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- Mesoscale patterns in the Cape Sao Vicente (Iberian Peninsula) upwelling regionPublication . Relvas, Paulo; Barton, Eric D.The coastal upwelling region near Cape Sao Vicente, the southwestern tip of the Iberian Peninsula where the southern zonal coast meets the meridional western coast, was studied using over 1200 advanced very high resolution radiometer (AVHRR) satellite images of sea surface temperature and time series of sea level height, wind velocities, and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape. Summer upwelling is more intense and persistent off the western coast than off the southern coast, where a recurrent warm coastal countercurrent flows westward, and at times turns northward along the western coast after reaching the cape. In this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast. Three preferred directions for the spreading of this water are identified. The most persistent is eastward along the southern shelf break and slope, possibly merging with waters previously upwelled locally, which becomes separated from shore by the coastal progression of the warmer counterflow. The second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet, which overshoots the cape. The least frequent feature to develop is a cold filament that grows westward at the latitude of the cape, appearing to result from the meandering of the equatorward jet. The coastal countercurrent is seen to interact with the equatorward jet at times of relaxation, not only by separating the cold upwelled water from the coast but, when it is energetic enough, breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters. Empirical evidence shows the presence of an alongshore pressure gradient, stronger in summer, driving the coastal progression of the warm counterflow. Wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients. The extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress, which is able to balance and reverse the alongshore flow, at least in the upper layers.
- Tidal MFP inversion for water depth and source range in the Intimate96 testPublication . Tolstoy, A.; Jesus, S. M.; Rodríguez, O. C.Examining Intimate96 hydrophone data we see clearly the effects of tide changes, i.e., of changing water depths. In this work we will examin Matched Field Processing sensitivity at a range of frequencies of expected tidal changes.
- Possible disruption of pheromonal communication by humic acid in the goldfish, Carassius auratusPublication . Hubbard, Peter; Barata, E. N.; Canario, Adelino V. M.Humic acids are large, complex, organic molecules which are ubiquitous components of aquatic environments as products of degradation of plant material. In aqueous solution they form microvesicles. As many teleost pheromones are steroidal in nature, we hypothesised that they would preferentially dissolve in the organic, hydrophobic core of these vesicles instead of in water and therefore be unavailable for detection. This would have obvious and profound effects on many aspects of fish biology. To test this hypothesis we recorded electro-olfactogram (EOG) response of the goldfish (Carassius auratus) olfactory epithelium to the pheromones 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P), its sulphated conjugate (17,20β-P-SO4) and prostaglandin F2α (PGF2α), all at 10−11 to 10−8 M, in the absence and presence of humic acids (1–1000 mg l−1). At nearly all concentrations of humic acid tested, there was a significant attenuation of the amplitude of the initial (phasic) response to 17,20β-P compared to 17,20β-P alone. At higher concentrations of humic acid, the EOG response to 17,20β-P was often completely obliterated, suggesting that the concentration of the pheromone available to the olfactory epithelium was below the threshold of detection. Exposure of the olfactory epithelium to humic acid did not cause any short-term loss of sensitivity to 17,20β-P per se. Furthermore, simultaneous recording of electro-encephalograms from the olfactory bulb demonstrated that the nervous activity evoked by the same concentration of 17,20β-P was less intense in the presence of humic acid than its absence. PGF2α is non-steroidal and much more soluble in water. In contrast to 17,20β-P, only the higher concentrations of humic acid (100 and 1000 mg l−1) significantly diminished the EOG amplitude. 17,20β-P-SO4 is detected via a distinct olfactory mechanism to the free form. Given that the sulphate group increases the water solubility, we predicted that the effect of humic acid would be reduced. However, the effect of humic acid on EOG amplitude in response to 17,20β-P-SO4 was similar to that of the free form. We suggest that the steroid portion of the molecule adsorbs onto the surface of the humic acid microvesicles and is still effectively unavailable for olfactory detection. In conclusion, humic acid may significantly reduce the concentration of 17,20β-P and 17,20β-P-SO4 available for detection by Carassius auratus in natural environments. Furthermore, as many teleost pheromones are steroid derivatives, this phenomenon may be applicable to chemical communication systems in teleosts in general.