Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean

Abstract

Abstract. Fossil fuel use, cement manufacture and land-use changes are the primary sources of anthropogenic carbon dioxide (CO 2 ) to the atmosphere, with the ocean absorbing approximately 30 % (Sabine et al., 2004). Ocean uptake and chemical equilibration of anthropogenic CO 2 with seawater results in a gradual reduction in seawater pH and saturation states ( ) for calcium carbonate (CaCO 3 ) minerals in a process termed ocean acidification. Assessing the present and future impact of ocean acidification on marine ecosystems requires detection of the multi-decadal rate of change across ocean basins and at ocean time-series sites. Here, we show the longest continuous record of ocean CO 2 changes and ocean acidification in the North Atlantic subtropical gyre near Bermuda from 1983-2011. Dissolved inorganic carbon (DIC) and partial pressure of CO 2 (pCO 2 ) increased in surface seawater by ∼40 µmol kg −1 and ∼50 µatm (∼20 %), respectively. Increasing Revelle factor (β) values imply that the capacity of North Atlantic surface waters to absorb CO 2 has also diminished. As indicators of ocean acidification, seawater pH decreased by ∼0.05 (0.0017 yr −1 ) and values by ∼7-8 %. Such data provide critically needed multi-decadal information for assessing the North Atlantic Ocean CO 2 sink and the pH changes that determine marine ecosystem responses to ocean acidification.

Twenty Years of Marine Carbon Cycle Observations at Devils Hole Bermuda Provide Insights into Seasonal Hypoxia, Coral Reef Calcification, and Ocean Acidification

“…The use of CRM samples for ocean time-series observations is very important for assessment of data comparability over time and subsequent calculation of pCO 2 and pH for example (Bates and Peters, 2007;Bates et al, 2012). At Harrington Sound, the routine measurement and calibration of DIC and TA measurements since 1996 ensured that the data are comparable over time with error estimated at less than ∼1-2 µmoles kg −1 .…”

“…However, meaningful trends have been established with open-ocean time-series data, including seawater CO 2 -carbonate chemistry, that span more than 10 years (e.g., Bates et al, 2012Bates et al, , 2014. Here, monthly mean climatologies for all hydrographic and chemical parameters were determined for all data spanning the 1996-2016 period.…”

Thermodynamic Forecasts of the Mediterranean Sea Acidification

“…However, time-series studies conducted in the North Pacific Ocean between 1988 and 2007 (Dore et al, 2009) and in the North Atlantic Subtropical gyre between 1983 and 2011 (Bates et al, 2012) have documented a significant long-term decreasing trend of 0.05 pH unit (0.0019 and 0.0017 unit yr -1 in the North Pacific and the North Atlantic respectively). At the end of the century, the model from Caldeira & Wickett (2003) predicted an increased acidification with a pH decrease between 0.3 and 0.4 pH unit.…”

“…The results indicate that these tipping points when Ω Ar = 1 and Ω Ca = 1, will occur when C ANT = 317 µmol.kg -1 and C ANT = 389 µmol. Taking into account that fCO 2 in seawater (fCO 2 sw ), follows that (fCO 2 air ) of the atmosphere (Royal Society, 2005;Bates et al, 2012;Zeebe, 2012), we can calculate the estimated anthropogenic carbon concentrations over the years as follows: 1) First, we can use results from both the most optimist/ecological (B1; fCO 2 air = 485 matm and 540 matm for year 2050 and 2100, respectively) and the most pessimistic (A1F1; fCO 2 air = 570 matm and 940 matm for year 2050 and 2100, respectively) of the SRES scenarios (IPCC 2007) to make such estimates at least to year 2100.…”

“…Thus, the Mediterranean Sea is acidifying quickly and its marine ecosystems are under stress. A surface pH decrease of 0.05 unit has been recorded since the preindustrial era (Dore et al, 2009;Bates et al, 2012) and models predict an additional pH decline by 0.3-0.5 pH unit during the 21 st century depending upon which Intergovernmental Panel on Climate Change (IPCC) CO 2 emission scenario (Caldeira & Wickett, 2005 ;Orr et al, 2005a;Feely et al, 2009) is used for the forecast. In the Mediterranean Sea, Géri et al (2014) forecasted an evolution ranging between 0.3 and 0.4 pH unit decrease in the surface water of the Northwestern Mediterranean Sea by the end of this century.…”