Synchronous Deglacial Overturning and Water Mass Source Changes

Roberts, Natalie L; Piotrowski, Alexander M; McManus, Jerry F; Keigwin, Lloyd D

doi:10.1126/science.1178068

Cited by 250 publications

(352 citation statements)

References 33 publications

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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: 90%

“…Bayon et al, 2002;Piotrowski et al, 2005;Gutjahr et al, 2007). A major deglacial shift of 3e43 Nd units towards more radiogenic signatures of bottom waters in deep NE and NW Atlantic core sites was interpreted as increased presence of Southern Source Water during the LGM and the deglaciation (Gutjahr et al, 2008;Yu et al, 2008;Roberts et al, 2010). In the deep NE Atlantic, radiogenic 3 Nd signatures as high as À8.4 during the LGM changed towards less radiogenic values as low as À11.2 during the early Holocene (Yu et al, 2008).…”

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 96%

“…The deeper Blake Ridge in the subtropical NW Atlantic recorded a change from radiogenic 3 Nd of about À10.3 during the LGM to unradiogenic 3 Nd as low as À14.0 during the early Holocene tracing the establishment of deep NADW (Gutjahr et al, 2008). Roberts et al (2010) recently reported initial deglacial deep water NADW ventilation at the Bermuda Rise as early as the BøllingeAllerød interstadial (w14.5e12.9 ka BP).…”

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 99%

“…The aim of our study is to evaluate provenance and mixing proportions of water masses in the deep western North Atlantic during MIS 3 using the authigenic FeeMn oxyhydroxide-derived Nd isotope composition of past deepwater recorded in marine sediments (Palmer and Elderfield, 1985;Rutberg et al, 2000;Bayon et al, 2002;Piotrowski et al, 2005;Gutjahr et al, 2007Gutjahr et al, , 2008Klevenz et al, 2008;Roberts et al, 2010). The isotopic composition of Nd in seawater is primarily set by riverine continental runoff (Frank, 2002;Goldstein and Hemming, 2003), exchange with shelf sediments at the ocean's boundaries (Lacan and Jeandel, 2005a), dust input and possibly submarine groundwater discharge (Johannesson and Burdige, 2007 (Jeandel et al, 1995;Tachikawa et al, 2003).…”

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 99%

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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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Section: Shallowing Of Northern Deep Watersmentioning

confidence: 90%

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 96%

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 99%

Section: Water-mass Tagging By Nd Isotopesmentioning

confidence: 99%

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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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“…Given that Nd has an average global oceanic residence time of ∼ 400-700 yr (Rempfer et al, 2011) and differences in ε Nd between water masses are large enough to be detectable (cf. Frank, 2002), Nd isotopes have been used as a quasi conservative tracer to infer changes in past deep-water sources and their mixing within the North Atlantic basin on different timescales (e.g., O'Nions et al, 1998;Burton et al, 1999;Roberts et al, 2010;Crocket et al, 2011;Piotrowski et al, 2012). .…”

Section: Introductionmentioning

confidence: 99%

A major change in North Atlantic deep water circulation 1.6 million years ago

Khélifi

2014

Clim. Past

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Abstract. The global ocean-climate system has been highly sensitive to the formation and advection of deep overflow water from the Nordic Seas as integral part of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution over the Pliocene-Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters that were involved in driving overturning throughout the Pliocene-Pleistocene climate transitions are not well constrained. Here we investigate the evolution of a substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic neodymium isotope (ε Nd ) variability obtained from three sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths between 2170 and 5050 m in the northeast Atlantic. We find that prior to the onset of major Northern Hemisphere glaciation (NHG) ∼ 3 million years ago (Ma), ε Nd values primarily oscillated between −9 and −11 at all sites, consistent with enhanced vertical mixing and weak stratification of the water masses during the warmer-than-today Pliocene period. From 2.7 Ma to ∼ 2.0 Ma, the ε Nd signatures of the water masses gradually became more distinct, which documents a significant advection of Nordic Seas overflow deep water coincident with the intensification of NHG. Most markedly, however, at ∼ 1.6 Ma the interglacial ε Nd signatures at sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.) synchronously and permanently shifted by 2 to 3 ε Nd units to less radiogenic values, respectively. Since then the difference between glacial and interglacial ε Nd values has been similar to the Late Quaternary at each site. A decrease of ∼ 2 ε Nd units at 1.6 Ma was also recorded for the deepest water masses by site 900 (∼ 5 050 m w.d.), which thereafter, however, evolved to more radiogenic values again until the present. This major ε Nd change across the 1.6 Ma transition reflects a significant reorganization of the overturning circulation in the northeast Atlantic paving the way for the more stratified water column with distinct water masses prevailing thereafter.

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Nd isotopic structure of the Pacific Ocean 70–30 Ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world

et al. 2014

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The oceanic meridional overturning circulation (MOC) is a crucial component of the climate system, impacting heat and nutrient transport, and global carbon cycling. Past greenhouse climate intervals present a paradox because their weak equator-to-pole temperature gradients imply a weaker MOC, yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients. To investigate the mode of MOC that operated during the early Cenozoic, we compare new Nd isotope data with Nd tracer-enabled numerical ocean circulation and coupled climate model simulations. Assimilation of new Nd isotope data from South Pacific Deep Sea Drilling Project and Ocean Drilling Program Sites 323, 463, 596, 865, and 869 with previously published data confirm the hypothesized MOC characterized by vigorous sinking in the South and North Pacific~70 to 30 Ma. Compilation of all Pacific Nd isotope data indicates vigorous, distinct, and separate overturning circulations in each basin until~40 Ma. Simulations consistently reproduce South Pacific and North Pacific deep convection over a broad range of conditions, but cases using strong deep ocean vertical mixing produced the best data-model match. Strong mixing, potentially resulting from enhanced abyssal tidal dissipation, greater interaction of wind-driven internal wave activity with submarine plateaus, or higher than modern values of the geothermal heat flux enable models to achieve enhanced MOC circulation rates with resulting Nd isotope distributions consistent with the proxy data. The consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients.

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Synchronous Deglacial Overturning and Water Mass Source Changes

Cited by 250 publications

References 33 publications

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

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

A major change in North Atlantic deep water circulation 1.6 million years ago

Nd isotopic structure of the Pacific Ocean 70–30 Ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world

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