Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declines over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands
Thecamoebians are testate protists that occur in a variety of freshwater habitats and brackish environments. They have been successfully used as proxies for a variety of environmental and climatic parameters in limnological and paleolimnological studies. The perennial Lake Sadatal is situated near the small town of Mallanwan (Latitude 27°3 ' 0" North and Longitude 80° 9' 0" East) in the Ganga-Yamuna Plains of North India. Lake Sadatal is a shallow remnant of a past oxbow lake left by the meandering Ganga River and its tributaries (maximum depth ~1.5 m during summer and ~3.0 m during July-August monsoon season). The soil around this region is saline, sodium rich, and the maximum soil alkalinity is pH 10. This region shows strong seasonality, and average atmospheric temperatures during winter (December-March) range between 7-20C and during summer (April-June) range between 21-45C (2005-2007). Taxonomically diverse and mixed thecamoebians were recovered from Lake Sadatal showing distinct summer and winter communities for three years. Centropyxids and Arcellenids dominate the low humidity, low precipitation cooler months (October-March) whereas Amphitrema spp. and Difflugia oblonga "triangularis" dominate summer and the high precipitation, high humidity monsoon months (April-September). Dominance of Amphitrema spp. is related to abundance of aquatic weed Lemna detritus at the lake bottom during summer. Total concentrations of thecamoebians were higher during summer monsoon months than winter.
Abstract. The 852/3 CE eruption of Mount Churchill, Alaska, was one of the largest first millennium volcanic events, with a magnitude of 6.7 (VEI 6) and a tephra volume of 39.4–61.9 km3 (95 % confidence). The spatial extent of the ash fallout from this event is considerable and the cryptotephra (White River Ash east; WRAe) extends as far as Finland and Poland. Proximal ecosystem and societal disturbances have been linked with this eruption; however, wider eruption impacts on climate and society are unknown. Greenland ice-core records show that the eruption occurred in winter 852/3 ± 1 CE and that the eruption is associated with a relatively moderate sulfate aerosol loading, but large abundances of volcanic ash and chlorine. Here we assess the potential broader impact of this eruption using palaeoenvironmental reconstructions, historical records and climate model simulations. We also use the fortuitous timing of the 852/3 CE Churchill eruption and its extensively widespread tephra deposition of the White River Ash (east) (WRAe) to examine the climatic expression of the warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) from precisely linked peatlands in the North Atlantic region. The reconstructed climate forcing potential of 852/3 CE Churchill eruption is moderate compared with the eruption magnitude, but tree-ring-inferred temperatures report a significant atmospheric cooling of 0.8 °C in summer 853 CE. Modelled climate scenarios also show a cooling in 853 CE, although the average magnitude of cooling is smaller (0.3 °C). The simulated spatial patterns of cooling are generally similar to those generated using the tree-ring-inferred temperature reconstructions. Tree-ring inferred cooling begins prior to the date of the eruption suggesting that natural internal climate variability may have increased the climate system’s susceptibility to further cooling. The magnitude of the reconstructed cooling could also suggest that the climate forcing potential of this eruption may be underestimated, thereby highlighting the need for greater insight into, and consideration of, the role of halogens and volcanic ash when estimating eruption climate forcing potential. Precise comparisons of palaeoenvironmental records from peatlands across North America and Europe, facilitated by the presence of the WRAe isochron, reveal no consistent MCA signal. These findings contribute to the growing body of evidence that characterizes the MCA hydroclimate as time-transgressive and heterogeneous, rather than a well-defined climatic period. The presence of the WRAe isochron also demonstrates that no long-term (multidecadal) climatic or societal impacts from the 852/3 CE Churchill eruption were identified beyond areas proximal to the eruption. Historical evidence in Europe for subsistence crises demonstrate a degree of temporal correspondence on interannual timescales, but similar events were reported outside of the eruption period and were common in the 9th century. The 852/3 CE Churchill eruption exemplifies the difficulties of identifying and confirming volcanic impacts for a single eruption, even when it is precisely dated.
The Ganges–Brahmaputra fluvial system drains the Himalayas and is one of the largest sources of terrestrial biosphere carbon to the ocean. It represents a major continental reservoir of CO2 associated with c. 1–2 billion tons of sediment transported each year. Shallow coastal environments receive substantial inputs of terrestrial carbon (900 Tg C yr−1), with allochthonous carbon capture on connected floodplains. Vegetated coastal ecosystems play a dominant role in the sequestration of carbon and operate as highly efficient carbon sinks. Mangrove sediments are subject to intense carbon-fixing processes that have a potentially high impact on the global carbon budget. The Sundarbans is the largest tidal mangrove forest in the world (10,200 km2 in area) and is located on the marine-terrestrial boundary of the Ganges-Brahmaputra delta and the Bay of Bengal, in West Bengal (India) and Bangladesh. Estimates of sedimentation on the tidal delta plain of the Ganges-Brahmaputra delta reveal mean rates of ∼1.1 cm yr−1 with accretion understood to approximately equal the regional rate of sea-level rise of ∼1.0 cm yr−1. In this study, the properties of sediments from the western Ganges-Brahmaputra delta are used to investigate controls on coastal carbon burial over the past 5,000 years. Our main findings are: (1) Beta regression of aluminium and silica ratio data is a robust method of estimating total organic carbon in sediment from the Indian Sundarbans; (2) the estimated rate of sediment deposition over last 5,000 years is between 1.0 and 2.5 mm yr−1, with uncertainty surrounding the reworked origins of sediment; and (3) temporal variation of total organic carbon accumulation through the last 5,000 years is generated by varying sedimentary depositional processes. The delivery and burial of total organic carbon is predicated on the continual supply of sediment to the Sundarbans, which future management strategies may need to consider given changing rates of deposition.
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