Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica
M. Vichi1,2, A. Coluccelli2,*, M. Ravaioli3, F. Giglio3, L. Langone3, M. Azzaro4, F. Azzaro4, R. La Ferla4, G. Catalano5, and S. Cozzi51Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy 2Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 3CNR-ISMAR Sezione di Bologna, Via Gobetti 101, 40129 Bologna, Italy 4CNR-IAMC Sezione di Messina, Spianata S. Ranieri 86, 82122 Messina, Italy 5CNR-ISMAR Sezione di Trieste, V. le Gessi 2, 34123 Trieste, Italy *now at: Universitá Politecnica delle Marche, Ancona, Italy
Received: 28 May 2009 – Accepted for review: 29 Jun 2009 – Discussion started: 08 Jul 2009
Abstract. Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175° E–74° S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990–2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces the observed magnitude of the biogenic fluxes, especially those found in the bottom sediment trap, but the peaks are markedly delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that the timing of the observed fluxes depends first and foremost on the timing of surface production and on a combination of size-distribution and quality of the autochtonous biogenic material. It is hypothesized that the bottom sediment trap collects material originated from the rapid sinking of freshly-produced particles and also from the previous year's production period.
Vichi, M., Coluccelli, A., Ravaioli, M., Giglio, F., Langone, L., Azzaro, M., Azzaro, F., La Ferla, R., Catalano, G., and Cozzi, S.: Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica, Ocean Sci. Discuss., 6, 1477-1512, doi:10.5194/osd-6-1477-2009, 2009.