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Century-Scale Variation of Seafloor Temperatures Inferred from Offshore Borehole Geothermal Data

By
Seiichi Nagihara
Seiichi Nagihara
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Kelin Wang
Kelin Wang
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Published:
January 01, 2001

ABSTRACT

A large amount of hydrographic data obtained in the last three to four decades indicates that temperatures in the deep ocean have been changing globally However, because of the scarcity of older data, it is difficult to trace the ocean thermal history farther back in time. In this study, we examine the possibility of using subseafloor borehole temperature data to estimate the history of the bottom-water temperature (BWT) in the last two to three centuries. The thermal signal associated with BWT fluctuation slowly propagates into the subseafloor rock formation, perturbing the otherwise steady-state temperature field. It is possible to extract this signal and reconstruct the BWT history by inverting the borehole temperature measurements. We make such an attempt using data obtained from a borehole drilled on 669-m-deep seafloor at Ocean Drilling Program Site 1006 in the Straits of Florida. The observed temperature-depth profile in the depth range of 26 through 349 m below seafloor shows significant curvature in the upper 100 m. The BWT history reconstructed from this profile indicates that the long-term average BWT in the early eighteenth century was about 1°C lower than the present value. It decreased to a minimum at about the turn of the century, and then gradually increased to the present value. The pattern of the inferred BWT variation is similar to that of the surface air temperature at Key West, Florida, and the global surface air temperature average.

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Contents

AAPG Studies in Geology

Geological Perspectives of Global Climate Change

Lee C. Gerhard
Lee C. Gerhard
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William E. Harrison
William E. Harrison
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Bernold M. Hanson
Bernold M. Hanson
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American Association of Petroleum Geologists
Volume
47
ISBN electronic:
9781629810669
Publication date:
January 01, 2001

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