Spatial variations in Ba/Cashell fingerprints of Glycymeris pilosa along the eastern Adriatic Sea

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Highlights

  • Mg/Cashell values increase through lifetime.

  • Ba/Cashell data series were synchronous within sampling sites.

  • Spatial variations of Ba/Cashell data indicate influence of local environmental factors.

  • Long-term changes in Ba/Cashell are at least partially caused by anthropogenic factors.

Abstract

The long living Glycymeris pilosa bivalve is an interesting target species for the sclerochronological research in the Mediterranean Sea. In this study, Ba/Cashell and Mg/Cashell variations were studied along the coast of the eastern Adriatic Sea. Specimens were collected alive by SCUBA and skin diving during several occasions in 2014, 2015 and 2016 from five sites including Pag, Pašman Channel, Cetina, Živogošće and Drače. Element-to-Cashell ratios were measured by LA-ICP-MS in line scan mode in three specimens of each site, ranging in age from 7 to 21. In addition, chemical analysis was conducted on three ontogenetically older specimens (68-97 years-old) from Drače. Mg/Cashell and annual growth lines were used to place the Ba/Cashell data in temporal context. Published monthly G. pilosa shell growth data were used for transferring elemental data from distance to time scale. To enable a direct comparison of Ba/Cashell data between specimens and sites (different time-averaging), as well as a comparison with environmental data, monthly mean values were calculated (re-sampling). Results of this study show that Mg/Cashell values in G. pilosa increase through lifetime and variations occur with respect to amplitude and seasonal patterns. Detailed comparison of Mg/Cashell data between sites was not possible because specimens varied in ontogenetic age. Ba/Cashell values ranged between 0.03 μmol/mol and 14.18 μmol/mol, and time-series showed noncyclic sharp peaks, which differed between years. Values were rather synchronous among specimens from the same site. Specimens from Pašman, Živogošće and Drače contain more peaks than specimens from Pag and Cetina, and these peaks are less synchronous among the time-series. Three northern sites were characterised by lower Ba/Cashell values than the two southern sites. Comparison of monthly Ba/Cashell times-series with available environmental data revealed variability of environmental conditions. Long-term Ba/Cashell data of G. pilosa from Drače showed a lower baseline and amplitude during the 1950s and 1960s than from the mid-1970s onward. It is possible that these long-term changes are at least partially caused by anthropogenic factors, including changes of the river Neretva management and development of agriculture in its delta.

Introduction

Bivalve shells contain periodic growth patterns, i.e., growth lines and increments visible on the shell surface and in cross-sections (Richardson, 2001). These growth patterns can be used to assign time (e.g., calendar years) to corresponding shell portions. Geochemical properties of deposited shell material can yield temporally aligned proxy data of environmental conditions prior to instrumental recordings (e.g., Schöne et al., 2011; Royer et al., 2013; Schöne and Gillikin, 2013; Füllenbach et al., 2015; Reynolds et al., 2016; Prendergast et al., 2017; Markulin et al., 2019). Longevity of some bivalve species exceeds several decades (eg. Tridacna gigas; Elliot et al., 2009) and even centuries (eg. Arctica islandica; Schöne et al., 2005a; Wanamaker et al., 2008; Butler et al., 2013). Pairing with fossil specimens can enable reconstruction of environmental change in the more distant past (e.g. Scourse et al., 2006; Schöne et al., 2011; Butler et al., 2013). In the last two decades, the field of sclerochronology has been rapidly developing, relating variations in growth increments widths and geochemical composition of shell carbonate (e.g. Schöne et al., 2005b; McConnaughey and Gillikin, 2008; Black et al., 2009; Thébault et al., 2009; Reynolds et al., 2017; Tanabe et al., 2017) with environmental variations.

Due to their worldwide distribution (Huber, 2010), longevity and distinct annual growth patterns (e.g., Reynolds et al., 2013, Walliser et al., 2016; Peharda et al., 2018), shells of glycymeridids represent an important sclerochronological archive of proxy data that can help to elucidate past changes in the marine environment. Several recent studies identified Glycymeris pilosa as an interesting target species for paleoclimate reconstructions as well as for investigating the relationship between environmental changes and biology in the Mediterranean Sea. Distinct annual growth lines present in shells of this species enable chronology construction (Peharda et al., 2016, 2018, 2019a) as well as to temporally align geochemistry data including stable isotope values (Peharda et al., 2019b, c), radioactive carbon (Peharda et al., 2019d) and trace and minor element data (Markulin et al., 2019).

