Fish scales in sediments from off Callao, central Peru

We study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains (P_fish) in a sediment core retrieved off Callao, Peru (12°1′S, 77°42′W; water depth=179 m; core length=52 cm). We interpret our results as a function of changing redox conditions based on ratios of redox-sensitive trace elements (Cu/Al, Mo/Al, Ni/Al, Zn/Al, V/Al), terrigenous indicators (Fe in clays, Ti, Al), and biogenic proxies (CaCO₃, biogenic opal, total nitrogen, organic carbon, barite Ba). The core covers roughly 700 years of deposition, based on ²¹⁰Pb activities extrapolated downcore and ¹⁴C dating at selected intervals. Our fish-scale record is dominated by anchovy (Engraulis ringens) scales followed by hake (Merluccius gayii) scales. The core presented an abrupt lithological change at 17 cm (corresponding to the early 19th century). Above that depth, it was laminated and was more organic-rich (10-15% organic carbon) than below, where the core was partly laminated and less organic-rich (<10%). The lithological shift coincides with abrupt changes in dry bulk density and in the contents of terrigenous and redox-sensitive trace elements, biogenic proxies, and fish scales. The remarkable increase in redox-sensitive trace elements in the upper 17 cm of the core suggests more reducing conditions when compared with deeper and older horizons, and is interpreted as an intensification of the oxygen minimum zone off Peru beginning in the early 19th century. Higher fish-scale contents and higher P_fish/P_total ratios were also observed within the upper 17 cm of the core. The behavior of biogenic proxies and redox-sensitive trace elements was similar; more reduced conditions corresponded to higher contents of CaCO₃, C_org, total nitrogen and fish scales, suggesting that these proxies might convey an important preservation signal.