Research papers Seasonal distribution of the inorganic carbon system and net ecosystem production in the north eastern shelf of the Gulf of Ca ´ diz (Southwest Iberian Peninsula) Mariana Ribas-Ribas n , Abelardo Go ´ mez-Parra, Jesu ´ s M. Forja Departamento de Quı ´mica-Fı ´sica, Facultad de Ciencias del Mar y Ambientales, Universidad de Ca ´diz, Campus Rı ´o San Pedro, s/n, Puerto Real, Ca ´diz, 11510, Spain article info Article history: Received 10 June 2010 Received in revised form 23 June 2011 Accepted 12 September 2011 Available online 21 September 2011 Keywords: Inorganic carbon system Net ecosystem production Carbon dynamics Seasonal variations Coastal ocean Gulf of Ca ´ diz abstract There is scatter information of the inorganic carbon system in the coastal zones and it is important to increment our knowledge and understand the global carbon cycle. We investigated the distribution of inorganic carbon system parameters and its controls in the coastal waters of the north eastern shelf of the Gulf of Ca ´ diz (GoC) during four cruises that took place in June 2006, November 2006, February 2007 and May 2007. The objectives of this study are: (1) to describe the spatio-temporal distribution of inorganic carbon system parameters in waters of the north eastern shelf of the GoC using four cruises, each undertaken in one of the four seasons, (2) to calculate net ecosystem production (NEP) and (3) to examine factors controlling these distributions. The distribution of inorganic carbon system parameters in the north eastern shelf of the Gulf of Ca ´ diz showed temporal and spatial variability. River input, mixing, primary production, respiration, CO 2 air–sea exchange, and remineralization were factors that controlled such distributions. The coastal zone of the GoC is autotrophic on an annual scale at a rate of 1.0 mmol m 2 d 1 . Further measurements are needed it to improve the NEP calculation and to evaluated to intra-annual variability. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction The continental margins are important in terms of the cycling of carbon and associated elements and act as a medium of exchange for oceanic, atmospheric and terrestrial carbon pools. Adding to the complexity, seawater CO 2 concentrations also vary due to the effects of the plankton community. Coastal waters are believed to account for significant net community production (Lee, 2001). Despite the potential importance of the coastal oceans to the CO 2 system, coastal ocean researchers tend to extrapolate their time and space-limited results over large areas. Thus, this study is important because of two facts: the first one is the location of the study site. The Gulf of Ca ´ diz (GoC) shelf is of special interest, being immediately adjacent to the Strait of Gibraltar (Fig. 1). It has already been emphasized that the GoC plays an important role in the carbon cycle of the eastern North Atlantic (Parrilla, 1998) and the Mediterranean Sea (Dafner et al., 2001). In the GoC several water masses mix together to form the ‘‘Atlantic inflow’’, which is responsible for supplying water to the Mediterranean Sea from the west (Minas et al., 1991). Moreover, this area is on the pathway of the ‘‘Mediterranean outflow’’ which thereafter enters the open ocean and influences water circulation in the entire North Atlantic, and the climate in general (Rahmstorf, 1998). The basin receives significant fluvial inputs associated with the discharge of large rivers such as the Guadiana, the Guadalquivir, the Guadalete and the Tinto-Odiel. The Gua- dalquivir River is the main fluvial source draining into the GoC margin. The second fact that makes this study important is that provide direct measurements of high spatio-temporal resolution of pH and total alkalinity (TA) and it is the first one to calculate net ecosystem production (NEP) rates from dissolved inorganic carbon (DIC) data in this coastal area. The physical processes of these areas are well documented (Ochoa and Bray, 1991; Price et al., 1993). However, given the high variability in short temporal and spatial scales in the coastal oceans (Hales et al., 2008) a better description of the CO 2 system is required. In the studied area until now, only a few papers on the biogeochemical processes of this shelf have been presented (Echevarrı ´a et al., 2002; Minas and Minas, 1993). Only a few studies have been carried out in the GoC to evaluate the variability of the carbon system. Gonza ´ lez-Da ´ vila et al. (2003) carried out a study during winter in one oceanic transect. Huertas et al. (2006) report data of alkalinity and pH during different seasons. Ribas-Ribas et al. (2011) report direct fCO 2 measurements and air–sea CO 2 flux for an annual cycle. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/csr Continental Shelf Research 0278-4343/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2011.09.003 n Corresponding author. Tel.: þ34 956016163; fax: þ34 956016040. E-mail addresses: mariana.ribas@uca.es (M. Ribas-Ribas), abelardo.gomez@uca.es (A. Go ´ mez-Parra), jesus.forja@uca.es (J.M. Forja). Continental Shelf Research 31 (2011) 1931–1942