Speleothem records of precipitation in the West Pacific Warm Pool from the LGM to present

Transcription

1 Speleothem records of precipitation in the West Pacific Warm Pool from the LGM to present Kim Cobb, Jud Partin Georgia Inst. of Technology Jess Adkins California Inst. of Technology Thanks to: Sarawak Forestry Department Brian Clark, Mulu National Park Dan Schrag, Harvard NSF Gary Comer Foundation

2 Through ENSO-colored lenses Timmermann et al, Nature 1999 forced coupled O-A model with greenhouse forcing ENSO variance in control run ENSO variance Observed ENSO variance in GHG run ENSO variance increases under greenhouse forcing trend towards El Nino-like mean state in tropical Pacific Clement et al, Paleoceanography 1999 forced Cane-Zebiak model with orbital insolation changes ENSO response to smooth forcing could be abrupt changes in ENSO could trigger abrupt climate changes observed in Greenland (and many other NH sites) ENSO shutdown

3 How will ENSO and/or tropical Pacific climate evolve under continued anthropogenic forcing? Relevant Scientific Questions: 1. Is there evidence that the tropical Pacific has responded to radiative forcing in the geologic past? look at Holocene 2. What role did the tropical Pacific play in abrupt climate change (as trigger and/or feedback?) look at deglaciation

4 ENSO variance (% change from present) 1. Holocene tropical precip. trends -response to precessional forcing? -role for tropical Pacific? # events/1y ENSO variability 6 ENSO variance changes relative to present Modelled ENSO variance Lake Pallcacocha 3 Age (kybp) 2 2 mean state Clement et al., 1999; Tudhope et al., 21; Moy et al, 22; Woodruffe et al., # events/5y W/m Cariaco Ti Warm Pool seawater δ 18 O 3 2 Huascaran ice δ 18 O Fossil coral estimates of mean temperature anomalies relative to present 5 4 JJA insolation (º) 3 Age (kybp) 2 1 Dongge cave δ 18 O Berger & Loutre, 1991; Haug et al., 21; Stott et al., 22; Thompson et al., 1998; Yuan et al., Ti (%) Estimated Temperature Anomaly (ºC)

5 2. Abrupt climate change -Greenland and Antarctic have very different patterns of rapid climate events -Chinese speleothem confirms Greenland pacing at 3N, 12E Wang et al., 21

6 Warm Pool sediments ambiguous tropical Pacific tracking Greenland or Antarctica? Stott et al., δd

7 Why Northern Borneo? - 3% of rainfall variance ENSO 2% seasonal cycle 2% instraseasonal - huge cave systems Dai and Wigley, 2 - reconstruct Warm Pool precip using δ 18 O of stalagmites JJA DJF NINO3.4 SST (C) N. Borneo Precip. vs NINO3.4 SST NINO3.4 SST 1 Borneo Precipitation Year 5 Precipitation Anomaly (mm/month)

8 The tropical amount effect : empirical negative correlation between rainfall and the d18o of rainfall (Dansgaard, 1964; Rozanski, 1993) nearest long-term rainfall d18o measurements Jayapura, Indonesia Precip Month of Year Precipitation (mm/month) Marine Terrestrial

9 Speleothem Formation 1. rain Carbonate dissolution/precipitation 3. dissolve CaCO 3 2. soil = high pco 2 CO 2 +CaCO 3 +H 2 O bedrock dissolution 2HCO 3- +Ca 2+ speleothem precipitation 5. precipitate CaCO 3 4. degas CO 2 Potential for complex isotopic effects: evaporation degassing en route non-equilibrium fractionation *important to check observed d13c and d18o records for these effects

10 Fieldtrips 23, 25 Rainwater and dripwater monitoring program

11 Age Distribution and Lengths of Borneo Speleothems secret 11 (5cm) secret 2 (75cm) secret 1 (12cm) ssr3 (38cm) ssr2 (13cm) ssr1 (46cm) ssc1 (75cm) sch3 (36cm) sch2 (86cm) sch1 (33cm) mj2 (2cm) mj1 (23cm) gc4 (6cm) gc3 (23cm) baby3 (5cm) baby2 (8cm) baby1 (1cm) ba4b (89cm) ba3 (135cm) ba2 (69cm) Age (kybp) Growth rates (1-1µm/yr) easily allow for decadal to centennial resolution. Low U (.1-1ppm), low 234U (-1 ) and high 232Th (1ppb) make U/Th dating challenging. Use MC-ICPMS. Many stals cover desired interval (LGM to present); allow for REPRODUCIBLITY

