Seasonal Cycle and Annual Reversal of the Somali Current in an Eddy-Resolving Global Ocean Model

Abstract. In the framework of the INDESO (Infrastructure evelopment of Space Oceanography) project, an operational ocean forecasting system was developed to monitor the state of the Indonesian seas in terms of circulation, biogeochemistry and fisheries. This forecasting system combines a suite of numerical models connecting physical and biogeochemical variables to population dynamics of large marine predators (tunas). The physical/biogeochemical coupled component (INDO12BIO configuration) covers a large region extending from the western Pacific Ocean to the Eastern Indian Ocean at 1/12° resolution. The OPA/NEMO physical ocean model and the PISCES biogeochemical model are coupled in "on-line" mode without degradation in space and time. The operational global ocean forecasting system (1/4°) operated by Mercator Ocean provides the physical forcing while climatological open boundary conditions are prescribed for the biogeochemistry. This paper describes the skill assessment of the INDO12BIO configuration. Model skill is assessed by evaluating a reference hindcast simulation covering the last 8 years (2007–2014). Model results are compared to satellite, climatological and in situ observations. Diagnostics are performed on chlorophyll a, primary production, mesozooplankton, nutrients and oxygen. Model results reproduce the main characteristics of biogeochemical tracer distributions in space and time. The seasonal cycle of chlorophyll a is in phase with satellite observations. The northern and southern parts of the archipelago present a distinct seasonal cycle, with higher chlorophyll biomass in the southern (northern) part during SE (NW) monsoon. Nutrient and oxygen concentrations are correctly reproduced in terms of horizontal and vertical distributions. The biogeochemical content of water masses entering in the archipelago as well as the water mass transformation across the archipelago conserves realistic vertical distribution in Banda Sea and at the exit of the archipelago.

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The Global Ocean Forecast System, Version 3.0 (GOFS 3.0) or the Hybrid Coordinate Ocean Model (HYCOM)

10.21236/ada570050 ◽

2012 ◽

Author(s):

Frank L. Bub

Keyword(s):

Ocean Model ◽

Global Ocean ◽

Forecast System ◽

Hybrid Coordinate Ocean Model

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Effects of Ocean Biology on the Penetrative Radiation in a Coupled Climate Model

Journal of Climate ◽

10.1175/jcli3828.1 ◽

2006 ◽

Vol 19 (16) ◽

pp. 3973-3987 ◽

Cited By ~ 100

Author(s):

Patrick Wetzel ◽

Ernst Maier-Reimer ◽

Michael Botzet ◽

Johann Jungclaus ◽

Noel Keenlyside ◽

...

Keyword(s):

Seasonal Cycle ◽

Marine Biology ◽

Climate Model ◽

Global Climate ◽

Ocean Model ◽

Equatorial Pacific ◽

Shortwave Radiation ◽

Upper Ocean ◽

Biogeochemical Model ◽

Coupled Climate Model

Abstract The influence of phytoplankton on the seasonal cycle and the mean global climate is investigated in a fully coupled climate model. The control experiment uses a fixed attenuation depth for shortwave radiation, while the attenuation depth in the experiment with biology is derived from phytoplankton concentrations simulated with a marine biogeochemical model coupled online to the ocean model. Some of the changes in the upper ocean are similar to the results from previous studies that did not use interactive atmospheres, for example, amplification of the seasonal cycle; warming in upwelling regions, such as the equatorial Pacific and the Arabian Sea; and reduction in sea ice cover in the high latitudes. In addition, positive feedbacks within the climate system cause a global shift of the seasonal cycle. The onset of spring is about 2 weeks earlier, which results in a more realistic representation of the seasons. Feedback mechanisms, such as increased wind stress and changes in the shortwave radiation, lead to significant warming in the midlatitudes in summer and to seasonal modifications of the overall warming in the equatorial Pacific. Temperature changes also occur over land where they are sometimes even larger than over the ocean. In the equatorial Pacific, the strength of interannual SST variability is reduced by about 10%–15% and phase locking to the annual cycle is improved. The ENSO spectral peak is broader than in the experiment without biology and the dominant ENSO period is increased to around 5 yr. Also the skewness of ENSO variability is slightly improved. All of these changes lead to the conclusion that the influence of marine biology on the radiative budget of the upper ocean should be considered in detailed simulations of the earth’s climate.

