Supplement Page 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., 1998 47 ). 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 32-32.5 pss (practical salinity scale), 2-3 pss lower than during the boreal summer monsoon (July-September).
Transcript
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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., 199847). 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 32-32.5 pss (practical salinity scale), 2-3 pss lower than during the boreal
summer monsoon (July-September).
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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 δ18Osw 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.
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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 location52-54. 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 periods12. Over long time periods, if G. ruber is
preferentially “produced" during the JAS boreal summer monsoon upwelling season in
the Makassar Strait, then the δ18O 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 δ18O
and δ18Osw 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.
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Supplementary Figure 2: Globigerinoides ruber Mg/Ca SST in the WPWP. 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 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
foraminfera22,23. 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
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should result in an apparent warming of 0.5°C22. 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 Maximim25,26, 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.
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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 10.21 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).
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Comparison to Holocene Speleothem and Coral Records in the Region
In Supplementary Figure 4 we compare our SSTa and δ18Osw paleo-records to:
(1.) speleothem-based δ18O data from Flores30,55 (eastern Indonesia), (2.) to Borneo
speleothem δ18Oref 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 δ18O 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
δ18Osw 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.
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Supplementary Figure 4: Regional Palaeo-climatic Data in the WPWP region. Comparison of our composite SSTa and δ18Osw reconstructions to other published paleo-data 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 δ18Osw from the same cores depicted in Figure 3B along with difference between S. Makassar and open-ocean WPWP cores (as in Figure 3b), (d) Borneo speleothem δ18O (Partin et al., 2007)56, (e); Flores speleothem δ18O (Griffiths et al., 2009; 2010)30,55
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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 13GGC48,51.
Supplementary Table 2: Mg/Ca cleaning protocols and Mg/Ca-SST calibrations used. Core ID; Location Core ID
in text
Lat./Long. Reference Mg/Ca cleaning method:
Red/Ox: = full reductive & oxidative trace metal cleaning**
Mg/Ca to SST calibration used
13GGC, Bali Basin-Makassar St.
13GGC 7°24’S, 115°12’E
This study Red/Ox: Rosenthal et al. (1999)64
Dekens et al. (2002)60, Anand et al. (2003)11
70GGC, SW Sulawesi-Makassar St.
70GGC 3°34’S, 119°23’E
This study Red/Ox: Rosenthal et al. (1999)64
Dekens et al. (2002)60, Anand et al. (2003)11
MD9821-62, S. Makassar St.
MD62 4°41’S, 117°54’E
Visser et al., 200318
Red/Ox: Boyle et al. (1995)59
Dekens et al. (2002)60, Hastings et al. (2001)65
MD9821-65, Sumba, Indonesia
MD65 9°39’S, 118°20’E
Levi et al., 200744
Red/Ox: Barker et al. (2003)58
Dekens et al. (2002)60
MD0123-78, Timor Sea
MD78 13°5’S, 121°47’E
Xu et al., 200821 Red/Ox: Martin and Lea (2002)61
Dekens et al. (2002)60, Anand et al., 200311
MD9721-41, Sulu Sea
MD41 8°47’N, 121°17’E
Rosenthal et al., 200314
Red/Ox: Rosenthal et al. (1999)64
Rosenthal and Lohmann, 200263
MD9821-81, W. Pacific-Mindano
MD81 6°27’N, 125°50’E
Stott et al., 200415
Red/Ox: Martin and Lea (2002)61
Nurnberg et al. (1996)62
MD9821-76, Banda Sea
MD76 5°00.18’S, 133°26’ E
Stott et al., 200415
Red/Ox: Martin and Lea (2002)61
Nurnberg et al. (1996)62
MD01-2390†, South China Sea
MD90 6°38.12'N,113°24.56'E
Steinke et al., 200845
Red/Ox: Barker et al. (2003)58
Dekens et al. (2002)60, Anand et al., 200311
† = 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
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