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The Fate of Oxygen in the Ocean and Its Sensitivity to Local Changes in Biological Production

Abstract. 

"We investigate the sensitivity of the oxygen content and true oxygen utilization of key low-oxygen regions Ω to pointwise changes in biological production. To understand how the combined water and biogenic particle transport controls the sensitivity patterns and the fate of oxygen in the ocean, we develop new relationships that link the steady-state oxygen content and deficit of Ω to the downstream and upstream oxygen utilization rate (OUR), respectively. We find that the amount of oxygen from Ω that will be lost per unit volume at point r is linked to OUR(r) through the mean oxygen age accumulated in Ω. [...]".

 

Source: Wiley Online Library 
Authors: Mark Holzer
DOI: https://doi.org/10.1029/2022JC018802

Read the full article here.


Sensitivity of Global Ocean Deoxygenation to Vertical and Isopycnal Mixing in an Ocean Biogeochemistry Model

Abstract. 

"Large-scale loss of oxygen under global warming is termed “ocean deoxygenation” and is caused by the imbalance between physical supply and biological consumption of oxygen in the ocean interior. Significant progress has been made in the theoretical understanding of ocean deoxygenation; however, many questions remain unresolved. The oxygen change in the tropical thermocline is poorly understood, with diverging projections among different models. Physical oxygen supply is controlled by a suite of processes that transport oxygen-rich surface waters into the interior ocean, which is expected to weaken due to increasing stratification under global warming. [...]".

 

Source: Wiley Online Library

Authors: Taka Ito et al.

DOI: https://doi.org/10.1029/2021GB007151

Read the full article here.


Sensitivity of asymmetric oxygen minimum zones to mixing intensity and stoichiometry in the tropical Pacific using a basin-scale model

Abstract.

"The tropical Pacific Ocean holds the two largest oxygen minimum zones (OMZs) in the world's oceans, showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the Equator. However, many models have difficulties in reproducing the observed asymmetric OMZs in the tropical Pacific. Here, we apply a fully coupled basin-scale model to evaluate the impacts of stoichiometry and the intensity of vertical mixing on the dynamics of OMZs in the tropical Pacific. We first utilize observational data of dissolved oxygen (DO) to calibrate and validate the basin-scale model. Our model experiments demonstrate that enhanced vertical mixing combined with a reduced O:C utilization ratio can significantly improve our model capability of reproducing the asymmetric OMZs. Our study shows that DO concentration is more sensitive to biological processes over 200–400 m but to physical processes below 400 m. [...]".

 

Source: Geoscientific Model Development 

Authors: Kai Wang et al. 

DOI: https://doi.org/10.5194/gmd-15-1017-2022 

Read the full article here.


Biogeochemical feedbacks may amplify ongoing and future ocean deoxygenation: a case study from the Peruvian oxygen minimum zone

Abstract.

"A new box model is employed to simulate the oxygen-dependent cycling of nutrients in the Peruvian oxygen minimum zone (OMZ). Model results and data for the present state of the OMZ indicate that dissolved iron is the limiting nutrient for primary production and is provided by the release of dissolved ferrous iron from shelf and slope sediments. Most of the removal of reactive nitrogen occurs by anaerobic oxidation of ammonium where ammonium is delivered by aerobic organic nitrogen degradation. Model experiments simulating the effects of ocean deoxygenation and warming show that the productivity of the Peruvian OMZ will increase due to the enhanced release of dissolved iron from shelf and slope sediments. A positive feedback loop rooted in the oxygen-dependent benthic iron release amplifies, both, the productivity rise and oxygen decline in ambient bottom waters. [...]". 

 

Source: Biogeochemistry

Authors: Klaus Wallmann et al.

DOI: https://doi.org/10.1007/s10533-022-00908-w 

Read the full article here.


Impacts of Ocean Currents on the South Indian Ocean Extratropical Storm Track through the Relative Wind Effect

Abstract.

