Holocene North Atlantic Overturning in an atmosphere‐ocean‐sea ice model compared to proxy‐based reconstructions

Blaschek, Michael; Renssen, H.; Kissel, Catherine; Thornalley, David

doi:10.1002/2015pa002828

Cited by 13 publications

(13 citation statements)

References 116 publications

(274 reference statements)

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“…The onset of the northward subsurface warm water transport agrees with the stabilization of the North Atlantic deepwater circulation that previously was related to the onset of LSW formation (Hoogakker et al, 2011;Thornalley et al, 2013). Alternatively, as recently discussed (Blaschek et al, 2015), this stabilization may be mainly related to an increase in Nordic sea deepwater convection, though more studies are needed to confirm this theory.…”

Section: Driving Factors For Subsurface Transport Changes and Af Posimentioning

confidence: 96%

“…South of the Denmark Strait, the IC returns southward, following the coast of Greenland into the Labrador Sea (Spall and Pickart, 2003). It thereby feeds warm saline waters into the counterclockwiserotating SPG and fuels deepwater convection in the Labrador Sea (Born and Stocker, 2014;Sarafanov et al, 2012;Våge et al, 2011).…”

Section: Regional Settingmentioning

confidence: 99%

“…In addition to the forcing by increases in atmospheric CO 2, four driving factors may be of importance for the observed Holocene changes in the Azores region: (1) changes in AC transport strength and position due to changes in Mediterranean Outflow Water (MOW) strength, (2) changes in the atmospheric circulation related to the northern hemispheric summer insolation (Renssen, 2005) and changes in North Atlantic Oscillation (NAO) patterns (e.g., Olsen et al, 2012;Wassenburg et al, 2016), (3) changes in meltwater forcing over the North Atlantic region due to melting of continental ice sheets (Mayewski et al, 2004), and (4) changes in solar activity (Bond et al, 2001). The latter will not be discussed due to the relatively low resolution of the late Holocene record, which hampers time series analyses.…”

Section: Driving Factors For Subsurface Transport Changes and Af Posimentioning

confidence: 99%

“…The causes of these cycles are controversially discussed, with hypotheses ranging from meltwater pulses induced by variations in solar irradiance to internal ocean-ice-atmosphere feedback mechanisms or volcanism (e.g., Andrews and Giraudeau, 2003;Bond et al, 2001;Campbell et al, 1998;Schulz et al, 2004;Viau et al, 2006;Wanner, 2008). Due to the wide range of feedback mechanisms, involving northern hemispheric oceanic and atmospheric circulation, climate patterns with strong local differences are observed for the Holocene.…”

Section: Introductionmentioning

confidence: 99%

“…A stable LSW formation relies on the interaction between warm water transport in the clockwisecirculating subtropical gyre (STG) and the subpolar gyre (SPG), circulating counterclockwise in the Irminger Basin and the Labrador Sea (Thornalley et al, 2009). Antiphase heat and salt storage within the STG during times when SPG freshens (Cléroux et al, 2012;Thornalley et al, 2009) and the subsequent advection of the warm saline water into the SPG leads to a strengthening of the deepwater formation by convection within the SPG (e.g., Born and Stocker, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Holocene evolution of the North Atlantic subsurface transport

Repschläger¹,

Garbe‐Schönberg²,

Weinelt³

et al. 2017

Clim. Past

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Abstract. Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ 18 O and Mg / Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.

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Section: Driving Factors For Subsurface Transport Changes and Af Posimentioning

confidence: 96%

Section: Regional Settingmentioning

confidence: 99%

Section: Driving Factors For Subsurface Transport Changes and Af Posimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Holocene evolution of the North Atlantic subsurface transport

Repschläger¹,

Garbe‐Schönberg²,

Weinelt³

et al. 2017

Clim. Past

View full text Add to dashboard Cite

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Eurasian Holocene climate trends in transient coupled climate simulations and stable oxygen isotope records

Danek

Gierz

Kostrova

et al. 2021

J Quaternary Science

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Transient simulations of the global fully coupled climate model COSMOS under realistic varying orbital and greenhouse gas forcings are systematically compared to diatom oxygen isotope ( δ 18 O 0.1em diatom0.1em) records from Russian lakes with focus on Eurasian Holocene climate trends. The measured δ 18 O 0.1em diatom0.1em decrease and other temperature proxies are interpreted as large‐scale cooling throughout the Holocene while the model simulations are biased too warm, likely through missing radiative forcings. This large‐scale warm bias also dictates the modeled δ 18 O 0.1em precipitation. Hence, at locations where the signs of model and proxy temperature/precipitation trends agree, measured δ 18 O 0.1em diatom0.1em and modeled δ 18 O 0.1em precipitation0.1em trends show notable accordance. An increased temporal variability of modeled δ 18 O 0.1em precipitation0.1em is linked to persistent atmospheric circulation patterns. Applying the transient forcings in an accelerated way (every 10th year only) yields a similar, yet weaker or delayed model response, especially in the ocean.

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Impact of freshwater release in the Mediterranean Sea on the North Atlantic climate

et al. 2019

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Sediment cores from the Mediterranean Sea have evidenced several periods of Sapropel deposition, which can be explained by events of anoxic bottom conditions. An explanation for such events calls for a very stratified sea, possibly related with freshwater input through increased precipitations and runoff discharges. It has been suggested that such a stratified Mediterranean Sea may in turn weaken the Atlantic meridional overturning circulation (AMOC) through changes in the Mediterranean overflow water (MOW). Nevertheless, models used to establish this result were relatively simple and the mechanisms leading to such an impact remained elusive. To improve on those previous studies, we analyse the impact of different freshwater releases with rates of 0.2, 0.1, 0.05 and 0.02 Sv (1 Sv=10 6 m 3 /s) in the Mediterranean Sea using the IPSL-CM5A-LR model in a few multicentennial simulations. We focus the analysis on the impact of a decrease in the Mediterranean overflow water (MOW) on the large-scale Atlantic circulation. We find a consistent change in horizontal currents in the upper Atlantic Ocean in all simulations in the first century, with a large enhancement of the northward current west of Rockall in the northeast Atlantic. Concerning the AMOC response, we identify three different processes that impact its fate. The first is related to changes in geostrophic currents at depth induced by the disappearance of the MOW, which tends to weaken the AMOC. On the contrary, the second enhances the AMOC and is associated with the increase in northward currents in the horizontal upper circulation. The last process is due to the spread of surface freshwater anomalies out of the Mediterranean Sea that freshens the North Atlantic convection sites and weakens the AMOC. Depending on the rate of the freshwater release, the strength and balance of these three processes are different. For rates larger than 0.05 Sv, we observe a strong reduction of the AMOC, while for lower rates, we notice an enhancement in the upper cell. The climatic response follows that of the upper AMOC with a warming of the North Atlantic for rates lower than 0.05 Sv and a cooling for higher rates. Given that past estimates of freshwater release in the Mediterranean Sea indicate rates lower than 0.05 Sv, we argue that Sapropel events may have enhanced of the upper AMOC and warmed of the North Atlantic.

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Holocene North Atlantic Overturning in an atmosphere‐ocean‐sea ice model compared to proxy‐based reconstructions

Cited by 13 publications

References 116 publications

Holocene evolution of the North Atlantic subsurface transport

Holocene evolution of the North Atlantic subsurface transport

Eurasian Holocene climate trends in transient coupled climate simulations and stable oxygen isotope records

Impact of freshwater release in the Mediterranean Sea on the North Atlantic climate

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