Microplastics in sea ice and seawater beneath ice floes from the Arctic Ocean.

Within the past decade, an alarm was raised about microplastics in the remote and seemingly pristine Arctic Ocean. To gain further insight about the issue, microplastic abundance, distribution and composition in sea ice cores (n = 25) and waters underlying ice floes (n = 22) were assessed in the Arctic Central Basin (ACB). Potential microplastics were visually isolated and subsequently analysed using Fourier Transform Infrared (FT-IR) Spectroscopy. Microplastic abundance in surface waters underlying ice floes (0-18 particles m-3) were orders of magnitude lower than microplastic concentrations in sea ice cores (2-17 particles L-1). No consistent pattern was apparent in the vertical distribution of microplastics within sea ice cores. Backward drift trajectories estimated that cores possibly originated from the Siberian shelves, western Arctic and central Arctic. Knowledge about microplastics in environmental compartments of the Arctic Ocean is important in assessing the potential threats posed by microplastics to polar organisms.

Microplastics in sub-surface waters of the Arctic Central Basin.

Polar oceans, though remote in location, are not immune to the accumulation of plastic debris. The present study, investigated for the first time, the abundance, distribution and composition of microplastics in sub-surface waters of the Arctic Central Basin. Microplastic sampling was carried out using the bow water system of icebreaker Oden (single depth: 8.5 m) and CTD rosette sampler (multiple depths: 8-4369 m). Potential microplastics were isolated and analysed using Fourier Transform Infrared Spectroscopy (FT-IR). Bow water sampling revealed that the median microplastic abundance in near surface waters of the Polar Mixed Layer (PML) was 0.7 particles m-3. Regarding the vertical distribution of microplastics in the ACB, microplastic abundance (particles m-3) in the different water masses was as follows: Polar Mixed Layer (0-375) > Deep and bottom waters (0-104) > Atlantic water (0-95) > Halocline i.e. Atlantic or Pacific (0-83).

Acoustic Mapping of Thermohaline Staircases in the Arctic Ocean.

Although there is enough heat contained in inflowing warm Atlantic Ocean water to melt all Arctic sea ice within a few years, a cold halocline limits upward heat transport from the Atlantic water. The amount of heat that penetrates the halocline to reach the sea ice is not well known, but vertical heat transport through the halocline layer can significantly increase in the presence of double diffusive convection. Such convection can occur when salinity and temperature gradients share the same sign, often resulting in the formation of thermohaline staircases. Staircase structures in the Arctic Ocean have been previously identified and the associated double diffusive convection has been suggested to influence the Arctic Ocean in general and the fate of the Arctic sea ice cover in particular. A central challenge to understanding the role of double diffusive convection in vertical heat transport is one of observation. Here, we use broadband echo sounders to characterize Arctic thermohaline staircases at their full vertical and horizontal resolution over large spatial areas (100 s of kms). In doing so, we offer new insight into the mechanism of thermohaline staircase evolution and scale, and hence fluxes, with implications for understanding ocean mixing processes and ocean-sea ice interactions.

Seasonal Study of Mercury Species in the Antarctic Sea Ice Environment.

Limited studies have been conducted on mercury concentrations in the polar cryosphere and the factors affecting the distribution of mercury within sea ice and snow are poorly understood. Here we present the first comprehensive seasonal study of elemental and total mercury concentrations in the Antarctic sea ice environment covering data from measurements in air, sea ice, seawater, snow, frost flowers, and brine. The average concentration of total mercury in sea ice decreased from winter (9.7 ng L-1) to spring (4.7 ng L-1) while the average elemental mercury concentration increased from winter (0.07 ng L-1) to summer (0.105 ng L-1). The opposite trends suggest potential photo- or dark oxidation/reduction processes within the ice and an eventual loss of mercury via brine drainage or gas evasion of elemental mercury. Our results indicate a seasonal variation of mercury species in the polar sea ice environment probably due to varying factors such as solar radiation, temperature, brine volume, and atmospheric deposition. This study shows that the sea ice environment is a significant interphase between the polar ocean and the atmosphere and should be accounted for when studying how climate change may affect the mercury cycle in polar regions.

Determination of Henry's law constant for elemental mercury.

