Ice fish otoliths record dynamics of advancing and retreating sea ice in Antarctica

Trace element concentrations within fish otoliths act as biological tags and environmental chronometers within aquatic environments. Linking patterns in elemental concentrations within ice fish otoliths to sea ice dynamics allows us to better understand the chemical dynamics of ice-covered environments. Here laser ablation inductively coupled plasma mass spectrometry was used to measure the concentrations of conservative and bioactive trace elements in yearly otolith bands of two benthic ice fishes and one cryopelagic ice fish collected from sites along the gradient in sea ice persistence in McMurdo Sound, Antarctica. We used a 12-yr time series of satellite images to define summertime extent of ice cover from 2002 to 2014. Elemental concentrations of Sr and Li were higher in the otoliths of the cryopelagic species, while Mn concentrations were higher in the otoliths of benthic species, reflecting differences in species' association with sea ice melt and formation. Multivariate dispersion of individual elemental concentrations was greater within the cryopelagic species, indicative of their more transient residence among sites. Key bioactive and conservative elements differed among years with contrasting sea ice dynamics for both cryopelagic and benthic ice fish species. These differences were likely due to sea ice formation concentrating trace metals from the water column and incorporating resuspended sediments, dust, or glacial meltwater with high metal content. Our results provide strong evidence for the effectiveness of trace element concentration profiles in otoliths as environmental recorders of the dynamics of sea ice conditions, and for the role of ice fish as environmental sentinels in Antarctica.