Correction notice Nature Geoscience 3, 374 375 (2010) Methane emissions from extinct megafauna Felisa A. Smith, Scott M. Elliott and S. Kathleen Lyons In the version of this supplementary file originally posted online on 23 May 2010, the caption for Supplementary Table 3 contained incorrect information about the ice core that was examined. This error has been corrected and this file has been replaced as of 21 July 2010.
SUPPLEMENTARY INFORMATION Supplementary Methods I. Determination of enteric fermentation factors We compiled data from empirical studies measuring methane emissions for various species of both foregut and hindgut herbivores spanning the body size spectrum; the few studies that relate methane production to body mass are based on domestic livestock with a relatively narrow range of body mass. Emissions from manure management were not included; although additional methane equal to 26.4-34% of that released in enteric fermentation is lost, much of this is owing to the operation of liquid manure management systems, such as lagoons and holding tanks used at larger swine and dairy operations. When manure is directly deposited on field and pastures less methane is released (http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/4_volume4/ V4_10_Ch10_Livestock.pdf ). Data were compiled from experimental studies for mammals spanning a spectrum of digestive strategies (e.g., hindgut versus foregut herbivores), life stages (e.g., growing, subadult, mature) and body mass (10-4,000 kg) to reflect the normal variation present in wild populations. Because ANCOVA revealed a highly significant influence of digestive strategy (P< 0.005) as well as body mass (P< 0.001) on methane production, separate regressions were conducted for foregut and hindgut herbivores. Both power and linear functions yielded highly significant fits to the data, explaining over ~90-99% of the variance. Equations for these relationships were (log-log in kg/yr with standard error): Hindgut herbivores, y = 1.559 (0.119) x - 2.894 (0.287), r 2 =0.955, P<0.001, df=9; Foregut herbivores, y = 1.057 (0.45) x 0.962 (0.10), r 2 =0.949; P<.001; df=31. We employed a power function because the linear relationship tended to substantially underestimate methane production at larger body masses and most extinct taxa were large. Note that there is more power in the analysis than represented by N; values for many species represent the mean of multiple individuals (range 1 to 118). Although small foregut herbivores produce almost an order of magnitude more methane than do hindgut herbivores, this difference decreases at larger body sizes perhaps owing to the disproportionate methanogene growth that occurs with longer residence times; the growth of such bacteria may be a limiting factor for large herbivores (S1). Moreover, large-bodied herbivores, such as those present in the late Pleistocene and early Holocene, may be digestively less efficient and thus experience greater methanogenesis (S1). We also computed methane production using a variation of the IPCC Tier 1 and the simplified Tier 2 approaches (http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_volume4/v4_10_ch10_livestock.pdf). The Tier 1 methodology multiplies the number of individuals of each species by a standard animal emission factor calibrated with the main types of domestic livestock. We modified this to account for size differences by scaling emission by body mass: (1) Pm = (Ef*BMe)/BMt; nature geoscience www.nature.com/naturegeoscience 1
