Search for: All records

Mercury (Hg) is a global pollutant with substantial human health impacts. While most studies focus on atmospheric total Hg (THg) deposition, contributions of methylated Hg (MeHg), including monomethylmercury (MMHg) and dimethylmercury (DMHg), remain poorly understood. To examine this, we use rain and aerosol Hg speciation data and high-resolution surface DMHg measurements, collected on a transect from Alaskan coastal waters to the Bering and Chukchi Seas. We observed a significant fivefold increase in the MeHg:THg fraction in rain and a 10-fold increase for aerosols, closely linked to elevated surface DMHg and the highest DMHg evasion (~9.4 picomoles per square meter per hour) found in upwelling waters near the Aleutian Islands. These data highlight a previously underexplored aspect of MeHg air-sea exchange and its importance to Hg cycling and human health concerns. Our findings emphasize the importance of DMHg evasion by demonstrating that atmospheric MeHg can be transported long distances (~1700 kilometers) in the Arctic, posing risks to human health and ecosystems. 

Abstract Export rates of organic matter (OM) were determined based on PO₄³⁻, NO₃⁻and O₂budgets during GEOTRACES cruise GP15 in the Pacific Ocean that crossed subpolar, subtropical and equatorial regimes. Lowest OM export rates at 3–5 mmol C/m²/yr were found in the subtropical regions and highest rates at 9–12 mmol C/m²/yr were found in the equatorial and subpolar regions. Satellite based OM export rates showed similar regional trends but with a significantly larger range. The budget and satellite‐based OM export rates were 3–15× higher than estimates of particle loss rates based on²³⁴Th and sediment trap collections, with the differences primarily due to non‐particle forms of OM export and different integration times of methods. The efficiency of export varied from 0.1 to 0.3, with the lowest efficiencies in the subtropics and highest efficiencies in the subpolar and equatorial regions. 

Beryllium-7, a radioactive isotope with a half-life of 53.3 days, is formed in the atmosphere, attaches to aerosol particles, and is deposited on the earth’s surface through wet and dry processes. In this project, we measured Be-7 concentrations in aerosol particles and in seawater samples (depths < 200 meters) collected on the GEOTRACES GP17-OCE cruise aboard R/V Roger Revelle. The cruise originated in Papeete, Tahiti, French Polynesia on 1 December 2022 and concluded on 25 January 2023 in Punta Arenas, Chile. Sixteen aerosol samples and seawater from twelve stations in the South Pacific and Southern Oceans were collected. The dataset will be used to study the deposition of trace elements and isotopes (TEIs) and upper ocean mixing processes. Aerosol deposition is an important source of TE micronutrients to open ocean areas that are far removed from riverine sources. But, while the collection aerosol of samples for TEI analysis is straightforward, estimating the deposition flux also requires an appropriate deposition velocity (i.e. deposition flux is the product of the aerosol concentration and deposition velocity). Because Be-7 is supplied to the open ocean exclusively through aerosol deposition and it is removed through radioactive decay, the water column inventory and aerosol concentration of Be-7 can be used to derive the deposition velocity applicable to aerosol TEIs. The penetration of dissolved Be-7 below the ocean mixed layer is limited by the isotope's half-life and the rate of vertical diffusive mixing. Through modeling, the shape of the Be-7 profile below the mixed layer provides an estimate for the vertical diffusivity coefficient (Kz), which can be used to calculate fluxes of chemical species (e.g. oxygen) and physical properties (e.g. heat). 

