0.2. coral 0.4. ductions of up to 70% (relative to the late 20th. reductions in ENSO variance occur sporadically

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1 SST through mid- to late H For example, estimates mid-holocene are statistically indisting those pt millennium (Fig. B). In fact, only period that stan th century, when are significantly higher than var timates Line Isls fossil C D), sessed a Monte Car approach that uses 1, pairs pse series to sess significance in - to (16 ever, high late th century is not unprecedented; early 17th centur is highest entire Lin Downloaded on January 3, 13 O SST Anomaly ( C) Anomaly ( ) O SST Anomaly ( C) Anomaly ( ) O reductions in occur sporadically. -1 throughout new collection fossil s, in-.4 dependently age or preservation. The -.4 d O reconstructions are broadly consistent range changes 196 con-. 1 tained in existing fossil doyear reconstructions (7,, 19). exped collection index [Extended Fig. 1. variability in LineThe Isls modern do records REPORTS Reconstructed Surface Temperatures, version 3 (ERSST v.3b)] fossilsea records shows no systematic shifts(9). in Coral do data are Christm [spliced record constructed data in (1, 14,to, 3); (fig. S3)]; Fanning [spliced record constructed through midlate Holocene. Our records reveal that h expected, magnitude -related Isls fossil collection, we benchmark palerom data in (14) a new strength Fanning modern do record (16)] (fig. S4); Palmyra (13). Each monthly example, over pt 7been ky (Fig. do anomalies scale isls proximity in a given fossil against late varied substantially resolvedfor series h - toa estimates bps filtered to highlight -related variability. -1 tablecorrelation S). Inmid-Holocene some sequences, interannual to. equator. Therefore, in order to sess relative th century recorded in mod- are statistically coefficients computed between indistinguishable bpsed records SST index variabilityareis.9, statistically insignificant, rechanges in across entire Line ern d O records same isl..8, for Christm, Fanning, those.8 pt millennium (Fig. 3, Palmyra, A respectively. ductions up to 7% (relative to late th B). In. fact, Such onlydramatic period that sts out is century) in to -.4 th century, when estimates reductions in occur sporadically arecollection significantly than esthroughout new fossilhigher s, in-.4 Aage or preservation. The B Year dependently timates Line Isls fossil s (Fig. 3, do reconstructions are broadly consistent C D), sessed a Monte Carlo bed Fig. 1. index [Extended range changes con-.variability in Line Isls modern d O records 1 that uses 1, pairs pseudo Reconstructed Sea Surface Temperatures, version 3 (ERSST v.3b)] (9). Coral do data are tained Christm in existingapproach fossil do reconstruc to sess significance observed tions (7,, 19). Theseries exped collection [spliced record constructed data in (1, 14,, 3); (fig. S3)]; Fanning [spliced record constructed a new Fanning modern do record (16)] (fig. S4); Palmyra fossil records shows no systematic in (16). How (13). Each in - toshifts data in (14) monthly through midlate Holocene. ever, highto late th century resolved series h been - to bps filtered to highlight -related variability. For example, estimates not unprecedented; early 17th century Correlation coefficients computed between bpsed records SST index areis statistically. -1 mid-holocene indistinguishable are.9,.8,.8 for Christm, Fanning, Palmyra, respectively. is (Fig. highest entire Line Isls those pt millennium 3, A C D Downloaded on January 3, Downloaded on January 3, 13 B). In fact, only period that sts out is th century, when estimates E than esare significantly higher Year timates Line Isls fossil s (Fig. 3, Fig.. Overview new published recons sessed A variability in Line Isls modern do records index [Extended C D), B C a Monte Carlo bed D spanning pt 7. ky. (A) Relative ch Fig. 1. fossil do