Seminario in modalità telematica del dott. Vincenzo Artale

Zoom Meeting ID: 817 0784 1598 
Passcode: 666353

Abstract

The  ocean  is  an  integral  component  of the Earth's  climate  system.  Heat  and CO2  are  absorbed  at  the  ocean's surface and transported throughout the ocean depths by overturning circulation. Exchange across the ocean's turbulent  surface  boundary  layer  can  happen  rapidly,  in  hours  or  days,  and  significant  exchange  of  water between the boundary layer and the stratified main thermocline occurs over timescales of years to decades.

On the  other  hand,  deep  water  takes  many  decades  to  millennia  to  return  to  the  surface,  acting  as  long-‐term storage for heat and CO2 and thereby lessening the near-term impacts of climate change. The understanding of mechanisms  and  rates  that  control  the  bottom  flows  is  crucial  for  quantifying  re-transfer  towards  the  upper layers  of  the  energy,  stored  at  the  seafloor  (de  Lavergne  et  al.,  2016). 

From  a  theoretical  point  of  view,  the relevance  of  the  bottom  dynamics  was  re-evaluated  by  the  recent  paper  by  Ferrari  et  al.  (2016)  in  which  the complex  interplay  between  downward  and  upward  energypropagation  updated  the  original  vision  of  Munk (1966).

These  processes  are  significantly  affecting  the  ocean  system  as  a  whole  and  could  contribute  to acceleratethe rising climate trends such as thermohaline circulation, sea‐level rise, and ocean acidification.  The Mediterranean  basins  can  be  taken  as  a  good  example  to  explore  this  physical  mechanism.  The  amount  of mechanical energy required for the mixing to occur is believed to be small due to the lack of strong tides and low winds  in  the  Mediterranean.  Therefore,  little  attention  has  been  given  to  direct  mixing  measurements  in  the Mediterranean Sea until Ferron et al. (2017) estimated the role of the diapycnal mixing via a unique set of full-depth microstructure profiles in the western Mediterranean, sampled mainly in 2013 and 2014.

Recently in the Ionian Sea was observed a significant positive shift of the ocean heat content between 4000 and 2000m during the period 1977-2011, due to the variability of the stratification between 2000 and 4000m depth created by the quasi‐‐periodical ventilation of the deep layers of two different source of deep water originated from  the  Adriatic  and  the  Aegean  Sea,  respectively  (Artale  et  al.,  2018).  These  results  have  heat  storage exceptionally  well  spread  throughout  the  abyssal  layers  twice  higher  than  that  assessed  globally  in  the  same period  due  to  the  greenhouse  effect. Besides,  this  heat will be  progressively  released  from  deep  layers  to  the upper layers acting as positive feedback inducing variability of the circulation and influencing the ability of the ocean  to  retain  and  transform  CO2.  At  a  more  local  scale,  in  Vladoiu  et  al.  (2019)  the  small-scale  turbulence measurement  along  two  main  deep  passages  of  the  Sicily  Channel  has  confirmed  that  the  Sicily  Channel  is  ahotspot for turbulence that strongly influences the hydrological exchange among the east and west part of the Mediterranean Sea.

From the above, we intend to discuss the necessity to set up a new formulation of the ocean bottom mixing, able to fill the knowledge gap for the case of the Mediterranean, following Ferrari's approach and considering new data that are exploring the deep dynamics (buoys, deep observatories (EMSO), CTDs cast, Deep ARGO, etc.)