scholarly journals Review of Deep water formation in the North Atlantic Ocean in high resolution global coupled climate models by Koenigk et al.

2020 ◽  
Author(s):  
Anonymous
Keyword(s):  
High Resolution ◽  
North Atlantic ◽  
Deep Water ◽  
Climate Models ◽  
North Atlantic Ocean ◽  
Deep Water Formation ◽  
The North ◽  
Coupled Climate Models ◽  
Water Formation ◽  
The North Atlantic

Deep water formation in the North Atlantic Ocean during the last ice age

Nature ◽  
1980 ◽  
Vol 286 (5772) ◽  
pp. 479-482 ◽  
Author(s):  
Jean-Claude Duplessy ◽  
J. Moyes ◽  
C. Pujol
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Ocean ◽  
Ice Age ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
Last Ice Age ◽  
The North Atlantic

Climate extremes in Loess of China coupled with the strength of deep-water formation in the North Atlantic

1998 ◽  
Vol 18 (3-4) ◽  
pp. 113-128 ◽  
Author(s):  
Zhengtang Guo ◽  
Tungsheng Liu ◽  
Nicolas Fedoroff ◽  
Lanying Wei ◽  
Zhongli Ding ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Climate Extremes ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
The North Atlantic

Closure of the Central American Isthmus and its effect on deep-water formation in the North Atlantic

Nature ◽  
1997 ◽  
Vol 386 (6623) ◽  
pp. 382-385 ◽  
Author(s):  
Kevin W. Burton ◽  
Hong-Fei Ling ◽  
R. Keith O'Nions
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Central American ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
The North Atlantic ◽  
Central American Isthmus

Constraining erosional input and deep-water formation in the North Atlantic using Nd isotopes

2006 ◽  
Vol 226 (3-4) ◽  
pp. 253-263 ◽  
Author(s):  
Ben C. Reynolds ◽  
Martin Frank ◽  
Kevin W. Burton
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Deep Water Formation ◽  
Nd Isotopes ◽  
The North ◽  
Water Formation ◽  
The North Atlantic

scholarly journals Freshening of the Labrador Sea as a trigger for Little Ice Age development

2017 ◽  
Vol 13 (4) ◽  
pp. 317-331 ◽  
Author(s):  
Montserrat Alonso-Garcia ◽  
Helga (Kikki) F. Kleiven ◽  
Jerry F. McManus ◽  
Paola Moffa-Sanchez ◽  
Wallace S. Broecker ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Deep Water ◽  
Little Ice Age ◽  
Ice Age ◽  
Labrador Sea ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
The North Atlantic

Abstract. Arctic freshwater discharges to the Labrador Sea from melting glaciers and sea ice can have a large impact on ocean circulation dynamics in the North Atlantic, modifying climate and deep water formation in this region. In this study, we present for the first time a high resolution record of ice rafting in the Labrador Sea over the last millennium to assess the effects of freshwater discharges in this region on ocean circulation and climate. The occurrence of ice-rafted debris (IRD) in the Labrador Sea was studied using sediments from Site GS06-144-03 (57.29° N, 48.37° W; 3432 m water depth). IRD from the fraction 63–150 µm shows particularly high concentrations during the intervals  ∼  AD 1000–1100,  ∼  1150–1250,  ∼  1400–1450,  ∼  1650–1700 and  ∼  1750–1800. The first two intervals occurred during the Medieval Climate Anomaly (MCA), whereas the others took place within the Little Ice Age (LIA). Mineralogical identification indicates that the main IRD source during the MCA was SE Greenland. In contrast, the concentration and relative abundance of hematite-stained grains reflects an increase in the contribution of Arctic ice during the LIA. The comparison of our Labrador Sea IRD records with other climate proxies from the subpolar North Atlantic allowed us to propose a sequence of processes that led to the cooling that occurred during the LIA, particularly in the Northern Hemisphere. This study reveals that the warm climate of the MCA may have enhanced iceberg calving along the SE Greenland coast and, as a result, freshened the subpolar gyre (SPG). Consequently, SPG circulation switched to a weaker mode and reduced convection in the Labrador Sea, decreasing its contribution to the North Atlantic deep water formation and, thus, reducing the amount of heat transported to high latitudes. This situation of weak SPG circulation may have made the North Atlantic climate more unstable, inducing a state in which external forcings (e.g. reduced solar irradiance and volcanic eruptions) could easily drive periods of severe cold conditions in Europe and the North Atlantic like the LIA. This analysis indicates that a freshening of the SPG may play a crucial role in the development of cold events during the Holocene, which may be of key importance for predictions about future climate.

