Post-Glacial Climate Forcing of Surface Processes in the Ganges-Brahmaputra River Basin and Implications for Carbon Sequestration

Christopher J. Hein, Valier Galy, Albert Galy, Christian France-Lanord, Hermann Kudrass, Tilmann Schwenk

SUPPLEMENTAL MATERIALS

1. Supplemental Methods

1.1. Seismic data collection

Sediment echosounder data were acquired with the hull-mounted parametric sediment

echosounder ParaSound during the February 1994 (Expedition SO93) cruise of the R/V SONNE.

The parametric frequency was set to 4 kHz, providing for decimal-scale vertical resolution. Data

processing and visualization were completed using the in-house software "PS32SGY" (H. Keil)

and the IHS Kingdom Seismic and Geological Interpretation Software. Bathymetric data were

acquired using the hull-mounted swath-sounder Hydrosweep DS2 during R/V SONNE cruises

SO93 (1994) and SO125 (1997), and Simrad EM 120 during Cruise SO188 (2006). These data

were processed by means of the open source software MB Systems and the software package

Fledermaus (QPS).

1.2. Radiocarbon Calibration

Published and new radiocarbon ages (Supplemental Table 1) were calibrated using OxCal

4.2 (Bronk Ramsey, 2009) with the IntCal13 curve (Reimer et al., 2013) and a marine reservoir

correction of 322 years (Southon et al., 2002).

Supplemental Table 1. Results and calibration (see supplemental materials) of radiocarbon analyses of planktonic foraminifera collected from BoB channel levee cores SO93-117, -118, and -120KL. New dates were produced from analyses conducted at the National Ocean Science Accelerator Mass Spectrometry facility (Woods Hole, MA, USA). All dates presented in the text are calibrated, 2-sigma (2-ϭ) years before present (BP; present = 1950 CE).

Core / Sample ID SourceDated Material

NOSAMS Accession Number

Mean Depth Within Core (cm)

Reported / Uncorrected† Δ14C Age (BP)

Calibrated 2-σ Age (yrs BP)‡

SO93-117KL 205-215cm this study G. ruber OS-112423 210 9430 ± 45 10357 ± 131SO93-117KL 205-215cm* this study G. sacculifer OS-112426 210 9770 ± 50 10784 ± 178SO93-117KL 242-257cm Weber et al., 1997 G. sacculifer N/A 249.5 9420 ± 180 10366 ± 493SO93-117KL 1209-1219cm this study G. ruber OS-109518 1214 14250 ± 110 16877 ± 387SO93-118KL 7-17cm this study G. ruber OS-113018 12 880 ± 35 554 ± 63SO93-118KL 7-17cm this study G. sacculifer OS-112994 12 470 ± 20 190 ± 79SO93-118KL 134-145cm this study G. ruber OS-109520 139.5 1570 ± 35 1214 ± 79SO93-118KL 220-230cm this study G. ruber OS-109531 225 2100 ± 65 1770 ± 165SO93-118KL 420-430cm this study G. ruber OS-112982 425 3570 ± 25 3551 ± 86SO93-118KL 565-575cm Weber et al., 1997 G. sacculifer N/A 570 6120 ± 180 6652 ± 409SO93-118KL 1130-1140cm this study G. ruber OS-113016 1135 8790 ± 65 9522 ± 143SO93-120KL 150-154cm Weber et al., 1997 G. sacculifer N/A 152 3620 ± 40 3734 ± 67SO93-120KL 238-248cm this study G. ruber OS-112425 243 7350 ± 40 7890 ± 89SO93-120KL 379-389cm this study G. ruber OS-112424 384 9290 ± 50 10205 ± 123SO93-120KL 420-440cm this study G. ruber OS-113010 430 9370 ± 65 10300 ± 153SO93-120KL 485-489cm Weber et al., 1997 G. sacculifer N/A 487 9950 ± 90 11008 ± 225SO93-120KL 632-642cm this study G. sacculifer OS-109516 637 9920 ± 80 10977 ± 213SO93-120KL 687-691cm Weber et al., 1997 G. sacculifer N/A 689 10830 ± 100 12408 ± 280SO93-120KL 853-857cm Weber et al., 1997 G. sacculifer N/A 855 11240 ± 110 12800 ± 221SO93-120KL 929-939cm this study G. ruber OS-109522 934 12150 ± 90 13683 ± 225SO93-120KL 990-1000cm this study G. ruber OS-109515 995 12550 ± 100 14157 ± 400SO93-120KL 1062-1072cm this study G. ruber OS-109523 1067 13450 ± 110 15741 ± 366SO93-120KL 1092-1096cm* Weber et al., 1997 G. sacculifer N/A 1094 15270 ± 220 18177 ± 499SO93-120KL 1130-1140cm* this study G. ruber OS-109542 1135 11850 ± 170 13398 ± 359

