Tree ring effects and ice core acidities clarify the volcanic record of the first millennium
Summary: Ice core acidities agree with historical volcanic eruptions and tree ring effects in recent centuries, but in the 1st millennium, ice acid dates appear offset from tree ring evidence. This offset appears real between AD 1000 and 50 BC. If correct, then current identification of Vesuvius tephra at AD 79 is erroneous, and geophysicists are working with a false volcanic record especially regarding multiple eruptions in AD 536 and 540-541, highlighting a major global hazard in proximate eruptions.
Drilling disturbance and constraints on the onset of the Paleocene–Eocene boundary carbon isotope excursion in New Jersey
Summary: The Paleocene-to-Eocene thermal maximum was a period of extreme global warming caused by perturbation to the global carbon cycle 56Mya. Evidence from marine sediment cores has been used to suggest that the onset of the event was very rapid, over just 11 years of annually resolved sedimentation. However, we argue that the supposed annual layers are an artifact caused by drilling disturbance, and that the microfossil content of the cores shows the onset took in the order of thousands of years.
On-line and off-line data assimilation in palaeoclimatology: a case study
Summary: We compare an off-line and an on-line ensemble-based data assimilation method, for the climate of the 17th century. Both schemes perform better than the simulations without DA, and similar skill on the continental and hemispheric scales is found. This indicates either a lack of control of the slow components in our setup or a lack of skill in the information propagation on decadal timescales. The temporal consistency of the analysis in the on-line method makes it generally more preferable.
Global sensitivity analysis of the Indian monsoon during the Pleistocene
Summary: By using a statistical tool termed emulator, we study the sensitivity of the Indian monsoon during the the Pleistocene. The originality of the present work is to consider, as inputs, several elements of the climate forcing that have varied in the past, and then use the emulator as a method to quantify the link between forcing variability and climate variability. The methodology described here may naturally be applied to other regions of interest.
Photic zone changes in the north-west Pacific Ocean from MIS 4–5e
Summary: New diatom isotope records are presented alongside existing geochemical and isotope records to document changes in the photic zone, including nutrient supply and the efficiency of the soft-tissue biological pump, between MIS 4 and MIS 5e in the subarctic north-west Pacific Ocean. The results provide evidence for temporal changes in the strength and efficiency of the regional soft-tissue biological pump, altering the ratio of regenerated to preformed nutrients in the water.
Thenardite after mirabilite deposits as a cool climate indicator in the geological record: lower Miocene of central Spain
Summary: Thenardite deposits from the lower Miocene unit of the Tajo basin, Spain, result from a mirabilite diagenetic transformation salt that forms under cool climatic conditions. The time of the mirabilite formation correlates with a Mi cooling event coincident with mammal assemblages related to a relatively cool and arid climate in other basins of the Iberian Peninsula. This diagenetic transformation can be used as an analog with deposits from extreme conditions such as Antarctica or Mars.
Millennial meridional dynamics of the Indo-Pacific Warm Pool during the last termination
Summary: 1. We have reconstructed new meridional thermal and precipitation stacked records in the Indo-Pacific Warm Pool (IPWP) during the last termination.
2. Meridional thermal gradient variations in the IPWP show tight links to the Northern Hemisphere millennial timescales event.
3. Anomalous warming in the south IPWP region could induce the southward shifting of the Intertropical Convergence Zone (ITCZ) in the IPWP during the Heinrich 1 and Younger Dryas events.
Laminated sediments in the Bering Sea reveal atmospheric teleconnections to Greenland climate on millennial to decadal timescales during the last deglaciation
Summary: Annually laminated sediments from the NE Bering Sea reveal a decadal-scale correlation to Greenland ice core records during termination I, suggesting an atmospheric teleconnection. Lamination occurrence is tightly coupled to Bølling-Allerød and Preboreal warm phases. Increases in export production, closely coupled to SST and sea ice changes, are hypothesized to be a main cause of deglacial anoxia, rather than changes in overturning/ventilation rates of mid-depth waters entering the Bering Sea.
Enhanced 20th-century heat transfer to the Arctic simulated in the context of climate variations over the last millennium
Summary: Temperature reconstructions for the Atlantic Water layer in Fram Strait have previously revealed a dramatic warming during the 20th century that is unprecedented in the last 2000 years. Our study presents results from climate model simulations over the last millennium that are able to reproduce such changes and relate them to increased oceanic heat transports to the Arctic and to a re-organization of the North Atlantic ocean circulation caused by global warming.
Investigating uncertainties in global gridded datasets of climate extremes
Summary: Observational data sets contain uncertainties, e.g. from the instrument accuracy, as well as from the fact that usually only a single method is used in processing. We have performed an assessment of the size of the uncertainties associated with choices in the method used. The largest effects come from changes which affect the station network or the gridding method used. However, for the temperature indices in places with many stations, these changes have little effect on the long-term behaviour.
Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)
Evidence for a three-phase sequence during Heinrich Stadial 4 using a multiproxy approach based on Greenland ice core records
M. Guillevic, L. Bazin, A. Landais, C. Stowasser, V. Masson-Delmotte, T. Blunier, F. Eynaud, S. Falourd, E. Michel, B. Minster, T. Popp, F. Prié, and B. M. Vinther Clim. Past, 10, 2115-2133, 2014 AbstractFinal Revised Paper (PDF, 858 KB)Supplement (16 KB)Discussion Paper (CPD)
02 Dec 2014
Annual proxy data from Lago Grande di Monticchio (southern Italy) between 76 and 112 ka: new chronological constraints and insights on abrupt climatic oscillations
Sensitivity of East African savannah vegetation to historical moisture-balance variation
Summary: Using fossil pollen assemblages to trace vegetation response to relatively modest historical climate fluctuations is difficult. In this study, pollen data from a lake-sediment record in Queen Elizabeth National Park (Uganda) show that its landscape has been an open wooded savannah throughout the past 200 years, with known historical moisture-balance variation exerting modest effects on local tree cover (mostly Acacia and Ficus) and the occurrence of damp soil areas (promoting Phoenix palms).