scholarly journals Simulating last interglacial climate with NorESM: role of insolation and greenhouse gases in the timing of peak warmth

2013 ◽  
Vol 9 (4) ◽  
pp. 4449-4473 ◽  
Author(s):  
P. M. Langebroek ◽  
K. H. Nisancioglu
Keyword(s):  
Greenhouse Gas ◽  
North Atlantic ◽  
Sediment Cores ◽  
Austral Summer ◽  
Hemispheric Differences ◽  
Last Interglacial ◽  
The North ◽  
Surface Temperatures ◽  
Summer Temperatures ◽  
Insolation Maximum

Abstract. The last interglacial (LIG) is characterized by high latitude warming and is therefore often considered as a possible analogue for future warming. However, in contrast to predicted future greenhouse warming, the last interglacial climate is largely governed by variations in insolation. Greenhouse gas (GHG) concentrations were relatively stable and similar to pre-industrial values, with the exception of the early last interglacial where GHGs were slightly lower. We performed six time-slice simulations with the low resolution version of the Norwegian Earth System Model covering the last interglacial. In four simulations only orbital forcing was changed, and in two simulations additionally GHG forcing was reduced to values appropriate for the early last interglacial. Our simulations show that insolation forcing results in seasonal and hemispheric differences in temperature. In contrast, a reduction in greenhouse gas forcing causes a global and seasonal-independent cooling. We also compare our modelled results to proxy data extracted from four marine sediment cores covering the entire last interglacial along a northeast-southwest transect in the North Atlantic. Our modelled North Atlantic summer sea surface temperatures capture the general trend of the proxy summer temperatures, with low values in the early last interglacial, a peak around 125 ka, and a steady decrease towards the end of the last interglacial. Temperatures computed by the simulations with reduced GHG forcing improve the fit as they show lower temperatures in the early last interglacial. Furthermore we show that the timing of maximum surface temperatures follows the local insolation maximum. Two exceptions are the temperatures on Antarctica that show maxima at both ~ 130 ka and ~ 115 ka, and the Southern Ocean austral summer temperatures that peak early at ~ 130 ka. This is probably due to the integrating effect of the ocean, storing summer heat and resulting in relatively warm winter temperatures.

scholarly journals Simulating last interglacial climate with NorESM: role of insolation and greenhouse gases in the timing of peak warmth

2014 ◽  
Vol 10 (4) ◽  
pp. 1305-1318 ◽  
Author(s):  
P.M. Langebroek ◽  
K. H. Nisancioglu
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Austral Summer ◽  
Sea Surface ◽  
Last Interglacial ◽  
The North ◽  
Surface Temperatures ◽  
Summer Temperatures ◽  
The North Atlantic ◽  
Insolation Forcing

Abstract. The last interglacial (LIG, ~130–116 ka, ka = 1000 yr ago) is characterized by high-latitude warming and is therefore often considered as a possible analogue for future warming. However, in contrast to predicted future greenhouse warming, the LIG climate is largely governed by variations in insolation. Greenhouse gas (GHG) concentrations were relatively stable and similar to pre-industrial values, with the exception of the early LIG when, on average, GHGs were slightly lower. We performed six time-slice simulations with the low-resolution version of the Norwegian Earth System Model covering the LIG. In four simulations only the orbital forcing was changed. In two other simulations, representing the early LIG, additionally the GHG forcing was reduced. With these simulations we investigate (1) the different effects of GHG versus insolation forcing on the temperatures during the LIG; (2) whether reduced GHGs can explain the low temperatures reconstructed for the North Atlantic; and (3) the timing of the observed LIG peak warmth. Our simulations show that the insolation forcing results in seasonal and hemispheric differences in temperature. In contrast, a reduction in the GHG forcing causes a global and seasonal-independent cooling. Furthermore, we compare modelled temperatures with proxy-based LIG sea-surface temperatures along a transect in the North Atlantic. The modelled North Atlantic summer sea-surface temperatures capture the general trend of the reconstructed summer temperatures, with low values in the early LIG, a peak around 125 ka, and a steady decrease towards the end of the LIG. Simulations with reduced GHG forcing improve the model–data fit as they show lower temperatures in the early LIG. Furthermore we show that the timing of maximum summer and winter surface temperatures is in line with the local summer and winter insolation maximum at most latitudes. Two regions where the maximum local insolation and temperature do not occur at the same time are Antarctica and the Southern Ocean. The austral summer insolation has a late maximum at ~115 ka. In contrast the austral summer temperatures in Antarctica show maxima at both ~130 ka and ~115 ka, and the Southern Ocean temperatures peak only at ~130 ka. This is probably due to the integrating effect of the ocean, storing heat from other seasons and resulting in relatively warm austral summer temperatures. Reducing the GHG concentrations in the early LIG (125 and 130 ka) results in a similar timing of peak warmth, except over Antarctica. There, the lower austral summer temperatures at 130 ka shift the maximum warmth to a single peak at 115 ka.

