Transitioning global change experiments on Southern Ocean phytoplankton from lab to field settings: Insights and challenges

The influence of global change on Southern Ocean productivity will have major ramifications for future management polar life. A prior laboratory study investigated the response a batch-cultured subantarctic diatom to projected simulating conditions 2100 (increased temperature/CO2/irradiance/iron; decreased macronutrients), showed twofold higher chlorophyll-derived growth rate driven mainly by temperature and iron. We translated this design field understand phytoplankton community response, within foodweb, conditions. 7-d shipboard utilizing 250-liter mesocosms was conducted in March 2016. outcome mirrors lab-culture experiments, yielding chlorophyll treatment relative control. This trend also evident intrinsic metrics including nutrient depletion. Unlike study, photosynthetic competence revealed transient effect mesocosm, peaking day 3 then declining. Metaproteomics significant differences protein profiles between treatments 7. control proteome enriched processes (c.f. 2100) exhibited iron-limitation signatures; exposed shift cellular energy production. Our findings enhanced are comparable model simulations, but underlying mechanisms (temperature, iron, and/or light) differ experiments models. Batch-culture approaches hinder cross-comparison mesocosm simulations (the latter akin “continuous-culture chemostats”). However, chemostat techniques problematic use with mesocosms, as mesozooplankton evade seawater flow-through, thereby accumulating. Thus, laboratory, field, modeling reveal challenges be addressed better how alter productivity.