-
AVANT-PROPOS I INTRODUCTION
La rner du Labrador au cours du Quaternaire
rbcent : Avant-propos
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CLAUDE
HILLAIRE-MARCEL,
ANNEDE VERNAL,
MARCLUCOTTE
ET ALFONSO
MUCCI
The Labrador Sea during the late Quaternary:
Introduction
CLAUDE
HILLAIRE-MARCEL,
ANNEDE VERNAL,
AND ALFONSO
MUCCI
MARCLUCOTTE,
Centre de recherche en gkochimie isotopique et en
g.4ochronologie (GEOTOP), Universitd du Qukbec a Montrkal,
C.P. 8888, succursale A, Montrkal, QC H3C 3P8, Canada
Centre de recherche en gkochimie isotopique et en
gkochronologie (GEOTOP), Universite' du Qudbec a Montrdal,
P 0. Box 8888, Station A, Montrkal, QC H3C 3P8, Canada
Recu le 1"' novembre 1993
Rkvision acceptbe le 3 novembre 1993
Received November 1, 1993
Revision accepted November 3, 1993
Can. J. Earth Sci. 31, 1-4 (1994)
La plupart des articles qui suivent prksentent les premiers
rtsultats d'un projet collaboratif spCcial du Conseil de
recherches en sciences naturelles et en gCnie du Canada
(CRSNG). Ce projet visait B reconstituer les conditions
paltoctanographiques et les flux de carbone dans la rner du
Labrador, au cours du Quaternaire rCcent. Bien qu'il ne fasse
pas partie, B proprement parler, du programme canadien
d'ttude des flux octaniques (Joint Global Ocean Flux Study),
le projet se voulait une contribution B cette ttude. En ce sens,
il a paru pertinent de jumeler, dans un mCme numCro, des articles traitant des conditions ocCanographiques actuelles, de la
~Cdimentation et de la diagenkse prCcoce, avec d'autres
travaux abordant les changements octanographiques ou de
productivitk que le bassin a connus au cours du Quaternaire
rCcent.
Un projet canadien concert6 sur la palCoctanographie de la
rner du Labrador se justifiait d'abord parce que celle-ci, au
mCme titre que les autres bassins subarctiques de 1'Atlantique
Nord, joue un r81e important dans la genbse des masses d'eau
intermtdiaire et profonde des octans, par suite, dans la circulation thermohaline gtntrale (Clarke et Gaskard 1983; ,Lazier
1988). La production de ces masses d'eau dtpend ttroitement
des conditions de surface dans les bassins.-~nce sens, les
fonctions de transfert entre les assemblages de dinokystes et
les conditions de tempkrature, de salinitt de la zone photique
et de couvert de glace saisonnier prtsenttes par de vernal
et al. (1994) s'avbrent un outil palCocCanographique inestimable. Rappelons que la rner du Labrador se situe sur la
trajectoire des masses d'eau constitutives de la masse d'eau
profonde de 1'Atlantique Nord (North Atlantic Deep Water).
La masse d'eau de fond, masse d'eau de dCbordement du
dttroit de Danemark (Denmark Strait Overflow Water).
,, issue
de la rner du ~roenland,et la masse d'eau profonde de 1'Atlantique du Nord-Est (North East Atlantic Deep Water), susjacente, provenant de la rner de Norvbge, y conservent une
signature thermohaline propre au cours de leur gyre, comme
l'indiquent les relevts hydrographiques de Lucotte et HillaireMarcel (1994). Les changements passCs et rCcents dans le
dtbit de ces masses d'eau entrainCes par le sous-courant c6tier
profond de l'Ouest (Western Boundary Undercurrent) ont
laisst des empreintes stdimentologiques et microfaunistiques
claires; plusieurs articles du prtsent numkro en donnent des
exemples (Wu et Hillaire-Marcel 1994; Stoner et al. 1994;
Bilodeau et al. 1994).
Printed in Canada 1 lmprime au Canada
Most of the following articles deal with the results of a Collaborative Special Project of the Natural Sciences and
Engineering Research Council of Canada (NSERC). This
project had the objective of simulating the paleoceanographic
conditions and the carbon flux in the Labrador Sea during the
late Quaternary. Although, strictly speaking, it is not part of
the Canadian Joint Global Ocean Flux Study, the project was
intended to contribute to it. In this vein, it was appropriate to
combine, in the same issue, articles dealing with current
oceanographic conditions, sedimentation, and early diagenesis
with other work discussing oceanographic or productivity
changes in the basin during the late Quaternary.
