Ventilation influence on Baja California oxygen minimum zone strength since the LGM: Constraints from benthic foraminiferal Mg/Ca
T. Marchitto, M. Vicarelli, J. Carriquiry, A. Sanchez, W. Dean, J. Ortiz, Y. Zheng, A. van Geen
Poster presented at XVI INQUA Congress, July 2003
Abstract. Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern Baja California (705 m water depth) vary in concert with Dansgaard/Oeschger climate oscillations. A measure of sediment color (the third principal component of the diffuse spectral reflectance) displays a particularly striking similarity to Greenland ice core temperature records over the past 50 kyr. High organic matter concentrations during interstadials and during the Holocene may have been caused by increased productivity and/or increased preservation due to reduced OMZ ventilation. Changes in ventilation could have been caused by competition between warm, salty, low-oxygen (tropical) intermediate waters and cool, fresh, high-oxygen (North Pacific) intermediate waters. Such fluctuations, if significant, should be recorded by benthic foraminiferal Mg/Ca (temperature) and d18O (temperature plus salinity).
We present high resolution records of Uvigerina Mg/Ca and d18O spanning the past 16 kyr. d18O displays two apparently abrupt decreases superimposed on the deglacial ice volume trend: one at the time of the Bolling warming, and another at the end of the Younger Dryas. Mg/Ca remains flat across the start of the Bolling, and actually suggests a slight cooling at the end of the Younger Dryas. These results suggest that the d18O is dominated by salinity changes, with freshening occurring at the starts of the Bolling and the Holocene. For the latter, the coincidence of cooling and freshening implies a shift toward more North Pacific-like intermediate waters. Since neither transition is consistent with reduced ventilation as a driver of organic matter increases, productivity was likely the dominant influence. Additionally, there is an abrupt shift toward cooler, fresher waters after ~5 ka that is not obviously reflected in organic carbon content. We also consider the possibility that Uvigerina Mg/Ca is complicated by environmental factors other than temperature.
Enhanced marine productivity off western North America during warm climate intervals of the past 52 kyr
J. Ortiz, S. O'Connell, J. DelViscio, W. Dean, J. Carriquiry, T. Marchitto, Y. Zheng, A. van Geen
Manuscript submitted to Nature, July 2003
Abstract. The influential study of Santa Barbara Basin (SBB) off California by Behl and
Kennett has linked changes in its bottom water oxygen content to millennial-scale
climate as recorded by the oxygen isotopic composition of Greenland ice. Using
detailed records from a sediment core collected off the Magdalena margin of Baja
California (BC), Mexico, we demonstrate that this teleconnection probably arises
from changes in marine productivity, rather than the ventilation of the north
Pacific as was originally proposed. One possible interpretation is that the deep
nutricline and low productivity in the region associated with modern El Niņo
conditions was dominant during the cooler climate intervals of the past 52 kyr.
Collaborative research: A high resolution record of productivity and/or ventilation of the northeastern Pacific from Soledad Basin, Baja California
A. van Geen, T. Marchitto, Y. Zheng, J. Ortiz
Project funded by NSF Earth Systems History program, 2002-2005
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