Sr/ 86 Sr reference maps (isoscapes) are a key tool for investigating past human and animal migrations. However, there is little understanding of which biosphere samples are best proxies for local bioavailable Sr when dealing with movements of past populations. In this study, biological and geological samples (ground vegetation, tree leaves, rock leachates, water, soil extracts, as well as modern and archeological animal teeth and snail shells) were collected in the vicinity of two early medieval cemeteries ("Thuringians", 5-6th century AD) in central Germany, in order to characterize 87 Sr/ 86 Sr of the local biosphere. Animal tooth enamel is not appropriate in this specific context to provide a reliable 87 Sr/ 86 Sr baseline for investigating past human migration. Archeological faunal teeth data (pig, sheep/goat, and cattle) indicates a different feeding area compared to that of the human population and modern deer teeth 87 Sr/ 86 Sr such as freshwater bivalve shells and tree cores were examined in order to track potential historic anthropogenic contamination of the water and the vegetation. The data obtained from the archeological bivalve shells show that the modern rivers yield 87 Sr/ 86 Sr ratios which are similar to those of the past. However, the tree cores registered decreasing 87 Sr/ 86 Sr values over time towards present day likely mirroring anthropogenic activities such as forest liming, coal mining and/or soil acidification. The comparison of 87 Sr/ 86 Sr of the Thuringian skeletons excavated in the same area also shows that the vegetation samples are very likely anthropogenically influenced to some extent, affecting especially 87 Sr/ 86 Sr of the shallow rooted plants.

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a b s t r a c tIt has been suggested that maximum latewood density (MXD) should be used instead of tree-ring width (TRW) data to reconstruct post-volcanic cooling effects. A thorough assessment of high frequency signals and potentially differing memory effects in long MXD and TRW chronologies, in response to large volcanic eruptions, is still missing, however. We here present a compilation of MXD and TRW chronologies from 11 sites in the Northern Hemisphere, covering the past 750+ years, and containing significant June-August temperature signals. Basic assessment of the data using Superposed Epoch Analysis reveals a temporally extended response in TRW, by 2-3 years, to large volcanic eruptions, though post-volcanic cooling patterns vary considerably within the Northern Hemisphere network. Comparison with instrumental temperature data demonstrates the TRW chronologies underestimate cold conditions associated with large volcanic eruptions, a bias that is mitigated in the MXD data. While species composition (pine, spruce, larch) has no detectable influence on the cooling patterns, trees from high latitude sites (>60 • N) indicate a stronger and delayed (1-2 years) response to large eruptions, compared to the lower latitude sites (<60 • N). These basic findings caution against using TRW data for quantitatively estimating post-volcanic cooling and for comparison against the simulated climate effects of volcanic eruptions in models.

Bivalve mollusks are biological chart recorders: their shells contain a record of environmental conditions in the form of geochemical variation. However, these records are often incomplete. Growth cessations and/or changing growth rates can reduce the range and resolution of the recorded environmental conditions.To investigate the effects of these variables on geochemical profiles, stable oxygen isotope (␦ 18 O) profiles were modeled using several growth parameters. Two sets of profiles were calculated: one with constant daily increment widths, the other based on the annual pattern of daily increment width variation observed in the northern Gulf of California bivalve mollusk Chione cortezi. In both sets of models, multiyear ␦ 18 O profiles were calculated assuming that the bivalve shell grows continuously throughout its life. Other profiles were calculated to simulate an ontogenetic decrease in growth rate by decreasing the growth period, daily growth rate, or both. Altering the growth period simulates the effects of thermal thresholds, above or below which no shell material is deposited. Decreasing the daily growth rate results in lower annual shell growth rates while keeping the growth period constant. Combining the two provides a more accurate representation of bivalve shell growth in many subtropical and temperate species.In addition to the modeling exercise, the shell of a Chione cortezi that lived in the northern Gulf of California was sampled in two ways. First, low-resolution (300 micron) samples were recovered from the entire growth profile along the axis of maximum shell height (umbo to the commissure). Second, high-resolution (50 micron) samples were taken from regions of the shell representing winter growth from late in the bivalve's life.Modeling results and observations indicate that the fullest range of environmental conditions only is reflected in the earliest years of growth; profiles from successive years have reduced amplitudes, sample resolutions, or both. Variation of intra-annual growth rate in models simulating continuous growth can produce cuspate ␦ 18 O profiles that mimic shutdowns. More detailed sampling in later stages of ontogeny can reconstruct a fuller range of environmental conditions. Finally, within-shell trends in isotopic amplitudes and averages may reflect decreases in growth rate rather than environmental fluctuations. Therefore, particular care should be taken when interpreting inter-annual isotope profiles from long-lived species.

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