A year in the life of a central California kelp forest: physical and biological insights into biogeochemical variability
Kelp forests are among the world's most productive marine ecosystems, yet little is known about their biogeochemistry. This study presents a fourteen-month time series (July 2013&ndash;August 2014) of surface and benthic dissolved inorganic carbon and total alkalinity measurements, along with accompanying hydrographic measurements, from six locations within a central California kelp forest. We present ranges and patterns of variability in carbonate chemistry, including pH
... (7.70&ndash;8.33), <i>p</i>CO<sub>2</sub> (172&ndash;952&thinsp;µatm), and the aragonite saturation state, Ω<sub>Ar</sub> (0.94&ndash;3.91). Surface-to-bottom gradients in CO<sub>2</sub> system chemistry were as large as the spatial gradients throughout the bottom of the kelp forest. Dissolved inorganic carbon variability was the main driver of the observed CO<sub>2</sub> system variability. The majority of spatial variability in the kelp forest can be explained by advection of cold, dense high CO<sub>2</sub> waters into the bottom of the kelp forest, with deeper sites experiencing high CO<sub>2</sub> conditions more frequently. Despite the strong imprint of advection on the biogeochemical variability of the kelp forest, surface waters were undersaturated with CO<sub>2</sub> in the spring through fall, indicative of the strong role of photosynthesis on biogeochemical variability. We emphasize the importance of spatially distributed measurements for developing a process-based understanding of kelp forest ecosystem function in a changing climate.