PALEOCEANOGRAPHY,
VOL. 16,NO. I, PAGES1-19,FEBRUARY2001
Formation of Holocenesedimentarylaminae in the Black
Seaand the role of the benthicflocculentlayer
CynthiaH. Pilskaln
Schoolof Marine Sciences,Universityof Maine, Orono
Jennifer Pike
Department
of EarthSciences,
Universityof Wales,Cardiff,Wales,UnitedKingdom
Abstract. HoloceneBlackSeasediments
recovered
in 1988and 1993fromboxcoresandgravitycoreswere analyzed
geochemically,
microscopically,
andwithbackscattered
electron
imagery
(BSEI)in orderto determine
thetemporal,
geochemical,
andsedimentological
relationships
between
thebenthic
flocculent
layer(oftenreferred
toastheflufflayer)
andthe formationof underlying
laminated
unitI sediments.
Existence
of a permanent
benthicfluff layerin the Black
Seabasinis suggested,
actingasa geochemical
transition
layerwithinwhichall sedimentary
particles
arehydraulically
sorted
andparticles
subject
to dissolution
or organic
remineralization
arealtered
priorto accumulation.
Wepropose
that
particle
residence
timewithinthebenthic
flufflayerisa keyfactorin determining
sedimentary
microfabric
andgeochemical
composition
of laminated
unitI sediments.
Wepresent
a schematic
modeldepicting
theaboverelationships
anduseit to propose
a paleofluxscenario
for laminae
formation
in theunitII sapropel.
1. Introduction
The Black Sea is the largestanoxic body of water in the
world, with waters below !00-200 m defined as sulfidic
[Deuser, 1970; Murray et al., 1989; Millero, 1991; Murray et
al., 1991]. During the lastglaciationandearliestHolocene,the'
Black Sea was a •freshwaterlake [Degensand Ross,1972]. As
global sea level rose during the Holocenedensesalinewater
from the Mediterraneanflowedoverthe Bosporussill, eitheras
a torrentor moreprogressively,
andsankbelowthefreshsurface
waters[Ryanet al., 1997;Lane-Serifet al., 1997;Arthurand
Dean, !998]. Very little mixing with the freshwatercapoccurred,stratification'
ensued,andthe bottomwatersof the Black
Seabecameanoxicat - 7.5 ka [Jonesand Gagnon,1994;Lane-
Serffet al., 1997;Arthurand Dean, 1998]. The changefrom
tological
andgeochemical
relationship
between
thebenthic
flocculentor "fluff" layerandthe underlyinglaminated
sediments
[Degens
et al., 1978;Hay, 1988;ttonjoet al., 1988;Hayet al.,
1990; Pilskaln,1991;Arthur et al., 1994;Jonesand Gagnon,
1994;Arthurand Dean, 1998]. The debatehascenteredonthe
interpretation
of the of the light/darklaminaeas annualvarves
andthe temporalandsedimentological
relationship
betweena
persistent
orintermittent
benthic
fluff layerandtheformation
of
theunderlying
sediment
laminae.Varvechronologies,
determinations of sediment accumulationrates from modern time series
sediment
trapsamples,
anddetailedcomparisons
of varveand
seasonal
sediment
trapsamplecomponents
support
thecontention that the light/darklaminaecoupletsrepresent
two-season
annualvarves[Arthuret at., 1994;Pilskaln,1991;Hay, 1988;
Hay et al., !990; Honjoet aI., 1988]. Thestudies
abovehave
oxic to anoxic conditions at the sediment-water interface re-
proposed
thatthethickerlightlaminae
of unitI resultfromthe
sultedin the preservation
of a laminated,organic-rich
sapropel
(unitII [CalvertandFontugne,1987;Calvert,1987;Hay et al.,
1991;Arthur et al., 1994; PVilkinet al., 1997;Arthur andDean,
1998]). Thetermination
of unitII sapropel
deposition
occurred
at -•2 ka, followingan increase
in salinityto above11%oassaline bottomwatersslowlymixedwith the freshsurfacewaters.
Increasing
salinityallowedfor the invasionof the coccolitho-
summer-fallflux of coccolith-rich
particulates
producedby E.
Degensand Ross[1974].
There has beenmuch discussion
over the past20 yearsre-
son,1992;Jonesand Gagnon,1994].
Thesuccessful
recoveryin ! 988 of boxcorescontaining
the
Copyright
2001bytheAmerican
Geophysical
Union
.tothe formationof the underlyinglight/darklaminae.Crusius
andAnderson
[1992]pointoutthenecessity
of determining
the
huxleyiblooms,mixingwith lesseramounts
of dinoflagellate
material
andresuspended
fineshelfsediments.
Thethinner
dark
!aminaearebelievedto be late winter-spring
depositional
productsof diatomsandsilicoflagellate
bloomsandseasonal
peaks
in riverineinputof terrestrial
lithogenics
[Hay,1988;Honjoet
al., 1988;Hayet al., 1990,1991]. In contrast
to varvecounting
andsediment
trapstudies,
radiocarbon
dating
and2•øpb
mass
phoreEmilianiahuxleyi,whoseseasonal
bloomsinitiatedthe
ratessuggest
thatthe light/darkcouplets
mayrepdeposition
of the coccolith
carbonate-rich
laminated
sediments accumulation
>1 yearof deposition
possibly
dueto thelackof complete
of unitI [Hayetal., 1991;Arthuretal., 1994;ArthurandDean, resent
couplets
for
years
when
annual
coccolithophore
blooms
maynot
1998].Comprehensive
reviews
of themodern
oceanography
of
[Hay,1988;Hayet al., 1991;Crusius
andAndertheBlackSeaareprovided
by IzdarandMurray[1991]and haveoccurred
benthicfluff layer,first documented
photographigardingthestratigraphy
of theHolocene
BlackSeasediments undisturbed
theopportunity
fordetailed
studand,in particular,
overthepast10yearsregarding
thesedimen- callyby Vine[1974],provided
iesof itsage,geochemistry,
andsedimentological
rolerelative
Papernumber1999PA000469
0883-8305/01/1999PA000469512.00
originofthesurficial
flufflayerin theBlackSeaasa means
of
addressing
whether
ornotthelaminae
couplets
doindeed
repre-
2
PILSKALN AND PIKE: BLACK SEA LAMINAE AND.THE FLUFF LAYER
sentvarvesor not. They suggestthreepossibleoriginsof the
fluff: (1) it represents
resuspended
surficialsediment,(2) it is
the productof an anomaloussingledepositionalevent,or (3) it
is a permanentfeatureand resultsfrom steadystateprocesses.
The first optioncan be ruled out becauseof the geochemically
distinctcharacterof the fluff, as comparedto the immediately
underlyingsediments,in terms of particulateorganiccarbon
(POC), opal,carbonate
and organiccompoundcomposition,
and
radionuclide
inventories[Beieret al., 1991;Moore and 0 'Neill,
1991; t'ilskaln, 1991]. The latter two scenariosfor the fluff
origin have significantlydifferent implicationsregardingthe
accumulation
of sedimentarylaminaebeneaththe fluff, andthus
a moreconciseunderstanding
is required. In the presentstudy,
we combinegeochemicaland sedimentarydata obtainedfrom
the fluff andthe immediatelyunderlyingunit I sediments,along
with detailedscanningelectronmicroscope(SEM) and back-
scattered
electronimagery(BSEI) analyses
of unitI and!I laminae from recently(1993) collectedBlack Sea gravitycoresto
characterize
therelationship
between
thefluff andthelight/dark
sediment laminae.
