Sea surface temperature and salinity reconstruction of sediment core GeoB3129-1

A sediment core from the western tropical Atlantic covering the last 21,000 yr has been analysed for centennial scale reconstruction of sea surface temperature (SST) and ice volume-corrected oxygen isotopic composition of sea water (delta18O(ivc-sw)) using Mg / Ca and delta18O of the shallow dwelling planktonic foraminifer Globigerinoides ruber (white). At a period between 15.5 and 17.5 kyr BP, the Mg / Ca SST and delta18O(ivc-sw), a proxy for sea surface salinity (SSS), reveals a warming of around 2.5 °C along with an increase in salinity. A second period of pronounced warming and SSS increase occurred between 11.6 and 13.5 kyr BP. Within age model uncertainties, both warming intervals were synchronous with air temperature increase over Antarctica and ice retreat in the southern South Atlantic and terminated with abrupt centennial scale SSS decrease and slight SST cooling in conjunction with interglacial reactivation of the meridional overturning circulation (MOC). We suggest that during these warm intervals, production of saline and warm water of the North Brazil Current resulted in pronounced heat and salt accumulation, and was associated with warming in the southern Atlantic, southward displacement of the intertropical convergence zone and weakened MOC. At the termination of the Younger Dryas and Heinrich event 1, intensification of cross-equatorial heat and salt transport caused centennial scale cooling and freshening of the western tropical Atlantic surface water. This study shows that the western tropical Atlantic served as a heat and salt reservoir during deglaciation. The sudden release of accumulated heat and salt at the end of Younger Drays and Heinrich event 1 may have contributed to the rapid reinvigoration of the Atlantic MOC.

Diversity of ocean acidification effects on marine N2 fixers

Considering the important role of N2 fixation for primary productivity and CO2 sequestration, it is crucial to assess the response of diazotrophs to ocean acidification. Previous studies on the genus Trichodesmium suggested a strong sensitivity towards ocean acidification. In view of the large functional diversity in N2 fixers, the objective of this study was to improve our knowledge of the CO2 responses of other diazotrophs. To this end, the single-celled Cyanothece sp. and two heterocystous species, Nodularia spumigena and the symbiotic Calothrix rhizosoleniae, were acclimated to two pCO2 levels (380 vs. 980 µatm). Growth rates, cellular composition (carbon, nitrogen and chlorophyll a) as well as carbon and N2 fixation rates (14C incorporation, acetylene reduction) were measured and compared to literature data on different N2 fixers. The three species investigated in this study responded differently to elevated pCO2, showing enhanced, decreased as well as unaltered growth and production rates. For instance, Cyanothece increased production rates with pCO2, which is in line with the general view that N2 fixers benefit from ocean acidification. Due to lowered growth and production of Nodularia, nitrogen input to the Baltic Sea might decrease in the future. In Calothrix, no significant changes in growth or production could be observed, even though N2 fixation was stimulated under elevated pCO2. Reviewing literature data confirmed a large variability in CO2 sensitivity across diazotrophs. The contrasting response patterns in our and previous studies were discussed with regard to the carbonate chemistry in the respective natural habitats, the mode of N2 fixation as well as differences in cellular energy limitation between the species. The group-specific CO2 sensitivities will impact differently on future biogeochemical cycles of open-ocean environments and systems like the Baltic Sea and should therefore be considered in models estimating climate feedback effects.

Geochemical data derived from an absolutely dated shell-based chronology for the Irish Sea

The identification in various proxy records of periods of rapid (decadal scale) climate change over recent millennia, together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric CO2, highlights the importance of a detailed understanding, at high spatial and temporal resolutions, of forcings and feedbacks within the system. Such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree-rings for the terrestrial environment and by corals for the tropical marine environment. Here we present the first annually resolved, multi-centennial (489-year), absolutely dated, shell-based marine master chronology. The chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long-lived bivalve mollusc Arctica islandica, collected from sites to the south and west of the Isle of Man in the Irish Sea. The strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree-ring chronologies. Analysis of the 14C signal in the shells shows no trend in the marine radiocarbon reservoir correction (DR), although it may be more variable before ~1750. The d13C signal shows a very significant (R**2 = 0.456, p < 0.0001) trend due to the 13C Suess effect.

Composition of standard reference samples of Fe-Mn nodules and bottom sediments

The first series of Soviet standard reference samples of composition of ore materials and ocean pelagic sediments has been created. It includes iron-manganese nodules (SDO-4, SDO-5 and SDO-6), ore crusts (SDO-7) diatomaceous ooze (SDO-8), and deep-sea red clays (SDO-9). The standards are intended to serve as a metrologic basis for physical, physicochemical and chemical analyses of iron-manganese minerals and ocean sediments. The standards are provided with certified analyses of rock-forming components and certain trace elements. Certified characteristics are based on statistical analysis of data obtained from an inter-laboratory experiment involving analysis of the standard reference samples by a variety of methods.