Norsk Geografisk Tidsskrift – Norwegian Journal of Geography Vol. 56, 56–61. Oslo. ISSN 0029-1951 Radiocarbon-dated Mytilus edulis and Modiolus modiolus from northern Svalbard: climatic implications OTTO SALVIGSEN Salvigsen, O. 2002. Radiocarbon-date d Mytilus edulis and Modiolus modiolus from northern Svalbard: climatic implications. Norsk Geogra sk Tidsskrift–Norwegian Journal of Geography Vol. 56, 56–61. Oslo. ISSN 0029-1951. Eighteen new age determinations on Mytilus edulis shells from northern Svalbard and two new age determinations on Modiolus modiolus shells are presented. Mytilus edulis appeared on the northern coast of Spitsbergen c. 9400 yr BP. Its maximum extension there seems to have been c. 7250 yr BP, which is also indicative of a climatic optimum. The rst nding of Modiolus modiolus shells from northern Spitsbergen is reported, and revealed the age of c. 8300 yr BP, which is also indicative of marine climatic optimum conditions . Mytilus lived at the head of Woodfjorden until at least 5300 yr BP, but it is not possible to date its nal dis- appearance from the northern coast. Mytilus has been absent from large parts of the coasts of Svalbard during the entire Holocene, indicating limited in uence of warm Atlantic water there. Recent reports of living Mytilus edulis on Bjørnøya indicate a probable new occurrence there, and the question about a further immigration to Spitsbergen should be kept in mind. Such a faunistic change may provide data about a more general climatic warming in this part of the Arctic. Keywords: Mytilus, Modiolus, palaeoclimate , radiocarbon dates, Svalbard Otto Salvigsen, Department of Geography, University of Oslo, Postboks 1042 Blindern, NO-0316 Oslo, Norway. E-mail: ottosa@ geogra .uio.no Introduction However, more detailed information from many localities is of course still of great interest. It should also be mentioned The occurrence of raised beach deposits with shells of that Mytilus edulis shells are known from interstadial Mytilus edulis (common mussel) in Svalbard has been known (Eemian) sediments at Kapp Ekholm, central Spitsbergen since 1861 (Blomstrand 1864, Chydnius 1865), when it was (Mangerud & Svendsen 1992, Funder 1993). They are, found in Isfjorden as well as in Sorgfjorden, northernmost however, beyond the scope of this paper. Spitsbergen. Since this is a thermophilous mollusc and not included in the present fauna of Svalbard, the palaeoclimatic implications of its former occurrence have been broadly discussed (see Feyling-Hanssen 1955, Salvigsen et al. 1992, Sampling and age determination Hjort et al. 1995). Most of the dated samples presented in Table 1 were After the introduction of the radiocarbon method for age collected during eldwork in 1995 and 1997. The purpose determination, the number of dated samples of shells steadily of the sampling was to expand the area of dated Mytilus grew, and 34 dates on Mytilus edulis from Svalbard were edulis localities in northern Svalbard. The aim was primarily presented in Salvigsen et al. (1992). Most of them were from to sample the oldest and the youngest shells in a speci c area, the west coast and the central fjord areas of Spitsbergen, respectively the highest lying and the lowest lying shells. showing that Mytilus edulis lived there from before 9500 yr Mytilus shells and shell fragments were found either in situ in BP to c. 3500 yr BP. Thereafter it probably brie y littoral cliff sections, or in raised beach gravel. In most cases, reimmigrated during the ‘Medieval warm period’ c. 1000 large samples were collected and whole shells or large yr BP. Only three dates, all >9000 yr BP, were from the fragments of good quality were sent to the dating laboratory northern coast of Svalbard. Salvigsen et al. (1992) also in Trondheim. The ages, determined by the conventional presented three radiocarbon dates on shells of Modiolus radiocarbon method (except TUa-2191 which is an AMS modiolus (horse mussel) from the shores of Isfjorden, with date), are corrected for a reservoir effect of 440 years ages from c. 8700 yr BP to 7700 yr BP which were supposed (Mangerud & Gulliksen 1975). They have¡also been to indicate a marine climatic optimum in this period. corrected to a d13C = 25% PDB, in most cases by using a 13 ¡ Hjort et al. (1995) presented 11 age determinations on standard value of d C = 1.0 for shells. Mytilus edulis from Edgeøya and one such date from Only ages of radiocarbon years are presented in this study, Svenskøya, Kong Karls Land. They all reveal ages between mostly for practical reasons. The referred literature uses c. 8800 yr BP and 5000 yr BP and roughly delimit the marine radiocarbon years, and comparisons with former studies are climatic optimum period in eastern Svalbard. The coloniza- facilitated by sticking to