The interannual variability of oceanic CO₂ parameters in the northeast Atlantic subtropical gyre at the ESTOC site

Abstract

[1] The long-term trends and average seasonal variability in the upper ocean inorganic carbon observations were investigated at the ESTOC Station (the European Time Series in the Canary Islands), on the basis of an existing 10-year series (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004). Hydrographic temperature and salinity, together with the pH in total scale at 25°C (pH T ), total alkalinity (A T ), partial pressure of CO 2 expressed as fugacity (fCO 2 ), computed dissolved inorganic carbon (C T ) and fluxes of CO 2 (FCO 2 ) reveal substantial variability over the years. Seasonal detrended data of salinity-normalized C T (NC T ) and experimental fCO 2 show upward trends of 0.99 ± 0.20 mmol kg À1 yr À1 and 1.55 ± 0.43 matm yr À1 , respectively, indicating direct control over the C T concentration due to increased atmospheric CO 2 concentration. Our series of experimental pH T data confirm the acidification of surface waters in the east Atlantic Ocean, with an interannual decrease of 0.0017 ± 0.0004 pH units yr À1. Interannual trends were examined by determining the variance in biogeochemical anomalies over time. The resulting anomalies in temperature and salinity revealed two scenarios in the ESTOC site, where there are periods of cooler and fresher water than the mean, driven by variations in winter mixed-layer depths, and periods with inverse temperature and salinity anomaly relationships, related to seasonal changes in the position of the subtropical gyre. Hydrographic and biogeochemical anomalies at ESTOC were linked to large-scale climate variability indexes, such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA). A delay of around 3 years in the oceanic response to the NAO best correlates with the anomalies observed for temperature (0.83), salinity (0.56), alkalinity (0.49), C T (0.41), fCO 2 (0.57) and the depth of the mixed layer (À0.64) with p < 0.05. The seasonal variability and its link-in to the large-scale climate variability of the North Atlantic subtropical gyre has been studied using the two long series, BATS and ESTOC.Citation: Santana-Casiano, J. M., M. González-Dávila, M.-J. Rueda, O. Llinás, and E.-F. González-Dávila (2007), The interannual variability of oceanic CO 2 parameters in the northeast Atlantic subtropical gyre at the ESTOC site, Global Biogeochem. Cycles, 21, GB1015,

Trends in anthropogenic CO2 in water masses of the Subtropical North Atlantic Ocean

“…The larger amounts of CO 2 entering into the ocean near Bermuda (Bates, 2007) would be thus advected to the eastern part of the section below the surface. The transport of C ant enriched waters towards the east could explain the existence of higher [C ant ] at this side of the section (tables in appendix A), despite the lower CO 2 uptake rates reported there (Santana-Casiano et al, 2007). It is important to note that there is no complete consensus among the four different methods used to evaluate the storage in C ant for uNACW in the western basin (Fig.…”

“…The equivalent mean DT suggests a slightly higher observed value of 0.93 ± 0.09 µmol·kg -1 ·yr -1 (Fig. 4) 1995 -2004), reported respectively for BATS (Bates, 2007) and ESTOC (Santana-Casiano et al, 2007), indicate that the eastern side of the NASTG has been acting as a much weaker sink for atmospheric CO 2 than the western side. These findings are consistent with previous results, where BATS was found to be in a region of strong spatial gradients in air-sea CO 2 flux (Nelson et al, 2001).…”

Ocean acidification off the south coast of Japan: A result from time series observations of CO2parameters from 1994 to 2008

“…In addition to habitat loss, water pollution, eutrophication, and overexploitation, ocean acidification may be another human-induced threat to coastal marine ecosystems and sustainable fisheries. However, little is known about the progress of acidification in coastal oceans at present [Santana-Casiano et al, 2007;Feely et al, 2008].…”

Impact of ocean acidification on benthic and water column ammonia oxidation

“…[2] Sustained observations and modeling studies have shown that oceanic pH is currently decreasing by 0.02 units per decade and is expected to decrease by up to 0.7 units by the year 2100 as a result of atmospheric CO 2 dissolution in the oceans [Bates, 2007;Caldeira and Wickett, 2003;Olafsson et al, 2009;Santana-Casiano et al, 2007]. This ocean acidification (OA) is predicted to affect marine ecosystems through the alteration of community structure [Fabry et al, 2008]; nutrient cycles [Hutchins et al, 2009]; productivity [Riebesell et al, 2007] and carbon export [Mari, 2008;Schulz et al, 2008].…”