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Coral Records of Climate Change

Coral Records of Climate Change. Kim M. Cobb Georgia Inst. of Technology Oceanography class, Oct 21, 2011. Research Goal:. To reconstruct tropical Pacific climate change of the recent past, so that we might better predict future climate change, and its regional signatures. Palmyra

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Coral Records of Climate Change

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  1. Coral Records of Climate Change Kim M. Cobb Georgia Inst. of Technology Oceanography class, Oct 21, 2011

  2. Research Goal: To reconstruct tropical Pacific climate change of the recent past, so that we might better predict future climate change, and its regional signatures. Palmyra 1997-? Fanning 2005-? Research Funded by: NOAA NSF Fieldwork funded by: NCL The Nature Conservancy Prince Khaled Bin Sultan Bin Abdulaziz Christmas 1998-?

  3. +6° +3° 0° -3° Why study tropical Pacific climate? Palmyra, Fanning, Christmas Islands El Niño-Southern Oscillation An ocean-atmosphere phenomenon that originates in the tropical Pacific but affects global climate patterns December 1997 ocean temperature anomalies Sea Surface Temperature Anomaly (ºC) El Niño impacts - the impacts are not confined to the tropical Pacific • ENSO extremes carry serious • economic and social costs - improved ENSO forecasts minimize the costs

  4. The instrumental record of El Niño’s 1982 El Niño 1997 El Niño El Niño La Niña Are severe El Niño events becoming more frequent as global temperatures increase?

  5. The instrumental record of El Niño’s is too short to answer some key questions: 1. Are late 20th century El Niño events more frequent and more severe than those of the recent past? 2. Is there a correlation between average global temperature and El Niño activity? 3. How much and how fast has ENSO changed in the past? A well-placed rope swing in the Palmyra lagoon

  6. Corals: The geologic record of El Niño CORALS from the tropical Pacific record ENSO in the geochemistry of their skeletons COMMON Living corals provide records for the last 200 years RARE Fossil corals enable us to extend the record (ex. 1320-1390A.D.)

  7. The search for fossil corals leads to the Northern Line Islands Palmyra Atoll

  8. Research Objective: To generate >100-yr-long, high-resolution, high-fidelity climate proxy records from the tropical Pacific Ocean; to extend the record of El Niño back in time Materials: Modern and Fossil Corals Methods: Dating: U-Th radioactive decay series Climate proxy: Coral skeletal oxygen isotopes Site December 1997 SST And Rainfall Anomalies A baby booby at Palmyra

  9. Generating climate reconstructions from the Palmyra corals: • Recover the corals, both modern (~10) and fossil (~100). • 2) Prove that the coral geochemistry tracks large-scale climate. • ie. Calibrate the modern coral record against the instrumental record of climate. • Apply geochemistry to fossil corals and date them (U/Th dating). Aerial view of Palmyra

  10. The Line Island Coral Collection: A work in progress… Palmyra 40 cores U/Th dated 28 cores undated Christmas 18 cores U/Th dated 63 cores undated Fanning 33 cores undated

  11. Medieval Warm Period (MWP) Greenland green Little Ice Age (LIA) canals frozen in Europe The Palmyra Island Coral Collection Modern

  12. Palmyra Coral δ18O (‰) Climate Proxy: Coral oxygen isotopes (δ18O) Drilled in May 1998 1995 Sampling transect Coral δ18O is primarily a function of sea-surface temperature BUT It also will record changes In the δ18O of seawater (i.e. salinity) 1990 1985 26 27 28 29 30 1980 SST (°C)

  13. How well do Palmyra corals record El Niños? Red = instrumental record of El Niños Black = modern coral δ18O Less smoothed More smoothed

  14. Turning to the fossil corals…. Palmyra Island Coral Collection

  15. 17th century fossil coral-based climate reconstruction splice As number of overlapping corals increases 3 corals, 13 dates, 3,000 δ18O measurements = 1 year of work

  16. Palmyra Island Coral Collection

  17. 14th-15th Century Splice splice 5 corals, 29 dates, 14,000 δ18O measurements = 3 years of work

  18. Palmyra Coral δ18O Sequences Single records 3-coral splice Modern 5-coral splice Single records 2-coral splice warmer 1°C 1°C colder Cobb et al., Nature, 2003 Date A.D. What does this coral reconstruction of tropical Pacific climate tell us?

  19. What about that Late 20th century Trend? Approach: use coral Sr/Ca ratios as an SST-only proxy combine Sr/Ca (SST) with δ18O (SST + δ18Osw) to obtain δ18Osw (salinity) Nurhati et al., 2009

  20. Answer: the late 20th century trend is mostly salinity! So climate change is affecting rainfall in this area. Nurhati et al., 2011

  21. Are late 20th century El Nino events unprecedented in the last millennium? 1997 El Niño El Niño La Niña Most frequent, intense El Niño events of reconstruction ENSO characteristics can change in less than a decade

  22. Conclusions Climate change is changing precipitation patterns in the tropical Pacific  more rain (What are the implications for rest of globe?) Present-day El Nino events are not unusual. (What caused the strong El Nino events in the 17th century, if anything?)

  23. Food for Thought Coral reefs are disappearing at alarming rates worldwide, due to the combined influence of rising ocean temperatures and human disturbances (sediment runoff, over-fishing, dynamite fishing, etc). Reef ecosystems have weakened to the point that natural climate variations, such as a large El Niño event, may cause widespread bleaching and coral mortality (ex: 16% of world’s coral died during 1997 El Nino event (WMO report #1063)) Web Resources My homepage: http://shadow.eas.gatech.edu/~kcobb General El Niño info: http://www.pmel.noaa.gov/tao/elnino NOVA El Niño page: http://www.pbs.org/wgbh/nova/elnino/

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