Abstract
Sustained observations provide critically needed data and understanding not only about ocean warming and water cycle reorganization (e.g., salinity changes), ocean eutrophication, and ocean deoxygenation, but also about changes in ocean chemistry. As an example of changes in the global ocean carbon cycle, consistent changes in surface seawater CO2-carbonate chemistry are documented by seven independent CO2 time series that provide sustained ocean observations collected for periods from 15 to 30 years: (1) Iceland Sea, (2) Irminger Sea, (3) Bermuda Atlantic Time-series Study (BATS), (4) European Station for Time series in the Ocean at the Canary Islands (ESTOC), (5) CArbon Retention In A Colored Ocean sites in the North Atlantic (CARIACO), (6) Hawaii Ocean Time-series (HOT), and (7) Munida in the Pacific Ocean. These ocean time-series sites exhibit very consistent changes in surface ocean chemistry that reflect the impact of uptake of anthropogenic CO2 and ocean acidification. The article discusses the long-term changes in dissolved inorganic carbon (DIC), salinity-normalized DIC, and surface seawater pCO2 (partial pressure of CO2) due to the uptake of anthropogenic CO2 and its impact on the ocean's buffering capacity. In addition, we evaluate changes in seawater chemistry that are due to ocean acidification and its impact on pH and saturation states for biogenic calcium carbonate minerals.
Highlights
Perturbation of the global carbon cycle through the production and release of anthropogenic carbon dioxide (CO2) to the atmosphere has important implications for Earth’s climate (Solomon et al, 2007) and for ocean chemistry
Other time-series data have contributed to establishing long-term trends in seawater CO2-carbonate chemistry, including: (1) annual reoccupations of a fixed location or ocean section (e.g., Line P, North Pacific Ocean, Wong et al, 2010; Ocean Weather Station Mike, Norwegian Sea, Skjelvan et al, 2008), (2) long-term opportunistic surface sampling efforts that are irregular in time and space but sufficient to establish long-term trends in ocean regions, and (3) lower-frequency sampling along an ocean section reoccupied through projects like World Ocean Circulation Experiment (WOCE) and CLIVAR/CO2 Repeat Hydrography (e.g., North Pacific Ocean: Byrne et al, 2010; Midorikawa et al, 2012; Rockall Trough: McGrath et al, 2012; Southern Ocean: van Heuven et al, 2011)
Ocean CO2 time-series data are important for understanding the rate of uptake of CO2 and for ground truthing indirect assessments of the rate of the ocean’s uptake and inventories of anthropogenic CO2 (Tanhua et al, 2013)
Summary
Perturbation of the global carbon cycle through the production and release of anthropogenic carbon dioxide (CO2) to the atmosphere has important implications for Earth’s climate (Solomon et al, 2007) and for ocean chemistry. Other time-series data have contributed to establishing long-term trends in seawater CO2-carbonate chemistry (see online Supplementary Table S1 for details), including: (1) annual reoccupations of a fixed location or ocean section (e.g., Line P, North Pacific Ocean, Wong et al, 2010; Ocean Weather Station Mike, Norwegian Sea, Skjelvan et al, 2008), (2) long-term opportunistic surface sampling efforts that are irregular in time and space but sufficient to establish long-term trends in ocean regions (e.g., surface pCO2 trends; Takahashi et al, 2009; McKinley et al, 2011), and (3) lower-frequency sampling along an ocean section reoccupied through projects like WOCE and CLIVAR/CO2 Repeat Hydrography (e.g., North Pacific Ocean: Byrne et al, 2010; Midorikawa et al, 2012; Rockall Trough: McGrath et al, 2012; Southern Ocean: van Heuven et al, 2011) Ocean climate stations such as HOT (Hawaii, Pacific Ocean, 2003– present), KEO (Kuroshio Extension Observatory, North Pacific Ocean, 2004–present), and Ocean Station Papa (50°N, 145°W, 2007–present) represent emerging moored surface seawater CO2carbonate chemistry data collection systems that will provide multidecadal understanding in the future.
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