ARTICLE IN PRESS Quaternary International 130 (2005) 3–30 Last Interglacial (Eemian) hydrographic conditions in the southeastern Baltic Sea,NE Europe,based on dinoflagellate cysts Martin J. Heada,*,Marit-Solveig Seidenkrantz b,Zofia Janczyk-Kopikowa c, Leszek Marksc,d,Philip L. Gibbard a a Godwin Institute for Quaternary Research, Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, UK b Department of Earth Sciences, University of Aarhus, DK-8000 Arhus( C, Denmark c Polish Geological Institute, Rakowiecka 4, PL-00-975 Warsaw, Poland d Institute of Geology, Warsaw University, Zwirki i Wigury 93, PL-02-089 Warsaw, Poland Available online 20 July 2004 Abstract A rich organic-walled dinoflagellate cyst and pollen record from the Licze borehole in northern Poland has been used to reconstruct the hydrographic history of the southeastern Baltic Sea during the Last Interglacial (Eemian Stage,Late Pleistocene). Warm,saline waters (ca. 10–15 psu) entered the site from the North Sea within the first few hundred years of the Eemian, corresponding to the Pinus–Betula (E1) or Pinus–Betula–Ulmus (E2) regional pollen assemblage zones (RPAZ). By about 300 years (beginning of RPAZ E3),dinoflagellate cyst assemblages were already indicating summer sea-surface salinities in excess of about 15 psu and temperatures that perhaps exceeded 27C. Warm and saline conditions of 15–20 psu or more,at least twice present levels, persisted throughout the early Eemian. A rise in sea level at Licze appears to correlate with a similar event in eastern Denmark,as both coincide with the increase in Corylus (ca. 750 years into the interglacial). This sea-level rise might therefore have a basinwide extent,and appears to correspond to an opening of the Danish Belts. There is little if any evidence of arctic waters throughout the sequence. Whereas dinoflagellate cysts reflect sustained high salinites within the upper water column,a concomitant increase in abundance of the chlorococcalean alga Pediastrum within the Carpinus–Corylus–Alnus (E5) RPAZ indicates an escalating freshwater input,presumably from the proto-Vistula whose mouth was nearby. This suggests the development of a thin,seasonal, low-salinity surface layer below which dinoflagellates lived in more saline waters. Increasing fluvial influence suggests shallowing through RPAZ E5. This study is the first to document dinoflagellate cysts from the Eemian of the southeastern Baltic Sea,and reveals a flora with distinctive Lusitanian/Mediterranean affinities. r 2004 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction temperatures and salinities soon exceeded those of today,and in addition to a narrow seaway across The Last Interglacial (equivalent to the Eemian Stage, northern Germany,two main portals developed: one and approximately to Marine Isotope Substage 5e; connecting to the North Sea in the Danish area,and Kukla et al.,2002 ) began at about 130 ka with the another that linked the Baltic Sea to the White Sea by retreat of glaciers that had extended over much of means of a seaway across the Karelian Isthmus in northern Europe in Saalian times. As a consequence the Russia (Fig. 1). This Karelian seaway was until recently Baltic Sea region was left isostatically depressed,and thought to have permitted free exchange between the rising global sea level at the start of the Eemian led Baltic and White seas (e.g., Donner,1995,fig. 6.1 ),but is swiftly to the establishment of marine conditions now considered to have been too restricted for this to (Liivrand,1984,1991 ; Kalnina,2001 ). Surface water have happened (Funder et al.,2002 ). The present study focuses on marine,organic-walled *Corresponding author. Tel.: +44-1223-339751; fax: +44-1223- dinoflagellate cysts and other aquatic palynomorphs in the 0 00 0 00 333392. Licze borehole (19 07 45 E,53 44 45 N),located about E-mail address: [email protected] (M.J. Head). 5 km to the west of Prabuty in northern Poland (Figs. 1 1040-6182/$ - see front matter r 2004 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2004.04.027 ARTICLE IN PRESS 4 M.J. Head et al. / Quaternary International 130 (2005) 3–30 GulfGulf ofof GdaGGdañskdañsksk n oo ag a l GdaGGda–skda–sksk tul VistulaVis lagoon Szkar pawa g n Vistula a io l t lb a Elblag ElblagE v le ElevationE Nogat Tczew Sztum Nowiny N Obrzynowo Kwidzyn Prabuty Licze Fig. 1. Eemian hydrography and geography of the Baltic Sea region during maximum inundation in the early Eemian (based on Funder km et al.,2002 ). The present study area is marked,along with other 0 5 10 15 20 Eemian sites mentioned in the text. RK=Ristinge Klint,M=Mom- mark. Fig. 2. Sketch of the Lower Vistula region,northern Poland with the marine limit of the Eemian sea and location of the Licze,Nowiny and Obrzynowo boreholes (solid dots) and nearby towns (open dots). The extent of marine Eemian deposits (horizontal shading) and coeval fluvial deposits (stippling) is also shown. and 2). The specific aims of our study are to understand the nature and