Historical record of trace elements since MIS 2 in a sediment core of Laizhou Bay, China.

The concentration of trace elements in sediments is a critical element in the quality of nearshore environments. Geochemical background values are the normal concentrations of trace elements in the natural environment, and the use of different background values has resulted in different evaluations. Trace element (Cu, Pb, Zn, Cr, Cd, As, and Hg) concentration profiles along a sediment core were investigated to obtain background values and to assess the depositional processes and contamination levels in Laizhou Bay. The average values of trace elements in the sediments formed during the Middle Holocene can be used as reference values for background values. Apart from As and Hg, all other metals had similar distribution patterns and could be divided into four stages since marine isotope stage (MIS) 2. The results of the enrichment factor, geoaccumulation index, and principal component analysis showed that element enrichment or contamination in the core sediments was absent, and that all trace elements were mainly naturally sourced. The changes in trace elements in the core sediments since MIS 2 were predominantly related to the sedimentary environment, sediment sources, and mean grain size.