Atlantic Carbon Experiments: preliminary results from the first cruise

This work intends to show the first and preliminary results from a research project called Atlantic Carbon Experiment (ACEx). The ACEX is part of an innovative and promising scientific effort, contributing to a better understanding of the chemical, physical and dynamic ocean-atmosphere interaction in micro-and meso-scales in the Southwest Atlantic trade flows in this interface. This project will conduct fieldwork aboard Brazilian ships. The first cruise was named ACEx1 and was conducted aboard the Brazilian Navy R/V Cruzeiro do Sul, in December 2010 and was divided into two phases, the first between the cities of Rio Grande (RS) and Itajai (SC) and the second stage between the cities of Itajai and Rio de Janeiro (RJ). The cruise comprised transects perpendicular to the shore, in order to capture contrasts between shore and off shore region. In the first stage, the activities of the group involved with the ACEx relied on measurements of atmospheric carbon dioxide concentration and standard meteorological variables. Weather balloons were launched with radiosonde sensors. In the second stage, there were no launched radiosondes, as these were intended for the study of ocean-atmosphere interaction in the areas where the largest thermal gradients were zonal (horizontal) in the ocean.

As an initial approach aiming at ultimately having in situ measurements of momentum, latent and sensible heat and CO2 fluxes, a simple eddy covariance system was installed aboard the ship. It consisted in an infrared gas analyzer (IRGA) a three-dimensional sonic anemometer and a motion sensor (used to the correction of flows). In this study, the limitations of such measurements are presented, in terms of the motion corrections necessary and their effect to the turbulence signals. Turbulent velocity spectra and scalar flux cospectra are largely affected by the motion and the associated correction. Energy fluxes are then compared to those obtained from classical parameterizations used in air-sea interaction studies.

In future campaigns, a more robust system will be used for flux observations. Therefore, through the realization of this project it is expected the training of a multidisciplinary team able to make in situ measurements of fluxes of momentum, heat and CO2 in the southwest Atlantic, a region of great importance for the sequestration of atmospheric carbon dioxide. By analyzing the results, it is expected to enhance the understanding of the modes and processes related to the variability of oceanic and atmospheric flows, as well as the possible impacts of these processes in the study region. The in situ observations will also be used for studies in conjunction with satellite-derived data and will feed numerical modeling studies.