The sedimentary stable nitrogen isotope compositions of bulk organic matter (δ<sup>15</sup>N<sub>bulk</sub>) and silicon isotope composition of diatoms (δ<sup>30</sup>Si<sub>BSi</sub>) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ<sup>15</sup>N<sub>bulk</sub> signal ultimately recorded within the sediments is also influenced by water column denitrification causing an increase in the subsurface δ<sup>15</sup>N signature of dissolved nitrate (δ<sup>15</sup>NO<sub>3</sub><sup>−</sup>) upwelled to the surface. Such conditions are found in the oxygen minimum zone off Peru, where at present an increase in subsurface δ<sup>15</sup>NO<sub>3</sub><sup>−</sup> from North to South along the shelf is observed due to ongoing denitrification within the pole-ward flowing subsurface waters, while the δ<sup>30</sup>Si signature of silicic acid (δ<sup>30</sup>Si(OH)<sub>4</sub>) at the same time remains unchanged.<br><br> Here, we present three new δ<sup>30</sup>Si<sub>BSi</sub> records between 11° S and 15° S and compare these to previously published δ<sup>30</sup>Si<sub>BSi</sub> and δ<sup>15</sup>N<sub>bulk</sub> records from Peru covering the past 600 years. We present a new approach to calculate past subsurface δ<sup>15</sup>NO<sub>3</sub><sup>−</sup> signatures based on the correlation of δ<sup>30</sup>Si<sub>BSi</sub> and δ<sup>15</sup>N<sub>bulk</sub> signatures at a latitudinal resolution for different time periods. Our results show source water δ<sup>15</sup>NO<sub>3</sub><sup>−</sup> compositions during the last 200 years, the Current Warm Period (CWP) and during short-term arid events prior to that, which are close to modern values increasing southward from 7 to 10 ‰ (between 11° S and 15° S). In contrast, humid conditions during the Little Ice Age (LIA) reflect consistently low δ<sup>15</sup>NO<sub>3</sub><sup>−</sup> values between 6 and 7.5‰. Furthermore, we are able to relate the short-term variability in both isotope compositions to changes in the ratio of nutrients (NO<sub>3</sub><sup>−</sup> : Si(OH)<sub>4</sub>) taken up by different dominating phytoplankton groups (diatoms and non-siliceous phytoplankton) under the variable climatic conditions of the past 600 years.