Author
Sharon Hoffmann
Bio: Sharon Hoffmann is an academic researcher from Lamont–Doherty Earth Observatory. The author has contributed to research in topics: Neoglaciation & Holocene. The author has an hindex of 3, co-authored 4 publications receiving 2766 citations.
Papers
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TL;DR: A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's “1500-year” cycle, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
Abstract: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
2,938 citations
TL;DR: Sedimentary ratios of the radionuclides thorium-230 and protactinium-231 record consistent evidence for the export of 231Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years.
Abstract: The Arctic Ocean has an important role in Earth's climate, both through surface processes such as sea-ice formation and transport, and through the production and export of waters at depth that contribute to the global thermohaline circulation. Deciphering the deep Arctic Ocean's palaeo-oceanographic history is a crucial part of understanding its role in climatic change. Here we show that sedimentary ratios of the radionuclides thorium-230 ((230)Th) and protactinium-231 ((231)Pa), which are produced in sea water and removed by particle scavenging on timescales of decades to centuries, respectively, record consistent evidence for the export of (231)Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years. Seven well-dated box-core records provide a comprehensive overview of (231)Pa and (230)Th burial in Arctic sediments during glacial, deglacial and interglacial conditions. Sedimentary (231)Pa/(230)Th ratios decrease nearly linearly with increasing water depth above the core sites, indicating efficient particle scavenging in the upper water column and greater influence of removal by lateral transport at depth. Although the measured (230)Th burial is in balance with its production in Arctic sea water, integrated depth profiles for all time intervals reveal a deficit in (231)Pa burial that can be balanced only by lateral export in the water column. Because no enhanced sink for (231)Pa has yet been found in the Arctic, our records suggest that deep-water exchange through the Fram strait may export (231)Pa. Such export may have continued for the past 35,000 years, suggesting a century-scale replacement time for deep waters in the Arctic Ocean since the most recent glaciation and a persistent contribution of Arctic waters to the global ocean circulation.
39 citations
TL;DR: In this paper, the authors present evidence from North Atlantic deep-sea sediment cores that rhyolitic glass shards in Ash Zone 1 and in the Vedde Ash may not have been produced by the same eruption as has been widely assumed.
31 citations
TL;DR: A geochemical study of sediments suggests that during recent glacial periods, the Arctic Ocean was completely isolated from the world ocean, with fresh water filling the basin for thousands of years as mentioned in this paper.
Abstract: A geochemical study of sediments suggests that, during recent glacial periods, the Arctic Ocean was completely isolated from the world ocean, with fresh water filling the basin for thousands of years. Isotopic analysis of sediments casts light on ancient ocean salinity.
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TL;DR: In this paper, an examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000-8000, 6000-5000, 4200-3800, 3500-2500, 1200-1000, and 600-150 cal yr B.P.
2,255 citations
TL;DR: A 5-year-resolution absolute-dated oxygen isotope record from Dongge Cave, southern China, provides a continuous history of the Asian monsoon over the past 9000 years, and shows that some, but not all, of the monsoon variability at these frequencies results from changes in solar output.
Abstract: A 5-year-resolution absolute-dated oxygen isotope record from Dongge Cave, southern China, provides a continuous history of the Asian monsoon over the past 9000 years. Although the record broadly follows summer insolation, it is punctuated by eight weak monsoon events lasting approximately 1 to 5 centuries. One correlates with the "8200-year" event, another with the collapse of the Chinese Neolithic culture, and most with North Atlantic ice-rafting events. Cross-correlation of the decadal- to centennial-scale monsoon record with the atmospheric carbon-14 record shows that some, but not all, of the monsoon variability at these frequencies results from changes in solar output.
2,139 citations
TL;DR: Comparison of measured sea surface temperatures in the Western Pacific with paleoclimate data suggests that this critical ocean region is approximately as warm now as at the Holocene maximum and within ≈1°C of the maximum temperature of the past million years.
Abstract: lobal temperature is a popular metric for summarizing the state of global climate. Climate effects are felt locally, but the global distribution of climate response to many global climate forcings is reasonably congruent in climate models (1), suggesting that the global metric is surprisingly useful. We will argue further, consistent with earlier discussion (2, 3), that measurements in the Western Pacific and Indian Oceans provide a good indication of global temperature change. Wefirstupdateouranalysisofsurfacetemperaturechangebased on instrumental data and compare observed temperature change with predictions of global climate change made in the 1980s. We then examine current temperature anomalies in the tropical Pacific Ocean and discuss their possible significance. Finally, we compare paleoclimate and recent data, using the Earth's history to estimate the magnitude of global warming that is likely to constitute dan-
1,848 citations
Oeschger Centre for Climate Change Research1, Swiss Federal Institute of Aquatic Science and Technology2, University of Edinburgh3, Free University of Berlin4, ETH Zurich5, Université catholique de Louvain6, École Polytechnique7, University of Bristol8, Russian Academy of Sciences9, University of Birmingham10
TL;DR: The authors used selected proxy-based reconstructions of different climate variables, together with state-of-the-art time series of natural forcings (orbital variations, solar activity variations, large tropical volcanic eruptions, land cover and greenhouse gases), underpinned by results from GCMs and Earth System Models of Intermediate Complexity (EMICs), to establish a comprehensive explanatory framework for climate changes from the mid-Holocene (MH) to pre-industrial time.
1,539 citations
TL;DR: In this paper, the authors present a continuous record of the Asian monsoon over the last 16 ka from δ18O measurements of stalagmite calcite, which is combined with a chronology from 45 precise 230Th dates.
1,527 citations