scholarly journals Sensitivity of the North Atlantic climate to Greenland Ice Sheet melting during the Last Interglacial

2012 ◽  
Vol 8 (3) ◽  
pp. 995-1009 ◽  
Author(s):  
P. Bakker ◽  
C. J. Van Meerbeeck ◽  
H. Renssen
Keyword(s):  
North Atlantic ◽  
Deep Convection ◽  
Greenland Ice Sheet ◽  
Last Interglacial ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
Summer Temperatures ◽  
The North Atlantic ◽  
The Impact

Abstract. During the Last Interglacial (LIG; ~130 000 yr BP), part of the Greenland Ice Sheet (GIS) melted due to a warmer than present-day climate. However, the impact of this melting on the LIG climate in the North Atlantic region is relatively unknown. Using the LOVECLIM Earth system model of intermediate complexity, we have systematically tested the sensitivity of the LIG climate to increased freshwater runoff from the GIS. In addition, experiments have been performed to investigate the impact of an idealized reduction of both surface elevation and extent of the GIS on the LIG climate. Based on changes in the maximum sea-ice cover and the strength of the overturning circulation, three regimes have been identified, which are characterized by a specific pattern of surface temperature change in the North Atlantic region. By comparing the simulated deep ocean circulation with proxy-based reconstructions, the most realistic simulated climate could be discerned. The resulting climate is characterized by a shutdown of deep convection and a subsequent ~4 °C cooling in the Labrador Sea. Furthermore, a cooling of ~1 °C over the North Atlantic Ocean between 40° N and 70° N is seen. The prescribed reduction in surface elevation and extent of the GIS results in a local warming of up to 4 °C and amplifies the freshwater-forced reduction in deep convection and the resultant cooling in the Nordic Seas. A further comparison of simulated summer temperatures with both continental and oceanic proxy records reveals that the partial melting of the GIS during the LIG could have delayed maximum summer temperatures in the western part of the North Atlantic region relative to the insolation maximum.

scholarly journals Sensitivity of the North Atlantic climate to Greenland Ice Sheet melting during the Last Interglacial

2011 ◽  
Vol 7 (4) ◽  
pp. 2763-2801 ◽  
Author(s):  
P. Bakker ◽  
C. J. Van Meerbeeck ◽  
H. Renssen
Keyword(s):  
North Atlantic ◽  
Deep Convection ◽  
Greenland Ice Sheet ◽  
Last Interglacial ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
Summer Temperatures ◽  
The North Atlantic ◽  
The Impact

Abstract. During the Last Interglacial (LIG; ~130 thousand years BP), part of the Greenland Ice Sheet (GIS) melted under the influence of a warmer than present-day climate. However, the impact of this melting on the LIG climate in the North Atlantic region is unknown. Using the LOVECLIM earth system model of intermediate complexity we have systematically tested the sensitivity of the LIG climate to increased freshwater runoff from the GIS. Moreover, additional experiments have been performed to investigate the impact of an idealized reduction of both altitude and extent of the GIS on the LIG climate. By comparing the simulated deep ocean circulation with proxy-based reconstructions, the most realistic simulated climate could be discerned. The resulting climate is characterized by a shutdown of deep convection in the Labrador Sea and a subsequent cooling here by ~6 °C and ~2 °C over the southern part of Baffin Island and the North Atlantic Ocean between 40° N and 60° N. The reduction of altitude and extent of the GIS results in a local warming of up to 6 °C and a reduction in deep convection and accompanying cooling in the Nordic Seas. Combining model results and proxy-based reconstructions enabled us to constrain the possible melt rate of the GIS to a flux between 0.052 Sv and 0.13 Sv. A further comparison of simulated summer temperatures with both continental and oceanic proxy-records reveals that the partial melting of the GIS during the LIG could have delayed maximum summer temperatures in the western part of the North Atlantic region relative to the insolation maximum.

scholarly journals Disruption of the Atlantic Meridional Circulation during Deglacial Climates Inferred from Planktonic Foraminiferal Shell Weights

2021 ◽  
Vol 9 (5) ◽  
pp. 519
Author(s):  
Stergios D. Zarkogiannis
Keyword(s):  
Atlantic Ocean ◽  
Meridional Circulation ◽  
Order Approximation ◽  
Planktonic Foraminifera ◽  
Sediment Cores ◽  
Meridional Overturning Circulation ◽  
Density Structure ◽  
Last Interglacial ◽  
Shell Weight ◽  
The North

