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1

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Hydrography in the northern tropical Atlantic at 1026.8 - 1027.3 kg/m 3 density range during 1950-2009 (2009)

Banyte, Donata [VerfasserIn]

Kiel

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Keywords: Hochschulschrift

Type of Medium: Online Resource

Pages: 1 Online-Ressource (30 Seiten = 4 MB) , Graphen

Edition: 2022

URL: https://oceanrep.geomar.de/10953/

Language: English

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2

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Diapycnal and along isopycnal mixing, estimated from the tracer release experiment, at the North Atlantic oxygen minimum zone (2013)

Banyte, Donata

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Keywords: Hochschulschrift ; Atlantischer Ozean Nord ; Thermische Sprungschicht ; Sauerstofftransport

Type of Medium: Online Resource

Pages: Online-Ressource (Online-Ressource)

URL: http://nbn-resolving.de/urn:nbn:de:gbv:8-diss-110451

URL: http://d-nb.info/1031189823/34

URL: http://macau.uni-kiel.de/receive/dissertation_diss_00011045

URN: urn:nbn:de:gbv:8-diss-110451

DDC: 500

Language: English

Note: Kiel, Univ., Diss., 2013

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3

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Diapycnal oxygen supply to the tropical North Atlantic oxygen minimum zone (2013)

Fischer, Tim ; Banyte, Donata ; Brandt, Peter ; [et al.]

Copernicus Publications (EGU)

In: Biogeosciences (BG), 10 . pp. 5079-5093.

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Publication Date: 2021-04-21

Description: The replenishment of consumed oxygen in the open ocean oxygen minimum zone (OMZ) off northwest Africa is accomplished by oxygen transport across and along density surfaces, i.e. diapycnal and isopycnal oxygen supply. Here the diapycnal oxygen supply is investigated using a large observational set of oxygen profiles and diapycnal mixing data from years 2008 to 2010. Diapycnal mixing is inferred from different sources: (i) a large-scale tracer release experiment, (ii) microstructure profiles, and (iii) shipboard acoustic current measurements plus density profiles. From these measurements, the average diapycnal diffusivity in the studied depth interval from 150 to 500m is estimated to be 1×10−5 m2 s−1, with lower and upper 95%confidence limits of 0.8×10−5 m2 s−1 and 1.4×10−5 m2 s−1. Diapycnal diffusivity in this depth range is predominantly caused by turbulence, and shows no significant vertical gradient. Diapycnal mixing is found to contribute substantially to the oxygen supply of the OMZ. Within the OMZ core, 1.5 μmol kg−1 yr−1 of oxygen is supplied via diapycnal mixing, contributing about one-third of the total demand. This oxygen which is supplied via diapycnal mixing originates from oxygen that has been laterally supplied within the upper CentralWater layer above the OMZ, and within the Antarctic Intermediate Water layer below the OMZ. Due to the existence of a separate shallow oxygen minimum at about 100m depth throughout most of the study area, there is no net vertical oxygen flux from the surface layer into the Central Water layer. Thus all oxygen supply of the OMZ is associated with remote pathways.

Type: Article , PeerReviewed , info:eu-repo/semantics/article

Format: text

DOI: 10.5194/bg-10-5079-2013

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On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic (2015)

Brandt, Peter ; Bange, Hermann W. ; Banyte, Donata ; [et al.]

Copernicus Publications (EGU)

In: Biogeosciences (BG), 12 . pp. 489-512.

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Publication Date: 2021-04-21

Description: Ocean observations carried out in the framework of the Collaborative Research Center 754 (SFB 754) "Climate-Biogeochemistry Interactions in the Tropical Ocean" are used to study (1) the structure of tropical oxygen minimum zones (OMZs), (2) the processes that contribute to the oxygen budget, and (3) long-term changes in the oxygen distribution. The OMZ of the eastern tropical North Atlantic (ETNA), located between the well-ventilated subtropical gyre and the equatorial oxygen maximum, is composed of a deep OMZ at about 400 m depth with its core region centred at about 20° W, 10° N and a shallow OMZ at about 100 m depth with lowest oxygen concentrations in proximity to the coastal upwelling region off Mauritania and Senegal. The oxygen budget of the deep OMZ is given by oxygen consumption mainly balanced by the oxygen supply due to meridional eddy fluxes (about 60%) and vertical mixing (about 20%, locally up to 30%). Advection by zonal jets is crucial for the establishment of the equatorial oxygen maximum. In the latitude range of the deep OMZ, it dominates the oxygen supply in the upper 300 to 400 m and generates the intermediate oxygen maximum between deep and shallow OMZs. Water mass ages from transient tracers indicate substantially older water masses in the core of the deep OMZ (about 120–180 years) compared to regions north and south of it. The deoxygenation of the ETNA OMZ during recent decades suggests a substantial imbalance in the oxygen budget: about 10% of the oxygen consumption during that period was not balanced by ventilation. Long-term oxygen observations show variability on interannual, decadal and multidecadal time scales that can partly be attributed to circulation changes. In comparison to the ETNA OMZ the eastern tropical South Pacific OMZ shows a similar structure including an equatorial oxygen maximum driven by zonal advection, but overall much lower oxygen concentrations approaching zero in extended regions. As the shape of the OMZs is set by ocean circulation, the widespread misrepresentation of the intermediate circulation in ocean circulation models substantially contributes to their oxygen bias, which might have significant impacts on predictions of future oxygen levels.

Type: Article , PeerReviewed

Format: text

DOI: 10.5194/bg-12-489-2015

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Diapycnal diffusivity at the upper boundary of the tropical North Atlantic oxygen minimum zone (2012)

Banyte, Donata ; Tanhua, Toste ; Visbeck, Martin ; [et al.]

