Paul Henderson

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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.

This past year's Cementing and Zonal Isolation papers indicated that our industry continues to maintain high levels of innovation and optimization. The evident collaboration between operators and service providers continues to propel technical developments at rates otherwise not possible.

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First published: 21 April 2024 Citations: LINKED CONTENT This article is linked to Malham et al papers.

Radium‐226( 226 Ra) and barium (Ba) exhibit similar chemical behaviors and distributions in the marine environment, serving as valuable tracers of water masses, ocean mixing, and productivity. Despite their similar distributions, these elements originate from distinct sources and undergo disparate biogeochemical cycles, which might complicate the use of these tracers. In this study, we investigate these processes by analyzing a full‐depth ocean section of 226 Ra activities ( T 1/2 = 1,600 years) and barium concentrations obtained from samples collected along the US GEOTRACES GP15 Pacific Meridional Transect during September–November 2018, spanning from Alaska to Tahiti. We find that surface waters possess low levels of 226 Ra and Ba due to export of sinking particulates, surpassing inputs from the continental margins. In contrast, deep waters have higher 226 Ra activities and Ba concentrations due to inputs from particle regeneration and sedimentary sources, with 226 Ra inputs primarily resulting from the decay of 230 Th in sediments. Further, dissolved 226 Ra and Ba exhibit a strong correlation along the GP15 section. To elucidate the drivers of the correlation, we used a water mass analysis, enabling us to quantify the influence of water mass mixing relative to non‐conservative processes. While a significant fraction of each element's distribution can be explained by conservative mixing, a considerable fraction cannot. The balance is driven using non‐conservative processes, such as sedimentary, rivers, or hydrothermal inputs, uptake and export by particles, and particle remineralization. Our study demonstrates the utility of 226 Ra and Ba as valuable biogeochemical tracers for understanding ocean processes, while shedding light on conservative and myriad non‐conservative processes that shape their respective distributions.