scholarly journals Coupled climate–carbon cycle simulation of the Last Glacial Maximum atmospheric CO<sub>2</sub> decrease using a large ensemble of modern plausible parameter sets

2019 ◽  
Vol 15 (3) ◽  
pp. 1039-1062
Author(s):  
Krista M. S. Kemppinen ◽  
Philip B. Holden ◽  
Neil R. Edwards ◽  
Andy Ridgwell ◽  
Andrew D. Friend
Keyword(s):  
Carbon Isotope ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Terrestrial Carbon ◽  
Large Ensemble ◽  
Last Glacial ◽  
The Impact ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. During the Last Glacial Maximum (LGM), atmospheric CO2 was around 90 ppmv lower than during the pre-industrial period. The reasons for this decrease are most often elucidated through factorial experiments testing the impact of individual mechanisms. Due to uncertainty in our understanding of the real system, however, the different models used to conduct the experiments inevitably take on different parameter values and different structures. In this paper, the objective is therefore to take an uncertainty-based approach to investigating the LGM CO2 drop by simulating it with a large ensemble of parameter sets, designed to allow for a wide range of large-scale feedback response strengths. Our aim is not to definitely explain the causes of the CO2 drop but rather explore the range of possible responses. We find that the LGM CO2 decrease tends to predominantly be associated with decreasing sea surface temperatures (SSTs), increasing sea ice area, a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a strengthening of the Antarctic Bottom Water (AABW) cell in the Atlantic Ocean, a decreasing ocean biological productivity, an increasing CaCO3 weathering flux and an increasing deep-sea CaCO3 burial flux. The majority of our simulations also predict an increase in terrestrial carbon, coupled with a decrease in ocean and increase in lithospheric carbon. We attribute the increase in terrestrial carbon to a slower soil respiration rate, as well as the preservation rather than destruction of carbon by the LGM ice sheets. An initial comparison of these dominant changes with observations and paleoproxies other than carbon isotope and oxygen data (not evaluated directly in this study) suggests broad agreement. However, we advise more detailed comparisons in the future, and also note that, conceptually at least, our results can only be reconciled with carbon isotope and oxygen data if additional processes not included in our model are brought into play.

The impact of tidal dissipation changes on the Last Glacial Maximum AMOC

2020 ◽  
Author(s):  
Sophie-Berenice Wilmes ◽  
Mattias Green ◽  
Andreas Schmittner
Keyword(s):  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Tidal Mixing ◽  
Tidal Dissipation ◽  
Last Glacial ◽  
Meridional Overturning ◽  
The Impact ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;The global mean sea-level decrease of 120 &amp;#8211; 130 m during the Last Glacial Maximum (LGM; 26 &amp;#8211; 19 kyr BP) is thought to have substantially altered semidiurnal tidal dynamics in the glacial North Atlantic. This more than doubled global open ocean tidal dissipation in comparison to present day and increased the amount of energy available for diapycnal mixing which is important for driving the global meridional overturning circulation. Reconstructions of the glacial ocean have generally suggested a more sluggish Atlantic meridional overturning circulation (AMOC) during the LGM together with weaker mixing. Here, we investigate the impact of tidal dissipation changes on the LGM AMOC and the carbon cycle using the intermediate complexity ocean model UVic coupled to the biogeochemistry model MOBI forced with three different LGM dissipation estimates. The simulations are constrained with LGM &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C and radiocarbon data from sediments. Our results suggest that our simulations, as previously inferred, most closely agree with a weakened LGM AMOC (8 &amp;#8211; 9 Sv), and importantly, that the agreement is consistent with increased LGM tidal mixing. These results firstly imply that a weakened AMOC state can occur with stronger tidal mixing without hampering the agreement with the sediment isotope data. Secondly, this work highlights the importance of considering tidal dissipation changes when modelling the paleo-ocean.&lt;/p&gt;

Northern-sourced water dominated the Atlantic Ocean during the Last Glacial Maximum

Geology ◽  
2020 ◽  
Vol 48 (8) ◽  
pp. 826-829 ◽  
Author(s):  
F. Pöppelmeier ◽  
P. Blaser ◽  
M. Gutjahr ◽  
S.L. Jaccard ◽  
M. Frank ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Water Mass ◽  
Stable Carbon Isotope ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Δ13c Values ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 concentrations. Remineralized carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here, we present new sediment-derived bottom-water neodymium isotope records that allow fingerprinting of water masses and provide a more complete picture of the Atlantic Meridional Overturning Circulation geometry during the Last Glacial Maximum. These results suggest that the vertical and meridional structure of the Atlantic water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern-sourced water substantially expanding to shallower depths and farther into the Northern Hemisphere than today, which had been previously inferred from stable carbon isotope (δ13C) reconstructions. We argue that depleted δ13C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern-sourced water. Instead, these values may represent a northern-sourced water mass with lower than modern preformed δ13C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation, corroborating previous evidence.

