Near-coastal circulation in the Northern Humboldt Current System from shipboard ADCP data

Abstract

[1] The near-coastal circulation of the Northern Humboldt Current System is described analyzing $8700 velocity profiles acquired by a shipboard acoustic Doppler current profiler (SADCP) during 21 surveys realized between 2008 and 2012 along the Peruvian coast. This data set permits observation of (i) part of the Peru Coastal Current and the Peru Oceanic Current that flow equatorward in near-surface layers close to the coast and farther than $150 km from the coast, respectively; (ii) the Peru-Chile Undercurrent (PCUC) flowing poleward in subsurface layers along the outer continental shelf and inner slope; (iii) the near-surfacing Equatorial Undercurrent renamed as Ecuador-Peru Coastal Current that feeds the PCUC; and (iv) a deep equatorward current, referred to as the Chile-Peru Deep Coastal Current, flowing below the PCUC. A focus in the PCUC core layer shows that this current exhibits typical velocities of 5-10 cm s À1 . The PCUC deepens with an increasing thickness poleward, consistent with the alongshore conservation of potential vorticity. The PCUC mass transport increases from $1.8 Sv at 5 S to a maximum value of $5.2 Sv at 15 S, partly explained by the Sverdrup balance. The PCUC experiences relatively weak seasonal variability and the confluence of eddy-like structures and coastal currents strongly complicates the circulation. The PCUC intensity is also affected by the southward propagation of coastally trapped waves, as revealed by a strong PCUC intensification in March 2010 coincident with the passage of a downwelling coastal wave associated with a weak El Niño event.

Strong and Dynamic Benthic-Pelagic Coupling and Feedbacks in a Coastal Upwelling System (Peruvian Shelf)

“…This is mainly caused by variability in the intensity of upwellingfavorable winds and the delivery of nutrient-rich Equatorial Subsurface Water (ESSW) that fuels phytoplankton production there (Pennington et al, 2006;Chavez et al, 2008;Chaigneau et al, 2013;Graco et al, 2016). Primary productivity ranges from 1.8 to 5.2 g C m −2 d −1 (Pennington et al, 2006;Quiñones et al, 2010) and leads to a permanent oxygen minimum zone (OMZ) where dissolved oxygen concentrations are essentially zero (Thamdrup et al, 2012;Ulloa et al, 2012).…”

Modulation of the vertical particles transfer efficiency in the Oxygen Minimum Zone off Peru

“…These typical methodological biases in sediment trap studies are known to potentially affect the collection of particles and its efficiency. Here, the mean alongshore current (poleward) reaches ~12 cm.s -1 (slower than 15 cm.s -1 ) over the duration of the experiment in vicinity of the sediment traps, according to in situ data (AMOP cruise), climatology (Chaigneau et al, 2013) and estimates from climatological regional model simulations (Montes et al, 2010;Dewitte et al, 2012). Therefore, the collection of particles is 25 considered to be marginally affected by currents in this transfer layer (Baker et al, 1988), confirmed by a small inclination of the mooring line (<5°).…”

Impact of mesoscale eddies on water mass and oxygen distribution in the eastern tropical South Pacific

“…It is suggested that anticyclones are generated due to instabilities of the Peru Chile Undercurrent (PCUC), whereas cyclonic eddies are formed from instabilities of the equatorward surface currents (Chaigneau et al, 2013). In this context the strength of the PCUC is essential (Thomsen et al, 25 2016).…”

“…In this context the strength of the PCUC is essential (Thomsen et al, 25 2016). Observations as well as models show a weak seasonal variability of the PCUC off Peru which is stronger in austral summer and fall (Thomsen et al, 2016;Chaigneau et al, 2013;Penven et al, 2005) Ocean Sci. Discuss., https://doi.org/10.5194/os-2018-5 Manuscript under review for journal Ocean Sci.…”

“…Kessler 2006;Czeschel et al, 2015) as well as poleward and equatorward current bands near the South American continent (e.g. Chaigneau et al, 2013). The shipboard zonal velocity component along about 86°W composed of three ADCP surveys showed larger regions with westward then eastward flow 20 between 13°S and 22°S (Brandt et al, 2015), however with influence by eddy features in ADCP measurements in November 2012 (Czeschel et al, 2015).…”