Early Bomb Radiocarbon Detected in Palau Archipelago Corals

Abstract

In order to evaluate the variability in surface water masses in the Western Pacific Warm Pool, we report high-precision radiocarbon measurements in annual and seasonal bands from Pontes lutea corals collected from the Palau Archipelago (7°N, 134°E). Annual coral bands from 1945 to 2008 and seasonal samples from 1953 to 1957 were analyzed to capture the initial early input of bomb 14C from surface thermonuclear weapons testing in the Marshall Islands. Results show a pre-bomb average δ14C value of-54.9% between 1945 and early 1953. Beginning early in 1954, there is a rapid increase to a maximum of-23.1% at the start of 1955. Values continued to rise after 1957 to a post-bomb peak of 141% by 1976. The large initial rise in δ14C cannot be accounted for by air-sea CO2 exchange. Results therefore suggest that the primary cause of this increase is the lateral advection of fallout-contaminated water from the Marshall Islands to Palau via the North Equatorial Current and then to the North Equatorial Countercurrent.

Penetration of Bomb 14C Into the Deepest Ocean Trench

“…Comparisons of amphipod Δ 14 C with the postbomb coral Δ 14 C records and with the body length. (a) Δ 14 C of tissues (diamonds) and gut contents (green circles) with temporal variations of Δ 14 C in surface seawater as recorded in banded corals from Guam (13°35.9′N, 144°50.2′E, solid red line; Andrews et al, ) and Palau (7.28°N, 134.25°E, solid black line; Glynn et al, ), DIC in WP (blue crosses; Ge et al, ), and estimation of DIC based on a decrease rate of 3.7 ± 0.1‰/year (Text S2 in the supporting information). (b) Least squares relationship (solid line) between the Δ 14 C values and amphipod body lengths, r 2 = 0.89.…”

“…Hadal amphipods are highly dependent on surface‐derived OM, and, therefore, can be 14 C dated similarly to surface pelagic animals. The muscle tissue with the highest Δ 14 C value (65 ± 2‰) shows a result between CE 2004 and CE 2007 based on the Palau coral record (Andrews et al, ; Glynn et al, ; Ishihara et al, ; Figure a). Although the utilization of muscle tissues does not provide definite ages, they provide an estimate of the magnitude of longevity of hadal amphipods, which is longer than 10 years.…”

Short‐term fluctuations in regional radiocarbon reservoir age recorded in coral skeletons from the Ryukyu Islands in the north‐western Pacific

“…(); (i) Palau from Glynn et al . (), (j) Guam from Andrews et al . (); (k) Nauru from Guilderson et al .…”

“…() reported that in the region of the North Equatorial Current (NEC), which is the source region of the Kuroshio Current, Δ R was 78 years in the early 1900s on the basis of analyses of pre‐bomb molluscan shells from Palau and Ponape. In contrast, Δ R values obtained from Δ 14 C data on corals from Guam, Palau, Hawaii and Fanning Island in the equatorial Pacific are negative for 1945–1950 (Druffel, ; Druffel et al , ; Grottoli et al , ; Glynn et al , ; Andrews et al , ). This may be biased because the Δ R values of the 1900s shown in Table are from data for 23 years, from 1892 to 1915, whereas Δ R values in the 1940s are for 10 years, for the period from 1940 to 1950.…”

Bomb‐14C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)

“… (a) The bomb‐ 14 C record reconstructed from M. stimpsoni shells (red) and seawater Δ 14 C values in Funakoshi Bay (blue diamonds) and Otsuchi Bay (light blue triangles). For comparison, the bomb‐ 14 C records reconstructed from reef‐building coral skeletons in the tropical to subtropical Pacific are shown: Galapagos (green, 1°S, 90°W; Druffel, ), Nauru (blue, 1°S, 167°E; Guilderson et al, ), Palau (purple, 7°N, 134°E; Glynn et al, ), and Kure Atoll (yellow, 28°N, 178°W; Andrews et al, ). Atmospheric Δ 14 C records (black lines) for the years 1930–1950 are from compiled data from INTCAL13 (Reimer et al, ); the records for the years 1950–1986 are compiled from data for the northern hemisphere (NH Zone 2; Hua et al, ); and records for the years 1986–2016 are from direct observations at Schauinsland in Germany (Hammer & Levin, ).…”