3:45 PM - 4:00 PM
[MIS34-16] Centennial-scale variability in lower trophic level productions off Tomakomai, Hokkaido
Keywords:centennial variability, lower trophic level production, Coastal Oyashio, nutrients, PDO
Results of biogenic opal, algal- and zooplankton-derived pigments showed centennial- or millennial-scale variability for the last 3000 years. Based on flux of biogenic opal, chlorophyll a + derivatives and SCEs, the centennial-scale variability caused depletions from a peak to a trough by 19-42%, 12-19% and 11-65%, respectively. This indicates that diatom productions have substantially varied on centennial timescales. Assuming that amplitude of the diatom production variations was directly attributed to nutrient levels, the depletions on centennial timescales is as large magnitude as that in PO4 (23%) in the late 20th century. The biogenic opal flux is low level at present and the decreasing trend since 19th century is considered to be part of centennial natural variability. Similar centennial-scale variability is also found in the sardine fossil scale records from Japan and off California, records of salmon abundance from Alaska, and PDO index reconstructed from tree ring width from the North America. Centennial climate changes over the Pacific may be associated with the centennial variability in the biological productivity in each region of the North Pacific and PDO. Further studies on this centennial natural variability, including a network of more productivity reconstructions in the western North Pacific and the driving mechanisms, are needed for long-term predictions of nutrient level and fisheries productions.