Sedimentary environments and climate change: a case study (late Miocene, central Crete)

In this study, conditions of deposition and stratigraphical architecture of Neogene (Tortonian, 11-6,7Ma) sediments of southern central Crete were analysed. In order to improve resolution of paleoclimatic data, new methods were applied to quantify environmental parameters and to increase the chronostratigraphic resolution in shallow water sediments. A relationship between paleoenvironmental change observed on Crete and global processes was established and a depositional model was developed. Based on a detailed analysis of the distribution of non geniculate coralline red algae, index values for water temperature and water depth were established and tested with the distribution patterns of benthic foraminifera and symbiont-bearing corals. Calcite shelled bivalves were sampled from the Algarve coast (southern Portugal) and central Crete and then 87Sr/86Sr was measured. A high resolution chronostratigraphy was developed based on the correlation between fluctuations in Sr ratios in the measured sections and in a late Miocene global seawater Sr isotope reference curve. Applying this method, a time frame was established to compare paleoenvironmental data from southern central Crete with global information on climate change reflected in oxygen isotope data. The comparison between paleotemperature data based on red algae and global oxygen isotope data showed that the employed index values reflect global change in temperature. Data indicate a warm interval during earliest Tortonian, a second short warm interval between 10 and 9,5Ma, a longer climatic optimum between 9 and 8Ma and an interval of increasing temperatures in the latest Tortonian. The distribution of coral reefs and carpets shows that during the warm intervals, the depositional environment became tropical while temperate climates prevailed during the cold interval. Since relative tectonic movements after initial half-graben formation in the early Tortonian were low in southern central Crete, sedimentary successions strongly respond to global sea-level fluctuation. A characteristic sedimentary succession formed during a 3rd order sea-level cycle: It comprises mixed siliciclastic-limestone deposited during sea-level fall and lowstand, homogenous red algal deposits formed during sea-level rise and coral carpets formed during late rise and highstand. Individual beds in the succession reflect glacioeustatic fluctuations that are most prominent in the mixed siliciclastic-limestone interval. These results confirm the fact that sedimentary successions deposited at the critical threshold between temperate and tropical environments develop characteristic changes in depositional systems and biotic associations that can be used to assemble paleoclimatic datasets.

Marine biodiversity survey in the Northern Red Sea: a large-scale monitoring carried out in collaboration with volunteer divers

Concerns over global change and its effect on coral reef survivorship have highlighted the need for long-term datasets and proxy records, to interpret environmental trends and inform policymakers. Citizen science programs have showed to be a valid method for collecting data, reducing financial and time costs for institutions. This study is based on the elaboration of data collected by recreational divers and its main purpose is to evaluate changes in the state of coral reef biodiversity in the Red Sea over a long term period and validate the volunteer-based monitoring method. Volunteers recreational divers completed a questionnaire after each dive, recording the presence of 72 animal taxa and negative reef conditions. Comparisons were made between records from volunteers and independent records from a marine biologist who performed the same dive at the same time. A total of 500 volunteers were tested in 78 validation trials. Relative values of accuracy, reliability and similarity seem to be comparable to those performed by volunteer divers on precise transects in other projects, or in community-based terrestrial monitoring. 9301 recreational divers participated in the monitoring program, completing 23,059 survey questionnaires in a 5-year period. The volunteer-sightings-based index showed significant differences between the geographical areas. The area of Hurghada is distinguished by a medium-low biodiversity index, heavily damaged by a not controlled anthropic exploitation. Coral reefs along the Ras Mohammed National Park at Sharm el Sheikh, conversely showed high biodiversity index. The detected pattern seems to be correlated with the conservation measures adopted. In our experience and that of other research institutes, citizen science can integrate conventional methods and significantly reduce costs and time. Involving recreational divers we were able to build a large data set, covering a wide geographic area. The main limitation remains the difficulty of obtaining an homogeneous spatial sampling distribution.

