scholarly journals Impact of melt water on high latitude early Last Interglacial climate

2016 ◽  
Author(s):  
Emma J. Stone ◽  
Emilie Capron ◽  
Daniel J. Lunt ◽  
Antony J. Payne ◽  
Joy S. Singarayer ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Climate Model ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Model Simulations ◽  
The North ◽  
Freshwater Forcing ◽  
The North Atlantic

Abstract. Recent data compilations of the early Last Interglacial period have indicated a bipolar temperature response at 130 ka, with colder-than-present temperatures in the North Atlantic and warmer-than-present temperatures in the Southern Ocean and over Antarctica. However, climate model simulations of this period have been unable to reproduce this response, when only orbital and greenhouse gas forcings are considered in a climate model framework. Here we show using full complexity General Circulation Model simulations at 130 ka with the magnitude of freshwater forcing derived from data, that meltwater from the remnant Northern Hemisphere ice-sheets during the glacial-interglacial transition accounts for the observed colder than present temperatures in the North Atlantic at 130 ka and also results in warmer than present temperatures in the Southern Ocean via the bipolar seesaw mechanism. This integrated model-data approach, for the first time, provides evidence that Northern Hemisphere freshwater forcing is an important player in the evolution of early Last Interglacial climate.

scholarly journals Impact of meltwater on high-latitude early Last Interglacial climate

2016 ◽  
Vol 12 (9) ◽  
pp. 1919-1932 ◽  
Author(s):  
Emma J. Stone ◽  
Emilie Capron ◽  
Daniel J. Lunt ◽  
Antony J. Payne ◽  
Joy S. Singarayer ◽  
...  
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Climate Model ◽  
Model Data ◽  
Last Interglacial ◽  
Model Simulations ◽  
The North ◽  
Freshwater Forcing ◽  
The North Atlantic ◽  
Climate Model Simulations

Abstract. Recent data compilations of the early Last Interglacial period have indicated a bipolar temperature response at 130 ka, with colder-than-present temperatures in the North Atlantic and warmer-than-present temperatures in the Southern Ocean and over Antarctica. However, climate model simulations of this period have been unable to reproduce this response, when only orbital and greenhouse gas forcings are considered in a climate model framework. Using a full-complexity general circulation model we perform climate model simulations representative of 130 ka conditions which include a magnitude of freshwater forcing derived from data at this time. We show that this meltwater from the remnant Northern Hemisphere ice sheets during the glacial–interglacial transition produces a modelled climate response similar to the observed colder-than-present temperatures in the North Atlantic at 130 ka and also results in warmer-than-present temperatures in the Southern Ocean via the bipolar seesaw mechanism. Further simulations in which the West Antarctic Ice Sheet is also removed lead to warming in East Antarctica and the Southern Ocean but do not appreciably improve the model–data comparison. This integrated model–data approach provides evidence that Northern Hemisphere freshwater forcing is an important player in the evolution of early Last Interglacial climate.

Variability of the North Atlantic thermohaline circulation during the last interglacial period

Nature ◽  
10.1038/36540 ◽  
1997 ◽  
Vol 390 (6656) ◽  
pp. 154-156 ◽  
Author(s):  
Jess F. Adkins§ ◽  
Edward A. Boyle ◽  
Lloyd Keigwin ◽  
Elsa Cortijo
Keyword(s):  
North Atlantic ◽  
Thermohaline Circulation ◽  
Interglacial Period ◽  
Last Interglacial ◽  
The North ◽  
Last Interglacial Period ◽  
The North Atlantic ◽  
Atlantic Thermohaline Circulation

scholarly journals Persistent influence of ice sheet melting on high northern latitude climate during the early Last Interglacial

2012 ◽  
Vol 8 (2) ◽  
pp. 483-507 ◽  
Author(s):  
A. Govin ◽  
P. Braconnot ◽  
E. Capron ◽  
E. Cortijo ◽  
J.-C. Duplessy ◽  
...  
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Surface Waters ◽  
Ice Sheet ◽  
Boreal Summer ◽  
Last Interglacial ◽  
High Northern Latitude ◽  
The North ◽  
Northern Latitudes ◽  
The North Atlantic