A Canadian project focussing on the paleoceanography of
the Labrador Sea was justified because, in the same way as the
other subarctic basins of the North Atlantic, the Labrador Sea
plays an important role in the genesis of intermediate and deep
ocean waters, and subsequently in the general thermohaline
circulation (Clarke and Gaskard 1983; Lazier 1988). Production of these water masses greatly depends on surface conditions within these basins. In this regard, the research by de
Vernal et al. (1994) on the transfer function between dinocyst
assemblages and water temperature, salinity of the photic
zone, and seasonal ice covers has proven to be an invaluable
paleoceanographic tool. Let us remember that the Labrador
Sea sits in the path of the water masses that make up the North
Atlantic Deep Water. As Lucotte and Hillaire-Marcel (1994)
have demonstrated through hydrographic surveys, its bottom
water mass, the Denmark Strait Overflow Water coming out
of the Greenland Sea, and the layer above, the North East
Atlantic Deep Water originating from the Norwegian Sea,
retain their distinct thermohaline characteristics during their
gyre. Past and recent changes in the flow of these water
masses brought about by the Western Boundary Undercurrent
have left clear sedimentological and microfaunistic imprints;
several articles in this issue provide examples (Wu and
Hillaire-Marcel 1994; Stoner et al. 1994; Bilodeau et al.
1994).
Another peculiarity of the Labrador Sea lies in the fact that it
has provided a link between the great polar ice caps (Inuitian,
Greenland, and northeast sector of the Laurentide Ice Sheet)
and the North Atlantic. Clear isotopic answers therefore characterize the periods of movement of the glacial water melt
through the basin (Hillaire-Marcel et al. 1994~).As articles
by Andrews et al. (1994) and Hillaire-Marcel et al. (1994~)
CAN. J. EARTH
SCI. VOL.
r
31, 1994
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Fraction > 125 Krn (46)
gvbnemeni
de type
Heinrich H,
J
0.8
3
2
0
0
20
y
40
F,
4
3
AMS
2
1
0
I4cAGES
(Corrected by -400 a)
Heinrich
Event HI
*141SOf110
FIG. 1 . Carottage 90-013-013-P au large du Groenland. DBtail de
l'intervalle de 14 - 8 ka BP. La fin du Dryas rBcent (YD) est marquCe
par un appauvrissement de 0,6%, en 180 de Neogloboquadrina
pachydem (1Cvogyre). La fraction granulomBtrique suptrieure i
125 pm marque les anomalies sBdimentologiques associBes aux
Bvbnements de type Heinrich Ho (= Dryas rBcent) et HI (g la base).
SMA, spectromktrie de masse par accC1Crateur.
Une autre ~articularittde la mer du Labrador reside dans le
fait que celle-ci a constitut un lien entre les grandes calottes
glaciaires (inuitienne, groenlandaise et secteur nord-est de
l'inlandsis laurentidien) et 1'Atlantique Nord. Des rtponses
isotopiques tranchtes marquent ainsi les tpisodes de transit
d'eaux de fonte glaciaire dans le bassin (Hillaire-Marcel et al.
1994~).Les stdiments mis en place dans 1'Atlantique Nord,
au cours des tvbnements brefs connus auiourd'hui sous
l'expression Heinrich events (tvbnements de type Heinrich)
(Broecker et al. 1992), sont largement issus des marges
hudsonienne et labradorienne de la mer du Labrador, comme
le dkmontrent les articles de Andrews et al. (1994) et de
Hillaire-Marcel et al. (1994~).
Enfin, et c'est la raison pour laquelle le projet collaboratif
avait t t t mis sur pied, la mer du Labrador constitue un bassin
propice ii la calibration d'indicateurs gtochimiques ou micropaltontologiques de productivitt et de flux de carbone. En
effet, les fortes vitesses de stdimentation observtes dans le
bassin autorisent l'ttablissement de series chronologiques de
bonne rtsolution ( - lo2 ans). En outre, les flux phytoplanctoniques et gtochimiques ont changt de plusieurs ordres de
grandeur, entre le dernier maximum glaciaire et le prtsent.
Ainsi trouvera-t-on, dans plusieurs articles du prtsent numtro,
des informations nouvelles sur le comportement de divers
traceurs gtochirniques et micropaltontologiques, B l'interface
eau-stdiment et au cours de la diagenbse prtcoce (e.g.,
Garitpy et al. 1994; Lucotte et al. 1994; Rochon et de Vernal
1994), ainsi qu'un essai de reconstitution des palkoflux de carbone au cours du dernier sous-cycle climatique (HillaireMarcel et al. 1994b).
