PEACETIME (ProcEss studies at the Air-sEa Interface after dust deposition in the MEditerranean sea)
Coordinatrices: Karine DESBOEUFS (LISA) and Cécile Guieu (LOV)
Processes occurring at the atmosphere-ocean interface are critical to the regulation of the Earth climate and the delivery of key services provided by marine ecosystems. The Mediterranean Sea (MS), a hot spot for biodiversity but also for climate change and anthropogenic pressure, is an ideal natural laboratory to study these processes (MERMeX Group, 2011). In an unprecedented joint effort between experimentalists and modelers from atmospheric and marine sciences, PEACETIME proposes to study the fundamental physical, chemical and biological processes and their interactions at this key interface in the MS. Our objective is to assess how these mechanisms impact, and will impact, the functioning of the marine biogeochemical cycles, the pelagic ecosystem and the feedback to the atmosphere. This 4-year project proposes in particular to focus on a crucial mechanism forcing the biogeochemical coupling between the ocean and the atmosphere: atmospheric Saharan dust deposits which is known as a major source of nutrients for marine biosphere in the MS (Guieu et al., 2014). The strategy is designed to ensure that the knowledge acquired is used to understand that forcing across the MS today and in the future.
PEACETIME strategy is two-fold: (1) a cruise in the central MS in May 2017 on the research vessel Pourquoi Pas? where and when strong dust deposition events usually occur (Figure 1) and (2) substantial atmospheric and oceanic modeling developments (from 0D to 3-D).
Figure 1: Illustration of large-scale dust events in the Central Mediterranean region occurring in May in the past years.
A 33 days cruise in the central part of the Mediterranean Sea is scheduled in May 2017 on R/V Pourquoi Pas? (Figure 2). We will characterize the chemical, biological and physical properties of the atmosphere, the microlayer, the mixed layer and the deep waters during the cruise. Several types of sampling will be operated: continuous sampling (both surface seawater and lower atmosphere, PEGASUS platform will operated during the cruise) while cruising between stations (a total of 2000 miles), sampling during 12 short and 3 long stations. Experiments in 8 large Climate Reactors that accurately simulate future climate conditions (changes in pH, T°, atmospheric inputs, etc.) will be conducted during the cruise. These large tanks will be artificially seeded with Saharan dust, and key processes will be studied both spatially (3 contrasted trophic regimes) and temporally (present and +100 years seawater pH and temperature conditions). The cruise includes also a Fast Action strategy to enable us to route the ship towards an area of forecasted dust deposition event in order to tentatively document the respective roles of deposition and ocean dynamics. It is the lynchpin of the cruise.
Figure 2: Cruise transect
PEACETIME associates ~80 people (of which 39 will embark the cruise) from 14 research laboratories in France and 12 foreign research laboratories. PEACETIME project constitutes the WP1 and 2 of the project PARI-Med21 (Pollution, Aridification, the ecological state of the Mediterranean Sea in 2100 : http://dev-lamp.obs-vlfr.fr/pari-med21/index.html) which purposes to predict potential distributions of oceanic plants and animals in 2100 and their consequences for ecosystem functioning and services over the Mediterranean basin.
The project is mainly co-funded by IFREMER (crew and running of R/V Pourquoi pas?), MISTRALS program (http://www.mistral-home.org) and from foreign partners.