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Abstract: Calcium carbonate can crystallize in a hydrated form as ikaite at low temperatures. The hydration water in ikaite grown in laboratory experiments records the δ18O of ambient water, a feature potentially useful for reconstructing δ18O of local seawater. We report the first downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP), a region sensitive to climate fluctuations. We are able to establish the zone of ikaite formation within shallow sediments, based on porewater chemical and isotopic data. Having constrained the depth of ikaite formation and δ18O of ikaite crystals and hydration waters, we are able to infer local changes in fjord δ18O versus time during the late Holocene. This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula. [Copyright &y& Elsevier]

Contents of Fe, Mn and other elements in four ferromanganese crusts recovered from the central North Pacific are analyzed at high depth-resolution by electron microprobe for reconstructing factors controlling their deposition. Manganese (IV) in hydrogenetic ferromanganese crusts is mainly supplied as colloidal precipitates from the Oxygen Minimum Zone (OMZ), which concentrates high amounts of dissolved Mn (II). The iron is derived from carbonate dissolution and silicate particles of eolian dust. An increase in paleoproductivity during cooler climate would potentially lead to a decrease in Mn deposition due to enlargement of the OMZ which has a "temporary storage" effect for Mn. On the other hand, not affected by the OMZ, the iron entering the Fe-Mn crust would likely increase with the eolian dust input and surface productivity at glacial stages. As a result, the increasing Fe/Mn ratio should indicate a cooling climate. This is supported by the following observations. In the profile of the past 1 Ma, the variations of Fe/Mn ratio coincide with benthic oxygen isotope fluctuation in glacial- interglacial cycles. Three episodes with high Fe/ Mn ratios, approximately at 2.6, 1.8 and 0.8 Ma, are detected within the past 3 Ma and coincide with major climate transitions and cooling events. The secular evolution pattern of Fe/Mn ratio in the Cenozoic is similar to the Pb isotope evolution which is mainly controlled by eolian dust and related to climate. The Fe/Mn evolution pattern is also broadly consistent with the global deep-sea oxygen isotope records. Therefore, Fe/Mn ratio recorded in the ferromanganese crusts may be a new proxy for climate change. [ABSTRACT FROM AUTHOR]

The catchment of the River Thames, a principal river system in southern England, is densely populated and highly vulnerable to changes in climate, land use and population. In order to predict it vulnerability to climate change, the Integrated Catchments Model for Nitrogen (INCA-N) has been applied to the whole of the River Thames. The model was calibrated from 1999 to 2006, to simula streamflow and nitrate (NO3-N) concentrations. Despite the highly variable land use and river flow within the catchment, INCA-N reproduced both the hydrological regime and NO3-N dynamics in th river. A sensitivity analysis was performed on measured flow and in-stream nitrogen transformatio rates. It showed that simulated NO3-N concentrations were sensitive to denitrification rates and flo velocity. Measured parameter values were generally within the range of behavioural model simulations. Temperature and precipitation scenarios from the UK Climate Projections 2009 climat model outputs were used to project possible future flow and NO3-N concentration changes. Result showed generally drier hydrological conditions, increased river NO3-N concentration in winter an decreases in summer. An assessment of the planned new reservoir at Abingdon showed that, if managed appropriately, it may help offset the impact of climate change on riverine NO3-N concentrations and London's water supply. [ABSTRACT FROM AUTHOR]