Tidal mixing and the Meridional Overturning Circulation from the Last Glacial Maximum

2009 ◽  
Vol 36 (15) ◽  
pp. n/a-n/a ◽  
Author(s):  
J. A. Mattias Green ◽  
Clare L. Green ◽  
Grant R. Bigg ◽  
Tom. P. Rippeth ◽  
James D. Scourse ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Tidal Mixing ◽  
Overturning Circulation ◽  
Last Glacial ◽  
Meridional Overturning ◽  
The Last Glacial Maximum ◽  
The Last Glacial

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

<p>The global mean sea-level decrease of 120 – 130 m during the Last Glacial Maximum (LGM; 26 – 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 δ<sup>13</sup>C and radiocarbon data from sediments. Our results suggest that our simulations, as previously inferred, most closely agree with a weakened LGM AMOC (8 – 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.</p>

Atlantic Meridional Overturning Circulation During the Last Glacial Maximum

Science ◽  
2007 ◽  
Vol 316 (5821) ◽  
pp. 66-69 ◽  
Author(s):  
J. Lynch-Stieglitz ◽  
J. F. Adkins ◽  
W. B. Curry ◽  
T. Dokken ◽  
I. R. Hall ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Atlantic Meridional Overturning Circulation ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Last Glacial ◽  
Meridional Overturning ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Meridional overturning circulation in the South Atlantic at the last glacial maximum

2006 ◽  
Vol 7 (10) ◽  
pp. n/a-n/a ◽  
Author(s):  
Jean Lynch-Stieglitz ◽  
William B. Curry ◽  
Delia W. Oppo ◽  
Ulysses S. Ninneman ◽  
Christopher D. Charles ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
South Atlantic ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
The South ◽  
Overturning Circulation ◽  
Last Glacial ◽  
Meridional Overturning ◽  
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.

scholarly journals Sequential changes in ocean circulation and biological export productivity during the last glacial cycle: a model-data study

2019 ◽  
Author(s):  
Cameron M. O'Neill ◽  
Andrew McC. Hogg ◽  
Michael J. Ellwood ◽  
Bradley N. Opdyke ◽  
Stephen M. Eggins
Keyword(s):  
Southern Ocean ◽  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Atmospheric Co2 ◽  
Overturning Circulation ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We conduct a model-data analysis of the ocean, atmosphere and terrestrial carbon system to understand their effects on atmospheric CO2 during the last glacial cycle. We use a carbon cycle box model SCP-M, combined with multiple proxy data for the atmosphere and ocean, to test for variations in ocean circulation and biological productivity across marine isotope stages spanning 130 thousand years ago to the present. The model is constrained by proxy data associated with a range of environmental conditions including sea surface temperature, salinity, ocean volume, sea ice cover and shallow water carbonate production. Model parameters for global ocean circulation, Atlantic meridional overturning circulation and Southern Ocean biological export productivity are optimised in each marine isotope stage, against proxy data for atmospheric CO2, δ13C and ∆14C and deep ocean δ13C, ∆14C and carbonate ion. Our model-data results suggest that global overturning circulation weakened at marine isotope stage 5d, coincident with a ∼ 25 ppm fall in atmospheric CO2 from the penultimate interglacial level. This change was followed by a further slowdown in Atlantic meridional overturning circulation and enhanced Southern Ocean biological export productivity at marine isotope stage 4 (∼−30 ppm). There was also a transient slowdown in Atlantic meridional overturning circulation at MIS 5b. In this model, the last glacial maximum was characterised by relatively weak global ocean and Atlantic meridional overturning circulation, and increased Southern Ocean biological export productivity (∼−15–20 ppm during MIS 2–4). Ocean circulation and Southern Ocean biology rebounded to modern values by the Holocene period. The terrestrial biosphere decreased by ∼ 500 Pg C in the lead up to the last glacial maximum, followed by a period of intense regrowth during the Holocene (∼ 750 Pg C). Slowing ocean circulation, a cooler ocean and, to a lesser extent, shallow carbonate dissolution, contributed ∼−75 ppm to atmospheric CO2 in the ∼ 100 thousand-year lead-up to the last glacial maximum, with a further ∼−10 ppm contributed during the glacial maximum. Our model results also suggest that an increase in Southern Ocean biological productivity was one of the ingredients required to achieve the last glacial maximum atmospheric CO2 level. The incorporation of longer-timescale data into quantitative ocean transport models, provides useful insights into the timing of changes in ocean processes, enhancing our understanding of the last glacial maximum and Holocene carbon cycle transition.

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 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.

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