2. Methods
2.1. Box Cores and Surface Sediments
Fifteenboxcores(50 x 50 cmsurfaceareaby 50 cmheight)
were collectedin 1988 on Leg 1 of the R/V Knorr Black Sea
Expedition,and four 6 m long gravitycoreswereobtainedin
1993onLeg I of theTREDMAR III cruise(Figure1) [IT'onjo
et
al., 1988;Limonovet aL, !994]. The 1988box coresusedin the
presentstudyrecovered
all of unit 1, includingthebenthicfluff
layerin 13 cores[t-Ionjoet al., 1988]. The 1993gravitycores
recovered
the majorityof unit I sediments
(with the lossof only
a topfew centimeters)
andtheentireunitII sapropel
(Figure2).
Detailed box coring and samplingproceduresare given by
Honjo et al. [1988] and Pilskaln [1991]. Approximately!00-
200cm• ofthesurficial
flufflayer(-2 cmthickness,
where
present)[Pilskaln,
1991
] and150-400
cm3 of theunderlying
2 cm
of sedimentweresubsampled
from eachbox coreandpoisoned
with 4% bufferedformalin. The sedimentsampleswere sieved
throughnylon sievesof 500, 250, 125, and 63 gm to size fractionatethe sedimentarycomponents;
the fluff sampleswere not
size fractionatedby sieving as the material was all <63 •tm.
Eachsedimentsizefractionand fluff samplewas examinedand
documentedusinglight and scanningelectronmicroscopyand
thenanalyzedin triplicatefor POC, calciumcarbonate,opaline
silica,and lithogeniccontentusingstandardwet-chemical
procedures[Pilskaln,1991]. A 1.0 M aceticacid leachmethodwas
usedto determineCaCO• contentbasedon dry sampleweight
loss. Decalcifiedsamples
werecombusted
at 500øCfor 3 hours
to quantifythe total amountof combustible(organic)and noncombustible(biogenicopal plus lithogenic)content. POC was
determinedfrom decalcifiedsampleswith a CHN analyzer.
Opaline silica contentwas analyzed by leaching decalcified
sampleswith a 1.0 M NaOH solutionand spectrometrically
determiningthe amountof reactivesilicain the !eachate(modified
fromEgglinenet al., [1980]). Lithogeniccontentwascalculated
asthe differencebetweentotalnoncombustible
andopalcontent
(equalto biogenicSiO2calculatedfrom reactivesilica.
2.2. Gravity Cores and Sediment Fabric Analysis
Detailed sedimentarylogs of the four gravity coresrecovered in 1993 were compiledfrom visual core descriptionand
smearslide analysis. Smearslideswere madeusingtoothpicksized sedimentsamplesfrom four white and four dark laminae
of unit I and four light and dark laminaesamplesfrom unit II
(coresBS254 and BS256; Figure2) andwere mountedusing
Naphraxmountingmedia. Five 2 cmx 2cmx-5 cm longintact
sedimentblockswerecut from coresBS250 andBS254(Figure
2) and embeddedusing a fluid displacive,low-viscosityresin
[Pike and Kemp, 1996]. Highly polishedthin sectionswere
producedfrom the resin-embedded
sedimentcore blocks, carbon-coated,and analyzedwith SEM BSEI followingthe procedtire of Pike and Kemp [1996]. BSEI hasbecomea widely em-
ployed
method
toanalyze
thesedime•t•.ry
fabricofbothmodern
and ancientlaminatedsediments[Krinsleyet al., 1983; Pye and
Krinsley,1984;Kemp, 1990;Macquakerand Gawthorpe,1993;
Pike and Kemp, 1996, 1997]. Sedimentarylaminaethat consist
primarily of calcite/aragonite
and terrigenousquartz and feldspargrains(comparativelylargeaverageatomicweights)havea
high backscattercoefficientthat producesrelativelybright images. Laminationsdominatedby porousmaterial(henceby low
atomicweight, carbon-based
resinfilling the porespaces),such
as dinoflagellate
thecaeor cystsandsiliceousdiatomfrustules,
have a low backscatter
coefficientand producedark images.
BSEI photomosaics
of the thin sections
wereproducedat 20X
magnificationand usedas basemapsfor high magnification
analyses
of thesediment
fabricandgrainandlaminaeboundary
relationships.
SEMenergydispersive
(EDS)elemental
mapping
of thethinsections
providedlaminaecompositional
information.
2.3. SedimentTrap Samples
Particulate material
collected with a time series sediment
trap that wasdeployedat 1200m in the far westernBlack Sea
[Honjoet al., 1988;Hay et al., 1990]wasexamined
microscopically with SEM for the presentstudy. The trap site,referredto
as BSC, was located80 km from the coastin 2100 m of water,
with the 1200 m trap operatingf¾omJune 1986-April 1988
[(Hay, 1988; Hay et al., 1990]. Splitsof particulatesamples
collectedin the springof 1987and1988(all prepoisoned
with a
4% bufferedformalinsolutionplacedin the trapcollectioncups
priorto deployment)wereusedin thepresentstudy.
3. Results
3.1. BSC 1200 m SedimentTrap, Fluff Layer, and
Underlying Surface Sediments
Closeinspectionand carefulsamplingof the topsof'the undisturbed1988 box coresreveala dark green-graysurfacefluff
layer of loosegelatin consistency(averagethicknessof 2 cm)
immediatelyunderlain by a 2 cm thick gray-white sediment
layerwe call a protolaminaelayer(Figure3). The term "protolaminae"is usedbecausethe layer doesnot displaythe typical
unit I white/darklaminaecoupletsor geochemicalcomposition.
Underneaththese gray/white protolaminaeare the distinctly
laminatedunit 1 sedimentswith the first clearly visible dark or
blacklaminadatedat-70 yearspriorto 1988 (Figure3; Arthur
PILSKALNAND PIKE: BLACKSEALAMINAE AND THE FLUFFLAYER
i
I
'
I'
i
!'"
I
3
!
46ON
..
-"••Z•
.
Sea of ;•
.,-"••J• Azov
,J•
44 ø
42 ø
-
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•
.
.....
40 ø
......
:;'.........
'....'•....
'
_•._
•-
?"",.?'.•
l( •
13J14 BSK2
•47 •'L"("•
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j ?.•-d0Bsc
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........
•.v•:::'t•:...-:
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...........
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'z*Zzø
Bosporus
I
28øE
!
30 ø
,,I,
32 ø
4. l
!
I .......
34 ø
36 ø
[
38 ø
•
40 ø
ß Black Sea 1988 Expedition Leg 1 box cores
o TREDIVIAR
ili 1993 Leg 1 gravity cores
• 1986-88BSCSediment
trap
Figue1. Location
ofBlack
Sea1988
boxcores,
1993
gravity
cores,
and1986-1988
BSC
time
series
sediment
trap
site.
et al, 1994). The size-fractionated,
dry weightpercentgeo-
ateamountsof surfaceetching;CaCO3contentis providedby an
chemical
composition
of thefluff layerandunderlying
surface abundanceof E. hto:le),icoccoliths(Figures5a-5d). Fecalpelsediments
from the fifteen 1988box coresis presented
in Table
letsconcentrated
just belowthe fluff layer andwithin the gray-
sediments
(Figures6a and6b) havea very
1. Meangeochemical
compositional
values
forallthesediment whiteproto-laminae
high
coccolith
carbonate
content
(always> 50% by dryweight),
sizefractions
andoverlying
flufflayerswerereported
previously
preservation
of the periotrophicmembrane,
andmibyPilskaln[1991]; herewereportthesedimentary
geochemical occasional
data for each stationto demonstratethe minimal variability oc-
nor to moderateamountsof intact diatom and silicoflagellate
tests(Figures6c-6f). Thefluff layerandtheunderlying
2 cmof
curring
among
the1988siteslocated
throughout
theBlackSea
sedimentsare both dominatedby CaCO3 and lithogenicmatebasin,alongwith newSEM and/orBSEIphotomicrographic
studies
completed
onthesediments,
flufflayers,
andBSCtrap rial, with calciumcarbonatebeing somewhatenrichedin the
material.Coccolithophore
E. huxleyi-dominated
zooplankton sedimentscomparedto the fluff layer (Table 1). There is a
in the percentopal contentbetweenthe fluff
fecal pelletsand coccolith-rich
aggregates
with moderate slightdecrease
amountsof diatomskeletalmaterialwerecollectedin the 1200
layerand the underlyingsediments
(withouta comparable
increasein the relativepercentage
of lithogenicmaterial),whereas
m BSCtrapsin summer
1987(Figure
4a). In comparison,
the
(Table1).
