SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo707 Supplementary Materials Wagner, J. D., J. E. Cole*, J. W. Beck, P. J. Patchett, G. M. Henderson, and H.R. Barnett, 2010. Moisture variability in the southwestern US linked to abrupt glacial climate change, Nature Geosciences. * = corresponding author Note – Supplemental figures are cited in order based on their citation in the paper. A. Supplementary Methods Field sampling and site characteristics: We recovered this sample (COB-01-02) in July 2001, from the Cave of the Bells, Santa Cruz County, AZ (31°45'N, 110°45'W). The cave lies at shallow depths beneath a small topographic high; modern cave activity results from water that falls as precipitation and not from older circulating groundwaters. Over a 16-month period, the cave temperature averaged 19.2 ± 0.1 °C with no seasonal cycle, consistent with mean local temperatures and a small geothermal offset as documented in nearby caves 1. Core handling and geochemical analyses: After removal from the cave, the stalagmite was cored with a 2.5cm drill bit and two slabs were taken from the core center. We used a drilled core for all sampling so that the stalagmite could be capped and returned to the cave, in accordance with our U.S. Forest Service agreement. One core slab was sectioned into 4-6 mm increments for U-Th dating using thermal ionization mass spectrometry (TIMS). The other slab was sampled for stable isotope analysis at 100 µm increments with a micromill along the growth axis, and for additional higher-resolution U-Th dating with a diamond-impregnated wire saw (1.5-3mm increments). A photo of the core slab used for isotopic analysis is shown in Supplementary Figure 3. 1 nature geoscience | www.nature.com/naturegeoscience S-1 supplementary information doi: 10.1038/ngeo707 U/Th methods and age-model development U/Th dating was performed using three different analytical facilities as indicated in Supplementary Table 1. All preparation was done under clean lab conditions at the University of Arizona. We used decay constants from Cheng et al. 2000 2 and corrected for initial Th assuming an estimated value for 230Th/232Th activity of 0.8 ± 50%; such age corrections were on the order of decades. TIMS analyses were performed at the University of Arizona 3 and multicollector inductively-coupled mass spectrometry (MC-ICP-MS) at Arizona and Oxford University 4 (Supplementary Table 1). All ages are reported as years before 1950 (years BP). U/Th data are plotted against depth in Supplementary Figure 4. Two hiatuses were identified at ~3.5mm and ~27mm depths, based on the presence of cloudy bands (0.6 and 1.3mm thin, respectively) and substantial reduction of growth rates. The age model was constructed separately for the section below the lower hiatus and the section between the two hiatuses. We did not attempt to provide an age model for stable isotope data above the uppermost hiatus, because no U/Th dates were derived exclusively from material above that cloudy band. Between the two hiatuses, we used a third-order polynomial to fit age-depth data pairs. Below the 27mm hiatus, we used a spline fit, which tracked the age-depth data more closely than a polynomial. Stable isotope methods We analyzed oxygen and carbon isotopes on a dual inlet stable isotope mass spectrometer (Micromass Optima) with an automated carbonate preparation system at University of Arizona. Analytical