Htlas, le prtsent numtro a dfi Ctre mis sous presse sans que
plusieurs contributions compltmentaires de l'tquipe puissent
Ctre incluses. Ainsi, les processus diagtnetiques prtcoces
sont-ils mal illustrts en l'absence de donntes sur la stabilitt
460
1
'141SOf110
FIG.1. Core 90-013-013-P off Greenland. Details of the 14 - 8 ka
BP interval. The end of the Younger Dryas (YD) shows a O.6%,drop
in the "0 content of Neogloboquadrina p a c h y d e m (left-coiling).
The grain-size fraction above 125 pm identifies the sedimentological
anomalies associated with the Heinrich Ho ( = Younger Dryas) and
H , (at the base) events. AMS, accelerator mass spectrometry.
demonstrate, sediments deposited in the North Atlantic during
the brief events known today as Heinrich events (Broecker et al.
1992) are largely drawn from the Hudson and Labrador margins of the Labrador Sea.
Finally, and this is the reason why the Collaborative Special
Project was launched in the first place, the Labrador Sea is a
basin that lends itself to the calibration of geochemical or
micropaleontological indicators of productivity and carbon
flux. Indeed, the high sedimentation rates in the basin allow
the establishment of chronological series with good resolution
( lo2years). In addition, the phytoplanktonic and geochemical fluxes have changed appreciably between the last glacial
maximum and the present one. Several articles in this issue
provide new information on the behavior of various geochemical and micropaleontological markers at water - sediment
interface and during early diagenesis (e.g., Garitpy et al.
1994; Lucotte et al. 1994; Rochon and de Vernal 1994),
another attempts to simulate the carbon paleoflux during the
last climatic subcycle (Hillaire-Marcel et al. 1994b).
Unfortunately, this issue had to go to print without several
complementary contributions from the team. Consequently,
the early diagenetic processes are poorly illustrated because of
the lack of data relating to the stability of carbonates or the
geochemistry of certain major elements. Similarly, we could
not include studies based on continuous subsampling (at 1 cm
intervals) of the major deep sea cores without undue delays in
the release of this issue. Yet only the chronological series with
such a resolution will allow us to establish unequivocal correlations between the Labrador Sea cores and those of the
Greenland ice cap (Dansgaard et al. 1993) or to show the short
duration of certain oceanographic changes. The end of the
Younger Dryas, shown in Fig. 1, constitutes an example: it is
marked by a drastic drop (within 1 cm, i.e., in less than 30
years) of 0.6%, in the 180content of the planktonic foraminifers.
-
3
Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Peking University on 06/04/13
For personal use only.
HILLAIRE-MARCEL ET AL.
des carbonates o u la gCochimie d e certains elements majeurs.
D e f a ~ o nsimilaire, les Ctudes a maille centimktrique des principales carottes d e forage n e pouvaient Ctre prCsentCes sans
retarder indilment la publication du n u m b o . Pourtant, seules
les d r i e s chronologiques B maille centimktrique permettront
d1Ctablir des corrClations univoques entre les carottes d e
forage d e la mer du Labrador et celles d e la calotte glaciaire
groenlandaise (Dansgaard et al. 1993) o u d e mettre e n Cvidence la brikvetC d e certains changements ocCanographiques.
L a fin du Dryas rCcent, illustree e n figure 1, e n est u n
exemple : elle est marqute par une diminution brutale (sur
1 c m soit e n moins d e 30 ans) et d e O,6%, des teneurs e n 1 8 0
des foraminiferes planctoniques .
Remerciements
Toutes les campagnes octanographiques B l'origine des
articles du prCsent n u m t r o ont CtC rCalisCes sur le CSS
Hudson ; l'importante moisson scientifique doit ainsi beaucoup
a u dCvouement d e ses officiers et d e son Cquipage. L e s o u t i 6
d e PCches et Octans Canada, e n terme d e temps-navire, et
celui du Centre gkoscientifique d e l'Atlantique, pour l'organisation matCrielle des campagnes, mCritent d'Ctre soulignCs. E n
laboratoire, l e personnel d u G E O T O P d e 1'UniversitC d u
QuCbec B MontrCal (UQAM) et celui d'IsoTrace, h l'universitk
d e Toronto, ont apportC u n concours analytique exceptionnel.
L e projet collaboratif sur la mer d u Labrador a reCu une subvention spCciale d u CRSNG; il a CtC Cgalement financC par le
Fonds pour la formation d e chercheurs et l'aide B la recherche
du Qukbec et a bCnCficiC des subventions d'infrastructure d e
la Chaire d e recherche e n environnement Hydro-QuCbecCRSNG -UQAM.
