Evaluation of redox-sensitive metals in marine surface sediments influenced by the oxygen minimum zone of the Humboldt Current System, Northern Chile

Abstract. Diel vertical migration (DVM) can enhance the vertical flux of carbon (C), and so contributes to the functioning of the biological pump in the ocean. The magnitude and efficiency of this active transport of C may depend on the size and taxonomic structure of the migrant zooplankton. However, the impact that a variable community structure can have on zooplankton-mediated downward C flux has not been properly addressed. This taxonomic effect may become critically important in highly productive eastern boundary upwelling systems (EBUSs), where high levels of zooplankton biomass are found in the coastal zone and are composed by a diverse community with variable DVM behavior. In these systems, presence of a subsurface oxygen minimum zone (OMZ) can impose an additional constraint to vertical migration and so influence the downward C export. Here, we address these issues based on a vertically stratified zooplankton sampling at three stations off northern Chile (20–30∘ S) during November–December 2015. Automated analysis of zooplankton composition and taxa-structured biomass allowed us to estimate daily migrant biomass by taxa and their amplitude of migration. We found that a higher biomass aggregates above the oxycline, associated with more oxygenated surface waters and this was more evident upon a more intense OMZ. Some taxonomic groups, however, were found closely associated with the OMZ. Most taxa were able to perform DVM in the upwelling zone withstanding severe hypoxia. Also, strong migrants, such as eucalanid copepods and euphausiids, can exhibit a large migration amplitude (∼500 m), remaining either temporarily or permanently within the core of the OMZ and thus contributing to the release of C below the thermocline. Our estimates of DVM-mediated C flux suggested that a mean migrant biomass of ca. 958 mg C m−2 d−1 may contribute with about 71.3 mg C m−2 d−1 to the OMZ system through respiration, mortality and C excretion at depth, accounting for ca. 4 % of the net primary production, and so implies the existence of an efficient mechanism to incorporate freshly produced C into the OMZ. This downward C flux mediated by zooplankton is however spatially variable and mostly dependent on the taxonomic structure due to variable migration amplitude and DVM behavior.

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Chlorophyll-a distribution and mesoscale physical processes in upwelling and adjacent oceanic zones off northern Chile (summer–autumn 1994)

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315401003642 ◽

2001 ◽

Vol 81 (2) ◽

pp. 193-206 ◽

Cited By ~ 15

Author(s):

Carmen E. Morales ◽

José L. Blanco ◽

Mauricio Braun ◽

Nelson Silva

Keyword(s):

Coastal Upwelling ◽

Current System ◽

Austral Summer ◽

Nutrient Concentrations ◽

Northern Chile ◽

Humboldt Current ◽

Oxygen Conditions ◽

Salinity Water ◽

Humboldt Current System ◽

Seasonal Signal

Chlorophyll-a (chl-a) distribution and associated physical (temperature, salinity) and chemical (dissolved oxygen) conditions off northern Chile (Humboldt Current System), during the austral summer (February–March) and autumn (May) of 1994, were studied in the region bounded by ∼18–24°S and 70–72°W (out to ∼200 km from the coast; 0–100 m depth); within this region, nutrients were measured in an area of persistent coastal upwelling (∼19–22°S, out to 80 km from the coast). Temperature and salinity distributions, as well as nutrient concentrations, indicated the occurrence of active upwelling during both cruises. Also, and together with maps of geopotential anomaly (0/200 dbar) and depth of the thermocline (15°C isotherm), their distribution suggested the presence of a mainly equatorward flow, anticyclonic eddy-like structures, and intrusions of warm (>19°C), high salinity (>35·0 psu), subtropical water towards the coast. A tongue of cooler and lower salinity water, and of lower flow fields, extended from the coast towards the offshore zone during both sampling periods, in association with higher chl-a concentrations (>1 mg m−3, >20 mg m−2 between 0 and 25 m depth) and predominance of net-phytoplankton (>20 μm). The comparison of these results with those for the winter and spring of 1993 in the same area suggest a relatively weak seasonal signal in chl-a concentration during the 1993–1994 period, with higher water column concentrations during the summer and spring periods in the selected upwelling area, though surface chl-a concentrations for the whole of the area did not vary significantly.

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Interplay between sedimentary organic matter and dissolved oxygen availability in a coastal zone of the Humboldt Current System; Mejillones Bay, northern Chile

Marine Geology ◽

10.1016/j.margeo.2009.07.004 ◽

2009 ◽

Vol 265 (3-4) ◽

pp. 157-166 ◽

Cited By ~ 5

Author(s):

J. Valdés ◽

A. Sifeddine ◽

Luc Ortlieb ◽

Catherine Pierre

Keyword(s):

Organic Matter ◽

Dissolved Oxygen ◽

Coastal Zone ◽

Current System ◽

Oxygen Availability ◽

Sedimentary Organic Matter ◽

Northern Chile ◽

Humboldt Current ◽

Humboldt Current System

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Short-term fate of phytodetritus in sediments across the Arabian Sea Oxygen Minimum Zone

Biogeosciences ◽

10.5194/bg-5-43-2008 ◽

2008 ◽

Vol 5 (1) ◽

pp. 43-53 ◽

Cited By ~ 36

Author(s):

J. H. Andersson ◽

C. Woulds ◽

M. Schwartz ◽

G. L. Cowie ◽

L. A. Levin ◽

...

Keyword(s):

Arabian Sea ◽

Inorganic Carbon ◽

Surface Sediments ◽

Dissolved Inorganic Carbon ◽

Oxygen Minimum Zone ◽

Short Term ◽

Minimum Zone ◽

Algal Material ◽

Oxygen Minimum

Abstract. The short-term fate of phytodetritus was investigated across the Pakistan margin of the Arabian Sea at water depths ranging from 140 to 1850 m, encompassing the oxygen minimum zone (~100–1100 m). Phytodetritus sedimentation events were simulated by adding ~44 mmol 13C-labelled algal material per m2 to surface sediments in retrieved cores. Cores were incubated in the dark, at in situ temperature and oxygen concentrations. Overlying waters were sampled periodically, and cores were recovered and sampled (for organisms and sediments) after durations of two and five days. The labelled carbon was subsequently traced into bacterial lipids, foraminiferan and macrofaunal biomass, and dissolved organic and inorganic pools. The majority of the label (20 to 100%) was in most cases left unprocessed in the sediment at the surface. The largest pool of processed carbon was found to be respiration (0 to 25% of added carbon), recovered as dissolved inorganic carbon. Both temperature and oxygen were found to influence the rate of respiration. Macrofaunal influence was most pronounced at the lower part of the oxygen minimum zone where it contributed 11% to the processing of phytodetritus.

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