Temporal variability of the Atlantic meridional overturning circulation at 26.5 degrees N   总被引：4，自引：0，他引：4  

Cunningham SA  Kanzow T  Rayner D  Baringer MO  Johns WE  Marotzke J  Longworth HR  Grant EM  Hirschi JJ  Beal LM  Meinen CS  Bryden HL 《Science (New York, N.Y.)》2007,317(5840):935-938

The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5 degrees N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 +/- 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 10(6) cubic meters per second). Interannual changes in the overturning can be monitored with a resolution of 1.5 Sv.  相似文献   

Development. Putting the brakes on regeneration     

McKerracher L  Ellezam B 《Science (New York, N.Y.)》2002,296(5574):1819-1820

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Genome streamlining in a cosmopolitan oceanic bacterium     

Giovannoni SJ  Tripp HJ  Givan S  Podar M  Vergin KL  Baptista D  Bibbs L  Eads J  Richardson TH  Noordewier M  Rappé MS  Short JM  Carrington JC  Mathur EJ 《Science (New York, N.Y.)》2005,309(5738):1242-1245

The SAR11 clade consists of very small, heterotrophic marine alpha-proteobacteria that are found throughout the oceans, where they account for about 25% of all microbial cells. Pelagibacter ubique, the first cultured member of this clade, has the smallest genome and encodes the smallest number of predicted open reading frames known for a free-living microorganism. In contrast to parasitic bacteria and archaea with small genomes, P. ubique has complete biosynthetic pathways for all 20 amino acids and all but a few cofactors. P. ubique has no pseudogenes, introns, transposons, extrachromosomal elements, or inteins; few paralogs; and the shortest intergenic spacers yet observed for any cell.  相似文献   

Climatic control of riverine and seawater uranium-isotope ratios     

Robinson LF  Henderson GM  Hall L  Matthews I 《Science (New York, N.Y.)》2004,305(5685):851-854

The large variation in the ratio of uranium-234 to uranium-238 (234U/238U) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater (234U/238U). Here, we demonstrate the importance of physical weathering and rainfall for (234U/238U), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem (234U/238U) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas-like cooling. A model of seawater (234U/238U) during glacial cycles indicates that rejection of corals based on modern (234U/238U) +/- <0.01 is not merited and may reject the highest quality ages.  相似文献   

RNA silencing genes control de novo DNA methylation   总被引：1，自引：0，他引：1  

Chan SW  Zilberman D  Xie Z  Johansen LK  Carrington JC  Jacobsen SE 《Science (New York, N.Y.)》2004,303(5662):1336

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Lhx2 selector activity specifies cortical identity and suppresses hippocampal organizer fate     

Mangale VS  Hirokawa KE  Satyaki PR  Gokulchandran N  Chikbire S  Subramanian L  Shetty AS  Martynoga B  Paul J  Mai MV  Li Y  Flanagan LA  Tole S  Monuki ES 《Science (New York, N.Y.)》2008,319(5861):304-309

The earliest step in creating the cerebral cortex is the specification of neuroepithelium to a cortical fate. Using mouse genetic mosaics and timed inactivations, we demonstrated that Lhx2 acts as a classic selector gene and essential intrinsic determinant of cortical identity. Lhx2 selector activity is restricted to an early critical period when stem cells comprise the cortical neuroepithelium, where it acts cell-autonomously to specify cortical identity and suppress alternative fates in a spatially dependent manner. Laterally, Lhx2 null cells adopt antihem identity, whereas medially they become cortical hem cells, which can induce and organize ectopic hippocampal fields. In addition to providing functional evidence for Lhx2 selector activity, these findings show that the cortical hem is a hippocampal organizer.  相似文献   

Dynamics of mammalian chromosome evolution inferred from multispecies comparative maps     

Murphy WJ  Larkin DM  Everts-van der Wind A  Bourque G  Tesler G  Auvil L  Beever JE  Chowdhary BP  Galibert F  Gatzke L  Hitte C  Meyers SN  Milan D  Ostrander EA  Pape G  Parker HG  Raudsepp T  Rogatcheva MB  Schook LB  Skow LC  Welge M  Womack JE  O'brien SJ  Pevzner PA  Lewin HA 《Science (New York, N.Y.)》2005,309(5734):613-617

The genome organizations of eight phylogenetically distinct species from five mammalian orders were compared in order to address fundamental questions relating to mammalian chromosomal evolution. Rates of chromosome evolution within mammalian orders were found to increase since the Cretaceous-Tertiary boundary. Nearly 20% of chromosome breakpoint regions were reused during mammalian evolution; these reuse sites are also enriched for centromeres. Analysis of gene content in and around evolutionary breakpoint regions revealed increased gene density relative to the genome-wide average. We found that segmental duplications populate the majority of primate-specific breakpoints and often flank inverted chromosome segments, implicating their role in chromosomal rearrangement.  相似文献   

Interpreting sequences from mastodon and T. rex     

Asara JM  Garavelli JS  Slatter DA  Schweitzer MH  Freimark LM  Phillips M  Cantley LC 《Science (New York, N.Y.)》2007,317(5843):1324-1325

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Retraction     

Davis ST  Benson BG  Bramson HN  Chapman DE  Dickerson SH  Dold KM  Eberwein DJ  Edelstein M  Frye SV  Gampe RT  Grifffen RJ  Harris PA  Hassell AM  Holmes WD  Hunter RN  Knick VB  Lackey K  Lovejoy B  Luzzio MJ  Murray D  Parker P  Rocque WJ  Shewchuk-Chapman L  Veal JM  Walker DH  Kuyper LF 《Science (New York, N.Y.)》2002,298(5602):2327

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The unusual nature of recent snowpack declines in the North American cordillera     

Pederson GT  Gray ST  Woodhouse CA  Betancourt JL  Fagre DB  Littell JS  Watson E  Luckman BH  Graumlich LJ 《Science (New York, N.Y.)》2011,333(6040):332-335

In western North America, snowpack has declined in recent decades, and further losses are projected through the 21st century. Here, we evaluate the uniqueness of recent declines using snowpack reconstructions from 66 tree-ring chronologies in key runoff-generating areas of the Colorado, Columbia, and Missouri River drainages. Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains and in their north-south synchrony across the cordillera. Both the snowpack declines and their synchrony result from unparalleled springtime warming that is due to positive reinforcement of the anthropogenic warming by decadal variability. The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on streamflow and water supplies across the western United States.  相似文献