Enriched Regions of 228 Ra Along the U.S. GEOTRACES Pacific Meridional Transect (GP15) - Université de Bretagne Occidentale Access content directly
Journal Articles Journal of Geophysical Research. Oceans Year : 2024

Enriched Regions of 228 Ra Along the U.S. GEOTRACES Pacific Meridional Transect (GP15)

Abstract

The half‐life of 228 Ra (5.7 years) aligns well with near‐surface and near‐bottom ocean mixing timescales. Because 228 Ra is sourced from sediments, regions of enhanced activity represent water that has recently interacted with sediments on the continental margin or seabed. The GP15 meridional transect from Alaska to Tahiti along152°W encountered several regions in the upper ocean where 228 Ra was enriched. These enrichments follow surface and subsurface ocean current patterns and pair with earlier measurements of 228 Ra and transient radionuclides to reveal the origins of these enriched regions. An enriched region at Alaska margin stations 1–3 was sourced locally but did not extend to the Alaskan trench at station 4. A large shallow region between 47° and 32°N. was sourced from the west by the North Pacific Current; another shallow enriched region between 11° and 5° N was also sourced from the west by the North Equatorial Countercurrent. Subsurface enrichments (100–400 m) between 18 and 47°N were associated with Central Mode Water and North Pacific Intermediate Water. The 228 Ra activities in the upper Pacific were six times lower than activities in the Atlantic. In deep waters the primary enrichment was 27°–47°N. Two stations (32° and 37°N) were especially enriched, having near‐bottom inventories several times greater than other stations. With these two exceptions the remaining Pacific stations exhibited averaged inventories lower than those in the Atlantic. There was one region of enriched 223 Ra (half‐life = 11 days) above the Puna Ridge near Hawaii.

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Oceanography
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Dates and versions

hal-04526460 , version 1 (02-04-2024)

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Attribution - NonCommercial - ShareAlike

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Willard Moore, Matthew Charette, Paul Henderson, Douglas Hammond, Nathaniel Kemnitz, et al.. Enriched Regions of 228 Ra Along the U.S. GEOTRACES Pacific Meridional Transect (GP15). Journal of Geophysical Research. Oceans, 2024, 129 (3), ⟨10.1029/2023JC020564⟩. ⟨hal-04526460⟩
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