- Email: [email protected]
Early deglaciation of the Greenland Sea during the last glacial to interglacial transition — Reply
169
reader the impression that this core was collected from a particularly cold m o d e m environment. In fact, it was collected close to the modern boundary between polar and subpolar watermasses and is in no way typical of the cold Greenland Sea. I thank F. Grousset for providing apreprint of his paper with J.C. Duplessy, J.C. Duplessy for discussing the results from KS 7707 prior to publication, and D.E. Kellogg for criticising drafts of this manuscript. Financial support was provided by National Science Foundation Grant DPP80-20000.
REFERENCES Denton, G.H. and Hughes, T.J., 1981. The Arctic Ice Sheet; an outrageous hypothesis. In: G.H. Denton and T.J. Hughes (Editors), The Last Great Ice Sheets. Wiley, N e w York, N.Y., pp.437--467. Denton, G.H. and Hughes, T.J., 1983. Milankovitch Theory of Ice Ages: hypothesis of ice-sheet linkage between regional insolation and global climate. Quat. Res., 20: 125-144. Duplessy, J.-C., Delibrias, G., Pujol, C. and Duprat, J., 1981. Deglacial warming of the northeastern Atlantic Ocean: correlation with the paleoclimatic evolution of the European continent. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35: 121--144. Fillon, R.H. and Harmes, R.A., 1982. Northern Labrador shelf glacial chronology and depositional environments. Can. J. Earth Sci., 19: 162--192. Grousset, F. and Duplessy, J.C., 1983. Early deglaciation of the Greenland Sea during the last glacial to interglacial transition. Mar. Geol., 52: M11--M17. Kellogg, T.B., 1975. Late Quaternary climatic changes in the Norwegian and Greenland Seas. In: G. Weller and S.A. Bowling (Editors), Climate of the Arctic. University of Alaska, Fairbanks, Alaska, pp.3--36. Kellogg, T.B., 1976. Late Quaternary climatic changes evidence from deep-sea cores of Norwegian and Greenland Seas. Geol. Soc. Am. Mere., 145: 77--110. Kellogg, T.B., 1980. Paleoclimatology and paleo-oceanography of the Norwegian and Greenland Seas: glacial--interglacial contrasts. Boreas, 9 : 115--137. Ruddiman, W.F. and McIntyre, A., 1981. The North Atlantic Ocean during the last deglaciation. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35 : 145--214. Vilks, G. and Muddle, P.J., 1978. Early deglaciation of the Labrador Shelf. Science, 202: 1181--1183.
EARLY DEGLACIATION OF THE GREENLAND SEA DURING THE LAST GLACIAL TO INTERGLACIAL TRANSITION -- REPLY
F. G R O U S S E T
and J.C. D U P L E S S Y
Institut de G~ologie du Bassin d 'Aquitaine, Universit~ de Bordeaux I, 351 Cours de la Liberation, 33405 Talence C}dex (France) Centre des Faibles Radioactivit~s, Laboratoire Mixte CNRS-CEA, Parc du CNRS, 91190 Gif-sur-Yvette (France)
(Received February 10, 1984; accepted for publication March 19, 1984)
170
Kellogg (1985, this volume) challenges our interpretation of the variations of clay mineralogy and trace elements in core KS 7707 as an indication that summer melting of sea ice began as early as 18,000 yrs B.P. at the core location. He suggests rather that the shift from smectite before the tast glacial m a x i m u m (oxygen isotope stage 3 and early stage 2) to a combination of illite, kaolinite and chlorite after the last glacial maximum (upper part of stage 2 and stage 1) could be due to a gradual increase in the advection of the North Atlantic water to the Norwegian Sea. Thus, according to him, the deglaciation process would start from the south and icebergs, which bring the detrital sediments to core KS 7707, would move northward into the Norwegian/Greenland Sea. Such icebergs would carry and progressively release clay minerals derived mainly from the erosion of the North American shield. This contrasts with our