precision on δ18O and δ13C measurements is better than 0.08‰ and 0.04‰ (1σ), respectively. These data are presented in Supplementary Table 2 and will be placed on file at the World Data Center for Paleoclimatology (www.ncdc.noaa.gov/~paleo). X-ray diffraction analysis on portions of the stalagmite indicated a calcite composition with no aragonite present. S-2 2 nature geoscience | www.nature.com/naturegeoscience doi: 10.1038/ngeo707 supplementary information To improve estimates of regional climate change from our isotopic record, we corrected the speleothem δ18O for the global effect of ice volume on water vapor using a marine sedimentderived estimate 5. We calibrated the radiocarbon-based age model of the sediment core to absolute ages using the online tool at http://radiocarbon.ldeo.columbia.edu/ and linearly interpolated between data points to obtain correction values for each of our depths. Isotopic equilibrium considerations: We selected this sample from deep in the cave to avoid disequilibrium effects on the stable isotope record. The classic “Hendy test,” which assesses correlation between contemporaneous δ18O and δ13C from samples along a growth band 6, is inappropriate for this sample due to its slow growth rate and rapid isotopic changes. A recent assessment suggests that disequilibrium can be detected using time-transgressive analysis of δ18O-δ13C covariation7; we explored such covariation for various time intervals and did not observe a strong correlation that would indicate disequilibrium (Supplementary Figure 5). Ongoing cave monitoring will help constrain the degree of disequilibrium present and the degree to which we can use equilibrium calculations to infer modern calcite values. B. Supplementary Discussion Modern isotope systematics To constrain interpretations of speleothem δ18O, we present data on dripwater and precipitation δ18O. Analysis of 20 years of modern precipitation isotopic data from Tucson (Supplementary Figure 1) shows that the relationship between precipitation δ18O and temperature is weak for both winter and summer 8. However, we observe a significant inverse relationship between precipitation δ18O and precipitation amount for both winter and summer, with a stronger relationship in summer (significant at 98% and 99.99%, respectively). We S-3 nature geoscience | www.nature.com/naturegeoscience 3 supplementary information doi: 10.1038/ngeo707 analyze the seasons separately because their sources and dynamics are very different. Winter precipitation δ18O is lower than that in summer by about 4‰. Within the cave, isotopic measurements on drip water collected monthly since late 2003 yield an average value of -9.56±0.29‰. This value is consistent with winter (October-March) precipitation values (Supplementary Figure 2), in Tucson 8,9, even though about half of the annual precipitation arrives during the summer monsoon (July-September). Summer precipitation provides little infiltration into the cave because it is intense, localized, and cooccurs with very high temperature and vegetation heat stress 10. We see isotopic evidence of summer precipitation in the dripwater values only during monsoons that are unusually strong; even then, the perturbation is small (<1‰) and/or short-lived (a few months). The cave dripwater values are also consistent with the composition of winter rainwater collected at the cave, although that record is shorter and