Abstract Atmospheric deposition is an important pathway for delivering micronutrient and pollutant trace elements (TEs) to the surface ocean. In the central Arctic, much of this supply takes place onto sea ice during winter, before eventual delivery to the ocean during summertime melt. However, the seasonality of aerosol TE loading, solubility, and deposition flux are poorly studied over the Arctic Ocean, due to the difficulties of wintertime sampling. As part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, aerosols collected during winter and spring (December–May) were analyzed for soluble, labile, and total TE concentrations. Despite low dust loading, mineral aerosol accounted for most of the variation in total Fe, Al, Ti, V, Mn, and Th concentrations. In contrast, soluble TE concentrations were more closely linked to non‐sea‐salt sulfate, and Fe solubility was significantly higher during Arctic winter (median = 6.5%) than spring (1.9%), suggesting an influence from Arctic haze. Beryllium‐7 data were used to calculate an average bulk deposition velocity of 613 ± 153 m d⁻¹over most of the study period, which was applied to calculate seasonal deposition fluxes of total, labile, and soluble TEs to the central Arctic. Total TE fluxes (173 ± 145 nmol m⁻² d⁻¹for Fe) agreed within a factor of two or three with earlier summertime estimates, with generally higher wintertime concentrations offset by a lower deposition velocity. Cumulative seasonal deposition of total, labile, and soluble Fe to the central Arctic Ocean was calculated at 25 ± 21, 5 ± 3, and 2 ± 2 μmol m⁻², respectively. 

Beryllium-7, a cosmogenic radioactive isotope with a half-life of 53.3 days, is formed in the atmosphere, attaches to aerosol particles, and is deposited on the earth's surface through wet and dry processes. In this project, we measured Be-7 concentrations in aerosol particles and in seawater samples (depths < 200 meters) collected on the French GEOTRACES section GS02 SWINGS cruise aboard R/V Marion-Dufresne. The cruise originated at Réunion Island on 11 January 2021 and concluded at Réunion on 8 March 2021. Nineteen aerosol samples and seawater from eleven stations in the South Indian Ocean were collected. The dataset will be used to study the deposition of trace elements and isotopes (TEIs) and upper ocean mixing processes. Aerosol deposition is an important source of TE micronutrients to open ocean areas that are far removed from riverine sources. But, while the collection aerosol of samples for TEI analysis is straightforward, estimating the deposition flux also requires an appropriate deposition velocity (i.e. deposition flux is the product of the aerosol concentration and deposition velocity). Because Be-7 is supplied to the open ocean exclusively through aerosol deposition and it is removed through radioactive decay, the water column inventory and aerosol concentration of Be-7 can be used to derive the deposition velocity applicable to aerosol TEIs. 

Abstract We use a tracer method involving the cosmogenic radioisotope beryllium‐7 (half‐life = 53.3 days) to follow the deposition of aerosols and the fate of snow on the MOSAiC ice floe during winter and spring 2019–2020. When examined alongside data from earlier studies in the Arctic Ocean that covered summer and fall, Be‐7 inventories indicate a summertime peak for aerosol Be‐7 deposition fluxes coinciding with seasonal minima boundary‐level aerosol concentrations, which suggests that deposition fluxes are primarily controlled by precipitation. This conclusion is supported by the linear relationship between Be‐7 fluxes and precipitation rates derived from data from the MOSAiC and SHEBA expeditions. Inventories of Be‐7 within the snow column exhibited evidence of significant redistribution. Be‐7 deficits, relative to the flux, were observed in areas of level sea ice while excess Be‐7 was found associated with deformed ice features such as pressure ridges, leading to the following estimates for the distribution of snow on the ice floe in May 2020: 75–93% of the snow mass is found on deformed sea ice with the remainder on level ice. Furthermore, uncertainties associated with measurements of Be‐7 concentrations within the ocean mixed layer would allow for losses of snow through open leads of up to approximately 20% of the flux. Our snow distribution estimates agree with data from repeat snow depth transect measurements. These results suggest that Be‐7 can be a useful tool in studying snow redistribution. 