Abstract. Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It is associated with (1) colder and fresher surface-water conditions in the North Atlantic, Labrador and Norwegian Seas, and (2) a weaker ventilation of North Atlantic deep waters during the early LIG (129–125 ka) compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka) than the late LIG (122 ka). Hence, insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. Additionally, we consider an idealized meltwater scenario at 126 ka where the freshwater input is interactively computed in response to the high boreal summer insolation. The model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka) compared to the late LIG (122 ka). This result suggests that both insolation and ice sheet melting have to be considered to reproduce the climatic pattern that we identify during the early LIG. Our model-data comparison also reveals a number of limitations and reinforces the need for further detailed investigations using coupled climate-ice sheet models and transient simulations.

scholarly journals The Ocean Carbon States Database: a proof-of-concept application of cluster analysis in the ocean carbon cycle

2018 ◽  
Vol 10 (1) ◽  
pp. 609-626 ◽  
Author(s):  
Rebecca Latto ◽  
Anastasia Romanou
Keyword(s):  
Data Mining ◽  
Wind Speed ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
North Atlantic ◽  
Climate Model ◽  
Proof Of Concept ◽  
The North ◽  
The North Atlantic ◽  
Ocean Carbon

Abstract. In this paper, we present a database of the basic regimes of the carbon cycle in the ocean, the “ocean carbon states”, as obtained using a data mining/pattern recognition technique in observation-based as well as model data. The goal of this study is to establish a new data analysis methodology, test it and assess its utility in providing more insights into the regional and temporal variability of the marine carbon cycle. This is important as advanced data mining techniques are becoming widely used in climate and Earth sciences and in particular in studies of the global carbon cycle, where the interaction of physical and biogeochemical drivers confounds our ability to accurately describe, understand, and predict CO2 concentrations and their changes in the major planetary carbon reservoirs. In this proof-of-concept study, we focus on using well-understood data that are based on observations, as well as model results from the NASA Goddard Institute for Space Studies (GISS) climate model. Our analysis shows that ocean carbon states are associated with the subtropical–subpolar gyre during the colder months of the year and the tropics during the warmer season in the North Atlantic basin. Conversely, in the Southern Ocean, the ocean carbon states can be associated with the subtropical and Antarctic convergence zones in the warmer season and the coastal Antarctic divergence zone in the colder season. With respect to model evaluation, we find that the GISS model reproduces the cold and warm season regimes more skillfully in the North Atlantic than in the Southern Ocean and matches the observed seasonality better than the spatial distribution of the regimes. Finally, the ocean carbon states provide useful information in the model error attribution. Model air–sea CO2 flux biases in the North Atlantic stem from wind speed and salinity biases in the subpolar region and nutrient and wind speed biases in the subtropics and tropics. Nutrient biases are shown to be most important in the Southern Ocean flux bias. All data and analysis scripts are available at https://data.giss.nasa.gov/oceans/carbonstates/ (DOI: https://doi.org/10.5281/zenodo.996891).

Circumpolar Deep Water Circulation and Variability in a Coupled Climate Model

2006 ◽  
Vol 36 (8) ◽  
pp. 1523-1552 ◽  
Author(s):  
Agus Santoso ◽  
Matthew H. England ◽  
Anthony C. Hirst
Keyword(s):  
Southern Ocean ◽  
Southern Hemisphere ◽  
Time Scales ◽  
North Atlantic ◽  
Deep Water ◽  
Climate Model ◽  
Coupled Climate Model ◽  
Circumpolar Deep Water ◽  
The North ◽  
The North Atlantic

