9713547 Weidman This study will produce an ocean temperature record for the northern North Atlantic covering the last 1000 years, based on stable oxygen isotope analysis of annual growth bands of the long-lived bivalve Arctica islandica. Bands from the period ca. 500-1000 yr B.P. will be dated by radiocarbon analysis, whereas those from 100-500 yr B.P. will be dated by aspartic acid racemization which will provide significantly better precision than radiocarbon for this period. An annual 18O record for the last 100 yr has already been constructed from live-collected Arctica (Weidman and Jones, in prep.). The study will be carried out using subfossil shells dredged from surface sediments in the Nantucket Shoals region. This outer continental shelf area is shallow enough to provide a temperature record of upper ocean waters but far enough off shore to be away from the influence of continental freshwater inputs. The site is further distinguished by being the location of a particularly long instrumental record of temperatures obtained from the former Nantucket Lightship and is currently a NOAA long-term weather monitoring site. A time series of ca. 25 shells, spanning the relevant age range and each containing a record of >50 years growth, will be selected for analysis. The second primary goal of this study is to evaluate cross-matching of band width variations among individuals to construct an annual time series, analogous to tree ring series. This has the potential to produce a continuous annual record of environmental changes in the North Atlantic over recent centuries. Long (>100 yr), high-resolution records of marine environments are rare, in contrast to terrestrial environments, and are largely absent for higher-latitude ocean regions. This paucity of suitable ocean temperature records restricts our understanding of linkages between atmospheric and oceanic climate variations. Such information is critical to understanding the nature and causes of recent climate changes. These include the long-term (century scale) variations of the Medieval Warm Period, the Little Ice Age, and the warming trend of the 20th century, which have been documented from terrestrial records, as well as shorter-term (decadal scale) fluctuations such as the North Atlantic Oscillation. The methods that are brought together in this study for the first time to extract such records from mollusk shells can also be used to obtain paleoclimatic records from other ocean regions. The 1000-year time series of shell growth bands that will be assembled will serve as an archive of the marine geochemical record and will be made available to other workers for other types of analyses. The proposed study constitutes a collaborative research project between G. Goodfriend at the Carnegie Institution of Washington and C. Weidman at the Woods Hole Oceanographic Institution.