scholarly journals Influence of dynamic vegetation on climate change and terrestrial carbon storage in the Last Glacial Maximum

2013 ◽  
Vol 9 (4) ◽  
pp. 1571-1587 ◽  
Author(s):  
R. O'ishi ◽  
A. Abe-Ouchi
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Terrestrial Carbon ◽  
Dynamic Global Vegetation Model ◽  
Vegetation Feedback ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

Modelling Global Vegetation Patterns and Terrestrial Carbon Storage at the Last Glacial Maximum

1993 ◽  
Vol 3 (3) ◽  
pp. 67 ◽  
Author(s):  
I. Colin Prentice ◽  
Martin T. Sykes ◽  
Michael Lautenschlager ◽  
Sandy P. Harrison ◽  
Olga Denissenko ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Vegetation Patterns ◽  
Terrestrial Carbon ◽  
Last Glacial ◽  
Global Vegetation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals N<sub>2</sub>O changes from the Last Glacial Maximum to the preindustrial – Part 1: Quantitative reconstruction of terrestrial and marine emissions using N<sub>2</sub>O stable isotopes in ice cores

2019 ◽  
Vol 16 (20) ◽  
pp. 3997-4021 ◽  
Author(s):  
Hubertus Fischer ◽  
Jochen Schmitt ◽  
Michael Bock ◽  
Barbara Seth ◽  
Fortunat Joos ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
N2o Emission ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Subsurface Water ◽  
N2o Emissions ◽  
Overturning Circulation ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Using high-precision and centennial-resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition, we quantitatively reconstruct changes in the terrestrial and marine N2O emissions over the last 21 000 years. Our reconstruction indicates that N2O emissions from land and ocean increased over the deglaciation largely in parallel by 1.7±0.3 and 0.7±0.3 TgN yr−1, respectively, relative to the Last Glacial Maximum level. However, during the abrupt Northern Hemisphere warmings at the onset of the Bølling–Allerød warming and the end of the Younger Dryas, terrestrial emissions respond more rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation. About 90 % of these large step increases were realized within 2 centuries at maximum. In contrast, marine emissions start to slowly increase already many centuries before the rapid warmings, possibly connected to a re-equilibration of subsurface oxygen in response to previous changes. Marine emissions decreased, concomitantly with changes in atmospheric CO2 and δ13C(CO2), at the onset of the termination and remained minimal during the early phase of Heinrich Stadial 1. During the early Holocene a slow decline in marine N2O emission of 0.4 TgN yr−1 is reconstructed, which suggests an improvement of subsurface water ventilation in line with slowly increasing Atlantic overturning circulation. In the second half of the Holocene total emissions remain on a relatively constant level, but with significant millennial variability. The latter is still difficult to attribute to marine or terrestrial sources. Our N2O emission records provide important quantitative benchmarks for ocean and terrestrial nitrogen cycle models to study the influence of climate on nitrogen turnover on timescales from several decades to glacial–interglacial changes.

Modeling the dynamics of terrestrial carbon storage since the Last Glacial Maximum

2002 ◽  
Vol 29 (22) ◽  
pp. 31-1-31-4 ◽  
Author(s):  
Jed O. Kaplan ◽  
I. Colin Prentice ◽  
Wolfgang Knorr ◽  
Paul J. Valdes
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Terrestrial Carbon ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Quantifying the roles of ocean circulation and biogeochemistry in governing ocean carbon-13 and atmospheric carbon dioxide at the last glacial maximum

2009 ◽  
Vol 5 (4) ◽  
pp. 695-706 ◽  
Author(s):  
A. Tagliabue ◽  
L. Bopp ◽  
D. M. Roche ◽  
N. Bouttes ◽  
J.-C. Dutay ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Last Glacial ◽  
Carbon 14 ◽  
Ocean Carbon ◽  
The Impact ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use a state-of-the-art ocean general circulation and biogeochemistry model to examine the impact of changes in ocean circulation and biogeochemistry in governing the change in ocean carbon-13 and atmospheric CO2 at the last glacial maximum (LGM). We examine 5 different realisations of the ocean's overturning circulation produced by a fully coupled atmosphere-ocean model under LGM forcing and suggested changes in the atmospheric deposition of iron and phytoplankton physiology at the LGM. Measured changes in carbon-13 and carbon-14, as well as a qualitative reconstruction of the change in ocean carbon export are used to evaluate the results. Overall, we find that while a reduction in ocean ventilation at the LGM is necessary to reproduce carbon-13 and carbon-14 observations, this circulation results in a low net sink for atmospheric CO2. In contrast, while biogeochemical processes contribute little to carbon isotopes, we propose that most of the change in atmospheric CO2 was due to such factors. However, the lesser role for circulation means that when all plausible factors are accounted for, most of the necessary CO2 change remains to be explained. This presents a serious challenge to our understanding of the mechanisms behind changes in the global carbon cycle during the geologic past.

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