Similarities and Contrasts in Time-Mean Striated Surface Tracers in Pacific Eastern Boundary Upwelling Systems: The Role of Ocean Currents in Their Generation

Ali Belmadani,Pierre-Amaël Auger,Katherine Gomez,Sophie Cravatte,Nikolai Maximenko

doi:10.3390/fluids6120455

Abstract

Eastern boundary upwelling systems feature strong zonal gradients of physical and biological properties between cool, productive coastal oceans and warm, oligotrophic subtropical gyres. Zonal currents and jets (striations) are therefore likely to contribute to the transport of water properties between coastal and open oceanic regions. For the first time, multi-sensor satellite data are used to characterize the time-mean signatures of striations in sea surface temperature (SST), salinity (SSS), and chlorophyll-a (Chl-a) in subtropical eastern North/South Pacific (ENP/ESP) upwelling systems. In the ENP, tracers exhibit striated patterns extending up to ~2500 km offshore. Striated signals in SST and SSS are highly correlated with quasi-zonal jets, suggesting that these jets contribute to SST/SSS mesoscale patterns via zonal advection. Striated Chl-a anomalies are collocated with sea surface height (SSH) bands, a possible result of mesoscale eddy trains trapping nutrients and forming striated signals. In the ESP, the signature of striations is only found in SST and coincides with the SSH bands, consistently with quasi-zonal jets located outside major zonal tracer gradients. An interplay between large-scale SST/SSS advection by the quasi-zonal jets, mesoscale SST/SSS advection by the large-scale meridional flow, and eddy advection may explain the persistent ENP hydrographic signature of striations. These results underline the importance of quasi-zonal jets for surface tracer structuring at the mesoscale.

Highlights

Eastern boundary upwelling systems (EBUS), such as those found along the Californian and Chilean coasts facing the eastern North and South Pacific subtropical gyres (Figure 1a), are unique regions known for their cool surface waters, extreme biological productivity, and key influence on climate [1,2]
Similar meridionally-alternating bands were found in Chl-a data with magnitudes reaching ~10% of full Chl-a, but they did not extend beyond ~500 km offshore (Figure 2e, see Figure A1c)
In the eastern North Pacific (ENP), while the expression of striations in sea surface temperature (SST) and sea surface salinity (SSS) coincide with that in zonal current, suggesting a dominant role of advection, the expression of striations in Chl-a is collocated with that in sea surface height (SSH), possibly involving water mass trapping by mesoscale eddy trains

Summary

Introduction

Eastern boundary upwelling systems (EBUS), such as those found along the Californian and Chilean coasts facing the eastern North and South Pacific subtropical gyres (Figure 1a), are unique regions known for their cool surface waters, extreme biological productivity, and key influence on climate [1,2]. Egions off the Californian and Chilean EBUS in the subtropical North and South Pacific, respectively. .AAmmoonnggsusucchhpprorocceesssseess,,mmeessoossccaaleleeeddddieiessare kanroewknnotowancttiovealcytivpealrytipciapratitceipinattehienctrhoessc-rsohsesl-fshtrealfnstrpaonrstpoofrtocoefaonceparnopperrotpieesrt[i3e,s4][.3,O4]t.her stOruthcetur rsetsruthctautrpesottehnattiaplolytecnotinatlrlyibucotenttroibtuhteesetoexthcehsaengexecshbauntghesavbeutrehcaeviveerdecleesivseadttleenstsion araettesntrtiaotnioanrse, swtrhiaictihonasr,ewmhuiclhtipalreeqmuausltii-pzloenqaul ajestis-zionnathl ejeltos nign-tehremloanvge-rteargme caivrceuralgaetion thcairtcuhlaavtieonrecthenattlyhabveeenredceisnctolyvebreednthdrioscuogvheoreudt tthherowugohrlodu’ts othceeawnsoraldn’ds poacretaincus larnldy in supbatrrtiocpuilcaarlyEiBnUsSu,butrsoinpgicsaal tEeBllUiteS, iunssinitgu,satnedllimte,oidnelsidtua,taan[5d–1m0o] d(Feligduartea 1[b5–).1T0]h(eFsiegubraends of alternating eastward/westward mean geostrophic currents have meridional scales of 3–5◦, extend from the surface to the intermediate or deep ocean, and spread out zonally for 1000 s of km [11]. Stationary or propagating striations may be extracted from the same data using either long or short averaging periods, while any stationary striations should be filtered out when considering velocity or sea level anomalies instead of the associated full fields [5,17]

Methods

Results

Conclusion