scholarly journals On the Movements of the North Atlantic Subpolar Front in the Preinstrumental Past*

2016 ◽  
Vol 29 (4) ◽  
pp. 1545-1571 ◽  
Author(s):  
Olivier Marchal ◽  
Claire Waelbroeck ◽  
Alain Colin de Verdière
Keyword(s):  
Least Squares ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Circulation Model ◽  
Recursive Least Squares ◽  
Reconstruction Method ◽  
Model Errors ◽  
Grand Banks ◽  
The North ◽  
The North Atlantic

Abstract Three sediment records of sea surface temperature (SST) are analyzed that originate from distant locations in the North Atlantic, have centennial-to-multicentennial resolution, are based on the same reconstruction method and chronological assumptions, and span the past 15 000 yr. Using recursive least squares techniques, an estimate of the time-dependent North Atlantic SST field over the last 15 kyr is sought that is consistent with both the SST records and a surface ocean circulation model, given estimates of their respective error (co)variances. Under the authors’ assumptions about data and model errors, it is found that the 10°C mixed layer isotherm, which approximately traces the modern Subpolar Front, would have moved by ~15° of latitude southward (northward) in the eastern North Atlantic at the onset (termination) of the Younger Dryas cold interval (YD), a result significant at the level of two standard deviations in the isotherm position. In contrast, meridional movements of the isotherm in the Newfoundland basin are estimated to be small and not significant. Thus, the isotherm would have pivoted twice around a region southeast of the Grand Banks, with a southwest–northeast orientation during the warm intervals of the Bølling–Allerød and the Holocene and a more zonal orientation and southerly position during the cold interval of the YD. This study provides an assessment of the significance of similar previous inferences and illustrates the potential of recursive least squares in paleoceanography.

scholarly journals Effect of vegetation on the Late Miocene ocean circulation

2006 ◽  
Vol 2 (4) ◽  
pp. 605-631 ◽  
Author(s):  
G. Lohmann ◽  
M. Butzin ◽  
A. Micheels ◽  
T. Bickert ◽  
V. Mosbrugger
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Late Miocene ◽  
Land Surface ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
The North ◽  
The North Atlantic

Abstract. A weak and shallow thermohaline circulation in the North Atlantic Ocean is related to an open Central American gateway and exchange with fresh Pacific waters. We estimate the effect of vegetation on the ocean general circulation using the atmospheric circulation model simulations for the Late Miocene climate. Caused by an increase in net evaporation in the Miocene North Atlantic, the North Atlantic water becomes more saline which enhances the overturning circulation and thus the northward heat transport. This effect reveals a potentially important feedback between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

Interaction of a Glacial Water Outflow with the Gulf Stream

2021 ◽  
Author(s):  
Olivier Marchal ◽  
Alan Condron
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Gulf Stream ◽  
Circulation Model ◽  
Liquid Form ◽  
Sea Levels ◽  
Grand Banks ◽  
The North ◽  
Cape Hatteras ◽  
Water Outflow

<p>A popular hypothesis in paleoclimatology posits that the episodic discharges of glacial water from the Laurentide Ice Sheet (LIS) to the North Atlantic caused abrupt changes in ocean circulation and climate during the last (de)glacial periods. Implicit in this hypothesis is that the glacial water spread away from the coast and reached critical sites of deep water formation. Among the processes that could favour the offshore export of glacial water released along the eastern North American coast is the entrainment with the Gulf Stream near Cape Hatteras, where the Stream is observed to detach from the coast in the modern climate, or at other locations between Cape Hatteras and the Grand Banks of Newfoundland.</p><p>Here we investigate the fate of glacial water released in the western North Atlantic from the Laurentian Channel, which geologic evidence suggests to have been the main route of ice discharge from the Québec-Labrador Ice Dome of the LIS. To this end, we conduct numerical experiments with an ocean circulation model with eddy-resolving resolution and configured to represent the region north of Bermuda and west of the Grand Banks. Experiments with different regional sea levels are performed which correspond to different estimates of global sea level since the Last Glacial Maximum. In each experiment, glacial water in liquid form is discharged from the Laurentian Channel, providing a paleoceanographic analogue of the dam-break problem. As expected from the action of the Coriolis force and from the properties of the glacial water inflow, the discharged water turns to the right of the Channel and then produces a narrow buoyant current that flows along the coast to the southwest towards Cape Hatteras. Our presentation will focus on the interaction of this current with the Gulf Stream, particularly with its meanders and rings, and on the role of this interaction both in the seaward export of glacial water and in the modification of the Stream itself.</p>

scholarly journals Minor effect of meltwater on the ocean circulation during deglaciation

2012 ◽  
Vol 3 (2) ◽  
pp. 801-825 ◽  
Author(s):  
G. Lohmann ◽  
K. Grosfeld ◽  
M. Butzin ◽  
P. Huybrechts ◽  
C. Zweck
Keyword(s):  
Northern Hemisphere ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Three Dimensional ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Minor Effect ◽  
Overturning Circulation ◽  
The North ◽  
The North Atlantic

Abstract. Decaying Northern Hemisphere ice sheets during deglaciation affect the high latitude hydrological balance in the North Atlantic and therefore the ocean circulation after the Last Glacial Maximum. Surprisingly, geological data suggest that meltwater fluxes of about 14–20 m sea-level equivalent flushed into the North Atlantic without significantly influencing the Atlantic meridional overturning circulation. Using a three-dimensional ocean circulation model coupled to an energy balance model of the atmosphere, we investigate the response of the ocean circulation to spatio-temporal variable deglacial freshwater discharges. Freshwater inputs are simulated by a three-dimensional thermo-mechanical ice sheet model of the Northern Hemisphere. In our experiments, we find a strong sensitivity of the ocean circulation when the deglacial meltwater is injected into the surface layers yielding a quasi shut-down. On the other hand, the parameterization of huge sub-glacial outbursts as so-called hyperpycnal flows are mimicked through bottom injections in ocean models leading to a reduced sensitivity of the overturning circulation against freshwater perturbations and providing a consistent representation of the deglacial climate evolution.

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

scholarly journals Marine productivity response to Heinrich events: a model-data comparison

2012 ◽  
Vol 8 (5) ◽  
pp. 1581-1598 ◽  
Author(s):  
V. Mariotti ◽  
L. Bopp ◽  
A. Tagliabue ◽  
M. Kageyama ◽  
D. Swingedouw
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Heinrich Events ◽  
The North ◽  
Heinrich Event ◽  
The North Atlantic ◽  
Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.

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