During research cruise M81/1 (GEOTRACES cruise GA11, RV Meteor, 04.02.-08.03.2010) 193 seawater samples were collected at 16 full water depth stations located in the (sub)tropical Atlantic. This cruise track covered an area from 30°N-11°S and 5°-50°W, which is characterized by different influencing parameters, e.g. dust input from the Saharan desert or riverine input from the Amazon. Seawater samples were collected with a trace metal clean CTD and filtration, subsampling and acidification was performed in the clean laboratory container onboard. Measurements were done land-based using an online-preconcentration method for the SeaFAST-system (ESI, seaFAST 1) with subsequent analysis by quadrupole inductively coupled plasma-mass spectrometry (Perkin-Elmer, ELAN DRC-e). Details on the preconcentration of Nb and the analytical measurement are provided in Poehle et al. 2015 (DOI: 10.1016/j.dsr.2014.11.014).
Data on dissolved Nb in the Atlantic Ocean are scarce and this study may serve future studies on the chemical twin pairs Nb/Ta and Zr/Hf, which in combination is promising as a proxy for the paleo-ocean circulation.
We observed an increase in concentration with depth contradicting the typical behavior of a particle-reactive element. Our results reveal that the influence of atmospheric dust input depends on its origin. While dust from the Canary Islands served as a source for Nb in surface waters dust particles from the Saharan desert worked as sorption sites. Since a correlation with nutrients (phosphate, nitrate, silicate) was not observed in this study Nb seems to be largely independent from nutrient cycling. Hence, distinct regional parameters influenced the depth distribution on a local scale while the observed concentration range of dissolved Nb in the (sub)tropical Atlantic agrees well with published data from the Pacific Ocean. The general depth profile of dissolved Nb with a slight surface depletion seems to be global feature.
