AMOC response to changing resolution in the Finite-volumE Sea ice–Ocean Model

The Atlantic meridional overturning circulation (AMOC) is the most common diagnostics of numerical simulations. Generally it is computed as a streamfunction of zonally averaged flow along the constant depth. More rarely it is computed as zonally averaged along constant isopycnals. The latter computation, however, allows one to better distinguish between water masses and physical processes contributing to the meridional transport. We analyze the AMOC in global simulations based on the Finite-volumE Sea ice&#8211;Ocean Model (FESOM 2.0) using eddy permitting to eddy resolving configurations in the North Atlantic. We (1) split the AMOC computed in density space into the constitutes induced by surface buoyancy fluxes and cross isopycnal transformations, (2) identify the water masses which contribute to the formation of the North Atlantic Deep Water and (3) study the AMOC response to the permitting or resolving eddies in the North Atlantic ocean.

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The Influence of Ocean Convection Patterns on High-Latitude Climate Projections

Journal of Climate ◽

10.1175/3174.1 ◽

2004 ◽

Vol 17 (22) ◽

pp. 4316-4329 ◽

Cited By ~ 13

Author(s):

M. Schaeffer ◽

F. M. Selten ◽

J. D. Opsteegh ◽

H. Goosse

Keyword(s):

Sea Ice ◽

North Atlantic ◽

North Atlantic Ocean ◽

Surface Air Temperature ◽

Deep Ocean ◽

Ocean Model ◽

Climate Projections ◽

The North ◽

The North Atlantic ◽

Convection Patterns

Abstract The mean state and variability of deep convection in the ocean influence the North Atlantic climate. Using an ensemble experiment with a coupled atmosphere–ocean–sea ice model, it is shown that cooling and subdued warming areas can occur over the North Atlantic Ocean and adjacent landmasses under global warming. Different “present-day” convection patterns in the Greenland–Iceland–Norway (GIN) Sea result in different future surface-air temperature changes. At higher latitudes, the more effective positive sea ice feedback increases the likelihood of changes in convection causing a regional cooling that is larger than the warming brought about by the enhanced greenhouse effect. The modeled freshening of deep ocean layers in the North Atlantic in a time period preceding a reorganization of GIN Sea convection is consistent with recent observations. Low-frequency internal variability in the ocean model has relatively little impact on the response patterns.

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From small whirls to the global ocean: how eddies affect the Atlantic Meridional Overturning Circulation

10.5194/egusphere-egu2020-5644 ◽

2020 ◽

Author(s):

Caroline Katsman ◽

Nils Brüggemann ◽

Sotiria Georgiou ◽

Juan-Manuel Sayol Espana ◽

Stefanie Ypma ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Boundary Current ◽

The North ◽

The North Atlantic ◽

Density Space

In the North Atlantic Ocean, intense downward motions connect the upper and lower limbs of the Atlantic Meridional Overturning Circulation (AMOC). In addition, the AMOC also displays a pronounced signature in density space, with lighter waters moving northward and denser waters returning southward.While at first glance it is appealing to associate this sinking of water masses in the North Atlantic Ocean with the occurrence of the formation of dense water masses by deep convection, this is not correct: the net vertical motion over convection areas is small. The downward flow required to connect the upper and lower branches of the AMOC thus has to occur outside the deep convection areas. Indeed, earlier studies have pointed out theoretically that strong sinking can only occur close to continental boundaries, where ageostrophic processes play a role. However, observations clearly indicate that convected water masses formed in marginals seas constitute an important component of the lower limb of the AMOC.This apparent contradiction is explored in this presentation, by studying the overturning in the AMOC from a perspective in depth space (Eulerian downwelling) and density space (downwelling across isopycnals). Based on analyses of both a high-resolution global ocean model and dedicated process studies using idealized models we analyze the characteristics of the sinking, of diapycnal mixing, and investigate how these are linked.&#160;It appears that eddies play a crucial role for the overturning, both in depth space and density space. They control the characteristics of the yearly cycle of convection and restratification, the magnitude of the Eulerian sinking near continental boundaries, and steer the export of dense waters formed in the interior of the marginal seas via the boundary current system.These studies thus reveal a complex three-dimensional view on sinking, diapycnal water mass transformation and overturning in the North Atlantic Ocean, involving the boundary current, the interior and interactions with the eddy field. &#160;This implies that it is essential to resolve these eddies to be able to properly represent the overturning in depth and density space in the North Atlantic Ocean and its response to changing conditions in a future climate.

