In the Arctic Ocean, Pacific source water can be distinguished from Atlantic source water by nitrate‐phosphate concentration relationships, with Pacific water having higher phosphate concentrations relative to those of nitrate. Furthermore, Pacific water, originally from the inflow through Bering Strait, is clearly recognizable in the outflows of low‐salinity waters from the Arctic Ocean to the northern North Atlantic Ocean through the Canadian Arctic Archipelago and through Fram Strait. In the Canadian Arctic Archipelago, we observe that almost all of the waters flowing through Lancaster and Jones sounds, most of the water in the top 100 m in Smith Sound (containing the flow through Nares Strait), and possibly all waters in Hudson Bay contain no water of Atlantic origin. Significant amounts of Pacific water are also observed along the western coast of Baffin Bay, along the coast of Labrador, and above the 200‐m isobath of the Grand Banks. There is a clear signal of Pacific water flowing south through Fram Strait and along the east coast of Greenland extending at least as far south as Denmark Strait. Pacific water signature can be seen near the east coast of Greenland at 66°N, but not in data at 60°N. Temporal variability in the concentrations of Pacific water has been observed at several locations where multiple‐year observations are available.

Abstract. Analysis of 20-year time-series of the vertically averaged salinity and nutrient data in the Southern Adriatic shows that the two parameters are subject to strong decadal variability. In addition, it is documented that nutrient and salinity variations are out of phase. Nutrients in the Ionian and in the Adriatic vary in parallel except that generally the nutrient content in the Adriatic is lower than in the Ionian, a fact that has been attributed to primary producer consumption following the winter convective mixing. As shown earlier, North Ionian Gyre (NIG) changes its circulation sense on a decadal scale due to the Bimodal Oscillating System, i.e. the feedback mechanism between the Adriatic and Ionian. Cyclonic circulation causes a downwelling of the nitracline along the borders of the NIG and a decrease in the nutrient content of the water flowing into the Adriatic across the Otranto Strait, and vice versa. In addition, the highly oligotrophic central area of the Ionian shows annual blooms only during cyclonic NIG circulation. Inversion of the sense of the NIG results in the advection of Modified Atlantic Water or of the Levantine/Eastern Mediterranean waters in the Adriatic. Here, we show that the presence of allochtonous organisms from Atlantic/Western Mediterranean and Eastern Mediterranean/temperate zone in the Adriatic are concurrent with the anticyclonic and cyclonic circulations of the NIG, respectively. On the basis of the results presented, a revision of the theory of Adriatic ingressions formulated in the early 1950s is proposed.

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Abstract. An updated climatology, based on a comprehensive data set (1911–2009) of temperature, salinity and dissolved oxygen, has been produced for the whole Adriatic Sea with the variational inverse method using the DIVA (Data-Interpolating Variational Analysis) software. Climatological maps were produced at 26 levels and validated with ordinary cross-validation and with a real vs. synthetic temperature–salinity diagram intercomparison. The concept of climatology–observation misfit (COM) has been introduced as an estimate of the physical variability associated with the climatological structures. In order to verify the temporal stability of the climatology, long-term variability has been investigated in the Middle Adriatic and the South Adriatic pits, regarded as the most suitable records of possible long-term changes. Compared with previous climatologies, this study allows a clear identification of the seasonal dynamic of the southern Adriatic, where a clear oxygen minimum is typically observed in the centre of the South Adriatic Gyre. New and better resolved features emerged from this analysis: (1) below 100 m all properties profoundly differ between the central and the southern Adriatic and seem characterized by different biogeochemical dynamics; (2) the South Adriatic Pit clearly shows the remote effects of the Eastern Mediterranean Transient, while no effect is observed in the Middle Adriatic Pit; (3) the deepest part of the southern Adriatic seems now to be significantly saltier (+0.18 psu since the period 1910–1914, with an increase of +0.018 decade−1 since the late 1940s) and warmer (+0.54 °C since 1910–1914) even though a long-term temperature trend could not be statistically demonstrated; (4) the Middle Adriatic Pit shows a long-term increase in apparent oxygen utilization (+0.77 mL L−1 since 1910–1914, with a constant increase of +0.2 mL L−1 decade−1 after the 1970s).

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A first synoptic and trans-domain overview of plankton dynamics was conducted across the aquatic sites belonging to the Italian Long-Term Ecological Research Network (LTER-Italy). Based on published studies, checked and complemented with unpublished information, we investigated phytoplankton and zooplankton annual dynamics and long-term changes across domains: from the large subalpine lakes to mountain lakes and artificial lakes, from lagoons to marine coastal ecosystems. This study permitted identifying common and unique environmental drivers and ecological functional processes controlling seasonal and long-term temporal course. The most relevant patterns of plankton seasonal succession were revealed, showing that the driving factors were nutrient availability, stratification regime, and freshwater inflow. Phytoplankton and mesozooplankton displayed a wide interannual variability at most sites. Unidirectional or linear long-term trends were rarely detected but all sites were impacted across the years by at least one, but in many case several major stressor(s): nutrient inputs, meteo-climatic variability at the local and regional scale, and direct human activities at specific sites. Different climatic and anthropic forcings frequently co-occurred, whereby the responses of plankton communities were the result of this environmental complexity. Overall, the LTER investigations are providing an unparalleled framework of knowledge to evaluate changes in the aquatic pelagic systems and management options.

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