tropical-subtropical ocean d15N compilation

This dataset contains δ15Nbulk and δ15Norg data of Site MD10-3340 and J1007, stacked δ15Nanomaly of seven N-fixation or water column denitrification provinces, and net N loss calculation of index and flux.

Samples are measured with a Thermo Finnigan DELTAplus XP isotope ratio mass spectrometer aligned to a CE EA1112 C/N/S analyzer for δ15N analyses.

For δ15Norg analyses, sediments are first treated with 1 M hydrochloric acid to remove carbonates, following with 5 M hydrofluoric acid and 1 M hydrochloric acid to remove clay minerals.

For each record, δ15Nanomaly is obtained by interpolating the original δ15N record to a common 1-kyr interval and normalizing by subtracting the mean over the last 140 kyr. Averaging δ15Nanomaly in each province gives stacked δ15Nanomaly. The uncertainty is determined by the standard deviation of included records in each stack, reflecting spatial variability within each province.

To remove the sea level component in the δ15Nanomaly of the SCS and CaS, the z-score normalization is applied on the two δ15Nanomaly records and a global composite sea level stack that is evenly spaced to 1 kyr54, using the mean value and the standard deviation of each. The detrended δ15Nanomaly is obtained by adding normalized sea level to normalized δ15Nanomaly.