interpretation which requires that icebergs drift southward and therefore carry continental material to the south from the high-latitude lands of Greenland or/and Scandinavia. While Kellogg's suggestion provides an interesting alternative to our discussion of the data, recent studies of 87Sr/S6Sr ratio in the non-carbonate bulk sediment in core KS 7707 (Ferragne et al., 1984) seem to favor our interpretation. Rocks and softs from Scandinavia and Greenland have 87Sr/S6Sr ratios greater than those of the North American continent (see Table I for a summary o f data from literature). At the location of core KS 7707, a n o t i c e able fraction of the clay minerals is derived from weathering of the Icelandic rocks. The smectites derived from those basalts have a relatively low 87Sr/86Sr ratio (Table I). Ferragne et al. (1984) have analyzed six samples in core KS 7707 (Table II). Since the carbonate-free bulk sediment is a mixture o f sialic material originating from the continents and mafic material originating from TABLE I 8VSr/~Sr of soils and rocks from the continents bordering the North Atlantic Ocean and from Iceland Location
87Sr/a6Sr averages
Authors
Canadian shield
0.725
Faur~ et at., 1963
North American shales
0.722
Faur~ and Hurley, 1960
>0.743
Springer, 1981 Rex and Gradhill, 1981
Northeast Greenland soils and rocks North Iceland Tertiary b a ~ l t s North Iceland Quaternary basalts North Iceland Quaternary soils Icelandic thermal brines
0.7033 0.7031 0.7030 0.7043
O'Nions and Pankhurst, 1974 White et al., 1978 Hart et al., 1973 Clatter and Olafsson, 1982
Spitzberg rocks
0.708-0.710
Lussiaa-Berdou-Potve and Vidal, 1973
Jan Mayen rocks
0.7034
Lussiaa-Berdou-Polve and Vidal, 1973
Scandinavia
>0.729
Priem et al., 1973
171 TABLE II
Theoretical estimations of 878r/~Sr continental values Levels Continental mineral (cm) contents (%) C% (rain)
22 72 122 172 222 372
25 11 35 42 1 7
C'% (max)
28 26 43 48 19 23
Icelandic mineral contents (%) I% (max)
75 89 65 58 99 93
I% (rain)
72 74 57 52 81 77
avSrlsSr bulk sediment values
Theoretical estimations of a~Sr/~Sr continental values
(Ferragne et al., 1984)
max
min
0.70815 0.70665 0.71979 0.72312 0.70476 0.70530
0.723 0.736 0.751 0.753 0.718 0.737
0.721 0.717 0.742 0.745 0.712 0.713
(c)
(c')
Iceland, the STSr/Sesr ratio of the continental sialic fraction may be calculated from 8~Sr/Sesr ratio of the carbonate-free bulk sediment (Table II), STSr/S6Sr ratio of the Icelandic material (measurements reported in Table I) and percentage of the Icelandic material in the bulk sediment. Upper limit and lower limits of this percentage can be estimated from mineralogical analysis of core KS 7707. Illite, chlorite, kaolinite and quartz are the weathering products of sialic continental material, whereas smectites are a weathering p r o d u c t of Icelandic basic material. Plagioclase feldspars, on the other hand, may be either of Icelandic or continental origin. In Table II, we assign an upper limit for the Icelandic mineral content of the sediment in core KS 7707 by assuming that all the plagioclase feldspar came from Iceland and a lower limit for the Icelandic mineral content by assuming that all the plagioclase feldspars came from the continents. Using these values, we then calculated a lower and an upper limit for the STSr/SeSr ratio of the continental sialic material (Table If). The two lower levels analyzed in core KS 7707 (222 and 372 cm) were deposited during isotope stage 3. They are composed of almost 100% icelandic material and have the corresponding STSr/S6Sr ratio. Ice-rafted continental material deposited during isotope stage 2 (172 cm) and the beginning of Termination IB (122 cm) have a STSr/S6Sr ratio higher than 0.74, a value which is currently obtained