Sedimentology, foraminiferal assemblage, and isotope record of the Agulhas Bank region

The Agulhas Bank region, south of Africa, is an oceanographically important and complex area. The leakage of warm saline Indian Ocean water into the South Atlantic around the southern tip of Africa is a crucial factor in the global thermohaline circulation. Foraminiferal assemblage, stable isotope and sedimentological data from the top 10 m of core MD962080, recovered from the western Agulhas Bank Slope, are used to indicate changes in water mass circulation in the southeastern South Atlantic for the last 450 kyr. Sedimentological and planktonic foraminiferal data give clear signals of cold water intrusions. The benthic stable isotope record provides the stratigraphic framework and indicates that the last four climatic cycles are represented (i.e. down to marine isotope stage (MIS) 12). The planktonic foraminiferal assemblages bear a clear transitional to subantarctic character with Globorotalia inflata and Neogloboquadrina pachyderma (dextral) being the dominant taxa. Input of cold, subantarctic waters into the region by means of leakage through the Subtropical Convergence, as part of Agulhas ring shedding, and a general cooling of surface waters is suggested by increased occurrence of the subantarctic assemblage during glacial periods. Variable input of Indian Ocean waters via the Agulhas Current is indicated by the presence of tropical/subtropical planktonic foraminiferal species Globoquadrina dutertrei, Globigerinoides ruber (alba) and Globorotalia menardii with maximum leakage occurring at glacial terminations. The continuous presence of G. menardii throughout the core suggests that the exchange of water from the South Indian Ocean to the South Atlantic Ocean was never entirely obstructed in the last 450 kyr. The benthic carbon isotope record and sediment textural data reflect a change in bottom water masses over the core location from North Atlantic Deep Water to Upper Southern Component Water. Planktonic foraminiferal assemblages and sediment composition indicate a profound change in surface water conditions over the core site approximately 200-250 kyr BP, during MIS 7, from mixed subantarctic and transitional water masses to overall warmer surface water conditions.

Planktic foraminiferal assemblage turnover at the Cretaceous-Tertiary boundary

Three uppermost Cretaceous through basal Paleocene stratigraphic sequences are examined for planktic foraminiferal assemblage stability and temporal succession patterns. These sequences are at mid-latitude South Atlantic DSDP Site 528, then-equatorial Pacific DSDP Site 577 and the Tethyan shelf Ben Gurion section of the Negev, Israel. In order to better estimate biogeographic patterns and habitat preferences, the results of these analyses are compared to previous Cretaceous biogeographic studies and to previous analyses of Cretaceous-Tertiary (K/T) boundary shelf and epicontinental sections. Results indicate that immediately following the K/T boundary, the examined epicontinental and open-ocean sites were exploited primarily by previously epicontinental planktic foraminiferal assemblages. This pattern of K/T boundary assemblage dominance suggests the geologically instantaneous break-down of Late Cretaceous epicontinental and open-ocean biogeographic provincialization. This shift in open-ocean foraminiferal assemblages is not consistent with models of nonselective K/T boundary extinctions, but is consistent with models of extinction resistence and offshore expansion of nearshore taxa. The re-establishment of stable biogeographic differences between open-ocean and epicontinental planktic foraminiferal assemblages occurs by the basal Parvularugoglobigerina eugubina Zone. At open-ocean sites 528 and 577 and the outershelf Ben Gurion section, P0 and P. eugubina Zone faunal records are marked by a pronounced alternation between Paleocene biserial- and non-biserial-dominated assemblages, This alternation appears strongly damped at shelf and epicontinental sections previously examined. The first appearance and peak magnitude of abundant earliest Paleocene trochospiral forms (Parvularugoglobigerina, Eoglobigerina, Morozovella, Globoconusa) also vary from site to site and may depend closely on levels of primary carbonate productivity.