12 Key observations: δ18o ( ) Buda Cave SCH2 SSC δ 13 C ( ) 1) reproducibility good within dating error bars 2) carbon and oxygen isotopic records are not correlated (kinetic effects do not dominate signal) 3) -9 calcite d18o value for present-day implies equilibrium precipitation from present-day rainwaters Age (kybp) ) carbon isotope records noisier than oxygen isotopic records

13 In best-dated record: no evidence of Younger Dryas GISP2 ice core hint of Antarctic Cold reversal; smooth S.H.-like deglaciation shared features with Chinese cave records, most notably H Dongge & Hulu Cave Buda Cave Byrd ice core Age (kybp)

14 What s so special about H1? Observed shut-down of Atlantic meridional overturning circulation (McManus et al., 24) which pushes ITCZs southward and decreases West Pacific Warm Pool precip by changing Walker circulation (Zhang and Delworth, 25)

15 June insol. 3N Dongge & Hulu Cave Most tropical hydrological records track summer insolation Is Borneo rainfall sensitive to N.H. October insolation (or S.H. March insolation?) Buda Cave 44 Or is something else going on? October insol. 4N X Data

16 Koutavas et al., 22

17 W/m Cariaco Ti JJA insolation (º) Warm Pool seawater δ 18 O Ti (%) Huascaran ice δ 18 O Fossil coral estimates of mean temperature anomalies relative to present Dongge cave δ 18 O Estimated Temperature Anomaly (ºC) Age (kybp)

18 Several big questions remain unanswered: What are the relative contributions of seasonal vs. ENSO precipitation variability locally? What are their respective amplitudes wrt d18o of precip? Over what spatial scales is climate driving d18o of precipitation? What parameters is d18o of precipitation most sensitive to? or more generally. How are local/regional climate changes recorded in cave stalagmite geochemistry?

19 On-site calibration efforts Rainwater 5-6 per mil seasonal cycle in rainfall d18o Dripwater 2-3 per mil seasonal cycle in dripwater d18o Rainfall Now working with daily station rainfall SMOW Rainfall (mm/month) Timeseries of rainwater and cave dripwater δ 18 O equil Local Rainfall Date Mulu driwpater (fast) Mulu dripwater (slow) 1/1/3 4/1/4 1/1/4 4/1/5 Buda dripwaters Long Napir rainwater Mulu rainwater Buda rainwater Mulu dripwaters -1 6 Station Rainfall Station Climatology SMOW

20 Mg/Ca up, Sr/Ca up, [Ca] down, d18o up consistent with prior precipitation idea (Fairchild et al., 2) data through Dec5 in process Mg/Ca Rainfall (mm/month) Mulu driwpater (fast) Mulu dripwater (slow) Date 1/1/4 3/1/4 5/1/4 7/1/4 1 1/1/4 3/1/4 5/1/4 7/1/4 Date 25% Mg/Ca 25% Sr/Ca 5% [Ca] dripwater Mg/Ca (slow) dripwater Sr/Ca (slow) dripwater [Ca] (slow) dripwater Mg/Ca (fast) dripwater Sr/Ca (fast) dripwater [Ca] (fast) 3.2e-4 3.e-4 2.8e-4 2.6e-4 2.4e-4 2.2e Sr/Ca SMOW [Ca] (umol/l)

21 Conclusions Malaysian stalagmites provide reproducible d18o signals, favoring a climatic interpretation LGM was drier than present, with prolonged additional drying during Heinrich1 Deglacial sequence more closely resembles the S.H. ice cores Holocene trends not driven by summer insolation Tentative support for amount effect at Malaysian site; large signals in d13c, Mg/Ca

22 and now for a reliable paleoproxy! Fossil corals collected during fieldtrips in 1998, 2, and 25 Beached fossil corals range from gravel-sized to 2m-diameter (~1-15yrs). rare longer cores: ENSO & decadal variability common short cores: mean climate

23 ENSO and coral δ 18 O in the Central Tropical Pacific (CTP) SST and rainfall anomalies during the 1982 El Nino During El Niño events, positive SST and precipitation anomalies both contribute to negative coral δ 18 O anomalies in the CTP Interpretation of coral δ 18 O on lower frequencies relies on assumption that warm SST drives higher precipitation in the CTP, and vice versa

24 How well does coral d18o reflect regional-scale SST? Palmyra coral vs. NIÑO3.4 SST 3 2 R = SST Anomoly ( C) SST Anomoly ( C) R = -.84 NIÑO3.4 SST Palmyra coral Year (A.D.)

