Long-term Trends in Thermohaline Properties of the Northern Adriatic

1. Long-term trends and variability inthermohalineproperties of the northern Adriatic Ivica Vilibić1, Petra Zemunik1, Natalija Dunić1, Oussama Marzouk2, Jadranka Šepić1, Hrvoje Mihanović1, Clea Denamiel1, Robert Precali3, Tamara Djakovac3 1 Institute of Oceanography and Fisheries, Split, Croatia 2student at SeaTech, University of Toulon, Toulon, France 3 CMR, Rudjer Bošković Institute, Rovinj, Croatia • Outline: • Motivation and the data • Seasonal cycle, variability and trends • Correlation to environmental parameters • Take-home messages

2. Motivation rivers Deep convection site (AdDW) EAC WAC SAG EAC • Northern Adriatic area is a key area for the Adriatic thermohaline circulation: • Large river inflow • Dense-water formation site Vilibić et al., DSR, 2004

3. The data Temperature and salinity data collected between 1979 and 2016 at the Po-Rovinj transect The best sampled is the Nb line, 6 stations (from Croatia to Italy): RV001, SJ107, SJ105, SJ103 SJ101, SJ108 Between 22 and 37 samples per month at Nb line RV001 SJ108

4. Seasonal cycle • The most of the temperature variance comes from seasonal changes • Low salinity seasonality in deep layers (> 5%), higher at surface • Seasonality in density comes from temperature

5. Interannual variations A A C C C BiOS phases • A substantial interannual variability

6. Trends • Strong warming, particularly in front of the Po River • Salinity trends are mostly insignificant, aside changes off the Po River • Density trends are dominantly temperature-driven

7. Trends • The largest temperature trends in spring-summer • Seasonal changes in density trends are thermally- and haline-driven in the eastern and haline-driven in the western section of the transect

8. Trends • Temperature trends are not sensitive to the series length, in contrast to salinity trends

9. Correlations with drivers NHF – monthly ECMWF net heat flux averaged over the northern Adriatic • February temperature correlated with December/January NHF, importance of preconditioning

10. Correlations with drivers PO – monthly Po River discharge • The Po River preconditioning is more important for salinity changes off Po (July-August and November-February)

11. Correlations with drivers TP – monthly ECMWF total precipitation averaged over the northern Adriatic • Precipitation is not the (direct) driver of the thermohaline changes in the northern Adriatic

12. Correlations with drivers BiOS – SSH difference between centre and perimeter of the Northern Ionian Gyre • The Adriatic-Ionian Bimodal Oscillating System (BiOS) is marginally influencing the northern Adriatic salinity off Croatian coast at periods up to 1 year

13. Correlations with drivers yearly scale • Among all regional indices, MOI (Mediterranean Oscillation Index) has the largest correlation to temperature and salinity, then EA and SCA, while NAO and EAWR are not correlated, but ... • The strongest connection is found between salinity and the BiOS at periods between 2 and 4 years

14. Take-home messages • Strong and persistent warming in the northernmost part of the Mediterranean in the last 40 years • Warming is the largest in spring-summer, following the air temperature trends • Salinity trends are a low; a change in the Po River plume dynamics occurred • Heat fluxes are shaping thermohaline properties at scales up to a few months, • River-driven freshening is acting at scales of months, up to a year, • Remote processes, i.e. the BiOS, is acting at processes up to a few years, • Consequences to the ecosystem and fisheries?