A potential feedback loop underlying glacial-interglacial cycles

AbstractThe sawtooth-patterned glacial-interglacial cycles in the Earth’s atmospheric temperature are a well-known, though poorly understood phenomenon. Pinpointing the relevant mechanisms behind these cycles will not only provide insights into past climate dynamics, but also help predict possible future responses of the Earth system to changing CO$$_2$$ 2 levels. Previous work on this phenomenon suggests that the most important underlying mechanisms are interactions between marine biological production, ocean circulation, temperature and dust. So far, interaction directions (i.e., what causes what) have remained elusive. In this paper, we apply Convergent Cross-Mapping (CCM) to analyze paleoclimatic and paleoceanographic records to elucidate which mechanisms proposed in the literature play an important role in glacial-interglacial cycles, and to test the directionality of interactions. We find causal links between ocean ventilation, biological productivity, benthic $$\delta ^{18}$$ δ 18 O and dust, consistent with some but not all of the mechanisms proposed in the literature. Most importantly, we find evidence for a potential feedback loop from ocean ventilation to biological productivity to climate back to ocean ventilation. Here, we propose the hypothesis that this feedback loop of connected mechanisms could be the main driver for the glacial-interglacial cycles.

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Tuning ocean biogeochemistry in the Earth system — insights from the HAMburg Ocean Carbon Cycle model

10.5194/egusphere-egu21-14984 ◽

2021 ◽

Author(s):

Fatemeh Chegini ◽

Lennart Ramme ◽

Jöran März ◽

Katharina Six ◽

Daniel Burt ◽

...

Keyword(s):

Ocean Circulation ◽

Circulation Model ◽

Global Ocean ◽

Earth System ◽

Carbon Cycle Model ◽

Tuning Parameters ◽

The Earth ◽

Ocean Biogeochemistry ◽

Ocean Carbon ◽

Model Ocean

<div>Ocean biogeochemistry as part of the Earth system impacts the uptake of atmospheric CO<sub>2</sub> and storage of carbon in the ocean. In the ICON-O (Icosahedral non-hydrostatic general circulation model) ocean model, ocean biogeochemistry is represented by the HAMburg Ocean Carbon Cycle model (HAMOCC; Ilyina et al. 2013, Mauritsen et al. 2019, Maerz et al. 2020). Here, we present the results of an ongoing effort to tune HAMOCC (i.e. adapt parameters within the uncertainty range) to accommodate the ocean circulation simulated by ICON-O.</div><div>The tuning of biogeochemical models, including HAMOCC, has previously been an iterative, and a rather random process combining expert knowledge and a suite of parameter testings. A documented, systematic procedure, describing how to tune these models is lacking. Therefore, while tuning HAMOCC in ICON-O, we aim at filling this gap by structuring the process and documenting the steps taken to tune a biogeochemistry model in a global general ocean circulation model.</div><div>The ocean circulation has a large impact on the distribution of biogeochemical tracers, as biases in the circulation will, for example, impact the upwelling of nutrients or the CO<sub>2</sub> exchange with the atmosphere. We investigate the impact of physical parameterization such as the Gent-McWilliam eddy parameterization and the vertical mixing scheme on the choice of HAMOCC tuning parameters. We then compare the spatial distribution of major state variables such as nutrients and alkalinity to observational data ( WOA; Garcia et al 2013, GLODAP; Key et al 2004) and evaluate the key tendencies such as CO<sub>2</sub> surface fluxes and attenuation of particulate organic matter fluxes. Furthermore, we discuss the tuning steps, choices of the tuning parameters and their impact on the simulated biogeochemistry. The envisioned outcome of this work is a tuned ocean biogeochemistry component for the here used ICON-O model and a more generalized tuning procedure that can be applied to other models or HAMOCC in different model configurations (coupled runs, different resolution).</div><div>&#160;</div><p>Garcia, H. E., et al. 2014: World Ocean Atlas 2013, NOAA Atlas NESDIS 76, Volume4: Dissolved Inorganic Nutrients (phosphate, nitrate, silicate), 25pp.</p><p>lyina, T., et al. 2013: Global ocean biogeochemistry model HAMOCC: Model architecture and performance as component of the MPI-Earth system model in different CMIP5 experimental realizations, J. Adv. Model. Earth Sy., 5, .</p><p>Key, R., et al. 2004: A global ocean carbon climatology: Results from Global Data Analysis Project, Global Biogeochem. Cycles, 18, 4, https://doi.org/10.1029/2004GB002247.</p><p>Maerz et al. 2020: Microstructure and composition of marine aggregates as co-determinants for vertical particulate organic carbon transfer in the global ocean, Biogeosciences, 17, 7, https://doi.org/10.5194/bg-17-1765-2020.</p><p>Mauritsen, T., et al. 2019: Developments in the MPI-M Earth System Model version 1.2 (MPI-ESM1.2) and Its Response to Increasing CO<sub>2</sub>, J. Adv. Model. Earth Sy., 11, https://doi.org/10.1029/2018MS001400.</p><p>&#160;</p>

