Reduced surface ocean temperature variability in the eastern Equatorial Pacific during the late glacial maximum

Author(s): Ford, H. L.; Ravelo, A. C.; Polissar, P. J.
Author Affiliation(s): Primary:
University of California Santa Cruz, Ocean Sciences, Santa Cruz, CA, United States
Other:
Lamont-Doherty Earth Observatory, United States
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: El Niño-Southern Oscillation is the largest source of global interannual variability with far-reaching climatic effects. Climate model simulations of future warming exhibit widely divergent behavior indicating an incomplete understanding of the factors that dictate tropical climate variability. Generating records of past tropical Pacific variability during times with different climate states is one approach to deepening our understanding of tropical climate change processes and improving predictions of future change. Here we reconstruct tropical Pacific ocean variability from the Last Glacial Maximum (LGM) and from the Holocene at ODP Sites 806 and 849, located in the western equatorial Pacific (WEP) warm pool and eastern equatorial Pacific (EEP) cold tongue, respectively. We reconstruct ocean temperature variability using the intra-sample distribution of Mg/Ca values from individual foraminifera. Sea surface temperature variability is reconstructed from individual specimens of G. sacculifer analyzed for Mg/Ca values with laser ablation ICP-MS (Photon Machines Analyte.193 with HelEx sample cell coupled with a Thermo ElementXS ICP-MS, LA-ICP-MS). Subsurface temperature variability is reconstructed from individual specimens of G. tumida analyzed for Mg/Ca values by ICP-OES. Our results indicate that the cooling of last glacial maximum SSTs was greater in the WEP compared to the EEP. Furthermore, we show this cooling is not an artifact of changes in seasonal or interannual foraminiferal fluxes, but rather, reflects overall cooler temperatures and thus changes in seasonal/interannual heat fluxes. At Site 806 in the WEP, variability during the Holocene and LGM was similar, suggesting the cooling was a direct response to pCO2-radiative forcing. In contrast, at Site 849, sea surface temperature variability during the LGM was greatly diminished in comparison to the Holocene suggesting reduced ENSO and seasonal variability. Therefore conditions in the EEP responded to both pCO2-radiative and dynamic oceanic-atmospheric forcing. Subsurface conditions were also different in the LGM compared to the Holocene. In the WEP, the subsurface temperature was cooler in the LGM, possibly reflecting changes in the upper ocean thermal structure and mid-latitude source water regions. In the EEP, the subsurface temperatures were also cooler, but additionally exhibited higher variability in the LGM compared to the Holocene. We interpret this subsurface data to reflect enhanced seasonality in the thermocline depth driven by enhanced seasonal variations in the cross-basin pressure gradients and winds stress. Our results show that by quantifying the distribution and variability of past ocean temperatures we can differentiate between the mechanisms responsible for temperature change.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; East Pacific; Equatorial Pacific; Last glacial maximum; Leg 130; Leg 138; North Pacific; Northeast Pacific; Northwest Pacific; ODP Site 806; ODP Site 849; Ocean Drilling Program; Ontong Java Plateau; Pacific Ocean; Sea surface water; Sea water; Sea-surface temperature; West Pacific
Coordinates: N001058 N001100 W1103110 W1103111
N001906 N001907 E1592142 E1592140
Record ID: 2014044772
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