Local Grid Refinement in New Zealand's Earth System Model: Tasman Sea Ocean Circulation Improvements and Super-Gyre Circulation Implications

The authors compare Community Earth System Model results to marine observations for the 1990s and examine climate change impacts on biogeochemistry at the end of the twenty-first century under two future scenarios (Representative Concentration Pathways RCP4.5 and RCP8.5). Late-twentieth-century seasonally varying mixed layer depths are generally within 10 m of observations, with a Southern Ocean shallow bias. Surface nutrient and chlorophyll concentrations exhibit positive biases at low latitudes and negative biases at high latitudes. The volume of the oxygen minimum zones is overestimated. The impacts of climate change on biogeochemistry have similar spatial patterns under RCP4.5 and RCP8.5, but perturbation magnitudes are larger under RCP8.5. Increasing stratification leads to weaker nutrient entrainment and decreased primary and export production (>30% over large areas). The global-scale decreases in primary and export production scale linearly with the increases in mean sea surface temperature. There are production increases in the high nitrate, low chlorophyll (HNLC) regions, driven by lateral iron inputs from adjacent areas. The increased HNLC export partially compensates for the reductions in non-HNLC waters (~25% offset). Stabilizing greenhouse gas emissions and climate by the end of this century (as in RCP4.5) will minimize the changes to nutrient cycling and primary production in the oceans. In contrast, continued increasing emission of CO2 (as in RCP8.5) will lead to reduced productivity and significant modifications to ocean circulation and biogeochemistry by the end of this century, with more drastic changes beyond the year 2100 as the climate continues to rapidly warm.

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Review for "Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model"

10.5194/cp-2019-151-rc1 ◽

2020 ◽

Author(s):

Anonymous

Keyword(s):

Ocean Circulation ◽

Middle Miocene ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Circulation Changes

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Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Climate of the Past ◽

10.5194/cp-17-2223-2021 ◽

2021 ◽

Vol 17 (5) ◽

pp. 2223-2254

Author(s):

Katherine A. Crichton ◽

Andy Ridgwell ◽

Daniel J. Lunt ◽

Alex Farnsworth ◽

Paul N. Pearson

Keyword(s):

Greenhouse Gas ◽

Ocean Circulation ◽

North Atlantic ◽

Middle Miocene ◽

Earth System Model ◽

System Model ◽

Global Ocean ◽

Earth System ◽

Cooling Trend

Abstract. Since the middle Miocene (15 Ma, million years ago), the Earth's climate has undergone a long-term cooling trend, characterised by a reduction in ocean temperatures of up to 7–8 ∘C. The causes of this cooling are primarily thought to be due to tectonic plate movements driving changes in large-scale ocean circulation patterns, and hence heat redistribution, in conjunction with a drop in atmospheric greenhouse gas forcing (and attendant ice-sheet growth and feedback). In this study, we assess the potential to constrain the evolving patterns of global ocean circulation and cooling over the last 15 Ma by assimilating a variety of marine sediment proxy data in an Earth system model. We do this by first compiling surface and benthic ocean temperature and benthic carbon-13 (δ13C) data in a series of seven time slices spaced at approximately 2.5 Myr intervals. We then pair this with a corresponding series of tectonic and climate boundary condition reconstructions in the cGENIE (“muffin” release) Earth system model, including alternative possibilities for an open vs. closed Central American Seaway (CAS) from 10 Ma onwards. In the cGENIE model, we explore uncertainty in greenhouse gas forcing and the magnitude of North Pacific to North Atlantic salinity flux adjustment required in the model to create an Atlantic Meridional Overturning Circulation (AMOC) of a specific strength, via a series of 12 (one for each tectonic reconstruction) 2D parameter ensembles. Each ensemble member is then tested against the observed global temperature and benthic δ13C patterns. We identify that a relatively high CO2 equivalent forcing of 1120 ppm is required at 15 Ma in cGENIE to reproduce proxy temperature estimates in the model, noting that this CO2 forcing is dependent on the cGENIE model's climate sensitivity and that it incorporates the effects of all greenhouse gases. We find that reproducing the observed long-term cooling trend requires a progressively declining greenhouse gas forcing in the model. In parallel to this, the strength of the AMOC increases with time despite a reduction in the salinity of the surface North Atlantic over the cooling period, attributable to falling intensity of the hydrological cycle and to lowering polar temperatures, both caused by CO2-driven global cooling. We also find that a closed CAS from 10 Ma to present shows better agreement between benthic δ13C patterns and our particular series of model configurations and data. A final outcome of our analysis is a pronounced ca. 1.5 ‰ decline occurring in atmospheric (and ca. 1 ‰ ocean surface) δ13C that could be used to inform future δ13C-based proxy reconstructions.

