Impact of ocean stratification on small-scale physical oases for pelagic life

Physical forcing of the surface ocean includes a variety of energetic processes, ranging from internal wave (IW) to submesoscale and mesoscale. Recent works based on acoustic data showed that, off Peru, the vertical displacements of the oxycline depth provide a robust proxy of isopycnals displacements over a wide range of horizontal scales. These studies revealed the importance of ephemeral hotspots (oases), which concentrate organisms ranging from zooplankton to seabirds, enhancing trophic interactions. Here, we address the question of the potential impact of climate variability on these fine-scale oases for life. Indeed, temperature and salinity changes induced by climate change are expected to lead to an ocean near-surface stratification increase that could have a negative impact on the intensity of physical small-scale structures and, consequently, on patterns distribution of marine life. For that we use 35 000 physical structures from acoustic data collected during twelve scientific surveys conducted between 2002 and 2011 off Peru. We estimate the strength of these structures, its power of aggregation on zooplankton and small pelagic fish and also ocean stratification conditions. Results show that higher the ocean stratification, less the strength and the power of aggregation of the fine scale physical structures. Climate variability, and potentially climate change, could thus lead to a reduction of the size and density of organisms patches with a potential impact on consequent trophic interactions.