radiocarbon years. tion of Mytilus in eastern Svalbard was supposed to be an effect of a maximum in ux of Atlantic water to the region. The purpose of this paper is to follow up the information given in Salvigsen et al. (1992) and Hjort et al. (1995) and Results discuss further the matters dealt with there. The paper shows Immigration of Mytilus edulis our present knowledge about the Holocene distribution of Mytilus edulis and Modiolus modiolus in northern Svalbard. Table 1 lists 22 radiocarbon dates on Mytilus edulis, of which # 2002 Taylor & Francis NORSK GEOGRAFISK TIDSSKRIFT 56 (2002) Radiocarbon-date d Mytilus edulis and Modiolus modiolus from northern Svalbard 57 Table 1. Radiocarbon-date d shells of Mytilus edulis and Modiolus modiolus from northern Spitsbergen. Hannevigodde n is located in southern Spitsbergen. The ages show radiocarbon years with one sigma and corrected for a marine reservoir age of 440 years (Mangerud & Gulliksen 1975). ¡ Site Age Lab. no. Field no. m a.s.l. Comments 1. Reinsdyr ya 9375 80 DIC-3076 SL84-33 9 Salvigsen et al. 1992 2. Vogtvatnet 9360 § 110 T-3098 Sa 78-17 8 Salvigsen & O¨ sterholm 1982 3. Mushamna 9335 § 45 T-12236 Sa 95-95 5 Littoral section § 4. GraÊ huken 9295 70 HD15707-15601 SPE-22a 5 Bru¨ckner 1996 5. Sjøvernbukta 9180 § 65 T-12370 Sa 95-90 1 Fragments on modern beach 6. Wigdehlpynten 9135 § 125 T-13548 Sa 97-85 18 Fragments on raised beach 7. Langgrunnodden 9070 § 190 U 173 B-47 9 Blake 1961 8. Mosselbukta 9065 § 130 T-12840 Sa 79-09 9 Raised beach section 9. Kapp Kjeldsen 9060 § 75 T-12227 Sa 95-69 4 Raised beach 10. Mossellaguna 9015 § 105 T-13255 Sa 97-32 12 Raised beach section § 11. GraÊ huken 8985 60 T-12237 Sa 95-98 3 Littoral section 12. Worsleyhamna 8865 § 65 T-12371 Sa 95-04 4 Fragments on raised beach 13. Danielodden 8845 § 105 T-13251 Sa 97-17 9 Littoral section 14. Breiddholme n 8170 § 120 T-13257 Sa 97-49 5 Raised beach sediments 15. Mosselbukta 8165 § 70 T-13551 Sa 97-11 3.5 Fragments on raised beach 16. Karlsbreen 7700 § 75 T-12230 Sa 95-77 40 Fragments on frontal moraine § 17. BraÊ nevatnet 7260 105 T-13426 Sa 97-100 10 Raised beach 18. Skamdalen 6935 § 105 T-14497 1106-3 6 Littoral section 19. Halvdandalen 6620 § 80 T-12369 Sa 95-84 1 Fragments on modern beach 20. Karlsbreen 6255 § 45 T-12229 Sa 95-78 11 Fragments on frontal moraine 21. Forkdalen 5655 § 100 T-13260 Sa 97-74 5 Littoral section 22. Breiddholme n 5310 § 60 T-113258 Sa 97-51 1 Shells on modern beach 14. Breiddholme n 8285 § 95 T-13256 Sa 97-46 5 Modiolus on raised beach Hannevigodden 6555 § 70 TUa-2191 Sa 87-44 4 Modiolus on raised beach § four have been published previously. The locations of the and numerous and constitute real Mytilus beds in sea-facing sampling sites are shown in Figs. 1 and 2. sediment cliffs. The four oldest dates are from the outer fjord area of Bockfjorden, the smallest branch of Woodfjorden, was Woodfjorden or from the western mouth of Wijdefjorden invaded by Mytilus edulis communities well before 9000 yr (site 2) and indicate that Mytilus edulis rst settled here after BP, as shown by dated samples from Sjøvernbukta (5) and passing the NW corner of Svalbard on its way from more Kapp Kjeldsen (9). The former sample was from the modern southern areas. This immigration took place c. 9400 yr BP, beach, where shell fragments had been washed ashore after which seems to be only 200 to 300 years later than its rst wave erosion of shallow sublittoral sediments. The latter appearance on the west coast (Salvigsen et al. 1992). In two sample, however, was picked from the highest-lying shell cases, Vogtvatnet (2) and Mushamna (3), the shells are large fragments on or near the surface of raised beach sediments. Mytilus edulis also lived in the inner part of Woodfjorden before 9000 yr BP. The highest-lying fragments at Wigdehl- pynten (6) show the minimum age for the Mytilus immigra- tion there. Fig. 1. Location map of Svalbard showing sites where Mytilus edulis, black dots, and Modiolus modiolus, black triangles, have been radiocarbon-dated , illustrating the geographical distribution of shells from these thermophilous Fig. 2. Location map of parts of northern Svalbard showing sites from where molluscs in Svalbard based on Salvigsen et al. 1992, Hjort et al. 1995 and this Mytilus edulis and Modiolus modiolus have been radiocarbon-dated. study. Numbers refer to Table 1. 58 O. Salvigsen NORSK GEOGRAFISK TIDSSKRIFT 56 (2002) The datings mentioned here indicate that Mytilus edulis Holocene than previously known (Salvigsen et al. 1992). rst appeared on the northern coast c. 9400 yr BP, and during The shell was dated to 8285 95 yr BP (T-13256), which is the following 200 years it spread to Bockfjorden as well to the same age as nearby lying§Mytilus edulis shells from the inner Woodfjorden.