[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

/pdf/a-pliocene-pleistocene-stack-of-57-globally-distributed-n5iphe7mt2.pdf

A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

Couplings Between Changes in the Climate System and Biogeochemistry Coordinating Lead Authors: Kenneth L. Denman (Canada), Guy Brasseur (USA, Germany) Lead Authors: Amnat Chidthaisong (Thailand), Philippe Ciais (France), Peter M. Cox (UK), Robert E. Dickinson (USA), Didier Hauglustaine (France), Christoph Heinze (Norway, Germany), Elisabeth Holland (USA), Daniel Jacob (USA, France), Ulrike Lohmann (Switzerland), Srikanthan Ramachandran (India), Pedro Leite da Silva Dias (Brazil), Steven C. Wofsy (USA), Xiaoye Zhang (China) Contributing Authors: D. Archer (USA), V. Arora (Canada), J. Austin (USA), D. Baker (USA), J.A. Berry (USA), R. Betts (UK), G. Bonan (USA), P. Bousquet (France), J. Canadell (Australia), J. Christian (Canada), D.A. Clark (USA), M. Dameris (Germany), F. Dentener (EU), D. Easterling (USA), V. Eyring (Germany), J. Feichter (Germany), P. Friedlingstein (France, Belgium), I. Fung (USA), S. Fuzzi (Italy), S. Gong (Canada), N. Gruber (USA, Switzerland), A. Guenther (USA), K. Gurney (USA), A. Henderson-Sellers (Switzerland), J. House (UK), A. Jones (UK), C. Jones (UK), B. Karcher (Germany), M. Kawamiya (Japan), K. Lassey (New Zealand), C. Le Quere (UK, France, Canada), C. Leck (Sweden), J. Lee-Taylor (USA, UK), Y. Malhi (UK), K. Masarie (USA), G. McFiggans (UK), S. Menon (USA), J.B. Miller (USA), P. Peylin (France), A. Pitman (Australia), J. Quaas (Germany), M. Raupach (Australia), P. Rayner (France), G. Rehder (Germany), U. Riebesell (Germany), C. Rodenbeck (Germany), L. Rotstayn (Australia), N. Roulet (Canada), C. Sabine (USA), M.G. Schultz (Germany), M. Schulz (France, Germany), S.E. Schwartz (USA), W. Steffen (Australia), D. Stevenson (UK), Y. Tian (USA, China), K.E. Trenberth (USA), T. Van Noije (Netherlands), O. Wild (Japan, UK), T. Zhang (USA, China), L. Zhou (USA, China) Review Editors: Kansri Boonpragob (Thailand), Martin Heimann (Germany, Switzerland), Mario Molina (USA, Mexico) This chapter should be cited as: Denman, K.L., G. Brasseur, A. Chidthaisong, P. Ciais, P.M. Cox, R.E. Dickinson, D. Hauglustaine, C. Heinze, E. Holland, D. Jacob, U. Lohmann, S Ramachandran, P.L. da Silva Dias, S.C. Wofsy and X. Zhang, 2007: Couplings Between Changes in the Climate System and Biogeochemistry. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

/pdf/couplings-between-changes-in-the-climate-system-and-s80hl32kar.pdf

Couplings between changes in the climate system and biogeochemistry

http://people.rses.anu.edu.au/lambeck_k/pdf/230.pdf

Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records

Several explanations for the 200 to 280 ppm glacial/interglacial change in atmospheric CO2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients. An hypothesis is presented herein in which arguments are made that new productivity in today's southern ocean (7.4 × 1013g yr−1) is limited by iron deficiency, and hence the phytoplankton are unable to take advantage of the excess surface nitrate/phosphate that, if used, could result in total southern ocean new production of 2−3 × 1015 g C yr−1. As a consequence of Fe-limited new productivity, Holocene interglacial CO2 levels (preindustrial) are as high as they were during the last interglacial (≈ 280 ppm). In contrast, atmospheric dust Fe supplies were 50 times higher during the last glacial maximum (LGM). Because of this Fe enrichment, phytoplankton growth may have been greatly enhanced, larger amounts of upwelled nutrients may have been used, and the resulting stimulation of new productivity may have contributed to the LGM drawdown of atmospheric CO2 to levels of less than 200 ppm. Background information and arguments in support of this hypothesis are presented.

glacial-interglacial Co2 change : the iron hypothesis

Using 95 epibenthic δ13C records, eight time slices were reconstructed to trace the distribution of east Atlantic deepwater and intermediate water masses over the last 30,000 years. Our results show that there have been three distinct modes of deepwater circulation: Near the stage 3-2 boundary, the origin of North Atlantic Deep Water (NADW) was similar to today (mode 1). However, after late stage 3 the source region of the NADW end-member shifted from the Norwegian-Greenland Sea to areas south of Iceland (mode 2). A reduced NADW flow persisted during the last glacial maximum, with constant preformed δ13C values. The nutrient content of NADW increased markedly near the Azores fracture zone from north to south, probably because of the mixing of upwelled Antarctic Bottom Water (AABW) from below, which then advected with much higher flux rates into the northeast Atlantic. Later, the spread of glacial meltwater over the North Atlantic led to a marked short-term ventilation minimum below 1800 m about 13,500 14C years ago (mode 3). The formation of NADW recommenced abruptly north of Iceland 12,800–12,500 years ago and reached a volume approaching that of the Holocene, in the Younger Dryas (10,800–10,350 years B.P.). Another short-term shutdown of deepwater formation followed between 10,200 and 9,600 years B.P., linked to a further major meltwater pulse into the Atlantic. Each renewal of deepwater formation led to a marked release of fossil CO2 from the ocean, the likely cause of the contemporaneous 14C plateaus. Over the last 9000 years, deepwater circulation varied little from today, apart from a slight increase in AABW about 7000 14C years ago. It is also shown that the oxygenated Mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30,000 years.

