Chapter 10 Pelagic Bacterial Processes in Polynyas

Abstract

Abstract Polynyas are considered model ecosystems for understanding high-latitude carbon cycling, especially with regards to climate-sensitivity of the biological pump. Explanations for highly efficient carbon export from polynyas and other marginal ice zones often focus on the balance of autotrophy and heterotrophy in these perennially cold ecosystems. The remineralization of algal production is controlled, at least in part, by the activities of pelagic heterotrophic bacteria. Here, we review these activities in both Arctic and Antarctic polynya ecosystems and include a discussion of commonly used methods. Recent research findings from the Northeast Water (NEW), North Water (NOW), and Ross Sea Polynya (RSP) programs are summarized and compared. Overall the pelagic bacteria of these ecosystems respond quickly to spring and summertime algal blooms, similar to their temperate counterparts. We find little evidence for growth rate limitation by low temperature, at least during the phytoplankton growing season. Despite sometimes significant rates of bacterivory and viral lysis, bacterial growth is fast enough for stocks to accumulate to levels similar to those observed in temperate oceans. Despite apparent differences in DOM cycling and availability, Arctic and Antarctic polynya bacteria are more similar than dissimilar in their seasonal activities. High-latitude food web structure, leading bacteria to a focus on hydrolysis and solubilization of particulate matter may partly explain this finding. We speculate about the impacts of global warming on these ecosystems and envision a scenario in which hemispheric differences in polynya microbial ecology and biogeochemical function will be amplified.