Dust record from the EPICA Dome C ice core, Antarctica, covering 0 to 800 kyr BP

Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation and it can be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport, and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution aeolian dust record from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the last eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggests that dust flux is increasingly correlated with Antarctic temperature as climate becomes colder. We interpret this as progressive coupling of Antarctic and lower latitudes climate. Limited changes in glacial-interglacial atmospheric transport time Mahowald et al. (1999, doi:10.1029/1999JD900084), Jouzel et al. (2007, doi:10.1126/science.1141038), and Werner et al. (2002, doi:10.1029/2002JD002365) suggest that the sources and lifetime of dust are the major factors controlling the high glacial dust input. We propose that the observed ~25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer atmospheric dust particle life-time in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.

A refined Pliocene to early Pleistocene chronostratigraphic frame at ODP Hole 653A (West Mediterranean)

Two planktonic foraminiferal oxygen isotope records of ODP Hole 653A (Tyrrhenian Sea) are presented for the time period extending from approximately 0.8 to 3.0 Ma. Six, generally accepted, synchronous bioevents were used to precise the oxygen isotope chronology and to identify the oxygen isotope stages 22 down to 114. Subsequently, this oxygen isotope chronology was used to determine the synchronism or diachronism of various other biostratigraphic events with those recorded in the Singa and Ficarazzi land sections (Italy) and those in other DSDP/ODP sites. New results concern the diachronity of the FOD of the planktonic foraminiferal species N. atlantica, G.truncatulinoides truncatulinoides and G. inflata between ODP Hole 653A and the Italian landsections. Because many species entered the Mediterranean in short term fluxes, strongly related to the southward migration of cool North Atlantic surface waters, their time distribution through the Pliocene-Pleistocene generally corresponds to alternated intervals of presence and absence. This should explain most of the apparently diachronous appearances and disappearances. Alternating presence-absence patterns are of less importance for the various nannofossil events. The LOD of D. surculus occurs during the transition of stage 100 to 101 in both ODP Hole 653A and the Singa section, which is in perfect agreement with the disappearance of this species from the open ocean. The LOD of D. pentaradiatus in the Mediterranean occurs in stages 100-99, which seems to be consistent with the extinction of this species in the southern Hemisphere. G. oceanica, which corresponds to the 4 µm < Gephyrocapsa spp <5.5 µm is recorded in stages 65 to 64 at ODP Hole 653A. The Gephyrocapsa spp. >5.5 µm first occurred in stage 51 at Hole 653A, which fits within the uncertainty interval for this event stretching from stage 51 to 47 in the open ocean and seems therefore a useful tool for conventional biostratigraphy in the Mediterranean.

Chlorofluorocarbons and noble gas measured on water bottle samples during three POLARSTERN cruises

We use a 27 year long time series of repeated transient tracer observations to investigate the evolution of the ventilation time scales and the related content of anthropogenic carbon (Cant) in deep and bottom water in the Weddell Sea. This time series consists of chlorofluorocarbon (CFC) observations from 1984 to 2008 together with first combined CFC and sulphur hexafluoride (SF6) measurements from 2010/2011 along the Prime Meridian in the Antarctic Ocean and across the Weddell Sea. Applying the Transit Time Distribution (TTD) method we find that all deep water masses in the Weddell Sea have been continually growing older and getting less ventilated during the last 27 years. The decline of the ventilation rate of Weddell Sea Bottom Water (WSBW) and Weddell Sea Deep Water (WSDW) along the Prime Meridian is in the order of 15-21%; the Warm Deep Water (WDW) ventilation rate declined much faster by 33%. About 88-94% of the age increase in WSBW near its source regions (1.8-2.4 years per year) is explained by the age increase of WDW (4.5 years per year). As a consequence of the aging, the Cant increase in the deep and bottom water formed in the Weddell Sea slowed down by 14-21% over the period of observations.

Distribution of macrozooplankton at time series station MIGZOO-1

Vertical distributions and diel migrations of the main species of micronekton, four euphausiids, one mysid, one decapod and three fishes, were described in detail in the 0-1000 m water column on a fixed station in the Northwestern Mediterranean Sea. The euphausiids Euphausia krohni and Thysanopoda aequalis, the decapod Gennadas elegans and, to a lesser extent, the fish Argyropelecus hemigymnus were shown to perform clear diel vertical migrations. Results of horizontal hauls at a given depth around sunrise and sunset showed a marked diurnal symmetry of the migratory cycles, particularly for E.krohni, T.aequalis and G.elegans. The behaviour of the euphausiid Nematoscelis megalops was more complex: it presented a repetitive bimodal day distribution and only part of its population migrated. As very weak or non-migrators we found the euphausiid Stylocheiron longicorne and the bathypelagic mysid Eucopia unguiculata, for which migration concerned only some of the older individuals. The fishes Cyclothone braueri and Cyclothone pygmaea appeared to be non-migrants. As depth increased, C.braueri was replaced by C.pygmaea, with maximum concentrations at 350-550 and 550-700 m depth, respectively.

Distribution of macrozooplankton at time series station MIGZOO-4

A large population of the colonial pelagic tunicate Pyrosoma atlanticum occurred in April 1991 in offshore waters of the Ligurian Sea (Northwestern Mediterranean). The high numbers of colonies caught allowed their vertical distribution and diel migration in the 0-965 m water column to be described as a function of their size. Daytime depths and amplitudes of the migration were correlated with colony size. The amplitude of the migration ranged from 90 m for 3-mm-length colonies to 760 m for 51-mm-length colonies, with a mean amplitude of 410 m for the whole population, all sizes pooled. The results of horizontal hauls at a given depth around sunrise and sunset showed a marked diurnal symmetry of the migratory cycle relative to noon, and that migration of the population was not cohesive. For example, the larger the colonies, the later after sunset they reached the upper layers during their upward migration.

Distribution and biomass of seston in the East Atlantic

Biomass of seston in the surface layers of coastal waters off Namibia reaches 1 g/m**2 and decreases with distance from the shore. Two regions of high seston biomass, one northern and one southern, are distinguished. A subsurface maximum of seston biomass, presumably coinciding with the stream of compensating countercurrent, is identified in the 200-500 m layer. Similar vertical distribution of plankton is known in upwelling areas of the eastern shores of the Atlantic and Pacific Oceans and in several other ocean areas, such as the area of the Kuril-Kamchatka Trench. This fact probably indicates that life cycles of pelagic animal forms of various taxonomic groups that inhabit them and phases of their ontogenic migrations are similar.