contents
of pellets
andaggregates
fromthe1200m BSCtrap percentPOCremainsrelativelyconstant
material
collected
in thespring1988showan abundance
of
diatomtests(primarily
Rhizosolenia
sp.)andsilicofiagellate3.2. Units I and II: BSEI Analysesand Laminated Sediment
skeletons
withnococcoliths
(Figures
4b-4d).Thesediment
fluff Fabric
layersamples
collected
during
thespring
of 1988havea mean
Thefourabyssal
plaingravitycoreswerecorrelated
withthe
composition
(over12sites)
of31%CaCO3,
6%opal,
7%POC
Holocene
stratigraphy
from
Hay
et
al.
[1990]
and
the
accelerator
and47%lithogenic
represented
byclayminerals
(Table1). Fhe
(AMS) radiocarbon
agesprovided
by .Iones
opalcontent
isprovided
bythepresence
of highly
etched
dia- massspectrometry
[1994](Figure2). Visualexamination
of thesplittomsandsilicoflagellate
skeletal
elements
withminor
tomoder- andGagnon
4
PILSKALN AND PIKE: BLACK SEA LAMINAE AND THE FLUFF LAYER
"it-
lad
UD
t.O
'"
•
ob ob
t.O
.--
ob
•
Description
ofUnrfs
ß
laminated
coccolith
ooze,
i--! white
Late
Holocene
dark
gray-black
and
--I
J- •
** !•i diatoms
and
silicaflagellate
present
in topfewcentimeters.
Baseof Unitl
ß
20 I
**
•
I I • Emiliana
huxleyi.
is
defined
by
the
first
invasion
of
I1
I
04
:
Black,laminatedsapropel
--!
*
t---,
tt
/
•
'E
Larger
abundance
of
:
0
/
Base
of
Unit
IIis
defined
by
the
marine
sediment.
first
deposition
of
organic-rich,
_
.•
•o
--
8o-
•
*
60'--
dinoflagellates
thanfor UnitI.
o
o
i
•
•"'-'"-'•
C)
',
,,
I
--
Lightgray-darkgraybanded
!
--
',
',
t=
duringtheearlyHolocene
•
whentheBlack
Seawasa
z
,,
120--
or laminated
lutitedeposited
',
freshwaterlake.
',
',
--
0
!
!
•
140-M
0
:
,..•..•
Sample
forthinsections
I used
inthis
study
** Pairoflight/dark
lamina
smearslides
* Sapropel
smearslides
'•-
Sapropel
• Gray, bandedlutite
--=--
• Void
Pale
green-gray,
structureless
mud
i
i Coccolith
ooze
Mudvolcanobreccia
Figure 2. 1tolocenestratiographic
correlationof four 1993BlackSeagravitycoreswith thatof Hay et al [1990] andwith Jones
and Gagnon[1994] radiocarbon
ages.
PILSKALN
ANDPIKE:BLACKSEALAMINAEANDTHEFLUFFLAYER
5
6
PILSKALN AND PIKE: BLACK SEA LAMINAE AND THE FLUFF LAYER
,,Table
1.,,,,,Ge0chem!cal
Composition
ofBlack
SeaFluff.
Laye
r an.d,,U.n,
der!ying
2 cmofSeive
dSed.!m,ents
Percent
Map site
SedimentSizeFraction
PercentOpal
PercentPOC
10
fluff
29
11
6
33
10
> 500 mm
66
3
4
23
10
500-250
rnm
57
3
8
26
10
250-125
mm
43
4
10
28
10
125-63 mm
37
4
9
39
10
< 63 mm
37
2
4
51
13/14
fluff
55
2
6
29
PercentCaCO3
........
Lithogenic
13/14
> 500 mm
58
4
6
23
13/14
500-250
mm
57
3
5
26
13/14
250-125
mm
45
4
9
31
13/14
125-63 mm
36
6
10
36
13/14
< 63 mm
41
4
7
36
BSKI
> 500 mm
64
4
5
23
BSK1
500-250
mm
56
4
7
25
BSK1
250-125
mm
36
4
8
36
BSK1
125-63 mm
46
4
10
30
BSK1
< 63 mm
40
6
7
38
BSK2
fluff
29
4
6
51
BSK2
> 500 mm
60
4
5
23
BSK2
500-250
mm
53
4
7
26
BSK2
250-125
mm
43
4
8
36
BSK2
125-63 mm
37
4
8
41
BSK2
< 63 mm
29
4
9
54
20
> 500 mm
68
3
4
21
20
500-250
mm
56
4
7
27
20
250-125 mm
47
3
8
31
20
125-63 mm
36
4
12
34
20
< 63 mm
41
3
6
42
BSK3
> 500 mm
48
3
6
41
BSK3
500-250 mm
54
4
10
23
BSK3
250-125 mm
44
6
12
24
BSK3
26
29
5
5
15
3
38
BSK3
125-63 mm
< 63 mm
48
fluff
51
4
6
31
48
> 500 into
70
3
4
19
48
500-250 mm
62
4
5
23
48
250-125 mm
41
6
9
31
48
125-63 mm
33
6
15
25
48
< 63 mm
54
3
5
32
47
fluff
33
9
7
29
47
> 500 mm
67
4
4
21
47
500-250 mm
58
2
6
26
47
250-125 mm
42
9
11
27
47
125-63 mm
34
6
13
32
47
<63 mm
51
3
5
34
27/28
fluff
30
7
8
45
27/28
> 500 mm
47
no data
4
no data
27/28
500-250 mm
48
4
7
34
27/28
250-125 mm
34
6
9
38
27/28
!25-63 mm
26
6
9
47
27/28
< 63 mm
29
6
4
54
36
fluff
29
6
4
54
37
fluff
28
6
7
49
BS
fluff
24
7
6
56
44
31
fluff
fluff
16
32
7
6
8
6
47
30
fluff
11
8
9
72
,
53
69
PILSKALNANDPIKE:BLACKSEALAMINAEANDTHEFLUFFLAYER
Table1. (continued)
Map site
Sediment
SizeFraction
,
ß
,,
Percent
CaCO3
PercentLithogenic
Percent
Opal
Percent
POC
31
6
7
47
,
All site mean
fluff
All site mean
> 500 mm
61
4
5
24
All site mean
500-250 mm
56
4
7
26
All site mean
250-125 mm
42
5
9
31
All site mean
125-63 mm
35
5
11
36
All site mean
< 63 mm
39
4
6
44
All site mean
all sizefractions(excludingfluff)
46
4
8
32.
,
'L
IeKU
o 47
x-•'T ' 31ø 0230
D
10KU
1 o? X•51o
0231
Figure4. Scanning
electron
microscope
(SEM)micrographs
offecalpellets
andfecalaggregates
collected
in the1200m BSC
sediment
trap,summer
1987andspring1988.(a)Summer
1987fecalaggregate
consisting
primarily
of coccolithophore
E. huxleyiandlesser
amount
of diatomfrustules.
(b)Spring1988fecalpelletpacked
withRhizosolenia
frustules.