series, calculated sliding 3Reconstructed Sea Surface Temperatures, version 3 (ERSST v.3b)] (9). Coral do data are Christm approach that uses 1, pairs pseudo dows ( a -year step) SD - to 7-ye [spliced record constructed data in (1, 14,, 3); (fig. S3)]; Fanning [spliced record constructed series to sess significance observed percent C.E. in data in (14) a new Fanning modern do record (16)] (fig. S4); Palmyra (13). Each monthly in - to (16). HowREPORTS corresponding modern do series resolved series h been - to bps filtered to highlight -related variability. ever, high late th century reconstruction. The choice a late th century tions in (Fig. E). These archives ogy, resolution, continuity) make it difficult divergent benchmark views Hol- intervals for non Line Isl s benchmark makes fossil strengths include two lake sediment records that record to fully reconcile [modern Correlation coefficients computed between bpsed records SST index is not unprecedented; early 17th century appear anomalously weak, when in fact it is fewer El Niño related flood events in mid- ocene evolution. However, instrumental observations suggest that itcircles. is possible for et- series 1 < length < Holocene< (8, 3 1, ) well are a marine sediment late thseries century that is anoma (tables3)]. strength < length cross-filled Coral are.9,.8,.8 for Christm, Fanning, Palmyra, respectively. T is highest Coral entire Line Isls record that exhibits a drop in foraminifera pop- ern Pacific precipitation anomalies to be muted lously strong. are open circles. The Fossil O estimates data are Christm (green) [this study (31)]; micro-atolls (pink) (); Fanning Isl (b central Pacific is relatively ulation (reflective Isl a decree in annual while -bed d dif- fer appreciably several lower-resolution re- /or interannual SST extremes) during mid- strong (1), various mid-holocene study); Palmyra (red) (1); Papua New Guinea (7) (9). gray in(19)]. (B) Relative changes over th century recorded in reflect such geographic complexities. Differences attributes proxies may cords etern equatorial Pacific that[yellow have Holocene used to infer sizable mid-holocene reduc- various archives (climate sensitivities, chronol- Whatever ir origin, underscore do records been SST index (ERSSTv.3b) (9), calculated sliding 3-year windows ( a -year step) SD need for rigorous comparison among differarchives, facilitated[modern by translation bpsed series, percent intervalsent ideally records benchmark intervals for non Line Isla tropical Pacific climate variability simulated by A B C differ by TD (table S3)]. Palmyra intoc.e.) explicit expectations for proxies (). Palmyra modern fossil NB9 (1) is re here (atbdate models 196 for comparison A The exped archive does allow for a during early th century. Modern d O data are Palmyra (red) (13); Fanning, (blue) (fig S4); Christm Isl (green) (fig. S3); Pa quantitative sessment long-term variability exhibited by coupled GCMs. The broad Guinea [(yellow (7) gray (19)]. (C) Relative changes in NCAR CCSM4 1 ky preindustrial run (3), calculated sliding range changes exhibited control by fossil databe is also characteristic windows ( a -year step) SD - to bpsed annual series, percent average changes in long, unforced integrations National Center for Atmospheric Reentire - to bpsed model series. (D) Relative changes in GFDL CM.1 ky preindustrial control run (), c E search (NCAR) Community Climate System Model sliding 3-year windows ( a -year step) SD - to bpsed version 4 monthly (CCSM4) (3) National Oceanic series, percent Atmospheric Administration (NOAA) Geophysical Fig.. average Overview model reconstructions SD new entire - topublished bpsed series. (E) Records Laboratory Ecuadorian Lake Pallcacocha (red; an 8-poin C Fluid Dynamics (GFDL) Climate Model.1 (CM.1) (4, ) fully coupled GCMs (Fig., pt raw red (8) Galapagos Lakechanges El Junco (black; s fraction) (1). spanning 