in the Greenland rocks and soils (Table I). The data therefore favor our previous interpretation (Grousset and Duplessy, 1983) that, from 18,000 to 10,000 yrs B.P., icebergs carried continental material to the south from high latitude of Greenland or Scandinavia. After 10,000 yrs B.P., the STSr/Sesr ratio of the continental contribution to core KS 7707 decreases, indicating that the North American shield became a major source for clay minerals brought to the Norwegian Sea sediments by the North Atlantic Drift. Kellogg claims that our interpretation of seasonal ice breakup as early as 18,000 yrs B.P. is n o t supported by the foraminiferal data, because the shift from a polar fauna (100% left-coiling N. pachyderma) to a mixture of this
172 species with subpolar species occurs after the deposition of ash layer 1, a b o u t 9800 yrs ago. This statement rests on a misinterpretation of the ecology of N. pachyderma (left coiling) described by B~ and Tolderlund (1971). As already discussed by Duplessy et al. (1981), the presence of 100% left-coiling N. pachyderma indicates that sea-surface temperatures are lower than 6°C during summer and lower than 0°C during winter. These conditions do not necessarily permit the occurrence of a sea-ice cover during the whole year. We believe that the Norwegian Sea was ice covered year round during the last Ice Age, because this sea was not a source of deep water for the North Atlantic at that time (Duplessy et al., 1975) and a perennial ice cover is the best explanation for a permanent stratification which prevents the sinking of surface water. However, the beginning of sea-ice breakup would correspond to summer sea-surface temperatures much lower than 6 ° C, resulting in no change in the foraminiferal assemblage. Finally, Kellogg suggests that the core studied by Vilks and Muddie (1978) might well have been as young as 10,000 yrs B.P., because of the possibility of contamination by old carbon. In that case, their study does n o t provide any evidence of early deglaciation on the Labrador continental shelf. Perhaps Kellogg is right, but this hypothesis affects neither our observations in core KS 7707 nor the time scale we used, since the latter is derived from the oxygen isotope stratigraphy of core KS 7707. ACKNOWLEDGEMENTS We thank T.B. Kellogg for his discussion which is certainly germane to our understanding o f the mechanism of the last deglaciation. This discussion began during the " N A T O meeting on the last deglaciation: timing and mechanism" held in Virginia in May 1983. We thank A. Ferragne for providing the Sr results prior to their publications and for useful discussions. This study was supported by EEC grant C.L.I.-005F of the European Climate programme community, CNRS, CEA and DGRST, as part of the French "Programme National d ' E t u d e de la Dynamique des Climats". REFERENCES B~, A.W.H. and Tolderlund, D.S., 1971. Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian oceans. In: B.M. Funnel and W,R. Riedel (Editors), The Micropaleontology of Oceans. Cambridge, pp,105--149. Clauer, N, and Olafsson, J., 1982. Icelandic thermal brines with a mantle Sr-Isotopic signature. Mere. Cent. Sedimentol. Geochim. Surface. Duplessy, J.C., Chenouard, L. and Villa,F., 1975. Weyl's theory of glaciationsupported by isotopic study of Norwegian Core Kll. Science, 188: 1208--1209. Duplessy, J.C., Delibrias, G., Turon, J.L., Pujol, C. and Duprat, J., 1981. Deglacial warming of the north eastern Atlantic Ocean. Correlation with the paleoclimatic evolution on the European Continent. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35: 121--144. Faur6, G. and Hurley, P.M., 1960. The ratio 'TSr/SSSr in oceanic and continental basalts. J. Geophys. Res., 66{8): p.2527.