(c andd)Zooplanktonfecalpelletfromspring1988packed
withsilicoflagellate
Distephanus
skeletal
material.Scalebarsin microns
areatbottom
of eachmicrograph.
PILSKALN
AND PIKE: BLACK SEA LAMINAE
AND THE FLUFF LAYER
• q
k
J
ß
PILSKALNAND'PIKE:BLACKSEALAMINAEANDTHE FLUFFLAYER
A
10KU
154X
•
-P
110
B 10KV
070.X
l•--•3P 0156
E
Figure
6. SEM
micrographs
of(aand
b)fecal
pellets
concentrated
below
the
fluff
layer
within
the
gray-white
protolaminae,
(c)preserved
pefiotrophic
membrane
onfecal
pellet
which
acts
toprotect
opaline
silica
constituents
from
dissolution,
and
(d-f)pellets
containing
large
amounts
ofcoccolith
carbonate
and
minor
amounts
ofdiatom
and
silicoflagellate
opal.Allscale
barsareinmicrons.
9
10
PILSKALN
AND
PIKE:
BLACK
SEA LAMINAE
core surfaces and smear slides made from Unit I sediments col-
AND
THE FLUFF
LAYER
'
lectedby the 1993 gravity coresshowsconsistentsubmillimeterto millimeter-scale alternation between white laminae, rich in E.
huxleyi coccoliths,and dark gray to black laminae containing
silt, clays, and organic debris, as expectedfrom the resultsof
previousBlack Sea core laminaeanalyses[tlay, 1988;Hay, and
Honjo, 1989; tlay et al., 1991;Arthur et al., 1994]. BSEI analysescombinedwith SEM elementalmapping showthat the compositionalalternationin unit I sedimentsconsistsof three lamina
types:(1) a white, CaCO3-rich laminadisplayingcomparatively
high backscattercoefficients;(2) lamina composedmainly of
lithogenic material, having an intermediatebackscattercoefficient and appearingdark gray in color; and (3) blackorganicrich lamina consistingof' amorphousorganic matter,occasional
diatom and siiicofiagciiatc skeletal elements, dinoflagellate
cysts, and coccolithswith a very low backscattercoefficient
(Figures7 and 8). Lamina types2 and 3 combineto producethe
dark gray to black laminationsseenin visual coreanalysisand
representthe dark or black lamina of the varve coupletsdescribedby Hay [ 1988] and Hay et al. [ 1990, 1991]. The thicker,
white (brightunderBSEI) laminaeare coccolith-rich,composed
primarily of coalesced,pellet-shapedaggregatesof coccoliths
with pinchedends and minor amountsof lithogcnicmaterial
(Figures8a, 8b, 8c, and 8e). Occasionaloccurrences
of coccolith-rich, white laminaein which the coccolithaggregates(200500 •tm in length)are not entirelycoalescedlaterallyare also
seenin the BSEI imagesof the cores(Figure 8b). The coccolith-rich laminaetend to have sharpboundariesand a distinct
bulbous/pinch-and-swell-type
character
(Figures8a, 8b, and8e).
Many of the thickestcoccolith-richlaminaeare laterallycontinuousacrossthe 2 cm wide sedimentblocks cut from the grav-
ity cores(Figure7). In the dark gray lithogenic-rich
laminae
displayingintermediate
backscatter
coefficient,loosecoccoliths
are observedalong with pellet-shapedlithogenicaggregates,
500-600 gm in length(Figure 8t). The lithogenicaggregates
oc•:asionally
coalesce
to producean appearance
similarto the
coalesced
coccolithaggregates
(compareFigures8e and 8f).
The black,low backscatter
coefficientlaminaeconsistprimarily
of amorphous
organicmatter,diatomskeletalremains,and
dinoflagellate
cysts(Figures8b,8d,8g,and8h)andappear
to be
sandwiched
or compressed
in between
thethicker,coccolith-rich
andlithogenic-rich
laminae,givingthema thin,wavycharacter
(Figures
8band8d). Oncloseinspection,
thesethin,darklaminaedisplaya moreporouscharacter
thaneitherof theothertwo
typesof laminations
(Figures8e-h). Coccolithaggregates
are
rare or absentfrom the dark, organic-richlaminae,although
occasionalloosecoccolithsare observed(Figures8a, 8b, 8d, and
8g). Subsamples
fromthe dark,organic-rich
laminaein the
upperpartof unitI (Figure2) arefoundto contain
moreskeletal
opalremains
thansimilarlaminae
atthebaseof unitI.
Unit II sediments
(Figure2; deposited
between-•2-7.5
ka,
[Jones
andGagnon,
1994]consist
of laminated,
grayto black,
finesilt/claysediments
witha complete
absence
of E. huxleyias
determined
by visualandsmearslideanalysis.BSEIanalyses
revealtwo distinctlaminaetypesin unit II, in contrast
with the
threeof unitI (Figure9, Figures10aand10b). Light-colored,
intermediatebackscattercoefficient laminae are composedof
coalesced
andnoncoalesced,
thick lens-shaped
lithogenicaggre-
gates
of upto several
100microns
in length
(Figures
',0a-10c).
Figure 7. BSEI photomosaic
of Itoloceneunit I coccolithooze from
1993 gravitycore(BS254, 23-25 cm).
PILSKALNANDPIKE:BLACKSEALAMINAEANDTHEFLUFFLAYER
11
Theselaminae
havea pinch-and-swell
appearance
similartothe '
white,coccolith-rich
laminae
of unitI (Figures
8b,8d,10a,and
merits.Thusthe very smallamountof biogenicopalpreserved
10b). Dark, low backscatter
coefficientlaminaeconsistof
inthe2 cmofsediment
immediately
underneath
thefluffand
in theBlackSeasediments
underlying
theflufflayer(4%opal
amorphous
organic
matter,
isolated
lithogenic
grains,
dinoflagel- <1% opaloverthe remainder
of unit I) is likelyderivedfrom
lates,and extremelyrare, poorly preserveddiatom.frustules pellet-bound
opalinematerial
produced
by suspension
feeding
(Figures10a, 10d, and 10e). The dark laminaeof unit II havea
thin,wavycharacter
andappear
moreporous
ascompared
tothe
thicker,
light-colored
lithogenic
laminae
(Figures
10a-d).Overall, the individuallaminaeof unit II tendto bethinnerthanthose
of unit I (Figures7 and9).
4. Discussion
4.1. Opal in the BenthicFluff Layer and theFormationof
Unit I Dark
Laminae
zooplankton
intheoverlying
watercolumn
throughout
theyear.
Themassflux of particulate
materialthrough
theBlackSea
watercolumnin thewinter-spring
consists
primarilyof biogenic
opal,lithogenic
particles
(clayminerals),
andterrigenous
debris
andisquantitatively
lessthanthaioccurring
during'
summer-fall
periods
of maximum
POCandCaCO3fluxes[Hay,1988;Hayet
al.,1990].Although
noseasonal
fecaipellet
counts
havebeen
completed
onBlackSeatrapsamples,
microscopic
examination
of theBSCtrapsamples
revealsa greaterabundance
of intact
fetal pelletsin ,thesummer-fallsamplesthan in the winterspringsamples.Pelletproductionmight be lower in winterspring,leading
to a reduced
deliveryof fecalpellets
to thesediment-water
interface
duringthistime of theyearascompared
to
thesummer-fall.