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Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

Biogeosciences ◽

10.5194/bg-16-1865-2019 ◽

2019 ◽

Vol 16 (9) ◽

pp. 1865-1881 ◽

Cited By ~ 4

Author(s):

Ulrike Löptien ◽

Heiner Dietze

Keyword(s):

Ocean Circulation ◽

Biogeochemical Cycles ◽

Model Parameters ◽

Climate Projections ◽

Ocean Mixing ◽

Earth System ◽

Feedback Mechanisms ◽

The Earth ◽

Model Component ◽

Warming World

Abstract. Anthropogenic emissions of greenhouse gases such as CO2 and N2O impinge on the Earth system, which in turn modulates atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and, at times, counterintuitive. So-called Earth system models have recently matured to standard tools tailored to assess these feedback mechanisms in a warming world. Applications for these models range from being targeted at basic process understanding to the assessment of geo-engineering options. A problem endemic to all these applications is the need to estimate poorly known model parameters, specifically for the biogeochemical component, based on observational data (e.g., nutrient fields). In the present study, we illustrate with an Earth system model that through such an approach biases and other model deficiencies in the physical ocean circulation model component can reciprocally compensate for biases in the pelagic biogeochemical model component (and vice versa). We present two model configurations that share a remarkably similar steady state (based on ad hoc measures) when driven by historical boundary conditions, even though they feature substantially different configurations (parameter sets) of ocean mixing and biogeochemical cycling. When projected into the future the similarity between the model responses breaks. Metrics such as changes in total oceanic carbon content and suboxic volume diverge between the model configurations as the Earth warms. Our results reiterate that advancing the understanding of oceanic mixing processes will reduce the uncertainty of future projections of oceanic biogeochemical cycles. Related to the latter, we suggest that an advanced understanding of oceanic biogeochemical cycles can be used for advancements in ocean circulation modules.

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How does ocean ventilation change under global warming?

Ocean Science Discussions ◽

10.5194/osd-3-805-2006 ◽

2006 ◽

Vol 3 (4) ◽

pp. 805-826

Author(s):

A. Gnanadesikan ◽

J. L. Russell ◽

F. Zeng

Keyword(s):

Global Warming ◽

Mixed Layer ◽

Climate Models ◽

Upper Ocean ◽

Earth System ◽

Ocean Ventilation ◽

The Earth ◽

Biological Cycling ◽

Coupled Climate Models ◽

Low Latitudes

Abstract. Since the upper ocean takes up much of the heat added to the earth system by anthropogenic global warming, one would expect that global warming would lead to an increase in stratification and a decrease in the ventilation of the ocean interior. However, multiple simulations in global coupled climate models using an ideal age tracer which is set to zero in the mixed layer and ages at 1 yr/yr outside this layer show that the intermediate depths in the low latitudes become younger under global warming. This paper reconciles these apparently contradictory trends, showing that a decrease in upwelling of old water from below is responsible for the change. Implications for global biological cycling are considered.

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Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

10.5194/bg-2018-491 ◽

2018 ◽

Author(s):

Ulrike Löptien ◽

Heiner Dietze

Keyword(s):

