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Steinke, Stephan; Groeneveld, Jeroen; Johnstone, Heather J H; Rendle-Bühring, Rebecca (2010): Stable isotope records of G. sacculifer-quadrilobatus, Mg/Ca ratios, and Mg/Ca-SST estimates of ODP Hole 184-1146A. doi:10.1594/PANGAEA.744704, Supplement to: Steinke, S et al. (2010): East Asian summer monsoon weakening after 7.5 Ma: Evidence from combined planktonic foraminifera Mg/Ca and delta 0-18 (ODP Site 1146; northern South China Sea). Palaeogeography, Palaeoclimatology, Palaeoecology, 289(1-4), 33-43, doi:10.1016/j.palaeo.2010.02.007

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The monsoon system represents one of the basic elements of global atmospheric circulation. Its evolution and variability over long periods of geologic time play a significant role in our understanding of global climate. In this study, we focus on the Late Miocene interval from 10 Ma to 6 Ma, a period of postulated profound ecological and environmental shifts in East and South Asia. The combined approach of measuring planktonic foraminiferal Mg/Ca ratios and stable oxygen isotopes from Ocean Drilling Program (ODP) Site 1146 enabled us to reconstruct temperature independent seawater delta18O (i.e. proxy for sea surface salinity) variations in order to reconstruct the hydrography in the northern South China Sea. Located offshore the Pearl (Zhujiang) River, or its predecessor, the location of ODP Site 1146 is considered to provide a most sensitive record for detecting potential changes in freshwater input/river run-off as a result of changes in continental humidity, and hence changes in East Asian summer monsoon (EASM) climate. Local seawater delta18O reconstructions reveal that monsoon development during the Late Miocene can be regarded as an abrupt weakening in the EASM around 7.5 Ma. We suggest that an EASM weakening was most likely the driving force for decreasing aridity in East and South Asia at 8-6 Ma, leading to widespread ecosystem changes in East and South Asia.
Latitude: 19.456680 * Longitude: 116.272710
Date/Time Start: 1999-03-21T23:45:00 * Date/Time End: 1999-03-25T13:30:00
Minimum DEPTH, sediment/rock: 309.395 m * Maximum DEPTH, sediment/rock: 414.010 m
184-1146A * Latitude: 19.456680 * Longitude: 116.272710 * Date/Time Start: 1999-03-21T23:45:00 * Date/Time End: 1999-03-25T13:30:00 * Elevation: -2091.1 m * Penetration: 607 m * Recovery: 603.85 m * Location: South China Sea * Campaign: Leg184 * Basis: Joides Resolution * Device: Drilling/drill rig (DRILL) * Comment: 64 cores; 607 m cored; 0 m drilled; 99.5 % recovery
(1) Mg/Ca ratios were transforemd to SST by using the calibration equation for G. sacculifer of Nürnberg et al. (2000)
(2) The Nürnberg et al. (2000) calibration were modified in order to account for differences in seawater Mg/Ca ratios between the Late Miocene (4.5 mol/mol) and present (5.1 mol/mol)
(3) calculation of local seawater d18O; see Steinke et al. (2010)
#NameShort NameUnitPrincipal InvestigatorMethodComment
1DEPTH, sediment/rockDepthmGeocode
2AGEAgeka BPGeocode
3Depth, compositeDepth compmcdSteinke, StephanIntercore correlation
4Sample code/labelSample labelSteinke, StephanODP sample designation
5Globigerinoides sacculifer quadrilobatus, d18OG. sacculifer quad d18Oper mil PDBSteinke, StephanMass spectrometer Finnigan MAT 251
6Globigerinoides sacculifer quadrilobatus, d13CG. sacculifer quad d13Cper mil PDBSteinke, StephanMass spectrometer Finnigan MAT 251
7Magnesium/Calcium ratioMg/Cammol/molSteinke, Stephansee reference(s)
8Sea surface temperatureSST°CSteinke, Stephansee commentMg/Ca-SST, unadjusted (1)
9Sea surface temperatureSST°CSteinke, Stephansee commentMg/Ca-SST, adjusted (2)
10delta 18O, waterd18O H2Oper mil SMOWSteinke, Stephansee comment(3)
1688 data points

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