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- AVANT-PROPOS I INTRODUCTION La rner du Labrador au cours du Quaternaire rbcent : Avant-propos Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Peking University on 06/04/13 For personal use only. 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 Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Peking University on 06/04/13 For personal use only. 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. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Peking University on 06/04/13 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.