Irene Laiz

Daily, biweekly, and seasonal temporal scales of pCO2 variability in two stratified Mediterranean reservoirs

Temporal scales of variability for the partial pressure of CO2 (pCO2) in the surface waters of two stratified Mediterranean reservoirs were examined through the temporal decomposition of 5 month time series with hourly sampling frequency. pCO2 time series included similar patterns of variability at daily, biweekly, and seasonal scales regardless of the difference in amplitude of the pCO2 variation in the two reservoirs studied. Daily variability was strongly related to the day-night cycles of metabolic activity, accounting for about one third of the total amplitude in pCO2 variation. At a biweekly scale, wind forcing led to higher rates of air-water CO2 exchange and subsequently temporary partial mixing events associated to relevant increase of CO2 concentration in surface waters. Seasonal variability accounted for one third of the amplitude of the pCO2 variability and was coupled to the seasonal dynamics of water temperature and thermal stratification of the water column. Our results provide evidence that CO2 emission from stratified water bodies shows significant variability at daily, biweekly, and seasonal scales; all of which should be taken into consideration in the analyses of the carbon fluxes. The wind-induced mixing events, operating at temporal scales between daily and seasonal cycles, may become a major factor controlling the pCO2 dynamics. Hence, some of the most common models for computing CO2 fluxes from pCO2 were not able to reproduce the biweekly response patterns of CO2 emissions to wind forcing.

Is oxidative stress related to cadmium accumulation in the Mollusc Crassostrea angulata

The kinetics of cadmium (Cd) accumulation in the gills and digestive gland of Crassotrea angulata at three concentrations of cadmium (0.088 μM, 0.44 μM and 2.22 μM) was monitored for 28 days. The relationship between accumulation and toxicity was studied using metallothionein-like protein (MTLP) concentration and reduced glutathione levels (GSH) as biochemical endpoints. The activity of enzymes which form part of the antioxidant defense system, in particular glutathione reductase (GR), total glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT), as enzymatic endpoints, was also assessed. A first order kinetic model demonstrated that the accumulation process does not take place linearly, as the Cd concentration in gills and digestive gland tended toward a stationary state. Metallothionein-like protein is clearly induced by Cd accumulation; however, at high Cd concentrations the detoxification mechanism of this protein is affected. High Cd concentrations (2.22 μM) lead to a decrease in GSH levels, and also inhibit antioxidant enzyme activities, demonstrating the adverse effect of this metal on the antioxidant balance system.

Estimation of the seasonal sea level variations in the Gulf of Cadiz (SW Iberian Peninsula) from in-situ measurements, satellite altimetry and numerical models

Time series (1997-2008) of near-shore altimetry data and in-situ tide gauge records have been analyzed to investigate the seasonal variability of sea level along the Gulf of Cadiz. A high level of agreement was obtained between altimeter and in-situ observations, indicating that altimeter data can be a valuable tool to study the sea level seasonal cycle near the coast. Harmonic analysis showed that more than 95% of the average seasonal cycle is explained by the annual and, to a lesser extent, semiannual components. The average seasonal cycle of sea level anomalies is very similar at the four coastal stations, with minimum values during winter and maximum during autumn. Atmospheric pressure accounts for 20-38% of the sea level variability, its effect diminishing toward the Strait of Gibraltar. The steric contribution is notable at the westernmost stations (32-37%) and it also decreases eastward (9-17%). River discharge explains about 15% of the sea level variability, indicating that its effects should be taken into account. The contribution of direct atmospheric forcing for a section of the sea level time series (1997-2001) has also been explored using the output of a barotropic oceanographic model (HIPOCAS project) forced with wind and atmospheric pressure, revealing that the contribution of wind is generally small (6-12%) at seasonal time scales. Small but significant correlations are found between the time series of winter-autumn mean sea level and the winter-autumn North Atlantic Oscillation (NAO) indices. Analysis show that the effect of NAO is mainly reflected on atmospheric pressure, wind and river runoff.

From ENVISAT RA-2 to CRYOSAT SIRAL: validation of altimeter products near the coast (the ALCOVA Project)

Satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean; however, its use is still limited in shallow waters near the coast where two main issues still need a more detailed analysis. On one side, the local characteristics of each coastal region imply that certain corrections applied to the altimetry measurements need to be reanalysed. On the other side, the radar signal retracking algorithms need to be improved because the waveforms do not follow the Browns model, which is designed for deep waters. The ESA mission Envisat was launched in March 2002 with a dual-frequency radar altimetry (RA-2). The satellite was operative until the end of the mission in May 2012. The ESA mission Cryosat-2 was launched in April 2010 being still in operation. The radar instrument on-board Cryosat-2 improves the capabilities of previous pulse-limited altimeters, such as Envisat RA-2. The Spanish-funded ALCOVA project aims at analyzing and improving the altimetry measurements obtained from these two altimetry missions. Regarding the RA-2 data a new prototype retracker -ALES- has been developed under the frame of the ESA-DUE eSurge project. Two pilot regions are proposed, namely, the Gulf of Cadiz and the Strait of Gibraltar in the Southwestern Iberian Peninsula. Cryosat-2 data (in SAR mode), the newly corrected RA-2 data (based on ALES) and the standard RA- 2 product (based on Browns model) are being validated with available in-situ data (sea level height) to ensure their correct performance in the selected coastal areas.

Spatial structure of the sea level seasonal cycle within the Gulf of Cadiz

Sea level anomaly maps from altimeter (AVISO) were retrieved for the Gulf of Cadiz (GoC) for the period 1997-2008, along with maps of Dynamic Atmospheric Correction (DAC), atmospheric pressure at sea level and satellite Sea Surface Temperature (SST). Data were averaged in time to obtain maps of monthly mean time series in order to analyze the seasonal variability of sea level and its main forcing agents along the GoC. Moreover, a very high resolution climatology for the region was combined with the SST maps to explore the steric contribution with enough spatial resolution near the coast. The AVISO sea level anomaly monthly maps were initially de-corrected using the DAC product and then corrected using the inverted barometer method. Atmospheric pressure explained more than 55% of the sea level variance offshore and between 35-45% within the continental shelf. The amplitude of the pressureadjusted sea level semiannual signal was considerably reduced, confirming its meteorological origin. The steric contribution on the pressure-adjusted sea level was addressed by considering local, open ocean, basin-wide and continental shelf steric effects. The open ocean contribution explained the highest percentage of variance all over the basin with the exception of the western shelf, where the best results were obtained with the local contribution. After correcting for the best steric contribution, the amplitude of the remaining offshore annual signal was negligible (0.5-1.0 ± 1 cm). As for the continental shelves, 2- 3 cm (± 0.5-1 cm) of the annual signal remained unexplained, probably due to local effects related with the shelves dynamics.