This article has been published in published been This has article or collective redistirbution other or collective or means this reposting, of machine, is by photocopy article only anypermitted of with portion the approval The O of Ripple Marks b y C h e ry l Ly n D y b a s

The Story Behind the Story , Volume 4, a quarterly 20, Number The O journal of Winter Ice on Lakes, Rivers, Ponds

G o ing , g o ing , g o n e ? If you’re planning to ice skate on a local lake or river this winter, you may need to think twice, according to scientists John Magnuson, Olaf Jensen, and Barbara Benson of the University of Wisconsin at Madison and their colleagues. ceanography Society. Copyright 2007 by The O From sources as diverse as newspaper archives, transportation ledgers, and reli- gious observances, the researchers have amassed 150 years of lake and river ice records spanning the Northern Hemisphere. during a period of rapid climate warming Almost all show a steady trend of fewer (1975–2004). They published their results days of ice cover. in the September 2007 issue of the journal Photos courtesy of John Magnuson, If the pattern continues, only in Currier Limnology & Oceanography. University of Wisconsin at Madison and Ives prints will ice skaters twirl across Average rates of change in ice freeze and ceanography Society. A ceanography Society. Send all correspondence to:ceanography Society. Send [email protected] Th e O or frozen rivers. breakup dates on inland lakes were 5.8 and the peak spring phytoplankton bloom and “Calendar dates of freezing and thaw- 3.3 times more rapid, respectively, than the population dynamics of some species of ing of lakes and rivers were being recorded historical rates from 1846 to 1995 for the zooplankton. Fewer days of ice cover are also

well before scientists began to measure Northern Hemisphere. Average ice dura- likely to reduce or eliminate winter kill in Permission is reserved. ll rights granted to in teaching copy this and research. for use article Republication, systemmatic reproduction, these freshwater systems,” said Magnuson. tion decreased by 5.3 days per decade in the shallow eutrophic lakes. “These simple records provide a season- recent study. Over the same time period, In contrast to the general observation that ally integrated view of global warming from average fall through spring climate changes are occurring more rapidly at regions where early measure- in this region increased by 0.7°C. The aver- higher latitudes, the greatest rate of change in ments are sparse.” age number of days with snow decreased ice breakup dates in the Great Lakes region is The records show that later freezing by 5.0 days per decade, and the average happening at lower latitudes, near the south- and earlier ice breakup occurred on lakes snow depth on those days decreased by ern boundary of the area in which lakes are and rivers across the Northern Hemisphere 1.7 cm per decade. routinely ice covered during winter. from 1846 to 1995. Over those 150 years, “The formation and breakup of ice are During the late 1980s and early 1990s, for ceanography Society, P changes in freeze dates averaged 5.8 days per important seasonal events in mid- to high- example, ice breakup occasionally occurred 100 years later, and changes in ice breakup latitude lakes and rivers,” the scientists wrote in midwinter on two lakes in southern dates averaged 6.5 days per 100 years earlier. in Limnology & Oceanography. “The timing of Michigan. These lakes previously hadn’t seen The findings translate to increasing air tem- these events—ice phenology—is sensitive to open water until spring. By the end of the Box 1931, Rockville, MD 20849-1931, US 1931, Rockville, O Box peratures of about 1.2°C each century. the characteristics of individual water bodies Great Lakes study period, in 1998 and 2002, Now the scientists have looked more spe- and to broader-scale weather patterns and several southerly lakes did not freeze over. cifically at trends in ice duration in 65 water climate variability.” In lakes from Big Green in Wisconsin to bodies across what might be called the last Changes in ice phenology have important Cranberry in New York, from Minnetonka in bastion of winter in the —the consequences for fish and zooplankton com- Minnesota to Gull in Michigan, winter—at Great Lakes region (Minnesota, Wisconsin, munities. Earlier ice breakup has created a least in the form of ice—is fast melting Michigan, Ontario, and New York)— temporal mismatch, for example, between around the edges. A .