7.intensity ky. (A)record) Relative in percent C D, respectively). In model simulations,.4 fossil do series, calculated sliding 3-year wincenturies-long epochs exhibit large changes in strength, where or epochs feature a relatively stable. The estidows68 ( a -year step) SD 4JANUARY - to 13 b, VOL 339 SCIENCE D mates Line Isls fossil s exhibit a similar range variability, fluctuating by T36% percent C.E. intervals (s) about an average 4% ( respect to late th century benchmark). In fact, corresponding modern d O series each site fossil distribution is cone F E sistent distribution in [modern benchmark intervals for non Line Isl s differ by models (Fig. 3F), sessed by subsampling Fig.. Overview new published reconstructions model series to match fossil lengths T (table S3)]. Coral series < length < 3 are cross-filled circles. Coral series 1 < length < by using a Monte Carlo bed approach (16). spanning pt 7. ky. (A) Relative changes in The actual Line Isls fossil distribution is are open circles. Fossil d O data are Christm Isl (green) [this dstudy (31)]; micro-atolls (pink) (); winfanning Isl (blue) (this contained by spread 1, pseudo fossil O series, calculated sliding 3-year realizations, falling well in s limits dows ( a -year step) changes SD over - toth b, recorded in modern model distribution. study); Palmyra (red) (1); Papua New Guinea [yellow (7) gray (19)]. (B) Relative century We conclude that model data provide a percent C.E. intervals reonably satisfactory representation d O records SST index (ERSSTv.3b) (9), calculated sliding 3-year windows ( a -year step) SD to Fig. 3.each Comparison probability density functions strength in Line Isls data distribution in real fossil data. corresponding modern d O series site different periods, in model output. (A) Distributions relative changes in Line The convergence between data-bed modelbpsed series, percent intervals benchmark records [modern benchmark for Isl Isls s in 6- to non Line 7-ky interval (black, n = 193 ), s compared - to 1-ky interval bed estimates long-term, intrinsic var[modern intervals for non Line Isl intervals s differ by (white, n = 47 ). (B) Significance test calculated difference between SD - to iability suggests that at let some current differtby T (table S3)]. (table S3)]. NB9 <(1) is re here date 196 C.E.) comparison Palmyra 6-modern to 7-ky Line Isls s versus - to 1-kystrength Line Isls s, benchmarked using generation models may accurately simulate Coral Palmyra series fossil < length 3 are (at cross-filled circles. Coralfor series 1 < length < in calculated 1, pseudo data sets constructed -ky-long GFDL CM.1 long-term changes in, even series (16). Red bar indicates calculated differencenew between mean SDs 6- to out inclusion solar volcanic natural are th opencentury. circles. Fossil d O data Christm (green) [this(13); studyfanning, (31)]; micro-atolls (); Fanning Isl (blue) (this during early Modern d are O data are Isl Palmyra (red) (blue) (fig (pink) S4); Christm Isl (green) (fig. S3); Papua 7-ky - to 1-ky intervals, compared threshold for pseudo SD significant at climate forcings in models. This data-model study); Palmyra (red) (1); Papua New Guinea [yellow (7) gray (19)]. (B) Relative changes over th century recorded in modern 9% level (black bar). (C) Distribution relative changes Guinea [(yellow (7) gray (19)]. (C) Relative changes in NCAR CCSM4 1 ky preindustrial control run (3),datacalculated sliding 3-yearin Line Isls modern agreement suggests that eir (i) models over(white; three isls relative changes in Fig. B have been estimate unforced variability or (ii) do records SST index (ERSSTv.3b) (9), calculated sliding 3-year windows ( a -year step) SD - totoger averaged to form a composite Line Isls modern ; n = 11 ) fossil data natural radiative forcing had little influence on windows ( a -year step) SD to bpsed annual series, percent average