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This special issue comprising 14 articles emerged from the PAGES supported meeting: Holocene Circum Arctic Peatland Carbon Dynamics Community Wide Data Synthesis and Modeling Initiatives which took place from the 12 16 October 2013 in Bethlehem Pennsylvania. It is a precursor product of PAGES' C PEAT Working Group. ABSTRACT: Each year a peatland has an annual net carbon balance (NCB) which can be positive (net uptake) zero or negative. Over centuries to millennia this NCB accumulates as a peat profile. Contemporary peatlands can be sampled (cored) and the past apparent carbon accumulation rate (aCAR) can be determined as the quantity of peat carbon in any particular dated interval down the core profile. We use a process based peatland carbon and water cycle model to compare peatland annual NCB during millennia of peat accumulation to the contemporary estimate of aCAR resulting from this accumulation. Integrating over the entire profile the accumulated NCB must equal the aCAR but for shorter time intervals these two quantities can diverge. A climate variation/perturbation that leads to persistent slow carbon loss or negligible carbon gain through enhanced decomposition will necessarily reduce the aCAR for time periods before the climate variation/perturbation occurred. This can compromise peatland climate–carbon balance relationships inferred from joint analysis of peat cores and paleoclimate reconstructions.

Five one-dimensional (1D) lake models were run for the open water season in 2006 for Lake Valkea-Kotinen (Finland) using on-lake measured meteorological forcing. The model results were validated using measurements of water temperature and of eddy covariance (EC) fluxes. The surface temperature is satisfactorily simulated by all models showing slight overestimation (by 0.1–1.1°C). Both sensible and latent heat fluxes are positively biased in respect to EC data, consistent with earlier studies. However, correlation coefficients between EC-fluxes and those simulated are relatively high ranging from 0.55 to 0.74. The skill to simulate vertical temperature profiles by different models is assessed as well. It is found that the lake models underestimate the EC-derived surface drag coefficient, however providing realistic temperature profiles. It is argued that the real momentum flux from the atmosphere is larger than simulated, however it is split up between the wave development and the acceleration of lake currents. Adopting the simple parameterisation for momentum flux partitioning in one of the models showed that this mechanism can be significant. Finally, the effect of including the lake bathymetry data in k-ɛ models was the drastic overheating of water below the thermocline. This is likely to be caused by omitting the heat flux at the lake margins. Thus, the parameterisation of heat flux at the lake’s margins should be included in the models; otherwise it is recommended to neglect bathymetry effects for such small water bodies as the Lake Valkea-Kotinen. Keywords: lakes, numerical modelling, stratification, surface fluxes (Published: 16 January 2014) Citation: Tellus A 2014, 66 , 21389, http://dx.doi.org/10.3402/tellusa.v66.21389 This publication is part of a Thematic Cluster entitled "Parameterization of lakes in numerical weather prediction and climate models". Read the other papers from this thematic cluster here