Abstract The natural variability of Circumpolar Deep Water (CDW) is analyzed using a long-term integration of a coupled climate model. The variability is decomposed using a standard EOF analysis into three separate modes accounting for 68% and 82% of the total variance in the upper and lower CDW layers, respectively. The first mode exhibits an interbasin-scale variability on multicentennial time scales, originating in the North Atlantic and flowing southward into the Southern Ocean via North Atlantic Deep Water (NADW). Salinity dipole anomalies appear to propagate around the Atlantic meridional overturning circulation on these time scales with the strengthening and weakening of NADW formation. The anomaly propagates northward from the midlatitude subsurface of the South Atlantic and sinks in the North Atlantic before flowing southward along the CDW isopycnal layers. This suggests an interhemispheric connection in the generation of the first CDW variability mode. The second mode shows a localized θ−S variability in the Brazil–Malvinas confluence zone on multidecadal to centennial time scales. Heat and salt budget analyses reveal that this variability is controlled by meridional advection driven by fluctuations in the strength of the Deep Western Boundary and the Malvinas Currents. The third mode suggests an Antarctic Intermediate Water source in the South Pacific contributing to variability in upper CDW. It is further found that NADW formation is mainly buoyancy driven on the time scales resolved, with only a weak connection with Southern Hemisphere winds. On the other hand, Southern Hemisphere winds have a more direct influence on the rate of NADW outflow into the Southern Ocean. The model’s spatial pattern of θ−S variability is consistent with the limited observational record in the Southern Hemisphere. However, some observations of decadal CDW θ−S changes are beyond that seen in the model in its unperturbed state.

scholarly journals Persistent influence of ice sheet melting on high northern latitude climate during the early Last Interglacial

2011 ◽  
Vol 7 (5) ◽  
pp. 3239-3286 ◽  
Author(s):  
A. Govin ◽  
P. Braconnot ◽  
E. Capron ◽  
E. Cortijo ◽  
J.-C. Duplessy ◽  
...  
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Surface Waters ◽  
Ice Sheet ◽  
Boreal Summer ◽  
Last Interglacial ◽  
The North ◽  
Northern Latitudes ◽  
Climate Evolution ◽  
The North Atlantic

Abstract. Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It suggests that the input of meltwater has maintained (1) colder and fresher surface-water conditions in the North Atlantic, Labrador and Norwegian Seas and (2) weaker ventilation of North Atlantic deep waters during the early LIG (129–125.5 ka) compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show that insolation variations alone lead to warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka) than the late LIG (122 ka). Hence insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. When freshwater input is interactively computed at 126 ka in response to the high boreal summer insolation, the model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka) compared to the late LIG (122 ka). This result indicates that both insolation variations and ice sheet melting have to be considered to reproduce the LIG climate evolution and supports our hypothesis that optimal thermal and deep ocean circulation conditions at high northern latitudes develop during the late LIG only, when the freshwater supply has already ceased.

scholarly journals The Effect of Northern Hemisphere Winds on the Meridional Overturning Circulation and Stratification

2018 ◽  
Vol 48 (10) ◽  
pp. 2495-2506 ◽  
Author(s):  
Paola Cessi
Keyword(s):  
Southern Ocean ◽  
Northern Hemisphere ◽  
Wind Stress ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Subpolar Gyre ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

AbstractThe current paradigm for the meridional overturning cell and the associated middepth stratification is that the wind stress in the subpolar region of the Southern Ocean drives a northward Ekman flow, which, together with the global diapycnal mixing across the lower boundary of the middepth waters, feeds the upper branch of the interhemispheric overturning. The resulting mass transport proceeds to the Northern Hemisphere of the North Atlantic, where it sinks, to be eventually returned to the Southern Ocean at depth. Seemingly, the wind stress in the Atlantic basin plays no role. This asymmetry occurs because the Ekman transport in the Atlantic Ocean is assumed to return geostrophically at depths much shallower than those occupied by the interhemispheric overturning. However, this vertical separation fails in the North Atlantic subpolar gyre region. Using a conceptual model and an ocean general circulation model in an idealized geometry, we show that the westerly wind stress in the northern part of the Atlantic provides two opposing effects. Mechanically, the return of the Ekman transport in the North Atlantic opposes sinking in this region, reducing the total overturning and deepening the middepth stratification; thermodynamically, the subpolar gyre advects salt poleward, promoting Northern Hemisphere sinking. Depending on which mechanism prevails, increased westerly winds in the Northern Hemisphere can reduce or augment the overturning.

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