Quantifying lateral export from the benthic boundary layer to the offshore eastern tropical South Pacific

Deoxygenation of shelf waters is known to enhance the sedimentary source of nutrients, including PO4 and Fe, into the water column. Yet substantial uncertainty remains with respect to what fraction of these nutrients are transported into the euphotic layer and ultimately advected offshore and thus how an increased benthic supply of nutrients affects offshore ecosystem productivity. In October 2015 a conservative tracer (CF3SF5) was released within the bottom boundary layer at 3 sites along the Peruvian coastline within the Peruvian Oxygen Minimum Zone (OMZ). During March/April 2017 the dispersion of this tracer along the shelf and laterally into the ETSP was tracked alongside a comprehensive suite of nutrient measurements including macronutrients (NO3, NO2, PO4, Si), dissolved organic nitrogen/phosphorus (DON/DOP) and dissolved trace metals (including Fe and Co). The tracer distribution demonstrated transport northwards along the shelf, in addition to lateral advection offshore, which was most pronounced along a transect at 17° S. Here we compare and contrast the distribution of our inert tracer with a broad range of nutrients along the 17° S transect in order to understand how internal cycling affects the lateral advection of bio-essential nutrients from anoxic shelf benthic boundary waters to offshore ecosystems. Constraining the relative strength of laterally advected Fe and bioavailable nitrogen/phosphorus sources will be critical to understanding how primary productivity and microbial community structure within the Peruvian Oxygen Minimum Zone will respond to intensified deoxygenation over the Peruvian shelf