173
Faur~, G., Hurley, P.M. and Fairbairn, H.W., 1963. A n estimate of the isotopic composition of strontium in rocks of the precambrian shield of North America. J. Geophys. Res., 68: 2323--2329. Ferragne, A., Parra, M., Esquevin, J. and Walgenwitz, F., 1984. Strontium isotope system in deep-sea North Atlantic sediments: further understanding of detritalsedimentation during late Quaternary. Isot. Geosci., in press. Grousset, F. and Duplessy, J.C., 1983. Early deglaciation of the Greenland sea during the last glacialto interglacialtransition.Mar. Geol., 52: Mll--M17. Hart, S.R., Schilling, J.G. and Powell, J.L., 1973. Basalts from Iceland and along the Reykjanes ridge: Sr isotope geochemistry. Nature, 246(155): 104--107. Kellogg, T.B., 1985. Early deglaciation of the Greenland sea during the last glacial to interglacialtransition -- Comment. Mar. Geol., 62:167--169 (thisvolume). Lussiaa-Berdou-Polve, M. and Vidal, P., 1973. Initialstrontium isotopic composition of volcanic rocks from Jan Mayen and Spitsbergen. Earth Planet. Sci. Lett., 18: 333--338. O'Nions, R.K. and Pankhurst, R.J., 1974. Petrogenic significance of isotope and traceelement variations in volcanic rocks from the Mid-Atlantic Ridge. J. Petrol., 15: 603-634. Priem, H.N.A., Beolrijk,M.A., Hebeda, E.H., Verdumen, E.A. and Verschure, R.M., 1973. Rb, Sr investigationson Precambrian granites,granitic gneisses and acidic metavolcanics in central Telemark (Norway). Metamorphic nesetting of Rb--Sr whole rock systems. Norg. Geol. Unders., 289: 37--53. Rex, D.C. and Gradhill, A.R., 1981. Isotopic studies in the East Greenland caledonide (72--74°N) Precambrian and Caledonian ages. Rapp. Gr~bnl. Geol. Unders., 104: 47--72. Springer, N., 1981. Preliminary Rb--Sr ages determinations from the North Greenland fold belt (Yohanes and Yansen land), with comments on the metamorphic grade. Rapp. Gr~bnl. Geol. Unders., 196: 77--84. Vilks, G. and Muddle, P.J., 1978. Early deglaciation of the Labrador shelf. Science, 202: 1181--1183. White, W.M. and Schilling, J.G., 1978. The Nature and origin of geochemical variation in Mid-Atlantic Ridge basalts from Central North Atlantic. Geochim. Cosmochim. Acta, 42(10): 1501--1516.
reader the impression that this core was collected from a particularly cold m o d e m environment. In fact, it was collected close to the modern boundary between polar and subpolar watermasses and is in no way typical of the cold Greenland Sea. I thank F. Grousset for providing apreprint of his paper with J.C. Duplessy, J.C. Duplessy for discussing the results from KS 7707 prior to publication, and D.E. Kellogg for criticising drafts of this manuscript. Financial support was provided by National Science Foundation Grant DPP80-20000.
REFERENCES Denton, G.H. and Hughes, T.J., 1981. The Arctic Ice Sheet; an outrageous hypothesis. In: G.H. Denton and T.J. Hughes (Editors), The Last Great Ice Sheets. Wiley, N e w York, N.Y., pp.437--467. Denton, G.H. and Hughes, T.J., 1983. Milankovitch Theory of Ice Ages: hypothesis of ice-sheet linkage between regional insolation and global climate. Quat. Res., 20: 125-144. Duplessy, J.-C., Delibrias, G., Pujol, C. and Duprat, J., 1981. Deglacial warming of the northeastern Atlantic Ocean: correlation with the paleoclimatic evolution of the European continent. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35: 121--144. Fillon, R.H. and Harmes, R.A., 1982. Northern Labrador shelf glacial chronology and depositional environments. Can. J. Earth Sci., 19: 162--192. Grousset, F. and Duplessy, J.C., 1983. Early deglaciation of the Greenland Sea during the last glacial to interglacial transition. Mar. Geol., 52: M11--M17. Kellogg, T.B., 1975. Late Quaternary climatic changes in the Norwegian and Greenland Seas. In: G. Weller and S.A. Bowling (Editors), Climate of the Arctic. University of Alaska, Fairbanks, Alaska, pp.3--36. Kellogg, T.B., 1976. Late Quaternary climatic changes evidence from deep-sea cores of Norwegian and Greenland Seas. Geol. Soc. Am. Mere., 145: 77--110. Kellogg, T.B., 1980. Paleoclimatology and paleo-oceanography of the Norwegian and Greenland Seas: glacial--interglacial contrasts. Boreas, 9 : 115--137. Ruddiman, W.F. and McIntyre, A., 1981. The North Atlantic Ocean during the last deglaciation. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35 : 145--214. Vilks, G. and Muddle, P.J., 1978. Early deglaciation of the Labrador Shelf. Science, 202: 1181--1183.
