Investigating upper ocean processes
The ocean plays a crucial role in the climate system of planet Earth by helping to transport excess heat from the Equator to northern latitudes. Interaction between the atmosphere and the sea and most biological productivity takes place in the upper ocean. However, scientists currently do not have a clear picture of the ocean processes responsible for controlling the circulation of the ocean's surface. The EU-funded 'Lagrangian approach to understand upper ocean processes' (LAGAPOCE) project was therefore established to give a better understanding of the physical processes behind upper ocean circulation. Project partners investigated two complementary ocean systems, the Kuroshio Current (outgoing phase) and the Canary Current (return current). The two currents are the western and eastern components of the north Pacific and Atlantic sub-tropical gyres. A gyre is a large system of rotating ocean currents, particularly one involving large wind movements. LAGAPOCE developed an innovative approach that combined surface Lagrangian velocities and satellite data. Lagrangian velocities describe the dynamics of a system and currently provide the most accurate and realistic picture of surface circulation in the open ocean. This methodology enabled for the first time detailed analysis of the actual surface circulation patterns of the Kuroshio Current and Canary Current. The Kuroshio results were compared with data from 1992 to determine if changes in eddy patterns had occurred. The project's main results involved a description of the different mechanisms that influence the intrusion of the Kuroshio Current into the waters of the continental shelf. A simulation was also developed for estimating the occurrence of an intrusion by the Kuroshio current. This was possible as eddies can be observed originating in the western Pacific several weeks before they impinge on the Kuroshio. Scientists also described the Canary Deep Poleward Undercurrent and developed a hypothesis regarding the mechanisms that drive it. They posited that the pressure gradient created by the encounter with the Mediterranean outflow waters and the Antarctic waters build up the poleward flow. The work was compared with a numerical model. Worked conducted by the LAGAPOCE project will help to predict changes in hydrodynamic conditions. It will also increase knowledge in the use of surface Lagrangian data to monitor and understand the upper ocean.
Keywords
Upper ocean, climate system, Lagrangian approach, ocean circulation, currents, sub-tropical gyre, eddy patterns, continental shelf, outflow waters, hydrodynamic
