| Coastal regions play a critical role in nutrient cycling, waste treatment and flood control and prevention, yet these productive ecosystems are among the most sensitive environments to climate change. Climate changes predicted for coming centuries pose a threat to marine ecosystems for degradation. Though coastal vulnerability to climate change is well documented, few coastal regions around the world have long-term monitoring records of oceanographic conditions and patterns of variability. This lack of knowledge makes it difficult to establish baseline climate conditions for coastal regions, limiting efforts to discriminate between natural cycles of variability and abnormal climate trends. Extending the coverage of available records beyond the instrumental period can help place present coastal climate into a longer historical context. To do this, geochemical proxy records can be used to reconstruct past climate conditions in rapidly changing coastal ecosystems. Here, a two century pre-bomb time series of near surface water radiocarbon activity (Δ 14C) was generated using shell material from a marine bivalve mollusk, Arctica islandica in the western interior Gulf of Maine. Additionally, a time history of potential hydrographic conditions was generated using the oxygen isotopic composition (δ18O) of shell carbonate. In the oxygen isotope reconstruction, a persistent increase in shell δ 18O is observed between 1920 and 1980, followed by a sharp reversal of that trend into recent decades. Results also show a radiocarbon-depleted signature for the Gulf of Maine, indicating that regional hydrography is dominated by a deepwater source. A highly variable regional reservoir age offset (ΔR) is also observed, meaning that the record constructed here may help improve age model resolution for other reconstructions on the North American continental shelf regions of the western North Atlantic. |
