The influence of oceanic convection in primary production

The influence of Oceanic Convection in Primary Production was investigated by both, numerical model studies and field observations. Cruises with RV VA LDIVIA were conducted in the North Atlantic/Nordic Seas in Spring with the purpose of investigating a hypothesised relationship between Oceanic Convec tion and phytoplankton dynamics in winter in open oceans. In the ocean phyt oplankton would sink down into deep waters after the breakdown of the seaso nal thermocline in autumn. The mechanism that in spring reliably initiates phytoplankton blooms by bringing cells back to the surface has yet only rar ely been investigated. The orbital motions of the water caused by Convectio n carries plankton up and down. Cells may therefore intermittently get back to the surface to receive enough light to stay alive during a winter. Duri ng VALDIVIA Cruise 176 (March 1999) a YOYO-station, covering 16 profiles me asured every hour were conducted, which showed a high temporal variability of convective penetration. A phytoplankton model was coupled to a 2.5 dimen sional non-linear, non-hydrostatic Convection model. In the first numerical study plankton was simulated by an Eulerian approach, in which plankton wa s introduced as an Eulerian tracer to investigate the temporal variability of the water column observed during the YOYO-station. The aim of the second numerical study is the provision of quantitative estimates of CONTACT time s of water parcels, i.e. plankton that was carried by the water motions, wi th the uppermost water column, where light is available for growth. This wa s done by a Lagrangian approach in which plankton ensembles are simulated b y Lagrangian tracers and a realistic stratification obtained during RV VALD IVIA Cruise 141 is prescribed as background field. In both cases the model domain is a vertical ocean slice. Horizontal dimensions of the model domain are chosen in accordance with expected convective aspect ratios, which var y between 1 and 3. Special attention was paid on the influence of Convectio n on the temporal variability of Chlorophyll a content in the water column. (C) 2001 Elsevier Science B.V. All rights reserved.