scholarly journals Evolution of mean ocean temperature in Marine Isotope Stage 4

2021 ◽  
Vol 17 (5) ◽  
pp. 2273-2289
Author(s):  
Sarah Shackleton ◽  
James A. Menking ◽  
Edward Brook ◽  
Christo Buizert ◽  
Michael N. Dyonisius ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Noble Gas ◽  
Ice Sheet ◽  
Heat Content ◽  
Marine Isotope Stage ◽  
Ocean Temperature ◽  
Last Interglacial ◽  
Co2 Solubility ◽  
Carbon Cycle Model ◽  
Mis 5

Abstract. Deglaciations are characterized by relatively fast and near-synchronous changes in ice sheet volume, ocean temperature, and atmospheric greenhouse gas concentrations, but glacial inception occurs more gradually. Understanding the evolution of ice sheet, ocean, and atmosphere conditions from interglacial to glacial maximum provides insight into the interplay of these components of the climate system. Using noble gas measurements in ancient ice samples, we reconstruct mean ocean temperature (MOT) from 74 to 59.7 ka, covering the Marine Isotope Stage (MIS) 5a–4 boundary, MIS 4, and part of the MIS 4–3 transition. Comparing this MOT reconstruction to previously published MOT reconstructions from the last and penultimate deglaciation, we find that the majority of the last interglacial–glacial ocean cooling must have occurred within MIS 5. MOT reached equally cold conditions in MIS 4 as in MIS 2 (−2.7 ± 0.3 ∘C relative to the Holocene, −0.1 ± 0.3 ∘C relative to MIS 2). Using a carbon cycle model to quantify the CO2 solubility pump, we show that ocean cooling can explain most of the CO2 drawdown (32 ± 4 of 40 ppm) across MIS 5. Comparing MOT to contemporaneous records of benthic δ18O, we find that ocean cooling can also explain the majority of the δ18O increase across MIS 5 (0.7 ‰ of 1.3 ‰). The timing of ocean warming and cooling in the record and the comparison to coeval Antarctic isotope data suggest an intimate link between ocean heat content, Southern Hemisphere high-latitude climate, and ocean circulation on orbital and millennial timescales.

scholarly journals Evolution of mean ocean temperature in Marine Isotope Stages 5-4

2021 ◽  
Author(s):  
Sarah Shackleton ◽  
James A. Menking ◽  
Edward Brook ◽  
Christo Buizert ◽  
Michael N. Dyonisius ◽  
...  
Keyword(s):  
Noble Gas ◽  
Ice Sheet ◽  
Ocean Temperature ◽  
Atmospheric Conditions ◽  
Last Deglaciation ◽  
Glacial Cycle ◽  
The Last Deglaciation ◽  
Gas Measurements ◽  
Mis 5 ◽  
The Last Glacial

Abstract. Deglaciations are characterized by relatively fast and near-synchronous changes in ice sheet volume, ocean temperature, and atmospheric greenhouse gas concentrations, but glacial inceptions occur more gradually. Understanding the evolution of ice sheet, ocean, and atmospheric conditions from interglacial to glacial maximum provides important insight into the interplay of these components of our climate system. Using noble gas measurements in ancient ice samples, we reconstruct mean ocean temperature (MOT) from 74 to 59.5 ka BP, covering the Marine Isotope Stage (MIS) 5-4 boundary, MIS 4, and part of the MIS 4-3 transition. Comparing this MOT reconstruction to previously published MOT reconstructions from the last glacial cycle, we find that the majority of interglacial-glacial ocean cooling occurred across MIS 5, and MOT reached full glacial levels by MIS 4 (−2.7 ± 0.3 °C relative to the Holocene). Comparing MOT to contemporaneous records of CO2 and benthic 𝛿18O, we find that ocean cooling and the solubility pump can explain most of the CO2 drawdown and increase in 𝛿18O across MIS 5. The timing of ocean warming and cooling in our record indicates that millennial scale climate variability plays a crucial role in setting mean ocean temperature during this interval, as seen during other periods, such as the last deglaciation.

scholarly journals Effect of changing ocean circulation on deep ocean temperature in the last millennium

2020 ◽  
Author(s):  
Jeemijn Scheen ◽  
Thomas F. Stocker
Keyword(s):  
Surface Temperature ◽  
Ocean Circulation ◽  
Little Ice Age ◽  
Heat Content ◽  
Deep Ocean ◽  
Ice Age ◽  
Ocean Temperature ◽  
Meridional Heat Transport ◽  
Temperature Anomalies ◽  
The Past