25 Number of cores Palmyra Fanning Christmas Length of core (yr) The Line Islands Fossil Coral Collection Evans et al., 1999

26 Tropical Pacific link to US West drought? Cook et al., 24 Evidence of La Niña-like conditions from ~9-125AD: Mono Lake lowstands (Stine et al., 1994) high Warm Pool temperatures (Sr/Ca MD81, Stott et al., 24) decreased Peru runoff (lithic counts, Rein et al., 24) cool Santa Barbara basin temperatures (G. bull. δ 18 O, Field et al., in prep) Question: So how important were centennial-scale changes in tropical Pacific climate over the last millennium?

27 New sequences from Christmas and Fanning Islands Age (kybp) kypb Fanning (4ºN) fossil coral 46-yr-old Christmas fossil coral Palmyra (6ºN) modern coral 2σ error mean δ 18 O Fanning (4ºN)? Date (A.D.) -4. Christmas (2ºN) modern coral Date (A.D.) 6ky: cooler, drier conditions?; reduced ENSO activity.5ky: statistically indistinguishable mean, ENSO variability wrt modern GOAL: A unified tropical Pacific climate reconstruction from Line Islands fossil corals?

28 Berger, A. and M. F. Loutre. Insolation Values for the Climate of the Last 1 Years. Quaternary Science Reviews 1(4): , Blunier, T., et al. Asynchrony of Antarctic and Greenland climate change during the last glacial period. Nature 394: , Clement, A. C., et al. An orbitally driven tropical source for abrupt climate change. Journal of Climate 14(11): , 21. Clement, A. C., et al. Orbital controls on the El Nino/Southern Oscillation and the tropical climate. Paleoceanography 14(4): , Cobb, K. M., et al. El Nino/Southern Oscillation and tropical Pacific climate during the last millennium. Nature 424(6946): , 23. Cook, E. R., et al. Long-term aridity changes in the western United States. Science 36(5698): , 24. Correge, T., et al. Evidence for stronger El Nino-Southern Oscillation (ENSO) events in a mid- Holocene massive coral. Paleoceanography 15(4): , 2. Dai, A. and T. M. L. Wigley. Global patterns of ENSO-induced precipitation. Geophysical Research Letters 27(9): , 2. Dansgaard, W. Stable isotopes in precipitation. Tellus 16: , Grootes, P. M., et al. Comparison of Oxygen-Isotope Records from the Gisp2 and Grip Greenland Ice Cores. Nature 366(6455): , Haug, G. H., et al. Southward migration of the intertropical convergence zone through the Holocene. Science 293(5533): , 21. Koutavas, A., et al. El Nino-like pattern in ice age tropical Pacific sea surface temperature. Science 297(5579): , 22. McGregor, H. V. and M. K. Gagan. Western Pacific coral delta O-18 records of anomalous Holocene variability in the El Nino-Southern Oscillation. Geophysical Research Letters 31(11), 24. McManus, J. F., et al. Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes. Nature 428(6985): , 24. Moy, C. M., et al. Variability of El Nino/Southern Oscillation activity at millennial timescales during the Holocene epoch. Nature 42(6912): , 22. Rozanski, K., et al. (1993). Isotopic patterns in modern global precipitation. Climate change in continental isotopic records. P. K. Swart, K. C. Lohmann and J. McKenzie. Washington D.C., American Geophysical Union. 78: Stine, S. Extreme and Persistent Drought in California and Patagonia During Mediaeval Time. Nature 369(6481): , Stott, L., et al. Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch. Nature 431(74): 56-59, 24. Stott, L., et al. Super ENSO and global climate oscillations at millennial time scales. Science 297(5579): , 22. Thompson, L. G., et al. A 25,-year tropical climate history from Bolivian ice cores. Science 282: , Timmermann, A., et al. Increased El Nino frequency in a climate model forced by future greenhouse warming. Nature 398: , Tudhope, A. W., et al. Variability in the El Nino - Southern oscillation through a glacialinterglacial cycle. Science 291(558): , 21.

29 Wang, Y. J., et al. A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294(555): , 21. Woodroffe, C. D., et al. Mid-late Holocene El Nino variability in the equatorial Pacific from coral microatolls. Geophysical Research Letters 3(7), 23. Xie, P. P. and P. A. Arkin. Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bulletin of the American Meteorological Society 78(11): , Yuan, D. X., et al. Timing, duration, and transitions of the Last Interglacial Asian Monsoon. Science 34(567): , 24. Zhang, R. and T. L. Delworth. Simulated tropical response to a substantial weakening of the Atlantic thermohaline circulation. Journal Of Climate 18(12): , 25.