SO93-120KL 1150-1154cm this study

Mixed G. ruber & G. sacculifer OS-113021 1152 14600 ± 210 17367 ± 580

*Reversal; date omitted from core age model†Published dates have been uncorrected for ocean residence time to raw Δ14C ages.

1.3. Bulk sedimentary inorganic analyses

Major and trace element concentrations were determined at SARM (Nancy, France) by

IPC-AES and ICP-MS following LiBO2 fusion (Carignan et al., 2001) of powdered sample

aliquots pre-rinsed with milli-Q water to minimize sea salt contributions. Total carbonate

analyses were performed on bulk sediments using a Thermo Gaz-Bench-IR-MS coupling

(CRPG). Acidification with 100% phosporic acid in septum tube under He atmosphere lasted for

more than 24 hours at 70°C, allowing a total dissolution of both calcite and dolomite. Total

carbonate contents were estimated on mass 44 area using calibration with internal standards of

Himalaya river sediments of known carbonate compositions. Concentrations (supplemental table

3) are expressed in weight percent equivalent CaCO3. The detrital carbonate content is estimated

by mass balance using δ18OPDB and assuming that total carbonates are mixtures of marine

carbonate at -2‰ and detrital carbonates at -11‰ (Lupker et al. 2012).

Sr and Nd isotopic compositions were measured on powdered sample aliquots following

carbonate removal via leaching with 10% acetic acid, following methods of Galy et al. (1996),

but with Sr separated using Sr-spec cationic resins (Horwitz et al., 1992). We measured isotopic

ratios using a Triton Plus(TM) multi-collector thermal ionization mass spectrometer at CRPG-

CNRS-UL (Nancy, France), with NBS-987 as standard and quality control. Nd isotopic ratios

were measured using a Neptune plus multi-collector inductively coupled plasma mass

spectrometer, at CRPG-CNRS-UL (Nancy, France). 143Nd/144Nd values were first normalized to

146Nd/144Nd =0.7219 using and exponential law and then to the JNdi-1 following a pseudo- (one

standard for each 4–5 samples) standard sample-bracketing method (Yang et al., 2017). Nd

isotopic compositions are reported as εNd(0). Average uncertainties (2ϭ) of major/trace

elemental compositions and of 87Sr/86Sr and εNd(0) isotopic compositions are better than 2%

(relative), 2x10-5 and 0.5 ε unit, respectively.

1.4. Sr, Nd isotopic compositions data compilation: εNd methodological bias

We combine our Sr/Nd data with those from these same sediment cores previously

published in Pierson-Wickmann et al. (2001), Galy et al. (2008a), and Lupker et al. (2013) to

generate a record of sediment provenance variations at sub-millennial resolution (n=41 over 17.5

kyrs). In this combined dataset, εNd values vary between -11.5 and -17.3. They show no clear

temporal trend but instead follow a somewhat bimodal distribution. We posit that this reflects

methodological bias. Specifically, Sr/Nd sediment aliquots of Galy et al. (2008a) and Lupker et

al. (2013) were leached with hydrochloric acid, which is more corrosive than the acetic acid used

here and by Pierson-Wickmann et al. (2001). Galy (1999) showed that acid-leaching results in

significant loss of Sm and Nd and that the leach is typically characterized by higher Sm/Nd than

the residue. Thus, we conclude that differential mobilization of Sm and Nd during acid-leaching

resulted in systematic differences in εNd values between the two acid-leaching techniques (HCl

leaching resulting in systematically lower εNd values) (Supplemental Fig. 1). However, this

methodological bias appears to be exclusive to εNd values as 87Sr/86Sr ratios did not differ

systematically between the two types of acid-leaching methods. Hence, εNd data from Galy et al.

(2008a) and Lupker et al. (2013) are excluded from further analyses.

Supplemental Figure 1. Comparison of strontium (87Sr/86Sr) and neodymium (εNd) stable isotopic compositions of samples from the BoB shelf and channel levee pre-processed (acid leaching) using acetic acid (Pierson-Wickman et al., 2001; this study) and hydrochloric acid (Galy et al., 2008a; Lupker et al., 2013).