scholarly journals Simulated stability of the AMOC during the Last Glacial Maximum under realistic boundary conditions

2020 ◽  
Author(s):  
Frerk Pöppelmeier ◽  
Jeemijn Scheen ◽  
Aurich Jeltsch-Thömmes ◽  
Thomas F. Stocker
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
Deep Water ◽  
Bering Strait ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
The North Atlantic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The response of the Atlantic Meridional Overturning Circulation (AMOC) to freshwater perturbations critically depends on its mean-state. Large swaths of icebergs melting in the North Atlantic during the last deglaciation constituted such perturbations, and thus can provide important constraints on the stability of the AMOC. Yet, the mean AMOC state during the Last Glacial Maximum (LGM), preceding the rapid disintegration of the ice-sheets during the deglaciation, as well as its response to these perturbations remain debated. Here we investigate the evolution of the AMOC responding to freshwater perturbations under improved LGM boundary conditions in the Bern3D intermediate complexity model. Particularly, we consider the effect of an open versus a closed Bering Strait. The vigorous and deep AMOC under these glacial boundary conditions, consistent with previous simulations with different models, reacts more strongly to North Atlantic freshwater forcings than under pre-industrial conditions. This increased sensitivity is mostly related to the closed Bering Strait that cuts off the freshwater escape route through the Arctic into the Pacific, thus facilitating faster accumulation of freshwater in the North Atlantic halting deep water formation. Proxy reconstructions of the LGM AMOC instead indicate a weaker and possibly shallower AMOC than today, in conflict with the particularly strong and deep circulation states coherently simulated with ocean circulation models for the LGM. Simulations with reduced North Atlantic deep water formation, as a consequence of potentially increased continental runoff from ice-sheet melt and imposed changes in the hydrological cycle, more closely resemble the overturning circulation inferred from proxies. These circulation states also show bistable behavior, where the AMOC does not recover after North Atlantic freshwater hosing. However, no AMOC states are found here that either comprise an extreme shoaling or vigorous and concurrent shallow overturning as previously proposed based on paleoceanographic data.

The Impact of Tropical Atlantic Freshwater Fluxes on the North Atlantic Meridional Overturning Circulation

2006 ◽  
Vol 19 (18) ◽  
pp. 4592-4604 ◽  
Author(s):  
J. Paul Spence ◽  
Andrew J. Weaver
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Tropical Atlantic ◽  
Deep Water Formation ◽  
The North ◽  
Freshwater Fluxes ◽  
Water Formation ◽  
Meridional Overturning ◽  
The North Atlantic ◽  
Freshwater Balance

Abstract The influence of ENSO-related changes in the Atlantic-to-Pacific freshwater budget on the North Atlantic meridional overturning is examined using the University of Victoria (UVic) Earth System Climate Model. The initial analysis of freshwater fluxes in the 50-yr NCEP–NCAR (NCEP50) reanalysis product and Global Precipitation Climatology Project (GPCP) dataset reveals that the transport of water vapor out of the tropical Atlantic drainage basin is enhanced during El Niño phases and reduced during La Niña phases; a one standard deviation in the Southern Oscillation index alters the tropical Atlantic freshwater balance by about 0.09 Sv (Sv ≡ 106 m3 s−1). A weaker link with ENSO is found in the 40-yr ECMWF Re-Analysis (ERA-40), although its usefulness is severely limited by a strong and spurious trend in tropical precipitation. Model results suggest that tropical Atlantic salinity anomalies generated with the frequency and amplitude of ENSO tend not to impact deep-water formation as they are diluted en route to the North Atlantic. Lower frequency, decadal time-scale anomalies, however, do have an impact, albeit weak, on the rate of North Atlantic Deep Water formation. In addition, and contrary to earlier results, it is found that even a shift of the tropical Atlantic freshwater balance toward permanent El Niño conditions only slightly mitigates the transient reduction of North Atlantic Deep Water formation associated with the increase of anthropogenic greenhouse gases. Taken together, the results suggest that the poleward propagation of salinity anomalies from the tropical Atlantic, associated with changes in ENSO, should not be considered a significant mechanism for the variability of the North Atlantic meridional overturning in the present and foreseeable future climate.