where Pm = production of methane by each animal in kg/yr; Ef = standard Tier 1 emission factors in kg CH4/yr by animal type, BMe = body mass of extinct megafauna in kg, and BMt = standard IPCC body mass for animal type in kg. Values for standard animal emission factors and body mass were taken from Table 10.10 (http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_volume4/v4_10_ch10_livestock.pdf). Total production was estimated by summing over all animals. The Tier 2 methodology first estimates gross energy consumption by individual animals within an inventory class and then multiplies by an estimate of methane production; values are summed across species. The standard Tier 2 approach requires information on demography of animal populations, energy requirements, animal diets, digestible energy, and methane conversion rates to compute methane emissions. Because we lacked data on a number of important parameters, we employed the simplified Tier 2 method given by equation 10.18a (http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/4_volume4/v4_10_ch10_livestock.pdf): (2) Pm = (365*(GEe * Ym))/ME where Pm = production of methane by each animal in kg/yr; GEe = gross energy in MJ/day, Ym = the methane conversation rate, or the fraction of gross energy in forage that is lost as methane, and ME = the energy content of methane in MJ/kg. Gross energy intake (GEe)) in MJ/day is computed in the simplified Tier 2 method as: (3) GEe = DMIe * De where DMIe, is dry matter digestibility in kg/day and De is the energy density of forage in MJ/kg. DMI can be determined from body mass as: (4) DMIe = BMe 0.75 *[ (0.0119*NEma 2 + 0.1938)/NEma] where BMe = body mass in kg, and NEma = estimated dietary net energy concentration of diet in MJ/kg (http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_volume4/v4_10_ch10_livestock.pdf). Our computations used a methane conversion factor of Ym = 6 (Table 10.12), an intermediate value of NEma = 6 corresponding to moderate forage (e.g., mid-season grasses) from Table 10.8 and the recommended default values of 55.65 MJ/kg and 18.45 MJ/kg DM for energy content of methane and energy density of forage, respectively (http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/4_volume4/v4_10_ch10_livestock.pdf). Comparison of the predictions by different methodologies with empirical data suggested that the Tier 2 approach severely and increasingly underestimated methane emissions at larger body masses. When scaled for animal body mass, the much simpler Tier 1 estimates closely approached those predicted by the allometric regressions; both were close to the actual empirical values. The Tier 2 approach incorporates body mass through its influence on intake, but ignores scaling of methane production with mass. 2 nature geoscience www.nature.com/naturegeoscience
II. Determination of historic geographic range Accurate geographic ranges of extinct species are difficult to determine not only because of taphonomic issues (e.g., preservation biases due to habitat, body size and other factors), but also due to a lack of data. Although late Pleistocene range maps are available for some species (e.g., http://www.museum.state.il.us/research/faunmap), these are largely restricted to the continental USA (representing only ~34% of land area of North America) and ranges within Canada, Mexico, Central or South America generally are not included. Fossil data are especially sparse for South America. We utilized a macroecological approach by bracketing the probable geographic range sizes of extinct megafauna using the relationship between