Andrews, J.T., Tedesco, K., Briggs, W.M., et Evans, L.W. 1994.
Sediments, sedimentation rates, and environments, southeast
Baffin Shelf and northwest Labrador Sea, 8 - 26 ka. Revue canadienne des sciences de la Terre, 31: 90- 103.
Bilodeau, G., de Vernal, A., et Hillaire-Marcel, C. 1994. Benthic
foraminiferal assemblages in Labrador Sea sediments: relations
with deep-water mass changes since deglaciation. Revue canadienne des sciences de la Terre, 31: 128-138.
Broecker, W.S., Bond, G., McManus, J., Klas, M., et Clark, E.
1992. Origin of the Northern Atlantic's Heinrich events. Climate
Dynamics, 6 : 265-273.
Clarke, R.A., et Gaskard, J.-C. 1983. The formation of Labrador
Sea water. Part 1: Large scale processes. Journal of Physical
Oceanography, 13 : 1764 - 1778.
Dansgaard, W., Johnsen , S.J., Clausen, H.B., Dahl-Jensen, D.,
Gundestrup, N.S., Hammer, C.U., Hviberg, C.S., Steffensen,
J.P., Sveinbjornsdottir, A.E., Jouzel, J., et Bond, G. 1993.
Evidence for general instability of past climate from a 250-kyr icecore record. Nature (London), 364 : 218 -220.
de Vernal, A,, Turon, J.-L., et Guiot, J. 1994. Dinoflagellate cyst
distribution in high-latitude marine environments and quantitative
reconstruction of sea-surface salinity, temperature, and seasonality. Revue canadienne des sciences de la Terre, 31: 48-62.
GariCpy, C., Ghaleb, B., Hillaire-Marcel, C., Mucci, A., et
Vallikres, S. 1994. Early diagenetic processes in Labrador Sea
sediments: uranium-isotope geochemistry. Revue canadienne des
sciences de la Terre, 3 1 : 28 -37.
Hillaire-Marcel, C., de Vernal, A , , Bilodeau, G., et Wu, G. 1994a.
Isotope stratigraphy, sedimentation rates, deep circulation, and
carbonate events in the Labrador Sea during the last -200 ka.
Revue canadienne des sciences de la Terre, 31: 63-89.
Hillaire-Marcel, C., de Vernal, A,, Lucotte, M., Mucci, A,,
Bilodeau, G., Rochon, A,, Vallikres, S., et Wu, G. 1994b.
ProductivitC et flux de carbone dans la mer du Labrador au cours
Acknowledgments
All oceanographic work in support of the articles contained
in this issue were carried out o n the CSS Hudson; much praise
is due, therefore, to its officers and crew for their contributions to the collection of valuable scientific information. The
support of Fisheries and Oceans Canada, in terms of ship time,
and of the Atlantic Geoscience Centre for its logistics support
in organizing the research campaigns must b e mentioned. The
staffs of the GEOTOP, at the UniversitC d u QuCbec h MontrCal
(UQAM), and of IsoTrace, at the University of Toronto, must
b e commended for their exceptional analytical input. T h e
study o n the Labrador Sea received a collaborative Special
Project award from NSERC as well as financing from the
Fonds pour la formation d e chercheurs et l'aide B la recherche
of Quebec. The project also benefitted from the infrastructure support of the Chaire d e recherche e n environnement
Hydro-QuCbec - CRSNG - UQAM.
Andrews, J.T., Tedesco, K., Briggs, W.M., and Evans, L.W. 1994.
Sediments, sedimentation rates, and environments, southeast
Baffin Shelf and northwest Labrador Sea, 8 -26 ka. Canadian
Journal of Earth Sciences, 31: 90- 103.
Bilodeau, G., de Vernal, A., and Hillaire-Marcel, C. 1994. Benthic
foraminiferal assemblages in Labrador Sea sediments: relations
with deep-water mass changes since deglaciation. Canadian Journal of Earth Sciences, 31: 128- 138.
Broecker, W.S., Bond, G., McManus, J., Klas, M., and Clark, E.
1992. Origin of the Northern Atlantic's Heinrich events. Climate
Dynamics, 6: 265 -273.
Clarke, R.A., and Gaskard, J.-C. 1983. The formation of Labrador
Sea water. Part 1: Large scale processes. Journal of Physical
Oceanography, 13: 1764 - 1778.
