Oceanographical patterns during a summer upwelling–downwelling event in the Northern Galician Rias: Comparison with the whole Ria system (NW of Iberian Peninsula)

Abstract

Summer upwelling and downwelling processes were characterized in the Northern Galician Rias during July and August 2008 by means of sampling carried out onboard R/V Mytilus (CSIC) and R/V Lura (IEO). Thermohaline variables, dissolved oxygen, nutrients, chlorophyll, phytoplankton, ciliates and zooplankton abundances were measured at sections located in the Rias of Viveiro, Barqueiro and Ortigueira and their adjacent shelves. Ekman transport was calculated from QuikSCAT satellite, upwelling intensity estimated with upwelling index from the average daily geostrophic winds, and SST maps obtained from NASA GHRSST satellite. Ekman transport and SST behaviour showed two different patterns: (i) offshore and upwelling favourable conditions on 13-22 nd of July; (ii) onshore and downwelling favourable conditions from 23 rd July to 19 th August). During upwelling, TS diagram showed an intrusion of Eastern North Atlantic Central Water affecting the continental shelf but not the rias. Nutrient salt concentrations increased with depth, reaching their maximum values near the mouth of Ortigueira Ria. During downwelling, coastal water increased its temperature (18.5-19.8ºC) and was retained inside rias; nutrients were nearly depleted, except for the innermost ria (estuarine zone) due to fluvial nutrient inputs. In this inner area, the maximum of chlorophyll-a (Barqueiro Ria) was observed. Low phytoplankton abundances were measured in both cases, even though a short increase in the plankton biomass was observed inside rias during upwelling, while under downwelling a small red tide of Lingulodinium polyedrum was detected. During the upwelling period Northern Rias tend to be mesotrophic systems as revealed by nutrient concentrations, chlorophyll levels and plankton abundances. On the contrary, in similar situations, the Western Rias behaves as eutrophics. In the Northern Galician shelf, the average of upwelling (downwelling) was 1.9±0.8 (2.1±1.0) events•yr-1 from May to September (1990-2008) considering at least one week with favourable wind conditions and UI averages out of the range of ±500 m 3 •s-1 •km-1. *Manuscript Click here to download Manuscript: MS_Ospina-Alvarez et al v3.docx Click here to view linked References

Soft-sediment crustacean diversity and distribution along the Portuguese continental shelf

“…Species from cold waters (e.g. Apherusa cirrus, Argissa hamatipes; Marques, 1989) are usually also found off the Portuguese coast due to upwelling events (López-Jamar et al, 1992;Nascimento et al, 2012;Ospina-Alvarez et al, 2010). However, Metopella sp.…”

Exchange of nutrients across the sediment–water interface in intertidal ria systems (SW Europe)

“…Although favorable upwelling conditions were found in the Northern Galician Rias during April and July (Ospina-Alvarez et al, 2010), these processes did not affect the inner part of the rias (Ospina- Alvarez et al, 2010;Prego et al 2012), and therefore it does not contribute to the sediment-water exchange in the rias of Ortigueira and…”

“…While in winter the strong freshwater inputs dominate the hydrography of these systems (Augas de Galicia, 2011), the oceanographic upwelling-downwelling events dominate in summer Ospina-Alvarez et al, 2010). Most studies have considered that nutrient regeneration in this area is driven by these processes (Alvarez-Salgado et al, 1996;Prego et al, 1999;Prego, 2002;Varela et al, 2005).…”

Environmental multi‐scale effects on zooplankton inter‐specific synchrony

“…The functioning of the Galician ecosystem has been intensely studied (e.g., Bode et al 1998;Nogueira et al 2000;Cabal et al 2008;Ospina-Alvarez et al 2010;Roura et al 2013). The region, influenced by contrasted seasonal fluctuations in upwelling and precipitation, offers a good case study to infer the relationship between environmental forcing and community dynamics.…”