Abstract. Paleoreconstructions and modern observations provide us with anomalies of surface temperature over the past millennium. The history of deep ocean temperatures is much less well-known and was simulated in a recent study for the past 2000 years under forced surface temperature anomalies. In this study, we simulate the past 800 years with an illustrative forcing scenario in the Bern3D ocean model, which enables us to assess the role of changes in ocean circulation on deep ocean temperature. We quantify the effect of changing ocean circulation by comparing transient simulations (where the ocean dynamically adjusts to anomalies in surface temperature – hence density) to simulations with fixed ocean circulation. We decompose temperature, ocean heat content and meridional heat transport into the contributions from changing ocean circulation and changing sea surface temperature (SST). In the deep ocean, the contribution from changing ocean circulation is found to be as important as the changing SST signal itself. Firstly, the small changes in ocean circulation amplify the Little Ice Age signal around 3 km depth by at least a factor of two, depending on the basin. Secondly, they fasten the arrival of this atmospheric signal in the Pacific and Southern Ocean at all depths, whereas they delay the arrival in the Atlantic between about 2.5 and 3.5 km by two centuries. This delay is explained by an initial competition between the Little Ice Age cooling and a warming due to an increase in relatively warmer North Atlantic Deep Water at the cost of Antarctic Bottom Water. Under the consecutive AMOC slowdown, this shift in water masses is inverted and aging of the water causes a late additional cooling. Our results suggest that small changes in ocean circulation can have a large impact on the amplitude and timing of ocean temperature anomalies below 2 km depth.

scholarly journals The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature

2008 ◽  
Vol 21 (11) ◽  
pp. 2558-2572 ◽  
Author(s):  
Paul R. Holland ◽  
Adrian Jenkins ◽  
David M. Holland
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Flow Speed ◽  
Ocean Warming ◽  
Ocean Temperature ◽  
Ice Shelf ◽  
Ice Shelves

Abstract A three-dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean-warming scenarios. The model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms. This occurs because the melt rate is proportional to the product of ocean flow speed and temperature in the mixed layer directly beneath the ice shelf, both of which are found to increase linearly with ocean warming. The behavior of this complex primitive equation model can be described surprisingly well with recourse to an idealized reduced system of equations, and it is shown that this system supports a melt rate response to warming that is generally quadratic in nature. This study confirms and unifies several previous examinations of the relation between melt rate and ocean temperature but disagrees with other results, particularly the claim that a single melt rate sensitivity to warming is universally valid. The hypothesized warming does not necessarily require a heat input to the ocean, as warmer waters (or larger volumes of “warm” water) may reach ice shelves purely through a shift in ocean circulation. Since ice shelves link the Antarctic Ice Sheet to the climate of the Southern Ocean, this finding of an above-linear rise in ice shelf mass loss as the ocean steadily warms is of significant importance to understanding ice sheet evolution and sea level rise.

scholarly journals Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31

2020 ◽  
Vol 228 ◽  
pp. 106069 ◽  
Author(s):  
Catherine Beltran ◽  
Nicholas R. Golledge ◽  
Christian Ohneiser ◽  
Douglas E. Kowalewski ◽  
Marie-Alexandrine Sicre ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ice Sheet ◽  
Marine Isotope Stage ◽  
Atmospheric Co2 ◽  
Ocean Temperature ◽  
Antarctic Ice Sheet ◽  
Temperature Records

scholarly journals Equilibrium simulations of Marine Isotope Stage 3 climate

2019 ◽  
Vol 15 (3) ◽  
pp. 1133-1151 ◽  
Author(s):  
Chuncheng Guo ◽  
Kerim H. Nisancioglu ◽  
Mats Bentsen ◽  
Ingo Bethke ◽  
Zhongshi Zhang
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Large Scale ◽  
Ice Sheet ◽  
Arctic Sea Ice ◽  
Meridional Overturning Circulation ◽  
Marine Isotope Stage ◽  
Quasi Equilibrium ◽  
Near Surface ◽  
Marine Isotope Stage 3

Abstract. An equilibrium simulation of Marine Isotope Stage 3 (MIS3) climate with boundary conditions characteristic of Greenland Interstadial 8 (GI-8; 38 kyr BP) is carried out with the Norwegian Earth System Model (NorESM). A computationally efficient configuration of the model enables long integrations at relatively high resolution, with the simulations reaching a quasi-equilibrium state after 2500 years. We assess the characteristics of the simulated large-scale atmosphere and ocean circulation, precipitation, ocean hydrography, sea ice distribution, and internal variability. The simulated MIS3 interstadial near-surface air temperature is 2.9 ∘C cooler than the pre-industrial (PI). The Atlantic meridional overturning circulation (AMOC) is deeper and intensified by ∼13 %. There is a decrease in the volume of Antarctic Bottom Water (AABW) reaching the Atlantic. At the same time, there is an increase in ventilation of the Southern Ocean, associated with a significant expansion of Antarctic sea ice and concomitant intensified brine rejection, invigorating ocean convection. In the central Arctic, sea ice is ∼2 m thicker, with an expansion of sea ice in the Nordic Seas during winter. Attempts at triggering a non-linear transition to a cold stadial climate state, by varying atmospheric CO2 concentrations and Laurentide Ice Sheet height, suggest that the simulated MIS3 interstadial state in the NorESM is relatively stable, thus underscoring the role of model dependency, and questioning the existence of unforced abrupt transitions in Greenland climate in the absence of interactive ice sheet–meltwater dynamics.