geographic range size and body size based on extant herbivores. Modern geographic range is only weakly related to body size. We suspected this was in part because modern ranges have been heavily modified owing to human activities. Thus, we used historic range, which resulted in highly robust relationship. Data were obtained from literature sources (S2, S3) and included the majority of the largest extant mammalian herbivores. Quartile regression was conducted to characterize the upper, lower and median constraint lines. Historically, the largest mammals in Africa ranged over ~85% of the continent; accordingly, we capped maximum range at 85% of the land area of North or South America. We also grouped body size to characterize the descriptive statistics of body size bins and used these to develop regression equations. Use of the median and maximum values resulted in robust predictive equations relating geographic range to body mass; because of the geometric shape of the relationship and because for some extant megaherbivores historic range is unknown, minimum size was much less constrained. Consequently, while maximum and median estimates of range are robust, we have considerably less confidence in our characterization of minimum range. Equations (log-log in Km 2 with standard error): Maximum historic range, y = 0.212 (0.042) x + 6.009 (0.235), r 2 =0.863, P<0.01, df=5; Median historic range, y = 0.413 (0.117) x + 4.262 (0.650), r 2 =0.756; P<.025; df=5; Minimum historic range, y = 0.567 (0.290) x + 2.666 (1.618), r 2 =0.488; P<0.123; df=5. nature geoscience www.nature.com/naturegeoscience 3
Supplemental References S1. Clauss, M. & Hummel, J. Mamma.l Rev. 35, 174-187 (2005). S2. Cellabos, G. & Ehrlich, P.R. Science 296, 904-907 (2002). S3. Laliberte, A.S. & Ripple, W.J. Bioscience 54, 123-138 (2004). S4. Lelieveld, J., Crutzen, P.J. & Dentener, P.J. Tellus 50B, 128-150 (1998). S5. Thompson, A.M. et al. Tellus, 45B, 242-257 (1993). S6. Fischer, H. et al. Nature 452, 865-869 (2008). S7. EPICA Community Members. Nature 429, 623-628 (2004). S8. Jouzel, J. et al. Science 317, 793-797 (2007). S9. Loulergue, L. et al. Nature 453, 383-386 (2008). S10. Brook, E.J., Sowers, T., & Orchardo, J. Science 273, 1087-1091 (1996). 4 nature geoscience www.nature.com/naturegeoscience
Supplementary Table 1. Computation of methane emissions by extinct megafauna. Comparison with modern numbers of domestic livestock suggest our computations are conservative; we estimate ~100 million herbivores were extirpated in North America (excluding lagomorphs). Today, domestic cattle alone in the USA number 97 million; this excludes other livestock as well as those in Mexico and Canada. Similarly, livestock in South America number more than 250 million, a value 2.5 times higher than our estimate of 102 million. nature geoscience www.nature.com/naturegeoscience 5
Continent Order Family genus species Body mass (kg) Herbivore type Median range (km2) Density (N/km2) Modified Tier 1 methane emissions (kg/animal yr) Modified Tier 2 methane emissions (kg/animal yr) Allometric methane emissions (kg/animal yr) Allometric with median range (kg/yr) NA Artiodactyla Antilocapridae Capromeryx minor 10 fg 820,352 12.101 1.67 1.39 1.24 12,354,843 NA Artiodactyla Antilocapridae Capromeryx mexicana 15 fg 969,897 8.300 2.50 1.89 1.91 15,378,944 NA Artiodactyla Bovidae Saiga spp. 50 fg 1,594,684 2.709 8.33 4.65 6.82 29,463,276 NA Artiodactyla Antilocapridae Stockoceros conklingi 51 fg 1,607,779 2.659 8.50 4.72 6.96 29,780,029 NA Artiodactyla Antilocapridae Stockoceros