EARLY DEGLACIATION OF THE GREENLAND SEA DURING THE LAST GLACIAL TO INTERGLACIAL TRANSITION -- REPLY
F. G R O U S S E T
and J.C. D U P L E S S Y
Institut de G~ologie du Bassin d 'Aquitaine, Universit~ de Bordeaux I, 351 Cours de la Liberation, 33405 Talence C}dex (France) Centre des Faibles Radioactivit~s, Laboratoire Mixte CNRS-CEA, Parc du CNRS, 91190 Gif-sur-Yvette (France)
(Received February 10, 1984; accepted for publication March 19, 1984)
170
Kellogg (1985, this volume) challenges our interpretation of the variations of clay mineralogy and trace elements in core KS 7707 as an indication that summer melting of sea ice began as early as 18,000 yrs B.P. at the core location. He suggests rather that the shift from smectite before the tast glacial m a x i m u m (oxygen isotope stage 3 and early stage 2) to a combination of illite, kaolinite and chlorite after the last glacial maximum (upper part of stage 2 and stage 1) could be due to a gradual increase in the advection of the North Atlantic water to the Norwegian Sea. Thus, according to him, the deglaciation process would start from the south and icebergs, which bring the detrital sediments to core KS 7707, would move northward into the Norwegian/Greenland Sea. Such icebergs would carry and progressively release clay minerals derived mainly from the erosion of the North American shield. This contrasts with our interpretation which requires that icebergs drift southward and therefore carry continental material to the south from the high-latitude lands of Greenland or/and Scandinavia. While Kellogg's suggestion provides an interesting alternative to our discussion of the data, recent studies of 87Sr/S6Sr ratio in the non-carbonate bulk sediment in core KS 7707 (Ferragne et al., 1984) seem to favor our interpretation. Rocks and softs from Scandinavia and Greenland have 87Sr/S6Sr ratios greater than those of the North American continent (see Table I for a summary o f data from literature). At the location of core KS 7707, a n o t i c e able fraction of the clay minerals is derived from weathering of the Icelandic rocks. The smectites derived from those basalts have a relatively low 87Sr/86Sr ratio (Table I). Ferragne et al. (1984) have analyzed six samples in core KS 7707 (Table II). Since the carbonate-free bulk sediment is a mixture o f sialic material originating from the continents and mafic material originating from TABLE I 8VSr/~Sr of soils and rocks from the continents bordering the North Atlantic Ocean and from Iceland Location
87Sr/a6Sr averages
Authors
Canadian shield
0.725
Faur~ et at., 1963
North American shales
0.722
Faur~ and Hurley, 1960
>0.743
Springer, 1981 Rex and Gradhill, 1981
Northeast Greenland soils and rocks North Iceland Tertiary b a ~ l t s North Iceland Quaternary basalts North Iceland Quaternary soils Icelandic thermal brines
0.7033 0.7031 0.7030 0.7043
O'Nions and Pankhurst, 1974 White et al., 1978 Hart et al., 1973 Clatter and Olafsson, 1982
Spitzberg rocks
0.708-0.710
Lussiaa-Berdou-Potve and Vidal, 1973
Jan Mayen rocks
0.7034
Lussiaa-Berdou-Polve and Vidal, 1973
Scandinavia
>0.729
Priem et al., 1973
171 TABLE II
Theoretical estimations of 878r/~Sr continental values Levels Continental mineral (cm) contents (%) C% (rain)
22 72 122 172 222 372
25 11 35 42 1 7
C'% (max)
28 26 43 48 19 23
Icelandic mineral contents (%) I% (max)
75 89 65 58 99 93
I% (rain)
72 74 57 52 81 77
avSrlsSr bulk sediment values
Theoretical estimations of a~Sr/~Sr continental values
(Ferragne et al., 1984)
max
min
0.70815 0.70665 0.71979 0.72312 0.70476 0.70530
0.723 0.736 0.751 0.753 0.718 0.737
0.721 0.717 0.742 0.745 0.712 0.713
(c)
(c')