1.5. Bulk organic carbon and nitrogen analyses

The bulk-sediment weight-percent total organic carbon content (TOC) and total nitrogen

content (TN), and stable isotopic composition of bulk organic carbon (δ13CTOC) and nitrogen

(δ15NTN), were analyzed in triplicate on an elemental analyzer coupled to a Finnegan Deltaplus

isotope ratio mass spectrometer (EA/IRMS). Total and isotopic nitrogen compositions were

measured on raw powdered sample aliquots. Following Whiteside et al. (2011), total and isotopic

carbon compositions were determined following fumigation acidification of powdered sample

aliquots. These were sealed in a vacuum desiccator with a beaker of 50 mL 12N HCl, fumigated

for 60–72 hours at 60–65°C to remove carbonates, and dried in a separate desiccator for an

additional 24 hours prior to measurement. Average precision (2-ϭ) of replicate measurements of

TOC, TN, δ13CTOC and δ15NTN determinations are 0.02%, 0.005%, 0.27‰, and 0.84‰ (1 s.d.),

respectively.

New TOC and TN analyses from cores SO93-117KL, -118KL, and -120KL supplement

those of Galy et al. (2008a). However, there is a systematic offset in TOC values for a given

grain size (Al/Si ratio) between our new data and those from Galy et al. (2008a) (Supplemental

Fig. 2). This is likely due to methodological differences: bulk TOC from Galy et al. (2008a) were

acidified via immersion in liquid HCl (see Galy et al., 2007 for details) as opposed to the

fumigation technique applied in this study. To explore this further, a set of Lower Meghna river

samples originally prepared via liquid acid immersion (Galy et al., 2008b) were re-analyzed for

TOC and δ13CTOC content following fumigation acidification. Comparison of data produced from

the same samples by each of these methods confirms that acidification via liquid emersion

produces systematically higher TOC values for a given sample than that originating from acid

fumigation (Supplemental Fig. 3). The liquid emersion method involves corrections for carbon

loss during acidification and for the mass of carbonates (Galy et al., 2007), two potential sources

of errors alleviated by the fumigation method (Whiteside et al., 2011). In the absence of any

systematic differences in δ13Corg values produced by the two methods (see below), we conclude

that the fumigation method yields the most accurate TOC data. Relative carbon loading for this

study was calculated independently for new samples and those from Galy et al. (2008a). The

resulting values for OC loading are discussed as relative deviations (expressed in %) with respect

to modern OC loading of the Lower Meghna River.

Comparisons of bulk δ13Corg values from Ganges, Brahmaputra, and Lower Meghna river

samples analyzed following each acid fumigation and acid immersion revealed no systematic

methodological difference (Supplemental Fig. 4); as such, new and published (Galy et al., 2008a)

bulk δ13Corg data from channel-levee cores SO93-117KL, -118KL and -120KL are merged.

Supplemental Figure 2. Bulk sediment TOC as a function of Al/Si, a proxy for sediment surface area. Samples from this study (closed symbols) are plotted along with those from previous studies of BoB channel levee cores SO93-117KL, -118KL, and -120KL (Galy et al., 2008a; Galy et al., 2014) (open symbols).

Supplemental Figure 3. Comparison of Lower Meghna River bed and suspended load sediment sample TOC, as determined each by fumigation acidification (new data) and liquid acidification (Galy et al., 2008b). The solid black line represents the best linear fit, the dashed line represents the 1:1 line.

Supplemental Figure 4. Comparison of bulk δ13Corg data produced on the same set of Lower Mengha River suspended load sediment samples by each liquid and fumigation acidification. Liquid fumigation data are from Galy et al. (2008b).

1.6. Lipid Extraction and Separation

Lipids were extracted from sample aliquots ranging between 1 g and 200 g (depending on

thickness core section sampled) with a 9:1 dichloromethane:methanol (DCM:MeOH) mixture

using a microwave-assisted reaction system (MARS, CEMS Corp.). Lipid extracts were dried

and saponified at 70°C for 2h with 15 mL 0.5 M KOH in MeOH and ca. 200 μL Milli-Q water

(to prevent methylation). Following saponification, a basic lipid fraction was extracted with 5 x 5

mL hexane. The pH of the remaining mixture was then lowered to ~2.5 by dropwise addition of

concentrated HCl, and an acidic lipid fraction was extracted with 6 x 5 mL 4:1 hexane:DCM.