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Response to Filchner-Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model. Part I: The ocean perspective

10.5194/os-2017-41 ◽

2017 ◽

Cited By ~ 1

Author(s):

Ralph Timmermann ◽

Sebastian Goeller

Keyword(s):

World Ocean ◽

Ice Sheet ◽

Coupled Model ◽

Freezing Temperature ◽

Ocean Model ◽

Climate Forcing ◽

Global Ocean ◽

Ice Shelf ◽

Marginal Seas ◽

Grounding Line

Abstract. A Regional Antarctic and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner-Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in-situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase of ice-shelf basal melt rates.

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Antarctic ice sheet fertilises the Southern Ocean

Biogeosciences ◽

10.5194/bg-11-2635-2014 ◽

2014 ◽

Vol 11 (10) ◽

pp. 2635-2643 ◽

Cited By ~ 53

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–0.2 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for seasonally very high in situ measurements of PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high measured marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

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M2 tidal dynamics in the Ross Sea

Antarctic Science ◽

10.1017/s0954102003001044 ◽

2003 ◽

Vol 15 (1) ◽

pp. 41-46 ◽

Cited By ~ 13

Author(s):

ROBIN ROBERTSON ◽

AIKE BECKMANN ◽

HARTMUT HELLMER

Keyword(s):

Continental Shelf ◽

Ross Sea ◽

Tidal Energy ◽

Ocean Model ◽

Internal Tides ◽

Global Ocean ◽

Tidal Dynamics ◽

Tidal Elevation ◽

Shelf Slope ◽

Continental Shelf Slope

In certain regions of the Southern Ocean, tidal energy is believed to foster the mixing of different water masses, which eventually contribute to the formation of deep and bottom waters. The Ross Sea is one of the major ventilation sites of the global ocean abyss and a region of sparse tidal observations. We investigated M2 tidal dynamics in the Ross Sea using a three-dimensional sigma coordinate model, the Regional Ocean Model System (ROMS). Realistic topography and hydrography from existing observational data were used with a single tidal constituent, the semi-diurnal M2. The model fields faithfully reproduced the major features of the tidal circulation and had reasonable agreement with ten existing tidal elevation observations and forty-two existing tidal current measurements. The differences were attributed primarily to topographic errors. Internal tides were generated at the continental shelf/slope break and other areas of steep topography. Strong vertical shears in the horizontal velocities occurred under and at the edges of the Ross Ice Shelf and along the continental shelf/slope break. Estimates of lead formation based on divergence of baroclinic velocities were significantly higher than those based on barotrophic velocities, reaching over 10% at the continental shelf/slope break.

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Genesis and Decay of Mesoscale Baroclinic Eddies in the Seasonally Ice-Covered Interior Arctic Ocean

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0054.1 ◽

2021 ◽

Vol 51 (1) ◽

pp. 115-129

Author(s):

Gianluca Meneghello ◽

John Marshall ◽

Camille Lique ◽

Pål Erik Isachsen ◽

Edward Doddridge ◽

...

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Seasonal Cycle ◽

Climate Models ◽

Baroclinic Instability ◽

Temporal Distribution ◽

Arctic Basin ◽

Ocean Model ◽

The Arctic ◽

Origin And Evolution

AbstractObservations of ocean currents in the Arctic interior show a curious, and hitherto unexplained, vertical and temporal distribution of mesoscale activity. A marked seasonal cycle is found close to the surface: strong eddy activity during summer, observed from both satellites and moorings, is followed by very quiet winters. In contrast, subsurface eddies persist all year long within the deeper halocline and below. Informed by baroclinic instability analysis, we explore the origin and evolution of mesoscale eddies in the seasonally ice-covered interior Arctic Ocean. We find that the surface seasonal cycle is controlled by friction with sea ice, dissipating existing eddies and preventing the growth of new ones. In contrast, subsurface eddies, enabled by interior potential vorticity gradients and shielded by a strong stratification at a depth of approximately 50 m, can grow independently of the presence of sea ice. A high-resolution pan-Arctic ocean model confirms that the interior Arctic basin is baroclinically unstable all year long at depth. We address possible implications for the transport of water masses between the margins and the interior of the Arctic basin, and for climate models’ ability to capture the fundamental difference in mesoscale activity between ice-covered and ice-free regions.

