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The Mediterranean Sea and its eastern sub-basin are marginal oceanic basins subjected to strong anthropogenic and natural pressures. During the last decades new findings have revised the way of assessing the circulation and physical functioning of the eastern Mediterranean Sea. Natural oscillations have been discovered while the impact of climate change has also been observed. Interannual variability has also been evident in the Aegean Sea, which is in close connection with the eastern Mediterranean. The continuous monitoring of the marine environment and the creation of long time series of marine observations is required in order to understand the functioning of the complex Mediterranean and Aegean ecosystems. The Hellenic Centre for Marine Research supports the creation of such time series by deploying multidisciplinary instrument moorings at specific key-points of the Aegean Sea, in an effort to provide scientific results essential for both sustainable development and mitigation of environmental pressures.

In order to assess seasonal and interranual variability in the export of particulate matter and its main constituents, sediment traps were deployed at five successive depths from February 2006 to March 2010 in the deepest basin of the Mediterranean (SE Ionian Sea, NESTOR site). The average total mass fluxes were 66, 58, 54, 34, and 52 mg m−2 d−1, at 700, 1200, 2000, 3200, and 4300 m, respectively. The interranual variability generally witnesses a gradual increase of fluxes during the experiment. The temporal variations of the mass flux showed similar seasonal signal at all sampling depths with higher values in spring–summer and lower in autumn–winter. Changes in the main constituents of the mass flux (organic carbon, carbonates, opal, and lithogenic matter) largely followed the same temporal variability with mass flux, revealing mechanisms of rapid vertical (top-down) transport from 700 m down to 4300 m-depth. Lateral inputs at the deepest trap are probably of importance, attributed to the influence of the deep Adriatic water, characterized by relatively higher turbidity than overlying water masses. The Ionian Sea displays high seasonal variability with maximum productivity rates observed during the late winter/spring convective mixing period. Our flux study proposes two additional processes, potentially of high importance for fuelling surface waters with nutrients at the NESTOR site: (1) the upwelling of intermediate waters in late spring-early summer, causing nutrient inputs in the surface layer which may lead to episodes of increased productivity, as witnessed by the organic carbon, carbonate, and opal fluxes in the mesopelagic and bathypelagic layers and (2) the influence of episodic dust input events, leading to enhanced fluxes of lithogenic matter.