Considering
thisaswellasthehighdissolution
Geochemical
andmicroscopic
analyses
of thefluff layercollectedin spring1988,ascompared
to theunderlying
protolaminaesediments,
suggest
thata significant
portionof thecomponentswithinthefluff layerrepresent
thesedimentation
products loss of opal relative to calciumcarbonatein the Black Sea
of the winter-springperiodwhen diatomand silicoflagellate [Shimkuset al., 1973; Shimkusand Trimonis,1974; Pilskaln,
bloomsoccur and terrigenousand lithogenicmaterialinputto
1991;Hay, 1988;Hay andHonjo,1989;Hay et al., 1990],one
the water column is enhancedowing to high river runoff and
wouldexpectthe winter-spring
depositional
laminaeto be substorm-generated
shelf resuspension
[Hay et al., 1990]. Numerstantiallythinneroverallthanthoseresultingfromthe coccolith
ous silicoflagellateskeletonsand highly etcheddiatomvalves
CaCO3/pellet-dominated
fluxesof the summer-fall
period[Hay,
are presentin the 1988 fluff layer, in additionto a high abundanceof singlecoccoliths
andclaymineralparticles.A significant sourceof the latter two particletypesis the winter storm
resuspension
and lateral offshoreadvectionof shelf sediments
containingdetritalclasticmaterialandcoccolithdebris[.Hayand
Honjo, 1989; Hay et al., 1990]. In contrastto thespring1200m
BSC trap samplesin which silicoflagellateand diatom-packed
pelletsare observed,no suchpelletscomposed
exclusivelyof
silicoflagellateor diatomsare seenin the fluff. However,fecal
pellets(somepossessing
a semi-intactperiotrophic
membrane)
composed
primarilyof coccoliths
andcontaining
well-preserved
diatomand silicoflagellatetestswere collectedfrom the sedimentsunderlyingthe fluff layerin 1988. Considering
themean
opalinesilicacontentof thespring1988trapmaterial(50%) and
the fluff layeropal contentof 6%, we assume
that the majority
of opalineskeletalmaterialwhichreachesthedeepwatersof the
Black Sea dissolves at the sediment-water interface within the
fluff layer. Evidencesupporting
highopallossratesat theinterfacecomesfrom the documentation
of diatom-poor
sediments
in
the Black Sea despiterelativelyhigh fluxesmeasuredin the
water columnand the occurrence
of extremelyetchedsurfaces
of opalskeletalcomponents
withinthe surfacesediments
immediatelyunderlyingthesurfacefluff layer[Shimkus
and Trimonis,
1974; Hay et al., 1990;Hay et al., 1991;Pilskaln,1991]. It
appearsthat even thoughthe upperBlack Seawatercolumn
(250 m) is highlyundersaturated
with respect
to silica[Brewer,
1971;Hay et al., 1990]ascompared
to deeperwaters(1200m),
opalineskeletalmaterialthat becomesincorporated
into fast-
settlingfecalpellets(andintosinkingalgalaggregates)
may
1988;Hay andHonjo, 1988]. The BSEI analysesof BlackSea
gravitycoressupportthis expectationwith thinner,dark,more
Iithogenicand opal-richdark laminae observedinterlayered
between the thicker, bulbous white coccolith laminae of unit I.
Ourdetailed
BSEIstudyindicates
thatwinter-spring
sedimentation eventsactuallyproducetwo distinguishable
lamina:a dark
gray,lithogenic-rich
laminaanda black,organic-rich/opal
lamina, whichtogetherform the singledark or blacklaminaof the
Black Sea varve coupletseasily recognizedin core sections.
Hay et al. [1990] suggest
that diatombloomsoccurringin the
winter-spring
might effectivelyremovemoresuspended
terrigenous/lithogenic
materialfrom the watercolumnby physical
scavengingcomparedto the summer-fallcoccolithophore
bloomsowingto the winter-spring
peakin riverdischarge
into
the Black Sea.
Our data indicate that the flux
of terri-
genous/lithogenic
materialmay not be primarilyassociated
with
the flux and deliveryof diatomopal as we observedistinctly
lithogenic-richlaminae as well as more organic-rich/diatom
opal-containing
laminae. However,the lack of diatomopal
resultingfrom dissolutionin the lithogenic-richlaminaemust
alsobe considered.The occurrence
of pellet-shaped,
lithogenic
aggregates
in ourtype2, darkgray,lithogenic-rich
laminaemay
representwinter-springdepositedzooplanktonfecal pelletsin
whichthe opalhasdissolved.
4.2. Role of Fecal Pellets in the Formation
of Unit I White
Laminae
Resultsfrom the abovedescribedanalysesindicatethat the
escapedissolution
in theupperwatercolumn,sinkto thedeep thick, white laminae in unit I result from the depositionof
watercolumn,andupondisintegration,
release
silicoflagellates denselypacked,coccolith-richzooplanktonfetal pelletsand
and diatomsto the basinfloor andfluff layer. Somedegreeof
dissolution
protection
of theopalwithinsinkingpelletsmaybe
providedby periotrophic
membranes,
therebyincreasing
the
probability
of successful
incorporation
of theopalintothesedi-
coccolith-packed
marinesnowaggregates
whichsettleoutof the
watercolumnduringthe summer-fallseasonwhenE. huxleyi
bloomsare prevalentin the Black Sea [Hay, 1988; Pilskaln,
1991;Diercksand Asper,1997]. The well-preserved
fecalpel-
12
PILSKALN AND PIKE: BLACK SEA L•,MINAE AND THE FLUFF LAYER
•
1opm
PILSKALN
ANDPIKE:
BLACK
SEALAMINAE
ANDTHEFLUFF
LAYER
letsrecoveredin 1988andconcentrated
belowthefluff arecoc-
13
heavyparticlesor aggregates
(suchas coccolith-packed
zoo-
colith~rich
andrepresent
themost
abundant
sedimentary
compo- planktonfecalpellets)will sink quickly but small,lessdense
nents
withinthetwolargest
sievefractions
(> 250gin)of the particles
(suchasindividual
coccoliths
andplatyclayminerals
surface
sediments
[Pilskaln,
1991
]. Thepellets
andpellet
frag- or spinosesilicofiagellates
andporousdiatomvalves),will not.
ments
appear
to beincorporated
intothepellet-rich
andCaCO•rich(> 90%CaCO3)
whitelaminae
of unitI [Hay,1988].•'his
laminatypedisplays
a highBSEIbackscatter
signalconsistent
witha dense,
coccolith
carbonate
content.Microscopic
examinationof thewhitelaminae
fabricreveals
a structure
highly
In thismanner,the fluff layerplaysan importantrole in determininghow rapidlyplanktonically
derivedparticulates
become
incorporated
into the underlyingsediments
and the extentof
preaccumulation
remineralization
of opal andPOC. A factorto
considerin examiningthe potentialhydraulicparticle-sorting
occurringin thefluff layeris theaccdmulation
of bacterialpopulationswithinthe layerandthe potentialphysical/chemical
effectswhichtheirpresence
mayhaveon particlesorting.A sec-
suggestive
of an accumulation
of fecalpelletsthatresemble
in
sizeandcomposition
thoseplanktonic
zooplankton
pelletscollectedin sediments
immediately
underlying
the!988flufflayer
(compare
Figures6a, 6b, and8e). Because
E. huxleyi
produces ondary maximum in sulfatereductionin the Black Sea occurs
massivebloomsin the summer-fallperiodas reflectedin the
composition
of Black Sea sediment
trap samples,
we concur
with Hay [1988] and Hay et aI. [1990; 1991]that the white
belowthe watercolumnoxic-anoxicinterfacein the underlying
surfacesedimentsandhasbeenattributedto a highabundance
of
fermentire bacteriaas well as methanogens,with the latter
in the benthiefluff layer [•lannasch
et
Iaminae
in unitI sediments
area summer-fall
depositional
prod- foundto be concentrated
uct,with the primarymechanisms
of transport
to the sediment- al., 1974;•lannasch,1991;Muramotoet al., 1991]. Karl [1978]
waterinterfacebeingzooplankton
fecal pelletswith a lesser reportsadeninctriphosphate(ATP) concentrations
within the
contributionby coccolith-rich
marinesnowaggregates.The
top I 0 cm of BlackSeasediments
that are4 ordersof magnitude
varyingthicknessof the whitelaminaeandthe pinch-and-swell higherthan thatof the overlyingwater column,a directindicacharacter is a reflection of the interannual variations in the total
massflux of coccolith-rich
pelletsand/ormarinesnow. Thisis
supported
by evidencefrom modernBlack Seasedimenttrap
showingthat the magnitudeof the E. huxleyi bloomsvaries
betweenyears and occasionallybloomsmay not occur [Hay,
1988;Hay and Honjo, 1988;Hay et al., 1990].
