Pacific Ocean Heat Content During the Past 10,000 Years

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<ul><li><p>DOI: 10.1126/science.1240837, 617 (2013);342 Science</p><p> et al.Yair RosenthalPacific Ocean Heat Content During the Past 10,000 Years</p><p> This copy is for your personal, non-commercial use only.</p><p> clicking here.colleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others</p><p> here.following the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles</p><p> ): October 31, 2013 (this information is current as ofThe following resources related to this article are available online at</p><p> of this article at: </p><p>including high-resolution figures, can be found in the onlineUpdated information and services, </p><p> can be found at: Supporting Online Material </p><p>, 4 of which can be accessed free:cites 29 articlesThis article </p><p>registered trademark of AAAS. is aScience2013 by the American Association for the Advancement of Science; all rights reserved. The title </p><p>CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience </p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p><p> on N</p><p>ovem</p><p>ber 1</p><p>, 201</p><p>3w</p><p>ww</p><p>.sci</p><p>ence</p><p>mag</p><p>.org</p><p>Dow</p><p>nloa</p><p>ded </p><p>from</p></li><li><p>interfaces do not contact any polymer throughoutthe process, reducing impurities trapped betweenthe layers. Figure 2C shows an atomic force mi-croscope (AFM) image of a BN-G-BN hetero-structure made by vdWassembly. The grapheneappears clean and free of macroscopic contam-ination over the entire device area, ~200 mm2. InFig. 2D, a high-resolution cross section STEMimage shows that the resulting interface is pristinedown to the atomic scale, with the graphene layernearly indistinguishable from the adjacent BNlattice planes.</p><p>Figure 3A shows electrical transport from alarge-area, 15 mm 15 mm, BN-G-BN device fab-ricated by combining vdW assembly with edge-contacts. The transport characteristics indicatethe graphene device to be remarkably pristine,reaching a room-temperature mobility in ex-cess of 140,000 cm2/Vs. At carrier density |n| =4.5 1012 cm2, the sheet resistivity is less than~40 ohms per square (fig. S13), correspondingto an equivalent 3D resistivity below 1.5 mohmcm,smaller than the resistivity of any metal at roomtemperature. Indeed, the remarkable feature ofthis device response is the simultaneous realizationof both high mobility and large carrier density.Using the simple Drude model of conductivity,s = nem, where m is the electron mobility, we cal-culate a mobility of ~40, 000 cm2/Vs at densitiesas large as n ~ 4.5 1012 cm2. In this high-densityregime, the measured mobility is comparable tothe acoustic-phonon-limited mobility theoretical-ly predicted for intrinsic graphene (28, 29). Theroom-temperature response of the graphene devicereported here outperforms all other 2D materials,including the highest mobility 2D heterostruc-tures fabricated from III-V (groups III and V in theperiodic table) semiconductors (30, 31) (Fig. 3B)by at least a factor of 2 over the entire range oftechnologically relevant carrier densities.</p><p>At low temperatures, four-terminal measure-ment yields a negative resistance (inset in Fig.3A), indicating quasiballistic transport (4) overat least 15 mm. In the diffusive regime, the meanfree path, Lmfp, can be calculated from the con-ductivity, s, according to Lmfp = sh/2e</p><p>2kF wherekF =</p><p>pnp</p><p>is the Fermi wave vector. In Fig. 3C,Lmfp versus applied gate voltage is shown for se-lected temperatures from 300 K down to 20 K.The mean free path increases with gate voltageuntil it saturates at a temperature-dependent valueat high density. This maximum Lmfp increasesmonotonically with decreasing temperature untilthe mean free path approaches the device size atT ~ 40 K (Fig. 3D). In the low-temperature bal-listic regime, four-terminal measurement is domi-nated by mesoscopic effects (32) and the calculatedmean free path exhibits large variation, depend-ing on the measurement geometry. The temper-ature dependence therefore provides only a lowerbound of the mean free path.</p><p>The negative resistance observed at base tem-perature indicates that electrons travel ballisticallyacross the diagonal of the square, correspond-ing to a mean free path as large as 21 mm in this</p><p>device. This value corresponds to an electronmobility of ~1,000,000 cm2/Vs at a carrier den-sity of ~3 1012 cm2. We repeated this mea-surement for devices varying in size from 1 to15 mm. As seen in Fig. 3E, the maximum meanfree path scales linearly with device size. Thisresult indicates that in our devices the low-temperature mobility is limited by the availablecrystal size, and we have not reached the in-trinsic impurity-limited scattering length. Evenhigher mobility could be expected for larger-area devices, which may be realized by combin-ing recent progress in scalable growth techniques(33, 34) together with the edge-contact geometrydescribed here.