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Change in the North Atlantic circulation associated with the mid-Pleistocene transition

Climate of the Past ◽

10.5194/cp-14-1639-2018 ◽

2018 ◽

Vol 14 (11) ◽

pp. 1639-1651 ◽

Cited By ~ 3

Author(s):

Gloria M. Martin-Garcia ◽

Francisco J. Sierro ◽

José A. Flores ◽

Fátima Abrantes

Keyword(s):

North Atlantic ◽

Major Change ◽

Water Masses ◽

Meridional Overturning Circulation ◽

The Arctic ◽

North Atlantic Current ◽

The North ◽

Oceanic Fronts ◽

Surface Circulation ◽

The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37∘34.285′ N, 10∘7.562′ W; 2585 m b.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55∘ N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100 ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100 ky cycles.

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Distinct flavobacterial communities in contrasting water masses of the North Atlantic Ocean

The ISME Journal ◽

10.1038/ismej.2009.142 ◽

2010 ◽

Vol 4 (4) ◽

pp. 472-487 ◽

Cited By ~ 105

Author(s):

Paola R Gómez-Pereira ◽

Bernhard M Fuchs ◽

Cecilia Alonso ◽

Matthew J Oliver ◽

Justus E E van Beusekom ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Water Masses ◽

The North ◽

The North Atlantic

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Variability of the meridional overturning circulation of the North Atlantic: sensitivity to overflows of dense water masses

Ocean Dynamics ◽

10.1007/s10236-003-0088-x ◽

2004 ◽

Vol 54 (1) ◽

pp. 92-106 ◽

Cited By ~ 28

Author(s):

Jens-Olaf Beismann ◽

Bernard Barnier

Keyword(s):

North Atlantic ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Dense Water ◽

The North ◽

Meridional Overturning ◽

The North Atlantic

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Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

Biogeosciences ◽

10.5194/bg-15-2075-2018 ◽

2018 ◽

Vol 15 (7) ◽

pp. 2075-2090 ◽

Cited By ~ 21

Author(s):

Maribel I. García-Ibáñez ◽

Fiz F. Pérez ◽

Pascale Lherminier ◽

Patricia Zunino ◽

Herlé Mercier ◽

...

Keyword(s):

North Atlantic ◽

Water Mass ◽

Water Levels ◽

Water Masses ◽

Meridional Overturning Circulation ◽

Labrador Sea ◽

Intermediate Water ◽

North East ◽

The North ◽

The North Atlantic

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.

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Decadal-scale progression of the onset of Dansgaard–Oeschger warming events

Climate of the Past ◽

10.5194/cp-15-811-2019 ◽

2019 ◽

Vol 15 (2) ◽

pp. 811-825 ◽

Cited By ~ 8

Author(s):

Tobias Erhardt ◽

Emilie Capron ◽

Sune Olander Rasmussen ◽

Simon Schüpbach ◽

Matthias Bigler ◽

...

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Ice Core ◽

Sea Salt ◽

Meridional Overturning Circulation ◽

Proxy Records ◽

The North ◽

Decadal Scale ◽

The North Atlantic ◽

North Greenland

Abstract. During the last glacial period, proxy records throughout the Northern Hemisphere document a succession of rapid millennial-scale warming events, called Dansgaard–Oeschger (DO) events. A range of different mechanisms has been proposed that can produce similar warming in model experiments; however, the progression and ultimate trigger of the events are still unknown. Because of their fast nature, the progression is challenging to reconstruct from paleoclimate data due to the limited temporal resolution achievable in many archives and cross-dating uncertainties between records. Here, we use new high-resolution multi-proxy records of sea-salt (derived from sea spray and sea ice over the North Atlantic) and terrestrial (derived from the central Asian deserts) aerosol concentrations over the period 10–60 ka from the North Greenland Ice Core Project (NGRIP) and North Greenland Eemian Ice Drilling (NEEM) ice cores in conjunction with local precipitation and temperature proxies from the NGRIP ice core to investigate the progression of environmental changes at the onset of the warming events at annual to multi-annual resolution. Our results show on average a small lead of the changes in both local precipitation and terrestrial dust aerosol concentrations over the change in sea-salt aerosol concentrations and local temperature of approximately one decade. This suggests that, connected to the reinvigoration of the Atlantic meridional overturning circulation and the warming in the North Atlantic, both synoptic and hemispheric atmospheric circulation changes at the onset of the DO warming, affecting both the moisture transport to Greenland and the Asian monsoon systems. Taken at face value, this suggests that a collapse of the sea-ice cover may not have been the initial trigger for the DO warming.