Basic and acidic lipid fractions were independently separated via column chromatography with a

stationary phase of 1g aminopropyl-silica gel (LC-NH2). Five fractions were eluted with 4 mL

hexane (F1, hydrocarbons), 7 mL 4:1 hexane:DCM (F2, ketones/esters), 10 mL 9:1

DCM:acetone (F3, alcohols and other polar lipids), 14 mL 98:2 DCM:formic acid (F4, acids),

and 18 mL 1:1 MeOH:DCM (F5, flush). Acidic and basic F4 fractions containing fatty acids

were combined and methylated at 70°C for 12 h in 10 mL 5% 12 N HCl in MeOH of known D/H

(δD) and δ13C composition (respectively determined via GCirMS analysis of phthalic acid

methylated using the same procedure and close tube combustion followed by dual inlet IRMS

analysis). The resulting fatty acid methyl esters (FAMEs) were liquid-liquid extracted with 6 x 5

mL 4:1 hexane:DCM and purified with a second LC-NH2 column via elution with 8 mL 4:1

hexane:DCM. When necessary to remove unsaturated contaminants, FAMES were further

purified with a silver nitrate (AgNO3) column via elution with 5 mL DCM (saturated FAMES)

and 7 mL 9:1 DCM:acetone (unsaturated FAMES). FAME identification and quantification were

achieved with an Agilent 5890 gas chromatograph/flame ionization detector (GC/FID) through

comparison with an external standard.

1.7. Stable Carbon Isotopic Analyses

The δ13C values of target even-numbered FAMES (C12–C34) were measured in either

duplicate or triplicate, depending upon sample size, on a Finnegan Deltaplus IRMS coupled to an

HP 6890 GC (GCirMS) via a combustion interface operated at 850°C. Several pulses of CO2

reference gas were inserted during each run and used to correct for instrument drift. The

reference gas was calibrated prior to sample measurement by running multiple external standards

at a range of concentrations. Average precision (2-ϭ) of replicate measurements of even-number

long-chain (C24–C32) FAMES (C24-32 FA) δ13C measurements was <0.25 ‰. Estimated average

accuracy was ≤0.3 ‰. Resulting measured FAMES δ13C values were mass-balance corrected for

contribution of one additional carbon atom per homolog during methylation.

1.8. Stable Hydrogen Isotopic Analyses

The δD values of target even-numbered FAMES (C12–C34) were measured in duplicate on

a Thermo Scientific DeltaVPlus isotope ratio mass spectrometer (IRMS) coupled to an Agilent

6980 GC via a pyrolysis interface (GC-TC) operated at 1440°C. The H3+ factor (Sessions and

Hayes, 2005) was measured daily and was under 2 ppm/mV throughout the measurement period.

Peaks of a propane reference gas were inserted at several points before and after analysis during

each run and used as internal calibration standards. Variability in instrumental fractionation was

accounted for by routinely injecting an external standard mix containing 8 FAMES and fatty acid

ethyl esters of known δD (F8 mixture, A. Schimmelmann, Indiana University) and adjusting the

reference propane δD value to minimize the average offset between the known and measured δD

values of the F8 compounds. Average precision (2-ϭ) of replicate measurements of long-chain

FAMES (C24-32 FA) δD measurements was 3.5 ‰. Estimated average accuracy was 5–10 ‰.

Resulting measured FAMES δD values were mass-balance corrected for contribution of three

additional hydrogen atoms per homolog during methylation.

1.9. Corrections of FAMES stable hydrogen isotopic values for ice-volume and vegetation

MeOH-corrected FAMES δD values (δDFA) were corrected for variations in seawater

isotope composition related to global ice volume variations during the deglaciation (Clark et al.,

2009). Specifically, we used a record of global relative sea-level changes (Lambeck and

Chappell, 2001) to infer variations in the oxygen isotope composition of sea water (δ18OSW)

related to variations in global ice volume across the deglaciation. Relative sea level variations

were converted to variations in δ18OSW using a scaling factor of 1.0‰ per 127.5 m of relative sea

level change (Clark et al., 2009). Variations in δ18OSW were subsequently converted to variations

in δDSW using a conversion factor of 8, i.e. the slope of the global meteoric water line. Finally,

ice-volume-corrected FAMES δD values (δDFA-IV) were calculated by correcting measured δDFA

for changes in δDSW relative to the modern seawater composition. δDFA values from time periods

following 5 ka were left unchanged, as global relative sea level has remained relatively stable

over that time period. Across the deglaciation, the maximum amplitude of the ice volume

correction is 6.7‰. δDFA-IV values were then corrected for variable D/H fractionation by each C3

and C4 vegetation endmembers (e.g., Sachse et al., 2012; Wang et al., 2013) to estimate

precipitation δD values (δDP). Estimated D/H fractionation factors (ε) of -125 ‰ (100% C3 trees

vegetation; εC3) and -145 ‰ (100% C4 grasses vegetation; εC4) were applied based on variable