</p><p>References and Notes1. M. Xu, T. Liang, M. Shi, H. Chen, Chem. Rev. 113,</p><p>37663798 (2013).2. A. K. Geim, I. V. Grigorieva, Nature 499, 419425 (2013).3. C. R. Dean et al., Nat. Nanotechnol. 5, 722726 (2010).4. A. S. Mayorov et al., Nano Lett. 11, 23962399 (2011).5. L. Wang et al., ACS Nano 6, 93149319 (2012).6. C. R. Dean et al., Nature 497, 598602 (2013).7. L. A. Ponomarenko et al., Nature 497, 594597 (2013).8. B. Hunt et al., Science 340, 14271430 (2013).9. L. Britnell et al., Science 335, 947950 (2012).</p><p>10. T. Georgiou et al., Nat. Nanotechnol. 8, 100103 (2013).11. L. Britnell et al., Science 340, 13111314 (2013).12. G. Giovannetti et al., Phys. Rev. Lett. 101, 026803</p><p>(2008).13. C. Gong et al., J. Appl. Phys. 108, 123711 (2010).14. F. Lonard, A. A. Talin, Nat. Nanotechnol. 6, 773783</p><p>(2011).15. F. Xia, V. Perebeinos, Y. M. Lin, Y. Wu, P. Avouris,</p><p>Nat. Nanotechnol. 6, 179184 (2011).16. M. S. Choi, S. H. Lee, W. J. Yoo, J. Appl. Phys. 110,</p><p>073305 (2011).17. D. Berdebes, T. Low, Y. Sui, J. Appenzeller, M. S. Lundstrom,</p><p>IEEE Trans. Electron. Dev. 58, 39253932 (2011).18. J. S. Moon et al., Appl. Phys. Lett. 100, 203512 (2012).19. J. T. Smith, A. D. Franklin, D. B. Farmer,</p><p>C. D. Dimitrakopoulos, ACS Nano 7, 36613667 (2013).</p><p>20. M. Ishigami, J. H. Chen, W. G. Cullen, M. S. Fuhrer,E. D. Williams, Nano Lett. 7, 16431648 (2007).</p><p>21. J. A. Robinson et al., Appl. Phys. Lett. 98, 053103(2011).</p><p>22. J. Yamaguchi, K. Hayashi, S. Sato, N. Yokoyama,Appl. Phys. Lett. 102, 143505 (2013).</p><p>23. N. Lindvall, A. Kalabukhov, A. Yurgens, J. Appl. Phys.111, 064904 (2012).</p><p>24. S. J. Haigh et al., Nat. Mater. 11, 764767 (2012).25. Y. Matsuda, W.-Q. Deng, W. A. Goddard III, J. Phys.</p><p>Chem. C 114, 1784517850 (2010).26. K. Cho et al., MRS Proc. 1259, S14S35 (2010).27. Y. Wu et al., AIP Adv. 2, 012132 (2012).28. E. Hwang, S. Das Sarma, Phys. Rev. B 77, 115449 (2008).29. J. H. Chen, C. Jang, S. Xiao, M. Ishigami, M. S. Fuhrer,</p><p>Nat. Nanotechnol. 3, 206209 (2008).30. B. R. Bennett, R. Magno, J. B. Boos, W. Kruppa,</p><p>M. G. Ancona, Sol. Stat. Elec. 49, 18751895 (2005).31. J. Orr et al., Phys. Rev. B 77, 165334 (2008).32. S. Datta, Electronic Transport in Mesoscopic Systems</p><p>(Cambridge Univ. Press, London, 1995).33. W. Yang et al., Nat. Mater. 12, 792797 (2013).34. Z. Liu et al., Nano Lett. 11, 20322037 (2011).</p><p>Acknowledgments: This work is supported by the Departmentof Defense through the National Defense Science andEngineering Graduate Fellowship Program, the NationalScience Foundation (DMR-1124894), the Air Force Officeof Scientific Research (FA9550-09-1-0705), the Office ofNaval Research (ONR) (N000141310662 and N000141110633),the Defense Advanced Research Projects Agency (under ONRGrant N000141210814), and the Nano Material TechnologyDevelopment Program through the National Research Foundationof Korea (2012M3A7B4049966). We thank E. H. Hwang andS. Das Sarma for helpful discussion.</p><p>Supplementary and MethodsSupplementary TextFigs. S1 to S14Tables S1 to S2References (3546)</p><p>7 August 2013; accepted 26 September 201310.1126/science.1244358</p><p>Pacific Ocean Heat Content Duringthe Past 10,000 YearsYair Rosenthal,1* Braddock K. Linsley,2 Delia W. Oppo3</p><p>Observed increases in ocean heat content (OHC) and temperature are robust indicators of globalwarming during the past several decades. We used high-resolution proxy records from sedimentcores to extend these observations in the Pacific 10,000 years beyond the instrumental record.We show that water masses linked to North Pacific and Antarctic intermediate waters were warmerby 2.1 T 0.4C and 1.5 T 0.4C, respectively, during the middle Holocene Thermal Maximumthan over the past century. Both water masses were ~0.9C warmer during the Medieval Warmperiod than during the Little Ice Age and ~0.65 warmer than in recent decades. Althoughdocumented changes in global surface temperatures during the Holocene and Common era arerelatively small, the concomitant changes in OHC are large.</p><p>Small, yet persistent perturbations in thebalance of incoming solar radiation (in-solation) reaching Earths surface and out-going long-wave radiation can lead to substantialclimate change. Nevertheless, relating climate var-iations to radiative perturbations is not straight-forward due to the inherent noise of the system</p><p>caused by large temporal (seasonal to decadal)and spatial variability of the climatic response. Along-term perspective of climate variability rel-ative to known radiative perturbations can placethe recent trends in the broader framework ofnatural variability. The comparison with paleo-climate reconstructions of surface temperatures</p><p> SCIENCE VOL 342 1 NOVEMBER 2013 617</p><p>REPORTS</p></li><li><p>is, however, complicated because of the limitednumber of proxy records, their uneven geograph-ical distribution, and the seasonal ecological biasesof the proxies (1, 2).