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Experimental and diagnostic protocol for the physical component of the CMIP6 Ocean Model Intercomparison Project (OMIP)

10.5194/gmd-2016-77 ◽

2016 ◽

Cited By ~ 4

Author(s):

Stephen M. Griffies ◽

Gokhan Danabasoglu ◽

Paul J. Durack ◽

Alistair J. Adcroft ◽

V. Balaji ◽

...

Keyword(s):

Sea Ice ◽

Global Climate ◽

Coupled Model ◽

Companion Paper ◽

Ocean Model ◽

Global Ocean ◽

Model Intercomparison ◽

Experimental Protocol ◽

Diagnostic Protocol ◽

Intercomparison Project

Abstract. The Ocean Model Intercomparison Project (OMIP) aims to provide a framework for evaluating, understanding, and improving the ocean and sea-ice components of global climate and earth system models contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses these aims in two complementary manners: (A) by providing an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing, (B) by providing a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) offering details for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows that of the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II have become the standard method to evaluate global ocean/sea-ice simulations and to examine mechanisms for forced ocean climate variability. The OMIP diagnostic protocol is relevant for any ocean model component of CMIP6, including the DECK (Diagnostic, Evaluation and Characterization of Klima experiments), historical simulations, FAFMIP (Flux Anomaly Forced MIP), C4MIP (Coupled Carbon Cycle Climate MIP), DAMIP (Detection and Attribution MIP), DCPP (Decadal Climate Prediction Project), ScenarioMIP (Scenario MIP), as well as the ocean-sea ice OMIP simulations. The bulk of this paper offers scientific rationale for saving these diagnostics.

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Antarctic Ice Sheet fertilises the Southern Ocean

Biogeosciences Discussions ◽

10.5194/bgd-10-12551-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 12551-12570 ◽

Cited By ~ 8

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–1.0 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for very high seasonally observed PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high observed marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

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Multi-grid algorithm for passive tracer transport in the NEMO ocean circulation model: a case study with the NEMO OGCM (version 3.6)

Geoscientific Model Development ◽

10.5194/gmd-13-5465-2020 ◽

2020 ◽

Vol 13 (11) ◽

pp. 5465-5483

Author(s):

Clément Bricaud ◽

Julien Le Sommer ◽

Gurvan Madec ◽

Christophe Calone ◽

Julie Deshayes ◽

...

Keyword(s):

Spatial Resolution ◽

Ocean Circulation ◽

Circulation Model ◽

Ocean Model ◽

Ocean Dynamics ◽

Global Ocean ◽

Passive Tracer ◽

Tracer Transport ◽

Ocean Circulation Model ◽

Grid Algorithm

Abstract. Ocean biogeochemical models are key tools for both scientific and operational applications. Nevertheless the cost of these models is often expensive because of the large number of biogeochemical tracers. This has motivated the development of multi-grid approaches where ocean dynamics and tracer transport are computed on grids of different spatial resolution. However, existing multi-grid approaches to tracer transport in ocean modelling do not allow the computation of ocean dynamics and tracer transport simultaneously. This paper describes a new multi-grid approach developed for accelerating the computation of passive tracer transport in the Nucleus for European Modelling of the Ocean (NEMO) ocean circulation model. In practice, passive tracer transport is computed at runtime on a grid with coarser spatial resolution than the hydrodynamics, which reduces the CPU cost of computing the evolution of tracers. We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and discuss its performance on the basis of a series of sensitivity experiments with global ocean model configurations. Our experiments confirm that the spatial resolution of hydrodynamical fields can be coarsened by a factor of 3 in both horizontal directions without significantly affecting the resolved passive tracer fields. Overall, the proposed algorithm yields a reduction by a factor of 7 of the overhead associated with running a full biogeochemical model like PISCES (with 24 passive tracers). Propositions for further reducing this cost without affecting the resolved solution are discussed.

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