Diurnal carbon cycling in the surface ocean and lower atmosphere of Santa Monica Bay, California

Abstract

[1] We investigate the diurnal carbon cycle in the near surface ocean and atmosphere of Santa Monica Bay, California on the basis of hourly measurements of the oceanic and atmospheric partial pressures of CO 2 (pCO 2 oc and pCO 2 atm ) and related parameters from a moored platform. The power spectrum of the data from three deployments during late spring, summer, and fall reveal a strong peak at 1 cycle/day for both oceanic and atmospheric pCO 2 . While the average diurnal peak-to-peak amplitude is about 15 to 20 matm for pCO 2 oc and about 10 matm for pCO 2 atm , the 10% largest amplitudes exceed 55 matm and 42 matm, respectively. The diurnal cycle of oceanic pCO 2 is primarily controlled by temperature, but biological processes substantially modify it. The contribution of lateral processes, such as tides, is likely small. For the fall deployment, our data suggest an average net primary production of about 30 mmol C m À2 day À1 . The diurnal cycle of atmospheric pCO 2 is primarily controlled by the air-sea breeze. Neglect of the diurnal variations in the flux calculations may result in biases of more than 0.2 mol C m À2 a À1

Direct observations of diel biological CO<sub>2</sub> fixation on the Scotian Shelf, northwestern Atlantic Ocean

“…1). Diel cycles in pCO 2 with hourly resolution were established by removing the 48-point moving average from the (hourly) observations, which is similar to the approach pursued by Leinweber et al (2009). We corrected the in-situ pCO 2 observations (pCO 2, obs ) for each day to the daily mean temperature (pCO 2, temp ) of that day using the full suite of carbonate system equations via the CO2SYS program (Lewis and Wallace, 1998) with the constants by Dickson and Millero (1987).…”

“…However, corresponding investigations of the oceanic CO 2 system are largely lacking. A few recent studies have focused on time scales of several days to months Bates et al, 2001;CopinMontegut et al, 2004;Lefèvre et al, 2008;Boutin and Merlivat, 2009;Leinweber et al, 2009;Bozec et al, 2011;Lefèvre and Merlivat, 2012). Investigations of processes at the rate of their occurrence in shelf and marginal seas are still sparse when it comes to full seasonal coverage (Vandemark et al, 2011).…”

Impact of episodic vertical fluxes on sea surface pCO 2

“…Global studies have focused on understanding the large-scale, seasonal patterns in sea-surface pCO 2 and in quantifying the related air-sea fluxes of CO 2 at coarse spatial and temporal resolution (4 • × 5 • monthly) [4]. On the other hand, disparate findings have been reported about the variability and controlling factors of surface pCO 2 on short space and time scales [5][6][7][8][9][10][11], suggesting that there is clearly need for a unified, mechanistic understanding of how surface pCO 2 responds to episodic, localized events that induce vertical mixing.…”

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

“…Although estuaries are known to be generally sources of CO 2 Cai et al, 1999Cai et al, , 2000Sarma et al, 2001Sarma et al, , 2011Abril et al, 2002;Dagg et al, 2005;Gao et al, 2005;Dai et al, 2008;Leinweber et al, 2009), only in the last few years have continental shelves been firmly established to absorb CO 2 from the atmosphere. (See, for example, Liu et al, 2000;Chen et al, 2003;Chen, 2004;Abril and Borges, 2005;Borges, 2005;Borges et al, 2005;Cai et al, 2006;Chen and Borges, 2009;Laruelle et al, 2010, and references therein.)…”