noisier. Based on these results, we interpret the century-millennium scale variations in our speleothem δ18O record as relative indicators of winter moisture, which is governed by the position of the westerly storm track11,12. The influence of temperature on this time scale is likely small; any effect on precipitation δ18O will be counterbalanced at least partly by opposing effects during calcification. We can’t rule out the influence of monsoon precipitation on the millennial variations we observe, but we favor the winter amount (storm track) explanation. Background climate conditions likely favored a weak monsoon at this time13, and studies that argue for a glacial monsoon14 still maintain that it did not exceed the strength of today’s monsoon (which exerts minimal influence on cave dripwaters). Unlike the century-millenium scale variations, the low-frequency behavior of the speleothem δ18O record may in fact reflect orbitally forced monsoon changes 8. Finally, vapor source and trajectory can also influence these records; S-4 4 nature geoscience | www.nature.com/naturegeoscience doi: 10.1038/ngeo707 supplementary information significant variation among storms with different trajectories has been noted in the White Mountains (CA), although the relationship is complex15. The significant correlation between winter precipitation amount and δ18O today (Supplementary Figure 1) suggests that even if this factor is important, it does not overwhelm the inverse relationship we observe between amount and δ18O of precipitation. In fact, large-scale stadial-interstadial changes across the Pacific could result in trajectory shifts that reinforce precipitation amount changes in our isotopic record, if for example stadial conditions included a shift to more distant moisture sources and a longer path for Rayleigh distillation, concurrent with a southward-displaced storm track that delivers more moisture. Supplementary References Cited: 1 2 3 4 5 6 7 8 9 10 11 Buecher, B. Microclimate study of Kartchner Caverns. Arizona. Journal of Cave and Karst Studies 61, 108-120 (1999). Cheng, H. et al. The half-lives of uranium-234 and thorium-230. Chemical Geology 169, 17-33 (2000). Placzek, C., Patchett, P. J., Quade, J. & Wagner, J. D. M. Strategies for successful U-Th dating of paleolake carbonates: An example from the Bolivian Altiplano. Geochemistry Geophysics Geosystems 7 (2006). Robinson, L. F., Henderson, G. M. & Slowey, N. C. U-Th dating of marine isotope stage 7 in Bahamas slope sediments. Earth And Planetary Science Letters 196, 175-187 (2002). Lea, D. W., Martin, P. A., Pak, D. K. & Spero, H. J. Reconstructing a 350 ky history of sea level using planktonic Mg/Ca and oxygen isotope records from a Cocos Ridge core. Quaternary Science Reviews 21, 283-293 (2002). Hendy, C. The isotopic geochemistry of speleothems - I: The calculation of the effects of different modes of formation on the isotopic composition of speleothems and their applicability to paleoclimatic reconstruction. Geochimica Cosmoshimica Acta 35, 801824 (1971). Mickler, P. J., Stern, L. A. & Banner, J. L. Large kinetic isotope effects in modern speleothems. Geological Society Of America Bulletin 118, 65-81 (2006). Wagner, J. D. M. Speleothem Record of Southern Arizona Paleoclimate, 3.5-54 KA, University of Arizona, (2006). Long, A. & Eastoe, C. Isotopic data from Tucson Arizona (University of Arizona, 2006). Sheppard, P. R., Comrie, A. C., Packin, G. D., Angersbach, K. & Hughes, M. K. The climate of the US Southwest. Clim. Res. 21, 219-238 (2002). Brito-Castillo, L., Douglas, A. V., Leyva-Contreras, A. & Lluch-Belda, D. The effect of large-scale circulation on precipitation and streamflow in the Gulf of California S-5 nature geoscience | www.nature.com/naturegeoscience 5 supplementary information 12 13 14 15 doi: 10.1038/ngeo707 continental watershed. International Journal of Climatology 23, 751-768, doi:Doi 10.1002/Joc.913 (2003). Cayan, D. R. & Peterson, D. H. in Aspects of Climate Variability in the Pacific and the Western Americas Geophysical Monograph (ed D.H. Peterson) 375-397 (American Geophysical Union, 1989). Anderson, R. S., Betancourt, J. L., Mead, J. I., Hevly, R. H. & Adam, D. P. Middle- and late-Wisconsin paleobotanic and paleoclimatic records from the southern Colorado Plateau, USA. Paleogeogr. Paleoclimatol. Paleoecol. 155, 31-57 (2000). Holmgren, C. A., Norris, J. & Betancourt, J. L. Inferences about winter temperatures and summer rains from the late Quaternary record of C-4 perennial grasses and C-3 desert shrubs in the northern Chihuahuan Desert. Journal Of Quaternary Science 22, 141-161 (2007). Friedman, I., Harris, J. M., Smith, G. I. & Johnson, C. A. Stable isotope composition of waters in the Great Basin, United States - 1. Air-mass trajectories. J. Geophys. Res.Atmos. 107, doi:4400.10.1029/2001jd000565 (2002). S-6 6 nature geoscience | www.nature.com/naturegeoscience supplementary information doi: 10.1038/ngeo707 Supplementary Table 1. Uranium-thorium measurements on Cave of the Bells speleothem COB-01-02. Ages were calculated using decay constants from Cheng et al. (2000) and corrected for initial Th assuming an estimated value for 230Th/232Th activity of 0.8 ± 50%; such age corrections were on the order of decades. Hiatuses at 3.5 and 27 mm are indicated by the H at right. # $ $ $ & # $ & & # & * * $ $ # $ $ $ # $ $ # * * * * * * # # $ * * * * * Depth Range Center Depth mm mm Agea yr before 1950 1-6 1-6R 3-5 5-7 7-10 7-12 7-12R 10-11.5 12.5-14 12.5-16.5 14-15.5 16-19 19-21.5 19.75-21.75 21.75-23.25 21-25 23.25-25 25-26.75 26.75-28.5 30-34 33-34.5 36-37.25 35-39 40.5-43 47.5-49.5 49.5-51.5 51.5-53.5 53.5-55.5 55.5-57.5 55-60 55-60R a 55-60R b 60-62 62-64 64-65.5 65.5-67 67-68.75 3.5 3.5 4 6 8.5 9.5 9.5 10.75 13.25 14.5 14.75 17.5 20.25 20.75 22.5 23 24.125 25.875 27.625 32 33.75 36.625 37 41.75 48.5 50.5 52.5 54.5 56.5 57.5 57.5 57.5 61 63 64.75 66.25 67.875 9487 10266 11009 11784 12469 12013 12211 13456 12997 12696 13137 14641 16746 16406 19781 18255 20868 23149 30441 31934 33809 34663 34566 36883 38607 38422 39776 40382 40424 39509 39974 40159 41025 40691 41491 41510 41260 Errorb 2σ 138 128 56 48 207 94 135 232 218 113 218 105 120 81 136 123 76 109 101 239 105 109 224 295 173 166 184 165 239 343 190 499 172 177 167 170 215 230 Th/238U measured 0.20526 0.22216 0.23712 0.25696 0.27294 0.26213 0.26730 0.29358 0.28360 0.27814 0.28585 0.32176 0.37209 0.36518 0.43519 0.40303 0.45925 0.50565 0.60944 0.63977 0.67389 0.69262 0.68410 0.73118 0.77468 0.77813 0.79912 0.80541 0.80756 0.79094 0.79678 0.80201 0.82267 0.81926 0.82660 0.82687 0.82097 230 Th/238U 230 Th/232Th corrected 0.20520 0.22198 0.23643 0.25666 0.27248 0.26208 0.26729 0.29351 0.28345 0.27799 0.28575 0.32047 0.37007 0.36400 0.43221 0.40198 0.45888 0.50421 0.60919 0.63974 0.67386 0.69259 0.68407 0.73111 0.77462 0.77761 0.79837 0.80530 0.80748 0.79089 0.79658 0.80184 0.82261 0.81920 0.82654 0.82675 0.82090 238 U (234U/238U)int ppm 2280 862 248 635 424 4011 17384 3032 1270 1371 1978 174 126 213 97 260 830 226 1491 11565 14191 13336 12067 5678 7543 847 586 3920 5538 8312 2235 2600 8012 7428 7043 3992 6371 0.160 0.158 0.153 0.191 0.187 0.188 0.183 0.168 0.218 0.200 0.206 0.247 0.234 0.226 0.227 0.225 0.245 0.217 0.197 0.186 0.183 0.208 0.188 0.188 0.206 0.213 0.205 0.188 0.187 0.188 0.188 0.187 0.208 0.232 0.205 0.198 0.200 2.47 2.48 2.48 2.52 2.54 2.53 2.54 2.55 2.54 2.55 2.54 2.58 2.63 2.64 2.65 2.65 2.68 2.69 2.57 2.59 2.61 2.62 2.60 2.63 2.69 2.71 2.71 2.70 2.71 2.70 2.69 2.70 2.73 2.73 2.71 2.71 2.71 H H S-7 nature geoscience | www.nature.com/naturegeoscience 7 supplementary information doi: 10.1038/ngeo707 * 68.75-71 69.875 42069 160 0.83658 0.83647 4331 0.228 2.72 * 73-75 74 43777 174 0.86890 0.86846 1054 0.236 2.74 * 75-76.5 75.75 44769 250 0.88994 0.88933 784 0.238 2.76 * 76.5-78.5 77.5 44494 207 0.89137 0.89118 2428 0.234 2.77 * 80.5-82 81.25 45465 253 0.90318 0.90313 9919 0.219 2.77 * 82-84 83 45627 254 0.90840 0.90831 5050 0.242 2.77 * 86-88 87 46244 170 0.90676 0.90667 5599 0.243 2.74 * 88-90 89 46194 207 0.90053 0.90046 6768 0.209 2.72 * 90-92 91 46638 193 0.90821 0.90813 5778 0.212 2.73 * 92-94.5 93.25 46654 242 0.90584 0.90576 6183 0.186 2.72 * 94.5-96.5 95.5 46770 170 0.90434 0.90427 6306 0.217 2.71 * 96.5-98.5 97.5 47767 233 0.92366 0.92356 4654 0.132 2.72 * 98.5-100 99.25 47034 211 0.90021 0.90012 5149 0.154 2.68 * 100-102 101 47512 226 0.90630 0.90622 5786 0.162 2.68 * 102-104.5 103.25 47585 220 0.89960 0.89952 5904 0.200 2.66 * 104.5-106 105.25 48202 285 0.90607 0.90598 5044 0.191 2.65 * 106-108 107 50075 343 0.94105 0.93655 106 0.195 2.67 * 108-109.5 108.75 50425 379 0.95594 0.95183 117 0.199 2.70 * 109.5-111 110.25 50256 308 0.96089 0.95966 392 0.181 2.73 # 110-114R 112 50657 734 0.96309 0.96047 185 0.176 2.71 * 114.5-115.5 115 52271 249 1.00886 1.00868 2834 0.157 2.78 # 115-121 118 50764 712 0.98177 0.98161 3112 0.156 2.77 $ 115-121R 118 51718 650 0.99514 0.99483 1582 0.152 2.77 # 121-126 123.5 52660 368 1.02352 1.02298 931 0.155 2.81 # 121-126R 123.5 52735 351 1.02130 1.02122 6803 0.166 2.80 a Ages corrected assuming initial Th has a value similar to bulk upper continental crust, 230Th/232Th = 0.8 b Error for all samples includes measurement error, decay constant uncertainty, and initial Th assuming an estimated value for 230Th/232Th activity of 0.8 ± 50% * UA-U on TIMS, Oxford-Th on MC-ICP-MS # UA-U and Th on TIMS $ UA- U and Th on MC-ICP-MS & UA- U on MC-ICP-MS, Oxford- Th on MC-ICP-MS S-8 8 nature geoscience | www.nature.com/naturegeoscience supplementary information doi: 10.1038/ngeo707 7.40 7.50 7.60 7.70 7.80 7.90 8.00 8.10 8.20 8.30 8.40 8.50 8.60 8.70 8.80 8.90 9.00 9.10 9.20 9.30 9.40 9.50 9.60 9.70 9.80 9.90 10.00 10.10 10.20 10.30 10.40 10.50 10.60 10.70 11.00 11.10 11.20 11.30 11.40 11.50 11.60 11.70 11.80 11.90 12.00 12.10 12.20 12.30 Supplementary Table 2 Oxygen isotopic data, COB-01-02. Depth (mm) 3.50 3.60 3.70 3.80 3.90 4.00 4.10 4.20 4.30 4.40 4.50 4.60 4.70 4.80 4.90 5.00 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 5.90 6.00 6.10 6.20 6.30 6.40 6.50 6.60 6.70 6.80 6.90 7.00 7.10 7.20 7.30 Age (years before 1950) 11484 11507 11529 11552 11573 11594 11615 11636 11655 11675 11694 11713 11731 11749 11767 11784 11801 11817 11833 11849 11865 11880 11895 11910 11924 11938 11952 11966 11980 11993 12006 12019 12032 12044 12057 12069 12081 12093 12105 Measured δ18O (‰) -8.510 -9.302 -9.406 -9.434 -9.517 -9.569 -9.514 -9.474 -9.349 -9.366 -9.531 -9.619 -9.491 -9.589 -9.553 -9.654 -9.808 -9.784 -9.836 -9.738 -9.455 -9.504 -9.778 -9.776 -9.802 -9.939 -9.872 -9.775 -9.790 -9.518 -9.663 -9.595 -9.298 -9.573 -9.603 -9.406 -9.448 -9.620 -9.787 Ice vol. corrected δ18O (‰) -8.852 -9.644 -9.748 -9.777 -9.861 -9.913 -9.858 -9.819 -9.695 -9.711 -9.877 -9.966 -9.837 -9.936 -9.901 -10.002 -10.156 -10.133 -10.184 -10.087 -9.804 -9.853 -10.127 -10.128 -10.154 -10.292 -10.226 -10.131 -10.147 -9.876 -10.022 -9.955 -9.660 -9.936 -9.967 -9.771 -9.815 -9.987 -10.155 12117 12128 12140 12151 12163 12174 12185 12196 12208 12219 12230 12241 12252 12264 12275 12286 12298 12309 12321 12332 12344 12356 12367 12379 12392 12404 12416 12429 12442 12455 12468 12481 12495 12509 12552 12567 12582 12597 12613 12629 12645 12662 12679 12696 12714 12732 12750 12769 -10.088 -10.145 -10.223 -10.063 -9.927 -9.673 -9.615 -9.470 -9.163 -9.049 -9.080 -9.035 -9.460 -9.698 -9.772 -9.833 -9.583 -9.587 -9.341 -9.056 -9.179 -9.085 -8.966 -9.277 -9.095 -9.321 -9.408 -9.331 -9.658 -9.648 -9.566 -9.561 -9.733 -9.812 -9.710 -9.124 -9.229 -9.271 -9.399 -9.217 -9.221 -9.423 -9.587 -9.621 -9.739 -9.755 -9.821 -9.837 -10.458 -10.516 -10.595 -10.436 -10.301 -10.048 -9.991 -9.848 -9.541 -9.428 -9.461 -9.416 -9.842 -10.082 -10.156 -10.219 -9.970 -9.975 -9.730 -9.446 -9.570 -9.477 -9.360 -9.671 -9.491 -9.717 -9.806 -9.730 -10.058 -10.049 -9.969 -9.965 -10.138 -10.219 -10.121 -9.536 -9.642 -9.686 -9.815 -9.634 -9.640 -9.843 -10.009 -10.045 -10.164 -10.183 -10.250 -10.268 S-9 nature geoscience | www.nature.com/naturegeoscience 9 supplementary information 12.40 12.50 12.60 12.70 12.80 12.90 13.00 13.10 13.20 13.30 13.40 13.50 13.60 13.70 13.80 13.90 14.00 14.10 14.20 14.30 14.40 14.50 14.60 14.70 14.80 14.90 15.00 15.10 15.20 15.30 15.40 15.50 15.60 15.70 15.80 15.90 16.00 16.10 16.20 16.30 16.40 16.50 16.60 16.70 16.80 16.90 17.00 17.10 17.20 12789 12808 12828 12849 12870 12891 12913 12935 12958 12982 13005 13030 13055 13080 13106 13132 13159 13187 13215 13244 13274 13304 13334 13366 13398 13430 13463 13497 13532 13567 13603 13640 13678 13716 13755 13795 13835 13876 13918 13961 14005 14049 14095 14141 14188 14236 14285 14334 14385 -9.763 -9.777 -9.690 -9.540 -9.434 -9.342 -9.380 -9.401 -9.376 -9.297 -9.163 -8.962 -8.937 -8.840 -8.858 -8.868 -8.949 -8.858 -8.735 -8.743 -8.693 -8.733 -8.758 -8.833 -8.805 -8.783 -8.702 -8.398 -8.688 -8.608 -8.971 -8.903 -8.633 -8.815 -9.235 -9.257 -9.202 -9.133 -8.976 -8.926 -8.800 -8.509 -8.516 -8.586 -8.446 -8.300 -8.185 -8.334 -8.324 -10.195 -10.211 -10.126 -9.978 -9.874 -9.785 -9.825 -9.847 -9.824 -9.748 -9.616 -9.417 -9.394 -9.300 -9.320 -9.333 -9.416 -9.328 -9.208 -9.218 -9.171 -9.213 -9.241 -9.320 -9.294 -9.276 -9.198 -8.896 -9.192 -9.118 -9.487 -9.426 -9.162 -9.351 -9.778 -9.807 -9.759 -9.697 -9.547 -9.504 -9.386 -9.103 -9.118 -9.196 -9.064 -8.926 -8.819 -8.977 -8.976 doi: 10.1038/ngeo707 17.30 17.40 17.50 17.60 17.70 17.80 17.90 18.00 18.10 18.20 18.30 18.40 18.50 18.60 18.70 18.80 18.90 19.00 19.10 19.20 19.30 19.40 19.50 19.60 19.70 19.80 19.90 20.00 20.10 20.20 20.30 20.40 20.50 20.60 20.70 20.80 20.90 21.00 21.10 21.20 21.30 21.40 21.50 21.80 21.90 22.00 22.10 22.20 22.30 14436 14489 14542 14596 14651 14707 14764 14822 14881 