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The iron budget in ocean surface waters in the 20th and 21st centuries: projections by the Community Earth System Model version 1

Biogeosciences Discussions ◽

10.5194/bgd-10-8505-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 8505-8559 ◽

Cited By ~ 2

Author(s):

K. Misumi ◽

K. Lindsay ◽

J. K. Moore ◽

S. C. Doney ◽

F. O. Bryan ◽

...

Keyword(s):

Ocean Circulation ◽

Surface Waters ◽

Ocean Surface ◽

Equatorial Pacific ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Iron Supply ◽

Eastern Equatorial Pacific ◽

Community Earth System Model

Abstract. We investigated the simulated iron budget in ocean surface waters in the 1990s and 2090s using the Community Earth System Model version 1 and the Representative Concentration Pathway 8.5 future CO2 emission scenario. We assumed that exogenous iron inputs did not change during the whole simulation period; thus, iron budget changes were attributed solely to changes in ocean circulation and mixing in response to projected global warming. The model simulated the major features of ocean circulation and dissolved iron distribution for the present climate reasonably well. Detailed iron budget analysis revealed that roughly 70% of the iron supplied to surface waters in high-nutrient, low-chlorophyll (HNLC) regions is contributed by ocean circulation and mixing processes, but the dominant supply mechanism differed in each HNLC region: vertical mixing in the Southern Ocean, upwelling in the eastern equatorial Pacific, and deposition of iron-bearing dust in the subarctic North Pacific. In the 2090s, our model projected an increased iron supply to HNLC surface waters, even though enhanced stratification was predicted to reduce iron entrainment from deeper waters. This unexpected result could be attributed largely to changes in the meridional overturning and gyre-scale circulations that intensified the advective supply of iron to surface waters, especially in the eastern equatorial Pacific. The simulated primary and export productions in the 2090s decreased globally by 6% and 13%, respectively, whereas in the HNLC regions, they increased by 11% and 6%, respectively. Roughly half of the elevated production could be attributed to the intensified iron supply. The projected ocean circulation and mixing changes are consistent with recent observations of responses to the warming climate and with other Coupled Model Intercomparison Project model projections. We conclude that future ocean circulation and mixing changes will likely elevate the iron supply to HNLC surface waters and will potentially buffer future reductions in ocean productivity. External inputs of iron to the oceans are likely to be modified with climate change. Future work must incorporate robust estimates of these processes affecting the marine iron cycle.

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Emergent constraints on the Southern Ocean anthropogenic carbon and heat uptake

10.5194/egusphere-egu21-5336 ◽

2021 ◽

Author(s):

Thomas Frölicher ◽

Jens Terhaar ◽

Fortunat Joos

Keyword(s):

Southern Ocean ◽

Ocean Circulation ◽

Earth System Model ◽

System Model ◽

Carbon Uptake ◽

Earth System ◽

Excess Heat ◽

The Past ◽

Heat Uptake ◽

Anthropogenic Carbon

The Southern Ocean south of 30&#176;S, occupying about a third of global surface ocean area, accounts for approximately 40% of the past anthropogenic carbon uptake and about 75% of excess heat uptake by the ocean. However, Earth system models have large difficulties in reproducing the Southern Ocean circulation, and therefore its historical and future anthropogenic carbon and excess heat uptake. In the first part of the talk, we show that there exists a tight relation across two Earth system model ensembles (CMIP5 and CMIP6) between present-day sea surface salinity in the subtropical-polar frontal zone, the formation region of mode and intermediate waters, and the past and future anthropogenic carbon uptake in the Southern Ocean. By using observations and Earth system model results, we constrain the projected cumulative Southern Ocean anthropogenic carbon uptake over 1850-2100 by the CMIP6 model ensemble to 158 &#177; 6 Pg C under the low-emissions scenario SSP1-2.6 and to 279 &#177; 14 Pg C under the high emissions scenario SSP5-8.5. Our results suggest that the Southern Ocean anthropogenic carbon sink is 14-18% larger and 46-54% less uncertain than estimated by the unconstrained CMIP6 Earth system model results. The identified constraint demonstrated the importance of the freshwater cycle for the Southern Ocean circulation and carbon cycle. In the second part of the talk, potential emergent constraints for the Southern Ocean excess heat uptake will be discussed.

