Late Quaternary paleoceanography of the northeast Pacific and Atlantic oceans based on diatom transfer functions.

摘要

Modern upwelling conditions and corresponding oceanographic properties are investigated and reconstructed for the Late Quaternary. The oceanographic conditions considered influence diatom ecology and the record of fossil diatom frustules in the sediments.;Diatoms from modern sediments are evaluated as paleoceanographic proxies and transfer functions (TFs) are calibrated using the Imbrie and Kipp (I&K) method and Weighted Averaging (WA) from Canonical Correspondence Analysis (CCA). CCA is used to define the most appropriate environmental variables to model.;TFs for productivity, sea-surface temperature, salinity and PO4 are developed from both methods (I&K and WA) for the northeast Pacific. WA is more efficient and robust than I&K, specially regarding extrapolations and weak no-analogs.;Downcore studies for the northeast Pacific revealed the presence of no-analogs related to late Pleistocene mega-floods that emanated from the Columbia River and reduced regional sea-surface salinities by as much as 10 PSU. Two methods were applied to address the no-analog problem: method 1 reflects the combination of all samples (downcore and modern) and method 2 reflects the removal of the species/groups that comprises the no-analogs. Some of the TFs had to be re-calibrated in order to apply them to the particular cores selected for the past reconstructions. For the northeast Pacific, the reconstructions go back 60,000 years (B.P.) and method 2 resulted in significant reconstructions for productivity and sea-surface temperature.;For the northeast Atlantic upwelling area, the TFs development is limited by the quality of the datasets (floral and environmental). The modern sample dataset characteristics precluded the use of the environmental datasets analogous to those from the northeast Pacific. Nevertheless, both I&K and WA resulted in significant TFs for the modern calibration, regarding "in situ" data for sea-surface temperature and chlorophyll. The downcore reconstructions have low resolution and only a realistic evaluation can be done between modern conditions and Oxygen Isotope Stage 2.;This dissertation reflects the necessary studies to develop paleoceanographic proxies and transfer functions for past oceanic reconstructions that can be linked to climate changes. Although this study contemplates only two geographic upwelling areas, the tools used here can be applied to other upwelling regions.