Phytoplankton pigment concentrations during POLARSTERN cruise ANT-XXVII/2

Photophysiological processes as well as uptake characteristics of iron and inorganic carbon were studied in inshore phytoplankton assemblages of the Western Antarctic Peninsula (WAP) and offshore assemblages of the Drake Passage. Chlorophyll a concentrations and primary productivity decreased from in- to offshore waters. The inverse relationship between low maximum quantum yields of photochemistry in PSII (Fv/Fm) and large sizes of functional absorption cross sections (sigma PSII) in offshore communities indicated iron-limitation. Congruently, the negative correlation between Fv/Fm values and iron uptake rates across our sampling locations suggest an overall better iron uptake capacity in iron-limited pelagic phytoplankton communities. Highest iron uptake capacities could be related to relative abundances of the haptophyte Phaeocystis antarctica. As chlorophyll a-specific concentrations of humic-like substances were similarly high in offshore and inshore stations, we suggest humic-like substances may play an important role in iron chemistry in both coastal and pelagic phytoplankton assemblages. Regarding inorganic carbon uptake kinetics, the measured maximum short-term uptake rates (Vmax(CO2)) and apparent half-saturation constants (K1/2(CO2)) did not differ between offshore and inshore phytoplankton. Moreover, Vmax(CO2) and K1/2(CO2) did not exhibit any CO2-dependent trend over the natural pCO2 range from 237 to 507 µatm. K1/2(CO2) strongly varied among the sampled phytoplankton communities, ranging between 3.5 and 35.3 µmol/L CO2. While in many of the sampled phytoplankton communities, the operation of carbon-concentrating mechanisms (CCMs) was indicated by low K1/2(CO2) values relative to ambient CO2 concentrations, some coastal sites exhibited higher values, suggesting down-regulated CCMs. Overall, our results demonstrate a complex interplay between photophysiological processes, iron and carbon uptake of phytoplankton communities of the WAP and the Drake Passage.

Acoplamiento coherente de cuatro ondas de Alfven

Interacciones no lineales de ondas de Alfvén existen tanto para plasmas en el espacio como en laboratorios, con efectos que van desde calentamiento hasta conducción de corriente. Un ejemplo de emisión de ondas de Alfvén en ingeniería aparece en amarras espaciales. Estos dispositivos emiten ondas en estructuras denominadas “Alas de Alfvén”. La ecuación Derivada no lineal de Schrödinger (DNLS) posee la capacidad de describir la propagación de ondas de Alfvén de amplitud finita circularmente polarizadas tanto para plasmas fríos como calientes. En esta investigación, dicha ecuación es truncada con el objetivo de explorar el acoplamiento coherente, débilmente no lineal y cúbico de cuatro ondas cerca de resonancia (k1 + k2 = k3 + k4). La onda 1 que corresponde al vector de onda k1 puede ser linealmente inestable y las tres restantes ondas 2, 3 y 4, correspondientes a k2, k3 y k4 respectivamente, son amortiguadas. Por medio de la utilización de este modelo se genera un flujo 5D formado por cuatro amplitudes y una fase relativa. En una serie de trabajos previos se ha analizado la transición dura hacia caos en flujos 3D (Sanmartín et al., 2004) y 4D (Elaskar et al., 2005; Elaskar et al., 2006; Sánchez-Arriaga et al., 2007). Se presenta en este artículo un análisis teórico-numérico del comportamiento del sistema cuando la tasa de crecimiento de la onda inestable es nula.