DOI: 10.25921/w9ca-1z10
title: NOAA/WDS Paleoclimatology - NICOPP Global Ocean Sediment Nitrogen Isotope Database

description: The stable isotopes of nitrogen offer a unique perspective on changes in the nitrogen cycle, past and present. However, the presence of multiple forms of nitrogen in marine sediments can complicate the interpretation of bulk nitrogen isotope measurements. Although the large-scale global patterns of seafloor d15N have been shown to match process-based expectations, small-scale heterogeneity on the seafloor, or alterations of isotopic signals during translation into the subseafloor record, could obscure the primary signals. Here, a public database of nitrogen isotope measurements is described, including both seafloor and subseafloor sediment samples ranging in age from modern to the Pliocene, and used to assess these uncertainties. In general, good agreement is observed between neighbouring seafloor sites within a 100 km radius, with 85% showing differences of < 1 per mil. There is also a good correlation between the d15N of the shallowest (< 5 ka) subseafloor sediments and neighbouring seafloor sites within a 100 km radius (R2 = 0.83), which suggests a reliable translation of sediments into the buried sediment record. Meanwhile, gradual d15N decreases over multiple glacial-interglacial cycles appear to reflect post-depositional alteration in records from the deep sea (below 2000 m). We suggest a simple conceptual model to explain these 100-kyr-timescale changes in well-oxygenated, slowly accumulating sediments, which calls on differential loss rates for pools of organic N with different d15N. We conclude that bulk sedimentary nitrogen isotope records are reliable monitors of past changes in the marine nitrogen cycle at most locations, and could be further improved with a better understanding of systematic post-depositional alteration. Furthermore, geochemical or environmental criteria should be developed in order to effectively identify problematic locations and to account for confounding influences where possible.
description: Nitrogen Cycle in the Ocean, Past and Present (NICOPP) database of global ocean marine sedimentary d15N measurements, from both seafloor samples and subseafloor records.

NICOPP is a joint working group of PAGES and IMAGES. NICOPP studies Nitrogen isotope (d15N) dynamics as recorded in the sedimentary record in order to learn about the dynamics of the marine nutrient cycle in the Quaternary and the present. For the seafloor compilation, d15N is given as point measurements along with the corresponding latitude and longitude. Currently, it contains data from about 2,300 samples. The subseafloor compilation includes almost all bulk marine sedimentary d15N records published in the literature. Along with the d15N measurements, we included the corresponding sediment depth, a published age model (if available), nitrogen content (N%), total organic carbon content (Corg%), and dry bulk density. There are currently about 140 d15N records included in the database. The timespans of the given records range from a few hundred years to four million years.

More information on NICOPP: http://pastglobalchanges.org/science/wg/former/nicopp/