Sensitivity of Last Interglacial sea-level high stands to ice sheet configuration during Marine Isotope Stage 6

2017 ◽  
Vol 171 ◽  
pp. 234-244 ◽  
Author(s):  
S. Dendy ◽  
J. Austermann ◽  
J.R. Creveling ◽  
J.X. Mitrovica
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Marine Isotope Stage ◽  
Last Interglacial

Tipping Points in Antarctic Climate Components (TiPACCs)

2020 ◽  
Author(s):  
Petra Langebroek ◽  
Svein Østerhus ◽  
TiPACCs Consortium
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
Tipping Point ◽  
Tipping Points ◽  
Last Interglacial ◽  
Antarctic Ice Sheet ◽  
Horizon 2020 ◽  
West Antarctic ◽  
Basal Melting ◽  
The Antarctic

<p><span><span>Recently, several of the West Antarctic ice shelves have experienced thinning driven by ocean-induced basal melting. The consequent reduction in buttressing of the Antarctic ice sheet causes an increase in the discharge of the grounded ice into the ocean.</span></span></p><p><span><span>In our new Horizon 2020 project “Tipping Points in Antarctic Climate Components” (TiPACCs) we address these processes by assessing the possible switch from “cold” to “warm” Antarctic continental shelf seas (tipping point 1) and the possible shift in the stability regime of the Antarctic ice sheet from a stable to an unstable configuration (tipping point 2). Investigating the coupled ocean-ice system, the tipping points and their feedbacks, will provide insight into the threat of abrupt and large sea-level rise. In TiPACCs we use a suite of state-of-the-art ocean circulation and ice sheet models, in stand-alone and coupled set-up. The proximity of the simulated tipping points will be determined by existing remote sensing and in-situ observations. The possibility that the tipping points were crossed during the Last Interglacial will be investigated and allow for a better understanding of how the ocean-ice system works during warmer than present-day conditions.</span></span></p><p><span><span>This EGU contribution will present the ideas, the planned work, and the consortium of TiPACCs.</span></span></p>

scholarly journals Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse

2016 ◽  
Vol 43 (6) ◽  
pp. 2675-2682 ◽  
Author(s):  
Johannes Sutter ◽  
Paul Gierz ◽  
Klaus Grosfeld ◽  
Malte Thoma ◽  
Gerrit Lohmann
Keyword(s):  
Ice Sheet ◽  
Ocean Temperature ◽  
Last Interglacial ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Temperature Thresholds

Estimating Global Ocean Heat Content Changes in the Upper 1800 m since 1950 and the Influence of Climatology Choice*

2014 ◽  
Vol 27 (5) ◽  
pp. 1945-1957 ◽  
Author(s):  
John M. Lyman ◽  
Gregory C. Johnson
Keyword(s):  
Heat Content ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Ocean Temperature ◽  
Vertical Separation ◽  
Ocean Heat Uptake ◽  
Expendable Bathythermograph ◽  
Heat Uptake ◽  
The Mean

Abstract Ocean heat content anomalies are analyzed from 1950 to 2011 in five distinct depth layers (0–100, 100–300, 300–700, 700–900, and 900–1800 m). These layers correspond to historic increases in common maximum sampling depths of ocean temperature measurements with time, as different instruments—mechanical bathythermograph (MBT), shallow expendable bathythermograph (XBT), deep XBT, early sometimes shallower Argo profiling floats, and recent Argo floats capable of worldwide sampling to 2000 m—have come into widespread use. This vertical separation of maps allows computation of annual ocean heat content anomalies and their sampling uncertainties back to 1950 while taking account of in situ sampling advances and changing sampling patterns. The 0–100-m layer is measured over 50% of the globe annually starting in 1956, the 100–300-m layer starting in 1967, the 300–700-m layer starting in 1983, and the deepest two layers considered here starting in 2003 and 2004, during the implementation of Argo. Furthermore, global ocean heat uptake estimates since 1950 depend strongly on assumptions made concerning changes in undersampled or unsampled ocean regions. If unsampled areas are assumed to have zero anomalies and are included in the global integrals, the choice of climatological reference from which anomalies are estimated can strongly influence the global integral values and their trend: the sparser the sampling and the bigger the mean difference between climatological and actual values, the larger the influence.

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