Iceland, the STSr/Sesr ratio of the continental sialic fraction may be calculated from 8~Sr/Sesr ratio of the carbonate-free bulk sediment (Table II), STSr/S6Sr ratio of the Icelandic material (measurements reported in Table I) and percentage of the Icelandic material in the bulk sediment. Upper limit and lower limits of this percentage can be estimated from mineralogical analysis of core KS 7707. Illite, chlorite, kaolinite and quartz are the weathering products of sialic continental material, whereas smectites are a weathering p r o d u c t of Icelandic basic material. Plagioclase feldspars, on the other hand, may be either of Icelandic or continental origin. In Table II, we assign an upper limit for the Icelandic mineral content of the sediment in core KS 7707 by assuming that all the plagioclase feldspar came from Iceland and a lower limit for the Icelandic mineral content by assuming that all the plagioclase feldspars came from the continents. Using these values, we then calculated a lower and an upper limit for the STSr/SeSr ratio of the continental sialic material (Table If). The two lower levels analyzed in core KS 7707 (222 and 372 cm) were deposited during isotope stage 3. They are composed of almost 100% icelandic material and have the corresponding STSr/S6Sr ratio. Ice-rafted continental material deposited during isotope stage 2 (172 cm) and the beginning of Termination IB (122 cm) have a STSr/S6Sr ratio higher than 0.74, a value which is currently obtained in the Greenland rocks and soils (Table I). The data therefore favor our previous interpretation (Grousset and Duplessy, 1983) that, from 18,000 to 10,000 yrs B.P., icebergs carried continental material to the south from high latitude of Greenland or Scandinavia. After 10,000 yrs B.P., the STSr/Sesr ratio of the continental contribution to core KS 7707 decreases, indicating that the North American shield became a major source for clay minerals brought to the Norwegian Sea sediments by the North Atlantic Drift. Kellogg claims that our interpretation of seasonal ice breakup as early as 18,000 yrs B.P. is n o t supported by the foraminiferal data, because the shift from a polar fauna (100% left-coiling N. pachyderma) to a mixture of this
172 species with subpolar species occurs after the deposition of ash layer 1, a b o u t 9800 yrs ago. This statement rests on a misinterpretation of the ecology of N. pachyderma (left coiling) described by B~ and Tolderlund (1971). As already discussed by Duplessy et al. (1981), the presence of 100% left-coiling N. pachyderma indicates that sea-surface temperatures are lower than 6°C during summer and lower than 0°C during winter. These conditions do not necessarily permit the occurrence of a sea-ice cover during the whole year. We believe that the Norwegian Sea was ice covered year round during the last Ice Age, because this sea was not a source of deep water for the North Atlantic at that time (Duplessy et al., 1975) and a perennial ice cover is the best explanation for a permanent stratification which prevents the sinking of surface water. However, the beginning of sea-ice breakup would correspond to summer sea-surface temperatures much lower than 6 ° C, resulting in no change in the foraminiferal assemblage. Finally, Kellogg suggests that the core studied by Vilks and Muddie (1978) might well have been as young as 10,000 yrs B.P., because of the possibility of contamination by old carbon. In that case, their study does n o t provide any evidence of early deglaciation on the Labrador continental shelf. Perhaps Kellogg is right, but this hypothesis affects neither our observations in core KS 7707 nor the time scale we used, since the latter is derived from the oxygen isotope stratigraphy of core KS 7707. ACKNOWLEDGEMENTS We thank T.B. Kellogg for his discussion which is certainly germane to our understanding o f the mechanism of the last deglaciation. This discussion began during the " N A T O meeting on the last deglaciation: timing and mechanism" held in Virginia in May 1983. We thank A. Ferragne for providing the Sr results prior to their publications and for useful discussions. This study was supported by EEC grant C.L.I.