Holocene Evolution of the Indonesian Throughflow and the Western Pacific Warm Pool

Transcription

1 SUPPLEMENTARY INFORMATION Holocene Evolution of the Indonesian Throughflow and the Western Pacific Warm Pool by Braddock K. Linsley, Yair Rosenthal and Delia W. Oppo Supplementary Discussion: Salinity Variability in the southern Makassar Strait Supplementary Figure 1 shows salinity at 20m water depth throughout Indonesian and the western Pacific (data from Conkright et al., ). The relatively low salinity in the southern Makassar Strait is evident. This is due to the seasonal influx of low salinity water from the South China Sea (SCS) and Java Sea during the boreal winter monsoon. The low salinity of the SCS and Java Sea results from heavy precipitation and river runoff from Southeast Asia and Borneo. Seasonal changes in the vertical salinity profiles in the regions of the two gray boxes are indicated in the lower half of figure. Note that the during the boreal winter monsoon, salinity throughout the entire southern Makassar Strait drops to pss (practical salinity scale), 2-3 pss lower than during the boreal summer monsoon (July-September). Supplement Page 1

2 Supplementary Figure 1: Mixed layer salinity in the WPWP and seasonal vertical salinity profiles in the southern Makassar Strait. (top) Annual mean salinity at 20m depth in the study area (Salinity data from Conkright et al. (1998) 47 ). The core locations of the SST and δ 18 O sw reconstructions shown in Figures 2 and 3 are indicated. The gray squares in the southern Makassar Strait indicate the location of the vertical salinity climatology profiles shown in the bottom two panels (Bali Basin on left; Makassar Strait on right). These profiles show a large 2 to 3 pss salinity reduction in the upper 50-75m of the water column during the boreal winter (NW monsoon)(january-june). The magnitude of the salinity reduction is the same at both of our study sites in the southern Makassar Strait. Supplement Page 2

3 Seasonality of Globigerinoides ruber flux to the sediment We considered the possible effects of changes in the seasonal flux of G. ruber to the sediments (G. ruber seasonality) in the southern Makassar Strait on our interpretations. Sediment trap studies indicate that in the tropics the seasonal preference of G. ruber varies with location Detailed sediment records over the last ~150 years in the southern Makassar Strait suggest that G. ruber seasonality varied through time with greater flux in JAS during the cooler periods 12. Over long time periods, if G. ruber is preferentially produced" during the JAS boreal summer monsoon upwelling season in the Makassar Strait, then the δ 18 O difference between the southern Makassar cores and the cores further east in the WPWP (MD81, MD76, and MD41) would be even greater after 9.5Kyr. This is because salinity is 2-3 pss higher in the southern Makassar Strait during the SE Monsoon but relatively unchanged over the course of the year in the cores further to the east (see Figures 1 and Supplementary Figure 1). Thus a JAS G. ruber seasonality preference in the southern Makassar Strait would tend to dampen the δ 18 O and δ 18 O sw difference between the Makassar Strait cores and the cores farther to the north and east outside of the strait. 200 year Binned Averages of G. ruber Temperatures Supplementary Figure 2 shows 200-year non-overlapping binned averages of the eight individual WPWP G. ruber Mg/Ca-based temperature records. Anomalies calculated as departures relative to average of last 2,000 years for each record (except for MD41, see table 1). This figure is meant to complement Figure 2A. Supplement Page 3

4 Supplementary Figure 2: Globigerinoides ruber Mg/Ca SST in the WPWP. 200 year nonoverlapping binned averages of the eight individual WPWP G. ruber Mg/Ca-based temperature records. Anomalies calculated as departures relative to average of last 2,000 years for each record (except for MD41, see table 1). This figure is another way of depicting the data shown in Figure 2A. Possible Salinity Influence on Foraminifera Mg/Ca It has been argued that seawater salinity has an effect on the Mg/Ca in planktonic foraminfera 22,23. G. ruber Mg/Ca results for core top samples and plankton tows compared to modern mean annual salinity indicate that the effect is such that a 1 pss decrease in salinity will result in an apparent warming of 1.6 C in foraminifera test Mg/Ca,23. However, culture experiments with G. ruber suggest that a 1 pss decrease Supplement Page 4

