Holocene millenial-scale productivity record in the Mediterranean Sea

The calcareous nannofossil assemblages of Ocean Drilling Program Hole 963D from the central Mediterranean Sea have been investigated to document oceanographic changes in surface waters. The studied site is located in an area sensitive to large-scale atmospheric and climatic systems and to high- and low-latitude climate connection. It is characterized by a high sedimentation rate (the achieved mean sampling resolution is <70 years) that allowed the Sicily Channel environmental changes to be examined in great detail over the last 12 ka BP. We focused on the species Florisphaera profunda that lives in the lower photic zone. Its distribution pattern shows repeated abundance fluctuations of about 10-15%. Such variations could be related to different primary production levels, given that the study of the distribution of this species on the Sicily Channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery. Productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone, led by the dynamics of the summer thermocline. Productivity changes were compared with oceanographic, atmospheric, and cosmogenic nuclide proxies. The good match with Holocene master records, as with ice-rafted detritus in the subpolar North Atlantic, and the near-1500-year periodicity suggest that the Sicily Channel environment responded to worldwide climate anomalies. Enhanced Northern Hemisphere atmospheric circulation, which has been reported as one of the most important forcing mechanisms for Holocene coolings in previous Mediterranean studies, had a remarkable impact on the water column dynamics of the Sicily Channel.

Stable isotope record of planktonic foraminifera from the Sulu Sea

A high-resolution, accelerator mass spectroscopy 14C dated sediment record from the Sulu Sea clearly indicates that the Younger Dryas event affected the western equatorial Pacific. Planktonic foraminiferal delta18O and abundance data both record significant changes during Younger Dryas time. In particular, a 0.4 per mil increase in the delta18O value of Globigerinoides ruber and the reappearance of the cool water planktonic foraminifera, Neogloboquadrina pachyderma, occur during the Younger Dryas at this location. These isotopic and faunal changes are a response to either surface water temperature or salinity changes, or some combination of the two. Changes in surface salinities could have been accomplished through either local or global processes. Intensification of the monsoon climate system and increased precipitation at approximately 11 ka is one mechanism that may have resulted in local changes in salinity. A meltwater pulse derived from the Tibetan Plateau is another mechanism which may have caused local changes in salinity. The presence of the Younger Dryas in the tropical western Pacific clearly indicates that this climatic event is not restricted to the North Atlantic or high latitudes, but rather is global in extent.

Population structure, growth and production of the surf clam Donax hanleyanus (Bivalvia: Donacidae) from northern Argentinean beaches

The surf clams Mesodesma mactroides Reeve, 1854 and Donax hanleyanus Philippi, 1847 are the two dominating species in macrobenthic communities of sandy beaches off northern Argentina, with the latter now surpassing M. mactroides populations in abundance and biomass. Before stock decimation caused by exploitation (during the 1940s and 1950s) and mass mortality events (1995, 1999 and 2007) M. mactroides was the prominent primary consumer in the intertidal ecosystem and an important economic resource in Argentina. Since D. hanleyanus was not commercially fished and not affected by mass mortality events, it took over as the dominant species, but did never reach the former abundance of M. mactroides. Currently abundance and biomass of both surf clams are a multiple smaller than those of forty years ago, indicating the conservation status of D. hanleyanus and M. mactroides as endangered. Therefore the aim of this study is to analyse the population dynamics (population structure, growth and reproductive biology) of D. hanleyanus and M. mactroides, and to compare the results with historical data in order to detect possible differences within surf clam populations forty years ago and at present.

Age determination of Southeast Atlantic sediment cores

Angola Basin and Cape Basin (southeast Atlantic) surface sediments and sediment cores show that maxima in the abundance of taraxerol (relative to other land-derived lipids) covary with maxima in the relative abundance of pollen from the mangrove tree genus Rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests. Together with the observation that Rhizophora mangle and Rhizophora racemosa leaves are extraordinarily rich in taraxerol, this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the SE Atlantic. The proxy-environment relations for taraxerol and Rhizophora pollen down-core show that increased taraxerol and Rhizophora pollen abundances occur during transgressions and periods with a humid climate. These environmental changes modify the coastal erosion and sedimentation patterns, enhancing the extent of the mangrove ecosystem and/or the transport of mangrove organic matter offshore. Analyses of mid-Pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity. This demonstrates the complex environmental response of the interaction between precession-related humidity cycles and obliquity-related sea-level changes on mangrove input.