NORTH ATLANTIC OSCILLATION SIGNAL IN NEW ENGLAND ESTUARINE FOSSIL PIGMENTS, PETTAQUAMSCUTT RIVER ESTUARY, RHODE ISLAND

The North Atlantic Oscillation (NAO) is the dominant pattern dictating climate variability in the North Atlantic region. In order to understand both the nature of the oscillation as well as biogenic responses to its shifts, it is important to produce long-term proxy records that start before anthropogenic alterations are evident. A number of multi-proxy studies have produced such records, however none of these uses marine nor coastal proxies in its reconstruction, thus inhibiting assessment of marine ecological ramifications of future NAO variability. In this study, we have produced a 475 year record of gross productivity in the Pettaquamscutt River Estuary, RI as inferred from fossil pigments preserved in permanently anoxic and varved sediments. The pigments measured allow us to examine the long-term fluctuations of phytoplankton productivity (chlorophyll a), anoxic bacterial productivity (bacteriochlorophyll e), and zooplankton activity/grazing (sterol chlorine esters). Spectral analyses of the fossil pigment records reveal a common significant peak at a periodicity of 8.1 years. This periodicity is also observed in the winter NAO index from instrumental records (1) and other proxy records (2, 3). Band-pass filtered data around this 8.1-year peak reveal positive correlations between our coastal productivity proxies and the NAO. This correlation is most likely due to the increased water temperatures from positive NAO years leading to better growing conditions for aquatic autotrophs. An interesting decrease in the filtered amplitudes arises in all three of our proxy records concurrent with the Maunder Minimum of solar irradiance. The decreased solar energy and temperatures associated with this time period likely dampened the NAO signal in the aquatic food web by limiting autotrophic productivity. The productivity data from the Pettaquamscutt River is the first coastal proxy data from the western North Atlantic that has been shown to correlate with the NAO. This study clearly illustrates the applicability of fossil pigment records to reconstructive studies of the NAO and perhaps other dominant climate patterns.

1. P. D. Jones et al., International Journal of Climatology 17, 1433-1450 (1997).

2. E. R. Cook et al., Journal of Climate 15, 1754-1764 (2002).

3. B. R. Schöne et al., Geology 31, 1037-1040 (2003).