Ripple Marks B Y C H E Ry L Ly N D Y B a S
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This article has This been published in or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any permitted articleonly photocopy by is of machine, reposting, this means or collective or other redistirbution Ripple Marks B Y C H E RY L LY N D Y B A S The Story Behind the Story Oceanography , Volume 20, Number 4, a quarterly journal of The 20, Number 4, a quarterly , Volume Winter Ice on Lakes, Rivers, Ponds GO 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. O ceanography Society. Copyright 2007 by The 2007 by Copyright Society. ceanography 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 O Average rates of change in ice freeze and Society. ceanography and Ives prints will ice skaters twirl across O ceanography Society. Send all correspondence to: [email protected] or Th e [email protected] Send Society. ceanography to: correspondence all 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 A well before scientists began to measure Northern Hemisphere. Average ice dura- likely to reduce or eliminate winter kill in reproduction, systemmatic Republication, article for use and research. this copy in teaching to granted ll rights reserved. is Permission 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 temperatures climate changes are occurring more rapidly at regions where early temperature 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 O ceanography Society, P Society, ceanography 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 O peratures of about 1.2°C each century. the characteristics of individual water bodies Great Lakes study period, in 1998 and 2002, Box 1931, Rockville, MD 20849-1931, US 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 United States—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 Anci E N T M icr O B E S L O C KE 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 Lif 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, Antarctica’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 metabolism. 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.