FN Archimer Export Format
PT J
TI Ekman transport as the driver of extreme interannual formation rates of Eighteen Degree Water
BT 
AF Li, Ke
   Maze, Guillaume
   Mercier, Herle
AS 1:1;2:2;3:3;
FF 1:PDG-ODE-LOPS-OH;2:PDG-ODE-LOPS-OH;3:;
C1 IFREMER University of Brest Laboratoire d’Océanographie Physique et Spatiale (LOPS) Brest, France
   IFREMER University of Brest CNRS IRD Laboratoire d’Océanographie Physique et Spatiale (LOPS) IFREMER Brest, France
   CNRS Laboratoire de Physique des Océans UMR 6523 CNRS/Ifremer/IRD/UBO Ifremer Centre de Brest CS 10 070, 29 280 Plouzané ,France
C2 IFREMER, FRANCE
   IFREMER, FRANCE
   CNRS, FRANCE
SI BREST
SE PDG-ODE-LOPS-OH
UM LOPS
IN WOS Ifremer UMR
   WOS Cotutelle UMR
   copubli-france
IF 3.6
TC 1
UR https://archimer.ifremer.fr/doc/00743/85551/90674.pdf
LA English
DT Article
DE ;North Atlantic Subtropical mode water;Ekman current;Argo floats;subtropical gyre;ocean stratification
AB In the North Atlantic subtropical gyre, the Eighteen Degree Water (EDW) is a voluminous heat reservoir, submerged under a seasonal pycnocline that can be progressively removed through the winter, allowing EDW ventilation in the early spring. We target the EDW formation extremes, namely 2004-2005, 2009-2010, and 2012-2013 for the strong years, and 2007-2008, 2008-2009, 2011-2012, and 2013-2014 for the weak years. We employ gridded hydrographic datasets mainly measured by Argo floats over the last 20 years, and provide a synthetic study on the extreme events of strong and weak EDW formation of this time period. We found that the Ekman transport is the indicator and driving mechanism explaining these extremes. Strong (Weak) EDW formation years correspond with atmospheric patterns resembling NAO- (NAO+), attributed to a strong (weak) winter air-sea surface heat loss, and a strong (weak) winter heat loss due to Ekman transport. Further, we show that such extreme Ekman advection patterns can be linked to mid-latitude storms, of which both intensity and duration have an impact on the extreme of EDW ventilation in the western subtropical North Atlantic. To yield a strong EDW formation, it requires a large winter heat deficit due to Ekman divergence, which can be sufficiently represented by numbers of strong winter storms, most notably, remnants of hurricanes and US east coast snowstorms. Meanwhile, to yield a weak EDW formation, apart from weak atmospheric forcings, a remnant positive heat content anomaly carried through from previous years would serve as an unfavorable preconditioning, hindering the EDW formation. Plain Language Summary The EDW is the most voluminous water body in the North Atlantic subtropical region. It is critical in the biology cycle and the ocean dynamics. For most of the year, EDW is buried underneath the sea surface. In winter, when sea surface loses enough heat, sinking cold water reaches the EDW bulk, forming fresh EDW. In this research, we target the EDW formation extremes, namely 2004-2005, 2009-2010, and 2012-2013 for the strong years, and 2007-2008, 2008-2009, 2011-2012, and 2013-2014 for the weak years. Using modern observational datasets, we found that the remnant hurricanes and US east coast snowstorms have an impact on the extreme interannual formation rate of EDW. To have a strong EDW formation, it is sufficient to have several strong winter storms passing by the EDW formation region, where the ocean loses more heat to the atmosphere than average over the winter. These winter-long sustained forcings have a cumulative effect on the ocean, and promote strong EDW formation. Conversely, when fewer winter storms pass, the ocean loses less heat to the atmosphere, promoting weak EDW formation. Meanwhile, the extra heat carried through from the previous years can also result in a weak EDW formation. 
PY 2022
PD JAN
SO Journal Of Geophysical Research-oceans
SN 2169-9275
PU American Geophysical Union (AGU)
VL 127
IS 1
UT 000751885800017
DI 10.1029/2021JC017696
ID 85551
ER

EF