The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts

Abstract. Filaments and fronts play a crucial role for a net offshore and downward nutrient transport in Eastern Boundary Upwelling Systems (EBUSs) and thereby reduce regional primary production. Most studies on this topic are based on either observations or model simulations, but only seldom are both approaches are combined quantitatively to assess the importance of filaments for primary production and nutrient transport. Here we combine targeted interdisciplinary shipboard observations of a cold filament off Peru with submesoscale-permitting (1/45∘) coupled physical (Coastal and Regional Ocean Community model, CROCO) and biogeochemical (Pelagic Interaction Scheme for Carbon and Ecosystem Studies, PISCES) model simulations to (i) evaluate the model simulations in detail, including the timescales of biogeochemical modification of the newly upwelled water, and (ii) quantify the net effect of submesoscale fronts and filaments on primary production in the Peruvian upwelling system. The observed filament contains relatively cold, fresh, and nutrient-rich waters originating in the coastal upwelling. Enhanced nitrate concentrations and offshore velocities of up to 0.5 m s−1 within the filament suggest an offshore transport of nutrients. Surface chlorophyll in the filament is a factor of 4 lower than at the upwelling front, while surface primary production is a factor of 2 higher. The simulation exhibits filaments that are similar in horizontal and vertical scale compared to the observed filament. Nitrate concentrations and primary production within filaments in the model are comparable to observations as well, justifying further analysis of nitrate uptake and subduction using the model. Virtual Lagrangian floats were released in the subsurface waters along the shelf and biogeochemical variables tracked along the trajectories of floats upwelled near the coast. In the submesoscale-permitting (1/45∘) simulation, 43 % of upwelled floats and 40 % of upwelled nitrate are subducted within 20 d after upwelling, which corresponds to an increase in nitrate subduction compared to a mesoscale-resolving (1/9∘) simulation by 14 %. Taking model biases into account, we give a best estimate for subduction of upwelled nitrate off Peru between 30 %– 40 %. Our results suggest that submesoscale processes further reduce primary production by amplifying the downward and offshore export of nutrients found in previous mesoscale studies, which are thus likely to underestimate the reduction in primary production due to eddy fluxes. Moreover, this downward and offshore transport could also enhance the export of fresh organic matter below the euphotic zone and thereby potentially stimulate microbial activity in regions of the upper offshore oxygen minimum zone.

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The fate of upwelled nitrate off Peru shaped by submesoscale filaments and fronts

10.5194/bg-2020-112 ◽

2020 ◽

Cited By ~ 1

Author(s):

Jaard Hauschildt ◽

Soeren Thomsen ◽

Vincent Echevin ◽

Andreas Oschlies ◽

Yonss Saranga José ◽

...

Keyword(s):

Primary Production ◽

Coastal Upwelling ◽

Nutrient Transport ◽

Model Simulations ◽

Fresh Organic Matter ◽

Upwelled Water ◽

Vertical Scale ◽

Nitrate Concentrations ◽

Additional Value ◽

Offshore Transport

Abstract. Filaments and fronts play a crucial role for a net offshore and downward nutrient transport in Eastern Boundary Upwelling Regions (EBUS) and thereby reduce primary production. Often studies are either based on observations or model simulations but seldom both approaches are combined quantitatively to assess the importance of filaments for primary production and nutrient transport. Here we combine targeted interdisciplinary shipboard observations of a cold filament off Peru with submesoscale-permitting (1/45°) coupled physical (CROCO) and biogeochemical (PISCES) model simulations to (i) evaluate the model simulations in detail, including the timescales of biogeochemical modification of the newly upwelled water and (ii) quantify the net effect of submesoscale fronts and filaments on primary production of the Peruvian upwelling system. The observed filament contains relatively cold, fresh and nutrient-rich waters originating in the coastal upwelling. Enhanced nitrate concentrations and offshore velocities of up to 0.5 m s−1 within the filament suggest an offshore transport of nutrients. Surface chlorophyll in the filament is a factor 4 lower than at the upwelling front while surface primary production is a factor 2 higher, highlighting the additional value of direct rate measurements for model validation. The simulation exhibits filaments that are similar in horizontal and vertical scale compared to the observed filament. Nitrate concentrations and primary pro- duction within filaments in the model are comparable to observations as well, justifying further analysis of nitrate uptake and subduction using the model. Virtual Lagrangian floats were released in the subsurface waters along the shelf and biogeochemical variables tracked along the trajectories of floats upwelled near the coast. In the submesoscale-permitting (1/45°) simulation 43.0 % of upwelled floats and 40.6 % of upwelled nitrate is subducted within 20 days after upwelling, which corresponds to an increase of nitrate subduction compared to a mesoscale-resolving (1/9°) simulation by 13.9 %. This suggests that submesoscale processes further reduce primary production by amplifying the downward and offshore export of nutrients found in previous mesoscale studies, which are thus likely to underestimate the reduction in primary production due to eddy-fluxes. Moreover, this downward and offshore transport could also enhance the export of fresh organic matter below the photic zone and thereby potentially stimulate microbial activity in the upper offshore oxygen minimum zone.

