Hydrological and Biogeochemical Patterns in the Sicily Channel: New Insights From the Last Decade (2010-2020)

Abstract

The hydrological and biogeochemical time series from 2010 to 2020 have highlighted specific relationships and trends in oceanographic processes and nutrient patterns in the Sicily Channel. Specifically, temperature and salinity time series in the intermediate waters showed a sharp annual increase of about 0.06°C and 0.09 within the period 2010-2020, at rates that are about 50% higher than what observed within the previous decade. Similar trends were also present in deep waters, although with lower variations of both temperature and salinity. The time series in the intermediate water, also highlighted the presence of quasi cyclic fluctuations that can be associated with the alternation of the circulation modes (cyclonic and anticyclonic) of the Northern Ionian Gyre. Moreover, an opposite trend emerged by comparing the nutrients and salinity time series in intermediate waters, while similar patterns has been evidenced between nutrients and chlorophyll-a concentration. This latter finding is not consistently present in the Mediterranean area, suggesting the need of further studies on a wider scale.

Relationship between thermohaline and biochemical patterns in the levantine upper and intermediate water masses, Southeastern Mediterranean Sea (2013–2021)

“…The averaged salinity and temperature time series of the LIW core present a good agreement with the presiding circulation pattern of the north Ionian, the BiOS mechanism (Civitarese et al, 2010;Gacic et al, 2010;Lavigne et al, 2018;Menna et al, 2022;Placenti et al, 2022). Periods of anticyclonic circulation (tinted in red in Figure 2) are characterized by a positive tendency in salinity and temperature, while cyclonic periods (tinted in blue) are accompanied by a decrease in the thermohaline values of LIW.…”

“…Thus, the mechanism of warming and shallowing the LIW core due to its increased buoyancy enabled a higher level of nutrients to become available to the photic zone from below, supporting the observed rise of the intergraded Chl.a (or algae biomass), with a maximum recorded during 2018-2019. Accordingly, we further suggest that this mechanism of warming and shallowing the LIW core may explain the general long-term rise of the integrated Chl.a (Figure 2 The 2013-2021 time series shows two distinct periods of BiOS, mainly cyclonic (2011-2016Placenti et al, 2022) and mostly anticyclonic Menna et al, 2022). It is expected that the biological response to BiOS is complex and exhibits certain delay and thus does not coincide with the detailed thermohaline interannual variations.…”

“…We observed a peak in the total alkalinity concentration coinciding with the 2018 salinity peak (Supplementary Figure S1), yet the existing data for 2013-2021 are too small to draw a firm behavior and display concentrations, which follow the conservative behavior (linear trend) of total alkalinity with salinity (Kolker et al, 2021, and references therein). (Menna et al, 2022;Placenti et al, 2022).…”

“…The Adriatic-Ionian Bimodal Oscillating System (BiOS), thoroughly described in Gacic et al, 2011;Gacic et al (2010 andexperimentally by Rubino et al (2020), controls the trajectory of the AW flow after passing through the Sicily Straits to both the Southern Adriatic (SA) and the LB, which correspond to quasi-decadal reversals in the North Ionian Gyre (NIG). The BiOS mechanism has been shown to have a significant effect on the physical and chemical dynamics in the SA (Civitarese et al, 2010;Gacic et al, 2010;Lavigne et al, 2018;Mihanovic et al, 2020;Menna et al, 2022;Placenti et al, 2022) as well as in the LB (Ozer et al, 2017). These studies proposed that the BiOS mechanism is a feedback mechanism between changes in the thermohaline structure of SA waters and the IB.…”

“…Light blue dotted line and formula show the calculated chlorophyll a trend. Periods of anticyclonic circulation (tinted in red in the salinity panel) and cyclonic periods (tinted in blue)(Menna et al, 2022;Placenti et al, 2022).…”