The growing capability of proxy ocean temperature data from months to millennia

In the century since the inception of ICES, the ability to make precise measurements using modern oceanographic instruments with ever increasing frequency and geographical coverage and to store and analyze these data using ever more powerful computers, has driven an explosion in our understanding of the oceans. It is sometimes easy to forget, then, that our longer-term knowledge of ocean variability is almost entirely built upon indirect fossil indicators or biorecords. Proxy records, spanning hundreds, thousands, and millions of years, give our handful of decades of instrument data needed perspective. Complementing the sophistication of today’s electronic sensors is the growing capability of paleoceanographic methods to provide unprecedented detail about ambient conditions in the modern as well as the ancient ocean. For the ICES centennial, this paper briefly reviews the development of one of the most widely used of these methods - the oxygen isotope composition of marine carbonates as a proxy for ocean temperature - from its origins over a half century ago to its expanding uses today. The paper focuses on recent developments that have sharpened the temporal resolution of these records. As examples, work on fish otoliths and the shells of long-lived bivalves from the North Atlantic Ocean, which have provided new and necessary insights for ICES investigations and have set the only available long-term context of change for ICES science and planning, are discussed.