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Influence of upwelling events on the estuaries of the north-western coast of the Iberian Peninsula

Marine and Freshwater Research ◽

10.1071/mf12298 ◽

2013 ◽

Vol 64 (12) ◽

pp. 1123 ◽

Cited By ~ 5

Author(s):

I. Alvarez ◽

J. M. Dias ◽

M. deCastro ◽

N. Vaz ◽

M. C. Sousa ◽

...

Keyword(s):

Primary Production ◽

Iberian Peninsula ◽

Biological Diversity ◽

Coastal Upwelling ◽

Western Coast ◽

External Forcing ◽

Ria De Aveiro ◽

The North ◽

Upwelled Water ◽

Ría De Vigo

Coastal upwelling is one of the best studied oceanographic phenomena because of its effects on primary production. The western coast of the Iberian Peninsula has high biological diversity, mainly due to this primary production. In this study, the response of salinity and temperature to the occurrence of upwelling was analysed at the Ria de Vigo– and Ria de Aveiro–ocean boundary over the course of a year. Both systems were influenced by similar external forcing, but the response of thermohaline properties differed. Salinity and temperature were dependent on external forcing throughout the water column at Ria de Aveiro, whereas near-bed measurements revealed the presence of upwelled water at Ria de Vigo. Eastern North Atlantic Central Water was observed during spring–summer (summer) at the southern (northern) mouth of Ria de Vigo, but it was not observed at Ria de Aveiro. This difference may be due to the shallowness and narrowness of the Ria de Aveiro mouth, which can limit the entrance of ocean water. The trends found are unlikely to be unique, suggesting that geomorphologic characteristics of system–ocean boundaries determine how physical processes occurring in adjacent coastal areas impact estuarine properties.

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Structure of coastal upwelling events observed off the south-east coast of South Australia during February 1983 - April 1984

Marine and Freshwater Research ◽

10.1071/mf9870439 ◽

1987 ◽

Vol 38 (4) ◽

pp. 439 ◽

Cited By ~ 67

Author(s):

RB Schahinger

Keyword(s):

Satellite Images ◽

East Coast ◽

Coastal Upwelling ◽

South Australia ◽

The South ◽

Shelf Circulation ◽

Upwelled Water ◽

Shelf Region ◽

Offshore Transport

Observations of upwelling along the south-east coast of South Australia during the summers of 1983 and 1984 are presented. In situ measurements were obtained from a number of current meters moored across the continental shelf near 37.5�S.,139.5�E. These were complemented by wind and sea level measurements along the coast and also monthly hydrographic surveys. Differences between summer and winter regimes are discussed in both physical and dynamical terms. The summer weather pattern gives rise to winds which are favourable to upwelling along this coast more than 50% of the time (i.e. winds from the south-east quarter). The evolution of two upwelling events and the associated shelf circulation are documented. Salient features include the offshore transport of water in a shallow surface layer 0 (20 m) in response to south-easterly winds; an onshore compensatory flow occurs almost immediately below. The summer thermocline shoals soon after the onset of winds favouring upwelling, leading to pronounced cross-shelf surface-temperature gradients with cooler (upwelled) water at the surface near the coast. The surfaced thermocline moves offshore and attains an equilibrium position in the vicinity of the shelf edge (after 4-5 days), as shown by infrared satellite images, while water from depths of 250-300 m encroaches onto the shelf. Alongshore currents reach speeds of more than 50 cm s-1 in the outer-shelf region and are strongly influenced by the position of the upwelling front. Brief comparisons are drawn with other upwelling regions.

