Productivity cycles in the coastal upwelling area off Concepción: The importance of diatoms and bacterioplankton in the organic carbon flux

Montero, Paulina; Daneri, Giovanni; Cuevas, L. Antonio; González, Humberto E.; Jacob, Bárbara; Lizárraga, Lorena; Menschel, Eduardo

doi:10.1016/j.pocean.2007.08.013

Cited by 114 publications

(70 citation statements)

References 39 publications

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“…Here, complete oxygen depletion is only observed during the austral summer (32-34) when upwellingfavorable southerly winds dominate, allowing nutrient-rich, oxygen-depleted equatorial subsurface waters to intrude across the shelf. This advection of nutrients stimulates primary productivity, enhancing organic matter export and thereby generating higher rates of subsurface respiration (34,35).…”

Section: Resultsmentioning

confidence: 99%

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Bristow

Dalsgaard

Tiano

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

207

209

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A major percentage of fixed nitrogen (N) loss in the oceans occurs within nitrite-rich oxygen minimum zones (OMZs) via denitrification and anammox. It remains unclear to what extent ammonium and nitrite oxidation co-occur, either supplying or competing for substrates involved in nitrogen loss in the OMZ core. Assessment of the oxygen (O 2 ) sensitivity of these processes down to the O 2 concentrations present in the OMZ core (<10 nmol·L −1 ) is therefore essential for understanding and modeling nitrogen loss in OMZs. We determined rates of ammonium and nitrite oxidation in the seasonal OMZ off Concepcion, Chile at manipulated O 2 levels between 5 nmol·L −1 and 20 μmol·L −1 . Rates of both processes were detectable in the low nanomolar range (5-33 nmol·L −1 O 2 ), but demonstrated a strong dependence on O 2 concentrations with apparent half-saturation constants (K m s) of 333 ± 130 nmol·L −1 O 2 for ammonium oxidation and 778 ± 168 nmol·L −1 O 2 for nitrite oxidation assuming one-component Michaelis-Menten kinetics. Nitrite oxidation rates, however, were better described with a two-component Michaelis-Menten model, indicating a high-affinity component with a K m of just a few nanomolar. As the communities of ammonium and nitrite oxidizers were similar to other OMZs, these kinetics should apply across OMZ systems. The high O 2 affinities imply that ammonium and nitrite oxidation can occur within the OMZ core whenever O 2 is supplied, for example, by episodic intrusions. These processes therefore compete with anammox and denitrification for ammonium and nitrite, thereby exerting an important control over nitrogen loss.is a key factor regulating biogeochemical cycling in the marine environment (1). Although the vast majority of the ocean remains well oxygenated, subsurface regions of extreme oxygen depletion can persist along eastern boundaries of the world's ocean basins. These regions are known as oxygen minimum zones (OMZs) and are located within the eastern tropical North and South Pacific, the Arabian Sea, and off the coast of Namibia, where oxygen depletion results from poor ventilation and a high export of organic matter from productive surface waters, generating high rates of subsurface oxygen consumption (2, 3).Oceanic waters characterized by oxygen-deficient conditions (<4.5 μmol·L −1 O 2 ) account for <0.1% of total ocean volume but for >30% of fixed nitrogen (N) loss (3-6) due to the onset of anaerobic processes, including denitrification and anammox (7-10). Both field and modeling observations point to the expansion of low oxygen regions as a result of global warming (11). Thus, to evaluate the biogeochemical impact of these regions, it is imperative to understand fully how oxygen controls the cycling of substrates involved in nitrogen loss pathways.Recent studies have quantified the oxygen sensitivity of anaerobic OMZ nitrogen transformations, finding that denitrification has relatively low oxygen tolerance with a half-inhibition concentration (IC 50 ) of 0.3 μmol·L −1 , compared with higher values for...