14941 15002 15064 15127 15192 15257 15323 15390 15458 15528 15598 15670 15743 15817 15892 15968 16045 16124 16203 16284 16366 16449 16534 16620 16706 16795 16884 16975 17067 17160 17255 17351 17448 17546 17850 17954 18059 18166 18274 18384 -8.077 -8.499 -8.681 -8.711 -8.787 -8.708 -8.720 -8.809 -8.856 -8.824 -9.111 -9.519 -9.932 -10.226 -10.250 -10.267 -10.398 -10.642 -10.515 -10.415 -10.329 -10.390 -10.411 -10.386 -10.414 -10.511 -10.479 -10.454 -10.392 -10.428 -10.546 -10.501 -10.534 -10.480 -10.517 -10.506 -10.484 -10.565 -10.474 -10.504 -10.427 -10.576 -10.705 -10.736 -10.744 -10.708 -10.608 -10.545 -10.606 -8.738 -9.169 -9.360 -9.400 -9.486 -9.416 -9.438 -9.538 -9.595 -9.572 -9.870 -10.289 -10.713 -11.019 -11.053 -11.083 -11.225 -11.474 -11.349 -11.252 -11.168 -11.232 -11.256 -11.234 -11.265 -11.364 -11.335 -11.313 -11.254 -11.292 -11.413 -11.372 -11.408 -11.357 -11.397 -11.390 -11.370 -11.455 -11.368 -11.401 -11.327 -11.480 -11.612 -11.643 -11.649 -11.612 -11.511 -11.446 -11.505 S-10 10 nature geoscience | www.nature.com/naturegeoscience supplementary information doi: 10.1038/ngeo707 22.40 22.50 22.60 22.70 22.80 22.90 23.00 23.10 23.20 23.30 23.40 23.60 23.70 23.80 23.90 24.00 24.10 24.20 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Climate-isotope relationships for Tucson precipitation, stratified by half-season. Winter (October-March) data are shown in blue, and summer monsoon (JulySept.) data are shown in red. We selected these seasons to isolate particular climate dynamics regimes (winter westerlies and summer monsoon, respectively); the remaining months contribute less than 10% to the region’s precipitation. All isotope data are amount-weighted means for seasons between 1984-2004. We omitted 1989 from this analysis because data are scarce and noisy 8. A. Temperature-isotope correlations are weak, even inverse, in this region. B. Correlations between precipitation amount and δ18O are significant at >98% (winter) and >99.9% (summer). If the April-September half-year is substituted for the monsoon season (to include the full annual cycle), the relationships do not change in sign, but the amount effect on precipitation is weakened (r2 = 0.25) and the temperature effect slightly strengthened (r2 = 0.07). Supplementary figure 2. Modern isotope and climate data from the Cave of the Bells region. A. Average monthly rainfall δ18O (red, with standard deviation indicated by vertical bars) from a 20-year dataset of episode-based rainfall isotope data 8,9. Average monthly rainfall amount (blue) and monthly air temperature (yellow) are also shown. Grey shading indicates the winter precipitation season; the monsoon season runs from late June-early September. Black horizontal line indicates average dripwater δ18O from Cave of the Bells, which matches winter precipitation. B. Oxygen isotopic data from the cave site; δ18O of rainwater from a gauge established above the cave (green line) and of drip waters from three sites within the cave (red, orange, and blue lines). The offset among the sites spans 0.35‰ and the standard deviation of precipitation within each site is 0.12-0.26‰. In summer 2006 (arrow) and afterwards, following an especially strong monsoon season, higher dripwater δ18O values are seen at two sites (red and S-22 22 nature geoscience | www.nature.com/naturegeoscience doi: 10.1038/ngeo707 supplementary information orange lines), and one of these (red line) shows an immediate pulse of isotopically heavier water. Winter months (Oct.