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Saltier WaterClimate change can slow ocean’s absorption of carbon dioxide gas

Adecrease in precipitationover the Pacific Ocean justnorth of Hawaii in recent

years has left the ocean theresaltier and has diminished itscapacity to soak up planet-warming carbon dioxide, a newanalysis shows.

Each month since the late1980s, researchers haverecorded ocean conditionsabout 100 kilometers north ofOahu, far enough out thatwaters aren’t affected by nutri-ents washed from any island. At5 km deep, the water at thissite—which scientists havedubbed station ALOHA—hasocean layers that mix just asmuch as they do in moreremote waters, says David M.Karl, a biogeochemist at the Uni-versity of Hawaii in Honolulu.

The scientists’ measurementsindicate that, averaged over ayear, surface waters at the sitesoak up carbon dioxide from theatmosphere. However, the rateof absorption of that greenhousegas has been slowing in recentyears. In 2001, the ocean at sta-tion ALOHA absorbed only about15 percent of the carbon dioxidethat it did in 1989, says Karl.

Other changes in the waterduring that same period—together with simple thermody-namics—help explain why. From1989 to 2001, the ocean-surfacesalinity at station ALOHA wentup about 1 percent. That’sbecause in recent years there’sbeen less rainfall and moreevaporation in the area, both ofwhich concentrate salt in thesurface water. When the con-

centration of dissolved sub-stances goes up, it becomesmore difficult for a liquid toabsorb a gas, says Karl.

Increased salinity accountsfor about 40 percent of thedecrease in carbon dioxideabsorption over the 13-yearperiod, says Karl. He and hiscolleagues haven’t identifiedthe cause of the rest of theabsorption slowdown, but somecandidates are changes in bio-logical productivity and fluctua-tions in ocean-surface mixing.The dip in carbon sequestrationdoesn’t seem to be related tosea-surface temperature, how-ever, because annual averagesat the site haven’t changedover the period. The research-ers report their findings in theAug. 14 Nature.

Station ALOHA is located inthe North Pacific subtropicalgyre, a swirl nearly the width ofthe Pacific that typically has lit-tle biological activity near thesea’s surface. Such gyresaccount for 40 percent ofEarth’s ocean area, says Karl.

The team’s study is the firstto look at the effect that achange in precipitation over anocean would have on the rateat which the water absorbscarbon dioxide, says Rik Wan-ninkhof, an oceanographer atthe Atlantic Oceanographicand Meteorological Laboratoryin Miami. The salinity changesthat Karl and his colleagueshave measured aren’t huge,he notes, but their effect “ismuch larger than I’d havethought.” —S. PERKINS

past infections by viruses known as bacte-riophages or phages. Scientists haverecently realized that such viruses haveinfected many ocean bacteria, providingone way that the bacteria acquired newgenes (SN: 7/12/03, p. 26).

Many phages, however, don’t make a per-manent home inside their host. In anotherNature report, for example, Mann and hiscolleagues reveal the DNA sequence of avirus that infects and replicates inside Syne-chococcus strains, eventually killing them.Mann’s team discovered that this particu-lar phage contains two genes for proteinsrequired by the Synechococcus’ photosyn-thetic process.

Normally, sunlight damages these twoproteins, so bacteria must keep makingreplacement copies. But Mann suspects thatwhen the virus infects a Synechococcus, thephage turns off most of the bacterium’sgenes. So, to keep energy flowing for its ownreproduction, the phage supplies copies ofthe photosynthetic genes. “It’s not an act ofaltruism on the part of the phage. It’s a cyn-ical takeover of the cell,” concludes Mann.

One theme emerging from these studiesof cyanobacteria, notes Donald A. Bryant ofPennsylvania State University in State Col-lege, is that the organisms don’t have as manygenes devoted to sensing and reacting to theenvironment as many other bacteria do. “Theocean is a big place and relatively constantas an environment. The concentration ofmany things in the ocean is relatively fixed,so there’s no reason to sense change,” he says.

