Drenzek Nicholas J.

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Drenzek
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Nicholas J.
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  • Preprint
    Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44°S)
    ( 2009-06-12) Sepulveda, Julio ; Pantoja, Silvio ; Hughen, Konrad A. ; Bertrand, Sebastien ; Figueroa, Dante ; Leon, Tania ; Drenzek, Nicholas J. ; Lange, Carina B.
    A high-resolution multi-proxy study including the elemental and isotopic composition of bulk organic matter, land plant-derived biomarkers, and alkenone-based sea surface temperature (SST) from a marine sedimentary record obtained from the Jacaf Fjord in northern Chilean Patagonia (~ 44°20'S) provided a detailed reconstruction of continental runoff, precipitation, and summer SST spanning the last 1750 years. We observed two different regimes of climate variability in our record: a relatively dry/warm period before 900 cal yr BP (lower runoff and average SST 1°C warmer than present-day) and a wet/cold period after 750 cal yr BP (higher runoff and average SST 1°C colder than present-day). Relatively colder SSTs were found during 750-600 and 450-250 cal yr BP, where the latter period roughly corresponds to the interval defined for the Little Ice Age (LIA). Similar climatic swings have been observed previously in continental and marine archives of the last two millennia from central and southern Chile, suggesting a strong latitudinal sensitivity to changes in the Southern Westerly Winds, the main source of precipitation in southern Chile, and validating the regional nature of the LIA. Our results reveal the importance of the Chilean fjord system for recording climate changes of regional and global significance.
  • Thesis
    The temporal dynamics of terrestrial organic matter transfer to the oceans : initial assessment and application
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007-06) Drenzek, Nicholas J.
    This thesis employs compound-specific stable carbon and radiocarbon isotopic analysis of organic biomarkers to (a) resolve petrogenic from pre-aged vascular plant organic carbon (OC) in continental margin sediments, (b) investigate the underlying mechanisms controlling the anomalously old ages that are often observed for the terrestrial component of sedimentary OC, and (c) address the associated consequences for biomarker-based climate reconstructions. In Chapters 2 and 3, coupled molecular isotope mass balances demonstrate that the amount of petrogenic OC residing on the Beaufort Shelf (Arctic Ocean) and the Eel River Margin (coastal California) has been previously overestimated due to the presence of significantly ‘pre-aged’ terrestrial OC. However, even though the contribution of organic matter emanating from sedimentary rocks may be smaller, these results reinforce the emerging notion that it is not completely oxidized during weathering and subsequent seaward transport. In Chapter 4, comparison of the down-core radiocarbon profiles for certain vascular plant biomarkers extracted from Cariaco Basin (Caribbean Sea) and Saanich Inlet (coastal British Columbia) sediments with the radiocarbon evolution of atmospheric carbon dioxide reveals that the vast majority of the terrestrial OC experiences multi-millennial residence times on land prior to entering the sea. Most of the remaining inventory is deposited in sediments within one or two decades, providing direct evidence that very little terrestrial organic matter is rapidly transferred to the marine environment. With this in mind, the striking modulation in the signal amplitude of a biomarker-based tropical paleoaridity record presented in Chapter 5 was instead used to evaluate the role of low versus high latitude forcing in abrupt paleoclimate oscillations during the last full glacial cycle. Seasonal variations in the position of the Intertropical Convergence Zone were interpreted to be a response to both high latitude adjustments in meridional overturning circulation and precessionally-driven modifications in local insolation. Finally, Chapter 6 addresses the broader implications of multi-millennial terrestrial residence times for paleoclimate records based on vascular plant biomarkers.