Changes in the density structure of the upper oceanic water masses are an important forcing of changes in the Atlantic Meridional Overturning Circulation (AMOC), which is believed to widely affect Earth’s climate. However, very little is known about past changes in the density structure of the Atlantic Ocean, despite being extensively studied. The physical controls on planktonic foraminifera calcification are explored here, to obtain a first-order approximation of the horizontal density gradient in the eastern Atlantic during the last 200,000 years. Published records of Globigerina bulloides shells from the North and Tropical eastern Atlantic were complemented by the analysis of a South Atlantic core. The masses of the same species shells from three different dissolution assessed sediment cores along the eastern Atlantic Ocean were converted to seawater density values using a calibration equation. Foraminifera, as planktonic organisms, are subject to the physical properties of the seawater and thus their shells are sensitive to buoyancy forcing through surface temperature and salinity perturbations. By using planktonic foraminifera shell weight as an upper ocean density proxy, two intervals of convergence of the shell masses are identified during cold intervals of the last two deglaciations that may be interpreted as weak ocean density gradients, indicating nearly or completely eliminated meridional circulation, while interhemispheric Atlantic density differences appear to alleviate with the onset of the last interglacial. The results confirm the significance of variations in the density of Atlantic surface waters for meridional circulation changes.

Correlated Millennial-Scale Changes in Surface Hydrography and Terrigenous Sediment Yield Inferred from Last-Glacial Marine Deposits off Northeastern Brazil

1998 ◽  
Vol 50 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Helge W. Arz ◽  
Jürgen Pätzold ◽  
Gerold Wefer
Keyword(s):  
North Atlantic ◽  
Isotope Composition ◽  
Sediment Cores ◽  
Ice Cores ◽  
Northeastern Brazil ◽  
Salt Flux ◽  
Terrigenous Sediment ◽  
The North ◽  
North Brazil ◽  
The North Atlantic

The stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern Brazil. Stable oxygen isotope records of the planktonic foraminiferal species Globigerinoides sacculiferand Globigerinoides ruber(pink) reveal sub-Milankovitch changes in sea-surface hydrography during the last 85,000 yr. Warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high XRF intensities of Ti and Fe, and which suggest humid conditions in northeast Brazil. These tropical signals correlate with climatic oscillations recorded in Greenland ice cores (Dansgaard-Oeschger cycles) and in sediment cores from the North Atlantic (Heinrich events). Trade winds may have caused changes in the North Brazil Current that altered heat and salt flux into the North Atlantic, thus affecting the growth and decay of the large glacial ice sheets.

scholarly journals Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 kyr

2018 ◽  
Vol 14 (9) ◽  
pp. 1315-1330 ◽  
Author(s):  
Claire Waelbroeck ◽  
Sylvain Pichat ◽  
Evelyn Böhm ◽  
Bryan C. Lougheed ◽  
Davide Faranda ◽  
...  
Keyword(s):  
Mass Transport ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Wavelet Transforms ◽  
Water Mass ◽  
Sediment Cores ◽  
Equatorial Atlantic ◽  
The North ◽  
Atmospheric Changes ◽  
Circulation Changes

Abstract. Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti ∕ Ca). New sedimentary Pa ∕ Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa ∕ Th and ln(Ti ∕ Ca) signals. We show that decreased water mass transport between a depth of ∼1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 yr at Dansgaard–Oeschger (D–O) frequencies, and by 280 to 980 yr at Heinrich-like frequencies. We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D–O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D–O stadials, with circulation slowdowns and subsequent changes remaining more limited during D–O stadials than Heinrich stadials.

scholarly journals Multimodel Future Projections of Wintertime North Atlantic and North Pacific Tropospheric Jets: A Bayesian Analysis

2018 ◽  
Vol 31 (6) ◽  
pp. 2533-2545 ◽  
Author(s):  
D. Whittleston ◽  
K. A. McColl ◽  
D. Entekhabi
Keyword(s):  
Greenhouse Gas ◽  
North Atlantic ◽  
North Pacific ◽  
Current Model ◽  
Systematic Bias ◽  
Weighting Method ◽  
The North ◽  
State Dependent ◽  
The North Atlantic ◽  
The Impact

The impact of future greenhouse gas forcing on the North Atlantic and North Pacific tropospheric jets remains uncertain. Opposing changes in the latitudinal temperature gradient—forced by amplified lower-atmospheric Arctic warming versus upper-atmospheric tropical warming—make robust predictions a challenge. Despite some models simulating more realistic jets than others, it remains the prevailing approach to treat each model as equally probable (i.e., democratic weighting). This study compares democratically weighted projections to an alternative Bayesian-weighting method based on the ability of models to simulate historical wintertime jet climatology. The novel Bayesian technique is developed to be broadly applicable to high-dimensional fields. Results show the Bayesian weighting can reduce systematic bias and suggest the wintertime jet response to greenhouse gas forcing is largely independent of this historical bias (i.e., not state dependent). A future strengthening and narrowing is seen in both winter jets, particularly at the upper levels. The widely reported poleward shift at the level of the eddy-driven jet does not appear statistically robust, particularly over the North Atlantic, indicating sensitivity to current model deficiencies.

Sign in / Sign up

Export Citation Format

Share Document