The oceanic sink for anthropogenic CO ₂ from 1994 to 2007

Abstract

We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO2inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year−1and represents 31 ± 4% of the global anthropogenic CO2emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.

Pacific Anthropogenic Carbon Between 1991 and 2017

“…The Pacific C anth inventory increased by 8.8 (±1.1) PgC between 1995 and 2005 and by 11.7 (±1.1) PgC (Figure ) between 2005 and 2015. These increases suggest an average increase of 0.94 (±0.11) PgC year −1 over the 1994–2007 time period, which compares well with Gruber, Clement, et al () findings of an average Pacific accumulation of 0.97 PgC year −1 (when using our Pacific basin bounds and integrated to 1,500‐m depth).…”

“…Finally, we develop an approach by which C anth accumulation can be estimated in regions not located directly along these specific sections. We produce results consistent with Gruber, Clement, et al (2019)'s recent finding that the Pacific took up 39 Figure 1. Map of the repeat hydrographic sections considered in this analysis color coded by the number of occupations with sufficient measurement density for analysis.…”

The Spatiotemporal Dynamics of the Sources and Sinks of CO2 in the Global Coastal Ocean

“…If we assume a preindustrial river outgassing rate of 0.45 ± 0.18 Pg C year −1 (Jacobson et al, ) and an outgassing flux of natural CO 2 of the order of 0.4 ± 0.2 Pg C year −1 (Gruber et al, ), our estimates implies an anthropogenic CO 2 uptake rate of −2.6 ± 0.4 Pg C year −1 for the 1998 through 2015 period. This uptake estimate is statistically identical to that recently estimated by Gruber et al () (−2.6 ± 0.3 Pg C year −1 ) on the basis of ocean interior changes in anthropogenic CO 2 between 1994 and 2007. It is also consistent with other independent estimates, such as those based on an Green's function ocean inversion method (−2.4 Pg C year −1 ; Gruber et al, , adjusted to the year 2007), those based on an inverse model (−2.6 Pg C year −1 ; DeVries, ), or those based on a compilation of models and observations (−2.0 ± 0.6 Pg C year −1 , Wanninkhof et al, ).…”

“…Globally, our net ocean carbon uptake of −1.7 ± 0.3 Pg C year −1 (coastal and open ocean) represents the sum of a net uptake of anthropogenic CO 2 , a net exchange flux of natural carbon in response to climate variability and change, plus an outgassing of river-derived carbon. If we assume a preindustrial river outgassing rate of 0.45 ± 0.18 Pg C year −1 and an outgassing flux of natural CO 2 of the order of 0.4 ± 0.2 Pg C year −1 (Gruber et al, 2019), our estimates implies an anthropogenic CO 2 uptake rate of −2.6 ± 0.4 Pg C year −1 for the 1998 through 2015 period. This uptake estimate is statistically identical to that recently estimated by Gruber et al (2019) This reduction is the result of (1) improved data coverage and (2) improved analysis methods.…”

“…Globally, the ocean is currently taking up each year about 2.4 ± 0.5 Petagrams (Pg) of the extra (anthropogenic) carbon added to the atmosphere as a consequence of fossil fuel burning, cement production, and land use change (Le Quéré et al, 2018). While this global ocean uptake is well established on the basis of many independent methods (e.g., Gruber et al, 2009Gruber et al, , 2019Keeling & Manning, 2014;Landschützer et al, 2014;Manning & Keeling, 2006;Rödenbeck et al, 2015;Takahashi et al, 2012), the net carbon dioxide (CO 2 ) source/sink characteristic of the coastal ocean (a term equivalent to continental shelves in the present study) is still poorly known and subject to intense scientific debates. The discussion was launched two decades ago when Tsunogai et al (1999) suggested, on the basis of an extrapolation of a single local study, that the coastal ocean takes up CO 2 from the atmosphere at a rate in excess of 1 Pg C year −1 (note that by convention, a negative flux value corresponds to a CO 2 transfer from the atmosphere to the sea surface).…”