</p><p>Globally averaged instrumental surface tem-peratures have registered little increase in recentdecades, despite a considerable imbalance in theplanetary energy budget (3). The apparent dis-crepancy is attributed to the warming of theoceans interior over the same period. Instrumentalrecords show that the increase in ocean heatcontent (OHC) accounts for ~90% of the ex-pected warming of Earth, thereby demonstratingthat OHC more reliably represents the responseof Earths energy budget to radiative perturba-tions than do surface temperatures (46). Fur-thermore, subsurface water masses are directlyventilated in the high-latitude oceans, where theyaverage the highly variable surface conditions,thereby providing an integrated measure of long-term trends.Here, we place the recent observationsof OHC in the framework of long-term changesduring the Holocene and the Common era.</p><p>We use a suite of sediment cores along bathy-metric transects in the Makassar Strait and FloresSea in Indonesia (figs. S1 and S2) to documentchanges in the temperature of western equatorialPacific subsurface and intermediate water massesthroughout the Holocene [0 to 10 thousand yearsbefore the present (ky B.P.)] (Table 1). This re-gion is well suited to reconstruct Pacific OHC, asthermocline and intermediate watermasses foundhere form in the mid- and high-latitudes of boththe northern and southern Pacific Ocean and canbe traced by their distinctive salinity and densityas they flow toward the equator (7) (fig. S3). TheMakassar Strait between Borneo and Sulawesi,the Lifamatola Passage east of Sulawesi on thenorthern side of the Indonesian archipelago, andthe Ombai and Timor Passages to the south serveas major conduits for exchange of water betweenthe Pacific and IndianOceans; water flow through</p><p>these passages is collectively referred to as theIndonesian Throughflow (ITF) (8). The upperthermocline component of the ITF (~0 to 200m)is dominated by contributions from North Pacificand, to a lesser extent, South Pacific subtropicalwaters, marked by a subsurface salinitymaximum(figs. S3 and S4). Within the lower thermocline(~200 to 500 m) the inflow of low-salinity NorthPacific IntermediateWater (NPIW) dominates theITF flow (fig. S4). The higher- and relativelyuniformsalinity water below the main thermo-cline (~450 to 1000 m) is referred to as Indo-nesian IntermediateWater, which is formed in theBanda Sea by strong vertical mixing between shal-low, warm, relatively fresh waters and deep, cold,relatively saltywaters (8, 9). At intermediate depths,the Banda Sea gets contributions from the SouthPacific through the northwestward-flowing NewGuinea Coastal Undercurrent (NGCUC). Studiessuggest that the NGCUC carries a substantialcontribution from the Antarctic IntermediateWater, spreading into the Banda Sea through theLifamatola andMakassar passages (10). Themainsubthermocline outflows through the Timor andOmbai passages reverse intermittently, therebyallowing inflow of Indian Ocean water into theIndonesian seas (8, 11, 12). Thus, the hydrographyof intermediate water in this region is linked toand influenced by surface conditions in the highlatitudes of the Pacific Ocean, as is also sug-gested from the distribution of anthropogenicallyproduced chlorofluorocarbon along these isopyc-nal layers (7).</p><p>We studied well-dated sediment cores (tableS1) in the Makassar Strait. Shallow cores (450 to600 m) are used to reconstruct the hydrographichistory of the lower thermocline, which currentlyis strongly influenced by NPIW. Deeper cores(650 to 900m) from the Bali Basin on the westernedge of the Flores Sea are arguably under greaterinfluence of Southern Hemisphere (SH) watermasses.</p><p>We use Mg/Ca measurements in the benthicforaminifer Hyalinea balthica for reconstruct-ing intermediate water temperatures (IWTs). Thisspecies is ideally suited to track small temper-ature changes due to its high Mg/Ca-temperaturesensitivity [Mg/Ca = (0.488 T 0.03)IWT] (13, 14).The error on IWT estimates is T0.7C for raw</p><p>data and T0.35C [one standard error of the es-timate (SEE)] for composite records. The oxygenisotopic composition of seawater (d18Osw), usedhere as an analog for salinity, is estimated fromthe paired benthic foraminiferal oxygen isotopiccomposition (d18Oc) and Mg/Ca data (15). Ourreconstructions show that IWTs at all depths weresubstantially warmer in the early andmiddle Holo-cene than during the late Holocene (Fig. 1). Spe-cifically, IWTat 500 mwas ~10C between 10.5and 9 thousand years ago (ka), increased to amaximumof ~10.7Cbetween 8 to 6 ka, and begandecreasing after 6 ka, reaching ~7.8C a...</p></li></ul>


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