Dansgaard, W., Johnsen, S.J., Clausen, H.B., Dahl-Jensen, D.,
Gundestrup, N.S., Hammer, C.U., Hviberg, C.S., Steffensen,
J.P., Sveinbjornsdottir, A.E., Jouzel, J., and Bond, G. 1993. Evidence for general instability of past climate from a 250-kyr icecore record. Nature (London), 364: 218 -220.
de Vernal, A , , Turon, J.-L., and Guiot, J. 1994. Dinoflagellate cyst
distribution in high-latitude marine environments and quantitative
reconstruction of sea-surface salinity, temperature, and seasonality. Canadian Journal of Earth Sciences, 31: 48 -62.
Garikpy, C., Ghaleb, B., Hillaire-Marcel, C., Mucci, A., and
Vallikres, S. 1994. Early diagenetic processes in Labrador Sea
sediments: uranium-isotope geochemistry. Canadian Journal of
Earth Sciences, 31: 28-37.
Hillaire-Marcel, C., de Vernal, A., Bilodeau, G., and Wu, G.
1994a. Isotope stratigraphy, sedimentation rates, deep circulation,
and carbonate events in the Labrador Sea during the last - 200 ka.
Canadian Journal of Earth Sciences, 31: 63-89.
Hillaire-Marcel, C., de Vernal, A,, Lucotte, M., Mucci, A.,
Bilodeau, G., Rochon, A., Vallikres, S., and Wu, G. 1994b.
ProductivitC et flux de carbone dans la mer du Labrador au cours
des derniers 40000 ans. Canadian Journal of Earth Sciences, 31:
139-158.
Lazier, J.R. 1988. Temperature and salinity changes in the deep
Labrador Sea, 1962 - 1986. Deep Sea Research, 35: 1247 - 1253.
Lucotte, M., and Hillaire-Marcel, C. 1994. Identification et distribution des grandes masses d'eau dans les mers du Labrador et
d'Irminger . Canadian Journal of Earth Sciences, 31: 5 - 13.
Lucotte, M., Mucci, A., Hillaire-Marcel, C., and Tran, S. 1994.
Early diagenetic processes in deep Labrador Sea sediments: reactive and nonreactive iron and phosphorus. Canadian Journal of
Earth Sciences, 31: 14-27.
Rochon, A., and de Vernal, A. 1994. Palynomorph distribution in
Recent sediments from the Labrador Sea. Canadian Journal of
Earth Sciences, 31: 115 - 127.
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For personal use only.
4
CAN. J. EARTH SCI. VOL. 31, 1994
des derniers 40000 ans. Revue canadienne des sciences de la
Terre, 31 : 139-158.
Lazier, J.R. 1988. Temperature and salinity changes in the deep
Labrador Sea, 1962- 1986. Deep Sea Research, 35 : 1247- 1253.
Lucotte, M., et Hillaire-Marcel, C. 1994. Identification et distribution des grandes masses d'eau dans les mers du Labrador et
d'Irminger. Revue canadienne des sciences de la Terre, 31 : 5 - 13.
Lucotte, M., Mucci, A,, Hillaire-Marcel, C., et Tran, S. 1994. Early
diagenetic processes in deep Labrador Sea sediments: reactive and
nonreactive iron and phosphorus. Revue canadienne des sciences
de la Terre, 31 : 14-27.
Rochon, A., et de Vernal, A. 1994. Palynomorph distribution in
Recent sediments from the Labrador Sea. Revue canadienne des
sciences de la Terre, 31 : 115- 127.
Stoner, J.S., Channell, J.E.T., Hillaire-Marcel, C., et Mareschal,
J.-C. 1994. High-resolution rock magnetic study of a Late Pleistocene core from the Labrador Sea. Revue canadienne des sciences
de la Terre, 31 : 104- 114.
Wu, G., et Hillaire-Marcel, C. 1994. Accelerator mass spectrometry
radiocarbon stratigraphies in deep Labrador Sea cores: paleoceanographic implications. Revue canadienne des sciences de la
Terre, 31 : 38-47.
Stoner, J.S., Channell, J.E.T., Hillaire-Marcel, C., and Mareschal,
J.-C. 1994. High-resolution rock magnetic study of a Late Pleistocene core from the Labrador Sea. Canadian Journal of Earth
Sciences, 31: 104-114.
Wu, G . , and Hillaire-Marcel, C. 1994. Accelerator mass spectrometry radiocarbon stratigraphies in deep Labrador Sea cores: paleoceanographic implications. Canadian Journal of Earth Sciences,
31: 38-47.