The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to ...redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean. Here we present new records from the South Atlantic that show rapid changes during the last deglaciation that were instantaneous (within dating uncertainty) and of opposite sign to those observed in the North Atlantic. Our results demonstrate a direct link between the abrupt changes associated with variations in the Atlantic meridional overturning circulation and the more gradual adjustments characteristic of the Southern Ocean. These results emphasize the importance of the Southern Ocean for the development and transmission of millennial-scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide.
Wally Broecker is one of the world's leading authorities on abrupt global climate change. More than two decades ago, he discovered the link between ocean circulation and climate change, in particular ...how shutdowns of the Great Ocean Conveyor--the vast network of currents that circulate water, heat, and nutrients around the globe--triggered past ice ages. Today, he is among the researchers exploring how our planet's climate system can abruptly "flip-flop" from one state to another, and who are weighing the implications for the future. InThe Great Ocean Conveyor, Broecker introduces readers to the science of abrupt climate change while providing a vivid, firsthand account of the field's history and development.
Could global warming cause the conveyor to shut down again, prompting another flip-flop in climate? What were the repercussions of past climate shifts? How do we know such shifts occurred? Broecker shows how Earth scientists study ancient ice cores and marine sediments to probe Earth's distant past, and how they blend scientific detective work with the latest technological advances to try to predict the future. He traces how the science has evolved over the years, from the blind alleys and wrong turns to the controversies and breathtaking discoveries. Broecker describes the men and women behind the science, and reveals how his own thinking about abrupt climate change has itself flip-flopped as new evidence has emerged.
Rich with personal stories and insights,The Great Ocean Conveyoropens a tantalizing window onto how Earth science is practiced.
Major changes in global rainfall patterns accompanied a northward shift of Earth's thermal equator at the onset of an abrupt climate change 14.6 kya. This northward pull of Earth's wind and rain ...belts stemmed from disintegration of North Atlantic winter sea ice cover, which steepened the interhemispheric meridional temperature gradient. A southward migration of Earth's thermal equator may have accompanied the more recent Medieval Warm to Little Ice Age climate transition in the Northern Hemisphere. As fossil fuel CO2 warms the planet, the continents of the Northern Hemisphere are expected to warm faster than the Southern Hemisphere oceans. Therefore, we predict that a northward shift of Earth's thermal equator, initiated by an increased interhemispheric temperature contrast, may well produce hydrologic changes similar to those that occurred during past Northern Hemisphere warm periods. If so, the American West, the Middle East, and southern Amazonia will become drier, and monsoonal Asia, Venezuela, and equatorial Africa will become wetter. Additional paleoclimate data should be acquired and model simulations should be conducted to evaluate the reliability of this analog.
During glacial periods of the Late Quaternary, mineral dust emissions from Earth’s dominant source areas were a factor of 2–4 higher than interglacial levels. The causes of these fluctuations are ...poorly understood, limiting interpretation of dust flux records and assessment of dust’s role in past climate changes. Here we consider several possible drivers of glacial–interglacial dust flux changes in an effort to assess their relative importance. We demonstrate that a wide range of data supports wind gustiness as a primary driver of global dust levels, with steepened meridional temperature gradients during glacial periods causing increases in dust emissions through increases in the intensity and frequency of high-speed wind events in dust source areas. We also find that lake level records near dust source areas do not consistently support the hypothesis that aridity controls glacial–interglacial dust emission changes on a global scale, and we identify evidence negating atmospheric pCO
2 and sea level as dominant controls. Glaciogenic sediment supply, vegetation and aridity changes appear to be locally important factors but do not appear to explain the global nature of glacial–interglacial dust flux changes. We suggest that the gustiness hypothesis is aviable explanation for the close correspondence between dust emissions and high-latitude temperatures observed in paleorecords and is worthy of further testing.
Ice Age Terminations Cheng, Hai; Edwards, R. Lawrence; Broecker, Wallace S ...
Science (American Association for the Advancement of Science),
10/2009, Letnik:
326, Številka:
5950
Journal Article
Recenzirano
²³⁰Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM ...records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO₂ and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO₂ and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO₂.
Was the Younger Dryas Triggered by a Flood? Broecker, Wallace S.
Science (American Association for the Advancement of Science),
05/2006, Letnik:
312, Številka:
5777
Journal Article
Recenzirano
Draining of a huge lake into the Northern Atlantic may have triggered a cold period ~12,900 years ago. The route taken by the flood waters remains unknown.
Carbon capture and storage (CCS) provides a solution toward decarbonization of the global economy. The success of this solution depends on the ability to safely and permanently store CO₂. This study ...demonstrates for the first time the permanent disposal of CO₂ as environmentally benign carbonate minerals in basaltic rocks. We find that over 95% of the CO₂ injected into the CarbFix site in Iceland was mineralized to carbonate minerals in less than 2 years. The result contrasts with the common view that the immobilization of CO₂ as carbonate minerals within geologic reservoirs takes several hundreds to thousands of years. Our results, therefore, demonstrate that the safe long-term storage of anthropogenic CO₂ emissions through mineralization can be far faster than previously postulated.
The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene–Holocene EAM rainfall intensity is reconstructed using a ...well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early andmiddle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ∼400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall “intensity based” interpretations of these deposits as opposed to an alternative “water vapor sourcing” interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (∼35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.
In this paper we describe the thermodynamic and kinetic basis for mineral storage of carbon dioxide in basaltic rock, and how this storage can be optimized. Mineral storage is facilitated by the ...dissolution of CO
2 into the aqueous phase. The amount of water required for this dissolution decreases with decreased temperature, decreased salinity, and increased pressure. Experimental and field evidence suggest that the factor limiting the rate of mineral fixation of carbon in silicate rocks is the release rate of divalent cations from silicate minerals and glasses. Ultramafic rocks and basalts, in glassy state, are the most promising rock types for the mineral sequestration of CO
2 because of their relatively fast dissolution rate, high concentration of divalent cations, and abundance at the Earth's surface. Admixture of flue gases, such as SO
2 and HF, will enhance the dissolution rates of silicate minerals and glasses. Elevated temperature increases dissolution rates but porosity of reactive rock formations decreases rapidly with increasing temperature. Reduced conditions enhance mineral carbonation as reduced iron can precipitate in carbonate minerals. Elevated CO
2 partial pressure increases the relative amount of carbonate minerals over other secondary minerals formed. The feasibility to fix CO
2 by carbonation in basaltic rocks will be tested in the CarbFix project by: (1) injection of CO
2 charged waters into basaltic rocks in SW Iceland, (2) laboratory experiments, (3) studies of natural analogues, and (4) geochemical modelling.
The Deglacial Evolution of North Atlantic Deep Convection Thornalley, David J. R.; Barker, Stephen; Broecker, Wallace S. ...
Science (American Association for the Advancement of Science),
01/2011, Letnik:
331, Številka:
6014
Journal Article
Recenzirano
Odprti dostop
Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use ...water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon (¹⁴C)-depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation.
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