5 should result in an apparent warming of 0.5 C 22. It seems, however, that there is also a salinity threshold where below 35 pss there is no measureable effect on foraminifera Mg/Ca (see data in references 22,23 ). The G. ruber Mg/Ca SST estimates from the WPWP are from regions with different salinity regimes (i.e.; > 1 pss difference between mean annual salinity in the Makassar Strait in eastern Indian Ocean and western Pacific or Banda Sea)(see Supplementary Figure 1). The fact that all eight Mg/Ca-SST records show the same basic pattern from the Last Glacial Maximum to the present argues for minimal salinity influence on G. ruber Mg/Ca in this region where mean annual salinity is <34.5 pss. In addition, our calculation of SST departures (anomalies) from the last 2,000 year average at each site, would have the effect of minimizing any potential salinity influence on G. ruber Mg/Ca SST. Sea Level Flooding of the Sunda Shelf Using current bathymetry and reconstructed regional sea level since the Last Glacial Maximim 25,26, Sathiamurthy and Voris (2006) 27 determined that the Karimata Strait in the Java Sea is the critical connection point to the SCS (see Supplementary Figure 3). The flooding of the Karimata Strait would have started around 9,500 yr BP and continued over a 2,000 to 3,000 year period until ~6,000 yr BP. Thus the timing of the observed lowering of surface salinity beginning ~9,500 yr BP agrees with the timing of the reconnection of the South China Sea with the Makassar Strait through the Java Sea. Supplement Page 5

6 Supplementary Figure 3: Flooding of Sunda Shelf at 10,200 and 9,500 year BP. Maps depicting the distribution of land and sea in Indonesia at Kyr and 9.53 Kyr (modified from Sathiamurthy and Voris 2006)27. Green and yellow areas depict exposed land areas. The location the Karimata Stait in the Java Sea is indicated. Flooding of this sill at ~9,500-10,000 yr BP would have reconnected the South China Sea with the Makassar Strait. The locations of cores discussed in this study are also indicated (with the exception of MD76 which is located further east in the Banda Sea). Supplement Page 6

7 Comparison to Holocene Speleothem and Coral Records in the Region In Supplementary Figure 4 we compare our SSTa and δ 18 O sw paleo-records to: (1.) speleothem-based δ 18 O data from Flores 30,55 (eastern Indonesia), (2.) to Borneo speleothem δ 18 O ref 56, and (3.) to uplifted fossil coral Sr/Ca estimates of SST from the southern edge of the WPWP off southern Sumatra and off northeastern Papua New Guinea (PNG) 57. The Borneo and Flores δ 18 O records may show evidence of a more northward position of the ITCZ in the mid-holocene near 5,000 yr BP. The mid- Holocene is also a relatively cooler time in the fossil coral record. This could partly be explained by the location of the coral sites on the southern edge of the WPWP in Sumatra and PNG. A more northerly position of the ITCZ in the mid-holocene could have been associated with a northward contraction of the IPWP. Our composite WPWP SSTa and δ 18 O sw reconstructions contain no clear evidence of concordant changes in the mid- Holocene. We note, however, that the coral SSTa records from the southern edge of the WPWP show larger amplitude Holocene variability (~-2-3 C) than the <1 C range observed in any of the WPWP foraminifera-based SSTa reconstructions. Supplement Page 7

8 Supplementary Figure 4: Regional Palaeoclimatic Data in the WPWP region. Comparison of our composite SSTa and δ 18 O sw reconstructions to other published paleodata in the region. (a) Coral Sr/Ca SST reconstructions for corals on the southern edge of the WPWP in Sumatra and Papua New Guinea (Abram et al., 2009) 57. (b) Composite SSTa reconstruction from all 8 WPWP cores shown in Figure 2B. (c) 400 year binned δ 18 O sw from the same cores depicted in Figure 3B along with difference between S. Makassar and openocean WPWP cores (as in Figure 3b), (d) Borneo speleothem δ 18 O (Partin et al., 2007) 56, (e); Flores speleothem δ 18 O (Griffiths et al., 2009; 2010) 30,55 Supplement Page 8

9 Supplementary Table 1. Radiocarbon measurements made on mixed planktonic foraminifera at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) and converted to calendar age using a reservoir age of 500 years for 70GGC and 400 years for 10 and 13GGC 48,51. CORE NOSAMS ID Depth (cm) 14 C Age (yr BP) S.D. (yr) Calendar age (yr BP) S.D. (yr) BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 70GGC OS BJ8 10GGC OS BJ8 10GGC OS BJ8 10GGC OS BJ8 10GGC OS BJ8 13GGC OS BJ8 13GGC OS BJ8 13GGC OS BJ8 13GGC OS BJ8 13GGC OS Supplement Page 9