Characteristics of introduced Aphididae species, an endemic fly (Anatalanta aptera) and an introduced ground beetle (Merizodus soledadinus) on the Kerguelen Islands

The suite of environments and anthropogenic modifications of sub-Antarctic islands provide key opportunities to improve our understanding of the potential consequences of climate change and biological species invasions on terrestrial ecosystems. The profound impact of human introduced invasive species on indigenous biota, and the facilitation of establishment as a result of changing thermal conditions, has been well documented on the French sub-Antarctic Kerguelen Islands (South Indian Ocean). The present study provides an overview of the vulnerability of sub-Antarctic terrestrial communities with respect to two interacting factors, namely climate change and alien insects. We present datasets assimilated by our teams on the Kerguelen Islands since 1974, coupled with a review of the literature, to evaluate the mechanism and impact of biological invasions in this region. First, we consider recent climatic trends of the Antarctic region, and its potential influence on the establishment, distribution and abundance of alien insects, using as examples one fly and one beetle species. Second, we consider to what extent limited gene pools may restrict alien species' colonisations. Finally, we consider the vulnerability of native communities to aliens using the examples of one beetle, one fly, and five aphid species taking into consideration their additional impact as plant virus vectors. We conclude that the evidence assimilated from the sub-Antarctic islands can be applied to more complex temperate continental systems as well as further developing international guidelines to minimise the impact of alien species.

Rarefied allelic richness of the ground beetle Abax parallelepipedus in Germany

Although genetic diversity is one of the key components of biodiversity, its drivers are still not fully understood. While it is known that genetic diversity is affected both by environmental parameters as well as habitat history, these factors are not often tested together. Therefore, we analyzed 14 microsatellite loci in Abax parallelepipedus, a flightless, forest dwelling ground beetle, from 88 plots in two study regions in Germany. We modeled the effects of historical and environmental variables on allelic richness, and found for one of the regions, the Schorfheide-Chorin, a significant effect of the depth of the litter layer, which is a main component of habitat quality, and of the sampling effort, which serves as an inverse proxy for local population size. For the other region, the Schwäbische Alb, none of the potential drivers showed a significant effect on allelic richness. We conclude that the genetic diversity in our study species is being driven by current local population sizes via environmental variables and not by historical processes in the studied regions. This is also supported by lack of genetic differentiation between local populations sampled from ancient and from recent woodlands. We suggest that the potential effects of former fragmentation and recolonization processes have been mitigated by the large and stable local populations of Abax parallelepipedus in combination with the proximity of the ancient and recent woodlands in the studied landscapes.

Benthic foraminiferal assemblage changes during interstadial 4 to 8 in ODP Site 146-893A, Santa Barbara Basin

Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40-400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth's ocean-atmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change.

Siliceous microfossil assemblage and accumulation rate variations across the Middle Eocene Climatic Optimum at ODP Site 171-1051

The Middle Eocene Climatic Optimum (MECO; ~ 40 million years ago [Ma]) is one of the most prominent transient global warming events in the Paleogene. Although the event is well documented in geochemical and isotopic proxy records at many locations, the marine biotic response to the MECO remains poorly constrained. We present new high-resolution, quantitative records of siliceous microplankton assemblages from the MECO interval of Ocean Drilling Program (ODP) Site 1051 in the subtropical western North Atlantic Ocean, which are interpreted in the context of published foraminiferal and bulk carbonate stable isotope (d18O and d13C) records. High diatom, radiolarian and silicoflagellate accumulation rates between 40.5 and 40.0 Ma are interpreted to reflect an ~ 500 thousand year (kyr) interval of increased nutrient supply and resultant surface-water eutrophication that was associated with elevated sea-surface temperatures during the prolonged onset of the MECO. Relatively low pelagic siliceous phytoplankton sedimentation accompanied the peak MECO warming interval and the termination of the MECO during an ~ 70 kyr interval centered at ~ 40.0 Ma. Following the termination of the MECO, an ~ 200-kyr episode of increased siliceous plankton abundance indicates enhanced nutrient levels between ~ 39.9 and 39.7 Ma. Throughout the Site 1051 record, abundance and accumulation rate fluctuations in neritic diatom taxa are similar to the trends observed in pelagic taxa, implying either similar controls on diatom production in the neritic and pelagic zones of the western North Atlantic or fluctuations in sea level and/or shelf accommodation on the North American continental margin to the west of Site 1051. These results, combined with published records based on multiple proxies, indicate a geographically diverse pattern of surface ocean primary production changes across the MECO. Notably, however, increased biosiliceous accumulation is recorded at both ODP Sites 1051 and 748 (Southern Ocean) in response to MECO warming. This may suggest that increased biosiliceous sediment accumulation, if indeed a widespread phenomenon, resulted from higher continental silicate weathering rates and an increase in silicic acid supply to the oceans over several 100 kyr during the MECO.