Changes in East Atlantic Deepwater Circulation over the last 30,000 years: Eight time slice reconstructions

Sarnthein, Michael; Winn, Kyaw; Jung, Simon; Duplessy, Jean‐Claude; Labeyrie, Laurent D; Erlenkeuser, Helmut; Ganssen, G.M.

doi:10.1029/93pa03301

Cited by 872 publications

(406 citation statements)

References 83 publications

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“…The reduction in deep convection and in overflow of dense waters we propose here, however, did not translate, as possibly expected, into advection of substantial volumes of southern source water such as during the LGM and the last glacial period (e.g., Sarnthein et al, 1994;Marchitto et al, 2002). On the contrary, the ε Nd values at deepest site 900 gradually followed the shift towards more negative values indicating the dominant presence of northern source waters in the abyssal North Atlantic.…”

Section: Resultsmentioning

confidence: 77%

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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Section: Resultsmentioning

confidence: 77%

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

Khélifi

2014

Clim. Past

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“…3c). This δ 13 C range was lower than almost everywhere else in the glacial ocean (Sarnthein et al, , 1994b, including the well-known glacial δ 13 C minima in the deep southern Indian Ocean (down to 1.0‰; Rosenthal et al, 1997) and along the northern margin of the SCS at 1700-3800 m depth (0 to 0.8‰ in core 17940 in Fig. 3c; more data in Winn et al, 1992).…”

Section: Changes In Monsoon-driven Deep-and Surface-water Oceanographymentioning

confidence: 99%

“…Based on a detailed and AMS-14 C-dated stratigraphy for the last glacial cycle, we particularly focus on the short-term, i.e. decadal to centennial, changes in monsoonal climate and trace their timing, phase relationship, and linkages in general to global climate changes such as Heinrich and=or Dansgaard-Oeschger (D-Oe) events defined in the North Atlantic realm (Bond et al, 1992(Bond et al, , 1997Cortijo et al, 1995) and the associated changes in the global thermohaline circulation (Broecker et al, 1988;Sarnthein et al, 1994b;Seidov et al, 1996). Similar teleconnections were recently found and=or postulated by Kennett and Ingram (1995) and Kotilainen and Shackleton (1995) by studying paleoclimatic sediment records from the eastern and northwestern Pacific margins.…”

Section: Introductionmentioning

confidence: 99%

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

et al. 1999

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Based on the study of 10 sediment cores and 40 core-top samples from the South China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,000 years. Climate proxies such as global sea level, estimates of paleotemperature, salinity, and nutrients in surface water, ventilation of deep water, paleowind strength, freshwater lids, fluvial and=or eolian sediment supply, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain sizes, planktonic foraminifera species, and the U K 37 biomarker index. Four cores were AMS-14 C-dated. Two different regimes of monsoon circulation dominated the SCS over the last two glacial cycles, being linked to the minima and maxima of Northern Hemisphere solar insolation. (1) Glacial stages led to a stable estuarine circulation and a strong O 2 -minimum layer via a closure of the Borneo sea strait. Strong northeast monsoon and cool surface water occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacials, hence the seasonality was strong. Low wetness in subtropical South China was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a strong inflow of warm water via the Borneo sea strait, intense upwelling southeast of Vietnam and continental wetness in China during summer, weaker northeast monsoon and high sea-surface temperatures during winter, i.e. low seasonality. On top of the long-term variations we found millennial-to centennial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and warm Dansgaard-Oeschger events recorded in Greenland ice cores, thus suggesting global climatic teleconnections. Holocene oscillations in the runoff from South China centered around periodicities of 775 years, ascribed to subharmonics of the 1500-year cycle in oceanic thermohaline circulation. 102=84-year cycles are tentatively assigned to the Gleissberg period of solar activity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from South China had already intensified right after the last glacial maximum (LGM) insolation minimum, coeval with the start of Antarctic ice melt Wang et al. / Marine Geology 156 (1999) prior to the δ 18 O signals of global sea-level rise. Vice versa, the strength of winter-monsoon winds decreased in short centennial steps only 3000-4000 years later, along with the melt of glacial ice sheets in the Northern Hemisphere.

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“…It has been shown that massive discharge of icebergs during Heinrich events produced a freshwater lid, which possibly caused a temporary stratification of the water column, hampering or even shutting down NADW formation (Broecker, 1994;Sarnthein et al, 1994;Maslin et al, 1995;Vidal et al, 1997;Chapman and Shackleton, 1999;Marchal et al, 1999). Low oxygen levels caused by reduced bottom-water ventilation may have led to dysaerobic conditions in the sediments.…”

Section: Bottom-water Conditions During Hl Deposition Inferred From Pmentioning

confidence: 99%

Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core

Tamburini

Huon

Steinmann

et al. 2002

Geochimica et Cosmochimica Acta

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Abstract-Reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments. The degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions, which may be linked to larger scale phenomena, such as bottom water circulation, water column ventilation, and organic carbon flux. Phosphorus phases of the Ͻ50-m-sized fraction of deep-sea sediments from core SU 90-09 (North Atlantic, 43°31'N, 30°24'W, 3375 m below sea level) have been analyzed using a sequential extraction technique (SEDEX method) to reconstruct phosphorus geochemistry during Heinrich events 4 and 5. Comparison with Holocene samples from the same site indicates that postdeposition diagenetic transformation has not affected phosphorus distribution in the deep part of the sediments. Total and reactive phosphorus average 0.40 Ϯ 0.04 mg/g and 0.30 Ϯ 0.05 mg/g, respectively, and are comparable to values found in analog deep-sea environments in the North Atlantic. Detrital phosphorus, the phase linked to igneous-and metamorphic-derived material, sharply increases during Heinrich events and covaries with the ice-rafted debris record, whereas authigenic and Fe-bound phosphorus phases, both influenced by redox conditions, decrease or even disappear. These findings suggest that during the deposition of Heinrich layers (HLs), environmental parameters hampered the precipitation of these phases. Large freshwater discharges in relation to iceberg surges may have provoked a temporary stratification of the water column. Accordingly, dysaerobic conditions in the sediments may have fostered the loss of dissolved phosphorus from the sediments to the water column, in a direct and rapid response to the changed conditions. Decreasing trends in organic matter elemental ratios (total organic carbon/organic phosphorus) and Rock-Eval oxygen index values, along with the presence of partly authigenic dolomite and ankerite within HLs, also support this assumption.

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Changes in East Atlantic Deepwater Circulation over the last 30,000 years: Eight time slice reconstructions

Cited by 872 publications

References 83 publications

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

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

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core

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