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A stochastic, Lagrangian model of sinking biogenic aggregates in the ocean (SLAMS 1.0): model formulation, validation and sensitivity

Geoscientific Model Development ◽

10.5194/gmd-9-1455-2016 ◽

2016 ◽

Vol 9 (4) ◽

pp. 1455-1476 ◽

Cited By ~ 18

Author(s):

Tinna Jokulsdottir ◽

David Archer

Keyword(s):

Primary Production ◽

Degradation Kinetics ◽

Mechanistic Model ◽

Euphotic Zone ◽

Lagrangian Model ◽

Zooplankton Grazing ◽

Aggregate Model ◽

Size Spectra ◽

Sea Floor ◽

Individual Particles

Abstract. We present a new mechanistic model, stochastic, Lagrangian aggregate model of sinking particles (SLAMS) for the biological pump in the ocean, which tracks the evolution of individual particles as they aggregate, disaggregate, sink, and are altered by chemical and biological processes. SLAMS considers the impacts of ballasting by mineral phases, binding of aggregates by transparent exopolymer particles (TEP), zooplankton grazing and the fractal geometry (porosity) of the aggregates. Parameterizations for age-dependent organic carbon (orgC) degradation kinetics, and disaggregation driven by zooplankton grazing and TEP degradation, are motivated by observed particle fluxes and size spectra throughout the water column. The model is able to explain observed variations in orgC export efficiency and rain ratio from the euphotic zone and to the sea floor as driven by sea surface temperature and the primary production rate and seasonality of primary production. The model provides a new mechanistic framework with which to predict future changes on the flux attenuation of orgC in response to climate change forcing.

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Primary Production and Phytoplankton in the Experimental Lakes Area, Northwestern Ontario, and other Low-Carbonate Waters, and a Liquid Scintillation Method for Determining 14C Activity in Photosynthesis

Journal of the Fisheries Research Board of Canada ◽

10.1139/f71-031 ◽

1971 ◽

Vol 28 (2) ◽

pp. 189-201 ◽

Cited By ~ 120

Author(s):

D. W. Schindler ◽

S. K. Holmgren

Keyword(s):

Primary Production ◽

Liquid Scintillation ◽

Species Abundance ◽

Euphotic Zone ◽

Phytoplankton Production ◽

Phytoplankton Species ◽

Experimental Lakes Area ◽

Phytoplankton Species Composition ◽

Northwestern Ontario ◽

Filtration Error

A modified 14C method is described for measuring phytoplankton production in low-carbonate waters. The procedure includes the use of the Arthur and Rigler (Limnol. Oceanogr. 12: 121–124, 1967) technique for determining filtration error, liquid scintillation counting for determining the radioactivity of membrane filters and stock 14C solutions, and gas chromatography for measuring total CO2.Primary production, chlorophyll a, and total CO2 were measured for two dates in midsummer from each of several lakes in the Experimental Lakes Area (ELA), ranging from 1 to 1000 ha in area and from 2 to 117 m in maximum depth. Phytoplankton species abundance and biomass were determined for the same dates. Production ranged from 0.02 to 2.12 gC/m3∙day and from 0.179 to 1.103 g C/m2∙day. Chlorophyll ranged from 0.4 to 44 mg/m3 and from 5 to 98 mg/m2 in the euphotic zone. The corresponding ranges for live phytoplankton biomass were 120–5400 mg/m3 and 2100–13,400 mg/m2. Chrysophyceae dominated the phytoplankton of most of the lakes.A system for classifying the lakes in terms of phytoplankton species composition and production–depth curves is developed.

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Quantum yield of the marine benthic microflora of near-shore coastal Penang, Malaysia

Marine and Freshwater Research ◽

10.1071/mf05007 ◽

2005 ◽

Vol 56 (7) ◽

pp. 1047 ◽

Cited By ~ 3

Author(s):

A. McMinn ◽

S. Sellah ◽

W. A. Wan Ab. Llah ◽

M. Mohammad ◽

F. Md. Sidik Merican ◽

...

Keyword(s):

Primary Production ◽

Suspended Solids ◽

Euphotic Zone ◽

Water Clarity ◽

Quantum Yields ◽

Chl A ◽

Near Shore ◽

High Concentrations ◽

A Minor ◽

Reduced Water

Benthic microalgal communities often contribute more than 30% of the primary production of shallow coastal and estuarine areas. At Muka Head Penang (Pulau Pinang) and the Songsong Islands (Pulau Songsong), Kedah, Malaysia, high concentrations of suspended solids and phytoplankton biomass (10.6 mg Chl a m−3) has reduced water clarity such that the euphotic zone of these areas is less than 2 m and 3 m deep respectively. The benthic microalgal communities, which were composed of the diatom genera Cocconeis, Fragilaria, Paralia and Pleurosigma, had a low biomass, had low maximum quantum yields (0.325 ± 0.129), were poorly adapted to their light environment and were constantly light limited. These characteristics suggest that the benthic microalgal communities were likely to have made only a minor contribution to the total primary production of the area.

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