JOURNAL OF QUATERNARY SCIENCE (1998) 13(2) 107–114 CCC 0267-8179/98/020107–08$17.50  1998 John Wiley & Sons, Ltd. Reconstruction of Holocene sea-surface salinity in the Skagerrak–Kattegat: a climatic and environmental record of Scandinavia HUI JIANG 1 *, SVANTE BJO ¨ RCK 2 and NILS-OLOF SVENSSON 1 1 Department of Quaternary Geology, Lund University, Tornava ¨gen 13, S-223 63 Lund, Sweden 2 Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark Brown III, J., Labe ´que, K., Paz Villa-Lobos, H. 1998. Reconstruction of holocene sea-surface salinity in the Skagerrak–Kattegat: a climatic and environmental record of Scandinavia. J. Quaternary Sci., Vol. 13, 107–114. ISSN 0267-8179 (No. of Figures: 3. No. of Tables: 2. No. of References: 31) Received 19 February 1997 Accepted 28 August 1997 ABSTRACT: Holocene sea-surface salinity in the Skagerrak–Kattegat is reconstructed using weighted averaging regression and calibration (WA) of diatom data from core Skagen 3. Diatom data from surface sediments together with 10-yr mean values of salinity and water temperature were used as a modern training set. Canonical correspondence analysis (CCA) was used to identify statistically significant directions of variation within the training set. The results of forward selection of the environmental variables and associated Monte Carlo permutation tests of the statistical significance of each variable, the canonical coefficients, and the intraset correlations of the environmental variables with the CCA axes suggest that summer and winter sea-surface salinities (SSS, WSS) are potentially reconstructable from fossil diatom assemblages. The changes in sea-surface salinity during the Holocene can be correlated with changes in climate of the circum-Baltic area, the current patterns of the Skagerrak–Kattegat, and the development of the Baltic Sea. Generally low SSS and large differences between WSS and SSS (Sw-s) during 9000–6000 yr BP might have resulted from a climate with higher precipitation than today in the circum-Baltic area and its catchment, or a climate with maximum precipitation in late spring or early summer. The mechanism behind these patterns may be the combination of the northward shift of the jet stream and a stronger surface westerly penetration into the continent caused by a reduced latitudinal insolation gradient and enhanced land–sea contrast in the early to middle Holocene. It was, however, complicated by local events such as changes in the strength of various currents in the Skagerrak–Kattegat, successions of Baltic brackish and freshwater phases, and hydrodynamic conditions in the circum-Baltic area.  1998 John Wiley & Sons, Ltd. KEYWORDS: Holocene sea-surface salinity; canonical correspondence analysis (CCA); weighted averaging regression and calibration (WA); diatom; Skagerrak–Kattegat. Introduction Sea-surface salinity is highly correlated with regional sea- current patterns. Changes in sea-surface salinity should thus reflect variations in sea-current patterns. The Skagerrak– Kattegat is hydrographically characterised by the outflow of low saline water of Baltic origin in the southern Kattegat and along the Swedish and the Norwegian coasts, and the inflow of highly saline water from the North Atlantic on the North Jutland Shelf (Fig. 1). The interaction of these two major components determines sea-surface salinity. Based on the variation in freshwater supply of one of the larger rivers * Correspondence to: Hui Jiang, Department of Earth Sciences, Aarhus Univer- sity, DK-8000 Aarhus C, Denmark. Contract grant sponsor: The Swedish Research Council (NFR) Contract grant sponsor: The Danish Research Council (SNF) to the Baltic Sea and surface salinity measured at Light Vessel Schultz’s Grund, southwestern Kattegat, Svansson (1975) concludes that low precipitation in the Baltic Sea and its catchment gives rise to high salinity in the Kattegat. Schott (1966), who carried out Fourier analysis of time series of monthly means of surface salinity, shows that long-term fluctuations of surface salinity in the North Sea can be correlated with fluctuations in river discharge and in precipi- tation. Although the salinity pattern shows similar behaviour during winter and summer, the salinity in summer is about 2gl -1 lower in the surface water entering from the Kattegat, and 1 g l -1 lower in the surface water entering from the North Sea than it is in winter (Rodhe, 1992). These results suggest that the outflow of water from the Baltic Sea has a greater influence on changes in sea-surface salinity in the Skagerrak–Kattegat than the inflow of water from the North Sea, in particular during summer. Hence, reconstruction of the sea-surface salinity in the Skagerrak–Kattegat could give