Introduction to the Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean (BOUM) experiment

Abstract

Abstract. The overall goal of the BOUM (Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean) experiment was to obtain a better representation of the interactions between planktonic organisms and the cycle of biogenic elements in the Mediterranean Sea (MS), in the context of global climate change and, more particularly, on the role of the ocean in carbon sequestration through biological processes. The BOUM experiment was organized around three main objectives: (1) to give a longitudinal description of the biogeochemistry and the biological diversity of the MS during the strongest stratified period, (2) to study processes at the centre of three anticyclonic eddies, and (3) to obtain a representation of the main biogeochemical fluxes and the dynamics of the planktonic trophic network. The international BOUM cruise took place between 16 June and 20 July 2008, involved 32 scientists on board, and covered around 3000 km in the MS from the south of Cyprus to Marseilles (France). This paper describes in detail the objectives of the BOUM experiment, the implementation plan of the cruise before giving an introduction of the 25 other papers published in this special issue. General contextThe additional CO 2 in the atmosphere, mainly resulting from fossil fuel emissions linked to human activities (anthropogenic CO 2 ), is the main cause of global warming.The ocean has acted as a major sink of anthropogenic CO 2 (Sabine et al., 2004) preventing a greater accumulation in the atmosphere and therefore a greater increase in the earth temperature. Although the biological pump (Fig. 1) provides the main explanation for the vertical gradient of carbon in the ocean, it was thought to be in an equilibrium state with an associated near-zero net exchange of CO 2 with the atmosphere (Broecker 1991, Murname et al., 1999. Climate alterations are beginning to disrupt this equilibrium, and the expected modification of the biological pump will probably considerably influence oceanic carbon sequestration (and therefore global warming) over a decadal time scale (Sarmiento and Grüber, 2006). CO 2 is exchanged at the atmosphere-ocean interface and reacts with carbonate ions (Fig. 1). The time scale for reaching equilibrium within the upper layer is about a year (Kleypas and Langdon, 2006). This dissolved inorganic carbon is then transported much more slowly into deeper layers via mixing. This second step limits the sequestration of anthropogenic CO 2 in the ocean on a decadal time scale and therefore influences the accumulation of CO 2 in the atmosphere and thus, subsequent climate alteration (Sarmiento and Grüber, 2006). Some of the CO 2 in the upper layer is incorporated into biomass by photosynthesis. This synthesis of particulate organic carbon is essentially dependent on the availability of light and nutrients (including trace metals). A fraction of the particulate organic carbon pool is transferred into the dissolved organic pool (Maranon et al., 2005). MostPublished by Copernicus Publications on behalf of the Eu...

Hydrographic situation during cruise M84/3 and P414 (spring 2011) in the Mediterranean Sea

“…However, most of them were restricted to special areas. METEOR cruise M84/3 constitutes an exception, as it is one of very few recent cruises (another one was the BOUM cruise, see Moutin et al, 2012), carried out after the appearance of the EMT, which ran on a section across the whole Mediterranean Sea with the goal of producing a quasi-synoptic view of the distribution of relevant physical and chemical properties in both basins. Furthermore, it reoccupied relevant stations of previous surveys, most importantly several of the stations from the METEOR survey M5/6 in 1987, which provided the last view of the situation before the EMT.…”

Ecology of aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea

“…The physical and hydrologic characteristics of the water masses in the Mediterranean Sea have been previously described and full details for the BOUM cruise can be found in Moutin et al (2011). During the summer BOUM cruise, surface seawater temperatures ranged from 24 • C in the western basin (station A) to 27.5 • C in the central-eastern part (station B).…”

“…The cruise was planned as a 3000 km transect of stations encompassing a large longitudinal gradient in the Mediterranean Sea (Fig. 1, see also Moutin et al, 2011). Hydrological, biological and chemical parameters were studied at 27 short-term stations and three long-term stations designed by letters (A, B, and C), located at the centre of anticyclonic gyres, where lateral advection was expected to be minimum (Fig.…”

Physical forcing and physical/biochemical variability of the Mediterranean Sea: a review of unresolved issues and directions for future research

“…These feedbacks display differences between the subbasins of the Mediterranean that need to be addressed better (e.g., Moutin et al, 2012). Furthermore, the functioning of the biological pump should be investigated, combining estimates of pCO 2 , satellite PP, Chia data and POC fluxes measured by sediment traps at various depths along with the role of community structure (D'Ortenzio and Ribera d'Alcala, 2009).…”