-March) are shaded grey. The dripwater values generally match the average winter-season (grey shaded) precipitation, although our precipitation dataset is noisy. Supplementary figure 3. Photo of COB slab used for isotopic analysis and U/Th dating. Thin red arrows (at sides) point to trench used for isotopic sampling. Thick black arrows indicate the presence of faint growth bands that were used to determine the sampling transect. This core displayed very faint growth features not obvious on this image that are consistent in orientation down the 140-mm length of the sample. The core appears homogeneous and translucent. Supplementary figure 4. Plot of U/Th date (age before 1950) versus depth for sample COB01-02. Colors indicate whether samples were run at the University of Arizona (UA) or Oxford, and the method used, either muticollector inductively coupled mass spectrometer (MC-ICP-MS) or thermal ionization mass spectrometry (TIMS). Red: UA TIMS; blue: UA MC-ICP-MS; green: U on UA MC-ICP-MS and Th on Oxford MC-ICP-MS; black: U on UA TIMS and Th on Oxford MC-ICP-MS. Thin lines indicate the models used to assign ages to oxygen isotopic samples. Error bars represent 2σ analytical uncertainty (vertical) and depth range of sample (horizontal). Supplementary figure 5. Correlation plot between δ18O and δ13C, for all data (black points and black linear fit) and for specific time intervals (MIS3 in pink with red linear fit; deglacial in light blue with blue linear fit). Note that the colored points overlie most of the black dots. If isotopic disequilibrium were significant in this sample, we would observe a strong correlation between oxygen and carbon isotope values7, but this plot demonstrates that the correlation is weak and thus that disequilibrium effects do not influence our record, according to published criteria7. S-23 nature geoscience | www.nature.com/naturegeoscience 23 supplementary information doi: 10.1038/ngeo707 Supplementary figure 1 Wagner et al. a. 0 y = -0.0129x - 8.7252 R2= 0.0002 Precipitation δ18O (‰) -2 -4 -6 -8 y = 0.3405x - 14.539 R2= 0.1116 -10 Winter (Oct-Mar) Monsoon (July-Sept) -12 -14 8 13 18 23 Mean Temperature b. 0 30 Winter (Oct-Mar) Monsoon (July-Sept) -2 Precipitation δ18O (‰) 28 y = -0.0138x - 2.824 R 2 = 0.5039 -4 -6 -8 -10 y = -0.0083x - 7.5677 R2= 0.2712 -12 -14 0 100 200 300 Seasonal precipitation total (mm) 400 S25 24 nature geoscience | www.nature.com/naturegeoscience supplementary information doi: 10.1038/ngeo707 Supplementary figure 2 Wagner et al. 2 A. 0 δ18O (‰) -2 -4 -6 -10 Rainfall (mm/month) 60 -8 40 -12 Temperature (°C) 20 0 30 20 10 Jan B. Mar May Jul Sep Nov Month 0 Precipitation δ18O (‰) -2 Local rainfall δ18O -4 -6 -8 -10 Cave drip water δ18O -12 -14 -16 Jan July Jan July Jan July Jan July Jan July 2003 2003 2004 2004 2005 2005 2006 2006 2007 2007 Month and year S-26 nature geoscience | www.nature.com/naturegeoscience 25 supplementary information doi: 10.1038/ngeo707 Supplementary figure 3 Wagner et al. Top Bottom 24 26 nature geoscience | www.nature.com/naturegeoscience doi: 10.1038/ngeo707 supplementary information Supplementary figure 4 Wagner et al. S-27 nature geoscience | www.nature.com/naturegeoscience 27 supplementary information doi: 10.1038/ngeo707 Supplementary figure 5 Wagner et al. S-28 28 nature geoscience | www.nature.com/naturegeoscience