C3 and C4 mixing proportions determined from sample FAMES δ13C values following Collins et

al. (2013). Specifically, δDP values were calculated as:

δDP=1000∗[( δDFA− IV+1000ε+1000 )−1]

where

ε=X 4∗εC 4+(1−X 4)∗εC 3

and

X 4=δ 13CFA+δ 13CC 3

δ 13CC 3+δ13 CC 4

and δ13C values of pure C3 plants (δ13CC3) is given as -32 ‰ and δ13C values of pure C4 plants

(δ13CC4) is given as -20 ‰.

2. Supplemental Results: Precipitation D/H values comparison to modern

Precipitation D/H values (δDP) calculated from measured C24-32 and C28 fatty acids,

corrected for ice-volume and vegetation effects, range from -59‰ to -7‰ and -64‰ to -7‰,

respectively. Calculated δDP values from the last 500 years range from -30 to -40‰. These

values compare favorably to measured precipitation δD values from the Indo-Gangetic

floodplain and the G-B delta in Bangladesh (i.e., within the G-B floodplain, the dominant source

of organic matter to the BoB due to extensive organic matter turnover and replacement during

floodplain transit; Galy et al., 2011). Across three GNIP stations with sufficient data density

distributed over the area (New Delhi, Dhaka, and Sylhet) the annual amount-weighted average

δD values of precipitation ranges between -30 and -35 ‰ (IAEA/WMO, 2016) statistically

indistinct from our calculated δDP values from the last 500 years.

3. Supplemental Discussion: Comparisons with Contreras-Rosales et al. (2014) leaf-wax

records

Our records of paleo-humidity (FA δD) and paleo-vegetation (δ13C) trends since LGM

compare favorably with those from a sediment core on the Eastern Bengal Slope (core SO188-

342KL, see location, Fig. 1) (Contreras-Rosales et al., 2014, 2016). Apparent temporal offsets

between these two are likely attributable to record resolution: average ca. 186 years (Contreras-

Rosales et al., 2014) vs. ca. 550 years (this study). Moreover, the magnitude of internal

variability of our δDFA-IV record (maximum shift of 40‰, occurring between H1 and EHCO) is

greater than that observed by Contreras-Rosales et al. (2014) (30 ‰, also between H1 and

EHCO); responses to millennial events are also larger in our dataset. Both of these are driven by

relatively more enriched Bølling-Allerød, and more depleted Younger Dryas, ice-corrected leaf-

wax δD values observed by Contreras-Rosales et al. (2014) as compared to our dataset. This is

particularly interesting given that our sampling scheme integrates over longer periods of time (on

average ca. 60–100 years) than that of Contreras-Rosales et al. (2014) (estimated to be decadal-

scale). Thus, our dataset would tend to preferentially smooth variability, indicating that we are

capturing larger scale precipitation changes than previous BoB leaf-wax reconstructions. This

difference may reflect temporal buffering of the signal in record, most likely reflecting

shelf/SoNG sediment storage prior to delivery to the channel-levee.

Comparison of our new δ13Corg and δ13CFA data with published paleo-vegetation records

(Galy et al., 2008a; Contreras-Rosales et al., 2014) provides further insight into apparent

discrepancies seen in δD data. As with δD, our channel-levee δ13CFA data show a higher degree of

internal variability through time (even excluding the Bølling-Allerød outlier) than do the δ13Calk

of Contreras-Rosales et al. (2014). Furthermore, our channel-levee δ13CFA data are systematically

heavier than the δ13Calk of Contreras-Rosales et al. (2014). Although this partly reflects

differences in carbon fractionation in the production of n-alkanes and FA, the δ13Calk values of

Contreras-Rosales et al. (2014) are significantly heavier than δ13Calk values presented in Galy et

al. (2008a) for sediments from channel-levee cores SO93- 117KL, -118KL, and -120KL.

