ALBERT

Description: Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition and seasonal patterns were determined in two sediment trap moorings in the open equatorial North Atlantic (M4 at 12°N 49°W and M2 at 14°N 37°W), which collected settling particles synchronously in successive 16-day intervals from October 2012 to November 2013, at 1200 m water depth. The two trap locations show a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage throughout the monitored year. Species fluxes were yearlong dominated by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus), but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 × 10**7 coccoliths m**-2 d**-1 (117 x 10**7 to 423 x 10**7 coccoliths m**-2 d**-1) at station M4, compared to only 66 x 10**7 coccoliths m**-2 d**-1 (25 x 10**7 to 153 x 10**7 coccoliths m**-2 d**-1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, although most UPZ species also contributed higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. In addition, we found two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi indicating a fast response to nutrient-enrichment of the UPZ, probably by wind-forced mixing, whereas increased fluxes of G. oceanica and E. huxleyi in October/November 2013 coincided with the occurrence of Amazon River affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks we propose a scenario where atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated to the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Still, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than "background" tropical productivity in the equatorial North Atlantic. This study illustrates how two seemingly similar sites in an open-ocean tropical setting actually differ greatly in ecological and oceanographic terms, and provides valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.

Description: Long chain n-alkanes are terrestrial higher plant biomarkers used to reconstruct continental paleoclimatic and paleohydrological conditions with marine sedimentary archives. Latitudinal variation in their concentration and distribution in marine sediments relatively close to the continent has been widely studied, but little is known on how far this continental signal extends into the ocean. Furthermore, no studies have examined the seasonal variation in the deposition of these biomarkers in marine sediments. Here we studied longitudinal variation in the composition of long chain n-alkanes and two other terrestrial higher plant biomarkers (long chain n-alkanols and long chain fatty acids) in atmospheric particles, as well as longitudinal and seasonal variation in long chain n-alkanes in sinking particles in the ocean at different water depths and in surface sediments, all collected along a 12°N transect across the tropical North Atlantic Ocean. The highest abundance of all three biomarker classes was closest to the African coast, as expected, because they are transported with Saharan dust and the largest part of the dust is deposited close to the source. At this proximal location, the seasonal variability in long chain n-alkane flux and the chain length distribution of the n-alkanes in sinking particles was most pronounced, due to seasonal change in the dust source or due to change in vegetation composition in the source area, related to the position of the Intertropical Convergence Zone (ITCZ). In contrast, in the open ocean the seasonal variability in both the long chain n-alkane flux and chain length distribution of the n-alkanes was low. The abundance of the alkanes was also lower, as expected because of the larger source-to-sink distance. At the western part of the transect, close to South America, we found an additional source of the alkanes in the sinking particles during spring and autumn in the year 2013. The d13C of the alkanes in the surface sediment closest to the South American continent indicated that the isotope signal is likely derived from C3 vegetation from the Amazon, implying an input from the Amazon River, as there is no significant aeolian input from South America there since the prevailing wind direction is from the east. Finally, the concentration of the alkanes was similar in the material collected from the atmosphere, the particles collected while settling through the marine water column, and in the surface sediments, providing evidence that degradation of long chain n-alkanes from the atmosphere to settling at the sediment-water interface at deep open ocean sites is minimal.

Description: The Central Andes of South America hosts the largest known lithium anomalies in a restricted area, but the primary lithium sources of the salar deposits and the mobilization process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered as the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate surface near chemical weathering in a cold and dry climate as the dominant mobilization process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favourite source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb, and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by surface near chemical weathering with only minor hydrothermal mobilization of Li.