onusrosagris 55 fg 1,658,707 2.479 9.17 5.00 7.54 31,019,377 NA Artiodactyla Antilocapridae Tetrameryx shuleri 60 fg 1,719,398 2.286 10.00 5.34 8.27 32,511,642 NA Artiodactyla Tayassuidae Mylohyus nasutus 75 fg 1,885,386 1.858 1.50 6.31 10.47 36,675,016 NA Artiodactyla Bovidae Oreamnos harringtoni 75 fg 1,885,386 1.858 9.38 6.31 10.47 36,675,016 NA Artiodactyla Camelidae Palaeolama mirifica 80 fg 1,936,316 1.750 9.85 6.62 11.21 37,975,703 NA Artiodactyla Camelidae Hemiauchenia macrocephala 11 0 fg 2,208,489 1.301 13.54 8.41 15.69 45,101,322 NA Artiodactyla Tayassuidae Platygonus compressus 11 0 fg 2,208,489 1.301 3.00 8.41 15.69 45,101,322 NA Artiodactyla Cervidae Sangamona fugitiva 157.5 fg 2,561,397 0.932 26.25 11.00 22.94 54,748,059 NA Artiodactyla Cervidae Navahoceros fricki 250 fg 3,099,911 0.606 41.67 15.56 37.38 70,262,699 NA Artiodactyla Bovidae Ovibos moschatus 286 fg 3,277,021 0.535 52.43 17.21 43.09 75,557,031 NA Artiodactyla Bovidae Bootherium bombifrons 300 fg 3,342,343 0.512 55.00 17.84 45.32 77,532,306 NA Artiodactyla Bovidae Symbos cavifrons 400 fg 3,764,010 0.392 73.33 22.13 61.43 90,562,754 NA Artiodactyla Bovidae Euceratherium collinum 450 fg 3,951,634 0.351 82.50 24.18 69.57 96,509,926 NA Artiodactyla Bovidae Bos grunniens 500 fg 4,127,381 0.318 91.67 26.17 77.77 102,160,034 NA Artiodactyla Cervidae Cervalces scotti 632 fg 4,546,698 0.256 105.33 31.19 99.62 115,937,638 NA Artiodactyla Cervidae Alces latifrons 850 fg 5,138,662 0.194 141.67 38.96 136.27 136,057,800 NA Artiodactyla Bovidae Bison priscus 900 fg 5,261,410 0.184 165.00 40.66 144.76 140,322,780 NA Artiodactyla Camelidae Camelops hesternus 1100 fg 5,716,039 0.153 88.77 47.27 178.96 156,382,904 NA Lagomorph Leoporidae Sylvilagus idahoensis 0.35 fg 205,447 273.435 0.10 0.11 0.04 2,021,315 SA Artiodactyla Cervidae Morenelaphus lujanensis 50 fg 1,594,684 2.709 8.33 4.65 6.82 29,463,276 SA Artiodactyla Tayassuidae Platygonus spp. 50 fg 1,594,684 2.709 1.50 4.65 6.82 29,463,276 SA Artiodactyla Cervidae Morenelaphus axpeitianus 50 fg 1,594,684 2.709 8.33 4.65 6.82 29,463,276 SA Artiodactyla Cervidae Agalmaceros spp. 60 fg 1,719,398 2.286 10.00 5.34 8.27 32,511,642 SA Artiodactyla Cervidae Charitoceros spp. 60 fg 1,719,398 2.286 10.00 5.34 8.27 32,511,642 SA Artiodactyla Camelidae Eulamaops parallelus 150 fg 2,510,300 0.975 12.11 10.61 21.78 53,324,465 SA Artiodactyla Cervidae Paraceros spp. 300 fg 3,342,343 0.512 50.00 17.84 45.32 77,532,306 SA Litopterna Macraucheniidae Windhausenia spp. 700 fg 4,742,698 0.233 56.49 33.68 110.99 122,515,254 SA Litopterna Macraucheniidae Macrauchenia patachonica 988 fg 5,468,077 0.169 79.73 43.61 159.76 147,572,684 SA Artiodactyla Camelidae Hemiauchenia paradoxa 1000 fg 5,495,409 0.167 123.08 44.01 161.81 148,537,881 SA Artiodactyla Camelidae Palaeolama spp. 1000 fg 5,495,409 0.167 123.08 44.01 161.81 148,537,881 SA Notoungulata Toxodontidae Mixotoxodon spp. 1000 fg 5,495,409 0.167 166.67 44.01 161.81 148,537,881 SA Notoungulata Toxodontidae Toxodon paradoxus 1000 fg 5,495,409 0.167 166.67 44.01 161.81 148,537,881 SA Notoungulata Toxodontidae Toxodon bilobidens 1100 fg 5,716,039 0.153 183.33 47.27 178.96 156,382,904 SA Notoungulata Toxodontidae Toxodon burmeisteri 1100 fg 5,716,039 0.153 183.33 47.27 178.96 156,382,904 SA Notoungulata Toxodontidae Toxodon platensis 1642 fg 6,744,490 0.105 273.67 63.84 273.31 194,150,596 NA Artiodactyla Camelidae Camelops huerfanensis 700 hg 4,742,698 0.233 56.49 33.68 34.79 38,408,680 NA Artiodactyla Bovidae Bison latifrons 900 hg 5,261,410 0.184 165.00 40.66 