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Can ocean deoxygenation accelerate global warming via enhanced marine N2O production?

10.5194/egusphere-egu2020-18281 ◽

2020 ◽

Author(s):

Angela Landolfi ◽

Wolfgang Koeve

Keyword(s):

Global Warming ◽

Ocean Circulation ◽

Positive Feedback ◽

Emission Scenario ◽

Earth System Model ◽

System Model ◽

Metabolic Rates ◽

Earth System ◽

N2o Production ◽

Ocean Deoxygenation

Ocean warming is projected to cause marine deoxygenation, reduce solubility, affect ocean circulation and enhance metabolic rates over this century. These changes, affecting oceanic N2O production and emissions, have been suggested to potentially rise atmospheric N2O concentrations and increase the positive feedback to anthropogenic climate change.However, current global model projections all suggest a decline in marine N2O emissions under global warming but the processes leading to this decline are poorly constrained. Here, using an Earth system model of intermediate complexity, we disentangle the contribution of ocean deoxygenation and the direct and indirect warming effects on oceanic N2O production and emissions changes under RCP8.5 emission scenario. We find that ocean deoxygenation and warming-reduced N2O solubility do in fact increase oceanic N2O emissions, however this increase is overcompensated by ocean circulation slow-down and reduced export production, suggesting a neglectable N2O-emssion feedback to climate on centennial timescales.

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231Pa and 230Th in the ocean model of the Community Earth System Model (CESM1.3)

Geoscientific Model Development ◽

10.5194/gmd-10-4723-2017 ◽

2017 ◽

Vol 10 (12) ◽

pp. 4723-4742 ◽

Cited By ~ 11

Author(s):

Sifan Gu ◽

Zhengyu Liu

Keyword(s):

Ocean Circulation ◽

Activity Ratio ◽

Marine Ecosystem ◽

Deep Ocean ◽

Ocean Model ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Direct Model ◽

Community Earth System Model

Abstract. The sediment 231Pa ∕ 230Th activity ratio is emerging as an important proxy for deep ocean circulation in the past. In order to allow for a direct model–data comparison and to improve our understanding of the sediment 231Pa ∕ 230Th activity ratio, we implement 231Pa and 230Th in the ocean component of the Community Earth System Model (CESM). In addition to the fully coupled implementation of the scavenging behavior of 231Pa and 230Th with the active marine ecosystem module (particle-coupled: hereafter p-coupled), another form of 231Pa and 230Th have also been implemented with prescribed particle flux fields of the present climate (particle-fixed: hereafter p-fixed). The comparison of the two forms of 231Pa and 230Th helps to isolate the influence of the particle fluxes from that of ocean circulation. Under present-day climate forcing, our model is able to simulate water column 231Pa and 230Th activity and the sediment 231Pa ∕ 230Th activity ratio in good agreement with available observations. In addition, in response to freshwater forcing, the p-coupled and p-fixed sediment 231Pa ∕ 230Th activity ratios behave similarly over large areas of low productivity on long timescales, but can differ substantially in some regions of high productivity and on short timescales, indicating the importance of biological productivity in addition to ocean transport. Therefore, our model provides a potentially powerful tool to help the interpretation of sediment 231Pa ∕ 230Th reconstructions and to improve our understanding of past ocean circulation and climate changes.