Iron concentrations, however, do changein the ocean, and there’s often a scarcity ofthat metal. Perhaps as a result, the cyanobac-teria possess extra genes for enzymes thatrequire nickel and copper, rather than iron,for their function. “That’s a particularlyinteresting adaptation, something rathernovel,” says Bryant. —J. TRAVIS

Brawny BrainsCreatine pills may aidmemory and cognition

The popular muscle-building supplementcreatine can boost performance on mentaltests. Students preparing for exams mightbenefit from taking creatine in much theway that some competitive athletes do, anAustralian neurochemist suggests.

Creatine, an amino acid produced bythe body and also obtained from meat ina person’s diet, helps cells store ready-to-use energy. When taken during weighttraining, pills containing synthetic crea-tine accelerate gains in muscle strength.Creatine’s popularity among athletes andbody builders fuels a market of more than$200 million per year for the pills in theUnited States.

Increased blood flow to the brain accel-erates metabolism when someone con-fronts a challenging mental task, but anenergy debt in taxed brain cells can last for

several seconds. To see whether extra cre-atine could help meet the brain’s demandsduring quick thinking, Caroline Rae of theUniversity of Sydney and her colleaguesgave a daily pill to each of 45 university stu-dents who were vegetarians. The research-ers suspected that creatine might help veg-etarians more than omnivores, who acquirethe compound from their diets.

For 6 weeks, half the volunteers receivedpills containing 5 grams of creatine. The restreceived sham pills. Researchers tested allvolunteers with a battery of memory andtimed analytical tasks at the beginning andend of the trial. After 6 weeks’ wait, theresearchers conducted an identical trial,except that volunteers got whichever treat-ment—creatine or placebo—they hadn’treceived the first time. Neither the volun-teers nor the administrators of the tests weretold who was taking which pill at which time.

In both trials, volunteers receiving crea-tine scored better than placebo-treated vol-unteers on measures of memory and ana-lytical skills, Rae and her colleagues willreport in the Oct. 22 Proceedings of theRoyal Society of London B. In one test, forexample, volunteers taking creatine couldrecall an average of 8.5 consecutive numer-ical digits, but those receiving the placebopill remembered only 7 digits.

The Australian government funded theresearch. Past studies had suggested thatcreatine supplements can protect againstthe effects of certain neurological diseases.

The new findings are “truly remarkable,”

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says Markus Wyss of Roche Vitamins inBasel, Switzerland. Roche does not cur-rently sell creatine supplements, he says.

“This is the first study to show a beneficialeffect of creatine supplementation on men-tal performance. If confirmed, the findingsmay . . . justify much broader use of creatine,”Wyss says. “Nevertheless, [larger] studiesneed to be performed before the potentialimpact on human health can be fully judged.”

If people use creatine to enhance mem-ory and mental performance, they mighttake it for years at a stretch, Wyss says. Thelong-term safety of creatine supplementa-tion hasn’t been well tested, but the com-pound can exacerbate health problems inpeople with diabetes or kidney dysfunction.

Ronald L. Terjung of the University of Mis-souri in Columbia questions whether non-vegetarians would enjoy the creatine bene-fits observed in the study. He also says that,despite the study’s design, volunteers mayhave known when they were getting the realsupplements. Creatine can cause bad breath,flatulence, and weight gain from excess waterretention—cues that might have encouragedvolunteers to unconsciously push harder onthe tests, he suggests. —B. HARDER

Risky High Life Mountain creatures proveextra-vulnerable

Climate change may literally knock the topoff the world’s terrestrial-animalpopulations, according to anAustralian analysis.

The species thathave specialized inliving at the heightsof a particularmountain andoccur nowhere elseface unusually direrisks from climatechange, says StephenE. Williams of JamesCook University in Townsville.

In a case study of such endemic ver-tebrates in a strip of mountainous rain for-est in Queensland, just 1°C of climate warm-ing will deprive them of 65 percent of theircore habitat, on average, Williams and hiscolleagues predict in an upcoming Proceed-ings of the Royal Society of London B. Andwith a rise of 3.5°C, which Williams calls a“moderate” scenario, the analysis shows a

complete loss of core habitat for 30 of the 65endemic vertebrates in these rain forests.

“I don’t think any other studies have pre-dicted such a catastrophic effect,” saysWilliams. “I’ve never written a paper I hopeso fervently is wrong.”