16 Oceanography Vol. 20, No. 4 The Tales Melting Ice Could Tell a N C I e n t M icr o b e s L o c k e d The microbes in the oldest ice were not in G l a ci e rs M ay R e t urn to only slow to grow; the scientists weren’t able l I F e . “Valleys of the dead,” Antarctic to identify them during the growth pro- explorer Captain Robert Falcon Scott called cess as their DNA had deteriorated. “There them in 1905. Indeed, ’s Dry is still DNA left after 1.1 million years,” said Valleys are among the most desolate places Bidle, “but 1.1 million years is the ‘half-life.’” on Earth. The ice-covered moonscapes seem The average size of DNA in microbes in Ice microbes. Courtesy of Kay Bidle, freeze dried and completely lifeless. the oldest ice was 210 base pairs. The aver- Rutgers University But scientists Kay Bidle, SangHoon Lee, age genome of a bacterium alive today is and Paul Falkowski of Rutgers University 3,000,000 base pairs. in on a comet or other debris from outside in New Brunswick, New Jersey, and David “Analyses of ice samples spanning the the solar system. Marchant of Boston University, have found last 8,000,000 years in this region dem- “The preservation of microbes and their that these glacier-covered landscapes harbor onstrated an exponential decline in the genes in icy comets may have allowed tiny frozen organisms that have remained average community DNA size,” the scien- transfer of genetic material among plan- “alive” for more than a million years, encased tists wrote in PNAS, “thereby constraining ets,” they wrote in PNAS. “However, given in the oldest ice on Earth. the geological preservation of microbes the extremely high cosmic radiation flux in The microorganisms, buried in glaciers in in icy environments.” space, our results suggest that it is highly Antarctica’s Mullins Valley and Beacon Valley, Bidle and colleagues chose glaciers in unlikely that life on Earth could have been may return to life as the ice sheets melt. Antarctica for their research because the seeded by genetic material external to Until this discovery, reported in the polar regions are subject to more cosmic the solar system.” August 14, 2007, issue of the journal radiation than elsewhere on Earth. “Cosmic But resuscitation of microbes from Proceedings of the National Academy of radiation is blasting DNA into pieces over Antarctic ice raises the question, said Bidle, Sciences (PNAS), scientists didn’t know geologic time,” said Bidle. Most organisms of whether the microorganisms were pre- whether such ancient microorganisms and can’t repair the damage. Due to the dete- served in ice in an inactive state, or were their DNA could be revived, or for how long rioration of the microbes’ DNA in the old- capable of in situ maintenance . the cells would be viable after they had been est ice, the scientists concluded that life on Liquid water may exist in ice as microlayers frozen in ice. Earth, however it may have arisen, didn’t ride around sediment grains or as microdiameter The researchers melted ice samples rang- veins caused by ionic impurities in the crys- ing from 100,000 to 8,000,000 years old tal structure of ice, raising the possibility of to find the microbes hidden within. “We metabolically active subpopulations, believe found more microorganisms in the ‘young’ the scientists. The analytical procedures in ice than in the ‘old,’” said Falkowski. “The their study, however, couldn’t directly dis- younger ones grew [in culture media] really cern the presence of aqueous microlayers or fast. Microorganisms from the older-age in situ metabolism. samples grew very slowly, doubling only “Nonetheless,” they wrote in their paper, every 70 days.” “our 16S rDNA reconstruction may reflect a metabolically active subset of the encased bacterial population or at least those capable (Below) Beacon Valley and (right) ice sample of preferential production of genomic DNA locations. Courtesy of Kay Bidle, Rutgers University by an unknown mechanism.” Scott wrote in his diaries that the valleys of the dead were “a God-awful place.” For humans, maybe. But oh, the microscopic tales of life— hidden and perhaps thriving—this icy realm could tell.