51.48 49,906,593 NA Lagomorph Leoporidae Sylvilagus leonensis 1.5 hg 374,736 70.644 0.10 0.34 0.00 63,581 NA Lagomorph Leoporidae Aztlanolagus agilis 2 hg 422,013 54.060 0.20 0.42 0.00 85,805 NA Perissodactyla Equidae Equus caballus 250 hg 3,099,911 0.606 8.18 15.56 6.99 13,136,834 NA Perissodactyla Equidae Equus hemionus 250 hg 3,099,911 0.606 8.18 15.56 6.99 13,136,834 NA Perissodactyla Equidae Equus fraternus 259 hg 3,145,523 0.587 8.48 15.98 7.38 13,629,991 NA Perissodactyla Tapiridae Tapirus veroensis 275 hg 3,224,367 0.555 9.00 16.71 8.11 14,508,479 NA Perissodactyla Equidae Equus conversidens 306 hg 3,369,791 0.502 10.01 18.11 9.58 16,216,568 NA Perissodactyla Tapiridae Tapirus copei 317 hg 3,419,302 0.486 10.37 18.59 10.12 16,824,454 NA Perissodactyla Equidae Equus niobrarensis 334 hg 3,493,874 0.463 10.93 19.33 10.98 17,765,648 6 nature geoscience www.nature.com/naturegeoscience
NA Perissodactyla Equidae Equus alaskae 372 hg 3,652,870 0.419 12.17 20.96 12.99 19,876,640 NA Perissodactyla Tapiridae Tapirus californicus 400 hg 3,764,010 0.392 13.09 22.13 14.54 21,437,974 NA Perissodactyla Equidae Equus complicatus 400 hg 3,764,010 0.392 13.09 22.13 14.54 21,437,974 NA Perissodactyla Equidae Equus giganteus 400 hg 3,764,010 0.392 13.09 22.13 14.54 21,437,974 NA Perissodactyla Equidae Equus scotti 555 hg 4,309,164 0.289 18.16 28.30 24.23 30,157,165 NA Perissodactyla Equidae Equus occidentalis 574 hg 4,369,489 0.280 18.79 29.02 25.54 31,233,699 NA Perissodactyla Equidae Equus laurentius 648 hg 4,593,889 0.250 21.21 31.78 30.85 35,440,381 NA Proboscidea Mammutidae Mammut americanum 4523.8 hg 10,249,977 0.041 213.62 136.51 638.16 268,455,165 NA Proboscidea Gomphotheriidae Cuvieronius tropicus 5000 hg 10,682,542 0.037 236.11 147.15 745.92 297,964,119 NA Proboscidea Elephantidae Mammuthus primigenius 5500 hg 11,111,426 0.034 259.72 158.05 865.42 329,075,195 NA Proboscidea Elephantidae Mammuthus columbi 8000 hg 12,971,081 0.024 377.78 209.34 1552.09 486,247,063 NA Proboscidea Elephantidae Mammuthus imperator 10000 hg 14,223,288 0.020 472.22 247.48 2197.86 613,532,008 NA Xenarthra Dasypodidae Holmesina septentrionalis 250 hg 3,099,911 0.606 11.81 15.56 6.99 13,136,834 NA Xenarthra Megatheriidae Nothrotheriops shastense 300 hg 3,342,343 0.512 14.17 17.84 9.29 15,885,379 NA Xenarthra Megalonychidae Megalonyx jeffersonii 600 hg 4,450,169 0.269 28.33 30.00 27.36 32,709,268 NA Xenarthra Glyptodontidae Glyptotherium floridanum 1100 hg 5,716,039 0.153 51.94 47.27 70.39 61,513,212 SA Perissodactyla Equidae Onohippidium spp. 310.7 hg 3,391,071 0.495 10.17 18.31 9.81 16,476,191 SA Perissodactyla Equidae Equus lasallei 350 hg 3,562,051 0.443 11.45 20.03 11.81 18,653,319 SA Perissodactyla Equidae Equus santaeelenae 350 hg 3,562,051 0.443 11.45 20.03 11.81 18,653,319 SA Perissodactyla Equidae Equus insulatus 351 hg 3,566,250 0.442 11.49 20.07 11.86 18,708,856 SA Perissodactyla Equidae Equus neogeus 378 hg 3,677,089 0.413 12.37 21.22 13.31 20,210,808 SA Perissodactyla Equidae Hippidion principale 5 11 hg 4,164,644 0.312 16.72 26.60 21.30 27,670,168 SA Xenarthra Mylodontidae Mylodon listai 1000 hg 5,495,409 0.167 47.22 44.01 60.67 55,697,695 SA Xenarthra Mylodontidae Scelidodon spp. 1000 hg 5,495,409 0.167 47.22 44.01 60.67 55,697,695 SA Xenarthra Glyptodontidae Panochthus tuberculatus 1061 hg 5,631,453 0.158 50.10 46.01 66.54 59,242,401 SA Xenarthra Glyptodontidae Neothoracophorus depressus 1100 hg 5,716,039 0.153 51.94 47.27 70.39 61,513,212 SA Xenarthra Mylodontidae Scelidotherium leptocephalum 111 9 hg 5,756,610 0.150 