Modelling tempo-spatial signatures of Heinrich Events: influence of the climatic background state

Prange, Matthias; Lohmann, Gerrit; Romanova, V.; Butzin, Martin

doi:10.1016/j.quascirev.2003.11.004

Cited by 33 publications

(27 citation statements)

References 39 publications

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“…The latter approach is similar to typical Heinrich modeling studies that add freshwater directly to large areas of the North Atlantic [e.g., Ganopolski and Rahmstorf, 2001;Prange et al, 2004]. In our case we find that although the floods give qualitatively similar results, the impact is larger than for the iceberg events, with significantly more weakening of the MOC and colder SST anomalies.…”

Section: Discussionsupporting

confidence: 86%

“…This reduces the impact on the MOC compared to less realistic experiments, whereby the freshwater flux is prescribed over a larger area of the North Atlantic. The fluxes needed to halt the MOC completely in other glacial climate models with such freshwater hosing lie in a range of 0.15-0.5 Sv [Ganopolski and Rahmstorf, 2001;Prange et al, 2004]. In our experiments we need a relatively large freshwater flux of 0.4 Sv to cause a complete shutdown of the MOC, because of our more realistic localized freshwater and iceberg input.…”

Section: Discussionmentioning

confidence: 96%

“…[4] Previous modeling efforts looking at the impact of abrupt freshwater fluxes on the glacial ocean have not included an explicit iceberg model, but have rather simulated Heinrich events by directly introducing freshwater into the North Atlantic Ocean [e.g., Ganopolski and Rahmstorf, 2001;Prange et al, 2004]. Another approach is taken by Seidov and Maslin [1999], who modeled these events by replacing Last Glacial Maximum (LGM) boundary conditions with Heinrich event sea surface conditions from proxy data.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

2008

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[1] We introduce explicit icebergs from a dynamic and thermodynamic iceberg model into an intermediate complexity climate model, which includes the coupled atmosphere-ocean system. This modeling approach allows iceberg meltwater to be injected into the ocean on the basis of thermodynamical considerations along the iceberg trajectories. Icebergs are seeded from known ice sheets in both hemispheres. Adding icebergs to the present-day climate model has a minimal impact, but during the Last Glacial Maximum (LGM), Atlantic overturning strength is reduced by a third, while producing a model state that is consistent with a steady state climate. We test the sensitivity of the model at the LGM to additional Heinrich event-scale fluxes of icebergs from three possible sources: Hudson Strait, the Gulf of Saint Lawrence, and the Norwegian Channel Ice Stream (NCIS). The sensitivity of the ocean is similar for all locations, with differences dominated by the length of the iceberg meltwater pathways to the main ocean convection region. The NCIS events result in more variability and a distinctly different, more northerly, salinity anomaly. We compare these results to a more typical modeling approach, whereby meltwater is injected directly into the ocean at the iceberg source locations, and find that these floods overestimate the oceanic response compared to the iceberg events. Our results suggest that 0.3-0.4 Sv of additional freshwater flux, either as icebergs or freshwater, is required to shut down the North Atlantic meridional overturning, a larger freshwater flux than sometimes suggested because of the localized nature of the release of the freshwater.Citation: Levine, R. C., and G. R. Bigg (2008), Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere-iceberg-ocean model, Paleoceanography, 23, PA4213,

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

2008

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“…Freshwater perturbation experiments with climate models suggest that decreased North Atlantic Deep Water formation and associated reduction in cross-equatorial northward Atlantic heat transport are the main drivers of this interhemispheric climate coupling [Crowley, 1992;Stocker, 1998;Ganopolski and Rahmstorf, 2001;Prange et al, 2004;Knutti et al, 2004]. An asymmetric temporal behavior between the hemispheres is also found for the onset of the large-scale ocean circulation during deglaciation.…”

Section: Introductionmentioning

confidence: 97%

Coupling of millennial‐scale changes in sea surface temperature and precipitation off northeastern Brazil with high‐latitude climate shifts during the last glacial period

et al. 2007

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High‐resolution records of alkenone‐derived sea surface temperatures and elemental Ti/Ca ratios from a sediment core retrieved off northeastern Brazil (4°S) reveal short‐term climate variability throughout the past 63,000 a. Large pulses of terrigenous sediment discharge, caused by increased precipitation in the Brazilian hinterland, coincide with Heinrich events and the Younger Dryas period. Terrigenous input maxima related to Heinrich events H6–H2 are characterized by rapid cooling of surface water ranging between 0.5° and 2°C. This signature is consistent with a climate model experiment where a reduction of the Atlantic meridional overturning circulation (AMOC) and related North Atlantic cooling causes intensification of NE trade winds and a southward movement of the Intertropical Convergence Zone, resulting in enhanced precipitation off northeastern Brazil. During deglaciation the surface temperature evolution at the core site predominantly followed the Antarctic warming trend, including a cooling, prior to the Younger Dryas period. An abrupt temperature rise preceding the onset of the Bølling/Allerød transition agrees with model experiments suggesting a Southern Hemisphere origin for the abrupt resumption of the AMOC during deglaciation caused by Southern Ocean warming and associated with northward flow anomalies of the South Atlantic western boundary current.

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“…It is likely that a massive freshwater infl ux slowed down the thermohaline circulation (THC) and the associated climate signal was propagated to the subtropics via the Canary Current in a way similar to Heinrich events and the Younger Dryas off Cape Blanc (Zhao et al, 1995). According to a freshwater modeling study for Holocene conditions (Lohmann, 2003;Prange et al, 2004), the site GeoB 6007-2 seems to be a proper location to detect the temperature response of THC slowdown induced by high-latitude freshening ( Fig. DR1; see footnote 1).…”

mentioning

confidence: 99%

Impacts of the North Atlantic gyre circulation on Holocene climate off northwest Africa

Kim

Meggers

Rîmbu

et al. 2007

Geol

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We present well-dated high-resolution Holocene records of seasurface temperature (SST) and upwelling intensity off northwest (NW) Africa. We identify long-term cooling trends over the Holocene in the subtropical North Atlantic in response to boreal summer insolation. A pronounced cooling event of ~1 °C ca. 8.5 cal ka indicates a large-scale reorganization of the ocean current system possibly induced by meltwater from the northern North Atlantic. Our alkenone SST record off Cape Ghir provides strong evidence for the impact of ocean circulation changes on subtropical North Atlantic SSTs. It is likely that cold waters were propagated to the subtropics via the Canary Current in a way similar to Heinrich events and the Younger Dryas off Cape Blanc. We fi nd 2-3 k.y. periodic variations in SST and upwelling intensity off NW Africa superimposed on the cooling trend. Such a cycle has been documented in various paleoclimate archives in phase with solar forcing. We show that these variations on millennial time scales are linked to the North Atlantic subtropical gyre circulation and the Northern Hemisphere atmospheric circulation, and in particular to changes in the pressure gradient between the Icelandic Low and the Azores High. This suggests that oceanic circulation, in response to solar forcing, played a more important role in the generation of 2-3 k.y. cyclicity than has been previously considered.

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Modelling tempo-spatial signatures of Heinrich Events: influence of the climatic background state

Cited by 33 publications

References 39 publications

Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

Coupling of millennial‐scale changes in sea surface temperature and precipitation off northeastern Brazil with high‐latitude climate shifts during the last glacial period

Impacts of the North Atlantic gyre circulation on Holocene climate off northwest Africa

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