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PRYSM v2 . 0: A Proxy System Model for Lacustrine Archives
  • Published Date:
    2018
  • Source:
    Paleoceanography and Paleoclimatology, 33(11), 1250-1269.
Filetype[PDF-2.91 MB]


Details:
  • Description:
    Reconstructions of temperature and hydrology from lake sedimentary archives have made fundamental contributions to our understanding of past, present, and future climate and help evaluate general circulation models (GCMs). However, because paleoclimate observations are an indirect (proxy) constraint on climatic variables, confounding effects of proxy processes complicate interpretations of these archives. To circumvent these uncertainties inherent to paleoclimate data-model comparison, proxy system models (PSMs) provide transfer functions between climate variables and the proxy. We here present a new PSM for lacustrine sedimentary archives. The model simulates lake energy and water balance, sensors including leaf wax delta D and carbonate delta O-18, bioturbation, and compaction of sediment to lend insight toward how these processes affect and potentially obfuscate the original climate signal. The final product integrates existing and new models to yield a comprehensive, modular, adaptable, and publicly available PSM for lake systems. Highlighting applications of the PSM, we forward model lake variables with GCM simulations of the last glacial maximum and the modern. The simulations are evaluated with a focus on sensitivity of lake surface temperature and mixing to climate forcing, using Lakes Tanganyika and Malawi as case studies. The PSM highlights the importance of mixing on interpretations of air temperature reconstructions from lake archives and demonstrates how changes in mixing depth alone may induce nonstationarity between in situ lake and air temperatures. By placing GCM output in the same reference frame as lake paleoclimate archives, we aim to improve interpretations of past changes in terrestrial temperatures and water cycling. Plain Language Summary Paleoclimate data from lakes provide some of the richest records of past changes in temperature and precipitation on Earth. Indeed, the wealth of data from and global coverage of large lake systems makes these records a particularly apt target for testing the performance of global climate models. However, comparing models to lake archives is nontrivial: the two data types are starkly different, and a model is required to "translate" between them. This paper builds a framework for modeling lakes that places climate model and paleoclimate proxy measurements in the same units by accounting for all the ways in which the climate signal of interest (e.g., temperature) is modified by the lake (e.g., the heat budget of the lake or sedimentation processes). By making more direct comparisons between data and models, we hope to build connections between researchers working with climate models and researchers who produce lake records of past climate. In general, our lake model helps the climate science community interpret the drivers of past climate changes from lakes. These records from the past give us context for how the climate system may respond to anthropogenic greenhouse gas forcing in the future.
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