Radiocarbon and stable isotopes in Palmyra corals during the past century

Abstract

Annual samples from two Palmyra Atoll corals (Porites lutea) that lived during the past 110 years were analyzed for radiocarbon (D 14 C) and d 18 O. The D 14 C values decreased 7.6& from 1896 to 1953, similar to other coral records from the tropical and subtropical Pacific. D 14 C values rose from $À60& to $+110& by 1980 due to the input of bomb radiocarbon from the atmosphere. Elevated D 14 C values were observed for the mid-to late-1950s, suggesting early input of bomb radiocarbon, possibly from the largest Marshall Islands bomb tests in 1954. Secondary aragonite precipitation was identified in a portion of one core using scanning electron microscopy and X-radiography, and was responsible for high d 18 O and d 13 C values and a correlation between them. The D 14 C results were more resistant to alteration, except when contamination was from the bomb era (>1956).

Bomb‐produced radiocarbon in the western tropical Pacific Ocean: Guam coral reveals operation‐specific signals from the Pacific Proving Grounds

“…In terms of ocean transport via surface currents, the coral bomb 14 C record that may be the most complicated was from Palmyra Atoll. While the Δ 14 C record from Palmyra is low resolution, a rise of up to 40‰ was attributed to nuclear testing in the PPG [ Druffel‐Rodriguez et al ., ]. The record appears to indicate the 14 C signal arrived within the first elevated sample (1955).…”

“…The coral 14 C records at Okinawa and Palmyra provided the lowest temporal resolution for comparison with the modeling. There was some agreement and general confirmation of speculation that the origin of these moderate, early 14 C spikes was from the PPG [ Konishi et al ., ; Druffel‐Rodriguez et al ., ]. For Okinawa, the first elevated Δ 14 C values were from Operation Castle arriving at 1955.2, which was primarily from initial sources that entered the upper surface strata (77% from 0 to 41 m).…”

“…monthly to bimonthly) Δ 14 C time series in a coral core from Guam. Given an early bomb 14 C signal was observed, the goals of this study were to describe the source dynamics—its temporal characteristics relative to known nuclear testing dates and current patterns across the western Pacific and into the Indo‐Pacific region—by utilizing other more distant coral records that have also registered an early bomb 14 C signal [i.e., Konishi et al ., ; Fallon and Guilderson , ; Guilderson et al ., ; Druffel‐Rodriguez et al ., ; Glynn et al ., ].…”

Intercolony δ18O and Sr/Ca variability among Porites spp. corals at Palmyra Atoll: Toward more robust coral‐based estimates of climate

“…Intercolony Sr/Ca and δ 18 O offsets observed at Palmyra cannot be explained by diagenesis, despite ample evidence that diagenesis can introduce significant artifacts in coral Sr/Ca and δ 18 O records (Sayani et al, ). Diagenesis levels can vary significantly on millimeter scales in any given coral core (e.g., Bar‐Matthews et al, ; Hathorne et al, ; Hendy et al, ), and typically produce large, nonclimatic fluctuations in coral Sr/Ca and δ 18 O instead of uniform offsets observed in our ensemble of modern coral records (e.g., Druffel‐Rodriguez et al, ). Furthermore, with the exception of the pre‐1997 section of P13, SEM images do not show evidence of significant or consistent alteration in any of the remaining cores (Figure S5).…”

Seasonal radiocarbon and oxygen isotopes in a Galapagos coral: Calibration with climate indices

“…The average of all ∆ 14 C results in the Galapagos coral (−68.4 ± 3.8‰ SD n = 129) from 1939 to 1954 is the lowest of any tropical or subtropical location studied to date in the nonpolar oceans. For comparison, the prebomb ∆ 14 C value at Palau (7°17′N, 134°15′E) was −56.7 ± 1.6‰ ( n = 18) [ Glynn et al ., ], Hawaii (19°31′N, 155°58′W) was −50.8 ± 2.0‰ ( n = 12) [ Druffel et al ., ], Palmyra (5°52′N, 162°07′W) was −57.9 ± 1.8‰ ( n = 15) [ Druffel‐Rodriguez et al ., ], Fanning (3°55′N, 159°19′W) was −47.1 ± 11.8‰ ( n = 129) [ Grottoli et al . ], Langkai in the Indonesian throughflow (5°02′S, 119°04′E) was −56.4 ± 3.0‰ ( n = 144) [ Fallon and Guilderson , ], Rarotonga in the southwest Pacific (21°14′S, 159°49′W) was −50.8 ± 4.3‰ ( n = 123) [ Guilderson et al ., ], and Nauru (0°32′S, 166°30′E) was −57.9 ± 6.1‰ ( n = 77) [ Guilderson et al ., ].…”