Iryna Tereshchenko

El Niño 1997–98 monitoring in mixed layer at the Pacific Ocean near mexico's West Coast

The field data collected on monthly polygonal hydrographic surveys off the West Coast of Mexico in 1996–98 are analyzed. Monthly measured temperature and salinity profiles have been computed from the experimental data. The profiles for the 1997 summer-fall and 1998 winter periods differ essentially from profiles computed for the same months in the year 1996. The inferred cause of the difference is the ingress of large volumes of relatively warm and fresh water whose T,S-characteristics identify these water masses as the Pacific Tropical Surface Water. By January 1998, those water masses had filled the entire upper 90-m layer. The heat storage of a 150-m column increased to 15.3 GJ/m², as compared with its January 1996 value of 10.1 GJ/m². The process which caused sea surface temperature anomalies in region B of the Pacific, occurred one month before the rise in temperature and drop down in salinity were observed on the site.

Diurnal frequency internal waves in the southern part of the California Current ecosystem as a nutrient source

Although the semidiurnal internal tide dominates internal motions at all sites studied to date off Mexico, a diurnal signal was detected on the shelf of the California Current System off Baja California Sur, even though the barotropic tide is exponentially stronger in the semidiurnal frequency along this coastline. In this study, diurnal thermocline shoaling events were measured in kelp beds in late summer and fall of 2004, very near their southern limit in the Northern Hemisphere. Sub-thermocline water bathed the base of the kelp beds at a diurnal frequency. Nitrate concentrations up to 1.4 μmol·L–1 were found in this sub-thermocline water of almost 20 oC entering the kelp beds, which is a much greater concentration of nitrate at this temperature than is typical for the California Current. Nitrate-rich pulses lasted from 35 min to 19 h and reduced bottom temperatures up to 5 oC in 1 h. The periodicity of temperature variability at the moorings showed significant coherence with the diurnal variability in zonal winds (>95% confidence interval) and was not coherent with the semidiurnal tide. We propose that windforced, diurnal internal motions may provide an important nutrient source for primary producers during reduced upwelling periods and merit further study as a fertilization source in the southern part of the California Current System. A pesar de que la marea semidiurna predomina en las ondas internas de casi todos los sitios estudiados hasta la fecha en Mexico, se detecto una marea interna diurna sobre la plataforma continental del Sistema de la Corriente de California frente a las costas de Baja California Sur, aunque la marea barotropica es exponencialmente mas fuerte en la frecuencia semidiurna. En este estudio, se midio la subida diurna de la termoclina en los mantos de kelp, localizados cerca del limite sureno de su distribucion en el hemisferio norte, durante el verano y el otono de 2004. Agua profunda cubrio la base de los mantos de kelp una vez al dia donde se encontraron concentraciones de nitrato de hasta 1.4 μmol·L–1 en agua de casi 20 oC, lo cual representa una concentracion elevada de nitrato a esa temperatura para la corriente de California. Los pulsos de agua rica en nitrato duraron de 35 min a 19 h en los mantos y redujeron la temperatura del fondo hasta 5 oC en 1 h. La periodicidad de la variabilidad de la temperatura mostro una coherencia significativa con la variabilidad diurna de los vientos zonales (>95% intervalo de confianza) y no fue coherente con la marea semidiurna. Proponemos que las ondas internas diurnas, forzadas por el viento, podrian proveer una fuente importante de nutrientes a los productores primarios durante periodos en los cuales la actividad de surgencias es reducida y requieren de mas estudio para evaluar su capacidad de actuar como una fuente de fertilizacion en la parte sur del Sistema de la Corriente de California.

Climatic Change in a Large Shallow Tropical Lake Chapala, Mexico

Measurements of temperature, currents and lake level taken in 2005–2014 are ana‐ lyzed and discussed. We obtained a conceptually new data set on the formation of the thermocline in Lake Chapala. It is showed that the thermocline in the lake occurs only during the daytime, in the top 0.5–1.0-m layer of the water column, whereby the vertical temperature gradient reaches 2.5°C/m within that layer. At night, the top layer is cooled, which causes strong vertical mixing down to the bottom. Moored measurements of temperature and level from Lake Chapala reveal the presence of seiches oscillations with periods of 5.7 and 2.8 hours with amplitudes of 15.4 and 8.1 mm. Temperature measurements on sections across the lake showed that in the northern part of the lake, the water column is warmer that in southern 2–3°C in all seasons. The lake currents were simulated for wet and dry seasons. The model results are in good agreement with the acoustic Doppler current profiler (ADCP) data. The presence of an anticyclone gyre in the central part of the lake in both seasons is detected.