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Keywords:

  • N2 fixation;
  • denitrification;
  • nitrogen isotope;
  • sedimentery record;
  • western Pacific

[1] A sedimentary δ15N record in the equatorial western Pacific (WP) shows glacial-interglacial variability from 6.2 to 11.2‰ during the last two climatic cycles, similar to the denitrification record in the eastern tropical Pacific (ETP). Contrastively, a record in the South China Sea (SCS) exhibits less changes from 4.4 to 6.4‰ and is quite alike previously published results in marginal seas in the WP. By ruling out several possible causes for theδ15N variability, the δ15N record in the equatorial WP is interpreted as the source nitrate δ15N signals advected from the ETP. Comparison of several δ15N records for the last 25 ka distributed in the WP brings out a pattern of northward decrease in δ15N values and variability from the equator to off Mindano and then to marginal seas, supposed to be caused by the northward increase of local N2fixation. Therefore, the less glacial-interglacial changes in someδ15N records in the WP could imply that the glacial decrease in subsurface δ15N due to less denitrification in source waters from the ETP would have been isotopically compensated by a synchronous decrease in local N2 fixation.