Articles | Volume 14, issue 1
Biogeosciences, 14, 31–44, 2017
Biogeosciences, 14, 31–44, 2017

Research article 05 Jan 2017

Research article | 05 Jan 2017

A year in the life of a central California kelp forest: physical and biological insights into biogeochemical variability

David A. Koweek1,a, Kerry J. Nickols2,3, Paul R. Leary2, Steve Y. Litvin2, Tom W. Bell4, Timothy Luthin1, Sarah Lummis2,b, David A. Mucciarone1, and Robert B. Dunbar1 David A. Koweek et al.
  • 1Department of Earth System Science, Stanford University, Stanford, CA 94305, USA
  • 2Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA
  • 3School of Natural Sciences, California State University Monterey Bay, Seaside, CA 93955, USA
  • 4Earth Research Institute, University of California, Santa Barbara, CA 93106, USA
  • apresent address: Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, USA
  • bpresent address: Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA 95060, USA

Abstract. Kelp forests are among the world's most productive marine ecosystems, yet little is known about their biogeochemistry. This study presents a 14-month time series (July 2013–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 (7.70–8.33), pCO2 (172–952 µatm), and the aragonite saturation state, ΩAr (0.94–3.91). Surface-to-bottom gradients in CO2 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 CO2 system variability. The majority of spatial variability in the kelp forest can be explained by advection of cold, dense high-CO2 waters into the bottom of the kelp forest, with deeper sites experiencing high-CO2 conditions more frequently. Despite the strong imprint of advection on the biogeochemical variability of the kelp forest, surface waters were undersaturated with CO2 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.

Short summary
This paper presents results from a year-long study of a kelp forest offshore of Pacific Grove, California. We use tools and techniques from chemistry to study the kelp forest. We find very large chemical variability in the kelp forest, primarily between the surface of the water and the bottom of the forest. There are many reasons for this variability; we conclude that both regional upwelling and kelp growth are responsible for contributing to this variability.
Final-revised paper