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The application of salt-marsh foraminifera to reconstruct historical sea-level trends was investigated for the Croatian coast of the Adriatic Sea using a transfer function approach. This technique, whilst well practised from north Atlantic sites along the shores of America and UK, has previously evaded any published study in the Mediterranean region. A total of 70 surface samples were collected across separate transects established at two micro-tidal salt-marsh sites from the central Croatian coastline to establish a modern dataset of foraminifera. In addition, environmental variables were also investigated including salinity, pH, organic matter, particle size, distance (from open water) and altitude, relative to the Croatian national datum. Three sediment cores were sampled for fossil foraminifera and composite chronologies involving short-lived radionuclides, radiocarbon dating and pollution indicators from XRF. Age-depth models were created using classical and Bayesian approaches. Quantitative analysis of the foraminiferal assemblages revealed on average three faunal zones in which characteristic species occurred. This comprised a faunal zone composed almost exclusively of agglutinated species; J. macrescens, T. inflata and M. fusca extending between mean tidal level (MTL) and beyond MHWST (higher altitude). A second faunal zone was more variable and comprised of a mixed assemblage of agglutinated species described above in addition to calcareous species; Ammonia spp., Elphidium spp., Haynesina germanica and Quinqueloculina spp. This zone spanned a large vertical range above and below MTL. In a third faunal zone calcareous species dominated and was restricted to the lower altitudes of the salt-marsh environments. Further quantitative measures were employed to test the hypothesis that foraminiferal distributions were controlled by altitude. Partial ordination techniques revealed altitude as a statistically significant control confirming their suitability as proxies for sea-level in transfer function reconstructions. An analysis of species environment relationships revealed strong linear response suggesting the use of PLS regression models. Transfer functions were then developed for both site specific and a total combined dataset, where small r2 jack values largely reflected the short environmental gradients despite relatively low predictions errors (RMSEP jack = <0.11). The total combined dataset was chosen and screened to remove sample outliers improving model performance (r2 jack = 0.54 and RMSEP jack = 0.08). Finally, the transfer function model was applied to core sediments to reconstruct mean sea-level where an inflexion observed at AD 1940 showed acceleration comparable to other proxy reconstructions. Indeed this trend was similar to instrumental data from Trieste tide-gauge records. Similarly the transfer function reconstruction identifies the dramatic increases in MSL observed in both tide-gauge (Split and Trieste) and satellite observations since the early 1990s.

The viability of using a foraminifera-based transfer function method to reconstruct the local relative sea-level for the Mersey Estuary was assessed in this study, which has not been previously investigated in the UK in the context of application in a strongly macrotidal setting. A total of 105 surface samples were collected across two saltmarshes. Foraminiferal analysis was carried out, along with several environmental variables (organic matter content, salinity, pH, and grain size) to establish the species distribution of foraminifera and their relationship with elevation. Two main zonations were found: a high-to-middle marsh zone occupied by Haplophragmoides spp., J. macrescens and M. fusca; and a low marsh zone composed of increasing numbers of calcareous species including Elphidium spp.; and Haynesina spp. Foraminiferal distributions along each transect were found to be controlled predominantly by elevation and distance from tidal influence, whilst combined datasets reflected intra- and inter-site variability in the assemblages. Elevation was still found to have an important control over the distributions, with a strong relationship between the species zonations and elevation (r2 = 0.8). Therefore, the dataset (82 samples) formed a local training set in which a transfer function for the relationship between foraminifera species and elevation was developed. WAPLS was used as it produced the highest predictive ability (r2 jack = 0.85) and lowest prediction errors (RMSEPjack = 0.11 m). Regional and combined (local plus regional) transfer functions were also developed but the local transfer function produced the most accurate and reliable reconstruction. Reconstructions were carried out for both saltmarshes with reference to a sediment chronology which was established using radionuclides and pollution indicators. The reconstructions demonstrated the vast difference in the saltmarsh development and record of sea level between the sites. Oglet Bay developed as a result of increased accommodation space arising from changing estuary morphology, resulting in rapid accretion (2.34 cm year-1) and was found to be strongly influenced by tidal channel migration. Decoy Marsh accreted at a slower pace (0.32 cm year-1) and was less affected by tidal or morphological changes. Both reconstructions were affected by decalcification resulting in the reconstructions dating back to 1978 at the most. The reconstructed rates of sea-level change were 1.8 cm year-1 for Oglet Bay and 1.1 cm year-1 for Decoy Marsh, both of which over-estimate the trend from the monthly instrumental record (1.04 cm year-1) over the same period. The study highlights the problems which may arise when conducting research in an inner estuary which is strongly macrotidal, including tidal range changes, tidal asymmetry, and decalcification, but also demonstrates that a relatively precise and reliable reconstruction is achievable.