Description: In summer 2015, The RV Atlântico Sul cruise collected water column samples for macronutrients, dissolved iron (DFe) concentrations and speciation and humic substances (HS) in a transect over the shelf of the South Brazil Bight (SBB) at Santa Marta Grande Cape (28.5°S, SE Brazil) during coastal downwelling episode. Samples were collected over the whole shelf and the initial section of the slope. All samples were collected using 12-liter Teflon-coated Go-Flo bottles suspended on a Kevlar line. Samples were divided into nutrients and trace metals onboard. Samples for nutrients were filtered through 0.45 µm filters (cellulose acetate, Millipore), and samples for dissolved DFe, organic iron speciation and HS were immediately filtered by 0.2 µm (cellulose nitrate ,Millipore). All samples were immediately frozen for analysis. In laboratory, samples were thawed and analyzed for nutrients the analytical methodology used was described in Strickland and Parsons, (1972). DFe concentrations, the samples were determined following a well-established CSV method (Laglera et al., 2013) adding a UV digestion step. Organic iron speciation was analyzed using a modified method described initially by (van den Berg, 2006), but modified removing the addition of bromate from the original method to avoid any underestimation of the contribution of HS to ligand concentrations (Laglera et al., 2011). The determination of HS concentrations and iron-humic complex concentrations following stablished CSV procedures (Laglera et al., 2007; Sukekava et al., 2018). Using those samples, the aim of this research was comprehending the effect of coastal downwelling such episodes in the distributions of macronutrients, DFe and humic substances in SBB.

Description: Mapping radon (222 Rn) distribution patterns in the coastal sea is a widely applied method for localizing and quantifying submarine groundwater discharge (SGD). While the literature reports a wide range of successful case studies, methodical problems that might occur in shallow wind-exposed coastal settings are generally neglected. This paper evaluates causes and effects that resulted in a failure of the radon approach at a distinct shallow wind-exposed location in the Baltic Sea. Based on a simple radon mass balance model, we discuss the effect of both wind speed and wind direction as causal for this failure. We show that at coastal settings, which are dominated by gentle submarine slopes and shallow waters, both parameters have severe impact on coastal radon distribution patterns, thus impeding their use for SGD investigation. In such cases, the radon approach needs necessarily to allow for the impact of wind speed and wind direction not only during but also prior to the field campaign.

Description: Important processes in the ocean can be evaluated with radioactive nuclides, including radium isotopes. An approach for quantifying radium isotopes in seawater with in-situ pumps has been developed in advance of the GEOTRACES program [1]. Precise measurements of 223Ra and 224Ra by means of the delayed coincidence counting system (RaDeCC) [2] are dependent on the moisture content of the medium [3]. In order to verify the optimum moisture content for this new approach, a set of measurements of the Mn-cartridge standards under different moisture conditions was conducted, as this was done previously for acrylic fiber. At a time, an amount of water equivalent to 5% of the cartridges weight was added, and the activities were determined. The variation of 224Ra activity occurs mainly between 0 to 15% of humidity. Under moisture conditions higher than 15%, the emanation efficiency reaches an optimum plateau until 100% of moisture. This result differs slightly from those found for 224Ra measurements using the acrylic fiber (plateau from 30 to 100 %) [3]. The 223Ra Mn-cartridge standard reaches the plateau under 5% of humidity, and above 50% moisture the activity seems to decrease. Considering the counting error (7%), it is hard to state that the effect of the moisture is critical. However, this decrease can be related to the shorter half-life of the 219Rn compared to the time needed to its diffusion through the water film, which could be a reason for the frequently observed lower efficiency of the 223Ra channel of the RaDeCC system [4]. [1] Henderson et al. (2013) J. Radioanal. Nucl. Chem. 296, 357–362. [2] Moore and Arnold (1996) J. Geophys. Res. 101, 321–1329. [3] Sun and Torgersen (1998) Mar. Chem. 61, 163–171. [4] Charette et al. (2012) Limnol. Oceanogr. 10, 451–463.

Description: Mapping radon (222Rn) distribution pat- terns in the coastal sea is a widely applied method for localizing and quantifying submarine groundwater discharge (SGD). While the literature reports a wide range of successful case studies, methodical problems that might occur in shallow wind-exposed coastal settings are generally neglected. This paper evalu- ates causes and effects that resulted in a failure of the radon approach at a distinct shallow wind-exposed location in the Baltic Sea. Based on a simple radon mass balance model, we discuss the effect of both wind speed and wind direction as causal for this fail- ure. We show that at coastal settings, which are domi- nated by gentle submarine slopes and shallow waters, both parameters have severe impact on coastal radon distribution patterns, thus impeding their use for SGD investigation. In such cases, the radon approach needs necessarily to allow for the impact of wind speed and wind direction not only during but also prior to the field campaign.