52.84 47.88 72.30 62,620,737 SA Xenarthra Mylodontidae Glossotherium myloides 1200 hg 5,925,184 0.141 56.67 50.46 80.62 67,351,005 SA Xenarthra Glyptodontidae Plaxhaplous canaliculatus 1300 hg 6,124,330 0.131 61.39 53.58 91.34 73,209,290 SA Xenarthra Glyptodontidae Doedicurus clavicaudatus 1468 hg 6,439,585 0.117 69.32 58.69 110.39 83,093,256 SA Xenarthra Mylodontidae Glossotherium robustum 1713 hg 6,863,439 0.101 80.89 65.89 140.42 97,591,591 SA Xenarthra Glyptodontidae Glyptodon clavipes 2000 hg 7,316,871 0.088 94.44 74.01 178.77 114,686,020 SA Xenarthra Mylodontidae Lestodon armatus 3397 hg 9,106,311 0.054 160.41 110.12 408.30 199,176,816 SA Xenarthra Megatheriidae Eremotherium rusconii 3500 hg 9,219,346 0.052 165.28 112.61 427.76 205,473,646 SA Xenarthra Megatheriidae Paramegatherium spp. 3500 hg 9,219,346 0.052 165.28 112.61 427.76 205,473,646 SA Proboscidea Gomphotheriidae Cuvieronius spp. 5000 hg 10,682,542 0.037 236.11 147.15 745.92 297,964,119 SA Proboscidea Gomphotheriidae Haplomastodon chimborazi 6000 hg 11,517,984 0.032 283.33 168.71 991.15 360,305,447 SA Proboscidea Gomphotheriidae Notiomastodon spp. 6193 hg 11,669,578 0.031 292.45 172.77 1041.30 372,390,120 SA Xenarthra Megatheriidae Megatherium americanum 6265 hg 11,725,420 0.030 295.85 174.27 1060.23 376,902,471 SA Proboscidea Gomphotheriidae Stegomastodon superbus 7580 hg 12,685,377 0.025 357.94 201.04 1426.94 459,676,749 NA Xenarthra Glyptodontidae Glyptotherium mexicanum 1100 hg? 5,716,039 0.153 51.94 47.27 70.39 61,513,212 NA Xenarthra Mylodontidae Glossotherium harlani 1587 hg? 6,650,255 0.109 74.94 62.23 124.65 90,123,569 NA Xenarthra Megatheriidae Eremotherium rusconii 3500 hg? 9,219,346 0.052 165.28 112.61 427.76 205,473,646 SA Primates Cebidae Caipora bambuiorum 20.5 hg 1,103,454 6.207 1.00 2.38 0.14 969,806 SA Xenarthra Dasypodidae Propraopus grandis 47 hg? 1,554,449 2.869 2.22 4.44 0.52 2,302,307 SA Xenarthra Megalonychidae Nothropus spp. 100 hg? 2,123,244 1.422 4.72 7.83 1.67 5,056,351 SA Xenarthra Dasypodidae Holmesina paulacoutoi 125 hg? 2,328,219 1.155 5.90 9.25 2.37 6,379,953 SA Xenarthra Dasypodidae Eutatus spp. 144 hg? 2,471,162 1.010 6.82 10.31 2.97 7,414,916 SA Xenarthra Megalonychidae Nothrotherium spp. 150 hg? 2,510,300 0.975 7.08 10.61 3.15 7,714,794 SA Xenarthra Dasypodidae Pampatherium humboldtii 150 hg? 2,510,300 0.975 7.08 10.61 3.15 7,714,794 SA Xenarthra Glyptodontidae Chlamydotherium spp. 175 hg? 2,675,314 0.845 8.26 11.91 4.01 9,059,054 SA Xenarthra Dasypodidae Holmesina occidentalis 200 hg? 2,826,997 0.746 9.44 13.16 4.94 10,411,432 SA Xenarthra Glyptodontidae Neosclerocalyptus spp. 200 hg? 2,826,997 0.746 9.44 13.16 4.94 10,411,432 SA Xenarthra Dasypodidae Pampatherium typum 200 hg? 2,826,997 0.746 9.44 13.16 4.94 10,411,432 SA Xenarthra Megalonychidae Valgipes spp. 200 hg? 2,826,997 0.746 9.44 13.16 4.94 10,411,432 SA Perissodactyla Equidae Equus andium 220 hg? 2,940,496 0.683 7.20 14.14 5.73 11,498,512 SA Xenarthra Glyptodontidae Lomaphorus spp. 250 hg? 3,099,911 0.606 11.81 15.56 6.99 13,136,834 SA Perissodactyla Equidae Hippidion saldiasi 265 hg? 3,175,415 0.574 8.67 16.25 7.65 13,959,165 SA Xenarthra Glyptodontidae Hoplophorus spp. 280 hg? 3,248,451 0.546 13.22 16.94 8.34 14,783,453 SA Xenarthra Glyptodontidae Sclerocalyptus ornatus 280 hg? 3,248,451 0.546 13.22 16.94 8.34 14,783,453 nature geoscience www.nature.com/naturegeoscience 7