Moreover, our higher resolution channel-levee δ13Corg data also show consistently greater

sensitivity to climate changes than the slope δ13Calk record. Moreover, the record of Contreras-

Rosales et al. (2014) shows a gradual transition from pure C4 at LGM to larger C3 contributions

through the Bølling-Allerød, whereas both our bulk and FA data indicate that the transition away

from pure C4-dominated vegetation did not occur until the early Bølling-Allerød.

Many of these differences between the datasets can be explained by differences in

sediment and OC provenance for the sites of channel-levee cores SO93-117KL, -118KL, and -

120KL (this study) and Eastern Bengal Slope core SO188-342KL. A long series of prior studies

(e.g., Coleman, 1969; Curray et al., 2003; Goodbred, 2003; Goodbred and Kuehl, 2000; Weber et

al., 1997, 2003), confirmed by published (e.g., Galy et al., 2008a; Lupker et al., 2013) and new

(section 5.2) sediment provenance data, document the Himalayan source and direct transfer of

sediments to the BoB channel-levee system via the SoNG. By contrast, the site of Eastern Bengal

Slope core SO188-342KL received only limited sediment from the G-B rivers at any point

during the last glacial cycle (Palamenghi, 2012; Contreras-Rosales et al., 2016). Sr/Nd isotopic

data from the Eastern Bengal Slope are instead consistent with contributions from rivers draining

the Indo-Burma range (Colin et al., 1999; Damodararao et al., 2016), especially during periods of

lower sea level (Colin et al., 1999; Contreras-Rosales et al., 2016). Moreover, published post-

glacial sedimentation rate changes from Eastern Bengal Slope core SO188-342KL (Contreras-

Rosales et al., 2014) show no evidence of the major shifts in sediment supply routes during this

time period: specifically, peak post-glacial G-B sediment discharge corresponding with

strengthened monsoon during the early Holocene – well recorded in the channel-levee system

(Goodbred and Kuehl, 2000) – coincides with a period of lowest accumulation rates in core

SO188-342KL, likely due to sediment trapping within the aggrading subaerial delta (Contreras-

Rosales et al., 2016). Thus, it is likely that terrestrial sediments within the hemipelagic to pelagic

core SO188-342KL are derived, at least in part, from a non-G-B source (e.g., the Indo-Burma

range or the Indian subcontinent via aeolian inputs). Different climate sensitivity in the G-B than

in the source area for hemipelagic slope core SO188-342KL (Contreras-Rosales et al., 2014,

2016) likely explains much of the discrepancies between these paleoclimatic and paleo-

vegetation records, and provides a stark example of the utility of producing concurrent source

and paleo-environmental proxy records from the same samples in elucidating past regional

change.

4. Other Supplemental Figures

Supplemental Figure 5. The size-independent Ca/Si weathering proxy closely correlates with detrital carbonate content. Outlier (from 3.7 ka) has high marine carbonate content (8.4%;

average for all samples is 1.2%).

Supplemental Figure 6. Comparison of grain-size-corrected chemical weathering proxies (K/Si*) and neodymium (εNd) isotopic compositions of samples from the BoB channel levee, slope, and central and distal fans. Samples with more enriched εNd and lower K/Si* values – including three from the channel-levee cores – have significant hemipelagic compositions.

Supplemental Figure 7. Bulk sediment TOC as a function TN.

Supplemental Figure 8. Biplots of weathering proxies from sediments from BoB channel-levee cores SO93-117KL, -118KL, and -120KL (this study only) and relative ISM strength given as δDp values (more depleted δDp = stronger ISM) calculated from leaf-wax fatty acid δDFA-IV values derived from those same samples. Note lack of correlation between ISM strength and Ca/Si (interpreted as a size-independent chemical weathering proxy by Lupker et al., 2013) and K/Si* proxies in (a) and weak correlation between ISM strength and H2O+ proxy in (b).

Supplemental Figure 9. Biplots of weathering proxies (K/Si* [open symbols] and Ca/Si [closed symbols]) vs. (a) TOC and (b) calculated OC* values from sediments from BoB channel-levee cores SO93-117KL, -118KL, and -120KL. Data from this study are shown as squares; TOC data are based on recalculation of TOC values from Al/Si values of Galy et al. (2008a) are shown as circles. Note lack of correlation (R2 = 0.043 [TOC vs. K/Si*], 0.048 [TOC vs. Ca/Si], 0.022 [OC* vs. K/Si*], 0.005 [OC* vs. Ca/Si] for combined dataset) indicating independence of carbon loading and chemical weathering.

