Strontium isotopic composition of modern and Holocene mollusc shells as a palaeosalinity indicator for the Baltic Sea
Introduction
The glacio-eustatic sea-level rise of approximately 130 m that occurred from ∼ 18 000 to 6000 BP was one of the most profound environmental changes of the Late Quaternary. In formerly glaciated areas that have experienced regional postglacial isostatic rebound, the resulting transgressions/regressions can be expected to have influenced the palaeoenvironment of coastal bays and epicontinental seas (cf. Fredén, 1988). This is clearly demonstrated by the dynamic Holocene history of the Baltic Sea, which resulted in regional changes in salinity and redox conditions (e.g., Sohlenius et al., 1996, Sohlenius et al., 2001) as well as in palaeoproductivity and palaeoecological conditions (e.g., Westman and Sohlenius, 1999). The absolute salinity changes experienced during the Holocene development of the Baltic Sea have been discussed extensively since the late nineteenth century (summarised by Westman et al., 1999). Earlier studies of the palaeosalinity of the Baltic Sea have been based on fossil assemblages (Munthe, 1894, Witkowski, 1994); on δ18O in mollusc shells (Punning et al., 1988), foraminifera (Winn et al., 1986) and rhodochrosite (Huckriede et al., 1996); and on the occurrence of cyanobacterial blooms (Bianchi et al., 1998). However, the palaeosalinity of the Baltic Sea is still incompletely understood, and estimates of the maximum surface salinity of the Baltic Proper over the last 8500 years range from 10‰ to 20‰, compared to the present-day salinity of 6–8‰.
Precise knowledge of the palaeosalinity of the Baltic Sea is required when reconstructing the environmental history of the Holocene Baltic (e.g., Winterhalter, 1992, Sohlenius et al., 1996, Westman and Sohlenius, 1999, Sternbeck et al., 2000, Sohlenius et al., 2001). Combined with the sedimentary record of palaeoproductivity and palaeoredox conditions (Westman and Sohlenius, 1999, Sohlenius et al., 2001), palaeosalinity data could also be used to predict the future, long-term effects of an expected climate-induced reduction of the salinity of the Baltic Sea (cf. Stigebrandt and Gustafsson, 2003).
It is well known that the Sr isotopic composition of fossil carbonate mollusc shells can be used as a proxy indicator of palaeosalinity (e.g., Ingram and Sloan, 1992, Ingram and DePaolo, 1993, Klingberg and Andersson, 1997, Israelson and Buchardt, 1999). The determination of proxy salinity data is based on the fact that the 87Sr/86Sr ratio in biogenic carbonate closely reflects that of dissolved Sr in the ambient water (Veizer, 1989). Due to the generally conservative nature of Sr in estuarine environments, proxy salinity data can then be obtained from the relationship between the 87Sr/86Sr ratio and the Sr concentration in the water (Ingram and Sloan, 1992, Faure and Mensing, 2005).
This study for the first time uses the Sr isotopic composition of 14C-dated carbonate mollusc shells as a palaeosalinity indicator for the Baltic Sea. Our aim is primarily to demonstrate the applicability of the method in a formerly glaciated area, using 87Sr/86Sr ratios in modern shells to elucidate the parameters and conditions to be used for palaeosalinity determinations based on subfossil shells.
Section snippets
Study area
The brackish Baltic Sea is a shallow epicontinental sea with a surface area of 370 000 km2 and a volume of 21 000 km3 (Fig. 1). Within the Baltic Sea, three major sub-basins–the Baltic Proper, Bothnian Sea, and Bothnian Bay–are separated by sills and shallow-water areas. Water exchange with the Atlantic Ocean occurs through the Belt Sea and Öresund (with approximate sill depths of 18 m and 8 m, respectively), via a transitional area in the Skagerrak-Kattegat (Ehlin, 1981).