SA Xenarthra Megalonychidae Ocnopus spp. 300 hg? 3,342,343 0.512 14.17 17.84 9.29 15,885,379 SA Xenarthra Megatheriidae Eremotherium laurillardi 800 hg? 5,011,597 0.206 37.78 37.23 42.85 44,142,507 SA Xenarthra Glyptodontidae Neothoracophorus elevatus 800 hg? 5,011,597 0.206 37.78 37.23 42.85 44,142,507 SA Xenarthra Glyptodontidae Glyptodon reticulatus 862 hg? 5,168,500 0.192 40.71 39.37 48.13 47,712,898 9612592412 TOTALS 9.61 8 nature geoscience www.nature.com/naturegeoscience
Supplementary Table 2: Fluctuations in methane concentration and global emissions. Maximum methane concentrations for 13.8 to 13.2 ka (bracketing the arrival of humans in the Americas); minimum values bracket the entire extinction interval from 13.8 to 10.8 ka. Methane atmospheric lifetime is currently about 8-9 years but photochemical modeling suggests it is shorter during cooler periods (S4, S5). Global average concentrations of the key oxidizer hydroxyl radical were likely 20 and 30% higher than modern values in the late pre-industrial Holocene and Last Glacial Maximum, respectively (S6). Enhanced removal was compensated in part by a temperature dependence of the bimolecular rate constant for reaction with the hydroxyl and there were minor sinks as well, but the time scale was likely 7-8 years during the late Quaternary (S4, S5). However, estimates specifically for the transition into the Younger Dryas taken from a set of Monte Carlo box modeling calculations (S6) suggest final residence times of 5.8 (Bølling- Allerød) and 4.4 years (Younger Dryas). Here we use upper limits (7.3 and 5.4 years, respectively) from the 50% likelihood bin (S6) to obtain values more consistent with multiple photochemical calculations for the pre-industrial, Holocene and LGM (S4, S5). Maximum Minimum Decrease in Decrease in Core methane methane Difference source pool source pool Reference (ppbv) (ppbv) (Tg/yr) a (Tg/yr) b EPICA Dome C 646 462 184 58 7 S7, S8, S9 GISP2 703 458 245 77 27 S10 a computed using an average 7.5 yr residence time for methane during the Pre-industrial Holocene and LGM. bcomputed using a value of 7.3 years for the Bølling-Allerød and 5.4 years for the Younger Dryas. nature geoscience www.nature.com/naturegeoscience 9
Supplementary Table 3. Comparison of methane decrease during the Bølling-Allerød to the Younger Dryas with earlier drops during the Pleistocene. The EPICA Dome C ice core (S8, S9) was examined to evaluate both the magnitude and uniqueness of the methane drop from the Bølling- Allerød to the Younger Dryas. Five time intervals of approximately equal length were chosen encompassing the most severe drops in methane over the past 500,000 years. We employed a sliding window to ensure the maximum absolute drop in methane was included. Linear regression coefficients were computed to examine the rate of change; Student s t-tests compared slopes between older time intervals and the Bølling- Allerød to Younger Dryas. Because multiple comparisons were performed a Bonferroni correction was applied and slopes were considered to be significantly different at! = 0.01. Results suggest a significantly more abrupt drop in methane concentration during the interval spanning the Bølling-Allerød to Younger Dryas than in any other interval over the past 500,000 years. Time Period Length of interval (yrs) Intercept Slope SEslope N Student s t Critical value P value 12,884-11,921 963-2337.864 0.235 0.030 11 400,592-399,415 1177-24401.64 0.063 0.019 4 4.884 3.106 < 0.001 332,875-331,782 1093-34987.25 0.108 0.014 6 3.880 3.012 < 0.01 241,977-240,937 1040-14548.51 0.063 0.010 10 5.477 2.898 < 0.001 128,108 127,030 1078-6778.791 0.058 0.006 8 5.805 2.947 < 0.001 10 nature geoscience www.nature.com/naturegeoscience