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GEOCLIM reloaded (v 1.0): a new coupled earth system model for past climate change

Geoscientific Model Development ◽

10.5194/gmd-4-451-2011 ◽

2011 ◽

Vol 4 (2) ◽

pp. 451-481 ◽

Cited By ~ 13

Author(s):

S. Arndt ◽

P. Regnier ◽

Y. Goddéris ◽

Y. Donnadieu

Keyword(s):

Ocean Circulation ◽

Ocean Model ◽

Climatic Conditions ◽

Earth System Model ◽

System Model ◽

Global Ocean ◽

Earth System ◽

Element Cycling ◽

Global Ocean Circulation ◽

Steady State Simulation

Abstract. We present a new version of the coupled Earth system model GEOCLIM. The new release, GEOCLIM reloaded (v 1.0), links the existing atmosphere and weathering modules to a novel, temporally and spatially resolved model of the global ocean circulation, which provides a physical framework for a mechanistic description of the marine biogeochemical dynamics of carbon, nitrogen, phosphorus and oxygen. The ocean model is also coupled to a fully formulated, vertically resolved diagenetic model. GEOCLIM reloaded is thus a unique tool to investigate the short- and long-term feedbacks between climatic conditions, continental inputs, ocean biogeochemical dynamics and diagenesis. A complete and detailed description of the resulting Earth system model and its new features is first provided. The performance of GEOCLIM reloaded is then evaluated by comparing steady-state simulation under present-day conditions with a comprehensive set of oceanic data and existing global estimates of bio-element cycling in the pelagic and benthic compartments.

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Iron and sulfur cycling in the cGENIE.muffin Earth system model (v0.9.21)

Geoscientific Model Development ◽

10.5194/gmd-14-2713-2021 ◽

2021 ◽

Vol 14 (5) ◽

pp. 2713-2745

Author(s):

Sebastiaan J. van de Velde ◽

Dominik Hülse ◽

Christopher T. Reinhard ◽

Andy Ridgwell

Keyword(s):

Ocean Circulation ◽

Solid Phase ◽

Atmospheric Oxygen ◽

Reaction Rates ◽

Sulfur Cycle ◽

Earth System Model ◽

System Model ◽

Sensitivity Analyses ◽

Earth System ◽

Triassic Boundary

Abstract. The coupled biogeochemical cycles of iron and sulfur are central to the long-term biogeochemical evolution of Earth's oceans. For instance, before the development of a persistently oxygenated deep ocean, the ocean interior likely alternated between states buffered by reduced sulfur (“euxinic”) and buffered by reduced iron (“ferruginous”), with important implications for the cycles and hence bioavailability of dissolved iron (and phosphate). Even after atmospheric oxygen concentrations rose to modern-like values, the ocean episodically continued to develop regions of euxinic or ferruginous conditions, such as those associated with past key intervals of organic carbon deposition (e.g. during the Cretaceous) and extinction events (e.g. at the Permian–Triassic boundary). A better understanding of the cycling of iron and sulfur in an anoxic ocean, how geochemical patterns in the ocean relate to the available spatially heterogeneous geological observations, and quantification of the feedback strengths between nutrient cycling, biological productivity, and ocean redox requires a spatially resolved representation of ocean circulation together with an extended set of (bio)geochemical reactions. Here, we extend the “muffin” release of the intermediate-complexity Earth system model cGENIE to now include an anoxic iron and sulfur cycle (expanding the existing oxic iron and sulfur cycles), enabling the model to simulate ferruginous and euxinic redox states as well as the precipitation of reduced iron and sulfur minerals (pyrite, siderite, greenalite) and attendant iron and sulfur isotope signatures, which we describe in full. Because tests against present-day (oxic) ocean iron cycling exercises only a small part of the new code, we use an idealized ocean configuration to explore model sensitivity across a selection of key parameters. We also present the spatial patterns of concentrations and δ56Fe and δ34S isotope signatures of both dissolved and solid-phase Fe and S species in an anoxic ocean as an example application. Our sensitivity analyses show that the first-order results of the model are relatively robust against the choice of kinetic parameter values within the Fe–S system and that simulated concentrations and reaction rates are comparable to those observed in process analogues for ancient oceans (i.e. anoxic lakes). Future model developments will address sedimentary recycling and benthic iron fluxes back to the water column, together with the coupling of nutrient (in particular phosphate) cycling to the iron cycle.

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Local Grid Refinement in New Zealand's Earth System Model: Tasman Sea Ocean Circulation Improvements and Super-Gyre Circulation Implications