Another modeler of climate effects agreesthat concern is justified. Chris D. Thomasof the University of Leeds in England says,“When you look at all the species, it becomesa very convincing pattern.”

Most other studies of climate change inecosystems have predicted major shifting ofanimal ranges with species losses only hereand there, says Williams. A 1999 study,however, shows that on a Costa Ricanmountain, lowland bird species movedupland in the face of climate change, whileupper-altitude amphibians dwindled.

“I didn’t start out to study climatechange,” Williams says. For 10 years or so,he and his various colleagues examinedhabitat use by surveying birds, mammals,and other vertebrates of a region that Aus-tralians designate as the wet tropics. Whenthe researchers modeled how about a dozenof the species’ ranges would change withtemperature rise, the dramatic results madeWilliams focus on climate change.

For the new study, he considered theregion’s 65 endemic rain forest species,including ring-tail possums, the goldenbowerbird, and microhylid frogs, whichskip the tadpole stage.

The most conservative climate changethat the team considered, a 1°C rise, “mightnot send a lot of species extinct but wouldmake them critically endangered,” Williamssays. With a 5°C rise, “there’s pretty muchno range left of anything among theendemics,” says Williams.

According to the United Nations’ Inter-governmental Panel on Climate Change,the most likely scenario for the next cen-tury is a 1.4°C to 5.8°C rise.

Jane Hill of York Universityin England welcomes the

new study as “impor-tant in highlighting

the scale of the losswith relativelysmall tempera-ture changes.”

Both Williamsand Thomas cau-

tion that fates ofparticular species

will differ from theoverall results of the model

described in theAustralian report.However, Thomassays, “I think thiswill be a veryinfluential paper.”

Williams saysthat internationalcooperation to

reduce greenhouse gases is necessary for thestrongest protection of mountain ecosys-tems. Yet keeping an ecosystem in the besthealth possible, by maintaining its biodi-versity, would cushion the insults of climatechange. “That’s something that can be donelocally,” he says. —S. MILIUS

Amending theGenetic CodeYeast adds new aminoacids to its proteins

With only rare exceptions, every organismconstructs proteins from just 20 buildingblocks called amino acids. Recently, how-ever, researchers modified Escherichia colibacteria so that the single-celled organismsalso make an alien amino acid and incor-porate it into proteins (SN: 1/25/03, p. 53).

Now, the same scientists have used geneticengineering techniques to coerce more-complicated organisms into placing unnat-ural amino acids into proteins. Led by PeterG. Schultz of the Scripps Research Institutein La Jolla, Calif., the team created yeast cellsthat add one of five unnatural amino acidsto their natural 20-piece construction set.To give the yeast this capability, the research-ers altered the cells’ biochemical machinerythat identifies amino acids and puts theminto particular locations within a protein.

Unlike the E. coli on which the team pre-viously reported, the yeast doesn’t manu-facture synthetic amino acids itself. Instead,it takes the molecules up from the nutrientmixture in which it’s grown. The research-ers describe this work on Saccharomycescerevisiae in the Aug. 15 Science.

The Scripps team suggests that scientistscould use this technology to produce pro-teins with new or enhanced properties. Forexample, improved drugs might result. Thedevelopment may also improve the study ofprotein function in yeast, the scientists report.

The unnatural amino acids used by theengineered yeast have various useful prop-erties, says Scripps team member T. AshtonCropp. For example, when activated bylight, two of these amino acids bond pro-teins together, a function that could provevaluable in studies of protein interactions.Another of the novel amino acids mighthelp researchers using X-ray crystallogra-phy studies to elucidate protein structure.

“It is another brilliant achievement fromthe Schultz group,” says Jack F. Kirsch ofthe University of California, Berkeley. “Thepotential applications are endless.”

“This technology will be very powerfuland very useful,” agrees Hung-wen (Ben)Liu of the University of Texas at Austin.He says he hopes the Scripps team willmake the technology available to other sci-

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HIGH RISKS Atangerine nursery frog,which lives only in the mountainousrain forests ofQueensland, Australia,faces grave perils fromclimate change.

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