scholarly journals Meltwater flooding events in the Gulf of Mexico revisited: Implications for rapid climate changes during the last deglaciation

2003 ◽  
Vol 18 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Paul Aharon
Keyword(s):  
Gulf Of Mexico ◽  
Climate Changes ◽  
Last Deglaciation ◽  
The Last Deglaciation ◽  
Flooding Events

scholarly journals Towards understanding potential atmospheric contributions to abrupt climate changes: characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation

2019 ◽  
Vol 15 (4) ◽  
pp. 1621-1646
Author(s):  
Heather J. Andres ◽  
Lev Tarasov
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Changes ◽  
Ice Sheet ◽  
Wind Forcing ◽  
Last Deglaciation ◽  
Sea Ice Extent ◽  
The North ◽  
The Last Deglaciation ◽  
Background Climate

Abstract. Abrupt climate shifts of large amplitudes were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately 20 000 years ago, but their causes are not yet established. Midlatitude atmospheric dynamics may have played an important role in these climate variations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterizes deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations using the PlaSim Earth system model (run at T42 resolution) and the TraCE-21ka (T31) simulation. Though driven with yearly updates in surface elevation, we detect multiple instances of NAtl jet transitions in the PlaSim simulations that occur within 10 simulation years and a sensitivity of the jet to background climate conditions. Thus, we suggest that changes to the NAtl jet may play an important role in abrupt glacial climate changes. We identify two types of simulated wind changes over the last deglaciation. Firstly, the latitude of the NAtl eddy-driven jet shifts northward over the deglaciation in a sequence of distinct steps. Secondly, the variability in the NAtl jet gradually shifts from a Last Glacial Maximum (LGM) state with a strongly preferred jet latitude and a restricted latitudinal range to one with no single preferred latitude and a range that is at least 11∘ broader. These changes can significantly affect ocean circulation. Changes to the position of the NAtl jet alter the location of the wind forcing driving oceanic surface gyres and the limits of sea ice extent, whereas a shift to a more variable jet reduces the effectiveness of the wind forcing at driving surface ocean transports. The processes controlling these two types of changes differ on the upstream and downstream ends of the NAtl eddy-driven jet. On the upstream side over eastern North America, the elevated ice sheet margin acts as a barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability in the jet at LGM, so the jet shifts in sync with ice sheet margin changes. In contrast, the downstream side over the eastern NAtl is more sensitive to the thermal state of the background climate. Our results suggest that the presence of an elevated ice sheet margin in the south-eastern sector of the North American ice complex strongly constrains the deglacial position of the jet over eastern North America and the western North Atlantic as well as its variability.

scholarly journals The last deglaciation: timing the bipolar seesaw

2011 ◽  
Vol 7 (2) ◽  
pp. 671-683 ◽  
Author(s):  
J. B. Pedro ◽  
T. D. van Ommen ◽  
S. O. Rasmussen ◽  
V. I. Morgan ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Core ◽  
Time Lag ◽  
Last Deglaciation ◽  
Atmospheric Teleconnections ◽  
The Last Deglaciation ◽  
The Antarctic ◽  
First Time ◽  
Coupling Mechanisms ◽  
Ice Core Records

Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

scholarly journals Low-latitude hydrological cycle and rapid climate changes during the last deglaciation

2007 ◽  
Vol 8 (5) ◽  
pp. n/a-n/a ◽  
Author(s):  
Camille Levi ◽  
Laurent Labeyrie ◽  
Franck Bassinot ◽  
François Guichard ◽  
Elsa Cortijo ◽  
...  
Keyword(s):  
Climate Changes ◽  
Hydrological Cycle ◽  
Last Deglaciation ◽  
Low Latitude ◽  
The Last Deglaciation

scholarly journals Abrupt Heinrich Stadial 1 cooling missing in Greenland oxygen isotopes

2021 ◽  
Vol 7 (25) ◽  
pp. eabh1007
Author(s):  
Chengfei He ◽  
Zhengyu Liu ◽  
Bette L. Otto-Bliesner ◽  
Esther C. Brady ◽  
Chenyu Zhu ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Core ◽  
Winter Precipitation ◽  
Oxygen Isotopic Composition ◽  
The Arctic ◽  
Last Deglaciation ◽  
Cold Event ◽  
Proxy Records ◽  
Oxygen Isotopic ◽  
The Last Deglaciation

