scholarly journals Does Net E − P Set a Preference for North Atlantic Sinking?

2012 ◽  
Vol 42 (11) ◽  
pp. 1781-1792 ◽  
Author(s):  
Selma E. Huisman ◽  
Henk A. Dijkstra ◽  
A. S. von der Heydt ◽  
W. P. M. de Ruijter
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
North Pacific ◽  
Multiple Equilibria ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Pacific

Abstract The present-day global meridional overturning circulation (MOC) with formation of North Atlantic Deep Water (NADW) and the absence of a deep-water formation in the North Pacific is often considered to be caused by the fact that the North Pacific basin is a net precipitative, while the North Atlantic is a net evaporative basin. In this paper, the authors study the effect of asymmetries in continent geometry and freshwater fluxes on the MOC both in an idealized two-dimensional model and in a global ocean model. This study approaches the problem from a multiple equilibria perspective, where asymmetries in external factors constrain the existence of steady MOC patterns. Both this multiple equilibria perspective and the fact that a realistic global geometry is used add new aspects to the problem. In the global model, it is shown that the Atlantic forced by net precipitation can have a meridional overturning circulation with northern sinking and a sea surface salinity that resembles the present-day salinity field. The model results are suggestive of the importance of factors other than the freshwater flux asymmetries, in particular continental asymmetries, in producing the meridional overturning asymmetry.

scholarly journals Impact of North Atlantic Freshwater Forcing on the Pacific Meridional Overturning Circulation under Glacial and Interglacial Conditions

2019 ◽  
Vol 32 (15) ◽  
pp. 4641-4659
Author(s):  
Hyo-Jeong Kim ◽  
Soon-Il An
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Overturning Circulation ◽  
The North ◽  
Freshwater Forcing ◽  
The Pacific ◽  
Meridional Overturning ◽  
The North Pacific

Abstract The Pacific meridional overturning circulation (PMOC) is not well known compared to the Atlantic meridional overturning circulation (AMOC), due to its absence today. However, considering PMOC development under different climate conditions shown by proxy and modeling studies, a better understanding of PMOC is appropriate to properly assess the past and future climate change associated with global ocean circulation. Here, the PMOC response to freshwater forcing in the North Atlantic (NA) is investigated using an Earth system model of intermediate complexity under glacial (i.e., Last Glacial Maximum) and interglacial [i.e., preindustrial with/without inflow through Bering Strait (BS)] conditions. The water hosing over NA led to the shutdown of the AMOC, which accompanied an active PMOC except for the preindustrial condition with the opening BS, indicating that the emergence of the PMOC is constrained by the freshwater inflow through the BS, which hinders its destabilization through enhancing ocean stratification. However, the closure of the BS itself could not explain how the sinking motion is maintained in the North Pacific. Here we found that various atmospheric and oceanic processes are involved to sustain the active PMOC. First, an atmospheric teleconnection associated with the collapsed AMOC encouraged the evaporation in the sinking region, causing buoyancy loss at the surface of the North Pacific. Second, the strengthened subpolar gyre transported saltier water northward, enhancing dense water formation. Finally, the vigorous upwelling in the Southern Ocean enabled a consistent mass supply to the sinking region, with the aid of enhanced westerlies.

scholarly journals Changes in the geometry and strength of the Atlantic Meridional Overturning Circulation during the last glacial (20–50 ka)

2016 ◽  
Author(s):  
Pierre Burckel ◽  
Claire Waelbroeck ◽  
Yiming Luo ◽  
Didier Roche ◽  
Sylvain Pichat ◽  
...  
Keyword(s):  
Flow Rate ◽  
North Atlantic ◽  
Deep Water ◽  
Water Mass ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract. We reconstruct the geometry and strength of the Atlantic Meridional Overturning Circulation during Heinrich Stadial 2 and three Greenland interstadials of the 20–50 ka period based on the comparison of new and published sedimentary 231Pa/230Th data with simulated sedimentary 231Pa/230Th. We show that the deep Atlantic circulation during these interstadials was very different from that of the Holocene. Northern-sourced waters likely circulated above 2500 m depth, with a flow rate lower than that of the present day North Atlantic Deep Water (NADW). Southern-sourced deep waters most probably flowed northwards below 4000 m depth into the North Atlantic basin, and then southwards as a return flow between 2500 and 4000 m depth. The flow rate of this southern-sourced deep water was likely larger than that of the modern Antarctic Bottom Water (AABW). At the onset of Heinrich Stadial 2, the structure of the AMOC significantly changed. The deep Atlantic was probably directly affected by a southern sourced water mass below 2500 m depth, while a slow southward flowing water mass originating from the North Atlantic likely influenced depths between 1500 and 2500 m down to the equator.

scholarly journals Causes of Interannual–Decadal Variability in the Meridional Overturning Circulation of the Midlatitude North Atlantic Ocean

2008 ◽  
Vol 21 (24) ◽  
pp. 6599-6615 ◽  
Author(s):  
Arne Biastoch ◽  
Claus W. Böning ◽  
Julia Getzlaff ◽  
Jean-Marc Molines ◽  
Gurvan Madec
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Overturning Circulation ◽  
Linear Character ◽  
The North ◽  
Basin Scale ◽  
Meridional Overturning

Abstract The causes and characteristics of interannual–decadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models [the Family of Linked Atlantic Model Experiments (FLAME)] and global ocean–ice models (ORCA), varying in resolution from medium to eddy resolving (½°–1/12°), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the midlatitude MOC variability by demonstrating that the anomalies of a (non–eddy resolving) hindcast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep-water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and midlatitude North Atlantic, this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30°–35°N, by internally induced (eddy) fluctuations.

