Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone

Abstract. Cobalt is a nutrient to phytoplankton, but knowledge about its biogeochemical cycling is limited, especially in the Pacific Ocean. Here, we report sections of dissolved cobalt and labile dissolved cobalt from the US GEOTRACES GP16 transect in the South Pacific. The cobalt distribution is closely tied to the extent and intensity of the oxygen minimum zone in the eastern South Pacific with highest concentrations measured at the oxycline near the Peru margin. Below 200 m, remineralization and circulation produce an inverse relationship between cobalt and dissolved oxygen that extends throughout the basin. Within the oxygen minimum zone, elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low O2. As these high cobalt waters are upwelled and advected offshore, phytoplankton export returns cobalt to low-oxygen water masses underneath. West of the Peru upwelling region, dissolved cobalt is less than 10 pM in the euphotic zone and strongly bound by organic ligands. Because the cobalt nutricline within the South Pacific gyre is deeper than in oligotrophic regions in the North and South Atlantic, cobalt involved in sustaining phytoplankton productivity in the gyre is heavily recycled and ultimately arrives from lateral transport of upwelled waters from the eastern margin. In contrast to large coastal inputs, atmospheric deposition and hydrothermal vents along the East Pacific Rise appear to be minor sources of cobalt. Overall, these results demonstrate that oxygen biogeochemistry exerts a strong influence on cobalt cycling.

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Size-Fractionated Contribution of Microbial Biomass to Suspended Organic Matter in the Eastern Tropical South Pacific Oxygen Minimum Zone

Frontiers in Marine Science ◽

10.3389/fmars.2020.540643 ◽

2020 ◽

Vol 7 ◽

Cited By ~ 1

Author(s):

Sebastian I. Cantarero ◽

Carlos Henríquez-Castillo ◽

Nadia Dildar ◽

Cristian A. Vargas ◽

Peter von Dassow ◽

...

Keyword(s):

Organic Matter ◽

Microbial Biomass ◽

South Pacific ◽

Oxygen Minimum Zone ◽

Suspended Organic Matter ◽

Minimum Zone ◽

Oxygen Minimum

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A cobalt plume in the oxygen minimum zone of the Eastern Tropical South Pacific

10.5194/bg-2016-169 ◽

2016 ◽

Cited By ~ 2

Author(s):

N. J. Hawco ◽

D. C. Ohnemus ◽

J. A. Resing ◽

B. S. Twining ◽

M. A. Saito

Keyword(s):

Hydrothermal Vents ◽

Euphotic Zone ◽

South Pacific ◽

Oxygen Minimum Zone ◽

Low Oxygen ◽

The South ◽

Phytoplankton Productivity ◽

The North ◽

Minimum Zone ◽

Oxygen Minimum

Abstract. Cobalt is a nutrient to phytoplankton, but knowledge about its biogeochemical cycling is limited, especially in the Pacific Ocean. Here, we report sections of dissolved cobalt and labile cobalt from the US GEOTRACES GP16 transect in the South Pacific. The cobalt distribution is closely tied to the extent and intensity of the oxygen minimum zone in the eastern South Pacific with highest concentrations measured at the oxycline near the Peru margin. Below 200 m, remineralization and circulation produce an inverse relationship between cobalt and dissolved oxygen that extends throughout the basin. Within the oxygen minimum zone, elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low O2. As these high cobalt waters are upwelled and advected offshore, phytoplankton export returns cobalt to low-oxygen water masses underneath. West of the Peru upwelling region, dissolved cobalt is less than 10 pM in the euphotic zone and strongly bound by organic ligands. Because the cobalt nutricline within the South Pacific gyre is deeper than oligotrophic regions in the North and South Atlantic, cobalt involved in sustaining phytoplankton productivity in the gyre is heavily recycled and ultimately arrives from lateral transport of upwelled waters from the eastern margin. In contrast to large coastal inputs, hydrothermal vents along the Eastern Pacific Rise appear to be a minor source of cobalt. Overall, these results demonstrate that oxygen biogeochemistry exerts a strong influence on cobalt cycling.

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Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

Biogeosciences ◽

10.5194/bg-10-6879-2013 ◽

2013 ◽

Vol 10 (11) ◽

pp. 6879-6891 ◽

Cited By ~ 10

Author(s):

L. Pozzato ◽

D. Van Oevelen ◽

L. Moodley ◽

K. Soetaert ◽

J. J. Middelburg

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Particulate Organic Matter ◽

Experimental Period ◽

Oxygen Minimum Zone ◽

Trophic Levels ◽

Isotope Tracer ◽

Oxygen Conditions ◽

Minimum Zone ◽

Oxygen Minimum

Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus.

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