Publication Abstract

High resolution stable isotope records from north Atlantic cod

C.R. Weidman and R.S. Millner

Stable oxygen (δ¹⁸O) and carbon isotope (δ¹³C) records were obtained from the otoliths of cod (sp. Gadus morhua), using micro-sampling methods that allow for high temporal resolution within the otoliths' seasonal growth bands (up to 20 plus samples per year). Eleven otoliths were sampled from specimens of varied age (2-12 years), collected from different locations in the eastern North Atlantic, including the Faroes, Irish Sea, North Sea and Barents Sea. The δ¹⁸O signals show a seasonal variation coincident with the otoliths' visible growth bands, generally supporting band-count age estimates. Cod otolith δ¹⁸O records show a close correspondence to the expected signal based on the bottom temperature characteristics of their respective capture regions. These results indicate that cod otolith aragonite is deposited in oxygen isotopic equilibrium with ambient conditions, and is an accurate (~ 1°C) recorder of ocean temperature. In contrast, cod otoliths appear to be in δ¹³C disequilibrium with ambient conditions. Cod otolith δ¹³C is interpreted as a combination of two carbon sources (80% dissolved inorganic carbon and 20% metabolic carbon), and varies as a result of diet, temperature and physiology.

Reference:

C.R. Weidman and R.S. Millner, 2000. High resolution stable isotope records from north Atlantic cod. Fisheries Research, 46(1-3): 327-342.