10 Supplementary Table 2: Mg/Ca cleaning protocols and Mg/Ca-SST calibrations used. Core ID; Location 13GGC, Bali Basin- Makassar St. 70GGC, SW Sulawesi-Makassar St. MD , S. Makassar St. MD , Sumba, Indonesia Core ID in text 13GGC 70GGC MD62 MD65 Lat./Long. Reference Mg/Ca cleaning method: 7 24 S, E 3 34 S, E 4 41 S, E 9 39 S, E This study This study Red/Ox: = full reductive & oxidative trace metal cleaning** Red/Ox: Rosenthal et al. (1999) 64 Red/Ox: Rosenthal et al. (1999) 64 Visser et al., Red/Ox: Boyle et al. (1995) 59 Levi et al., Red/Ox: Barker et al. (2003) 58 Mg/Ca to SST calibration used (2002) 60, Anand et al. (2003) 11 (2002) 60, Anand et al. (2003) 11 (2002) 60, Hastings et al. (2001) 65 (2002) 60 MD , Timor Sea MD S, E Xu et al., Red/Ox: Martin and Lea (2002) 61 (2002) 60, Anand et al., MD , Sulu Sea MD N, E Rosenthal et al., Red/Ox: Rosenthal et al. (1999) 64 Rosenthal and Lohmann, MD , W. Pacific-Mindano MD N, E Stott et al., Red/Ox: Martin and Lea (2002) 61 Nurnberg et al. (1996) 62 MD , Banda Sea MD S, E Stott et al., Red/Ox: Martin and Lea (2002) 61 Nurnberg et al. (1996) 62 MD , South China Sea MD 'N, ' E Steinke et al., Red/Ox: Barker et al. (2003) 58 (2002) 60, Anand et al., = not used in SSTa composite reconstructions due to location **: all these cleaning methods relate back to the original developmental work of Boyle and Keigwin (1985) 66 and Rosenthal et al. (1997) 67 Supplement Page 10

11 References in Supplement 51. Southon, J., Kashgarian, M., Fontugne, M., Metiver, B., & Yim, W. W. S. Marine reservoir corrections for the Indian Ocean and Southeast Asia. Radiocarbon 44, (2002). 52. Kawahata, H., Nishimura, A. & Gagan, M. Seasonal change in foraminiferal production in the western equatorial Pacific warm pool: evidence from sediment trap experiments. Deep-Sea Res. II 49, (2002). 53. Mohtadi, M. et al. Low-latitude control on seasonal and interannual changes in planktonic foraminiferal flux and shell geochemistry off south Java: a sediment trap study. Paleoceanography 24, PA1201 (2009). 54. Thunell, R. C. & Reynolds, L. A. Sedimentation of planktonic foraminifera: seasonal changes in species in the Panama Basin. Micropaleontology 30, (1984). 55. Griffiths, M.L., et al., Evidence for Holocene changes in Australian-Indonesian rainfall from stalagmite trace element and stable isotope ratios, Earth Plan. Sci Lett., 292, (2010). 56. Partin, J.W., Cobb, K.M., Adkins, J.F., Clark, B., Fernandez, D. F., Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum, Nature, 449, , doi: /nature06164 (2007). 57. Abram, N.J., McGregor, H.V., Gagan, M. K., Hantoro, W. S., Suwargadi, B. W., Oscillations in the southern extent of the Indo-Pacific Warm Pool during the Holocene, Quaternary Science Reviews, 28, (2009). 58. Barker, S., Greaves, M., Elderfield, H., A study of cleaning procedures used for foraminiferal Mg/Ca paleothermometry. Geochemistry, Geophysics, Geosystems 4, 8407 (2003). 59. Boyle, E., Labeyrie, L., Duplessy, J-C. Calcitic foraminiferal data confirmed by cadmium in aragonitic Hoeglundina; application to the last glacial maximum in the northern Indian Ocean. Paleoceanography 10, 7, , (1995). 60. Dekens, P.S., Lea, D.W., Pak, D.K., Spero, H.J., Core top calibration of Mg/Ca in tropical foraminifera: refining paleotempe- rature estimation. Geochemistry, Geophysics, Geosystems 3, 1022 (2002). 61. Martin, P.A., Lea, D.W., A simple evaluation of cleaning procedures on fossil benthic foraminiferal Mg/Ca. Geochem. Geophys. Geosyst. 3, (10), 8401, (2002). 62. Nurnberg, D., Bijma, J., Hemleben, C., Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperature. Geochimica et Cosmochimica Acta 60, (1996). 63. Rosenthal, Y., Lohmann, G.P., Accurate estimation of sea surface temperatures using dissolutioncorrected calibrations for Mg/Ca paleothermometry, Paleoceanography, 17(3), 1044 (2002). 64. Rosenthal, Y., Field, M.P., Sherrell, R.M., Precise determination of element/calcium ratios in calcareous samples using sector field inductively coupled plasma mass spectrometry, Anal. Chem., 71, , (1999). 65. Hastings, D., Kienast, M., Steinke, S., Whitko, A. A Comparison of three independent paleotemperature estimates from a high resolution record of deglacial SST records in the tropical South China Sea. Eos 82, PP12B-10 (2001). 66. Boyle, E. A., Keigwin, L. D., Comparison of Atlantic and Pacific paleochemical records for the last 250,000 years: changes in deep ocean circulation and chemical inventories, Earth Planet. Sci. Lett., 76, (1985). 67. Rosenthal, Y., Boyle, E. A. Labeyrie L., Deepwater circulation in the Southern Ocean during the last glacial maximum: evidence from foraminiferal cadmium. Paleoceanography, 12, (1997). Supplement Page 11