High Pacific Native Druffel 2

Core/Site name:

French Frigate Shoals

Archive:

corals

Species:

Porties

Proxy measurement:

carbon 14

Sampling resolution:

annual

Startyear:

1958.4 AD

Endyear:

1978.4 AD

All uncertainties:

Age model error plus or minus 0.3 yearsdC14 error 3-4 per mil for the whole data set

Description:

Banded corals are used as proxy recorders of bomb radiocarbon in the surface of the PacificOcean. Bomb radiocarbon levels appeared to still be rising in the tropical Pacific by 1982, in contrast to temperate locations that peaked in the early 1970's. This is representative of the geostrophic transport of bomb-laden waters from higher latitudes toward the equator. The seasonal radiocarbon signal at Canton Island (3S, 172W) during the early 1970's was twice the amplitude of that at Fanning Island (4N, 159W), and the radiocarbon minima at these locations were offset by several months. The phase lag is caused primarily by the seasonally variant transequatorial Ekman transport, which funnels more upwelled, 14C_poorwater from summer to winter hemisphere. The seasonal variation of ~14Cat Canton is larger because the peak input of 14C_poorSouth Equatorial Current water is coincident with the period of greatest transequato- rial Ekman transport to this region. Whereas, at the Fanning site, these inputs reach their maxima during opposing seasons, which causes a damping of the seasonal ~ 14Csignal.A time-stepped, multi-box model calculation is made to describe bomb radiocarbon distribu- tions in the tropical Pacific, and hence to determine the influence of the South Equatorial Current flow on the chemistry of the central equatorial Pacific. The annual model results show that radiocarbon is influenced to a minor extent by this lateral flow, in agreement with previous studies. However, the seasonal version of the model reveals that the South Equatorial Current flow varies by a factor of 2-3 in order to explain the seasonal variations in bomb radiocarbon. Meridional geostrophic convergence and transequatorial Ekman transport from summer to winter hemisphere alone are not sufficient for defining the observed seasonal signals.

Data entered by name:

Katherine Esswein

Data entered by email:

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Main reference(s):

Druffel, E.R.M. 1987. Bomb radiocarbon in the Pacific: Annual and seasonal timescale variations. Journal of Marine Research 45:667-698

Data storage link 1:

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/coral/east_pacific/french-frigate-shoals1995.txt

Data storage link 2:

http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:4209842883803967::::P1_STUDY_ID:1837

Current dating method:

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Annual snow acc rate:

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Category: Ocean2k