Abrupt climate changes during the last deglaciation have been well preserved in proxy records across the globe. However, one long-standing puzzle is the apparent absence of the onset of the Heinrich Stadial 1 (HS1) cold event around 18 ka in Greenland ice core oxygen isotope δ18O records, inconsistent with other proxies. Here, combining proxy records with an isotope-enabled transient deglacial simulation, we propose that a substantial HS1 cooling onset did indeed occur over the Arctic in winter. However, this cooling signal in the depleted oxygen isotopic composition is completely compensated by the enrichment because of the loss of winter precipitation in response to sea ice expansion associated with AMOC slowdown during extreme glacial climate. In contrast, the Arctic summer warmed during HS1 and YD because of increased insolation and greenhouse gases, consistent with snowline reconstructions. Our work suggests that Greenland δ18O may substantially underestimate temperature variability during cold glacial conditions.

The last deglaciation simulated with a coupled atmosphere/ocean/ice sheet/solid earth model

2021 ◽  
Author(s):  
Uwe Mikolajewicz ◽  
Olga Erokhina ◽  
Marie-Luise Kapsch ◽  
Clemens Schannwell ◽  
Florian Ziemen
Keyword(s):  
Deep Water ◽  
Climate Changes ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Earth Model ◽  
Last Deglaciation ◽  
The Holocene ◽  
Simulated Climate ◽  
The Last Deglaciation

<p>It is challenging to model the last deglaciation, as it is characterized by abrupt millennial scale climate events, such as ice-sheet surges, that are superimposed on long-term climate changes, such as a global warming and the decay of a substantial part of the glacial ice sheets. Within PMIP, several groups have simulated the last deglaciation with CMIP-type models prescribing ice sheets from reconstructions. Whereas this type of simulations accounts for the effects of ice-sheet changes including meltwater release on climate, the prescribed ice sheet evolution is typically not consistent with the simulated climate evolution. Here we present a set of deglacial simulations that include fully interactive ice sheets that respond to changes in the climate. The setup also allows for feedbacks between ice sheets and climate and , hence, allows for a more realistic representation of the mechanisms of the last deglaciation, as the simulated climate and ice sheet changes are fully consistent..</p><p>The model consists of the coarse resolution set-up of MPI-ESM coupled to the ice sheet model mPISM (Northern Hemisphere and Antarctica) and the solid earth model VILMA. The model includes interactive icebergs and an automated calculation of the land-sea mask and river routing directions. A set of synchronously coupled simulations were started from an asynchronously coupled spin-up at 26ky and integrated throughout the deglaciation into the Holocene. The only prescribed external forcing are atmospheric concentrations of greenhouse gases and earth orbital parameters. One goal of this ensemble was to find the optimal combination of model parameters for the simulation of the deglaciation.</p><p>The model simulates the decay of the ice sheets, the rise of sea level, the flooding of shelf seas and the opening of passages. A large fraction of the ice sheet retreat is due to dynamical events (e.g. the final decay of the ice sheets on Barents Shelf or the Hudson Bay). Superimposed on the relatively slow glacial/interglacial transition are abrupt climate changes, triggered for example by recurrent ice sheet surges. These surges correspond to Heinrich Events tand result in a weakening of the AMOC. Three source regions for ice sheet surges occur during these simulations: from the Laurentide ice sheet through Hudson Strait, from the Laurentide ice sheet northward directly to the Arctic ocean, and from the Fennoscandian ice sheet into the Norwegian Sea. The characteristic climate response shows a large dependence on the surge location.</p><p>The simulated changes in strength of the AMOC are except for millennial-scale reduction events only moderate. However, during glacial periods, brine release is the central process for deep water formation in both hemispheres, in contrast to the Holocene. dDuring the deglaciation the ventilation of the deep ocean is strongly reduced, leading to a strong increase of the simulated deep water ages. This effect lasts longest in the deep North Pacific and extends in some simulations into the Holocene.</p>