Ocean Circulation ◽

Biogeochemical Cycles ◽

Earth System Model ◽

System Model ◽

Model Parameters ◽

Ocean Mixing ◽

Earth System ◽

Feedback Mechanisms ◽

The Earth ◽

Model Component

Abstract. Anthropogenic emissions of greenhouse gases such as CO2 and N2O impinge on the earth system which, in turn, modulates atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and, at times, counterintuitive. So-called Earth System Models have recently matured to standard tools tailored to assess these feedback mechanisms in a warming world. Respective model applications range from being targeted at basic process understanding to the assessment of geo-engineering options. A problem endemic to all these applications is the need to estimate poorly known model parameters, specifically for the biogeochemical component, based on observational data (e.g. nutrient fields). In the present study, we illustrate that by such an approach biases in the physical ocean-circulation model component of an Earth System Model can reciprocally compensate biases in the pelagic biogeochemical model component (and vice versa). We present two configurations of an Earth System Model that share a remarkably similar steady state (based on ad-hoc measures) when driven by historical boundary conditions, even though they feature substantially different configurations (sets) of ocean-mixing and biogeochemical cycling (model parameters). When projected into the future the similarity between the model responses breaks. Metrics like total oceanic carbon content and suboxic volume diverge in the model configurations as the Earth warms. Our results reiterate that advancing the understanding of oceanic mixing processes will reduce the uncertainty of future projections of the oceanic biogeochemical cycles. Vice versa, we suggest that an advanced understanding of oceanic biogeochemical cycles can be used for advancements in the ocean circulation modules.

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A pause in Southern Hemisphere circulation trends due to the Montreal Protocol

10.5194/egusphere-egu21-611 ◽

2021 ◽

Author(s):

Antara Banerjee ◽

John C. Fyfe ◽

Lorenzo M. Polvani ◽

Darryn Waugh ◽

Kai-Lan Chang

Keyword(s):

Southern Hemisphere ◽

Ocean Circulation ◽

Stratospheric Ozone ◽

Southern Annular Mode ◽

Montreal Protocol ◽

Hadley Cell ◽

Positive Trend ◽

Earth System ◽

Near Surface ◽

The Earth

<p>Observations show robust near-surface trends in Southern Hemisphere tropospheric circulation towards the end of the twentieth century, including a poleward shift in the mid-latitude jet, a positive trend in the Southern Annular Mode and an expansion of the Hadley cell. It has been established that these trends were driven by ozone depletion in the Antarctic stratosphere due to emissions of ozone-depleting substances. Here we show that these widely reported circulation trends paused, or slightly reversed, around the year 2000. Using a pattern-based detection and attribution analysis of atmospheric zonal wind, we show that the pause in circulation trends is forced by human activities, and has not occurred owing only to internal or natural variability of the climate system. Furthermore, we demonstrate that stratospheric ozone recovery, resulting from the Montreal Protocol, is the key driver of the pause. Because pre-2000 circulation trends have affected precipitation, and potentially ocean circulation and salinity, we anticipate that a pause in these trends will have wider impacts on the Earth system. Signatures of the effects of the Montreal Protocol and the associated stratospheric ozone recovery might therefore manifest, or have already manifested, in other aspects of the Earth system.</p>

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A Novel Approach to Carrying Capacity: From a priori Prescription to a posteriori Derivation Based on Underlying Mechanisms and Dynamics

Annual Review of Earth and Planetary Sciences ◽

10.1146/annurev-earth-053018-060428 ◽

2020 ◽

Vol 48 (1) ◽

pp. 657-683

Author(s):

Safa Mote ◽

Jorge Rivas ◽

Eugenia Kalnay

Keyword(s):

Carrying Capacity ◽

Fossil Fuels ◽

A Priori ◽

Logistic Equation ◽

Earth System ◽

A Posteriori ◽

Human System ◽

The Earth ◽

Novel Approach ◽

Underlying Mechanisms

The Human System is within the Earth System. They should be modeled bidirectionally coupled, as they are in reality. The Human System is rapidly expanding, mostly due to consumption of fossil fuels (approximately one million times faster than Nature accumulated them) and fossil water. This threatens not only other planetary subsystems but also the Human System itself. Carrying Capacity is an important tool to measure sustainability, but there is a widespread view that Carrying Capacity is not applicable to humans. Carrying Capacity has generally been prescribed a priori, mostly using the logistic equation. However, the real dynamics of human population and consumption are not represented by this equation or its variants. We argue that Carrying Capacity should not be prescribed but should insteadbe dynamically derived a posteriori from the bidirectional coupling of Earth System submodels with the Human System model. We demonstrate this approach with a minimal model of Human–Nature interaction (HANDY). ▪ The Human System is a subsystem of the Earth System, with inputs (resources) from Earth System sources and outputs (waste, emissions) to Earth System sinks. ▪ The Human System is growing rapidly due to nonrenewable stocks of fossil fuels and water and threatens the sustainability of the Human System and to overwhelm the Earth System. ▪ Carrying Capacity has been prescribed a priori and using the logistic equation, which does not represent the dynamics of the Human System. ▪ Our new approach to human Carrying Capacity is derived from dynamically coupled Earth System–Human System models and can be used to estimate the sustainability of the Human System.

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