scholarly journals Overturning circulation, nutrient limitation, and warming in the Glacial North Pacific

2020 ◽  
Vol 6 (50) ◽  
pp. eabd1654
Author(s):  
J. W. B. Rae ◽  
W. R. Gray ◽  
R. C. J. Wills ◽  
I. Eisenman ◽  
B. Fitzhugh ◽  
...  
Keyword(s):  
North Pacific ◽  
Global Climate ◽  
Regional Climate ◽  
Climatic Conditions ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
The North ◽  
The Pacific ◽  
Meridional Overturning ◽  
And Migration

Although the Pacific Ocean is a major reservoir of heat and CO2, and thus an important component of the global climate system, its circulation under different climatic conditions is poorly understood. Here, we present evidence that during the Last Glacial Maximum (LGM), the North Pacific was better ventilated at intermediate depths and had surface waters with lower nutrients, higher salinity, and warmer temperatures compared to today. Modeling shows that this pattern is well explained by enhanced Pacific meridional overturning circulation (PMOC), which brings warm, salty, and nutrient-poor subtropical waters to high latitudes. Enhanced PMOC at the LGM would have lowered atmospheric CO2—in part through synergy with the Southern Ocean—and supported an equable regional climate, which may have aided human habitability in Beringia, and migration from Asia to North America.

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 Variability of Southern Ocean Transports

2018 ◽  
Vol 48 (11) ◽  
pp. 2667-2688
Author(s):  
Brady S. Ferster ◽  
Bulusu Subrahmanyam ◽  
Ichiro Fukumori ◽  
Ebenezer S. Nyadjro
Keyword(s):  
Southern Ocean ◽  
Global Climate ◽  
Potential Temperature ◽  
Volume Transport ◽  
Meridional Overturning Circulation ◽  
Lower Branch ◽  
Overturning Circulation ◽  
Salinity Transport ◽  
The Pacific ◽  
Meridional Overturning

AbstractThe Southern Ocean (SO) is capable of transporting vast amounts of salt, heat, and nutrients, which allows it to influence and regulate global climate. The variability of depth- and density-integrated volume transports in the SO is studied using the Estimating the Circulation and Climate of the Ocean (ECCO), version 4, release 3 (1992–2015), ocean state estimate. The estimate has a net eastward transport of 150.6 ± 5.5, 162.6 ± 7.4, and 148.2 ± 5.4 Sv (1 Sv ≡ 106 m3 s−1) between the Atlantic–Indian, Indian–Pacific, and Pacific–Atlantic basins, respectively. The time-mean meridional volume transport across 30°S in the Atlantic is estimated to be −1.4 ± 0.6 Sv, −14.4 ± 3.5 Sv in the Indian basin, and 15.5 ± 4.1 Sv in the Pacific, where negative values are southward. Trends in net volume transport between the basins are statistically insignificant. Within the water column, however, the middle and lower branches of the meridional overturning circulation have trends of −0.289 and 0.248 Sv decade−1 in the Atlantic basin. The Indian and Pacific basins have decreasing trends in their lower overturning cells. These results indicate increased overturning circulation within the lower branch in the South Atlantic and decreased lower branch circulation within the Indian and Pacific basins and have implications on the thermohaline-driven circulation. Using ECCO, we estimate a southward potential temperature transport of −176.2° ± 197.2°C Sv and salinity transport of −1.71 ± 22.4 psu Sv into the SO and indicate potential temperature transport is increasing by −15.0° ± 13.2°C Sv decade−1.

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.

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.

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>

scholarly journals Effects of the Pacific Diapycnal Mixing and Wind Stress on the Global and Pacific Meridional Overturning Circulation*

2005 ◽  
Vol 35 (10) ◽  
pp. 1876-1890 ◽  
Author(s):  
Ryo Furue ◽  
Masahiro Endoh
Keyword(s):  
Wind Stress ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Overturning Circulation ◽  
The North ◽  
Vertical Diffusivity ◽  
The Pacific ◽  
Meridional Overturning ◽  
The Pacific Ocean

Abstract Numerical experiments are conducted using an idealized basin to investigate roles of the deep vertical diffusivity and wind stress of the Pacific Ocean in the global and Pacific meridional overturning circulation. The Pacific middepth diffusivity is found to be enhancing the global meridional overturning circulation; when this part of diffusivity is reduced to the background value, not only is the layered circulation of the Pacific greatly weakened, but also the production of the North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) is significantly reduced. The deeper part of the Pacific diffusivity is found to be enhancing the production of the AABW in the model. When the wind stress is turned off in the Pacific, the deep meridional overturning circulation of the Pacific is reduced and the production of the NADW and AABW is also significantly reduced. This is likely due to the reduction of the wind-enhanced upwelling in the subpolar and equatorial regions. These results suggest the importance of the diapycnal diffusion and sea surface conditions in the Pacific not only to the circulation within the Pacific but also to the global meridional overturning circulation.

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