Intense Subsurface Upwelling Associated with Major Western Boundary Currents

<p>Western boundary currents (WBC), fast flowing currents on the western side of ocean basins, transport a huge amount of warm water poleward, affect the atmospheric conditions along their paths, take up a large amount of carbon dioxide, and regulate the global climate (Minobe et al. 2008; Takahashi et al. 2009; Wu et al. 2012). In contrast to their widely examined horizontal motions, much less attention has been paid to the vertical motions associated with the WBC systems. Here, we examined the spatial and temporal characteristics of vertical motions associated with the major WBC systems by analyzing vertical velocity estimates from five ocean synthesis products and one eddy-permitting ocean simulation over an overlapping period from Jan 1992 to Dec 2009. Robust and intense subsurface upwelling occurs in the five major subtropical WBC systems. These upwelling systems together with the vast downwelling inside subtropical ocean basins form basin-scale zonal overturning circulations and play a crucial role in the vertical transport of ocean properties and tracers inside the global ocean. Also, the vertical motions in the Kuroshio Current and the Eastern Australian Current regions display robust interannual and decadal oscillations, which are well correlated with El Ni&#241;o&#8211;Southern Oscillation and Pacific Decadal Oscillation, respectively. This study unveils an overlooked role of the WBCs in the subsurface oceanic vertical transport and is expected to be a starting point for more in-depth investigations on their dynamics and roles in the climate system.</p>

[1]  M. Spall,et al.  Sinking of dense North Atlantic waters in a global ocean model : location and controls , 2018 .

[2]  C. Wunsch,et al.  Global ocean vertical velocity from a dynamically consistent ocean state estimate , 2017 .

[3]  A. Meijers,et al.  High-latitude ocean ventilation and its role in Earth's climate transitions , 2017, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[4]  A. Gordon,et al.  Pacific western boundary currents and their roles in climate , 2015, Nature.

[5]  C. Wunsch,et al.  Vertical Redistribution of Oceanic Heat Content , 2015 .

[6]  Tong Lee,et al.  The Ocean Reanalyses Intercomparison Project (ORA-IP) , 2015 .

[7]  M. Ohman,et al.  Contributions of mesozooplankton to vertical carbon export in a coastal upwelling system , 2013 .

[8]  C. Wolfe,et al.  Adiabatic Eastern Boundary Currents , 2013 .

[9]  A. Rosati,et al.  An assessment of oceanic variability for 1960–2010 from the GFDL ensemble coupled data assimilation , 2013, Climate Dynamics.

[10]  A. Timmermann,et al.  Enhanced warming over the global subtropical western boundary currents , 2012 .

[11]  K. Speer,et al.  Closure of the meridional overturning circulation through Southern Ocean upwelling , 2012 .

[12]  C. Wolfe,et al.  Eastern-Boundary Contribution to the Residual and Meridional Overturning Circulations , 2010 .

[13]  Taka Ito,et al.  Anthropogenic carbon dioxide transport in the Southern Ocean driven by Ekman flow , 2010, Nature.

[14]  C. S. Wong,et al.  Climatological mean and decadal change in surface ocean pCO2, and net seaair CO2 flux over the global oceans , 2009 .

[15]  Saleem H Ali,et al.  Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2 , 2008, Science.

[16]  M. Spall.  Buoyancy-Forced Downwelling in Boundary Currents , 2008 .

[17]  Shoshiro Minobe,et al.  Influence of the Gulf Stream on the troposphere , 2008, Nature.

[18]  R. Ferrari,et al.  The vertical structure of ocean heat transport , 2005 .

[19]  L. Talley.  Shallow, Intermediate, and Deep Overturning Components of the Global Heat Budget , 2003 .

[20]  J. Gregory.  Vertical heat transports in the ocean and their effect on time-dependent climate change , 2000 .

[21]  Frank O. Bryan,et al.  Parameter sensitivity of primitive equation ocean general circulation models , 1987 .

[22]  K. Wyrtki.  An Estimate of Equatorial Upwelling in the Pacific , 1981 .

[23]  J. Ryther.  Photosynthesis and fish production in the sea. , 1969, Science.

[24]  R. Reid,et al.  The Gulf Stream: a Physical and Dynamical Description , 1960 .

[25]  Yan Xue,et al.  EVALUATION OF THE GLOBAL OCEAN DATA ASSIMILATION SYSTEM AT NCEP: THE PACIFIC OCEAN , 2003 .

[26]  Deborah K. Steinberg,et al.  Upper Ocean Carbon Export and the Biological Pump , 2001 .

[27]  S. L. Bennett.  The Relationship between Vertical, Diapycnal, and Isopycnal Velocity and Mixing in the Ocean General Circulation , 1986 .

[28]  A. Huyer.  Coastal Upwelling in the California Current System , 1983 .

[29]  W. S. V. Arx.  Introduction to Physical Oceanography , 1962 .