Search

In this study, we focusing on understanding changes in air and water quality during the Covid-19 lockdown in the Venice Lagoon. We are re-using existing Research Objects, and in particular Jupyter Notebooks that were created in previous studies.

Long-term time-series are a fundamental prerequisite to understand and detect climate shifts and trends. Understanding the complex interplay of changing ocean variables and the biological implication for marine ecosystems requires extensive data collection for monitoring and hypothesis testing and validation of modelling products. In marginal seas, such as Mediterranean Sea, there are still monitoring gaps, both in time and in space. To contribute filling these gaps, an extensive dataset of dissolved inorganic nutrients profiles (nitrate, NO3; phosphate, PO43−; and silicate, SiO2) have been collected between 2004 and 2017 in the Western Mediterranean Sea and subjected to quality control techniques to provide to the scientific community a publicly available, long-term, quality controlled, internally consistent biogeochemical data product. The database includes 870 stations of dissolved inorganic nutrients sampled during 24 cruises, including temperature and salinity. Details of the quality control (primary and secondary quality control) applied are reported. The data are available in PANGAEA (https://doi.org/10.1594/PANGAEA.904172, Belgacem et al. 2019).

Ocean life relies on the loads of dissolved inorganic nutrients (nitrate, phosphate and silicate) and other micro-nutrients into the euphotic layer. They fuel phytoplankton growth that maintains the equilibrium of the food web. Ocean circulation and physical processes continually drive the large -scale distribution of chemicals toward a homogeneous distribution (Williams and Follows, 2003). The biological and biochemical processes counteract this tendency. Therefore, describing nutrient dynamics is important to understand the overall ecosystem functioning.At global scale, most of the biogeochemical descriptions are based on model simulations and satellite data, since nutrient in situ observations are generally infrequent and not homogeneously distributed in space and time. Climatological mapping is often used to understand the biogeochemical state of the ocean representing monthly, seasonally or annual averaged fields.Within this context, the western Mediterranean Sea climatology (BGC-WMED) presented here is a product derived from in situ observations, derived from various data sources: in total, 2253 in-situ inorganic nutrient profiles over the period 1981-2017 have been used (Medar/MEDATLAS, Fichaut et al., 2003; the CNR-WMED biogeochemical dataset, Belgacem et al., 2020; SeaDataNet data product, https://www.seadatanet.org; Mediterranean Ocean Observing System for the Environment, MOOSE, http://www.moose-network.fr/).Annual mean gridded nutrient fields for the period 1981-2017, and sub-periods 1981-2004 and 2005-2017, on a horizontal 1/4° × 1/4° grid have been produced. The biogeochemical climatology is built on 19 depth levels and for the dissolved inorganic nutrients nitrate, phosphate and orthosilicate. To generate smooth and homogeneous interpolated fields, an advanced N-dimensional version of DIVA, DIVAnd v2.5.1 (Barth et al., 2014), which is based on the variational inverse method (VIM) (Brasseur et al., 1996), has been used.A sensitivity analysis was carried out to assess the comparability of the data product with the observational data. The BGC-WMED has then been compared to other available data products, i.e. the medBFM biogeochemical reanalysis and the biogeochemical component of WOA18.Keywords: Mediterranean Sea, climatology, inorganic nutrient, in situ observations.

It is well known that in the Mediterranean major oceanic processes may occur, of which the most important example is deep water formation (DWF) that sustains the basin-wide thermohaline circulation cell. This is also the main oceanic mechanism that sustains the physical carbon pump: once carbon dioxide is dissolved in surface water, it can enter into the ocean carbon cycle and be sequestered and transported to different depths and parts of the ocean thanks to the processes of DWF and thermohaline circulation. The deep waters that are formed via DWF have long residence times, thus trapping great parts of the anthropogenic carbon released to the atmosphere. The most ubiquitous water mass of the Mediterranean Sea is the IntermediateWater (IW). It forms via salinification and densification of the surface waters in the Levantine Basin and in the Cretan Sea. After sinking to its equilibrium depth, the IW spreads throughout the whole Mediterranean Sea. The core of this water mass can be easily identified by its absolute maximum in salinity (and relative maximum in temperature), when looking at vertical profiles of these properties. While flowing back towards the Western Mediterranean (WMED), it tends to gradually lose its characteristics, due to dilution with adjacent water masses, becoming thus less salty and less warm. Not only salinity and temperature change along the IW path across the WMED, but also its biogeochemical and carbonate system properties: these non-conservative properties change also as a consequence of bio-chemical processes. The aim of this investigation is to understand the evolution of physical (temperature, salinity), biogeochemical (AOU, nutrients and DOM) and carbonate system properties (TA, pH) of the IW along its pathway through the WMED, assessing the role of changes induced by physical mixing of the IW with adjacent water masses and those induced by biological and biochemical processes. To discriminate between the acting processes and assess their relative roles, a mixing analysis has been performed. Along IW path the increase of AOU with age of the water mass indicates the preponderance of respiration over the production. The most important increase of AOU occurs while the IW enters and circulates within the Tyrrhenian Sea. In all other areas persistent strong hypoxic conditions are maintained with scarce changes. The decrease in TA is consistent with the change in salinity, as expected given the strong linear relationship between these two parameters, while the decrease of pH and the increases of the concentrations of the main inorganic nutrients (+77%, +34 and +26 %, for phosphates, nitrates and silicates, respectively) indicated an active remineralization of organic matter in this water mass. The process of acidification of IW also causes a shift of the carbonate equilibrium, toward more acidic species, and a decrease of the saturation state of calcite and aragonite, indicating a reduction of the oversaturation of these calcium carbonate minerals along IW path. The concomitant increase of the Revelle buffer factor suggest that this water is potentially less efficient to take up atmospheric CO2 with aging.