Although the summer-fallwhite laminaeare full of coccoliths, they are poor in organiccarbonrelativeto the black,organic-rich/opal
Iaminae.This is somewhat
puzzlingconsidering
the fact that sedimenttrapshave measuredthe highestannual
POC fluxes throughthe water columnduringthe summer-fall
period of coccolithophorid
blooms [Hay, 1988; Hay et al.,
1990]. Organicbiomarkerstudiesof Black Sea surfacesedimentsare somewhatambiguousin termsof the relativeimportanceof coccolithophores,
diatoms,and terrestrialhigherplants
in contributingto sedimentary
organiccarbon[Wakehamand
Beier, 1991]. One possibleexplanation
for the lack of POC in
the white laminaemay be that the POC producedand exported
to the sediment-water
interfacein the form of pelletsandaggregatesfollowingcoccolithophorid
bloomsis highlylabile,rapidly
oxidized,andresultsin a relativelyorganic-poor
but calcite-rich
whitelamina. The amorphous
organicmatterwithinourBlack
Seatype3 thinblacklaminaeandwithinthelargelyterrigenous
blackiaminaedescribed
by Hay [1988]maybe of higherplant
originandpossiblyof a morerefractorynature.
4.3. HydraulicSortingand Geochemical
Transformations
Within the Fluff Layer
tion of the elevated level of bacterial metabolicactivity in the
uppermostsediments. Additionally, .lannaschet al. [1974] report the presenceof atypicalanaerobic,sulfide-oxidizingbacteria in the surfacesediments. Unlike the more typical sulfideoxidizingthiobacillithat are absentfrom the Black Sea surface
sedimentsandtendto lowerthe pH of culturemediaby forming
sulfate,the atypicalisolatesactuallyraiseor havelittle effecton
the pH of themedium[•lannasch
et aI., 1974]. Analysesof the
organicbiomarkercomposition
of Black Seasurfacesediments
and benthiefluff layer tend to corroboratethe findingsof the
abovemicrobialstudies. Beier et al. [1991] and Walceham
and
Beier [1991] suggestthe presenceof a patchymicrobialcommunityconcentrated
withinthe upper 1 mm of the benthiefluff
layer basedon steroland fatty acid analysesof the fluff layer.
High concentrations
of bacteriaeither on the surfaceor within
the fluff layer may impedeor slow the movementof platy,
spinoseand/orporousparticlesthroughthe layer,thusreducing
theirpotentialburialrateandpossiblyenhancing
the degradation
of the morelabileorganic-richparticlesand/orthe dissolutionof
opal material. Resultsof the Jannaschet al. [1974] studysuggeststhat the presenceof particularbacteriamight producea
slightincreasein the pH of the fluff or surfacesediments,
which
wouldfacilitateopaldissolution.
We proposethat the fluff layer represents
a geochemical
transitionlayer within which all sinkingparticulatematerialis
hydraulically
sortedandopalandPOCcomponents
areremineralized. The mean 1986-1988opaline silica contentof trapcollected
particulates
fromthe 1200m BSCtrapis 20 and50%
for summer-falland winter-springsamples,respectively.This
Owingto itsgelatinous
nature,
we suggest
thatthebenthie
to an opal contentof 6% determined
for the 1988
fluff layeractsasa hydraulic
sorting
layerthrough
whichdense, compares
Figure8. BSEImicrographs
ofsections
fromunitI mosaic
(Figure
7) showing
(a)bright
pinch-and-swell-type
CaCO•-rich
laminae;
(b)laminae
ofnoncoalesced
pellet-shaped
aggregates
of coccoliths
(indicated
byarrow),
withathicker
lamina
composed
oflithogenic
material
andorganic
debris
atthetop(labeled
L/O);(c)co½coliths
within
aCaCO•-rich
aggregate,
withintact
coccolithophore
sphere
indicated
byarrow;
(d)thin,wavylamination
composed
oflithogenic
material
(L),discontinuous
organic-rich
lamina
(O),andpinch-and-swell-type
CaCO3-rich
laminae
(C);(e)coalesced
CaCO•-rich
coccolith
aggregates
(C)
above
organic-rich
lamina
composed
ofdinoflagellate
cysts
(D)andlithogenic-rich
lamina
(L);(f) large
(600I•m)lithogenic/silt
aggregate
(L),withintermediate
backscatter
signal;
(gandh)remains
ofdiatoms
(black
arrows)
anddinoflagellate
cysts
(white
arrows)
inthemoreporous,
dark,lowbackscatter
laminae.
14
PILSKALNAND PIKE: BLACK SEALAMINAE AND THE FLUFFLAYER
Figure9. BSEI photomosaic
of unitII sapropel
from1993gravitycore(BS250,50-51.2cm).
PILSKALNAND PIKE:BLACKSEALAMINAE AND THE FLUFFLAYER
15
c
o
,,
10grn
,,
.
..
o
E
EHT'20.0KV Idl)-20 mm
20.0•
PHOTO10
'-
.- 10pm
.,
R-
[
Figure10. BSEImicrographs
of sections
fromunitII mosaic(Figure9) showing
(a) thin,dark,wavyorganic-rich
laminations
(indicated
by arrows)andnoncoalesced,
brighter!ithogenic
aggregates
(S); (b) coalesced
lithogenic-rich
aggregates
forming
bulbous,
pinch-and-swell-type
iaminaealternating
withthin,dark,organic-rich
iaminae
(O);(c)silt-andclay-sized
particles
in a
lithogenic
aggregate;
(d) dinofiagellate
cystswithina dark,organic-rich
lamina;(e) lastvestiges
of diatomfrustules
withina
dark,organic-rich
lamina(micrograph
isoverbrightened
toshowtheverypoorlypreserved
opaline
I?ustules).
collectedfluff within whichhighlyetcheddiatomvalve fragments are found. If minimal dissolutionof the settling opal
materialoccursbetween1200 m andthe bottom(--2000 m) with
the majorityoccurringat the sediment-water
interface,as suggestedby Ilay et al. [1990],thenwe observe
a 70-80%dissolu-
tion lossof biogenicsilicawithin the fluff layer. Spinosesilicoflagellates
and porousdiatomvalvessettlingslowly through
the gelatinous
fluff layerare particularlyvulnerableto dissolution with their characteristically
high surfacearea:volumeratios.
Furtherpostdepositional
dissolutionof opal mustoccuras it is
16
PILSKALNAND PIKE:BLACKSEALAMINAEANDTHE FLUFFLAYER
and thus would be expectedto display substantiallyreducedto
compacted
and incorporated
into the laminaeof unit I (supportedby porefluid datafromManheimand Chart[1974]), negligibleindividual settlingvelocitiesthroughthe gelatinous
whichhasa meanopalcontentof < 1% [Shimkus
andTrimonis, fluff layer. Becausethesecomponentsare not subjectto the
of dissolutionor degrada1974;Hay, 1988]. Dissolution
lossof coccolith
CaCO3appears geochemicaltransformationprocesses
tion that affectthe opal and organiccarbonparticleelementsin
to be minimalto negligiblethroughout
the deepwaters,fluff
in the layerfor long
layer,andsurface
sediments
of theBlackSea.Thehighcalcium the fluff layer,they may remainsuspended
periodsof time. On the basisof our hypothesis
that the benthic
carbonate
contentof the summer-fall
settlingparticulate
matefluff layeris a permanentparticlesortingandgeochemical
tranrial, fluff. andunderlying
sediments
is preserved
in unitI (and
enhanced
by additional
POCandopaldegradation
loss),which sitionlayer,we expectthe compositionof the layer at any one
point in time to reflect the sortingand geochemicalprocesses
has a meanCaCO3contentof 65% [Hay, 1988;Hay et al.,
1991).
