Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

Karstensen, Johannes; Schütte, Florian; Pietri, Alice; Krahmann, Gerd; Fiedler, Björn; Grundle, Damian S.; Hauss, Helena; Körtzinger, Arne; Löscher, Carolin R.; Testor, Pierre; Vieira, Nuno; Visbeck, Martin

doi:10.5194/bg-14-2167-2017

Cited by 53 publications

(74 citation statements)

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“…Here it is hard to see any intrusion at the rim of the SCV, the gradients separating the SCV and the surroundings being pretty sharp for each eddy crossing by the glider (see Figure c). Anticyclonic eddies can also trap downward propagating near‐inertial waves, as it has already been observed [ Joyce et al ., ; Cuypers et al ., ; Sheen et al ., ; Karstensen et al ., ]. The energy dissipation of those waves and their influence on the decay of small‐scale postconvective SCVs would need to be assessed in future studies with help of complementary turbulence measurements and numerical models.…”

Section: Discussionmentioning

confidence: 99%

“…[] reveal sediments being trapped within cyclonic SCVs in the NW Mediterranean Sea. In oxygen‐depleted oceans, they have been identified as local spots for denitrification [ Löscher et al ., ; Karstensen et al ., ] and habitat compression due to their very low oxygen content [ Lachkar et al ., ]. Especially in tropical oceanic basins, subsurface eddies can be tentatively be detected from space when combined with infrared satellite images [ Klemas and Yan , ], even though the surface expression of deep subsurface eddies is often small [ Ciani et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

et al. 2017

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In June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full‐depth CTD casts (T, S, and oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s−1 in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of −0.45. The vorticity at the eddy center reaches −0.8f. Cross‐stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m2 s−1. The deep core is nutrients‐depleted with concentrations of nitrate, phosphate, and silicate, 13–18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20–50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll‐a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrates the important impact of postconvective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

et al. 2017

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“…A mode-water eddy observed by Stramma et al (2014) was generated in year 2011, which is considered as a La Niña period, when generally lower oxygen and higher salinity values exist in the upper Stramma et al (2014) For the Atlantic Ocean the low-oxygen eddy cores have been attributed to high productivity in the surface (Schütte et al, 2016b), enhanced respiration of sinking organic material at subsurface depth , and a strong isolation of the eddy core (Karstensen et al, 2017). An anticyclonic mode-water eddy observed in the Pacific at the Stratus mooring in February/March 2012 indicated high primary production just below the mixed layer (Stramma et al, 2014).…”

Section: Discussion and Outlookmentioning

confidence: 99%

Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific

et al. 2018

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Abstract. The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.

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“…Third, the relevant share of C org found in the offshore region within mesoscale eddies, which are mostly laterally isolated structures (Chelton et al, Karstensen et al, 2017;Stramma et al, 2013), also tells us that a fraction of the offshore biological activity is fueled discontinuously. In particular, both the transit of an eddy, which is associated with enhanced vertical export (Subha Anand et al, 2017;Waite et al, 2016), and the death of an eddy provide a discontinuous, but substantial, input of carbon for the oligotrophic waters.…”

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Mesoscale contribution to the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

2018

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Abstract. Several studies in upwelling regions have suggested that mesoscale structures, such as eddies and filaments, contribute substantially to the long-range transport of the organic carbon from the nearshore region of production to the offshore region of remineralization. Yet this has not been demonstrated in a quantitative manner for the entire Canary Upwelling System (CanUS). Here, we fill this gap using the Regional Oceanic Modeling System (ROMS) coupled to a Nutrient, Phytoplankton, Zooplankton, and Detritus (NPZD) ecosystem model. We run climatological simulations on an Atlantic telescopic grid with 5 an eddy-resolving resolution in the CanUS. Using both a Reynolds flux decomposition and structure-identification algorithms, we quantify and characterize the organic carbon fluxes driven by filaments and eddies within the upper 100 m and put them in relationship to the total offshore transport. Our analyses reveal that both coastal filaments and eddies enhance the offshore flux of organic carbon, but that their contribution is very different. Upwelling filaments, with their high speeds and high organic carbon concentrations, transport this carbon offshore in a very intense, but coastally-confined, manner, contributing nearly 10 80% to the total flux at 100 km offshore distance. The filament contribution tapers off quickly to near zero values at 1000 km distance, leading to a strong offshore flux divergence that is the main lateral source of organic carbon in the first 500 km offshore. Some of this divergence is also due to the filaments inducing a substantial vertical subduction of the organic carbon below 100 m. Owing to the temporal persistence and spatial recurrence of filaments, the filament transport largely constitutes a time-mean flux and only to a limited degree represents a turbulent flux. At distances beyond 500 km from the coast, eddies 15 dominate the mesoscale offshore transport. Although their contribution represents only 20 % of the total offshore flux and of its divergence, eddies, especially cyclones, transport organic carbon offshore to distances as great as 2000 km from the coast.The eddy transport largely represents a turbulent flux, but striations in this transport highlight the existence of typical formation spots and recurrent offshore propagation pathways. While they propagate slowly, eddies are an important organic carbon reservoir for the open waters, since they contain on average a third of the offshore organic carbon, two third of which is found 20 in cyclones. Our analysis confirms the importance of mesoscale processes for the offshore organic carbon transport and the fueling of the heterotrophic activity in the eastern subtropical North Atlantic, and highlights the need to consider the mesoscale flux in order to fully account for the three-dimensionality of the marine biological pump.

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Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

Cited by 53 publications

References 50 publications

A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific

Mesoscale contribution to the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

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