Quantitative visual analysis of marine barite microcrystals: Insights into precipitation and dissolution dynamics

Abstract

The accumulation rate of authigenic barite (BaSO 4 ) in marine sediments is a promising proxy for reconstructing marine export production, but many aspects of barite precipitation and dissolution in the water column remain unknown. Here, we collected, imaged, and quantitatively analyzed 5481 barite microcrystals in bottle casts from the Eastern Pacific water column to gain a better understanding of in situ barite dynamics. Barite crystal abundance increases rapidly between the surface and 500 m in depth and then declines to predominantly low abundances below~1000 m. The falloff in barite abundance between the oxygen minimum zone (OMZ) and the ocean interior suggests 60% AE 20% loss of barite by dissolution, nearly all of which is complete by water depths of 1000 m. However, there are occasional samples, as deep as 1250 m, with unusually high barite abundance that may represent marine snow deposition events. We found that microcrystals associated with organic matter substrates were smaller and less solid than free crystals, which suggests ongoing barite precipitation toward larger, more regularly shaped microcrystals within organic matter aggregates. Trends in barite microcrystal size with depth suggest that organic matter aggregates also play a role in shielding barite microcrystals from dissolution. In addition, our extensive data set raises new questions regarding marine barite nucleation and spatial heterogeneity. By helping bridge the gap between hypothesized barite dynamics and in situ observations of barite microcrystals, this study advances our understanding of water column Ba processes and the utility of sediment barite as an export production proxy.

Controls on Dissolved Barium and Radium‐226 Distributions in the Pacific Ocean Along GEOTRACES GP15

“…The origin of these anomalies is related to the transfer of dissolved 226 Ra and Ba from the dissolved phase to particles, with a stronger removal of Ba relative to 226 Ra. The mechanism of removal likely relates to pelagic BaSO 4 precipitation, which is thought to occur in the upper mesopelagic realm (e.g., Light & Norris, 2021; Stroobants et al., 1991). The negative anomalies in 226 Ra and Ba extend into the bathypelagic region implies that considerable BaSO 4 formation occurred in these waters between their surface source region and the GP15 section, substantial deep BaSO 4 precipitation in the North Pacific (e.g., van Beek et al., 2007; van Beek et al., 2022), or a combination of both processes.…”

Effect of barite-bound Sr on detrital Sr isotope systematics in marine sediments

“…ray diffraction, microscopic counting, and microprobe techniques (Dehairs et al, 1980;Gingele and Dahmke, 1994;Martinez-Ruiz et al, 2000;Robin et al, 2003;Light and Norris, 2021). However, these approaches are labor intensive and could be quantitative only for samples with barite contents exceeding 0.4% (Gingele and Dahmke, 1994;Robin et al, 2003).…”

Barium in seawater: Dissolved distribution, relationship to silicon, and barite saturation state determined using machine learning

“…Particulate Ba in seawater occurs mostly in the form of discrete, micron-sized crystals of the mineral barite (BaSO4(s), barium sulfate; e.g., Dehairs et al, 1980;Stroobants et al, 1991). Pelagic BaSO4 is an ubiquitous component of marine particulate matter (e.g., Light & Norris, 2021) and constitutes the principal removal flux of dissolved Ba from seawater (Paytan & Kastner, 1996). Pelagic BaSO4 is thought to precipitate within ephemeral particle-associated microenvironments that develop during the microbial oxidation of sinking organic matter (e.g., Chow & Goldberg, 1960;Bishop, 1988).…”