scholarly journals The impacts of deglacial meltwater forcing on the South Atlantic Ocean deep circulation since the Last Glacial Maximum

2014 ◽  
Vol 10 (5) ◽  
pp. 1723-1734 ◽  
Author(s):  
J. M. Marson ◽  
I. Wainer ◽  
M. M. Mata ◽  
Z. Liu
Keyword(s):  
Last Glacial Maximum ◽  
Atlantic Water ◽  
South Atlantic ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
The South ◽  
Climate System Model ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. A NCAR-CCSM3 (National Center for Atmospheric Research – Community Climate System Model version 3) state-of-the-art transient paleoclimate simulation with prescribed freshwater inflows is used to investigate the changes and evolution of the South Atlantic water mass structure from the Last Glacial Maximum (LGM) to the present day. Model results show that 21 000 yr ago the water column was substantially stratified due to the presence of a saltier-than-today Antarctic Bottom Water (AABW), forming a salinity barrier that prevented dense waters from the Northern Hemisphere from sinking. This salinity barrier started to erode after the termination of the Heinrich event 1, when its associated meltwater was transported southward, freshening the AABW. The removal of the barrier after 14 ka triggered the production of the North Atlantic Deep Water (NADW), which spread into the deeper layers of the South Atlantic at the onset of the Holocene. At this point, the NADW acquired its modern-day structure, establishing a deeper Atlantic meridional overturning circulation (AMOC).

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

A numerical study of the South Atlantic circulation at the Last Glacial Maximum

2007 ◽  
Vol 253 (3-4) ◽  
pp. 509-528 ◽  
Author(s):  
Gabriel Clauzet ◽  
Ilana Wainer ◽  
Alban Lazar ◽  
Esther Brady ◽  
Bette Otto-Bliesner
Keyword(s):  
Last Glacial Maximum ◽  
Numerical Study ◽  
South Atlantic ◽  
Glacial Maximum ◽  
The South ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals The impacts of Meltwater Pulse-1A in the South Atlantic Ocean deep circulation since the Last Glacial Maximum

2013 ◽  
Vol 9 (6) ◽  
pp. 6375-6395 ◽  
Author(s):  
J. M. Marson ◽  
I. Wainer ◽  
Z. Liu ◽  
M. M. Mata
Keyword(s):  
Atlantic Ocean ◽  
Sea Level ◽  
Last Glacial Maximum ◽  
South Atlantic ◽  
Glacial Maximum ◽  
South Atlantic Ocean ◽  
The South ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Since 21 000 yr ago, the oceans have received large amounts of freshwater in pulses coming from the melting ice sheets. A specific event, known as meltwater pulse 1A (MWP-1A), has been identified in sea-level and temperature proxy records as responsible for the increase of ~20 m in sea level in less than 500 yr. Although its origin and timing are still under discussion, MWP-1A seems to have had a significant impact on several components of the climatic system. The present work aims to elucidate these impacts on the water mass distribution of the South Atlantic Ocean through the analysis of a transient simulation of the climate evolution from the Last Glacial Maximum to Present Day using a state-of-art CGCM, the National Center for Atmospheric Research Community Climate System Model version 3 (NCAR CCSM3). Results show that the freshwater discharge associated with the timing of MWP-1A was crucial to establish the present thermohaline structure associated with the North Atlantic Deep Water, marking the transition between a shallower and a deeper Atlantic Meridional Overturning Circulation.

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.

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>

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.

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