Oceanography December 2007 17 R ipp l e M a r k s

Clams Make Food from Thin Air

Only plants can take nitrogen gas from the mals to feed and suggests that other animals fixed nitrogen is used for host metabolism. air and use it to make the protein they need in the sea and elsewhere may be able to “This approach,” said Lechene, “introduces to grow. Or so biologists thought. Now sci- survive with only air as a source of protein. a powerful new way to study microbes and entists at Ocean Genome Legacy in Ipswich, Understanding how these clams make use of global nutrient cycles.” Massachusetts, and their colleagues at this process is also helping researchers gain Bacteria and archaea responsible for bio- Harvard Medical School have shown that insights into how plants fix nitrogen, respon- logical nitrogen fixation can be found in animals, too, can convert food into air. sible for a large percentage of the protein free-living form or in symbiosis with algae, The animals are marine clams called ship- made by plants and ultimately eaten by live- higher plants, and some animals. Although worms. They burrow into and eat wood, stock and humans. these microbes are a critical part of the global causing more than a billion dollars in dam- Distel and colleagues Claude Lechene nitrogen cycle, “there has previously been no age to ships and piers each year. and Gregory McMahon of Harvard Medical means to evaluate this fixation process at a “Wood has very little nutritional value,” School and Yvette Luyten of Ocean Genome subcellular resolution,” wrote Lechene et al. in said biologist Dan Distel, executive director Legacy published a paper on their findings in their paper. “This is now possible with MIMS.” of Ocean Genome Legacy. “It contains almost the September 14, 2007, issue of Science. Wood and woody plant materials are no protein. But these clams use bacterial Using multi-isotope imaging mass spec- abundant in the biosphere and are impor- symbionts living inside a special organ in their trometry (MIMS), they directly imaged and tant nitrogen sources for fungi and micro- gills to convert dissolved air (which is about measured nitrogen fixation by individual organisms. But few animals are able to feed 80% nitrogen) into the protein they need.” bacteria in host cells, and demonstrated that primarily on wood. Although rich in carbon, The discovery reveals a new way for ani- said Distel, wood contains two orders of mag- nitude less nitrogen per unit of carbon than does animal tissue. Animals using wood as food must therefore obtain other sources of combined nitrogen for biosynthesis. Wood- eating termites, for example, supplement L. pedicellatus. Photo their diet with nitrogenous compounds pro- courtesy of Daniel L. Distel, duced by nitrogen-fixing bacteria in their gut. Ocean Genome Legacy Along came shipworms, able to do the same thing. “Although conspicuous communities of nitrogen-fixing bacteria have not been found in the guts of shipworms,” said Distel, “dense populations of intracellular symbionts have been observed in cells in shipworm gills.” A bacterium capable of fixing nitrogen gas, Teredinibacter turnerae, has been isolated from the gills of shipworms in the species This image depicts nitrogen fixation Lyrodus pedicellatus. by individual bacteria within bacte- Distel, Lechene, and co-workers localized riocytes in the marine bivalve Lyrodus pedicellatus. A color-coded image of and measured nitrogen fixation by individual 15N/14N has been overlaid on a trans- cells of T. turnerae using MIMS to measure mission electron micrograph to show the incorporation of nitrogen gas enriched in the accumulation and distribution of 15 the stable isotope 15N. Nitrogen-fixing the rare stable isotope N. “MIMS technol- bacteria are revealed by elevated ogy has allowed us to localize, quantify, and 15N/14N ratios (green to brown). Field: compare nitrogen fixation in single cells and 25 x 30 um. Credit: National Resource subcellular structures,” said Distel. for Imaging Mass Spectroscopy, Harvard Medical School and Brigham Indeed, it turns out, animals—or at least 18 Oceanography Vol. 20, No. 4 & Women’s Hospital, Boston, MA this clam—can make food from thin air. Left photo. Steve Irwin and the Zoo team capturing a croc. Right photo. Croc with a tracker. Photos courtesy of Craig Franklin, University of

Out-Swimming an Estuarine

D o n ’ t t Ry T h is at H o m e . Crocs have a wide distribu- Estuarine , Crocodylus porosus, tion, often in remote areas, and have a remarkable ability to find their way are secretive and easily disturbed home, even across great distances, said by human presence, said Franklin. biologist Craig Franklin of the University of “Their capacity for large-scale Queensland in Australia. He and colleagues movements has been poorly describe in a September 2007 paper in the known. Ours is the first study of journal PLoS ONE how they caught and post-release patterns in translo- tagged three large male “salties,” as Franklin cated adult crocodiles, and the first refers to them, transported the crocs 59, application of satellite telemetry to 99, and 411 kilometers, respectively, along a crocodilian.” the Australian coastline, then tracked their Three large male crocodiles were movements via satellite telemetry. captured in northern Australia and translo- Co-authors of the PLoS ONE paper are cated by helicopter along the coastline, the daily movements of 10 to 30 kilometers, Mark Read of the Queensland Parks and longest distance stretching across Cape York often consecutively.” Service; Gordon Grigg and Danielle Peninsula from west to east. It’s noteworthy, said Franklin, that all Shanahan of the ; “All crocodiles returned rapidly and three crocs spent a brief “stopover” time at and Steve Irwin of the , the apparently purposefully to their capture their release points before making a beeline wildlife biologist known as “The Crocodile locations,” said Franklin. “The animal that for home. Could the animals be gleaning Hunter” who died last year after being fatally circumnavigated Cape York Peninsula to information from local waters and thence stabbed by a barb. return to its capture site traveled more than going in the direction required? After a short period of swimming around 400 kilometers in 20 days.” “Our observations clearly indicate that in new areas, all three crocs set off for home Such impressive homing ability is signifi- crocodilians are skillful at interpreting a suite with “unnerving accuracy,” said Franklin. The cant, say the scientists, because translocation of complex cues for orientation and naviga- findings show the longest known “home- is used to manage dangerous crocs inching tion,” the biologists wrote in their paper. ward bound” effort by a crocodile. “What ever closer to human settlements. “It’s clear, If a problem crocodile lives near humans, we saw should make public officials think though, that estuarine crocodiles can exhibit options other than translocation need to be twice before moving dangerous saltwater strong site fidelity, have remarkable naviga- explored, the researchers believe. crocodiles away from human settlements,” tion skills, and may move great distances, fol- For crocs as well as humans, there’s appar- Franklin believes. “It looks like they’ll just lowing a coastline as they go,” said Franklin. ently no place like home. swim straight back.” “These long journeys include impressive

Cheryl Lyn Dybas ([email protected]) is a marine scientist and policy analyst by train- ing. She also writes on a freelance basis about the seas for The Washington Post, BioScience, National Wildlife, Wildlife Conservation, and many other publications. Oceanography December 2007 19