Thermohaline instability in the North Atlantic during meltwater events: Stable isotope and ice‐rafted detritus records from Core SO75‐26KL, Portuguese Margin

Zahn, Rainer; Schönfeld, Joachim; Kudrass, H. R.; Park, Myong-Ho; Erlenkeuser, Helmut; Grootes, P. M.

doi:10.1029/97pa00581

Cited by 231 publications

(160 citation statements)

References 61 publications

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“…In the northern hemisphere D/O stadial intervals within MIS 3 are characterized by significant coolings and are thought to be associated with suppression of GNSDW formation leaving GNSIW as the major subsurface but not 'deep' water of northern origin, and even cessation of convective water mass transformation during the extreme stadial Heinrich events [3,12]. During these Heinrich events fresh water, released by melting of icebergs, is thought to decrease the sea surface salinity (SSS) and thus density in the North Atlantic resulting in a reduction in deep water formation by convection [49][50][51][52]. Modelling experiments show that increased fluxes of freshwater to sites of North Atlantic Deep Water formation cause a decrease in deep water formation, resulting in reduced meridional heat transport with cooling in the northern North Atlantic and warming in the southern South Atlantic [53,54].…”

Section: Discussionmentioning

confidence: 99%

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

Hoogakker

McCave

Vautravers

2007

Earth and Planetary Science Letters

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Section: Discussionmentioning

confidence: 99%

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

Hoogakker

McCave

Vautravers

2007

Earth and Planetary Science Letters

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“…Indicators of vertical variability of the water mass boundary between NSW and SSW have been detected in carbon isotope time series and records of other proxies at various locations in the North Atlantic (Oppo and Lehman, 1995;Zahn et al, 1997;Hagen and Keigwin, 2002;Rasmussen et al, 2003;Peck et al, 2007b), as well as in NW Atlantic Nd isotope records shown here and previously (Gutjahr et al, 2008;Roberts et al, 2010). Based on benthic foraminiferal assemblages, Rasmussen et al (2003) suggested the presence of relatively warm, poorly ventilated and nutrient rich deep water akin to water of southern origin during Heinrich Events in the southeast Labrador Sea and the presence of NADW in between.…”

Section: Shallowing Of Northern Deep Watersmentioning

confidence: 99%

Changes in North Atlantic Deep Water strength and bottom water masses during Marine Isotope Stage 3 (45–35kaBP)

Gutjahr

Hoogakker

McCave

2010

Quaternary Science Reviews

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a b s t r a c tThe strength of the North Atlantic Meridional Overturning Circulation during climatically highly variable Marine Isotope Stage (MIS) 3 has attracted much attention in recent years. Here we present highresolution Nd isotope compositions of past seawater derived from authigenic FeeMn oxyhydroxides recovered from drift sediments on the Blake Ridge in the deep western North Atlantic (ODP Leg 172, Site 1060, 3481 m water depth). The data cover the period from 45 to 35 ka BP, tracing circulation changes during major Heinrich iceberg discharge event 4 (H4, w40e39 ka BP). The Nd isotope record suggests that there was no northern-source water (NSW) mass like modern NADW at the deeper part of Blake Ridge at any time between 45 and 35 ka. This is fundamentally different from the hydrographic situation during the Holocene where NADW extends below 4500 m at this location. The 3 Nd of past deep water recorded in the Blake Ridge sediments was least radiogenic during Dansgaard/Oeschger (D/O) Interstadial (IS) 8 (3 Nd ¼ À11.3) and most radiogenic immediately preceding IS 9 (3 Nd ¼ À9.8). More radiogenic compositions were also recorded during H4 (À10.2 3 Nd À9.9). The Nd isotope variability in MIS 3 matches that of a physical bottom current strength reconstruction from the same location. Neither record follows the pattern of Northern Hemisphere D/O climatic cycles. In our record, reduced mixing with northern source waters started in stadial 12 and lasted until after H4 in stadial 9, followed by a rapid increase in NSW contribution thereafter. This major change in the Nd isotope record predates the iceberg discharge event Heinrich 4 by more than 3 ka indicating a shallowing of the water mass boundary between Glacial North Atlantic Intermediate Water and Southern Source Water beneath. This early change in bottom water properties at the deep Blake Ridge suggests that North Atlantic deep water advection may already have decreased several thousand years before the actual iceberg discharge event and associated freshening of the surface waters in the North Atlantic. The change can thus not be attributed to climatic events in the North Atlantic but may be related to changes in flux of deep water from the South.

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“…The abrupt transitions of the AMOC from "on" to "off," or vice versa, could induce significant cooling or warming events in the North Atlantic and surrounding regions by disrupting or enhancing the northward ocean heat transport in the Atlantic basin. Therefore, this AMOC hysteresis behavior has been used as a plausible mechanism to explain the abrupt climate transitions recorded in the Greenland Ice core record and supported by paleo-proxy observations (1)(2)(3)(4)(5)(11)(12)(13).…”

mentioning

confidence: 99%

“…While it is still debated as to whether these variations in North Atlantic climate are driven externally-e.g. by solar forcing or originating from internal climate instabilities (6-10)-it has been established that the Atlantic Meridional Overturning Circulation (AMOC, or the ocean conveyor belt circulation) is at least involved (11)(12)(13). It also remains an open question why D/O events were absent during the Holocene and the beginning of the last glacial period, and more importantly whether this type of abrupt climate transition could occur in a future warmer climate associated with elevated atmospheric greenhouse gases.…”

mentioning

confidence: 99%

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability

Meehl

Han

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80–11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open.

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Thermohaline instability in the North Atlantic during meltwater events: Stable isotope and ice‐rafted detritus records from Core SO75‐26KL, Portuguese Margin

Cited by 231 publications

References 61 publications

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

Changes in North Atlantic Deep Water strength and bottom water masses during Marine Isotope Stage 3 (45–35kaBP)

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability

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