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Section: Resultsmentioning

confidence: 99%

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Bristow

Dalsgaard

Tiano

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

207

209

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“…The annual depth-integrated GPP estimated for the Puyuhuapi study site (329 g C m -2 y -1 ) amounts to ca. 40% of the yearly GPP estimated for the exceptionally productive upwelling system off Concepción in central Chile (Daneri et al, 2000;Montero et al, 2007), and is of a similar order to estimates in other highly productive fjord ecosystems, such as the Howe sound (500 g C m -2 y -1 ) on the southern coast of British Columbia (Albright & McRae, 1987) and the Gullmar Fjord (300 g C m -2 y -1 ) on the Swedish Skagerrak coast (Lindahl et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

Diatom blooms and primary production in a channel ecosystem of central Patagonia

Montero

Daneri

Tapia

et al. 2017

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ABSTRACT.Here we report on the seasonal productivity cycle at a fixed station in the Puyuhuapi Channel (44ºS, 73ºW), Chilean Patagonia. The analysis of in situ water column data and longer-term records of satellitederived surface ocean color (Chl-a) highlighted two contrasting seasons. A more productive period occurred between August and April, where depth-integrated gross primary production (GPP) estimates ranged from 0.1 to 2.9 g C m -2 d -1, and a shorter, less-productive season lasted from May to July with GPP ranging from 0.03 to. Diatoms of the genera Pseudo-nitzschia, Skeletonema and Chaetoceros dominated the phytoplankton, and showed a pronounced seasonality greatly influenced by prevailing environmental conditions. Warmer waters were associated with high concentrations of Pseudo-nitzschia spp., while high abundances of Skeletonema spp. and Chaetoceros spp. were associated with fresher silicate-rich waters. A marked Skeletonema spp. bloom characterized the onset of the productive season in August 2008, and with some exceptions, the highest levels of GPP (1.5 to 2.9 g C m -2 d -1) were measured when Skeletonema dominated the phytoplankton community. Reduced production (low GPP) was observed during periods of increased discharge from the Cisnes River, whereas the "spring" diatom bloom (or late winter bloom in Puyuhuapi Channel) observed during August 2008 coincided with a ~50% drop in the freshwater discharge. We therefore suggest that periods of intensive freshwater Input, that increase the silicic acid concentrations in the upper layers, provide ideal growing conditions for diatoms as the freshwater flow subsequently recedes. Principal component analysis (PCA) suggests that a decrease in salinity, increase in silicic acid concentration, and growth of Skeletonema spp. and Chaetoceros spp., are probably key factors in the annual cycle of GPP in Puyuhuapi Channel.

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“…During austral spring-summer (SeptemberApril), a marked upwelling-favourable period driven by persistent southwesterly winds, ESSWs arrive at the coastal area off central Chile, impinging on one of the widest continental shelves in Chile (Sobarzo and Djurfeldt, 2004;Sobarzo et al, 2007). Throughout the upwelling season high primary production rates (Daneri et al, 2000) occur along with a large downward flux of organic matter, leading to an increase in respiration rates at depth (Montero et al, 2007). These conditions, coupled with the presence of already O 2 -deficient waters, and greater availability of electron donors and acceptors (as a result of the advection of inorganic substrates, local organic matter respiration, and autotrophic redox reactions), create steep gradients for O 2 and other chemicals, with the establishment of hypoxic-anoxic conditions at middle-bottom depths.…”

Section: Introductionmentioning

confidence: 99%

Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

2017

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Abstract. The upwelling system off central Chile (36.5 • S) is seasonally subjected to oxygen (O 2 )-deficient waters, with a strong vertical gradient in O 2 (from oxic to anoxic conditions) that spans a few metres (30-50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N 2 and/or N 2 O, were studied using 15 N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25 m depth) and bottom waters (85 m depth) over the continental shelf off Concepción, Chile. Results of 15 N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N 2 -producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O 2 fluctuation between 270 and 40 µmol L −1 ) relative to the hypoxic bottom waters (< 20 µmol O 2 L −1 ). Different pathways were responsible for N 2 O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N 2 O production. The temporal and vertical variability of δ 15 N-NO − 3 confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substratesPublished by Copernicus Publications on behalf of the European Geosciences Union. 4796A. Galán et al.: Vertical segregation among pathways mediating nitrogen loss are responsible for substantial accumulation of N 2 O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.

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Productivity cycles in the coastal upwelling area off Concepción: The importance of diatoms and bacterioplankton in the organic carbon flux

Cited by 114 publications

References 39 publications

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Diatom blooms and primary production in a channel ecosystem of central Patagonia

Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

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Productivity cycles in the coastal upwelling area off Concepción: The importance of diatoms and bacterioplankton in the organic carbon flux

Cited by 114 publications

References 39 publications

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Diatom blooms and primary production in a channel ecosystem of central Patagonia

Vertical segregation among pathways mediating nitrogen loss (N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O production) across the oxygen gradient in a coastal upwelling ecosystem

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Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem