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Abstract:
We measured TEX86 indices in surface sediments and sediment cores from marginal seas and open ocean
sites in the North Pacific to test the accuracy of TEX86 paleothermometry in the region. Application of the
global core top TEXL
86 and TEXH
86 calibrations in the Sea of Okhotsk and northern North Pacific sub-polar
region results in over- and under-estimations of TEX86 derived SSTs in surface sediments in deep-ocean
and coastal areas, respectively. Further challenges apparent in applying TEXL
86 and TEXH
86 in late Quaternary
sediment cores from the Okhotsk Sea (MR06-04 PC7) and northwestern Pacific (MR00-K03 PC1) are
unrealistically warm Holocene mean annual reconstructed temperatures ðTEXL
86Þ and excessively cold
Glacial temperatures ðTEXH
86Þ, compared with other high-latitude records and climate models. Application
of a calibration based on a sub-set of deep (<1000 m) core-top sites appears to improve temperature
reconstructions in the Holocene, but still yields underestimation of SSTs (mean annual = 5 C for
TEXH
86) in the Glacial period in the Okhotsk Sea core MR06-04 PC7. However, a regional comparison of
Okhotsk Sea and sub-polar surface sediment TEXL
86 values with observational sea-water temperatures
at different seasons and water depths reveals that an optimized positive correlation is obtained with
summer sub-surface temperatures (August, 20 m depth). The unique hydrographic setting of the Okhotsk
Sea region likely exerts a strong control on the ecology of GDGT producers (assumed to be primarily be
marine Thaumarchaeota), resulting in highly season and depth specific export production and a distinct
regional gradient in surface sediment TEX86 values. When our new regional TEXL
86 calibration is applied to
the sediment cores, TEXL
86 and alkenone UK0
37 temperature estimates overlap in the Holocene and TEXL
86
produces plausible LGM to Holocene temperature reconstructions. Our study provides a region specific
calibration and confirms the importance of acquiring local calibration equations, to optimize TEX86 paleothermometry
for specific regions and ocean basins.
