CLIMATE ARCHIVES FROM A VIKING AGE SITE, SCOTLAND: SEASONAL TEMPERATURE VARIABILITY DURING THE MEDIEVAL WARM PERIOD

The Medieval Warm Period (MWP; 700-1100 YBP) represents a relatively recent period of warm climate that can be compared to today’s warming trend. However, the spatial and temporal variability inherent in the MWP makes it difficult to differentiate between global climate trends and regional variability. Acquiring high-resolution temperature data from this period will allow for the better understanding of temperature variability during this important climate interval.

Our study area is located in the Orkney Islands of Scotland and consequently offers the opportunity to target a critical area in the understanding of climate dynamics. The North Atlantic Oscillation and Gulf Stream heavily influence climate in this region. Thus, the study of seasonal variability during the MWP may lead to a more accurate understanding of the behavior of these climate mechanisms during the study interval. Furthermore, the vast majority of climate archives have been derived from deep marine or arctic environments. Studying a coastal environment will offer insight into the behavior of coastal climate during the MWP, insight which is especially valuable due to the large percentage of the human population that currently lives near the coast.

We used oxygen isotope ratios (δ¹⁸O) preserved in archaeological limpet shells (Patella vulgata) collected from Viking aged midden deposits as a proxy for sea surface temperature. Five MWP limpets were micromilled to achieve submonthly to fortnightly resolution. Summer and winter temperatures averaged 14.0 +/- 0.97 ^oC and 6.4 +/- 0.83 ^oC, respectively. When compared to regional data from NOAA (13.3 +/- 0.84 ^oC and 7.4 +/- 0.49 ^oC) collected from 1981-2007, MWP summer temperatures were warmer than current averages, and winter temperatures were cooler than today. Our results indicate that seasonality during the MWP was greater than that observed during present times.