Description: Eastern Boundary Upwelling Ecosystems (EBUEs) are associated with high biological productivity, high fish catch and they highly contribute to marine carbon sequestration. Whether coastal upwelling has intensified or weakened under climate change in the past decades is controversially discussed and different approaches (e.g., time-series of chlorophyll, wind, sea surface temperature, modeling experiments) have been considered. We present a record of almost two decades of particle fluxes (1991–2009) from ca. 600 to 3100 m water depth in the Canary Basin at site ESTOC (European Station for Time series in the Ocean Canary Islands; ca. 29°N, 15°30.W, ca. 3600 m water depth), located in the offshore transition zone of the northern Canary Current-EBUE. We compare these flux records with those measured at a mesotrophic sediment trap site further south off Cape Blanc (Mauritania, ca. 21°N). The deep ocean fluxes at ESTOC in ca. 3 km recorded the evolution of the coastal Cape Ghir filament (30–32°N, 10–12°W) due to lateral advection of particles, whereas the upper water column sediment traps in ca. 1 km reflected the oligotrophic conditions in the overlying waters of ESTOC. We observed an increased emphasis in spring-time fluxes since 2005, associated with a change in particle composition, while satellite chlorophyll biomass did not show this pattern. Due to its northern location in the CC-EBUEs, spring biogenic fluxes at ESTOC provide a better relationship to the forcing of the North Atlantic Oscillation than those recorded further south off Cape Blanc. Off Cape Blanc, deep fluxes showed the best overlap with the deep ESTOC fluxes during the spring season before 2005. On the long-term, both chlorophyll and particle fluxes showed an increasing trend at ESTOC which was not observed further south at the mesotrophic Cape Blanc site. This might indicate that, depending on their location along the NW African margin, coastal upwelling systems react differently to global change.

Description: Calcium carbonate hexahydrate (ikaite) is a rare mineral that forms as metastable species in the organic-carbon-rich sediments of the King George Basin, Bransfield Strait, Antarctica, as a consequence of early diagenetic decomposition of organic matter under cold water (−1.4 °C) and high pressure (200 bar) conditions. Large crystals grow in the sediment immediately below the diagenetic transition between microbial sulfate reduction and methanogenesis at ~320 cm below sea floor (bsf). This process is reflected in the dissolved sulfate, total carbon dioxide, and methane concentrations, as well as in the carbon, hydrogen, and oxygen isotope chemistries of the interstitial fluids and dissolved gases of the host sediment. The ikaite crystal faithfully records in its zonal structure the changing carbon isotope ratio of the total dissolved carbon dioxide pool as it gradually diminishes during methanogenesis (δ13Cikaite = −17.5 to −21.4‰). These changes in the crystal’s host environment follow general Rayleigh carbon isotope fractionation. The oxygen isotopes of the ikaite carbonate (δ18Oikaite = 1.46 to 4.45‰) also show a strong zonal distribution, unrelated to temperature of formation, but perhaps controlled by the degree of recrystallization of ikaite to calcite. The crystal water of the ikaite is depleted 11‰ in 2H/1H (VSMOW) relative to the coexisting interstitial water, which is in excellent agreement with the isotope fractionation of other hydrated minerals. In addition to the in situ temperature and pressure, nucleation of the ikaite crystals in the Bransfield Basin sediments may be induced by the high alkalinity, high phosphate concentrations, and dissolved organic compounds. Intense microbial metabolism generates such compounds; of these, aspartic acid and glutamic acid may play an important role, as they do in biological and extracellular carbonate mineral precipitation. All indications are that low temperatures (such as of polar environments), high calcium carbonate supersaturation caused by interstitial methanogenesis, and a sufficiently large supply of dissolved phosphate and amino acids favor metastable ikaite formation. These conditions, modified by recrystallization, may be preserved in calcite glendonites, thinolites, and other calcitic pseudomorphs derived from ikaite and found throughout the ancient sedimentary record.