metals. However, in the presence of both a strong and a weak complexing agent, metal uptake rate may decrease at low pH if formation of the weak complex decreases and the metal in the weak complex is more “available” than in the strong complex. We obtained proof of concept for such a two-ligand mechanism for Zn uptake in the presence of EDTA + phytochelatin and EDTA + cysteine. Weak ligands that bind a small fraction of essential metals in surface seawater may thus be important in metal uptake by phytoplankton, and the dual effects of strong and weak complexing agents may control not just the magnitude but also the sign of the effect of pH-PCO₂ on metal uptake rates.

End-Permian mass extinction in the oceans: An ancient analog for the twenty-first century?

The greatest loss of biodiversity in the history of animal life occurred at the end of the Permian Period (~252 million years ago). This biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of Earth’s largest continental flood basalt provinces, the Siberian Traps. Volatile release from basaltic magma and sedimentary strata during emplacement of the Siberian Traps can account for most end-Permian paleontological and geochemical observations. Climate change and, perhaps, destruction of the ozone layer can explain extinctions on land, whereas changes in ocean oxygen levels, CO₂, pH, and temperature can account for extinction selectivity across marine animals. These emerging insights from geology, geochemistry, and paleobiology suggest that the end-Permian extinction may serve as an important ancient analog for twenty-first century oceans.

Ocean acid threatens food chain

Aboard the Aurora Australis, Southern Ocean, Jan 7 AAP – They call themselves Team Acid and are trawling the Southern Ocean with fine nets to see if the shells of tiny marine snails are thinning because of ocean acidification.

Scientists label this acid trend “the evil twin of climate change”.

And they are concerned that shell-thinning could threaten the survival of many small marine creatures and in turn impact on animals further up the food chain, including fish caught commercially for human consumption.

Aboard the Australian Antarctic Division icebreaker Aurora Australis, a small team of scientists are dropping specially designed nets in a bid to catch pteropods, tiny creatures just visible to the naked eye and a key part of the ocean’s food chain.

Marine biologist Donna Roberts says they expect to find evidence of pteropod shell thinning due to ocean acidification, a consequence of carbon absorption in the oceans.

The Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart where she works has already published evidence that the shell weights of other small shelled marine creatures known as foraminifera have decreased by up to 35 per cent.

The uptake of carbon dioxide into the oceans drives a change in ocean chemistry, changing hydrogen levels and the concentration of carbonate ions that pteropods and other organisms use to build their calcium carbonate shells.

Taking fears of acid oceans with a grain of salt

Coral reefs around the world are suffering badly from overfishing and various forms of pollution. Yet many experts argue that the greatest threat to them is the acidification of the oceans from the dissolving of man-made carbon dioxide emissions.

The effect of acidification, according to J.E.N. Veron, an Australian coral scientist, will be “nothing less than catastrophic…. What were once thriving coral gardens that supported the greatest biodiversity of the marine realm will become red-black bacterial slime, and they will stay that way.”

This is a common view. The Natural Resources Defense Council has called ocean acidification “the scariest environmental problem you’ve never heard of.” Sigourney Weaver, who narrated a film about the issue, said that “the scientists are freaked out.” The head of the National Oceanic and Atmospheric Administration calls it global warming’s “equally evil twin.”

But do the scientific data support such alarm? Last month scientists at San Diego’s Scripps Institution of Oceanography and other authors published a study showing how much the pH level (measuring alkalinity versus acidity) varies naturally between parts of the ocean and at different times of the day, month and year.

NOAA educational curricula and activities on ocean acidification for the high school classroom

This web site contains several curricula and activities materials on the following subjects:

• OA Data-in-the-classroom
• OA Lab Activities
• Power of pH
• Calculate Your Carbon Footprint
• Climate Change & Coral Activities
• Ocean Osteoporosis
• Ocean Acidification
• OA-Will the Reefs Survive?