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

N R Bates,R Garley,K Neely,M H P Best,R J Johnson,A G Dickson

doi:10.5194/bg-9-2509-2012

Abstract

Abstract. Fossil fuel use, cement manufacture and land-use changes are the primary sources of anthropogenic carbon dioxide (CO2) to the atmosphere, with the ocean absorbing approximately 30% (Sabine et al., 2004). Ocean uptake and chemical equilibration of anthropogenic CO2 with seawater results in a gradual reduction in seawater pH and saturation states (Ω) for calcium carbonate (CaCO3) 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 CO2 changes and ocean acidification in the North Atlantic subtropical gyre near Bermuda from 1983–2011. Dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) 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 CO2 has also diminished. As indicators of ocean acidification, seawater pH decreased by ~0.05 (0.0017 yr−1) and ω values by ~7–8%. Such data provide critically needed multi-decadal information for assessing the North Atlantic Ocean CO2 sink and the pH changes that determine marine ecosystem responses to ocean acidification.

Highlights

The emissions of anthropogenic CO2 to the atmosphere due to fossil fuel use, cement manufacture and land-use changes (Houghton, 2008) have increased rapidly over the last decade (Friedlingstein et al, 2010)
Slopes and statistics of regressions are listed in Table 1. (A) Sea surface temperature (◦C; black line) and salinity. (B) Surface total alkalinity (TA, μmol kg−1, blue symbol) and salinity normalised TA. (C) Surface dissolved inorganic carbon (DIC, μmol kg−1, green symbol) and salinity normalised DIC. (D) Seawater pCO2 and Revelle factor (β). (E) Surface seawater pH and [CO23−] (F) Surface saturation state of calcite and aragonite
Time series analysis of data at Bermuda Atlantic Time-series Study (BATS) reveal significant long-term trends in the temperature and salinity of the surface ocean increasing at www.biogeosciences.net/9/2509/2012/

Summary

Introduction

The emissions of anthropogenic CO2 to the atmosphere due to fossil fuel use, cement manufacture and land-use changes (Houghton, 2008) have increased rapidly over the last decade (Friedlingstein et al, 2010). The cumulative total global ocean uptake of anthropogenic CO2 since pre-industrial times is estimated at ∼120–140 Pg C (Sabine et al, 2004; Khatiwala et al, 2009). Assessments of rates of ocean CO2 uptake over multidecadal timeperiods, changes in the capacity of the ocean to absorb CO2 and ocean acidification impacts are important for predicting future climate change and marine ecosystem responses (e.g., Fabry et al, 2009). These ocean carbon cycle and ocean acidification data provide critically needed observational tests of global coupled ocean-atmosphere models and allow attribution of changes to both anthropogenic and natural causes (e.g., Le Quereet al., 2010).

Methods

Results

Discussion

Conclusion