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Hui-Juan PAN Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan

High-resolution Sediment Content and Paleo-environmental change Estimated from Diffuse Spectral Reflectance of Marine Cores 海洋岩心反射色推估之高解析度沉積物含量與古環境變遷紀錄. Hui-Juan PAN Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan. Introduction.

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Hui-Juan PAN Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan

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  1. High-resolution Sediment Content and Paleo-environmental change Estimated from Diffuse Spectral Reflectance of Marine Cores海洋岩心反射色推估之高解析度沉積物含量與古環境變遷紀錄 Hui-Juan PAN Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan

  2. Introduction • Terrigenous sediments from Ceara Rise in the western tropical Atlantic Ocean record Pleistocene Amazon Basin climate variability. • Lowland Amazon Basin precipitation changes, monitored by the percentage of goethite relative to total iron oxides, lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt.

  3. Introduction • Rapid climate changes over the Amazon basin may reflect shifts in the position of the Intertropical Convergence Zone (ITCZ) forced by northern hemisphere insolation at precessional (23k) and obliquity(41k) frequencies. • The early response of Amazon precipitation to insolation, ahead of high-latitude ice volume(δ18O ) at all orbital frequencies. =>tropical aridity is part of the chain of events leading to ice ages, rather than response to glacier oscillation.

  4. Introduction Ceara Rise:Atlantic coast of South America, Southeast of the Amazon Fan Primary from site 926, spliced with the upper 2.6m of site 925. ODP 925 : 4°12’N 43°29’W 3041 m ODP 926 : 3°43’N 42°54’W 3598 m

  5. Introduction • Two primary sediment source • Calcareous tests of plankton from surface water. • Terrigenous sediment from the Amazon River • The composition of the terrigenous depends on the source and/or weathering of erosive products.

  6. Introduction • Use the changing composition of oxides in the terrigenous fraction of the marine recordto infer past climate condition in Amazonia. • More than 75% of Amazon Basin soil are mixtures of quartz、kaolinite、 gibbsite (clay minerals), and hematite(H) & goethite(G). G(%) serves as a proxy for lowland V.S highland erosion. G/(G+H) serves as a proxy for lowland precipitation and vegetation.

  7. Methods Hand-held Minolta CM-2002 spectrophotometer

  8. Methods • Reflectance Spectra • Spectral resolution: 0.68 nm • Wavelengths: spanning UV、VIS& nIR (250-950nm)。 • Commonly use derivatives of the spectrum to compute spectral shape.

  9. Methods • Goethite針鐵礦( FeO(OH) ) Composition: Fe(62.9%)、O(27.0%)、H2O(10.1%) • Hematite赤鐵礦(Fe2O3) Composition: Fe(70%)、O(30.0%) 為針鐵礦經脫水作用(dehydration)後的產物。 • 針鐵礦和赤鐵礦的相對組成變化，可反應區域性降雨量關係: 赤鐵礦含量高，氣候相對乾燥，針鐵礦含量高，氣候相對潮濕。

  10. G H Methods • Factor analysis The three factors explain 79% of the variability in first derivative spectra. (d) The peak of factor 2 similar to first derivative spectra of goethite. (e) The peak of factor 3 similar to first derivative spectra of hematite. (f) Communalities are >0.95 for wavelengths spanning the main G & H peak.

  11. termination 雨多 陸源少 雨少 陸源多 Summer insolation at 65°N 冰小 海高 冰大 海低 Results • Low %CaCO3 coincide with high δ18O. • Max in G% and H%, occur during transitions from glacial to interglacial. • Variations in G/(G+H) are visually similar to -δ18O, but G/(G+H) maxima precede sea level highstands and minima precede lowstands.

  12. termination 雨多 陸源少 雨少 陸源多 Summer insolation at 65°N 冰小 海高 冰大 海低 Results • Peaks in G/(G+H) are broader than deglacial G% or H% peaks. • G/(G+H) values tend to remain relatively high into interglacial periods => Indicating continued high levels of precipitation.

  13. 100K 100K 100K 23K 23K 23K A B C 41K 41K 41K 19K 19K 19K lag lead Results • Three iron oxide records is concentrated at orbital frequencies. • Negative phase indicate that changes in the oxide indices lead -δ18O(sea level).

  14. Discussion • Source and weathering of Terrigenous Material • Change in the precipitation balance may influence the relative contributions from highland source areas and lowland source areas. • Precipitation and temperature can also affect chemical weathering. Source and weathering influences are not mutually exclusive. lowland precipitation ↑ chemical weathering products ↑

  15. Pleistocene Amazonian climate Over the past million years, maximum %G and G/(G+H) are statistically in phase with or slightly lag maximum Northern Hemiphere summer insolation at high latitude(Q65Njun) at 41K and 23K frequencies. hematite lag lead goethite G/(G+H) carbonate δ18O Discussion

  16. Discussion Pleistocene Amazonian climate • The only insolation forcing for which both tilt and precession phases are consistent with the climate response in G/(G+H) is summer (June) insolation at Northern high latitude (both arrows pointing up). 1. The austral summer position of the ITCZ was further north during glacial termination. 2. Enhanced formation of North Atlantic Deep Water during deglacial periods.

  17. 100K 41K -δ18O ---- -δ18O ---- G/(G+H) G/(G+H) Q65N ……. Q65N ……. Discussion • Amazon climate system may respond in such an asymmetrical manner. • Tropical atmospheric and oceanic circulation in Amazon region, may be part of the chain of events that contribute to global 100K climate cycles.

  18. Conclusion • Increases in goethite and hematite during major deglacial transitions imply relative increases in erosion from lowland source. • The major climate variable controlling changes in relative erosion is variability in the highland-lowland balance of precipitation. • During the late Pleistocene, high values of lowland Amazon precipitation, as measured by G/(G+H), coincide with ice-melting events and maximum June insolation at 65°N.

  19. Conclusion • At precessional and obliquity frequencies, these precipitation changes may be driven by high northern latitude summer insolation. • Analysis of these long times series shows that late Pleistocene climate extremes in Amazonia precede northern hemisphere ice extremes, suggesting that tropical climate changes may affect, rather than respond to, global ice age climate cycles.

  20. Future study • Based on previous researches, the diffuse reflectance method is demonstrated to provide high-resolution, empirical predictions of biogenic content using multiple linear regression on diffuse spectral reflectance measurements. This empirical equation will be tested and validated for other marine sedimentary cores such as from the South China Sea.

  21. Reference Mix, A.C, Harris, S.E. (1999), Pleistocene precipitation balance in the Amazon Basin Recorded in Deep Sea Sediments. Quaternary Research 51, 14-26. Ortiz, J., Mix, A.C, Harris, S.E. S. O’Connell (1999), Diffuse spectral reflectance as a proxy for percent carbonate content in north Atlantic sediments. Paleoceanography 14, 171-186. Balsam, W.L., Deaton, B.C.(1991), Visible spectroscopy-A rapid method for determining hematite and goethite concentration in geological materials. Journal of Sedimentary Petrology 61, 628–632. Haug, G.H., Hughen, K.A., Sigman, D.M., Peterson, L.C., U. Ro¬hl (2001), Science 293, 1304

  22. ~The End~ Thank you for listening.

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