The outflow of low-saline
Mixing model for Sr in the Baltic Sea and palaeosalinity calculation
In this study, the Sr isotopic composition is expressed as 87Sr/86Sr ratios or using the ε notation, i.e., as fractional deviations in parts in 104 from that of modern seawater, as follows:
The general equations for a mixture of two components having different Sr concentrations and 87Sr/86Sr ratios can be found in Faure and Mensing (2005, Chap. 16). In Baltic Sea water (BW) the concentration of Sr (CSrBW) is controlled by a two-component,
Strontium isotope data and present-day salinity
To validate the proxy salinity data obtained from mollusc shells, salinities calculated using Sr isotope data for modern shells from seven localities were compared with measured, present-day salinities (Fig. 1, Table 2, Table 3). In most cases, M. edulis was used for the salinity determination. Today, M. edulis colonises hard bottoms to water depths of 35–40 m (Kautsky, 1981), so this can be considered as the maximum depth to which modern shells of this species reflect the salinity. The salinity
Conclusions
This study shows that reliable palaeosalinity data for the Baltic Sea can be obtained from the Sr isotopic composition of Holocene carbonate mollusc shells occurring in raised-beach sediments. However, this presupposes that the post-depositional alteration of shells is of little or no significance. Based on replicate determinations of the 87Sr/86Sr ratio in modern shells, proxy salinity data can be quantified with a relative precision of better than ± 5% for salinities up to ∼ 10‰. The comparison
Acknowledgements
This study was funded by grants from Magnus Bergvall's Foundation. We greatly appreciate the assistance of Marina Fischerström and Hans Schöberg with sample preparation and TIMS instrument operation. We are grateful for the comments and assistance with mollusc species identification provided by Tommy Sörlin. We also thank Analytica AB for their support with chemical analyses and Milan Vnuk for skilfully drafting the figures. Salinity data for the Baltic Sea (SHARK database) were kindly provided
References (48)
- et al.
The sources and transport of Sr and Nd isotopes in the Baltic Sea
Earth Planet. Sci. Lett.
(1992) A review of the history of the Baltic Sea, 13.0–8.0 ka BP
Quat. Int.
(1995)Strontium isotope diagensis of biogenic aragonite and low-Mg calcite
Geochim. Cosmochim. Acta
(1991)- et al.
Mollusc shell microstructures and crystallographic textures
J. Struct. Geol.
(2000) Hydrology of the Baltic Sea
- et al.
Reconstruction of Holocene precipitation patterns in Europe using pollen and lake-level data
Quat. Res.
(1993) - et al.
Uptake of alkali and alkaline-earth elements on suspended iron and manganese in the Kalix River, northern Sweden
Geochim. Cosmochim. Acta
(1994) - et al.
Strontium and oxygen isotopic composition of East Greenland rivers and surface waters: implication for palaeoenvironmental interpretation
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(1999) Physical oceanography
- et al.
Testing 87Sr/86Sr as a paleosalinity indicator on mixed marine, brackish-water and terrestrial vertebrate skeletal apatite in late Paleocene–early Eocene near-coastal sediments, Mississippi
Chem. Geol.
(1997)
Origin of interstitial water compositions in postglacial black clays (northeastern Sweden)
Chem. Geol.
Holocene history of the Baltic Sea as recorded in a sediment core from the Gotland Deep
Mar. Geol.
Development of anoxia during the Holocene fresh-brackish water transition in the Baltic Sea
Mar. Geol.
Response of the Baltic Sea to climate change—theory and observations
J. Sea Res.
Geology of the Baltic Sea
Variations of 87Sr/86Sr in water from streams discharging into the Bothnian Bay, Baltic Sea
Nord. Hydrol.
A shell deposit near Åkroken at Kalix in northern Sweden
Geol. Fören. Stockh. Förh.
Climatic changes and uplift patterns—past, present and future
Swedish Nuclear Fuel and Waste Management Co, SKB Technical Report TR-92-38
Radiocarbon ages and stable isotope composition of Holocene shells in Finland
Application of the solubility profiling technique to recent and fossil fish teeth
Bull. Soc. Géol. Fr.
Isotopes: Principles and Applications
Marine life and deglaciation chronology of the Vänern basin, southwestern Sweden
Sver. Geol. Unders. Ser. Ca Avh. Upps.