The assessment of the global mercury cycle involves estimations of the evasion of mercury form oceanic waters. In such estimations Henry's law constant is often used. In this study the Henry's law constant for elemental mercury has been re-determined in MQ water and artificial sea water. Moreover, for the first time it has been determined for 1.5M sodium chloride (NaCl) solution which is of relevance for modeling of atmospheric waters at coastal locations. For all solutions, experiments has been conducted at five different temperatures between 278 and 308K, using a novel technique, for mercury, based on direct measurements of the portioning of mercury between the aqueous and gaseous phase. Elemental mercury was extracted from the water column and the logarithm of the mass of extracted mercury was plotted against time. A dimensionless Henry's law constant, defined as: [see text] was obtained from the slope of the curve. Almost no difference was observed in the values comparing the Milli-Q water and artificial sea water, however for the 1.5M NaCl solution a salting-out effect was seen, i.e. the solubility of mercury in the water phase decreased. The decreased solubility will generate an increase in the value of Henry's law constant.

A description of an automatic continuous equilibrium system for the measurement of dissolved gaseous mercury.

A novel continuous equilibrium system with high time resolution, i.e. every ten minutes, was developed to sample and determine dissolved gaseous mercury (DGM) in natural surface waters. The system is based on the opposite flow principle, can be connected to a ship's bow water system, and can be applied under most ambient conditions, such as high wind speeds and onboard a moving ship. For the DGM determination the system uses the measured equilibrium concentration of mercury established between the aqueous and gaseous phases, i.e. DGM = Hg(extr)/k(H'), where Hg(extr) is the measured mercury concentration in the outgoing gas phase and k(H') is the dimensionless Henry's Law constant at the desired temperature and salinity. The efficiency of the system was investigated via theoretical calculations and by comparing the continuous equilibrium system with discrete samples. The measurements obtained by the continuous equilibrium system agree within 13% at the 95% confidence level with the measurements of discrete samples obtained by the traditional technique. The theoretical calculations estimated that the continuous equilibrium system described here had an efficiency of 99% for determining the DGM concentration.

Distribution of TPM in Northern Europe.

Total particulate mercury (TPM) in air has been measured during five 2-week campaigns at five measurement sites in Northern Europe. The measurements covered four seasons and the result constitutes a unique TPM data set from this region. Evidence for transport of TPM on a regional scale is reported as well as the historical trend of TPM in south of Sweden. All TPM measurements were made using a new mini particulate sampler. The device consists of a quartz fibre filter contained in a quarts glass filter holder and is a modified version of the MiniSamplr. This approach proves to be reliable and more cost efficient in comparison to alternative methods. Tests made to evaluate the performance of the sampler in terms of precision and comparability with sampling on Teflon membrane filters are also reported.

A kinetic study on the abiotic methylation of divalent mercury in the aqueous phase.

The mechanism and kinetics of the formation of methylmercury from an experimental solution containing divalent mercury and acetic acid has been investigated. The experiments were performed in a 2-dm(3) Teflon reactor. The organic mercury was measured with time resolutions varying between minutes and hours, after derivatisation, gas chromatography separation and Cold vapour atomic fluorescence detection. (GC)-CVAFS. CVAFS technique was used for determination of inorganic mercury in the aqueous phase using an automated mercury analyser. The experiments were carried out in concentrations relevant for natural waters. Our result shows that the reaction proceeds via mercury acetate complexes. A first order reaction coefficient has been calculated at various pH values, and was found to be (9.0+/-0.9) x 10(-7) s(-1) at pH 3.6-3.7. The rate was not found to be enhanced by UV-light when taking into account the photolytical degradation of methylmercury. The reaction rate at various pH values, the influences of some other relevant reaction parameters, and implications for atmospheric and terrestrial waters are discussed.

Comparison of procedures for measurements of dissolved gaseous mercury in seawater performed on a Mediterranean cruise.

A comparison of manual procedures for measurements of dissolved gaseous mercury (DGM) in seawater was accomplished. The experiments were performed on board the Italian research vessel Urania during July 2000 as a subtask in the CNR "Med-Oceanor Project 2000". Water samples for DGM were collected by Go-Flo bottles and subsequently analysed for DGM on board the ship. Determinations of DGM were made in parallel by two groups using different analytical routines. The two sets of data obtained compare favourably. Based on the fieldwork and an additional laboratory study, analytical procedures are discussed and an optimised method to determine DGM is presented. In addition, a method for automated in situ measurements of DGM positioned in the water body was tested. This method has the potential to simplify studies of DGM dynamics, that is variation in concentration as a function of water temperature and solar radiation etc.