Multiple pathways of pteropods impacting the carbonate budget in the North Pacific

Pteropods are one of the most important ecological and biogeochemical players in the North Pacific beyond 50 ^◦N latitudinal range, the area that is experiencing rapid changes in ocean acidification (OA). Pteropods are sensitive to OA intensification, as demonstrated by reduced calcification, increased dissolution and reduced growth, all the processes that additively contribute to the carbonate budget. Limited knowledge exists on the impact of OA seasonal variability and associated environmental parameters on such biological processes. This is important in the regions where the abundance of pteropods predominates over all the other calcifiers, such as in the case of this investigated region. To understand regional changes in pteropod contribution towards the carbon fluxes, we used a combination of different methods (micro CT scanning, scanning electron microscopy and length frequency analyses) combined with physical-chemical OA observations. Our results indicate that shell density correlates with the calcification capacity and is impacted by mean conditions, seasonal OA variability, as well as the temperature experienced in the larval stages. Shell dissolution, which is related to mean OA conditions, is not seasonally specific process, and is impacting pteropods across different life stages. The growth is seasonally dependent, with temperature and food availability impacting summer cohorts, and OA being the only driver to impact the growth of the winter cohorts. These processes can cumulatively impact carbon fluxes mostly during the winter time. Since the regional increases in total alkalinity have been observed, we present several hypotheses to link biogeochemical and pteropod biological processes to make inferences about future carbonate budget across the regional scales of the Eastern North Pacific.