Causal feedbacks in climate change
Nes, E.H. van; Scheffer, M. ; Brovkin, V. ; Lenton, T.M. ; Ye, H. ; Deyle, E. ; Sugihara, G. - \ 2015
Nature Climate Change 5 (2015). - ISSN 1758-678X - p. 445 - 448.
carbon-cycle - ice core - antarctic temperature - last deglaciation - atmospheric co2 - global climate - dioxide - record - model - lag
The statistical association between temperature and greenhouse gases over glacial cycles is well documented1, but causality behind this correlation remains difficult to extract directly from the data. A time lag of CO2 behind Antarctic temperature—originally thought to hint at a driving role for temperature2, 3—is absent4, 5 at the last deglaciation, but recently confirmed at the last ice age inception6 and the end of the earlier termination II (ref. 7). We show that such variable time lags are typical for complex nonlinear systems such as the climate, prohibiting straightforward use of correlation lags to infer causation. However, an insight from dynamical systems theory8 now allows us to circumvent the classical challenges of unravelling causation from multivariate time series. We build on this insight to demonstrate directly from ice-core data that, over glacial–interglacial timescales, climate dynamics are largely driven by internal Earth system mechanisms, including a marked positive feedback effect from temperature variability on greenhouse-gas concentrations.
Homo erectus at Trinil on Java used shells for tool production and engraving
Joordens, J.C.A. ; d’Errico, F. ; Wesselingh, F.P. ; Munro, S. ; Vos, J. de; Wallinga, J. ; Ankjaergaard, C. ; Reimann, T. ; Wijbrans, J.R. ; Kuiper, K.F. ; Mücher, H.J. ; Coqueugniot, H. ; Prié, V. ; Joosten, I. ; Os, B. van; Schulp, A.S. ; Panuel, M. ; Haas, V. van der; Lustenhouwer, W. ; Reijmer, J.J.G. ; Roebroeks, W. - \ 2015
Nature 518 (2015). - ISSN 0028-0836 - p. 228 - 231.
quartz osl ages - luminescence signals - south-africa - indonesia - sediments - reliability - sangiran - record - rates
The manufacture of geometric engravings is generally interpreted as indicative of modern cognition and behaviour1. Key questions in the debate on the origin of such behaviour are whether this innovation is restricted to Homo sapiens, and whether it has a uniquely African origin1. Here we report on a fossil freshwater shell assemblage from the Hauptknochenschicht (‘main bone layer’) of Trinil (Java, Indonesia), the type locality of Homo erectus discovered by Eugène Dubois in 1891 (refs 2 and 3). In the Dubois collection (in the Naturalis museum, Leiden, The Netherlands) we found evidence for freshwater shellfish consumption by hominins, one unambiguous shell tool, and a shell with a geometric engraving. We dated sediment contained in the shells with 40Ar/39Ar and luminescence dating methods, obtaining a maximum age of 0.54 ± 0.10 million years and a minimum age of 0.43 ± 0.05 million years. This implies that the Trinil Hauptknochenschicht is younger than previously estimated. Together, our data indicate that the engraving was made by Homo erectus, and that it is considerably older than the oldest geometric engravings described so far4, 5. Although it is at present not possible to assess the function or meaning of the engraved shell, this discovery suggests that engraving abstract patterns was in the realm of Asian Homo erectus cognition and neuromotor control.
Reconstructing Early Pleistocene (1.3 Ma) terrestrial environmental change in western Anatolia: Did it drive fluvial terrace formation?
Veldkamp, A. ; Candy, I. ; Jongmans, A.G. ; Maddy, D. ; Demir, T. ; Schoorl, J.M. ; Schreve, D. ; Stemerdink, C. ; Schriek, T. van der - \ 2015
Palaeogeography Palaeoclimatology Palaeoecology 417 (2015). - ISSN 0031-0182 - p. 91 - 104.
paleoenvironmental significance - volcanic disruption - gediz river - turkey - climate - paleosols - genesis - record - variability - carbonates
A terrestrial environmental reconstruction of an Early Pleistocene landscape from western Anatolia is presented. The basis of this reconstruction is a sedimentary stack comprising fluvial and colluvial slope deposits. Contained within this stack is a sequence comprising two massive laminar calcretes alternating with three reddish palaeosols. This evolutionary sequence is situated on top of a fluvial terrace staircase capped by a 1.3 Ma (40Ar/39Ar plateau age) lava flow. The micro-morphological properties of the observed calcretes and reddish palaeosols combined with the stable oxygen and carbon isotopic composition of the carbonates suggest the alternation of three stable relatively warm–humid (vegetation rich) and two stable relatively arid–cool (bare surface) cycles. In addition, there is also ample evidence for landscape instability in between these phases causing local soil truncation and slope instability in an open grassland–shrub environment. These landscape instability phases match well with known fluvial incisional phases of the Gediz during this period. This suggests that climate-forced landscape environmental dynamics were of sufficient magnitude to drive fluvial terrace formation of the Early Pleistocene Gediz.
