Recent Climatic Changes in the Se Bay of Biscay Affecting Pelagic and Coastal Ecosystems

Not to be cited without prior reference to the author ICES CM 2009/G:11 Comparative study of climate impact on coastal and continental shelf ecosystems in the ICES area: assessment and management. RECENT CLIMATIC CHANGES IN THE SE BAY OF BISCAY AFFECTING PELAGIC AND COASTAL ECOSYSTEMS. V. VALENCIA1, A. FONTÁN1, A. BORJA1, N. GOIKOETXEA1 and J. SÁENZ2. 1AZTI Foundation, Marine Research Division. Herrera Kaia, Portualdea, z/g, 20110-Pasaia (Spain). Tel: +34-943-004800; fax: +34-943-00480. E-mail: [email protected] 2Department of Applied Physics II, Fac. of Science and Technology, University of the Basque Country, Barrio Sarriena s/n, 48940-Leioa (Spain). Abstract Troughout the last decade, several regime shifts and anomaly patterns for different climatic indices (ENSO, NAO, EA, etc.) have been described, due to unusual values and/or persistent cumulative anomalies. For the inner (southeastern) Bay of Biscay, the prevalence of positive values of the East Atlantic (EA) pattern, since 1998, affects the transport and subsequent properties of the upper water masses. The mesoscale effect, related mainly to the intensification of the British Isles low atmospheric pressure centre, drives also the moisture transport, storm frequency and intensity, etc. As a consequence of the shift in the EA pattern, several structural factors of the coastal and pelagic ecosystems show seasonal and/or annual anomaly patterns, in recent years. For instance, assessment of the recruitment of the Bay of Biscay anchovy, as well as of the benthic communities (macroalgae, barnacles, etc.), based upon climatic and oceanographic variables, show also responses to these anomaly patterns. Factors such as the turbulence-stability and upwelling-downwelling dualities; saline stratification and coastal fertilisation by precipitation and continental runoff; and other coupled oceano-meteorological variables are considered. The patterns observed are representatives of the response, in terms of local and seasonal or annual anomalies in the coastal and pelagic ecosystems, to the shifts in some mesoscale or large scale climatic indices such as the EA pattern. Keywords: oceano-meteorological coupling, pelagic ecosystem, East Atlantic pattern, Bay of Biscay. Introduction Throughout the last decade, several regime shifts and anomaly patterns for different modes of atmospheric and oceanic variability (ENSO, NAO, EA, etc.) have been described, due to unusual values and/or persistent cumulative anomalies (Conrad et al., 2003; Bode et al., 2006; Beaugrand, 2009; Drinkwater et al., 2009). Consequently, there has been a growing concern about changes in climate in the North Atlantic Ocean. Many studies concerning decadal changes in climate and ecosystems are being undertaken: invasive species management (Occhipinti- Ambrogi, 2007; Rahel et al., 2008); changes in biodiversity (Beaugrand et al., 2008; Hemery et al., 2008; Menge et al., 2008; Molinero et al., 2008); or impacts on fisheries (Stenevik and Sundby, 2007; Travers et al., 2007; Tourre et al., 2007; deYoung et al., 2008; Hiddink and ter Hofstede, 2008; Cury et al., 2008; Borja et al., 2008). Such changes in climate are related often to changes in climatic indices. The North Atlantic climatic variability is driven largely by the North Atlantic Oscillation (NAO). The second main pattern in the Atlantic basin is the East Atlantic pattern (EA) (Conrad et al., 2003). Whilst the variability of climate linked to the NAO has been widely studied so far (Hurrell and Deser, 2009), the impacts of the EA on the climate has not been so widely documented (Wallace and Gutzler, 1981). The wintertime NAO exhibits significant multi-decadal variability (Hurrell, 1995; Parsons and Lear, 2001). The negative phase of the NAO dominated the circulation from the mid-1950's through the 1978/79 winter. An abrupt transition, to recurring positive phases of the NAO, occurred during the 1979/80 winter, with the atmosphere remaining constrained within this mode through to the 1994/95 winter season. During this 15-year interval, a substantial negative phase of the pattern appeared only twice, in the winters of 1984/85 and 1985/ 86. However, November 1995 - February 1996 (NDJF 95/96) was characterised by a return to the strong negative phase of the NAO (Halpert and Bell, 1997). Also, the EA pattern exhibits very strong multi-decadal variability in the 1950-2004 record, with the negative phase prevailing during much of 1950- 1976, and the positive phase occurring during much of 1977-2004. The positive phase of the EA pattern was particularly strong and persistent during 1997-2004 (Climate Prediction Center, NOAA). The changes in climate, as illustrated by changes in climatic indices, result in changes in atmospheric/oceanic variables, such as: local solar incoming radiation and temperature, moisture transport and regional rainfall, circulation and stratification, among others (Sáenz et al., 2001a; Trigo et al., 2002; Krichak and Alpert, 2005; Sutton and Hodson, 2005). Finally, these effects are transmitted to marine ecosystems, with substantial impacts on the species