Mercury (Hg) concentrations and speciation within surface waters of the Arctic Ocean are controlled by a complex set of processes including photochemical and microbial transformations, redox reactions, and air-sea exchange of gaseous and particulate Hg species. In this study, our aim was to estimate the magnitude of volatile Hg fluxes across the air-sea interface, and examine the influence of ice cover on this process. While gas exchange in the open ocean has been modeled as a function of wind speed, the parameterization is problematic in the presence of sea ice, which can physically block gas exchange, as well as reduce fetch and dampen waves. By using measurements of Radon-222 (Rn-222) gas and it parent isotope, Radium-226 (Ra-226), to accurately measure gas exchange velocities (k), the relative impacts of chemical and biological processes on mercury distributions within the surface waters can then be deduced. This dataset contains Radon-222 and Radium-226 activity concentrations from R/V Sikuliaq cruise SKQ202108S in the Bering Sea, through the Bering Strait, and in shelf waters of the Chukchi Sea during May – June 2021. Samples include seawater (16 water column profiles), as well as ice cores and brine from four ice stations. At the time of the cruise, sampling locations in the Bering Sea were ice free and gas transfer velocities (k) estimated from Rn-222 deficits (with respect to Ra-226 concentrations) were in general agreement with published parameterizations of k as a function of wind speed. The springtime retreating ice edge was located at 69-70 degrees north latitude in the Chukchi Sea, and sampling locations there were located along the ice edge, in areas of open water, and at sites within the pack ice up to ~10 kilometers (km) from the ice edge. Gas transfer velocities in the marginal ice zone also reflected recent wind histories, with k values generally at the high end of or exceeding those predicted from the wind speed parameterizations. 

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition was an international initiative in which research vessel (R/V) Polarstern drifted with the sea ice in the Central Arctic Ocean from October 2019 to September 2020. Here, we present data from a study in which Beryllium-7, a naturally occurring radioactive isotope with a half-life of 53 days, is used as a tracer for the atmospheric deposition of trace elements to the ocean / ice surface and their partitioning among the seawater, ice and snow catchments during winter and spring. The data sets include measurements of Be-7 in 1) aerosol particles collected on filters using a high volume sampler on Polastern, 2) seawater from the upper water column (8-60 meters depth) collected using the ship’s seawater intake system and using pumps on the ice floe, and 3) ice cores, snow, and frost flowers collected from sites on the MOSAiC and surrounding ice floes. Be-7 analysis was performed using high purity germanium gamma detectors. 

Abstract Distributions of the natural radionuclide²¹⁰Po and its grandparent²¹⁰Pb along the GP15 Pacific Meridional Transect provide information on scavenging rates of reactive chemical species throughout the water column and fluxes of particulate organic carbon (POC) from the primary production zone (PPZ).²¹⁰Pb is in excess of its grandparent²²⁶Ra in the upper 400–700 m due to the atmospheric flux of²¹⁰Pb. Mid‐water²¹⁰Pb/²²⁶Ra activity ratios are close to radioactive equilibrium (1.0) north of ∼20°N, indicating slow scavenging, but deficiencies at stations near and south of the equator suggest more rapid scavenging associated with a “particle veil” located at the equator and hydrothermal processes at the East Pacific Rise. Scavenging of²¹⁰Pb and²¹⁰Po is evident in the bottom 500–1,000 m at most stations due to enhanced removal in the nepheloid layer. Deficits in the PPZ of²¹⁰Po (relative to²¹⁰Pb) and²¹⁰Pb (relative to²²⁶Ra decay and the²¹⁰Pb atmospheric flux), together with POC concentrations and particulate²¹⁰Po and²¹⁰Pb activities, are used to calculate export fluxes of POC from the PPZ.²¹⁰Po‐derived POC fluxes on large (>51 μm) particles range from 15.5 ± 1.3 mmol C/m²/d to 1.5 ± 0.2 mmol C/m²/d and are highest in the Subarctic North Pacific;²¹⁰Pb‐derived fluxes range from 6.7 ± 1.8 mmol C/m²/d to 0.2 ± 0.1 mmol C/m²/d. Both²¹⁰Po‐ and²¹⁰Pb‐derived POC fluxes are greater than those calculated using the²³⁴Th proxy, possibly due to different integration times of the radionuclides, considering their different radioactive mean‐lives and scavenging mean residence times.