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.本数据集涵盖MD10-3340与J1007两个站位的总氮稳定同位素组成δ¹⁵Nbulk及有机氮稳定同位素组成δ¹⁵Norg数据、7个固氮或水柱反硝化省的堆叠式δ¹⁵N异常值，以及指标与通量的净氮损失计算结果。 样品的δ¹⁵N分析采用与CE EA1112型碳/氮/硫元素分析仪联机的Thermo Finnigan DELTAplus XP型同位素比率质谱仪完成。 针对有机氮稳定同位素δ¹⁵Norg分析，沉积物样品首先经1 mol/L盐酸处理以去除碳酸盐，随后依次使用5 mol/L氢氟酸与1 mol/L盐酸去除黏土矿物。 对于每条记录，δ¹⁵N异常值的获取流程为：将原始δ¹⁵N记录插值至统一的1千年时间分辨率，再通过减去过去14万年的平均值完成标准化。对每个省份的δ¹⁵N异常值取平均，即可得到堆叠式δ¹⁵N异常值。不确定性由每个堆叠组内纳入记录的标准差确定，用以反映该省份内部的空间变异性。 为去除南海（South China Sea, SCS）与CaS海域δ¹⁵N异常值记录中的海平面分量，需对这两条δ¹⁵N异常值记录，以及经均匀插值至1千年分辨率的全球复合海平面堆叠序列（标注为1 kyr54）分别以各自的平均值与标准差进行Z分数标准化。随后将标准化后的海平面序列与标准化后的δ¹⁵N异常值序列相加，即可得到去趋势后的δ¹⁵N异常值。