Decadal increases of anthropogenic CO₂ in the South Pacific subtropical ocean along 32°S

Abstract

[1] To estimate decadal increases of anthropogenic CO 2 in the ocean, distributions of dissolved inorganic carbon (C T ) corrected by apparent oxygen utilization and salinity (nC T ANT ) were investigated along the World Ocean Circulation Experiment (WOCE Hydrographic Programme (WHP)) P6 section based on data obtained 10 years apart. Significant increases of nC T CAL were detected down to 1500 m (ffi27.5s q ) water depth, above which the Sub-Antarctic Mode Water (SAMW) and the Antarctic Intermediate Water (AAIW) are found. The decadal increases of nC T CAL on the isopycnal surfaces (26.6-26.9s q ) of SAMW were higher (5-8 mmol kg À1 ) to the east of 160°W than to the west of it, while the increases in AAIW were almost constant on the isopycnal surfaces (27.0-27.5s q ). The averaged increases of nC T CAL in SAMW and AAIW were 10 ± 3.1 and 4.1 ± 2.0 mmol kg À1 , respectively. Small but significant increases of nC T CAL and salinity-normalized C T (nC T ) were also found (approximately 3.0 and 5.0 mmol kg À1 , respectively) in abyssal waters occupying depths greater than 3500 m at longitude 180°-160°W, which correspond to Circumpolar Deep Water. Spatial differences of anthropogenic CO 2 accumulation are discussed in terms of water mass distributions. The water column inventory of increases of anthropogenic CO 2 in the South Pacific subtropical ocean was estimated to be 1.0 ± 0.4 mol m À2 yr À1 , which is almost the same as that previously reported.

Global ocean storage of anthropogenic carbon

“…In the North Pacific, most of the observed increase in DIC is due to changes in ocean circulation, as indicated by changes in apparent oxygen utilization (AOU), rather than uptake of C ant (Sabine et al, 2008). In contrast, an increase in DIC in the South Pacific can be attributed to uptake of C ant that is absorbed and transported by Southern Ocean-origin water masses such as SAMW and AAIW (Murata et al, 2007). There are significant spatial variations in storage rate across the Pacific basin.…”

“…There are significant spatial variations in storage rate across the Pacific basin. For example, both the GF and repeat hydrography estimates show higher storage in the South compared with the North Pacific (Murata et al, 2007;Sabine et al, 2008). On the other hand, while the GF method and an earlier hydrographic study (Sabine et al, 2008) suggest higher storage rates in the western as compared with the eastern North Pacific, a more recent study (Waters et al, 2011) finds the opposite pattern along 30 • S. The latter study is based on data from a section repeated in 1992 and 2010.…”

Decadal changes in the CaCO3 saturation state along 179°E in the Pacific Ocean

“…Subtropical mode water is known to be a pool of anthropogenic CO 2 [Murata et al, 2009. As CO 2 uptake by the ocean is a primary cause of ocean acidification [Orr et al, 2005], we suspected that anthropogenic CO 2 storage contributed greatly to the minimum DW arg .…”

“…In this calculation, we neglected the terms for surface disequilibrium of CO 2 and for preindustrial preformed CO 2 [Murata et al, 2007].…”

“…[14] After removing spatial trends of the saturation horizon by linear or quadratic function fitting based on Murata et al [2009], we evaluated changes in the saturation horizon of W arg by one-tailed t-test and found that between 10 N and 50 N the saturation horizon rose by 17 dbar (1.2 dbar a À1 ) between 1993 and 2007 (significant at the 95% level).…”