Changes in East Atlantic Deepwater Circulation over the last 30,000 years: Eight time slice reconstructions

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic δ13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic δ13C by 0.4–0.5‰. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.

Global variations of surface ocean productivity in low and mid latitudes: Influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years

The glacial to interglacial δ13C records of the benthic foraminifera Cibicidoides wuellerstorfi and the Uvigerina peregrina group from deep-sea cores cannot be adjusted by a generally valid constant. The δ13C values of the U. peregrina group largely correlate with the accumulation rates of organic carbon, suggesting a local "habitat effect"; those of C. wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the δ13C of the ambient bottom water isotopic composition.

Benthic foraminiferal δ13C and accumulation rates of organic carbon: Uvigerina Peregrina group and Cibicidoides Wuellerstorfi

Possible mechanisms for the 80 ppm reduction of atmospheric CO2 partial pressure during the last glaciation were investigated using the Hamburg Ocean Carbon Cycle Model. The three-dimensional carbon cycle model is based on the velocity field of the Hamburg Large-Scale Geostrophic Ocean General Circulation Model and uses the same grid as that model. The horizontal resolution (3.5° × 3.5°) is lower than the length scale of narrow upwelling belts which could not be represented adequately in this study, but the large-scale features of the ocean carbon cycle are reproduced rather well. Sensitivity experiments were carried out to investigate the role of chemical and biological parameters (nutrient cycling, composition of biogenic particulate matter, CO2 solubility) and different circulation regimes for the atmospheric CO2 content. The model responses were compared to deep-sea sediment core records and ice core data from the last glaciation. Each experiment was compared with observed average tracer patterns during 18–65 kyr B.P. It was found that none of the sensitivity experiments alone could explain all observed tracer changes (atmospheric pCO2, Δδ13Cplanktonic-benthic, δ13Cbenthic differences, CaCO3 corrosivity indices) simultaneously, even in a qualitative sense. Thus according to the model none of the scenarios tested proves to be completely acceptable. The residual discrepancies between the observed and modeled tracer records can probably be attributed to the as yet inadequate reconstruction of the glacial ocean circulation. It is therefore suggested that more effort should be devoted to realistically reproducing the ice age ocean circulation field making use of the forthcoming glacial radiocarbon data base. The residuals between the realistically modeled and observed carbon cycle tracers (δ13C, CaCO3 saturation) should then reveal more clearly the real cause for the observed pCO2 decrease in the glacial atmosphere.

Glacial pCO2 Reduction by the World Ocean: Experiments With the Hamburg Carbon Cycle Model

In addition to variations in the Earth’s orbit, changes in atmospheric pC02 represent an important factor in creating global climatic and ice volume changes. Atmospheric pC02 fluctuations are largely controlled by the exchange rates of C02 between the atmosphere and ocean reservoirs, an exchange which greatly depends upon plankton primary productivity in oceanic upwelling regions, where the carbon to carbonate “Rain Ratio” (Berger and Keir, 1984) is high. In order to test this model, a new equation to calculate the local ocean paleoproductivity has been developed. The formula is based on the relationships between carbon accumulation rate, water depth, and carbon-free bulk sedimentation rates (as a “sealing factor”) of deep-sea sediments, and is independent of a large range of bottom water 02 concentration. For comparison with paleoproductivity, δ13C fluctuations of Cibicidoides wuellerstorfi serve to record the total C02 dissolved in North Atlantic Deep Water (NADW). In the region of coastal upwelling off northwest Africa, paleoproductivity increased by a factor of three from interglacial to glacial stages depicting a clear 100,000 year cycle. In oceanic “deserts”, the productivity varied much less, but approximately with the same cycle during the last 0.5 my. Phase relationships during the last two Terminations show that trade wind strength and related productivity due to upwelling in the east Atlantic started to decrease slightly prior to or simultaneously with global ice melting, synchronously with a drastic increase in atmospheric pC02 (after Neftel et al., 1982). On the other hand, C02 depletion in the NADW only followed after some 2500 to 4500 years, and thus, cannot have caused the change in atmospheric C02. The high latitude insolation balance which causes changes in sea-ice cover and thus, of meridional trade wind intensity, is regarded as the prime factor responsible for this massive feedback mechanism for climatic change.

Kyaw Winn

Papers

Changes in East Atlantic Deepwater Circulation over the last 30,000 years: Eight time slice reconstructions

Global variations of surface ocean productivity in low and mid latitudes: Influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years

Benthic foraminiferal δ13C and accumulation rates of organic carbon: Uvigerina Peregrina group and Cibicidoides Wuellerstorfi

Glacial pCO2 Reduction by the World Ocean: Experiments With the Hamburg Carbon Cycle Model

Paleoproductivity of Oceanic Upwelling and the Effect on Atmospheric C02 and Climatic Change during Deglaciation Times