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

Abstract

This study presents nearly continuous air-sea CO 2 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 CO 2 flux at different time scales using time series decomposition. Monthly variations in CO 2 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 CO 2 uptake positively on an hourly scale. Interannual variations in CO 2 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 CO 2 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 CO 2 sink into the sea (CO 2 flux of ca. 2260 g C m 22 yr 21 ). If all coastal areas inhabited by macrophytes had a similar CO 2 uptake rate, the net CO 2 uptake from these areas alone would roughly equal the net CO 2 sink estimated for the entire global coastal ocean to date. A similar-strength CO 2 flux, ranging between 20.09 and 20.01 g C m 22 h 21 , was also observed over another kelp bed from a pilot study of boat-based eddy covariance measurements.

Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements

“…The frequency-weighted cospectrum of O 3 with w has a well-characterized form with exhibited dependence on wind speed and measuring height (Kaimal et al, 1972). Comparison of the observed cospectra shape against the idealized Kaimal cospectra is useful for validating that the observed signal was not significantly attenuated at low or high frequencies.…”

“…for EC flux observations by our group and others (Ikawa and Oechel, 2015;Kim et al, 2014;Porter et al, 2018). The Ox-CIMS was housed in a temperature-controlled trailer at the end of the pier.…”

“…(a) Mean binned frequency-weighted cospectra O 3 and sensible heat flux with vertical wind from the average of two consecutive flux periods from 14:10 to 15:20 local time on 20 July. The Kaimal trace is the idealized cospectraKaimal et al (1972) for a mean wind speed of 4.4 m s −1 and an unstable atmosphere. The sensible heat trace is inverted, and the observed net sensible heat flux was positive for this period.…”

Reviews and syntheses: Hidden forests, the role of vegetated coastal habitats in the ocean carbon budget

“…The strong autotrophic nature of macroalgal and seagrass habitats is further reflected in their role as strong sinks for atmospheric CO 2 (e.g. Gazeau et al, 2005;Unsworth et al, 2012;Tokoro et al, 2014;Ikawa and Oechel, 2015). Seagrass, salt marshes, macroalgae and mangroves all contribute significant loads of material to adjacent beaches, where they can accumulate large carbon stocks (e.g.…”

Improved Post-processing of Eddy-Covariance Data to Quantify Atmosphere–Aquatic Ecosystem CO2 Exchanges

“…Despite the promise of EC measurements, their application in aquatic environments remains challenging (Tsukamoto et al, 2004;Rutgersson and Smedman, 2010;Vesala, 2012;Blomquist et al, 2013;Ikawa and Oechel, 2014;Kondo et al, 2014;Landwehr et al, 2014). The main difficulty is that the air-water CO 2 flux is small compared with the air-land CO 2 flux (Vesala, 2012;Landwehr et al, 2014).…”