'operating
ontheseasonally
delivered
particle
components.
Thus
The fluff layermicrobialcommunitymostlikely facilitates the benthicfluff will likely have a high contentof individual
remineralization
of POC deliveredto the benthicfluff layer.
coccolithand clay mineralsand an absenceof dense,heavy
(suchas fecal pelletsand marinesnowaggregates),
POC fluxesto the sediment-water
interfacearehighestduring aggregates
regardlessof the season,owing to hydraulicsortingas well as
the summer-fall,representing
15% of the total flux (by dry
weight) at BSC comparedto a meanof 8% POC contentfor the
winter-spring
trapmaterial[Hay, 1988;Hay and Honjo, 1989;
ttay et al., 1990]. If we compare
thesevaluesto the7-8% POC
contentof boththe 1988fluff layerandthe underlying
protolaminae sediments,a maximumloss of 50% of the seasonally
deliveredPOC is observed.Considering
the findingthat the
majorityof sinkingPOC recyclingoccursin the shallow(60-80
m) suboxicwatersof the BlackSea,with relativelylow ratesof
decompositionin the permanentlyanoxic zone [Karl and
Knauer, 1991], high remineralizationratesof POC at the sediment-water interface and within the surface sediments are neces-
sary to explain the differencebetweenthe POC contentof the
deeptrappedparticulates,
benthicfluff, and underlyingsurface
sediments.
4.4. Temporal RelationshipsBetweenthe Fluff Layer,
SeasonalParticulate Fluxes, and Laminae Formation
A widespread,permanentbenthicfluff layer probablydevelopedsoonafter the establishment
of anoxicbasinconditions
andthe exclusionof a benthicmacrofaunalcommunity[Deuser,
1974; Rossand Degens, 1974; Calvert, 1987]. Extremelyslow
mixing of the bottom waters, with a near-bottomconvective
layerof an agethatis of the orderof the meanresidence
time of
the basin,indicatesthat physicalflow doesnot play a role in the
disturbance
and/ordispersalof the benthiefluff layer [Ozsoyet
al., 1991]. Physicaldisturbanceof the fluff layer shouldbe
expectedduringthe emplacement
of homogeneous,
fine-grained
layersof what have been termedturbiditesin Black Sea cores
[Rossand Degens,1974; Hay et al., 1991; Lyons,1991;Arthur
et al., !994). However,the depositionof theselayers(several
centimeters
to tensof centimetersthick) appearsto occurwith
little or no erosionas evidencedby the lack of anydisruptionof
the conditionsthat favor chemicalpreservationof calcium carbonatein the Black Sea basin [Shimkusand Trimonis, 1974;
Hay, 1988]. The amountof opalinesilica and POC within the
fluff layer will vary intra-annuallyasthe deliveryrateor flux of
thesematerialsfluctuatesseasonallyand as they are subjectto
dissolutionand degradationprocessesupon reachingthe sediment-waterinterface. In thismanner,the fluff layer'scomposition is geochemicallytransitionalon a seasonalbasisdependent
uponthe seasonaldeliveryof particulateflux constituents
(i.e.,
relativelyhigheropal followingspringblooms,highercoccolith
carbonatefollowing summer-fallperiods,etc.), but it is a physically permanentfeature of the Black Sea sediment-waterinterface. Heavy or denseaggregatedparticulatematerialwill tend
to settlethroughthe fluff and accumulateat the base,although
fecal pelletsfull of opalinediatom and silicoflagellatematerial
and without a periotrophicmembranemay disintegratequickly
at the sediment-water
interface.The amountof opal accumulating at the baseof the fluff layer will largely be a functionof
whetheror not it is protectedwithin fecalpellets.
On thebasisof ourstudyandthedatingof theuppermost
laminated sediment of unit I recovered in the 1988 box cores
[Arthuret al., 1994]we areableto placethesurfacesediments
and fluff layer into a temporalframeworkrelativeto the seasonalparticulate
flux andtheunderlying
laminated
sediments
of
unit I. In Figure11 we presenta modelof Holocenelaminae
formationusingthe datapresented
in this paper,alongwith
previously
published
BlackSeasediment
trapflux andgravity
coredata. A distinctive
blacklaminalocatedat approximately
the baseof our 2 cm protolaminae
layer,whichwe sampled
beneath
thefluff layer,hasbeendatedat 70 yearspriorto 1988
[Arthuret al., 1994].Thuswepropose
thatthis2 cmprotolaminae layerrepresents
-70 yearsof deposition
priorto our sampling of it in 1988, with an estimatedsedimentationrate of 28
laminaecoupletchronology
[Arthuret al., 1994]. Thusthefluff
cm kyr-•. Thisratecompares
reasonably
well withthe
layer must be left relatively undisturbedand/or becomereestab-
sedimentation
ratesreportedby Hay [1998] andArthuret aI.
lishedimmediatelyfollowing the low-energyeraplacement
of
theselayers. Supportfor this scenariocomesfromthe observation thatmanyof the box coresobtainedin 1988 sampledthick,
well-developedfluff layers immediatelyoverlying a finegrained,gray "turbiditc"layerof severalcentimeters
thickness
[Honjoet aI., 1988;Lyons,199! ].
The fluff layer collected in 1988 consistsof spring-
[1994]rangingfrom 20 to 27 cm kyr-•. Thusthe heavy,
aggregated,and/or pellet-protectedseasonalparticle flux
components
will settlethroughthe fluff layerandaccumulate
at
thebase,formingthe protolaminae.
Earlydiagenetic
processes
of POCoxidation
andopaldissolution
will alterthegeochemical
and microfossilcontentsof these protolaminaeas they
accumulateand are buried. Pelletsor aggregates
settling
produced,
biogenicopalparticles
anda notablehighabundance throughthefluff layermayshedsmallcoccoliths,
clayminerals,
of singlecoccoliths
and clay particles. Both coccoliths
and
spinosesilicoflagellates,
and diatoms. Thesesmall particles
claysare extremelysmallparticles,only micron-scale
in size,
couldalsobedeliveredindividually
to thebenthicfluff layervia
PILSKALN
ANDPIKE:BLACKS•A LAMINAEANDTHEFLUFFLAYER
17
Black Sea ParticulateSedimentationand LaminaeFormation
Time
Period:
Summer-Fall
Winter-Spring
Water
Resuspension
Coccolithophorid
Silicoflag. High river in-flux
Column'
of coccoliths
blooms
blooms
Diatom/
,
of !ithogenics
.....
and
,
,
h•!fresuspension
&terrigenous
I
material
off
shelf•
BSC 1200 m Trap
50% CaCO3
15% CaCO3
ParticleFlux
10%Lithogenic
(1986-1988
Average 20%BiogenicOpal
Composition*):
20%Lithogenic
50%BiogenicOpal
15% POC
8% POC
<_50% POC
>80% Opal
Remineralized
•
•
Remineralized
•-
•
•
•
•
•
Highbacte
'. •; ":'• • • •1DiatomiSilicofi.
Opal:
6ø/d
I• =Permanent
w/suspended
>80%
Opal
-
'
POC
Dissolved
/
Unit
1'
4%
POC
<1% Opal
65% CaCO3
......
fall coccoli•hs
andclays
Coccolith CaCO3:46%
50%
Remineralized
.- , '
•'
•.'
