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Journal ArticleDOI

Deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation

01 Jun 1988-Paleoceanography (John Wiley & Sons, Ltd)-Vol. 3, Iss: 3, pp 343-360
TL;DR: In this paper, a detailed reconstruction of the geographic distribution of ∂13C in benthic foraminifera in the Atlantic Ocean during the last glacial maximum was presented.
Abstract: The degree of similarity of the ∂13C records of the planktonic foraminiferal species N. pachyderma and of the benthic foraminiferal genus Cibicides in the high-latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle. Whereas continuous formation of deep water is recognized in the southern ocean, the Norwegian Sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation. However, deep water formed in the north Atlantic south of the Norwegian Sea during the last climatic cycle as early as isotope substage 5d, and this area was also the only active northern source during stages 4–2. A detailed reconstruction of the geographic distribution of ∂13C in benthic foraminifera in the Atlantic Ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean, whereas the Glacial North Atlantic Deep Water cannot be traced south of 40°N. At shallower depth an oxygenated 13C rich Intermediate Water mass extended from 45°N to 15°S. In the Pacific Ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700–2600 m and is best explained by stronger formation of Intermediate Water in high northern latitudes.
Citations
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Journal ArticleDOI
TL;DR: In this paper, robust regressions were established between relative sea-level (RSL) data and benthic foraminifera oxygen isotopic ratios from the North Atlantic and Equatorial Pacific Ocean over the last climatic cycle.

1,908 citations

Journal ArticleDOI
19 Oct 2000-Nature
TL;DR: A version of the hypothesis that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting is presented.
Abstract: Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's 'biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involving both the biology and physics of that region.

1,273 citations


Cites background from "Deepwater source variations during ..."

  • ...4‰ lower than that of Holocene shells, a shift that has been interpreted as reflecting a transfer of continental organic carbon, which has a low 13 C/ 12 C ratio, to the ocean/atmosphere inorganic carbon reservoir during ice age...

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Journal ArticleDOI
28 Mar 2003-Science
TL;DR: Policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies.
Abstract: Large, abrupt, and widespread climate changes with major impacts have occurred repeatedly in the past, when the Earth system was forced across thresholds. Although abrupt climate changes can occur for many reasons, it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious. Unpredictability exhibited near climate thresholds in simple models shows that some uncertainty will always be associated with projections. In light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies.

1,218 citations


Cites background from "Deepwater source variations during ..."

  • ..., 2002); and (3) formation of Glacial North Atlantic Intermediate Water south of Iceland (Duplessy et al., 1988; Sarnthein et al., 1994; Pflaumann et al., 2003)....

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  • ...Those that are the most robust and, therefore, the most useful for evaluating model performance are (1) a shallower boundary, at a level of about 2,000–2,500 m, between Glacial North Atlantic Intermediate Water and Antarctic Bottom Water (Duplessy et al., 1988; Boyle, 1992; Curry and Oppo, 2005; Marchitto and Broecker, 2006); (2) a reverse in the north-south salinity gradient in the deep ocean to the Southern Ocean being much saltier than the North Atlantic (Adkins et al....

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  • ...1 Water Mass Tracers The most widely used proxy of millennial-scale changes in the AMOC is δ13C of dissolved inorganic carbon, as recorded in the shells of bottom-dwelling (benthic) foraminifera, which differentiates the location, depth, and volume of nutrient-depleted North Atlantic Deep Water (NADW) relative to underlying nutrient-enriched Antarctic Bottom Water (AABW) (Boyle and Keigwin, 1982; Curry and Lohmann, 1982; Duplessy et al., 1988)....

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  • ...During the LGM, however, these proxies indicate that the deep water masses below 2 kilometers (km) depth appear to be older (Keigwin, 2004) and more nutrient rich (Duplessy et al., 1988; Sarnthein et al., 1994; Bickert and Mackensen, 2004; Curry and Oppo, 2005; Marchitto and Broecker, 2006) than the waters above 2 km, suggesting a northward expansion of AABW and corresponding shoaling of NADW to form Glacial North Atlantic Intermediate Water (GNAIW) (Fig....