Global Thermohaline Circulation. Part I: Sensitivity to AtmosphericMoisture Transport

1999 ◽  
Vol 12 (1) ◽  
pp. 71-82 ◽  
Author(s):  
Xiaoli Wang ◽  
Peter H. Stone ◽  
Jochem Marotzke
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Conveyor Belt ◽  
Freshwater Flux ◽  
Deep Water Formation ◽  
The North ◽  
Freshwater Fluxes ◽  
Water Formation ◽  
The North Atlantic ◽  
Moisture Transports

Abstract A global ocean general circulation model of idealized geometry, combined with an atmospheric model based on observed transports of heat, momentum, and moisture, is used to explore the sensitivity of the global conveyor belt circulation to the surface freshwater fluxes, in particular the effects of meridional atmospheric moisture transports. The numerical results indicate that the equilibrium strength of the North Atlantic Deep Water (NADW) formation increases as the global freshwater transports increase. However, the global deep water formation—that is, the sum of the NADW and the Southern Ocean Deep Water formation rates—is relatively insensitive to changes of the freshwater flux. Perturbations to the meridional moisture transports of each hemisphere identify equatorially asymmetric effects of the freshwater fluxes. The results are consistent with box model results that the equilibrium NADW formation is primarily controlled by the magnitude of the Southern Hemisphere freshwater flux. However, the results show that the Northern Hemisphere freshwater flux has a strong impact on the transient behavior of the North Atlantic overturning. Increasing this flux leads to a collapse of the conveyor belt circulation, but the collapse is delayed if the Southern Hemisphere flux also increases. The perturbation experiments also illustrate that the rapidity of collapse is affected by random fluctuations in the wind stress field.

scholarly journals Freshwater routing in eddy-permitting simulations of the last deglacial: the impact of realistic freshwater discharge

2021 ◽  
Vol 17 (6) ◽  
pp. 2327-2341
Author(s):  
Ryan Love ◽  
Heather J. Andres ◽  
Alan Condron ◽  
Lev Tarasov
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Large Scale ◽  
Bering Strait ◽  
Deep Water Formation ◽  
The North ◽  
Water Formation ◽  
Glacial Runoff ◽  
The North Atlantic ◽  
The Impact

Abstract. Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial- to millennial-scale climate variability, such as the Younger Dryas and Dansgaard–Oeschger events, but this relationship is not straightforward. Large-scale glacial runoff events, such as Meltwater Pulse 1a (MWP1a), are not always temporally proximal to subsequent large-scale cooling. Moreover, the typical design of hosing experiments that support this relationship tends to artificially amplify the climate response. This study explores the impact that limitations in the representation of runoff in conventional “hosing” simulations has on our understanding of this relationship by examining where coastally released freshwater is transported when it reaches the ocean. We particularly focus on the impact of (1) the injection of freshwater directly over sites of deep-water formation (DWF) rather than at runoff locations (i.e. hosing), (2) excessive freshwater injection volumes (often by a factor of 5), and (3) the use of present-day (rather than palaeo) ocean gateways. We track the routing of glaciologically constrained freshwater volumes from four different inferred injection locations in a suite of eddy-permitting glacial ocean simulations using the Massachusetts Institute of Technology General Circulation Model (MITgcm) under both open and closed Bering Strait conditions. Restricting freshwater forcing values to realistic ranges results in less spreading of freshwater across the North Atlantic and indicates that the freshwater anomalies over DWF sites depend strongly on the geographical location of meltwater input. In particular, freshwater released into the Gulf of Mexico generates a very weak freshwater signal over DWF regions as a result of entrainment by the turbulent Gulf Stream. In contrast, freshwater released into the Arctic with an open Bering Strait or from the Eurasian ice sheet is found to generate the largest salinity anomalies over DWF regions in the North Atlantic and GIN (Greenland–Iceland–Norwegian) seas region respectively. Experiments show that when the Bering Strait is open, the Mackenzie River source exhibits more than twice as much freshening of the North Atlantic deep-water formation regions as when the Bering Strait is closed. Our results illustrate that applying freshwater hosing directly into the North Atlantic with even “realistic” freshwater amounts still overestimates the amount of terrestrial runoff reaching DWF regions. Given the simulated salinity anomaly distributions and the lack of reconstructed impact on deep-water formation during the Bølling–Allerød, our results support that the majority of the North American contribution to MWP1a was not routed through the Mackenzie River.

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