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 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 Millennial-scale variations in sedimentary oxygenation in the western subtropical North Pacific and its links to North Atlantic climate

2020 ◽  
Vol 16 (1) ◽  
pp. 387-407 ◽  
Author(s):  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Selvaraj Kandasamy ◽  
Xun Gong ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Deep Ocean ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Intermediate Water ◽  
The North ◽  
Geochemical Parameters ◽  
The North Pacific ◽  
Millennial Scale

Abstract. The deep-ocean carbon cycle, especially carbon sequestration and outgassing, is one of the mechanisms to explain variations in atmospheric CO2 concentrations on millennial and orbital timescales. However, the potential role of subtropical North Pacific subsurface waters in modulating atmospheric CO2 levels on millennial timescales is poorly constrained. An increase in the respired CO2 concentration in the glacial deep-ocean due to biological pump generally corresponds to deoxygenation in the ocean interior. This link thus offers a chance to study oceanic ventilation and coeval export productivity based on redox-controlled sedimentary geochemical parameters. Here, we investigate a suite of geochemical proxies in a sediment core from the Okinawa Trough to understand sedimentary oxygenation variations in the subtropical North Pacific over the last 50 000 years (50 ka). Our results suggest that enhanced mid-depth western subtropical North Pacific (WSTNP) sedimentary oxygenation occurred during cold intervals and after 8.5 ka, while oxygenation decreased during the Bölling-Alleröd (B/A) and Preboreal. The enhanced oxygenation during cold spells is linked to the North Pacific Intermediate Water (NPIW), while interglacial increase after 8.5 ka is linked to an intensification of the Kuroshio Current due to strengthened northeast trade winds over the tropics. The enhanced formation of the NPIW during Heinrich Stadial 1 (HS1) was likely driven by the perturbation of sea ice formation and sea surface salinity oscillations in the high-latitude North Pacific. The diminished sedimentary oxygenation during the B/A due to a decreased NPIW formation and enhanced export production, indicates an expansion of the oxygen minimum zone in the North Pacific and enhanced CO2 sequestration at mid-depth waters, along with the termination of atmospheric CO2 concentration increase. We attribute the millennial-scale changes to an intensified NPIW and enhanced abyss flushing during deglacial cold and warm intervals, respectively, closely related to variations in North Atlantic Deep Water formation.

Persistent millennial-scale links between North Pacific intermediate-water ventilation and North Atlantic Climate during the deglaciation and last glaciation

2020 ◽  
Author(s):  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Yuan-Pin Chang ◽  
Min-Te Chen ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Meridional Overturning Circulation ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
Last Glaciation ◽  
The North Pacific ◽  
Millennial Scale

<p>The deep ocean carbon cycle, especially carbon sequestration and outgassing, is one of the mechanisms to explain variations in atmospheric CO<sub>2</sub> concentrations on millennial and orbital timescales. However, the potential role of subtropical North Pacific subsurface waters in modulating atmospheric CO<sub>2</sub> levels on millennial timescales is poorly constrained. Here, we investigate a suite of geochemical proxies in a sediment core from the northern and middle Okinawa Trough to understand variations in intermediate-water ventilation of the subtropical North Pacific over the last 50,000 years (50 ka). Our results suggest that enhanced mid-depth western subtropical North Pacific (WSTNP) sedimentary oxygenation occurred during cold intervals during the last deglaciation and last glaciation, while oxygenation decreased during the Bölling-Alleröd (B/A) and warm interstadials. The enhanced oxygenation during cold spells is linked to the intensified North Pacific Intermediate Water (NPIW), while interglacial increase after 8.5 ka is linked to an intensification of the Kuroshio Current due to strengthened northeast trade winds over the tropics. The enhanced formation of NPIW during Heinrich Stadials was likely driven by the perturbation of sea ice formation and sea surface salinity oscillations in high-latitude North Pacific. The diminished sedimentary oxygenation during the B/A and interstadials due to decreased NPIW formation and enhanced export production, indicates an expansion of oxygen minimum zone in the North Pacific and enhanced CO<sub>2</sub> sequestration at mid-depth waters. We attribute the millennial-scale changes to intensified NPIW and enhanced abyss flushing during deglacial cold and warm intervals, respectively, closely related to variations in North Atlantic Deep Water formation. Out study extends the millennial-scale links between ventilation in the subtropical North Pacific Ocean and the Atlantic Climate into the last glaciations, highlighting the key roles of Atlantic Meridional Overturning Circulation in regulating the North Pacific environment at millennial timescales. Note: Financial support was provided by the National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-04) and by the National Natural Science Foundation of China (Grant Nos.: 41876065, 41476056, and U1606401).</p>

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.

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