Contrasting effects of temperature and winter mixing on the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean

Abstract

Abstract. Future climate change as a result of increasing atmospheric CO 2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary production and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic The inter-annual differences in late winter concentrations of nitrate (2.8 ± 1.1 µmol l −1 ) and dissolved inorganic carbon (22 ± 6 µmol kg −1 ), with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the chlorophyll a-fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO 2 fluxes (ranging from +3.7 to −4.8 mmol m −2 d −1 ) showed an increased oceanic CO 2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences.Correspondence to: E. P. Achterberg

Key controls on the seasonal and interannual variations of the carbonate system and air‐sea CO2 flux in the Northeast Atlantic (Bay of Biscay)

“…The North Atlantic Oscillation (NAO) is the dominant mode of the atmospheric pressure variation over Bates et al [1996], Bates [2001Bates [ , 2007. c Padin et al [2008], Dumousseaud et al [2010], and this study. the North Atlantic [Marshall et al, 2001;Visbeck et al, 2003].…”

“…Coccolithophore abundances were counted using scanning electron microscopy [Smith et al, 2012]. Details of these analytical methods were previously described by Dumousseaud et al [2010] and are summarized in Table 1.…”

“…7. Interannual Variability of DIC, pCO 2 , and Air-Sea CO 2 Flux [46] The time series of carbon system observations in the Bay of Biscay can be extended back from 2010 to 2002 by including earlier observations [Padin et al, 2008;Dumousseaud et al, 2010]. The available data from 2002 to 2010 are shown in Figure 9, and the key points are summarized in Table 4.…”

“…[5] To overcome this problem, monthly sampling of carbon-related variables in addition to high-frequency underway measurements were carried out since 2003 along the route of the MV Pride of Bilbao between Portsmouth (UK) and Bilbao (Spain) (http://www.noc.soton.ac.uk/ops/ ferrybox_index.php) [Hydes et al, 2003[Hydes et al, , 2009]. This operation enabled some earlier studies of biogeochemical dynamics of surface waters on this route, particularly analyses of new production based on dissolved oxygen (DO) [Bargeron et al, 2006], variability of the carbonate system during 2005-2007[Dumousseaud et al, 2010, and seasonal changes in the morphotypes of the coccolithophore Emiliania huxleyi [Smith et al, 2012].…”

“…To examine the regional differences in seasonal patterns in the carbonate system in the North Atlantic, the data from the Bay of Biscay are compared to the time series observation results at BATS [Bates, 2001[Bates, , 2007Bates et al, 1996, http://bats.bios.edu/], ESTOC [González-Dávila et al, 2003, 2007Santana-Casiano et al, 2007], and OWSM . Furthermore, trends in 2008-2010 are compared to those inferred from the 2005-2007 data along the same route [Dumousseaud et al, 2010[Dumousseaud et al, ] and the 2002[Dumousseaud et al, -2004 data along an orthogonal route [Padin et al, 2008] (Figure 1). This extends the time series over which we can compare interannual variations to cover the years from 2002 to 2010.…”