Global Teleconnections in Response to a Shutdown of the Atlantic Meridional Overturning Circulation*

2008 ◽  
Vol 21 (12) ◽  
pp. 3002-3019 ◽  
Author(s):  
Lixin Wu ◽  
Chun Li ◽  
Chunxue Yang ◽  
Shang-Ping Xie
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Atlantic Meridional Overturning Circulation ◽  
Tropical Pacific ◽  
Meridional Overturning Circulation ◽  
Tropical Atlantic ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The Tropical Pacific

Abstract The global response to a shutdown of the Atlantic meridional overturning circulation (AMOC) is investigated by conducting a water-hosing experiment with a coupled ocean–atmosphere general circulation model. In the model, the addition of freshwater in the subpolar North Atlantic shuts off the AMOC. The intense cooling in the extratropical North Atlantic induces a widespread response over the global ocean. In the tropical Atlantic, a sea surface temperature (SST) dipole forms, with cooling north and warming on and south of the equator. This tropical dipole is most pronounced in June–December, displacing the Atlantic intertropical convergence zone southward. In the tropical Pacific, a SST dipole forms in boreal spring in response to the intensified northeast trades across Central America and triggering the development of an El Niño–like warming that peaks on the equator in boreal fall. In the extratropical North Pacific, a basinwide cooling of ∼1°C takes place, with a general westward increase in intensity. A series of sensitivity experiments are carried out to shed light on the ocean–atmospheric processes for these global teleconnections. The results demonstrate the following: ocean dynamical adjustments are responsible for the formation of the tropical Atlantic dipole; air–sea interaction over the tropical Atlantic is key to the tropical Pacific response; extratropical teleconnection from the North Atlantic is most important for the North Pacific cooling, with the influence from the tropics being secondary; and the subtropical North Pacific cooling propagates southwestward from off Baja California to the western and central equatorial Pacific through the wind–evaporation–SST feedback.

scholarly journals Changes in the geometry and strength of the Atlantic meridional overturning circulation during the last glacial (20–50 ka)

2016 ◽  
Vol 12 (11) ◽  
pp. 2061-2075 ◽  
Author(s):  
Pierre Burckel ◽  
Claire Waelbroeck ◽  
Yiming Luo ◽  
Didier M. Roche ◽  
Sylvain Pichat ◽  
...  
Keyword(s):  
Flow Rate ◽  
North Atlantic ◽  
Deep Water ◽  
Water Mass ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract. We reconstruct the geometry and strength of the Atlantic meridional overturning circulation during the Heinrich stadial 2 and three Greenland interstadials of the 20–50 ka period based on the comparison of new and published sedimentary 231Pa / 230Th data with simulated sedimentary 231Pa / 230Th. We show that the deep Atlantic circulation during these interstadials was very different from that of the Holocene. Northern-sourced waters likely circulated above 2500 m depth, with a flow rate lower than that of the present-day North Atlantic deep water (NADW). Southern-sourced deep waters most probably flowed northwards below 4000 m depth into the North Atlantic basin and then southwards as a return flow between 2500 and 4000 m depth. The flow rate of this southern-sourced deep water was likely larger than that of the modern Antarctic bottom water (AABW). Our results further show that during Heinrich stadial 2, the deep Atlantic was probably directly affected by a southern-sourced water mass below 2500 m depth, while a slow, southward-flowing water mass originating from the North Atlantic likely influenced depths between 1500 and 2500 m down to the equator.

Pacific Meridional Overturning Circulation during the Mid-Pliocene Warm Period

2020 ◽  
Author(s):  
Heather L. Ford ◽  
Natalie Burls ◽  
David Hodell
Keyword(s):  
North Pacific ◽  
Deep Ocean ◽  
Warm Period ◽  
Meridional Overturning Circulation ◽  
Future Climate Change ◽  
Intermediate Water ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning ◽  
The North Pacific

<p>Today in the North Pacific only intermediate water forms because of a strong halocline, but Pacific Meridional Overturning Circulation (PMOC) may have existed in the past. The mid-Pliocene warm period (3.264-3.025 Ma) is a time of sustained warmth where atmospheric carbon dioxide concentrations were similar to today and the northern hemisphere was relatively ice free – making it a pseudo-analogue for future climate change. North Pacific sedimentological and climate modeling evidence suggests a PMOC formed during this time.  To determine the spatial extent of a PMOC during the mid-Pliocene warm period, we constructed a depth transect of sites between 2400 to 3400 m water depth on Shatsky Rise by measuring stable isotopes of <em>Cibicidoides wuellerstorfi</em>. We compare these new results with previously published records and calculate anomalies using the OC3 water column and core-top data products. The δ<sup>13</sup>C spatial pattern is consistent with a modest PMOC of intermediate depth (core ~2000 m) extending to the equator during the mid-Pliocene warm period. Ventilation of the North Pacific by a PMOC has broad implications for deep ocean carbon storage as the North Pacific contains the oldest, carbon-rich waters today. Future work will include minor and trace element analyses to determine the temperature and carbon characteristics of the PMOC water mass and comparisons with PlioMIP modeling outputs.</p>

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