North Pacific-wide spreading of isotopically heavy nitrogen from intensified denitrification during the Bølling/Allerød and post-younger dryas periods: Evidence from the Western Pacific

Abstract

Sedimentary δ15N record for the past 30 ka buried in the Okinawa Trough in the western North Pacific mimicking the pattern from the Eastern Tropical North Pacific (ETNP), but the values (4.45.8) and the amplitude of the variation were much smaller than those (917) of the previous site. All but three values in the record were lower than the mean δ15N (5.6) of nitrate in the upper 800 m of the Kuroshio water suggesting additional inputs of isotopically light nitrogen from N2-fixation. The peak values of δ15N occurred during the Bølling/Allerød period and the warming period right after the Younger Dryas, synchronous to those found in the Eastern North Pacific. It is highly probable the high δ15N values are originated from the influence of the intensified denitrification in the ETNP during the warming periods. These new data represent the sedimentary record most distant from the intensive denitrifying zone in the ETNP and may serve as critical constraints to better quantify the nitrogen budget in the last climate cycle.