-005F of the European Climate programme community, CNRS, CEA and DGRST, as part of the French "Programme National d ' E t u d e de la Dynamique des Climats". REFERENCES B~, A.W.H. and Tolderlund, D.S., 1971. Distribution and ecology of living planktonic foraminifera in surface waters of the Atlantic and Indian oceans. In: B.M. Funnel and W,R. Riedel (Editors), The Micropaleontology of Oceans. Cambridge, pp,105--149. Clauer, N, and Olafsson, J., 1982. Icelandic thermal brines with a mantle Sr-Isotopic signature. Mere. Cent. Sedimentol. Geochim. Surface. Duplessy, J.C., Chenouard, L. and Villa,F., 1975. Weyl's theory of glaciationsupported by isotopic study of Norwegian Core Kll. Science, 188: 1208--1209. Duplessy, J.C., Delibrias, G., Turon, J.L., Pujol, C. and Duprat, J., 1981. Deglacial warming of the north eastern Atlantic Ocean. Correlation with the paleoclimatic evolution on the European Continent. Palaeogeogr., Palaeoclimatol., Palaeoecol., 35: 121--144. Faur6, G. and Hurley, P.M., 1960. The ratio 'TSr/SSSr in oceanic and continental basalts. J. Geophys. Res., 66{8): p.2527.
173
Faur~, G., Hurley, P.M. and Fairbairn, H.W., 1963. A n estimate of the isotopic composition of strontium in rocks of the precambrian shield of North America. J. Geophys. Res., 68: 2323--2329. Ferragne, A., Parra, M., Esquevin, J. and Walgenwitz, F., 1984. Strontium isotope system in deep-sea North Atlantic sediments: further understanding of detritalsedimentation during late Quaternary. Isot. Geosci., in press. Grousset, F. and Duplessy, J.C., 1983. Early deglaciation of the Greenland sea during the last glacialto interglacialtransition.Mar. Geol., 52: Mll--M17. Hart, S.R., Schilling, J.G. and Powell, J.L., 1973. Basalts from Iceland and along the Reykjanes ridge: Sr isotope geochemistry. Nature, 246(155): 104--107. Kellogg, T.B., 1985. Early deglaciation of the Greenland sea during the last glacial to interglacialtransition -- Comment. Mar. Geol., 62:167--169 (thisvolume). Lussiaa-Berdou-Polve, M. and Vidal, P., 1973. Initialstrontium isotopic composition of volcanic rocks from Jan Mayen and Spitsbergen. Earth Planet. Sci. Lett., 18: 333--338. O'Nions, R.K. and Pankhurst, R.J., 1974. Petrogenic significance of isotope and traceelement variations in volcanic rocks from the Mid-Atlantic Ridge. J. Petrol., 15: 603-634. Priem, H.N.A., Beolrijk,M.A., Hebeda, E.H., Verdumen, E.A. and Verschure, R.M., 1973. Rb, Sr investigationson Precambrian granites,granitic gneisses and acidic metavolcanics in central Telemark (Norway). Metamorphic nesetting of Rb--Sr whole rock systems. Norg. Geol. Unders., 289: 37--53. Rex, D.C. and Gradhill, A.R., 1981. Isotopic studies in the East Greenland caledonide (72--74°N) Precambrian and Caledonian ages. Rapp. Gr~bnl. Geol. Unders., 104: 47--72. Springer, N., 1981. Preliminary Rb--Sr ages determinations from the North Greenland fold belt (Yohanes and Yansen land), with comments on the metamorphic grade. Rapp. Gr~bnl. Geol. Unders., 196: 77--84. Vilks, G. and Muddle, P.J., 1978. Early deglaciation of the Labrador shelf. Science, 202: 1181--1183. White, W.M. and Schilling, J.G., 1978. The Nature and origin of geochemical variation in Mid-Atlantic Ridge basalts from Central North Atlantic. Geochim. Cosmochim. Acta, 42(10): 1501--1516.