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Predictability and Decadal Variability of the North Atlantic Ocean State Evaluated from a Realistic Ocean Model

Journal of Climate ◽

10.1175/jcli-d-16-0323.1 ◽

2017 ◽

Vol 30 (2) ◽

pp. 477-498 ◽

Cited By ~ 6

Author(s):

Florian Sévellec ◽

Alexey V. Fedorov

Keyword(s):

Atlantic Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

North Atlantic ◽

Decadal Variability ◽

North Atlantic Ocean ◽

Meridional Overturning Circulation ◽

Sea Surface ◽

The North ◽

The North Atlantic

This study investigates the excitation of decadal variability and predictability of the ocean climate state in the North Atlantic. Specifically, initial linear optimal perturbations (LOPs) in temperature and salinity that vary with depth, longitude, and latitude are computed, and the maximum impact on the ocean of these perturbations is evaluated in a realistic ocean general circulation model. The computations of the LOPs involve a maximization procedure based on Lagrange multipliers in a nonautonomous context. To assess the impact of these perturbations four different measures of the North Atlantic Ocean state are used: meridional volume and heat transports (MVT and MHT) and spatially averaged sea surface temperature (SST) and ocean heat content (OHC). It is shown that these metrics are dramatically different with regard to predictability. Whereas OHC and SST can be efficiently modified only by basin-scale anomalies, MVT and MHT are also strongly affected by smaller-scale perturbations. This suggests that instantaneous or even annual-mean values of MVT and MHT are less predictable than SST and OHC. Only when averaged over several decades do the former two metrics have predictability comparable to the latter two, which highlights the need for long-term observations of the Atlantic meridional overturning circulation in order to accumulate climatically relevant data. This study also suggests that initial errors in ocean temperature of a few millikelvins, encompassing both the upper and deep ocean, can lead to ~0.1-K errors in the predictions of North Atlantic sea surface temperature on interannual time scales. This transient error growth peaks for SST and OHC after about 6 and 10 years, respectively, implying a potential predictability barrier.

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Impacts of three types of solar geoengineering on the North Atlantic Meridional Overturning Circulation

10.5194/acp-2021-877 ◽

2021 ◽

Author(s):

Mengdie Xie ◽

John C. Moore ◽

Liyun Zhao ◽

Michael Wolovick ◽

Helene Muri

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Atlantic Meridional Overturning Circulation ◽

Arctic Sea Ice ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

The North ◽

Solar Geoengineering ◽

Meridional Overturning ◽

The North Atlantic

Abstract. Climate models simulate lower rates of North Atlantic heat transport under greenhouse gas climates than at present due to a reduction in the strength of the North Atlantic meridional overturning circulation (AMOC). Solar geoengineering whereby surface temperatures are cooled by reduction of incoming shortwave radiation may be expected to ameliorate this effect. We investigate this using six Earth System Models running scenarios from GeoMIP (Geoengineering model intercomparison project) in the cases of: i) reduction in the solar constant, mimicking dimming of the sun; ii) sulfate aerosol injection into the lower equatorial stratosphere; and iii) brightening of the ocean regions mimicking enhancing tropospheric cloud amounts. We find that despite across model differences, AMOC decreases are attributable to reduced air-ocean temperature differences, and reduced September Arctic sea ice extent, with no significant impact from changing surface winds or precipitation-evaporation. Reversing the surface freshening of the North Atlantic overturning regions caused by decreased summer sea ice sea helps to promote AMOC. Comparing the geoengineering types after normalizing them for the differences in top of atmosphere radiative forcing, we find that solar dimming is more effective than either marine cloud brightening or stratospheric aerosol injection.

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