Was a change in thermohaline circulation responsible for the Little Ice Age?

Broecker, Wallace S.

doi:10.1073/pnas.97.4.1339

Cited by 156 publications

(98 citation statements)

References 18 publications

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“…The first attempts in this line aimed at reconstructing the volume transport of the Florida Current (FC), the southern expression of the Gulf Stream (Lynch-Stieglitz et al 1999;Lund et al 2006). This reconstruction led to the inference that the AMOC strength was about 10 % weaker during the LIA than it is today, thus supporting previous suggestions that a reduced northward oceanic heat transport might have contributed to the anomalously cold conditions over Europe at that time (Broecker 2000). A recovery of the surface AMOC during the nineteenth and twentieth centuries following a minimum in the LIA was also reconstructed from 14 C shallowwater sea-shells off North Iceland (Wanamaker et al 2012).…”

Section: Introductionsupporting

confidence: 62%

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

et al. 2016

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the simulated variability at deep/shallow levels. Density changes responsible for the pseudo-reconstructed FCT are mainly driven by zonal temperature differences; salinity differences oppose but play a minor role. These results thus support the use of the thermal-wind relationship to reconstruct the oceanic circulation past variability, in particular at multidecadal timescales. Yet model-data comparison highlights important differences between the simulated and the proxy-based FCT variability. ECHO-G simulates a prominent weakening in the North Atlantic circulation that contrasts with the reconstructed enhancement. Our model results thus do not support the reconstructed FC minimum during the Little Ice Age. This points to a failure in the reconstruction, misrepresented processes in the model, or an important role of internal ocean dynamics.

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Section: Introductionsupporting

confidence: 62%

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

et al. 2016

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“…The cause of a related climatic anomaly, the Little Ice Age, has also been vigorously debated. Proposed factors include solar variability and volcanic eruptions [4][5] and a change in thermohaline circulation [6]. Nevertheless, the Bond cycles are quite clear in the deep sea sediment record and can be integrated into a world-wide bi-polar oceanic oscillation that is consistent with observed major northern and southern high-latitude climate variations during the last 1000yrs.…”

Section: Introductionmentioning

confidence: 82%

“…During this interval the winter sea ice area has varied M a r c h 1 7 , 2 0 1 5 widely over a 7.5% range of 18.0x10 6 km 2 to 19.4x10 6 km 2 . Therefore the observed ~2% increase in frequent maxima from ~19.0x10 6 km 2 in 1980 to ~19.4x10 6 km 2 in 2013 may not be statistically significant. Nevertheless the large seasonal Antarctic sea ice area that has been sustained near a historical record maximum contrasts with the ~8% decrease in area of Arctic winter sea ice since 1980 [20], which is presumably caused by high latitude CO2 warming.…”

Section: [13] a Sinusoidal Modelmentioning

confidence: 99%

“…A comparison of the model with the record is equally interesting in the Antarctic region. Broecker [6] has noted evidence from CFC-11 tracer measurements indicating that: "The formation rate of ventilated deep water in the Southern Ocean is currently several times smaller than its average for the last deep ocean-mixing cycle (that is ~800yrs)." Over the last two decades the measurements indicate an average rate of ABW formation of only 4sv.…”

Section: [13] a Sinusoidal Modelmentioning

confidence: 99%

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Did a bi-polar multi-level oceanic oscillation cause the Little Ice Age and other high latitude climate extremes?

Johnson

2015

JNS

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Variations of ice-rafted sand and sediment from deep-sea cores beneath the North Atlantic Drift imply 1500yr cycles of the Drift flow and its associated climate warmth in northern North Atlantic regions. The Drift cycle is part of a complex bi-polar oceanic oscillation. Central to the oscillation is the relatively higher sea surface salinity of the high-latitude Greenland Sea that enables the winter sinking of surface water to form North Atlantic Deep Water (NADW). This drives the oscillation, and the NADW is replaced by water from the Drift. The oscillation causes climate extremes in both northern and southern high latitudes and is framed here in a sinusoidal model. The model is consistent with and may explain the early medieval climate optimum, the subsequent Little Ice Age, the recent record maximum area of Antarctic winter sea ice, and the related record low rate of Antarctic Bottom Water (ABW) formation. The negative feedback of lower salinity ABW entering the northern North Atlantic tends to inhibit NADW formation and the northward Drift flow. The positive feedback of warmer and higher salinity NADW mixing into the Southern Ocean around Antarctica tends to reduce sea ice formation and enhance the rate of ABW formation. Because of these feedbacks, the rate of NADW formation oscillates over a range less than a maximum without feedback, the rate of ABW formation oscillates over a range greater than a minimum without feedback, and the phase of NADW oscillation in the model leads the ABW oscillation by 375 years. The model predicts another northern North Atlantic climate optimum about 2500 AD. However, increases in penetration of the polar ocean by flow of Atlantic water in the process of replacing the sinking NADW suggest that an interval of extreme warmth in the northeastern North Atlantic may occur within decades. This penetration could result in the loss of perennial sea ice along the northern coast of Greenland. Much of the inferred increase of northward winter flow of northeastern North Atlantic water into the Greenland Sea in recent decades may be due to stronger NADW formation caused by greater salt contributions to the Drift from the Mediterranean outflow.