Barium (Ba) has been identified as an important trace element for studying geochemical and oceanic processes (Stecher et al., 1996) and is incorporated in bivalve shells making them an important data archive of past environmental variability (for review see Gillikin et al., 2008). Ba/Cashell time-series obtained from marine bivalves are characterised by flat background signals erratically interrupted by pronounced peaks that are synchronous between studied specimens indicating external forcing (e.g. Gillikin et al., 2006; Elliot et al., 2009; Thébault et al., 2009; Marali et al., 2017a; Doré et al., 2020). Ba/Cashell time-series data can potentially be used to distinguish between different sampling sites (Norrie et al., 2019).

According to previous studies, background Ba/Cashell data may reflect salinity (e.g., Gillikin et al., 2006, 2008; Marali et al., 2017a), whereas the interpretation of Ba/Cashell peaks is still debated (Marali et al., 2017a; Ballestra-Artero et al., 2018). Dissolved or particulate Ba in ambient seawater (Gillikin et al., 2006; Carroll et al., 2009), primary production (e.g. Stecher et al., 1996; Carroll et al., 2009; Elliot et al., 2009; Thébault et al., 2009) and spawning events (Gillikin et al., 2006) have been suggested as possible controls of Ba/Cashell. Recent laboratory studies showed that a large number of environmental and physiological variables, such as temperature, food level, Ba/Cawater and shell growth control Ba/Cashell (Zhao et al., 2017; Ballestra-Artero et al., 2018; Wanamaker and Gillikin, 2019).

The main objective of this study was to test the hypothesis that Ba/Cashell signals in G. pilosa shells do not vary along the coastal areas of the eastern Adriatic Sea. Recent study conducted by Markulin et al. (2019) analysed elements in G. pilosa shells from one site in the north Adriatic Sea and showed highly synchronised Ba/Cashell peaks coinciding with the dense water formation during early 2012. By analysing specimens from different sites along the Adriatic Sea coast, we wanted to gain an understanding on how local versus regional drivers influence the geochemical composition of the shells in the Mediterranean Sea. To achieve this, we analysed Ba/Cashell over nine consecutive years in G. pilosa collected from five sites. Furthermore, we wanted to gain an insight into temporal variations of Ba/Cashell and have analysed shells of three older (>50 years) bivalves from Drače.

Section snippets

Sample collection and preparation

Glycimeris pilosa specimens were collected alive by SCUBA and skin diving from five sites along the eastern Adriatic Sea: (1) Pag (3–5 m depth, 44°27′42.012″ N, 015°1′36.012″ E); (2) Pašman Channel (1.5–3 m depth, 43°56′52.68″N, 015°23′15.03″E); (3) Cetina (3–5 m depth, 43°26′12.984″ N, 016°41′13.992″E); (4) Živogošće (3–5 m depth, 43°10′57.02″N, 17°9′42.91″E) and (5) Drače (4–5 m depth, 42°56′10.54″N, 017°28′23.71″E) (Fig. 1). Sampling was performed during several occasions in 2014, 2015 and

Results

In polished cross-sections, the growth pattern was divided into dark grey growth bands and opaque, white increments (Fig. 2). A distinct annual growth line was seldom observed when viewed under the light microscope, which made it difficult to define precisely where a growth increment (representing the main growing season) started and ended. However, based on findings of previous studies, we suspect the annual winter line (representing ca. January to March) within the centre of the white

Ba/Cashell time-series

At each locality, studied Glycymeris pilosa specimens showed synchronous Ba/Cashell signals, suggesting that the incorporation of barium into the shells was controlled by the same environmental events. Furthermore, during some time intervals (e.g., 2009–2010), Ba/Cashell signals were even synchronous among different sites, indicating large-scale environmental controls on barium availability. In a recent study of three aragonitic bivalves including G. pilosa, Markulin et al. (2019) found highly

CRediT authorship contribution statement

Krešimir Markulin: Conceptualization, Methodology, Writing - original draft, Visualization, Writing - review & editing. Hana Uvanović: Methodology, Visualization, Writing - review & editing. Regina Mertz-Kraus: Conceptualization, Methodology, Writing - review & editing. Bernd R. Schöne: Conceptualization, Methodology, Writing - review & editing. Žarko Kovač: Methodology, Writing - review & editing. Jasna Arapov: Methodology, Writing - review & editing. Melita Peharda: Conceptualization,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Sampling at Pag Bay, Pašman Channel and Cetina River mouth was conducted in the framework of Marie Curie ITN project ARAMACC (604802), while in Živogošće and Drače it was conducted as a part of Croatian Science Foundation, Croatia, SCOOL (IP-2014-09-5747). Precipitation data were provided by the Meteorological and Hydrological Service of the Republic of Croatia. Ivica Janeković provided temperature and salinity modelled data. Data related to river Neretva were obtained from the Federal

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