Hydrographic and climatic changes recorded in Holocene sediments of the central Baltic Sea
Baltica
Cited by (34)
Strontium isotope analysis in prehistoric cod otoliths by laser ablation multi-collector inductively coupled plasma mass spectrometry
2021, Journal of Archaeological Science: ReportsCitation Excerpt :In the Baltic Sea, strontium ratios vary considerably as a consequence of large freshwater influxes from rivers which drain basins with sediments of different geological origin (Löfvendahl et al., 1990). While 87Sr/86Sr increases with lower salinity, it reaches values of > 0.7095 in the Gulf of Bothnia (Andersson et al., 1992; Widerlund and Andersson, 2006, 2011). Close to the large rivers in the north the 87Sr/86Sr values are even higher than > 0.7095 as a result of riverine influx (Andersson et al., 1992).
Seawater paleotemperature and paleosalinity evolution in neritic environments of the Mediterranean margin: Insights from isotope analysis of bivalve shells
2020, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :One way to overcome this limitation is to combine conventional oxygen isotope (δ18O) with clumped isotope (Δ47) analyses of bivalves because carbonate clumped isotope (Δ47) composition is solely linked to temperature during mineral formation, and independent from the isotopic composition of the ambient water (Ghosh et al., 2006; Schauble et al., 2006; Eiler et al., 2009; Henkes et al., 2013). Additional information on environmental conditions is provided by the Sr isotopic system applied on bivalves, as the 87Sr/86Sr ratios recorded in their umbo has been shown to record the occurrence of large freshwater discharge in their living marine environment (Ingram and Sloan, 1992; Bryant et al., 1995; Widerlund and Andersson, 2006; El Meknassi et al., 2018; Zaky et al., 2018). In this context, we propose to test the potential of a multi-proxy approach applied on bivalves thriving in coastal environments to reconstruct the evolution of shallow (<50 m) seawater temperatures over the latest Oligocene to Middle Miocene interval.
Major hydrological shifts in the Black Sea “Lake” in response to ice sheet collapses during MIS 6 (130–184 ka BP)
2019, Quaternary Science ReviewsTonian-Cryogenian boundary sections of Argyll, Scotland
2018, Precambrian ResearchCitation Excerpt :However, this is contradicted by evidence from modern fluvial systems and marine embayments. Canadian rivers, for example, display three orders of magnitude lower Sr concentration than seawater (Veizer, 1989) and studies of the modern Baltic imply that a upwards shift of 87Sr/86Sr of 0.0002–0.003 would require a mixed solution with <5% seawater (Widerlund and Andersson, 2006) whereas the dolomites have (evaporative) marine oxygen isotope signatures. Relatively high-Sr dolomites could provide useful chemostratigraphic information in Neoproterozoic successions where high-Sr limestones are absent and the multiple leach technique optimizes recovery of a less-altered signal.
Stable isotope composition of subfossil Cerastoderma glaucum shells from the Szczecin Bay brackish deposits and its palaeogeographical implications (South Baltic Coast, Poland)
2012, Quaternary ResearchCitation Excerpt :These changes, which were essentially induced by the amounts of water inflowing from the North Sea and climatic changes in the Baltic Sea basin, can be reconstructed utilizing cores of preserved sediments from deep basins (Sohlenius et al., 2001; Harff et al., 2011) alike those from the Baltic littoral zones (Borówka et al., 2005; Lampe, 2005; Uścinowicz, 2006; Miettinen et al., 2007; Kabailiene et al., 2009; Rotnicki, 2009). For paleoecological reconstructions of salinity, temperature, and bottom-water oxygen content, various approaches have been used including paleobotanical (Witak, 2002; Witkowski et al., 2004; Brenner, 2005; Jankowska et al., 2005; Witak and Dunder, 2007; Leśniewska and Witak, 2008; Miotk-Szpiganowicz et al., 2008) paleozoological (Damušyte, 2009) and isotopic methods (Punning et al., 1988; Emeis et al., 2003; Widerlund and Andersson, 2006, 2011). Paleoclimatic studies based on the records from adjacent continental areas, particularly those used for modeling of temperature and precipitation during the late glacial period and the Holocene, were also important for understanding the environmental changes of the Baltic Sea.