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  • 1
    Publication Date: 2019-05-22
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
    Publication Date: 2023-02-08
    Description: An ocean iodine cycling model is presented, which predicts upper ocean iodine speciation. The model comprises a three-layer advective and diffusive ocean circulation model of the upper ocean, and an iodine cycling model embedded within this circulation. The two primary reservoirs of iodine are represented, iodide and iodate. Iodate is reduced to iodide in the mixed layer in association with primary production, linked by an iodine to carbon (I:C) ratio. A satisfactory model fit with observations cannot be obtained with a globally constant I:C ratio, and the best fit is obtained when the I:C ratio is dependent on sea surface temperature, increasing at low temperatures. Comparisons with observed iodide distributions show that the best model fit is obtained when oxidation of iodide back to iodate is associated with mixed layer nitrification. Sensitivity tests, where model parameters and processes are perturbed, reveal that primary productivity, mixed layer depth, oxidation, advection, surface fresh water flux and the I:C ratio all have a role in determining surface iodide concentrations, and the timescale of iodide in the mixed layer is sufficiently long for non-local processes to be important. Comparisons of the modelled iodide surface field with parameterisations by other authors shows good agreement in regions where observations exist, but significant differences in regions without observations. This raises the question of whether the existing parameterisations are capturing the full range of processes involved in determining surface iodide, and shows the urgent need for observations in regions where there are currently none.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2022-01-07
    Description: Iodine is a critical trace element involved in many diverse and important processes in the Earth system. The importance of iodine for human health has been known for over a century, with low iodine in the diet being linked to goitre, cretinism and neonatal death. Research over the last few decades has shown that iodine has significant impacts on tropospheric photochemistry, ultimately impacting climate by reducing the radiative forcing of ozone (O3) and air quality by reducing extreme O3 concentrations in polluted regions. Iodine is naturally present in the ocean, predominantly as aqueous iodide and iodate. The rapid reaction of sea-surface iodide with O3 is believed to be the largest single source of gaseous iodine to the atmosphere. Due to increased anthropogenic O3, this release of iodine is believed to have increased dramatically over the twentieth century, by as much as a factor of 3. Uncertainties in the marine iodine distribution and global cycle are, however, major constraints in the effective prediction of how the emissions of iodine and its biogeochemical cycle may change in the future or have changed in the past. Here, we present a synthesis of recent results by our team and others which bring a fresh perspective to understanding the global iodine biogeochemical cycle. In particular, we suggest that future climate-induced oceanographic changes could result in a significant change in aqueous iodide concentrations in the surface ocean, with implications for atmospheric air quality and climate.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2019-05-22
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
    Publication Date: 2024-02-07
    Description: Reaction with iodide (I-) at the sea surface is an important sink for atmospheric ozone, and causes sea-air emission of reactive iodine which in turn drives further ozone destruction. To incorporate this process into chemical transport models, improved understanding of the factors controlling marine iodine speciation, and especially sea-surface iodide concentrations, is needed. The oxidation of I- to iodate (IO3-) is the main sink for oceanic I-, but the mechanism for this remains unknown. We demonstrate for the first time that marine nitrifying bacteria mediate I- oxidation to IO3-. A significant increase in IO3- concentrations compared to media-only controls was observed in cultures of the ammonia-oxidising bacteria Nitrosomonas sp. (Nm51) and Nitrosoccocus oceani (Nc10) supplied with 9-10 mM I-, indicating I- oxidation to IO3-. Cell-normalised production rates were 15.69 (+/- 4.71) fmol IO3- cell(-1) d(-1) for Nitrosomonas sp., and 11.96 (+/- 6.96) fmol IO3- cell(-1) d(-1) for Nitrosococcus oceani, and molar ratios of iodate-to-nitrite production were 9.2 +/- 4.1 and 1.88 +/- 0.91 respectively. Preliminary experiments on nitrite-oxidising bacteria showed no evidence of I- to IO3- oxidation. If the link between ammonia and I oxidation observed here is representative, our ocean iodine cycling model predicts that future changes in marine nitrification could alter global sea surface I fields with potential implications for atmospheric chemistry and air quality.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 27–59, doi:10.1002/2015JC011299.
    Description: Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings in heat, fresh water, and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper, pathways of PW are investigated using simulations with six state-of-the art regional and global Ocean General Circulation Models (OGCMs). In the simulations, PW is tracked by a passive tracer, released in Bering Strait. Simulated PW spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along the continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The second begins in the vicinity of the Herald Canyon and transports PW along the continental slope of the East Siberian Sea into the Transpolar Drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW into the Beaufort Gyre. In the models, the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind affects the simulated PW pathways by changing the vertical shear of the relative vorticity of the ocean flow in the Canada Basin.
    Description: National Science Foundation (NSF). Grant Numbers: PLR-0806306 , PLR-85653100 , PLR-82486400 , PLR-1313614; NASA Advanced Supercomputing (NAS) Division; JPL Supercomputing and Visualization Facility (SVF) Grant Numbers: ARC-0806306 , ARC-85653100 , ARC-82486400; Russian Foundation of Basic Research; Ministry of the Education and Science of the Russian Federation; UK Natural Environment Research Council Grant Number: NE/I028947/
    Keywords: Arctic Ocean ; Beaufort Gyre ; Pacific Water ; Ocean dynamics ; Wind forcing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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