distribution and abundance (Parsons and Lear, 2001; Southward et al., 2005; Bode et al., 2006; Mackenzie et al., 2007; Hemery et al., 2008; Hiddink and ter Hofstede, 2008; Drinkwater et al., 2009). Within the Northeastern Atlantic, coupling mechanisms between climatic indices and water masses properties (Eastern North Atlantic Central Water: ENACW) and circulation (Iberian Poleward Current (IPC), North Atlantic Current (NAC), etc.) have been documented (Pérez et al., 2000; García-Soto et al., 2002; Pingree, 2005). The correlation level between atmospheric and oceanic patterns depends on the spatial scale, as well as the integration period considered. Although the NAO influences greatly the circulation in the North Atlantic, its influence is less significant in the Northeastern Atlantic, especially in the intergyre zone and the inner Bay of Biscay. Within the Bay of Biscay, the NAO influences to a lesser extent, when comparing with that observed at the North Atlantic. The most influential atmospheric pattern appears to be the EA, particularly for the southeastern Bay of Biscay, by means of the influence of a low pressure centre to the west of the British Isles. Several studies have demonstrated that, over the area adjacent to the Bay of Biscay, the EA pattern is related to the variability of: precipitation through the position of the Atlantic storm track (Rogers, 1997); winter land temperature through heat fluxes (Sáenz et al., 2001a); anchovy recruitment (Borja et al., 2008); or oceanic latent heat fluxes (Cayan, 1992), amongst others. The British low pressure centre determines the prevalence of northwesterly wind conditions over the southeastern Bay of Biscay. This wind regime modulates, in turn, air temperature and precipitation. Conversely, the south-southewesterly regime (in winter) and the north-northeasterly regime (in summer) are related to the position of two centres of activity: the Azores High and the Iceland Low. Within this context, the influence of wintertime NAO pattern in the atmospheric/oceanic variables can be anticipated in the southeastern Bay of Biscay; however, it accounts for a much lower fraction of variance, than the EA index (Sáenz et al., 2001a, b). Additionally, the EA index influences the water circulation patterns, since the relative occurrence of ENACWT y ENACWP (sensu Ríos et al., 1992) in the area is related to events of intensification or moderation of the eastward and poleward transports (Valencia et al., 2003). Moreover, this index influences the upwelling-downwelling balance over the area (Borja et al., 2008). In this context, the aims of the present study are to: (i) examine the anomalous patterns observed within the 1998-2008 period; and (ii) discuss the potential impact on pelagic and coastal ecosystems, in the southeastern Bay of Biscay. Data and Methods Study area The study area is located in the innermost part of the Bay of Biscay (Basque coast), lying between the west-east oriented coast of Spain and the north-south oriented coast of France (Figure 1). 49º N 500 m 2000 m 47º N FRANCE NOAA 45º N BAY OF BISCAY AQUARIUM San Sebastián 43º N MO SPAIN 41º N 10º W 8º W 6º W 4º W 2º W 0º W Figure 1. Location of the study area, showing the position of the data series. Bathymetric contours show the 200 m and 500 m isobaths. Key: MO - Meteorological Observatory of San Sebastián; NOAA - PFEL-NOAA; and AQUARIUM - Aquarium of San Sebastián (Oceanographic Society of Gipuzkoa). The Basque coast is clearly a marginal area of the northeastern Atlantic and even of the Bay of Biscay itself; it has some distinctive climatic and geographic characteristics. Thus, the concavity of the southeastern corner of the Bay of Biscay results in a continental influence in this region and, consequently, the shelf waters of the area are colder in winter and warmer and less saline in summer, than the waters of western areas at equivalent latitudes (Valencia et al., 2003, 2004). Oceanographic and meteorological data A description of the available data, including their source, record length and sampling rate, is presented in Table 1. Further, the location of the monitoring sampling stations is shown in Figure 1. The meteorological data were obtained from the Observatory of San Sebastián (Spanich Meteorological Agency); SST daily data were obtained from the Aquarium of San Sebastián (Oceanographic Society of Gipuzkoa); and vectorial data of wind velocity were provided by the PFEL-NOAA. Climatic indices NAO and EA indices were selected for use in this investigation. Such indices were obtained from the Climate Prediction Centre (CPC) of the National Centre of Environmental Prediction (NCEP) (http://www.cpc.noaa.gov/). One of the most prominent climatic patterns throughout all seasons, is the NAO (Barnston and Livezey 1987). The NAO combines parts of the East-Atlantic and West Atlantic patterns, identified originally by Wallace and Gutzler (1981) for the winter season. The NAO consists of a north-south dipole of anomalies, with one centre located over Greenland and the other centre (of opposite sign) spanning the central latitudes of the North Atlantic, between 35°N and 40°N.

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