"This study examines the role of the relative wind (RW) effect (wind relative to ocean current) in the regional ocean circulation and extratropical storm track in the south Indian Ocean. Comparison of two high-resolution regional coupled model simulations with and without the RW effect reveals that the most conspicuous ocean circulation response is the significant weakening of the overly energetic anticyclonic standing eddy off Port Elizabeth, South Africa, a biased feature ascribed to upstream retroflection of the Agulhas Current (AC).[...]"

 

Source: AMS- American Meteorological Sciety 
Authors: Hyodae Seo et al.
DOI: https://doi.org/10.1175/JCLI-D-21-0142.1

Read the full article here.


Variability-based constraint on ocean primary production models

Abstract.

"Primary production (PP) is fundamental to ocean biogeochemistry, but challengingly variable. Satellite models are unique tools for investigating PP, but are difficult to compare and validate because of the scale separation between in situ and remote measurements, which also are rarely coincident. Here, I argue that satellite estimates should be log-skew-normally distributed, because of this scale separation and because PP measurements are log-normally distributed.[...]"

 

Source: ASLO- Association for the Sciences of the Limnology and Oceanography 
Authors: B. B. Cael et al.
DOI: https://doi.org/10.1002/lol2.10196

Read the full article here.


Investigating the Roles of External Forcing and Ocean Circulation on the Atlantic Multidecadal SST Variability in a Large Ensemble Climate Model Hiera

Abstract.

"This paper attempts to enhance our understanding of the causes of Atlantic Multidecadal Variability, the AMV. Following the literature, we define the AMV as the SST averaged over the North Atlantic basin, linearly detrended and low-pass filtered. There is an ongoing debate about the drivers of the AMV, which include internal variability generated from the ocean or atmosphere (or both), and external radiative forcing. We test the role of these factors in explaining the time history, variance, and spatial pattern of the AMV using[...]"

 

Source: American Meteorological Soceity 
Authors: Lisa N. Murphy et al.
DOI: https://doi.org/10.1175/JCLI-D-20-0167.1

Read the full article here.

 

 


Sensitivity of 21st-century projected ocean new production changes to idealized biogeochemical model structure

Abstract.

"While there is agreement that global warming over the 21st century is likely to influence the biological pump, Earth system models (ESM) display significant divergence in their projections of future new production. This paper quantifies and interprets the sensitivity of projected changes in new production in an idealized global ocean-biogeochemistry model. The model includes two tracers that explicitly represent nutrient transport, light- and nutrient-limited nutrient uptake by the ecosystem (new production), and export via sinking organic particles. Globally, new production declines with warming due to reduced surface nutrient availability, as expected. However, the magnitude[...]"

 

Source: Biogeosciences
Authors: Genevieve Jay Brett et al.
DOI: https://doi.org/10.5194/bg-2020-479

Read the full article here.


Oceanic and atmospheric methane cycling in the cGENIE Earth system model

Abstract.

"The methane (CH4) cycle is a key component of the Earth system that links planetary climate, biological metabolism, and the global biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However, currently lacking is a numerical model capable of simulating a diversity of environments in the ocean where CH4 can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth’s CH4 cycle but also to probe CH4 cycling and associated climate impacts under the very low-O2 conditions characteristic of most of Earth history and likely widespread on other Earth-like planets. [...]"

Source: Geoscientific Model Development
Authors: Christopher T. Reinhard et al.
DOI: 10.5194/gmd-2020-32

Read the full article here.


Tracer Versus Observationally-Derived Constraints on Ocean Mixing Parameters in an Adjoint-Based Data Assimilation Framework

Abstract.

"This study investigates the possibility of using an ocean parameter and state estimation framework to improve knowledge of mixing parameters in the global ocean. Multiple sources of information about two ocean mixing parameters, the diapycnal diffusivity and the Redi coefficient, are considered. It is first established that diapycnal diffusivities derived from multiple observational data sets with a strain-based parameterization of finescale hydrographic structure can be used to ameliorate model biases in diapycnal diffusivities from the Estimating the Circulation & Climate of the Ocean (ECCO) framework and the GEOS-5 coupled Earth system model. [...]"

Source: Earth and Space Science Open Archive
Authors: David Trossman et al.
DOI: 10.1002/essoar.10502123.1

Read the full article here.


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