5. Supplemental References

Bronk Ramsey, C.B., 2009. Bayesian analysis of radiocarbon dates, Radiocarbon, v. 51, p.337-

360.

Carignan, J., Hild, P., Mevelle, G., Morel, J. and Yeghicheyan, D., 2001. Routine analyses of

trace elements in geological samples using flow injection and low pressure on‐line liquid

chromatography coupled to ICP‐MS: a study of geochemical reference materials BR,

DR‐N, UB‐N, AN‐G and GH, Geostandards Newsletter, v. 25, p.187-198.

Clark, P.U., Dyke, A.S., Shakun, J.D., Carlson, A.E., Clark, J., Wohlfarth, B., Mitrovica, J.X.,

Hostetler, S.W. and McCabe, A.M., 2009. The last glacial maximum, Science, v. 325, p.710-

714.

Coleman, J.M., 1969. Brahmaputra River: Channel processes and sedimentation, Sedimentary

Geology, v. 3, p. 129-239.

Colin, C., Turpin, L., Bertaux, J., Desprairies, A. and Kissel, C., 1999. Erosional history of the

Himalayan and Burman ranges during the last two glacial–interglacial cycles, Earth and

Planetary Science Letters, v. 171, p.647-660.

Collins, J.A., Schefuß, E., Mulitza, S., Prange, M., Werner, M., Tharammal, T., Paul, A. and

Wefer, G., 2013. Estimating the hydrogen isotopic composition of past precipitation using

leaf-waxes from western Africa, Quaternary Science Reviews, v. 65, p. 88-101.

Contreras-Rosales, L.A., Jennerjahn, T., Tharammal, T., Meyer, V., Lückge, A., Paul, A., and

Schefuß, E., 2014. Evolution of the Indian Summer Monsoon and terrestrial vegetation in the

Bengal region during the past 18 ka, Quaternary Science Reviews, v. 102, p. 133-148.

Contreras-Rosales, L.A., Schefuß, E., Meyer, V., Palamenghi, L., Lückge, A. and Jennerjahn,

T.C., 2016. Origin and fate of sedimentary organic matter in the northern Bay of Bengal

during the last 18ka, Global and Planetary Change, v. 146, p. 53-66.

Curray, J.R., Emmel, F.J., and Moore, D.G., 2003. The Bengal Fan: morphology, geometry,

stratigraphy, history and processes, Marine and Petroleum Geology, v. 19, p. 1191-1223.

Damodararao, K, Singh, S.K., Rai, V.K., Ramaswamy, V. and Rao, P.S., 2016. Lithology,

monsoon and sea-surface current control on provenance, dispersal and deposition of

sediments over the Andaman Continental Shelf. Frontiers in Marine Science, v. 3, 118.

Galy, A., France-Lanord, C. and Derry, L.A., 1996. The Late Oligocene-Early Miocene

Himalayan belt. Constraints deduced from isotopic compositions of Early Miocene turbidites

in the Bengal Fan. Tectonophysics, v. 260, p. 109-118.

Galy, A., 1999. Étude géochimique de l'érosion actuelle de la chaîne himalayenne, Ph.D.

dissertation, Nancy, France: Institut National Polytechnique de Lorraine, 464 p.

Galy, V., Bouchez, J. and France‐Lanord, C., 2007b. Determination of total organic carbon

content and δ13C in carbonate‐rich detrital sediments. Geostandards and Geoanalytical

Research, v. 31, p.199-207.

Galy, V., François, L., France-Lanord, C., Faure, P., Kudrass, H., Palhol, F. and Singh, S.K.,

2008a. C4 plants decline in the Himalayan basin since the Last Glacial Maximum.

Quaternary Science Reviews, 27(13), pp.1396-1409.

Galy, V., France-Lanord, C. and Lartiges, B., 2008b. Loading and fate of particulate organic

carbon from the Himalaya to the Ganga–Brahmaputra delta. Geochimica et

Cosmochimica Acta, 72(7), pp.1767-1787.

Goodbred, S.L., 2003. Response of the Ganges dispersal system to climate change: a source-to-

sink view since the last interstade, Sedimentary Geology, v. 162, p.83-104.

Goodbred, S.L., and Kuehl, S.A., 2000. Enormous Ganges-Brahmaputra sediment discharge

during strengthened early Holocene monsoon, Geology, v. 28, p. 1083-1086.

