SupportingMaterial

Understandingthesortablesiltflowspeedproxyinmarinesystemswithvaryingsupply

Thesortablesiltproxyispredicateduponthepremisethatthegrain-sizeofdepositedsedimentata

pointisprimarilycontrolledbytheshortterm(afewtensofyears)timehistoryofflowspeedsatthat

pointactingonabroadspectrumoffinesedimentsizesdeliveredalongthetransportpath.Controlof

depositionisexpressedintheclassicalKroneequation(EinsteinandKrone,1962;Krone,1962)forthe

selectivedepositionoffinesuspendedmaterial.Theamountdepositedisgivenby:

ΣRit=ΣCiwsi(1-τo/τdi)t

whereRiistherateofdeposition(dimensionsmass/area.time;ML-2T-1),thusΣRitis(ML-2),tobe

summedoverisizefractions.Thecontrolsare;settlingvelocitywsi,criticaldepositionalstressτdi,

boundaryshearstressτoandtheconcentrationCiforeachfractionaccordingtothesizedistribution

suppliedinsuspensionfromupstream.

ThishasbeensetoutextensivelyinthepublicationsofMcCave,2008,2007;McCaveetal.,1995;

McCaveandHall,2006.Allthematerialthatisconsideredintheanalysisoftheproxyisderivedfrom

terrestrialsourcesbecausecareistakentoremovebiogeniccomponents(carbonateandsilica)of

marineorigin.Thesesedimentsaredeliveredtotheoceanbeyondtheshelfviaavarietyofroutes,

primarilybygravityflows(turbiditycurrentsanddebrisflows)andshelf-edgeresuspension/spill-

over,butalsoinanumberofcasesbyaeolianfalloutandviaiceraftinginpolarareas.Directfluvial

supplyisrare,particularlyatpresentunderhighsea-levelstand.Evenunderglaciallyloweredsea-

levelsmanydeltasdidnotreachtheshelfedgeandmanyothersdeboucheddirectlyintotheheads

ofsubmarinecanyons,feedingturbiditycurrentswhichledintothedeepsea(seereviewsbye.g.

McCave,2002;Thomsenetal.,2002).

Atestofwhethersedimentsarecurrentsortedornotisderivedfromcross-plotsof𝑆𝑆againstSS%.

Underacurrentsortedregime,𝑆𝑆correlatespositivelywithSS%,whereasunsortedsedimentsshow

nocorrelation.Thelattercaseisevidentinafluvially-suppliedlake(Gammonetal.,2017)orinthe

sedimentsfromtheMississippideltatop(Xuetal.,2016)(FigureS5).Incontrast,themarine

sedimentcoresintheDrakePassageinLamyetal.,(2015)showahighdegreeofsedimentsorting

(Lamyetal.,(2015),theirFigureS3).Similarly,GC528(presentedinthisstudy)showsastrong

correlationbetween𝑆𝑆 andSS%(FigureS2a)suggestingthatthesedimenthasbeencurrentsorted.

Furthermore,eventhoughtherearehighIRDconcentrationsinsomeintervals,thereisno

correlationbetweenIRDconcentrationand𝑆𝑆(FigureS2b)andthesamplescontainingIRDdonot

deviatefromthe𝑆𝑆-SS%trend(FigureS2a).

SupplementaryFigures

FigureS1:Assessingtheimpactofchangesinsealevelonthepatternsofsedimentation.(Left)Map

showingthepositionofthecoastlineatvariousintervalsduringthelastdeglaciation(seeinsetbox)

basedonbathymetry.(Right)(A)Globalrelativesealevelchangeoverthelastdeglaciation(Lambeck

etal.,2014);(B)MassaccumulationrateatsiteGC528;(C)SedimentationrateatsiteMR806-PC9

(Lamyetal.,2015).

0 5 0 0

0

1000

2000

3000

4000

5000

Bath

ym

etr

y /

m

Distance / km

GC528

MR806-PC9

SAF

PF

SACCF125m (LGM)110m (20-17 ka)60m (13-12 ka)0m (7-0 ka)

−150

−100

−50

0

50

RS

L (m

)

(A)

0.000.020.040.060.080.100.12

MA

R (g

/cm

2 /yr)

(B)

01020304050607080

Sed

. rat

e (c

m/k

yr) (C)

0 5 10 15 20 25Age (ka)

FigureS2:AssessingthecurrentsortingincoreGC528.(A)Cross-plotofweightpercentagesortable

siltfraction(10-63μm)versusthemeansortablesiltgrainsize.Samplesthatcontainsignificant

quantitiesofIRD(grains>300μm)areshowninorange.(B)Cross-plotofmeansortablesiltgrainsize

versusIRD(grains>300μm)concentration.

0 20 40 60 80 10010

15

20

25

30

35

40SS

(µm

)

SS %

R2= 0.84

(A)

●● ●●●● ●● ●● ●●●●● ●●● ●● ●●●●●●● ●● ●●● ●● ●●● ●●●

●

●

●

●●●

●

●●

●

●

●

●

●

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●

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●

●

●

●

●

●

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●

●

●

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●●●

●● ●● ●●●● ●● ●●

●● ●●

●●

●

●

●

●

●

●

●●

●

●

● ●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

15 20 25 30 350

20

40

60

80

(A) GC528

R2= 0.06

SS (µm)

> 3

00µ

m (#

/g)

(B)

FigureS3:ComparisonoftheIRDrecordsfromtheSouthwestAtlantic(GC528)andtheScotiaSea

(Weberetal.,2014).(A)GC528IRDconcentration;(B)GC528IRDflux(basedonmass

accumulationrates);(C)ScotiaSeaIRDflux.GreybarsshowtheAntarcticIcesheetDischarge

events(AIDS;Weberetal.,2014)

0

20

40

60

80

IRD

(gra

ins/

g)

GC528 IRD concentration

0.0

0.5

1.0

1.5

2.0

2.5

IRD

(gra

ins/

cm

2 /yr)

GC528 IRD flux

0.0

0.2

0.4

0.6

0.8

1.0

1.2

IRD

(gra

ins/

cm

2 /yr)

Scotia Sea IRD flux

0 5 10 15 20 25Age (ka)

FigureS4:AssessingthepotentialforreworkedalkenoneshavingaffectedtheLGMalkenone-SST

record.(A)Alkenone-derivedSSTrecordsfromdownstream(GC528-black)oftheDrakePassage;(B)

TotalorganiccarbonconcentrationinGC528;(C)TotalalkenoneconcentrationinGC528;(D)

PlanktonicforaminiferaNeogloboquadrinapacherma(sinistral)δ18OfromGC528.

024681012

Alke

none−S

ST (o C

)

(A)

0.6

0.8

1.0

1.2

[TO

C] (

%) (B)

0

1

2

3

4

5

[C37

] (µ

g/g)

(C)

5

4

3

2

1

0 1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25

δ18O

Nps

(‰)

(D)

Age (ka)

FigureS5:Unsortedsedimentcross-plotsfromthefluviallydominatedAlbertaLake(left;Gammonetal.,2017)andtheMississippideltatop(right;Xuetal.,2016)

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