Jonathan R. Dean

Is there an isotopic signature of the Anthropocene

We consider whether the Anthropocene is recorded in the isotope geochemistry of the atmosphere, sediments, plants and ice cores, and the time frame during which any changes are recorded, presenting examples from the literature. Carbon and nitrogen isotope ratios have become more depleted since the 19th century, with the rate of change accelerating after ~ad 1950, linked to increased emissions from fossil fuel consumption and increased production of fertiliser. Lead isotope ratios demonstrate human pollution histories several millennia into the past, while sulphur isotopes can be used to trace the sources of acid rain. Radioisotopes have been detectable across the planet since the 1950s because of atmospheric nuclear bomb tests and can be used as a stratigraphic marker. We find there is isotopic evidence of widespread human impact on the global environment, but different isotopes have registered changes at different times and at different rates.

Early Holocene palaeoseasonality inferred from the stable isotope composition of Unio shells from Çatalhöyük, Turkey

Seasonal δ13C and δ18O data are presented from 14 Unio sub-fossil shells unearthed at the archaeological site of Çatalhöyük in central Turkey, spanning the occupation period ca. 9150–8000 cal years BP. The shells likely lived in the small lakes/wetlands around the site before being gathered and taken to Çatalhöyük. Wet-dry seasonal cycles are clearly apparent in the δ18Oshell profiles with low winter values reflecting winter precipitation and high δ18O in the summer resulting from evaporation. The most striking trend in the δ18O data is the drop in maximum summer δ18O ca. 8300 years BP, which we infer as indicating lower summer evaporation and hence a reduction in seasonality. Previous palaeoclimate records from the area have suggested cooler and more arid conditions, with reduced precipitation, around this time. While the drop in summer δ18O values could be due to reduced summer temperatures reducing summer evaporation, but there was little change in winter δ18O, perhaps suggesting winter growth cessation or reduced influence of winter climate change on δ18O. This shift in seasonal climate could be linked to solar-forced climate change beginning ca. 8600 years BP, and enhanced by the regional expression of the 8·2k event. Changing water balance over the occupation period is likely an important contributory factor behind observed cultural changes at Çatalhöyük in the Late Neolithic/Early Chalcolithic period. Our results might be considered to support the fission-fusion farming hypothesis as we provide additional evidence for wet winter/early spring conditions during the Early Holocene which likely caused flooding of the Çarşamba Fan. The changing water balance after ca. 8300 years BP (i.e. reduced seasonality and potentially reduced local summer evaporation) is also coincidental with the proposed end of this farming system due to multi-decadal drought.

A review of the stable isotope bio-geochemistry of the global silicon cycle and its associated trace elements

Silicon (Si) is the second most abundant element in the Earth’s crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13 C, δ15 N, δ18 O, δ30 Si) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies.

Seasonality of Holocene hydroclimate in the Eastern Mediterranean reconstructed using the oxygen isotope composition of carbonates and diatoms from Lake Nar, central Turkey

A positive shift in the oxygen isotope composition (δ18O) of lake carbonates in the Eastern Mediterranean from the early to late Holocene is usually interpreted as a change to drier (reduced precipitation and evaporation (P/E)) conditions. However, it has also been suggested that changes in the seasonality of precipitation could explain these trends. Here, Holocene records of δ18O from both carbonates and diatom silica, from Lake Nar in central Turkey, provide insights into palaeoseasonality. We show how Δδ18Olakewater (the difference between spring and summer reconstructed δ18Olakewater) was minimal in the early Holocene and for most of the last millennium, but was greater at other times. For example, between ~4100 and 1600 yr BP, we suggest that increased Δδ18Olakewater could have been the result of relatively more spring/summer evaporation, amplified by a decline in lake level. In terms of change in annual mean δ18O, isotope mass balance modelling shows that this can be influenced by changes in seasonal P/E as well as inter-annual P/E, but lake level falls inferred from other proxies confirm that there was a mid-Holocene transition to drier climatic conditions in central Turkey.

V. Gornitz (ed.): Encyclopedia of paleoclimatology and ancient environments

Intended as a companion to the Encylopedia of World Climatology, and in the Encyclopedia of Earth Sciences Series, the Encyclopedia of Paleoclimatology and Ancient Environments provides a comprehensive overview of how the climate has changed in the past and the methods of reconstructing this. It is the first major reference work covering the field of palaeoclimatology through the whole of Earth’s history from the early Precambrian to recent times. The 230 articles are presented alphabetically and written by over 200 contributors from the various disciplines that make up the field. They deal with subjects ranging from the general (causes of climate change, history of palaeoclimatology and Holocene climates) to the more specific (atmospheric composition of Mars, radiolaria and palaeotempestology), from methods (pollen analysis, luminescence dating and dendroclimatology) to climate events (Younger Dryas, Little Ice Age and the Messinian Salinity Crisis), and from research programmes (IODP, CLIMAP and SPECMAP) to climate forcings (North Atlantic Oscillation records, bolide impacts and volcanic eruptions). Entries range from small one page overviews of a subject to more detailed [10 page reviews. They are easily intelligible, aided by the abundant use of well reproduced graphs, maps and diagrams, in colour where necessary. Cross referencing between entries in addition to the 50 page index makes the encyclopaedia easy to use and the reference lists at the end of most sections will point readers in the direction of more detailed sources of information. Although there is a fair amount of overlap between entries, this means the reader has the benefit of being introduced to the same topic from different perspectives. An obvious comparison is with the Encyclopedia of Quaternary Science (Elsevier). As would be expected, the Encyclopedia of Paleoclimatology differs by offering articles on Triassic-Jurassic climates, mass extinctions and the Snowball Earth Hypothesis. However, on many topics it is less detailed, for example offering just two pages specifically on diatoms and four pages on lake level fluctuations compared to 122 and 63 pages on the same topics, respectively, in the Encyclopedia of Quaternary Science. Furthermore, the Encyclopedia of Quaternary Science offers whole articles on subjects that may be relevant to palaeolimnologists such as pigments analysis, plant macrofossils and Oribatid Mites, topics that are not covered in as much detail, if at all, in the Encyclopedia of Paleoclimatology. Consequently, the former may, on the whole, be of more use to readers of the Journal of Paleolimnology. In addition, as with many such reference works, the price (R.R.P. £359) will put it out of the reach of most individuals. Finally, many articles would benefit from more up-to-date references (there are very few from 2005 onwards). Understandably, it takes time for submitted entries to be edited J. R. Dean (&) School of Geography, University of Nottingham, Nottingham NG7 2RD, UK e-mail: lgxjd@nottingham.ac.uk