Post on 28-Jan-2022
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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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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