Rivkin¹, Richard B., and Louis Legendre²

¹Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NF A1C 5S7, Canada, Tel: 709-737-3720, Fax: 709-737-3220, E-mail: rrivkin@mun.ca and ²Laboratoire d'Oceanographie de Villefranche, B.P. 28, 06234 Villefranche-sur-Mer Cedex, France

Biogenic carbon cycling and remineralization in the mesopelagic

The region between 100 and 1000 m is usually referred to as the mesopelagic layer or "twilight zone". It contains ~25% of the volume of the ocean and the bulk of the ocean's living biomass. Processes occurring in the mesopelagic layer feed back to the upper ocean and ultimately the atmosphere. Despite the importance of the mesopelagic layer to ecosystem processes and climate change, remarkably little is known about spatial patterns and processes controlling inputs, cycling, degradation and outputs of organic matter. We used comparative and meta-analysis to characterise microbial properties in the upper and mesopelagic layer of the World Ocean. We computed the rate of carbon remineralisation and organic carbon turnover in this region. This allows the estimation of two important parameters: the minimum euphotic zone primary production that is required to balance the remineralization in the upper 1000 m and the sequestration of organic carbon. Based upon our analyses, we propose that euphotic zone primary production and export is at least 50% higher than current estimates.