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“…Therefore, particle reactions cannot solely account for the discrepancies found between model estimates and the observed data, although we cannot really quantify the effect of particles using equation (5) as water parcels arriving at the DSC site spend different amount of times at different depths and locations, and the particle effect cannot be modeled with a single k_scv and freg. Broecker, 2000). We have also tested bimodal TTDs to allow a more freedom to the shape of TTDs, as shown in some flow simulations (e.g.…”

Section: Discrepancies Between Model Estimate and Observationmentioning

confidence: 99%

Evolution of anthropogenic Pb and Pb isotopes in the deep North Atlantic Ocean and the Indian Ocean

Lee¹

2013

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, in partial fulfillment of the Requirement for the degree of Doctor of PhilosophyPb and Pb isotopes in the ocean have varied on decadal to centennial time scales due to anthropogenic Pb inputs. Thus, tracing the temporal variation of Pb and Pb isotopes in the ocean provides information on the major sources of Pb and the transport of Pb from sources to the ocean surface and into the ocean interior. In this thesis study, first, a method was developed for the analysis of dissolved Pb and other trace elements in seawater using single batch nitrilotriacetate resin extraction and isotope dilution ICP-MS, which was applied in analyzing seawater Pb concentrations in the rest of the study. A -550 year history of the Pb and Pb isotopes in the deep North Atlantic Ocean is reconstructed using a deep-sea coral, showing the infiltration of anthropogenic Pb to deep sea. Comparing the results to the surface North Atlantic Ocean Pb record using a Transit Time Distribution model, the mean transit time of Pb is estimated to be -64 years. This is longer than the transit time estimate assuming simple advection from a source, showing the importance of advective-diffusive mixing in the transport of Pb to the ocean interior. The later part of the thesis investigates Pb in the Indian Ocean, where no useful Pb data have been previously reported. First, using annually-banded surface growing corals, I reconstruct variations of Pb and isotopes in the surface waters of the central and eastern Indian Oceans during the past half-century. Results of the study show the increase of Pb concentrations from the mid-1970s, and major sources of the Pb are discussed, including leaded gasoline and coal burning, based on their emission histories and Pb isotope signatures. Second, Pb concentration and isotope profiles are presented from the northern and western Indian Oceans. AcknowledgementI would like to thank all the people who made this work possible. First, I owe a big thank to my advisor Ed Boyle. He taught me a lot about trace metal techniques, guided me to find right and important scientific questions whenever I was lost, and supported all my work. Not only that, he was also supportive of me having a family, very understanding and patient, which I cannot be grateful enough.I'd like to thank my committee: Bill Jenkins, Carl Lamborg, Phoebe Lam, and Konrad Hughen. Interests they showed during committee meetings were so inspiring and encouraging. I usually had this magical experience that my work, which looked so boring beforehand, turns into the most interesting one in the world after the committee meeting.I also would like to thank Jess Adkins and Selene Eltgroth, who provided the deep-sea coral and the radiocarbon data used in Chapter 3, and shared their expertise in deep-sea coral analysis with me. My work in Chapter 4 and 5 could not be completed without these people who helped me to collect corals and seawater samples from the Indian Ocean: Miriam Pfeiffer, Aron Meltzner, Kerry Sieh, Bambang Suwargadi, Danny Natawidjaja, Toshitaka Gamo, Hajim...

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Was a change in thermohaline circulation responsible for the Little Ice Age?

Cited by 156 publications

References 18 publications

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

Did a bi-polar multi-level oceanic oscillation cause the Little Ice Age and other high latitude climate extremes?

Evolution of anthropogenic Pb and Pb isotopes in the deep North Atlantic Ocean and the Indian Ocean

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