Evaluation of sinks and sources of CO₂ in the global coastal ocean using a spatially‐explicit typology of estuaries and continental shelves

Abstract

[1] The exchange of CO 2 between the atmosphere and the global coastal ocean was evaluated from a compilation of air-water CO 2 fluxes scaled using a spatially-explicit global typology of inner estuaries (excluding outer estuaries such as large river deltas) and continental shelves. The computed emission of CO 2 to the atmosphere from estuaries (+0.27 ± 0.23 PgC yr −1 ) is ∼26% to ∼55% lower than previous estimates while the sink of atmospheric CO 2 over continental shelf seas (−0.21 ± 0.36 PgC yr −1 ) is at the low end of the range of previous estimates (−0.22 to −1.00 PgC yr −1 ). The air-sea CO 2 flux per surface area over continental shelf seas (−0.7 ± 1.2 molC m −2 yr −1 ) is the double of the value in the open ocean based on the most recent CO 2 climatology. The largest uncertainty of scaling approaches remains in the availability of CO 2 data to describe the spatial variability, and to capture relevant temporal scales of variability. Citation: Laruelle, G. G., H. H. Dürr, C. P. Slomp, and A. V. Borges (2010), Evaluation of sinks and sources of CO 2 in the global coastal ocean using a spatially-explicit typology of estuaries and continental shelves,

Carbon dioxide dynamics and fluxes in coastal waters influenced by river plumes

“…We notice that this flux only represents 12−26% of the currently best estimated global continental shelf CO 2 sink of ß−0.25 PgC yr −1 Laruelle et al 2010) and does not balance the CO 2 source from inner estuaries (ß+0.25 PgC yr −1 ) ( Table 7.1). The global river plume CO 2 sink is much smaller compared with the CO 2 sink in the open ocean ranging between −1.4 PgC yr −1 and −2.2 PgC yr −1 (Gruber et al 2009;Takahashi et al 2009).…”

“…Although the numbers of inner estuaries included in the CO 2 flux estimation have increased in recent years, all global extrapolations have relied on the surface areas of inner estuaries -roughly estimated four decades ago by Woodwell et al (1973), with the exception of a recent publication by Laruelle et al (2010), which based extrapolations on typology (Dürr et al (2011). The Woodwell et al (1973) global estimate of surface areas of estuaries was based on the extrapolation of the estuarine area to coastline length for the United States that was extrapolated to the global coastline length.…”

“…The datasets (Borges 2005;Borges et al 2005) grew gradually, and in 2009 an assessment including 32 estuaries was published (Chen and Borges 2009). This database has been further extended to 60 inner estuaries in 2010 (Laruelle et al 2010) and 106 inner estuaries in 2012 .…”

“…For example, recent comparisons have been made between stratified fjords and wellmixed macro-tidal estuaries (Borges 2005) and stratified and well-mixed lagoons (Koné et al 2008). Laruelle et al (2010) scaled up the inner estuarine CO 2 fluxes using the following four estuarine types: small deltas and estuaries (8% of total surface), tidal systems and embayments (26% of total surface), lagoons (24% of total surface), and fjords and fjärds (43% of total surface).…”

“…Freshwater plumes of some large rivers (e.g., Amazon, Congo, Niger) often even extend beyond the continental shelf into the continental slope and ocean basin (Bianchi and Allison 2009). Because of the lack of reliable air-water CO 2 flux estimates and the absence of global estimates of surface areas, river plumes have not been included in previous syntheses of global coastal water CO 2 fluxes (Borges 2005;Borges et al 2005;Cai et al 2006;Chen and Borges 2009;Laruelle et al 2010).…”