timing of marine transgression into the southeastern Baltic Sea during the early Eemian,and to assess whether the Karelian seaway influenced surface water conditions by facilitating the inflow of arctic waters. Summer upper-water-column salinity and temperature are reconstructed accordingly,but because the proto-Vistula 2. Dinoflagellate cysts entered the sea nearby during Eemian times,it has been necessary to differentiate as far as possible between local Dinoflagellates are almost exclusively unicellular and regional influences on hydrography. Pollen stratigra- protists,and include both autotrophic and heterotrophic phy and its correlation to the well-dated pollen record at species (Fensome et al.,1993 ). Dinoflagellates are BispingeninnorthernGermany(Muller,1974. ; Field et al., mostly planktonic,but unlike diatoms have a motile 1994) provides a tentative chronostratigraphic control for stage in their life cycle that allows them to control and the Licze borehole. optimise their position in the water column (Levan- This study is part of a larger investigation into the dowsky and Kaneta,1987 ). Many dinoflagellates Eemian of both the Licze core and a nearby core at produce a resting cyst (as a strategy for over-wintering Obrzynowo (Fig. 2). The mollusc faunas have been in mid to high latitudes) whose wall is generally very published by Makowska (2001) whereas publications on resistant to degradation,and the geological record of the foraminifera,ostracods and diatoms are forth- dinoflagellates is based on these species (Head,1996 ). coming. Previous studies of dinoflagellate cysts from Owing to the sensitivity of dinoflagellates to salinity, the Eemian of the Baltic Sea are limited to the Gulf of temperature,and nutrient levels over a wide range of Bothnia (Eriksson et al.,1999 ),Denmark ( Head and environmental parameters,and to the high preserva- Gibbard,2000 ) and to a brief general account (Head bility of the cysts,the Quaternary record of dino- et al.,2001 ) and short taxonomic study (Head,2003 ). flagellate cysts is becoming increasingly used for The present work is therefore the first to document reconstructing sea-surface conditions (Dale,1996 ; Eemian dinoflagellates in detail from the southeastern Rochon et al.,1999 ; Matthiessen and de Vernal,2001 ; Baltic. Dale and Dale,2002 ). ARTICLE IN PRESS M.J. Head et al. / Quaternary International 130 (2005) 3–30 5 3. Present hydrography and Rewal (Krzyszkowski et al.,1999 ). These deposits consist of fine-grained sand to sandy silt and shell The present day Baltic Sea is one of the world’s largest detritus,and represent a beach or lagoonal facies. bodies of brackish water,with surface salinities gen- However,it is in the Lower Vistula region that erally not exceeding 10 psu. Summer sea-surface tem- Eemian marine sequences are most complete. Here, peratures are generally above 19C over most of the evidence from shoreface and deeper-water molluscs, southern and eastern Baltic Sea (Bundesamt fur. particularly from Elblag and the Nowiny borehole Seeschiffahrt und Hydrographie,2002 ),largely due to (Makowska,1986 ; Funder et al.,2002 ; Fig. 2),depicts water stratification. The Gulf of Gdansk is characterised a protected embayment in which sea-surface salinities by a highly dynamic hydrography (Pastuszak,1995 ), and temperatures were considerably higher than today, and is strongly influenced by freshwater outflow from resulting from an early connection to the North Sea. In the Vistula,the largest freshwater source entering the the Nowiny borehole,marine incursion began at the Baltic Sea in the area. Surface water salinity reaches onset of the Quercus–Fraxinus–Ulmus regional pollen about 8 psu,but lower salinities averaging about 4.0 psu assemblage zone (RPAZ E3) of Mamakowa (1988, are found close to the mouth of the Vistula. Sea-surface 1989) and lasted until some time into the Picea–Abies– temperatures in the Gulf of Gdansk reach between 19C Alnus zone (RPAZ E6) (Makowska,1986 ). Molluscs, and 24C during summer (Nowacki and Jarosz,1998 ). including the foreshore/tidal zone species Retusa umbi- In the outer part of the Gulf of Gdansk during summer, licata,indicate that salinity culminated in RPAZ E3 a thermocline is established at about 20 m and halocline where it periodically rose above 30 psu,which is more at about 70 m,but in the inner parts of the bay a than 20 psu higher than present,although surface-water freshened surface layer 1 or 2 m deep results from salinity was in general probably not higher than 25 psu. discharge from the Vistula (Nowacki and Jarosz,1998 ). High salinities persisted from RPAZ E3 until the end of the Carpinus–Corylus–Alnus zone (RPAZ E5; Makows- ka,1986 ; Funder et al.,2002 ). It is also noteworthy that 4. Geological and palaeoenvironmental background the occurrence of Lusitanian mollusc species indicates a winter sea-surface temperature of about 9C,which is An embayment of the Baltic Sea occupied the Lower 6C warmer than today (Funder et al.,2002 ).