Mertz Regional Diversity Assessment Project

Research sites

The Mertz-DIVA project is one of the 22 projects that were selected for the ACE circumnavigation that will take place between December 2016 and march 2017 on board the research icebreaker A. Tryoshnikov. This project focuses on the Adélie Land, a region under the strong influence of the Mertz glacier.

Through deployment of state-of-the art instrumentation, the Mertz-DIVA project team aim to describe in great detail glacial, hydrological and geological environments as well as the exceptional biodiversity and ecosystem functioning of a key region of the Antarctic.

This area, located in East Antarctica between the 140th and 145th meridians and, although discovered in 1840 by the Admiral J. Dumont d’Urville, was really explored for the first time between 1912 and 1914 during the «l’Australasian Antarctic Expedition». During this expedition, D. Mawson and collègues, overwintered in a bay closed to the Mertz glacier and performed a very detailed cartographic investigation of the area. They also conducted the first biological, geological and hydrological study of the area (Mawson, 1914). Despite the loss of two of their colleagues, Dr X. Mertz and Lt B. Ninnis –in the memory of which the two main glacier of the area were named-, Mawson’s team realised excellent topographic surveys providing a very precise map of the extent of these two ice giants and the position of both pack and permanent ice in 1914. These first observations reveal that in 1914 surface oceanic conditions and the length of the floating tongue of the Mertz glacier were identical to those observed in January 2010 few days before the calving of the tongue. This 150km long floating tongue extending northward and prolonged by a string of icebergs grounded onto the east flank of the Mertz bank was protecting the area downstream from the drifting ice pack. These conditions were favouring the presence of a large polynya during winter and an intense production of high salinity shelf water. Indeed, recent studies show that up to 25% of Antarctic Bottom water originates from this area (Jacob, 2004; Rintoul, 1998). In addition to this key role on global oceanic circulation, the absence of sea ice in the polynya favour the presence of intense spring blooms (Arrigo, 2003) that contribute to the exceptional biological richness of the region. An extensive study conducted between 2007 and 2008 (prior to the calving) onto the shelf in front of the George V land confirmed its exceptional biodiversity with, in particular, the presence of deep coral assemblages in the canyons

dissecting the shelf. In other Antarctic regions, these observations led to the creation of marine protected areas (MPA) and the identification of vulnerable marine ecosystems (VME; Post et al., 2010). A proposal for creating a MPA in the Dumont d’Urville sea is actually being drafted. In January 2010, the ice tongue suddenly lost over 80km calving a massive iceberg. The loss of the floating tongue deeply impacted the surface oceanic conditions of the area (Tamura et al., 2012; Campagne et al., 2015) and stopped dense water formation (Lacarra et al., 2014). Some areas previously located under a thick ice cover for decades suddenly became exposed while others usually ice free were suddenly recovered by a permanent ice cover. First observations in Commonwealth bay since the calving reveal profound impacts onto the local ecosystems: Adélie penguin populations from cape Denison and Mackellar archipelago decreased by over 50% between 2011 and 2113 (Clark et al. 2015). Benthic ecosystems were also deeply impacted as revealed by the quasi-disappearance of macroalgae in the sub-tidal area (Wilson et al., 2016). In January 2011, few months after the calving a first oceanographic cruise provided (1) preliminary information about the structure and diversity of benthic ecosystems previously located under permanent ice cover, (2) few images of iceberg scours, (3) confirm the presence of deep coral assemblages (Errina spp.) though without being able to precisely locate them (Smith & Riddle, 2011). The combined deployment of a science-class ROV (ROPOS- http://www.ropos.com/) and gliders for the first time in these environments with a complete oceanographic survey (with several CTD casts and 2 mooring deployments) will provide the information that will be necessary for finely characterizing these communities and the environmental conditions controlling them.