Temporal variations in air‐sea CO2 exchange near large kelp beds near San Diego, California

Abstract

AbstractThis study presents nearly continuous air‐sea CO2 flux for 7 years using the eddy covariance method for nearshore water near San Diego, California, as well as identifying environmental processes that appear to control temporal variations in air‐sea CO2 flux at different time scales using time series decomposition. Monthly variations in CO2 uptake are shown to be positively influenced by photosynthetically active photon flux density (PPFD) and negatively related to wind speeds. In contrast to the monthly scale, wind speeds often influenced CO2 uptake positively on an hourly scale. Interannual variations in CO2 flux were not correlated with any independent variables, but did reflect surface area of the adjacent kelp bed in the following year. Different environmental influences on CO2 flux at different temporal scales suggest the importance of long‐term flux monitoring for accurately identifying important environmental processes for the coastal carbon cycle. Overall, the study area was a strong CO2 sink into the sea (CO2 flux of ca. −260 g C m−2 yr−1). If all coastal areas inhabited by macrophytes had a similar CO2 uptake rate, the net CO2 uptake from these areas alone would roughly equal the net CO2 sink estimated for the entire global coastal ocean to date. A similar‐strength CO2 flux, ranging between −0.09 and −0.01 g C m−2 h−1, was also observed over another kelp bed from a pilot study of boat‐based eddy covariance measurements.