ALBERT

Description: Highlights: • The distribution of particulate matter was studied using Argo float measurements. • Its spatio-temporal properties were analyzed in the eastern tropical North Atlantic. • Surface, subsurface, intermediate and bottom nepheloid layers were considered. • High correlations between particulate matter and phytoplankton were verified. • The depth of subsurface particle maxima correlated to the distance to shore. Abstract: The spatial and temporal distribution of particulate matter in the water column of the eastern tropical North Atlantic between 16.9–22.9°N and 16.6–29.3°W was investigated using optical measurements from transmissometers mounted on Argo floats. The corresponding profiles of beam attenuation coefficients measured from February 2008 to May 2009 were used to study particulate matter in different layers such as the surface nepheloid layer (SNL), subsurface nepheloid layer (SSNL), intermediate nepheloid layer (INL) and bottom nepheloid layer (BNL) as well as to investigate sinking particles (SP). The SNL were down to about 60 m water depth at thicknesses between 20 and 60 m. Our analyses verified high correlation between particulate matter and phytoplankton in the SNL. High offshore SNL extension of up to 750 km was found in the area of Cape Blanc filaments in January 2009. Their typical widths ranged from 11 to 72 km. Furthermore, float-borne observations even resolved atmospheric dust deposition into the surface water layer during a strong Saharan dust event in October 2008. The observed dust concentration in the mixed water layer was found to vary between 0.0021 and 0.0168 g m−3 depending on applied assumptions. An abrupt change from a SNL to a SSNL regime over distances of only 80 to 90 km was observed. The particulate matter in the SSNL showed lateral extensions from 420 to 1020 km offshore. A statistically significant correlation between the depth of subsurface particle maxima and the distance to shore was found. An averaged diameter of 30 km was determined for the sharply isolated patches of INL which was consistent with model simulations of other studies. The lateral transport of particulate matter in these INL features in the area of the giant Cape Blanc filaments was found to be more pronounced than reported in earlier studies. The distribution of particulate matter within the INL filaments reached up to 610 km off the shelf edge. The frequency of INL decreased with increasing distance to shore. The sinking velocity of particulate matter of one long-term observed INL was approximately 1.3 m day−1. Highly concentrated BNLs with beam attenuation coefficients of up to 4.530 m−1 were observed in the continental slope region. INLs appeared more frequently than SP events which lead to the conclusion that the lateral transport of particulate matter in INL features in the study area was more important than their passive vertical sinking.

Description: In order to investigate biogeochemical cycling and dynamics of nutrients, measurement capabilities with sufficient spatial and temporal resolution are required. New ultraviolet-based methods and instrumentation for in situ determination of nitrate provide a powerful tool for these purposes. Here, we present a full dataset obtained by an UV-based process spectrophotometer (ProPS) during a cruise in 2008 in the south-eastern North Sea. Due to highly turbid conditions and mixing water masses, an improved calculation algorithm was performed on the UV absorption data. Nitrate concentrations ranged from 0 to 9 μmol/L on very short timescales, mainly due to tidal effects. Comparison of continuous optical nitrate measurements was performed against conventional wet-chemical analyses of discrete water samples which lead to a standard deviation of 1.7 μmol/L NO3−. High resolution measurements performed at a tidal inlet demonstrated the capability to map nitrate dynamics in turbid coastal environments. Research highlights: ► We present a new method for in situ determination of nitrate in turbid waters. ► UV spectrophotometer data is coupled with salinity and temperature sampling. ► A full dataset from a coastal inlet in the south-eastern North Sea is presented. ► Comparison against wet-chemical analyses lead to an accuracy of 1.7 μmol/L NO3−. ► High resolution sampling enabled time-space mapping of nitrate dynamics.

Description: Marine ecosystem dynamics in the context of climate change is a growing scientific, political and social concern requiring regular monitoring through appropriate observational technologies and studies. Thus, a wide range of tools comprising chemical, biogeochemical, physical, and biological sensors, as well as other platforms exists for marine monitoring. However, their high acquisition and maintenance costs are often a major obstacle, especially in low-income developing countries. We designed an advanced low-cost synoptic marine ecosystem observation system that operates at relatively high temporal frequencies, named PlasPi TDM. This instrument is an improved version of the camera system (PlasPI marine cameras) developed in 2020 by Autun Purser from the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research (Germany), and collaborators. It incorporates several innovative developments such as multispectral (records the spectrum of any object photographed), temperature and pressure sensors. The PlasPi TDM operates to a depth of 200 m. The various field deployments demonstrate the operational capability of the PlasPi TDM for different applications and illustrate its considerable potential for in-situ observations and marine surveillance in Africa. This device is intended as an open-source project and its continued development is encouraged for a more integrated, sustainable and low-cost ocean observing system.