A MULTI-PROXY EXTRATROPICAL NORTH PACIFIC TEMPERATURE RECONSTRUCTION FROM BIVALVES AND TREES

The extratropical North Pacific plays an important role in the global climate system, however, regional reconstructions of sea surface temperature from this region poorly agree with one another, and considerable uncertainty remains around variability prior to 1900 CE. Pacific geoduck (Panopea generosa) growth increment chronologies, that highly correlate with sea surface temperature, could provide useful insights into past climate variability over the pre-industrial era. Dead geoduck samples were collected at three key sites where growth in live-collected chronologies has been shown to be especially sensitive to broad-scale environmental variability. All shells were embedded in epoxy, cut through the center, polished, and etched with hydrochloric acid before an acetate impression was taken. Acetate peels were then photographed at approximately 200x magnification and growth-increment widths were measured using Image Pro Premier. The growth increment series were crossdated using the semi-automated skeleton-plotting program RingdateR. The chronology currently extends from 1728 to 2003, with an expressed population signal > 0.85 along the full chronology length and an average series intercorrelation of 0.79. The chronology has a stable relationship with local instrumental SST (r² = 0.23, n = 62) as well as to a preliminary tree-ring based SST reconstruction that fully overlaps with the geoduck chronology (r² = 0.25, n = 276). Geoducks and trees provide complimentary perspectives of SST variability and are characterized by a strong 20^th century warming trend, and strong 20^th century interdecadal variability that followed relatively cool and quiescent conditions over the 19^th century. Moreover, the latter Little Ice Age was characterized by relatively high variability, including a strongly anomalous cool event around the year 1810 CE.