•
Proto-White
(2-4
cm)
• :'•'"''•1
Lithogenic:33%
oI•Lamina
;i •;;;••ic;fl:-Opai:
4%[• ,*Accumulation
ofhea•/
.• ,' • • POC:
7%
•
•
•
• dense
paKiculates;
represents
•
•
priorto
spring
1988
•. • • • • '•• Laminated
Unit
......
.
1
Sediments
.
' From: Hay. 1988; Hay and Honlo, 1989; Hay et al.. 1990.
Figure
11.Schematic
model
oœ
particulate
sedimentation
and
Holocene
laminac
œormation
intheab;yssal
Black
Sea
based
on
modern
sediment
trapdataandanalyses
o•surface
sediments
andgravity
cores.
magnitude
butshort
duration
fluxevents
such
asalgal
winterresuspension
andlateraloffshore
advection
of shelf- large
might
result
intherap•d
deposition
ofdense
aggregates
deposited
coccoliths
and clays,disintegration
of pelletsor blooms
pellets
thatcould
physically
disrupt
theprevious
seamarine
snow
aggregates
within
thedeep
water
andashedding
of andfecal
protolaminae
atthebase
ofthefluff.This
might
produce
opaline
andcalcareous
components,
orviaindividual
sinking
of son's
discontinuous
horizontal
structure
ofsome
individfrustules
through
thewatercolumn.
Those
particles
notsubject theobserved
ual
lamina
and
a
partial
disruption
of
the
laminae
chronology.
torapiddissolution
ordegradation
willremain
intheflufflayer
thatcomplete
couplets
maynotbedeposited
assemipermanent
components.
Individual
coccoliths
andplaty Thepossibility
every
year
because
of
the
occasional
lack
ofacoccolithophore
clayminerals
appear
to bethemostabundant
semipermanent
makes
light/dark
laminae
counts
problematic
andfurther
components
of thefluff layeraswellasconsistent
components bloom
complicates
the
formation
of
the
ideal
laminated
sediment
reoftheprotolaminae
above
theunitI laminated
sediments.
Theidealsedimentological
consequence
of theaboveproc- cord in the Black Sea.
esses
is the formation
of a thick,lightandthin,darklaminae 4.5. LaminaeFormationin BlackSeaUnit II
couplet
orvarve
peryear.In reality,
interannual
variability
in
themagnitude
ofphytoplankton
blooms
andriverrunoff
leads
to
thedocumented
variations
in therelativethickness
of individual
lamina
fromyeartoyear.Additionally,
it ispossible
thatvery
We propose
fortheunitII sapropel
a similarscenario
of
laminae
couplet
formation
androleof theflufflayerasforunit
I. BSEIanalyses
of unitsI andII laminae
revealthatalthough
!$
PILSKALNAND PIKE:BLACKSEALAMINAEANDTHEFLUFFLAYER
theyaredifferent
in macroscopic
appearance
andcomposition lets)andPOMexportlevelswererelatively
smaller
[Sorokin,
(unitII hasnococcolith-CaCO•
andunitII brightlaminae
are 1983]. If the scenarioaboveis correct,thesummer-falllaminae
thinner
thanthewhite,coccolith-rich
laminae
of unitI), the mightcontain
some
diatom
fragments
butwould
consist
largely
overallmicroscopic
sedimentfabricsof thetwo unitsaresimilar.
of dinoflagellate
and amorphous
organicdebrisas our BSEI
Botharetypifiedby thick,laterallycontinuous
light-colored analyses
haveshown.Therefore,
assuggested
by Hayet al.
laminae
witha pinch-and-swell
character
anda backscatter
sig- [1990],thelightanddarklaminae
ofunitII, likeunitI, represent
nal thatmakesthemappearlightcoloredor white. In between the depositional
products
of contrasting
seasons
andassociated
thesebrightlaminaeare the dark,thinner,morediscontinuous plankton
blooms,
withpostdepositional
dissolution
of opaland
laminaewith a wavy characterand a weak BSEI backscatter organic
carbonremineralization
producing
a predominantly
signal.The light-colored
laminaeof unit II havea coalesced
and
terrigenous
andlithogenic
laminaecomposition.
noncoalesced
pellet-shapecharactersimilarto the thick white
laminaeof unitI, suggesting
thattheyare alsocomposed
of
primarily
zooplankton
fecalpellets
andfecalaggregates.
The seasonal
representation
of the unitII laminae
maybe
differentthanthathypothesized
for the laminaeof unit I. We
speculate
thatthehighest
seasonal
POCfluxesoccurring
during.
thetimeof unitII deposition
wereconcentrated
duringspring
diatombloomperiods(especially
between5 and3 ka, when
elevatedorganiccarbonaccumulation
ratesin unit II havebeen
attributed
to highlevelsof primaryproductivity)
[Hay, 1988;
Hay et al., 1990]. Siliceous
diatomandsilicoflagellate
material
waspackaged
intorapidlysettling,POC-richzooplankton
fecal
pelletsand algalaggregates
in the spring,the latterof which
may have scavengedlarge amountsof suspended
terrigenous/Iithogenic
materialfrom the watercolumn,assuming
riverinputandstormrcsuspension
of shelfsediments
washigh
duringthe winter-spring
period. The light,bulbous
laminaeof
unitII represent
thedepositional
product
of thesefecalpellets
andalgalaggregates.
However,dissolution
lossof themajority
of the pelletandaggregate-bound
opalmaterialcoupled
with
microbialdegradation
of an unknownamountof the organic
matterdeliveredin thepelletsandalgaIaggregates
hasproduced
the largelyterrigenous/lithogenic
composition
of theseunit II
laminae[Hayet al., 1990]. In contrast,
thethinner,darklaminae
of unit II probablyresultedfromsummer-fall
particleexport
whenproduction
wasdominated
by dinoflagellates
(whichtend
to sinkindividually
andrarelyareincorporated
intofecalpel-
5. Conclusions
Resultsof this study provide a hypothesizedmodel of the
temporaland geochemicalrelationshipsbetweenthe seasonal
particleflux, the benthicfluff layer, and underlyingHolocene
unit I sediments.Chemicaltransformations
andparticlehydraulic sortingoccurringin the permanentbenthicfluff layer are
importantprocesses
that are key to understanding
underlying
laminaeformation. The new data presentedhere confirm but
alsorefinethe basicinterpretations
presentedby previousworkers of the paleofiuxeventsresponsiblefor the seasonalvarve
formationin the Black Sea. High-resolutionBSEI examination
of unit I laminaeandgeochemicaland microscopicexamination
of the top 4 cm of sedimentary
materialin the Black Sea indicatesthat seasonalpaleofluxesof zooplanktonfecal pelletsappearto betheprimarymechanism
by whichseasonal
deposition
occursandsiliceousmicrofossilsare preserved.
Acknowledgements. C.H.P. thanks the captain and crew of the
R/V Knorrfor thesuccessful
1988BlackSeaExpedition,acknowledges
NSF grantOCE-8614557for funding,andthanksE. Degens(postmortem), S. Honjo, B. Hay, S. Manganini,J. Broda,J. Muromoto,and V.
Asperfor assistance
at sea/inthe lab and for helpfuland insightfuldiscussions.J.P. gratefullyacknowledges
NERC for her participationon
the 1993 TREDMAR
III R/V Gelendzhik Black Sea cruise and thanks
Kate Davies at SouthamptonOceanographyCentre for drafting assistance. C.H.P. dedicates
thispaperto the memoryofF. D'Escrivan-Hay,
a greatsourceof support,laughter,andfriendship
for manymembers
of
the 1988BlackSeaExpedition.
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