Selecting parameters for the environmental interpretation of peat molecular chemistry - A pyrolysis-GC-MS study
Schellekens, J.F.P. ; Buurman, P. ; Pontevedra Pombal, X. - \ 2009
Organic Geochemistry 40 (2009)6. - ISSN 0146-6380 - p. 678 - 691.
soil organic-matter - chromatography mass-spectrometry - southern south-america - record - climate - carbon - bogs - preservation - peatlands - patterns
A number of samples from a deep peat bog in Tierra del Fuego were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in order to extract parameters that might be used to interpret the peat chemistry in terms of vegetation change, anaerobic and aerobic decomposition, and fire incidence. The choice of parameters was based on factor analysis of 177 pyrolysis products, quantified for 13 samples, separated into extract and residue, as well as the total samples. Factor analysis of extracts, residues and total samples yielded similar classifications in terms of vegetation and decomposition. Pyrolysis products and ratios that most clearly differentiated samples were used to interpret the depth profile. Although interpretation was not always straightforward, indications of parameters to describe vegetation shifts, aerobic and anaerobic decomposition, and fire largely coincided. These parameters will be used in a forthcoming study for a more complete interpretation of the peat profile.
TransCom model simulations of hourly atmospheric CO2: Experimental overview and diurnal cycle results for 2002
Law, R. ; Peters, W. ; Krol, M.C. - \ 2008
Global Biogeochemical Cycles 22 (2008). - ISSN 0886-6236 - 15 p.
carbon-dioxide - transport - europe - variability - inversions - trends - impact - record - fluxes - forest
A forward atmospheric transport modeling experiment has been coordinated by the TransCom group to investigate synoptic and diurnal variations in CO2. Model simulations were run for biospheric, fossil, and air-sea exchange of CO2 and for SF6 and radon for 2000-2003. Twenty-five models or model variants participated in the comparison. Hourly concentration time series were submitted for 280 sites along with vertical profiles, fluxes, and meteorological variables at 100 sites. The submitted results have been analyzed for diurnal variations and are compared with observed CO2 in 2002. Mean summer diurnal cycles vary widely in amplitude across models. The choice of sampling location and model level account for part of the spread suggesting that representation errors in these types of models are potentially large. Despite the model spread, most models simulate the relative variation in diurnal amplitude between sites reasonably well. The modeled diurnal amplitude only shows a weak relationship with vertical resolution across models; differences in near-surface transport simulation appear to play a major role. Examples are also presented where there is evidence that the models show useful skill in simulating seasonal and synoptic changes in diurnal amplitude.
Fingerprinting of soil organic matter as a proxy for assessing climate and vegetation changes in last interglacial paleosols (Veldwezelt, Belgium)
Vancampenhout, K. ; Wouters, K. ; Caus, A. ; Buurman, P. ; Swennen, R. ; Deckers, J. - \ 2008
Quaternary Research 69 (2008)1. - ISSN 0033-5894 - p. 145 - 162.
solid-state c-13 - analytical pyrolysis - central-asia - humic substances/ - loess belt - record - reconstruction - fractions - history - carbon
Soil characteristics in palaeosols are an important source of information on past climate and vegetation. Fingerprinting of soil organic matter (SOM) by pyrolysis-GC/MS is assessed as a proxy for palaeo-reconstruction in the complex of humic layers on top of the Rocourt pedosequence in the Veldwezelt-Hezerwater outcrop (Belgian loess belt). The fingerprints of the extractable SOM of different soil units are related to total organic carbon content, ¿13C and grain-size analysis. Combined results indicate that the lower unit of the humic complex reflects a stable soil surface, allowing SOM build-up, intensive microbial activity and high decomposition. Higher in the profile, decomposition and microbial activity decrease. This is supported by a shift in the isotopic signal, an increased U ratio and evidence of wildfires. Although the chemical composition of the extracted SOM differed greatly from recent SOM, fingerprinting yielded detailed new information on SOM degree of decomposition and microbial contribution, allowing the reconstruction of palaeo-environmental conditions during pedogenesis.
Late holocene linkages between decade-century scale climate variability and productivity at Lake Tanganyika, Africa
Cohen, A.S. ; Lezzar, K.E. ; Cole, J. ; Dettman, D. ; Ellis, G.S. ; Gonneea, M.E. ; Plisnier, P.D. ; Langenberg, V.T. ; Blaauw, M. ; Zilifi, D. - \ 2006
Journal of Paleolimnology 36 (2006)2. - ISSN 0921-2728 - p. 189 - 209.
anthropogenic environmental-change - east-africa - paleolimnological investigations - rainfall variability - aquatic ecosystem - solar variability - varve formation - uganda-congo - pacific - record
Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ~~2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals. Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual¿centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual ¿14C record for this same time period, two large ¿14C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal¿ centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light¿dark couplets at decadal¿centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake.
Late-Holocene evolution of the Mahakam delta, East Kalimantan, Indonesia
Storms, J.E.A. ; Hoogendoorn, R.M. ; Dam, R.A.C. ; Hoitink, A.J.F. ; Kroonenberg, S.B. - \ 2005
Sedimentary Geology 180 (2005)3-4. - ISSN 0037-0738 - p. 149 - 166.
brahmaputra river system - ganges-brahmaputra - sediment transport - subaqueous delta - shelf - ocean - quaternary - record
The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide-fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons. This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand-mud couplets. The distribution of the sand-mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand-mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments. Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand-mud couplets indicate that deposition is driven by the spring-neap tide cycles instead of the daily tidal cycle