SDmarks (black; compiled Fig. A; n = 99 ). The red arrow late-th-century bpsed series, percent intervals records [modern benchmark intervals for non Linebenchmark Isl(%s by definition) for Line Isls s. (D) Same (B), but for modern versus fossil paleo-. In any ce, one main imentirediffer - to bpsed model series. (D) Relative changes in GFDL CM.1 ky preindustrial control run (), calculated distributions in (C). (E) Distribution relative changes in unforced NCAR plication both - model-bed estiby T (table S3)]. Palmyra fossil NB9 (1) is re here (at date 196 C.E.) for comparison Palmyra modern strength CCSM4 (black) GFDL CM.1 (white) control runs, compiled Fig., C D, respectively. (F) mates intrinsic variability is that Plot Papua distribution relative changes in actual Line Isls fossil data (red), detection ( attribution) any changes in during sliding windows -year step) SDPalmyra (red) - to(13); bpsed series, percent 3-year early th century. ( Moderna do data are Fanning, (blue) (fig monthly S4); Christm Isl (green) (fig. S3); New compared distribution 1, pseudo fossil databes compiled by extracting 99 properties would require very long series GFDL model output in segment lengths8-point corresponding to actual fossil lengths (gray, envelope spanning many centuries, to extent that deguinea gray (C) Relative changes in NCAR CCSM4 ky preindustrial control run (3), sliding 3-year average SD[(yellow (7) entire - to(19)]. bpsed model series. (E) 1Records Ecuadorian Lakecalculated Pallcacocha (red; an smooth individual pseudo ensemble distributions; black, pseudo mean 1s bars), dis- tection such changes is even possible (6). Taken toger, Line Isls fossil tributionsd relative changes full -ky-long series GFDL ( a -year record) step) - to bpsed series, percent windows raw red intensity (8)SD Galapagos Lake El Juncoannual (black; percent s fraction) (1). average data suggest that much observed model (blue) entire - to bpsed model series. (D) Relative changes in GFDL CM.1 ky preindustrial control run (), calculated sliding 3-year windows ( a -year step) SD - to bpsed monthly series, percent average SD entire - to bpsed model series. (E) Records Ecuadorian Lake Pallcacocha (red; an 8-point smooth 4 JANUARY 13 VOL 339 SCIENCE changes by T4% (s); some SCIENCE VOL JANUARY

2 Laguna Pallcacocha, Ecaudor Sediment core displayed abundant light-colored cltic laminae Hyposize that cltic laminae were deposited during El Nino-induced alluviation events in drainage bin Utilize a new continuous sediment core identify frequency components wavelet analysis Image Cole (1) Number Study Record Time Span Resolution 1 North Australia; McGlone et al. (199) Shulmeister Lees (199) Lake Sediment: Pollen Holocene Inter-Decadal Great Barrier Reef, Australia; Gagan et al. (1998) Coral: Sr/Ca δo Years; ~4 cal yr BP Annual 3 Norrn New Guinea, Tudhope et al. Coral: δo 49 Years at ~6 cal yr BP ~9 at -3 cal yr BP Annual 4 Ecuador, Rodbell et al. (1999) Moy () Lake Sediment: Grayscale Color ~1, Years Sub-Decadal Cotal Peru, Sweiss et al. (1) Midden: Mollusks Holocene Discontinuous

3 CORTEX XRF Scanner Univ. Bremen Geotek Linescan Camera Jansen et al. (1998) Jansen et al. (1998) 3

4 Age Models Constant Carbon Accumulation Model: -Distributes age bed on carbon content sediment Event Model: -All laminae signed a value 6 months bed on Rio Chira discharge data Both models sign higher sedimentation rates to light-colored laminae Red Color Intensity dark Linescan Results Ag e (cal yr B P) P b Y ears (AD ) Events * 1 yr -1 4 light Average Gray Scale (Std. Dev. Units) RelaOonship to Modern Ag e (cal yr B P) 4

5 4/17/17 Red Color Intensity (K + TI) / Fe XRF Results Age (cal yr BP) Red Color Intensity Period () Period () Time (cal yr BP) Time (cal yr BP) Time (cal yr BP) Model Comparison 3 Number Events * 1 yr Number W arm Events * 1 yr Age (cal yr BP) B Clement et al. ()

6 4/17/17 6