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Journal ArticleDOI
TL;DR: Starr et al. as mentioned in this paper showed that the 23,000 and 41,000-year cycles of glaciation are continuous, linear responses to orbitally driven changes in the Arctic radiation budget, and used the phase progression in each climatic cycle to identify the main pathways along which the initial, local responses to radiation are propagated by the atmosphere and ocean.
Abstract: Time series of ocean properties provide a measure of global ice volume and monitor key features of the wind-driven and density-driven circulations over the past 400,000 years. Cycles with periods near 23,000, 41,000, and 100,000 years dominate this climatic narrative. When the narrative is examined in a geographic array of time series, the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles. We argue that the 23,000- and 41,000-year cycles of glaciation are continuous, linear responses to orbitally driven changes in the Arctic radiation budget; and we use the phase progression in each climatic cycle to identify the main pathways along which the initial, local responses to radiation are propagated by the atmosphere and ocean. Early in this progression, deep waters of the Southern Ocean appear to act as a carbon trap. To stimulate new observations and modeling efforts, we offer a process model that gives a synoptic view of climate at the four end-member states needed to describe the system's evolution, and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems. “Solutions to problems involving systems of such complexity are not born full grown like Athena from the head of Zeus. Rather they evolve slowly, in stages, each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step.” —Victor P. Starr

939 citations

Journal ArticleDOI
TL;DR: In this paper, a case is made that glacial-to-interglacial transitions involve major reorganizations of the ocean-atmosphere system, and that these reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere.

892 citations

References
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Journal ArticleDOI
01 Jan 1985
TL;DR: In this article, the results from 2252 samples from 107 hydrographic stations are presented as north-south vertical (depth) sections with δ13C contoured at intervals of 0.5−0.0075·AOU.
Abstract: Measurements of the δ13C of total dissolved inorganic carbon (ΣCO2) in the world oceans are presented. Most of the samples are from the GEOSECS expeditions which covered the Atlantic, Pacific, and Indian oceans between 1971 and 1978. The results from 2252 samples from 107 hydrographic stations are presented as north-south vertical (depth) sections with δ13C contoured at intervals of 0.1%. The data show that the distribution of δ13C is controlled mainly by the input of organically produced material and its subsequent oxidation as it falls through the water column. This covariance can be summarized by the regression equation: δ13C=1.5−0.0075·AOU, where AOU represents the oxygen utilization within a water sample after leaving the surface. Other factors influencing the distribution of δ13C are the dissolution of inorganic carbonate and the addition of anthropogenic CO2 to the oceans. A complex mathematical model was employed to estimate the levels of ΣCO2 and δ13C in pre-industrial oceanic surface waters. The results suggest that the ΣCO2 of surface waters has increased by 40 μmole kg−1 from a pre-industrial level of approximately 2135 μmole kg−1. The δ13C of the ΣCO2 has decreased by 0.5% from a pre-industrial value of approximately 2.5%.

907 citations

Journal ArticleDOI
01 Nov 1987-Nature
TL;DR: In this paper, the authors show that during a surface cooling event 10,000 to 12,000 years ago, higher Cd/Ca and lower 13C/12C ratios are observed in benthic foraminifera shells from rapidly accumulating western North Atlantic sediments.
Abstract: During a surface cooling event 10,000 to 12,000 years ago, higher Cd/Ca and lower 13C/12C ratios are observed in benthic foraminifera shells from rapidly accumulating western North Atlantic sediments. Data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial North Atlantic Deep Water flux. It is proposed that cold high-latitude sea surface temperatures enhance intermediate-water formation at the expense of deep-water formation.

837 citations

Journal ArticleDOI
TL;DR: In this article, detailed Cd/Ca and δ 13 C data have been obtained for benthic foraminifera from western North Atlantic and Equatorial Pacific sediment cores, which indicate that bottom waters overlying the Atlantic site have been nutrient depleted relative to those at the Pacific site over the last 215,000 years.

699 citations

Journal ArticleDOI

546 citations


"Deepwater source variations during ..." refers background in this paper

  • ...However, it has long been observed that in contrast with the deep north Atlantic Ocean, dissolution was less intense in most of the Pacific Ocean during isotope stage 2, with a deepening of a few hundred meters of the carbonate compensation depth [Broecker, 1982]....

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