Inspired by the classic textbook “Tracers in the Sea” (Broecker and Peng, 1982) for the session’s name, we invite contributions bearing on chemical and isotopic tracers used in paleoceanography. Proxies are the backbone of paleoceanography and undergo frequent new developments. New analytical techniques and applications allow for the investigation of new proxy systems as well as the exploration of existing proxies with new substrates or more challenging sample sizes. Growing datasets have led, and are leading, to comprehensive compilations, proxy inter-comparisons, and quantitative tests of paleoceanographic model simulations. For this session, we invite presentations on both (i) modern calibrations and downcore applications, (ii) single and multiple proxies, and (iii) proxy measurements and modeling. Despite their wide applications, paleoceanographic proxies suffer generally from significant limitations. As illustrated in a famous figure by the late H. Elderfield, our confidence in a proxy goes from an optimism phase, to a pessimism phase, and eventually to a realism phase. In this spirit, both “good” and “bad” news during the development and application of proxies are welcome.