Horwitz, E.P., Chiarizia, R., and Dietz, M.L., 1992. A novel strontium-selective extraction

chromatographic resin. Solvent Extraction and Ion Exchange. v. 10, p. 313-336.

Joussain, R., Colin, C., Liu, Z., Meynadier, L., Fournier, L., Fauquembergue, K., Zaragosi, S.,

Schmidt, F., Rojas, V. and Bassinot, F., 2016. Climatic control of sediment transport from

the Himalayas to the proximal NE Bengal Fan during the last glacial-interglacial cycle,

Quaternary Science Reviews, v. 148, p.1-16.

Lambeck, K. and Chappell, J., 2001. Sea level change through the last glacial cycle, Science, v.

292, p.679-686.

Lupker, M., Blard, P.H., Lave, J., France-Lanord, C., Leanni, L., Puchol, N., Charreau, J. and

Bourlès, D., 2012. 10Be-derived Himalayan denudation rates and sediment budgets in the

Ganga basin, Earth and Planetary Science Letters, v. 333, p.146-156.

Lupker, M., France-Lanord, C., Galy, V., Lavé, J. and Kudrass, H., 2013. Increasing chemical

weathering in the Himalayan system since the Last Glacial Maximum, Earth and Planetary

Science Letters, v. 365, p.243-252.

Palamenghi, L., 2012. Tectonic and Sea Level Control on the Transport and Depositional

Processes in a Siliciclastic Sedimentary Basin: Insights From the Ganges-Brahmaputra

Delta, Bengal Basin, Bangladesh, Ph.D. Dissertation, Bremen, Germany: University of

Bremen, 147 p., http://elib.suubuni-bremen.de/edocs/00102878-1.pdf.

Pierson-Wickmann, A.-C., Reisberg, L., France-Lanord, C., and Kudrass, H., 2001. Os-Sr-Nd

results from sediments in the Bay of Bengal: Implications for sediment transport and the

marine Os record, Paleoceanography, v. 16, p. 435-444.

Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E.,

Cheng, H., Edwards, R.L., Friedrich, M. Grootes, P.M., Guilderson, T.P., Haflidason, H.,

Hajdas, I., Hatté, C., Heaton, T.J., Hoffmann, D.L., Hogg, A.G., Hughen, K.A., Kaiser, K.F.,

Kromer, B., Manning, S.W., Niu, M., Reimer, R.W., Richards, D.A., Scott, E.M., Southon,

J.R., Staff, R.A., Turney, C.S.M., and van der Plicht, J., 2013. IntCal13 and Marine13

radiocarbon age calibration curves 0-50,000 years cal BP, Radiocarbon, v. 55, p. 1869-1887.

Sessions, A.L. and Hayes, J.M., 2005. Calculation of hydrogen isotopic fractionations in

biogeochemical systems, Geochimica et Cosmochimica Acta, v. 69, p.593-597.

Southon, J., Kashgarian, M., Fontugne, M., Metivier, B. and Yim, W.W., 2002. Marine reservoir

corrections for the Indian Ocean and Southeast Asia, Radiocarbon, v. 44, p.167-180.Wang,

Y.V., Larsen, T., Leduc, G., Andersen, N., Blanz, T., Schneider, R.R., 2012. What does leaf

wax dD from a mixed C3/C4 vegetation region tell us?, Geochimica et Cosmochimica Acta,

v. 111, p. 128-139.

Weber, M.E., Wiedicke, M.H., Kudrass, H.R., Hübscher, C., and Erlenkeuser, H., 1997. Active

growth of the Bengal Fan during sea-level rise and highstand, Geology, v. 25, p. 315-318.

Weber, M.E., Wiedicke-Hombach, M., Kudrass, H.R., and Erlenkeuser, H., 2003. Bengal Fan

sediment transport activity and response to climate forcing inferred from sediment physical

properties, Sedimentary Geology, v. 155, p. 361-381.

Whiteside, J.H., Olsen, P.E., Eglinton, T.I., Cornet, B., McDonald, N.G. and Huber, P., 2011.

Pangean great lake paleoecology on the cusp of the end-Triassic extinction,

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 301, p.1-17.

Yang, Y., Galy, A., Fang, X., Yang, R.S., Zhang, W., and Zan, J., 2017. Eolian dust forcing of

river chemistry on the northeastern Tibetan Plateau since 8 Ma. Earth and Planetary

Science Letters, v. 464, p. 200-210.