Coastal Sulfur Plumes off Peru During El Niño, La Niña, and Neutral Phases

Abstract

For the first time, the impact of the El Niño‐Southern Oscillation (ENSO) on the surface sulfur plumes off the Peruvian upwelling system has been studied. The investigations demonstrated a strong correlation between the ENSO and the sulfur plumes in the coastal areas of Callao and Pisco. During the El Niño phases, the sulfur plumes disappeared almost completely because of equatorial remotely forced oxygenation episodes. The La Niña events were associated with strong oxygen deficiency over the Peruvian shelf, supporting the formation of hydrogen sulfide and, consequently, the occurrence of sulfur plumes. This impact was smaller at Callao, because the La Niña phases in this coastal area were interrupted by weak oxygenation events. During the neutral phases, oxygen‐poor waters were also present in the Peruvian shelf areas, promoting the large size of sulfur plumes. However, they were not forced by the remotely driven processes resulting from ENSO phenomena.

Sulfur cycling in oceanic oxygen minimum zones

“…However, the evidence for cross‐shelf advected elemental sulfur, and sulfur‐accumulating SUP05 bacteria described above, raises the possibility that sulfur‐driven denitrification could be another pathway contributing to offshore ETSP nitrogen loss. Furthermore, the frequent transport of coastal sulfur plumes into the open ocean (Weeks et al 2002, 2004; Ohde et al 2007; Ohde 2018; Ohde and Dadou 2018) (e.g., Fig. 2A), implies that sulfur‐driven chemolithoautotrophy might have a larger impact on offshore ETSP nitrogen loss and carbon fixation than previously believed.…”

“…Despite the absence of dissolved sulfide, recent evidence indicates that the offshore OMZ receives a large inflow of cross‐shelf transported elemental sulfur, which forms at the chemocline in a sulfidic event (Callbeck et al 2018). Cross‐shelf transported elemental sulfur can also be observed in remote sensing images in both the ETSP and ETSA regions (Weeks et al 2002, 2004; Ohde et al 2007; Ohde 2018; Ohde and Dadou 2018) (e.g., Fig. 2A,B).…”

“…Abbreviations indicated stand for: eastern tropical South Pacific (ETSP), eastern tropical North Pacific (ETNP), eastern tropical South Atlantic (ETSA), Arabian Sea (AS), and the Bay of Bengal (BOB). ( C , D ) Seasonality of chlorophyll and sulfur plume development in the ETSP and ETSA regions reproduced from Ohde 2018 and Echevin et al 2008, and from Ohde and Dadou 2018 and Lamont et al 2018, respectively. Panel c also includes a marker gene associated to the SUP05 clade; the cbbM gene is involved in carbon fixation via the Calvin–Benson–Bassham cycle, data is reproduced from Léniz et al 2017.…”

“…Apart from seasonal and local patterns, sulfidic events also exhibit strong intraseasonal and interannual variability driven by remote wind-forcing (Ohde 2018). Wind-driven equatorial Kelvin waves produce nearshore coastal-trapped waves that propagate along the length of the ETSP coastline (Belmadani et al 2012).…”

The control of hydrogen sulfide on benthic iron and cadmium fluxes in the oxygen minimum zone off Peru

“…Because of their contrasting tendency to form sulfide minerals and different supply pathways to the sediment, Fe and Cd can serve as prototypes to provide information about how sedimentary fluxes of different TMs may respond to declining oxygen concentrations. Under more reducing conditions, the mobility of TMs can either be enhanced or diminished, e.g., through precipitation of sulfide minerals that are buried in the sediments (e.g., Westerlund et al, 1986;Rigaud et al, 2013;Olson et al, 2017). Increased burial or release of TMs at the seafloor can have an impact on the amplitude of primary productivity, especially at the eastern ocean boundaries where the near-bottom water column is connected to the surface ocean via upwelling.…”