Detecting the progression of ocean acidification from the saturation state of CaCO₃ in the subtropical South Pacific

Abstract

Progression of ocean acidification in the subtropical South Pacific was investigated by using high-quality data from trans-Pacific zonal section at 17°S (World Ocean Circulation Experiment section P21) collected in 1994 and 2009. During this 15 year period, the CaCO 3 saturation state of seawater with respect to calcite (Ω cal ) and aragonite (Ω arg ) in the upper water column (<400 dbar) decreased at rates of 0.037 a À1 and 0.025 a À1, respectively, east of 145°W longitude; these rates are among the fastest in the world's oceans. In contrast, at longitudes 170°E-145°W, Ω cal and Ω arg decreased relatively slowly, at 0.008 a À1 and 0.005 a À1, respectively. The Ω arg saturation horizon occurred at a depth of about 1200 dbar at the westernmost end of the section and shoaled eastward to about 20 dbar. From 1994 to 2009, it migrated upward at a rate of 5.2 dbar a À1 west of 145°W. Decomposition of the temporal changes of Ω (ΔΩ) showed that the accumulation of anthropogenic CO 2 in the ocean accounted for more than half of ΔΩ. The more rapid rate of decline of Ω in the eastern section was attributable to a relatively large contribution of organic matter remineralization, whereas the slower rate in the central section was attributed to a decrease of anthropogenic CO 2 uptake caused by rising water temperatures. An important finding of this study was that acidification of the upper water column was enhanced by processes related to the oxygen minimum zone in the eastern subtropical South Pacific Ocean.

Oceanographic patterns and carbonate chemistry in the vicinity of cold-water coral reefs in the Gulf of Mexico: Implications for resilience in a changing ocean

“…Finally, over 70% of known scleractinian cold‐water coral habitats are predicted to be undersaturated by the year 2100 (Guinotte et al ; Cao et al ), with numerous lines of experimental evidence suggesting that L. pertusa and other cold‐water corals may be severely physiologically challenged in acidified conditions (Maier et al ; Lunden et al , but see Form and Riebesell ). Ocean acidification is already reducing Ω ARAG in other deep‐sea regions, with measured decreases of 0.005–0.025 units per year in the South Pacific (< 400 dbar; Murata et al ), between 0.0021 and 0.0048 units per year in the North Atlantic (300–600 m; González‐Dávila et al ), and 0.034 units per year in the Pacific Ocean (200–300 dbar; Murata and Saito ). Similar reductions in the deep GoM would result in the undersaturation of L. pertusa habitats within just a few decades, making it imperative to better understand the carbonate dynamics over these vulnerable communities.…”

Carbonate system distribution, anthropogenic carbon and acidification in the western tropical South Pacific (OUTPACE 2015 transect)

“…Since 2000, efforts have been made to revisit oceanic sections according to the WOCE strategy in order to assess oceanic changes at the scale of a decade. These programs have generated important databases T. Wagener et al: Carbonate system in the WTSP for oceanic carbonate chemistry (e.g., GLODAPv2, Olsen et al, 2016;Key et al, 2015).…”

“…Here, C ANT estimates based on the TrOCA (Tracer combining Oxygen, inorganic Carbon and total Alkalinity) method will be used as as a tool to investigate changes in C T . Moreover, comparing our data with the high-quality data (internally consistent through a secondary quality control; Olsen et al, 2016) available in the Global Ocean Data analysis Project version 2 (GLODAPv2 database) will allow us to evaluate C T , A T , C ANT (from TrOCA) and pH T trends in subsurface waters and at depth.…”

Processes of multibathyal aragonite undersaturation in the Arctic Ocean

“…For example, aragonite saturation horizons in the North Pacific and the North Atlantic are at depths of ∼500 m and ∼1500 m, respectively [ Millero , ]. Generally, the main saturation horizon is deeper in the tropics and shallower at higher latitudes, although minor horizons may occur locally coincident with oxygen minimum zones [e.g., Bianucci and Denman , ; Murata et al ., ]. A recent synthesis of 14 years data from the North Pacific Ocean has shown an upward migration of the aragonite saturation horizon at ∼1–2 m/yr due to increases in anthropogenic CO 2 in the water column [ Feely et al ., ].…”