Characterising Dansgaard-Oeschger cycles: from MIS3 to today

2021 ◽  
Author(s):  
Heather Andres ◽  
Lev Tarasov
Keyword(s):  
Climate Changes ◽  
Ice Cores ◽  
Ocean Dynamics ◽  
System Model ◽  
Last Deglaciation ◽  
Large Magnitude ◽  
Atmospheric Physics ◽  
The Last Deglaciation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>One of the main contributors to palaeoclimate variability on millennial timescales is understood to be Dansgaard-Oeschger (D-O) cycles. Our awareness of these phenomena arises primarily from quasi-periodic, abrupt transitions of large magnitude detected in δ<sup>18</sup>O records from Greenland ice cores (e.g. Dansgaard et al, 1982; Johnsen et al, 1992), although there is evidence of similar variability in other archives and regions. D-O cycles have plenty to capture the imagination:</p><ul><li> <p>the strength and rapidity of climate changes over Greenland,</p> </li> <li> <p>their regularity throughout MIS3 (~60 to 30 thousand years before present) and occurrence during the last deglaciation contrasting with their relative absence during the Last Glacial Maximum and Holocene,</p> </li> <li> <p>their opposed characteristics in Greenland and Antarctica,</p> </li> <li> <p>and that different models require different boundary conditions to reproduce this phenomena, if they can reproduce it at all.</p> </li> </ul><p> </p><p>This talk characterises D-Olike cycles in two different models: Planet Simulator (PlaSim, an Earth System Model with simplified atmospheric physics, thermodynamic sea ice, and simplified ocean dynamics), and COSMOS (a CMIP3-era ESM). We identify four phases to D-O cycles and commonalities and differences in their representations in these models. Finally, we examine which phases of this type of variability continue to contribute to climate variability today and what that looks like.</p>

scholarly journals Climate bifurcation during the last deglaciation?

2012 ◽  
Vol 8 (4) ◽  
pp. 1127-1139 ◽  
Author(s):  
T. M. Lenton ◽  
V. N. Livina ◽  
V. Dakos ◽  
M. Scheffer
Keyword(s):  
Climate Variability ◽  
Early Warning ◽  
Bifurcation Point ◽  
Climate Changes ◽  
Younger Dryas ◽  
Cold Climate ◽  
Last Deglaciation ◽  
Overturning Circulation ◽  
Slowing Down ◽  
The Last Deglaciation

Abstract. There were two abrupt warming events during the last deglaciation, at the start of the Bølling-Allerød and at the end of the Younger Dryas, but their underlying dynamics are unclear. Some abrupt climate changes may involve gradual forcing past a bifurcation point, in which a prevailing climate state loses its stability and the climate tips into an alternative state, providing an early warning signal in the form of slowing responses to perturbations, which may be accompanied by increasing variability. Alternatively, short-term stochastic variability in the climate system can trigger abrupt climate changes, without early warning. Previous work has found signals consistent with slowing down during the last deglaciation as a whole, and during the Younger Dryas, but with conflicting results in the run-up to the Bølling-Allerød. Based on this, we hypothesise that a bifurcation point was approached at the end of the Younger Dryas, in which the cold climate state, with weak Atlantic overturning circulation, lost its stability, and the climate tipped irreversibly into a warm interglacial state. To test the bifurcation hypothesis, we analysed two different climate proxies in three Greenland ice cores, from the Last Glacial Maximum to the end of the Younger Dryas. Prior to the Bølling warming, there was a robust increase in climate variability but no consistent slowing down signal, suggesting this abrupt change was probably triggered by a stochastic fluctuation. The transition to the warm Bølling-Allerød state was accompanied by a slowing down in climate dynamics and an increase in climate variability. We suggest that the Bølling warming excited an internal mode of variability in Atlantic meridional overturning circulation strength, causing multi-centennial climate fluctuations. However, the return to the Younger Dryas cold state increased climate stability. We find no consistent evidence for slowing down during the Younger Dryas, or in a longer spliced record of the cold climate state before and after the Bølling-Allerød. Therefore, the end of the Younger Dryas may also have been triggered by a stochastic perturbation.

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