AGU (American Geophysical Union)

In: Journal of Geophysical Research: Oceans, 117 (C9). C09016.

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Publication Date: 2019-09-23

Description: A deliberate tracer release experiment in 2008–2010 was used to study diapycnal mixing in the tropical northeastern Atlantic. The tracer (CF3SF5) was injected on the isopycnal surface σΘ = 26.88 kg m−3, which corresponds to about 330 m depth. Three surveys, performed 7, 20, and 30 months after the release, sampled the vertically and laterally expanding tracer patch. The mean diapycnal mixing estimate over the entire region occupied by the tracer and the period of 30 months was found to be (1.19 ± 0.18) × 10−5 m2 s−1, or, alternatively, (3.07 ± 0.58) × 10−11 (kg m−3)2 s−1 as computed from the advection-diffusion equation in isopycnal coordinates with the thickness-weighted averaging. The latter method is preferable in the regions of different stratification for it yields local diapycnal mixing estimates varying less with stratification than their Cartesian coordinate counterparts. Results of this study are comparable to the results of the North Atlantic tracer release experiment (NATRE). However, the internal wave-wave interaction models predict reduced mixing from the breaking of internal waves at low latitudes. Thus, the diapycnal diffusivity found in this study is higher than parameterized by the low latitude of the site (4°N–12°N).

Type: Article , PeerReviewed

Format: text

DOI: 10.1029/2011JC007762

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Diapycnal diffusivity at the upper boundary of the North Tropical Atlantic Oxygen Minimum Zone (2012)

Banyte, Donata ; Tanhua, Toste ; Visbeck, Martin ; [et al.]

In: [Poster] In: EGU General Assembly 2012, 22.-27.04.2012, Vienna, Austria .

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Publication Date: 2012-11-27

Type: Conference or Workshop Item , NonPeerReviewed

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Diapycnal oxygen supply to the tropical North Atlantic oxygen minimum zone (OMZ) (2013)

Fischer, Tim ; Banyte, Donata ; Brandt, Peter ; [et al.]

In: [Poster] In: EGU General Assembly 2013, 07.-12.04.2013, Vienna, Austria .

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Publication Date: 2013-05-06

Type: Conference or Workshop Item , NonPeerReviewed

Format: text

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8

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Dynamics of tropical oxygen minium zones (OMZ): The role of vertical mixing and eddy stirring in ventilating the OMZ in the tropical Atlantic (2013)

Visbeck, Martin ; Banyte, Donata ; Brandt, Peter ; [et al.]

In: [Talk] In: AGU Fall Meeting 2013, 09.-13.12.2013, San Francisco, USA .

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Publication Date: 2013-12-20

Type: Conference or Workshop Item , NonPeerReviewed

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The Oxygen Supply Tracer Release Experiment in the tropical North East Atlantic Oxygen Minimum Zone (2014)

Köllner, Manuela ; Banyte, Donata ; Tanhua, Toste ; [et al.]

In: [Talk] In: 46. International Liege Colloquium, 05.-09.05.2014, Liege, Belgium .

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Publication Date: 2019-09-23

Type: Conference or Workshop Item , NonPeerReviewed

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10

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Diapycnal and along isopycnal mixing, estimated from the tracer release experiment, at the North Atlantic oxygen minimum zone (2013)

Banyte, Donata

In: (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 132 pp

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Publication Date: 2016-01-13

Description: A deliberate Guinea Upwelling Tracer Release Experiment (GUTRE) in 2008 - 2010 was used to study diapycnal mixing and lateral stirring in the thermocline of tropical northeastern Atlantic. The ultimate goal of this work was to investigate oxygen supply pathways at the upper boundary of North Atlantic oxygen minimum zone. The mean diapycnal mixing coefficients were computed for a tracer patch integrated over 30 months. The strong variation of stratification in the tracer occupied area offered the advantage of using the advection-diffusion equation in isopycnal coordinates with the thickness-weighted averaging, when analyzing the diapycnal tracer spread. Overall, the vertical mixing estimates were found about 30% smaller than estimates in North Atlantic Tracer Release Experiment (NATRE), performed about 15° to the north from our experiment. In general, the internal wave-wave interaction models predict reduced mixing from the breaking of internal waves at low latitudes. Thus, GUTRE results are larger than parametrized by the low latitude of the site (4°N - 12°N). The mean isopycnal mixing coefficient was estimated by computing the growth of the second moment of a cloud of tracer. The zonal component of lateral mixing was found more than two times larger than the meridional component. The finding reflects the stretching effect of zonal jets prevalent in the tropical Atlantic Ocean. The application of conceptual jet model allowed to evaluate the mean zonal jet velocities which cause an enhancement of mixing in zonal direction. Additionally, the effective mixing coefficient was computed which indicated that zonal jets do not merely stretch the tracer patch in zonal directions, but increase mixing by increasing tracer gradients. The uncertainties of the estimates were inferred from synthetic particle release using a high resolution ocean circulation model. Finally, a large database of vertical oxygen profiles in oxygen minimum region and high precision diapycnal mixing estimates allowed for a good estimate of diapycnal oxygen supply through the upper boundary into the oxygen minimum zone. In comparison to conceptual model of oxygen consumption with depth, the diapycnal oxygen supply was estimated to be as large as about half of the lateral oxygen supply. Furthermore, in the oxygen minimum region, the separate shallow oxygen minimum was found at about 100 m depth. The finding indicates that there is no direct net vertical oxygen flux from the surface layer into the oxygen minimum zone. All of oxygen supply, hence, is associated with remote pathways.

Type: Thesis , NonPeerReviewed

Format: text

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