Biotic and Abiotic Properties Mediating Plant Diversity Effects on Soil Microbial Communities in an Experimental Grassland

Plant diversity drives changes in the soil microbial community which may result in alterations in ecosystem functions. However, the governing factors between the composition of soil microbial communities and plant diversity are not well understood. We investigated the impact of plant diversity (plant species richness and functional group richness) and plant functional group identity on soil microbial biomass and soil microbial community structure in experimental grassland ecosystems. Total microbial biomass and community structure were determined by phospholipid fatty acid (PLFA) analysis. The diversity gradient covered 1, 2, 4, 8, 16 and 60 plant species and 1, 2, 3 and 4 plant functional groups (grasses, legumes, small herbs and tall herbs). In May 2007, soil samples were taken from experimental plots and from nearby fields and meadows. Beside soil texture, plant species richness was the main driver of soil microbial biomass. Structural equation modeling revealed that the positive plant diversity effect was mainly mediated by higher leaf area index resulting in higher soil moisture in the top soil layer. The fungal-to-bacterial biomass ratio was positively affected by plant functional group richness and negatively by the presence of legumes. Bacteria were more closely related to abiotic differences caused by plant diversity, while fungi were more affected by plant-derived organic matter inputs. We found diverse plant communities promoted faster transition of soil microbial communities typical for arable land towards grassland communities. Although some mechanisms underlying the plant diversity effect on soil microorganisms could be identified, future studies have to determine plant traits shaping soil microbial community structure. We suspect differences in root traits among different plant communities, such as root turnover rates and chemical composition of root exudates, to structure soil microbial communities.

n-Alkane analyses from an transect of marine surface sediments off southwest Africa

An isobathic transect of marine surface sediments from 1°N to 28°S off southwest Africa was used to further evaluate the potential of the chain length distribution and carbon stable isotope composition of higher plant n-alkanes as proxies for continental vegetation and climate conditions. We found a strong increase in the n-C29-33 weighted mean average d13C values from -33 per mil near the equator to around -26 per mil further south. Additionally, C25-35n-alkanes reveal a southward trend of increasing average chain length from 30.0 to 30.5. The data reflect the changing contribution of plants employing different photosynthetic pathways (C3 and C4) and/or being differently influenced by the environmental conditions of their habitat. The C4 plant proportions calculated from the data (ca. 20% for rivers draining the rainforest, to ca. 70% at higher latitude) correspond to the C4 plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows. Furthermore, the C4 plant contribution to the sediments correlates with the mean annual precipitation and aridity at selected continental locations in the postulated catchment areas, suggesting that the C4 plant fraction in marine sediments can be used to assess these environmental parameters.

Chemobiostratigraphy of the Cretaceous/Paleocene boundary at ODP Hole 120-750A

An integrated biostratigraphic and stable isotope investigation was conducted on a high-latitude sequence across the Cretaceous/Paleogene (K/P) boundary recovered in Hole 750A in the southern Indian Ocean. The sequence consists of nannofossil chalk and is discontinuous across the boundary; missing is an estimated 0.3-m.y. late Maestrichtian and early Danian interval. Nonetheless, because calcareous nannofossil Zones NP1 and NP2 are well-developed, micropaleontological studies of the sequence have yielded a detailed record of Danian high-latitude microplankton evolution. In addition, stable carbon isotope analyses of planktonic and benthic foraminifer and bulk samples provide a record of late Maestrichtian and early Danian surface- and deep-water carbon isotope variations. Together, the carbon isotope and carbonate accumulation records serve as an index of regional marine net productivity across the boundary. Earliest Danian nannoplankton assemblages consisted mainly of persistent genera that were generally rare or absent in the Upper Cretaceous at Hole 750A. However, by 0.5-0.6 m.y. after the boundary, newly evolving Danian taxa became dominant. The turnover in nannofossil assemblages was accompanied by significant changes in rates of net productivity as gauged by carbon isotope distributions and carbonate accumulation rates. During the period dominated by persistent taxa, net productivity was extremely low, as reflected by the absence of vertical delta13C gradients and reduced carbonate accumulation rates. Later in the Danian, as new species evolved and flourished, vertical delta13C gradients reappeared and carbonate accumulation rates increased, signaling partial recovery of net productivity in this region. The absolute timing and magnitude of late Maestrichtian and early Danian biotic and geochemical changes in the southern Indian Ocean were similar to those recorded in other pelagic K/P boundary sequences from low- and mid-latitude Atlantic and Pacific sites, indicating that these events were ubiquitous.

(Figure 2) Organic carbon content, stable isotope ratios, TEX86 index and sea surface temperature reconstruction for the early Aptian of ODP Hole 198-1207B

The Cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric CO2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events (OAEs). Yet, the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained. Here we present a high-resolution record of sea-surface temperatures (SSTs) reconstructed using the TEX86 paleothermometer for a sequence of early Aptian organic-rich sediments deposited during the first Cretaceous OAE (OAE1a) at Shatsky Rise in the tropical Pacific. SSTs range from ~30 to ~36 °C and include two prominent cooling episodes of ~4 °C. The cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter. SST instability recorded during the early Aptian in the Pacific is comparable to that reported for the late Albian-early Cenomanian in the Atlantic, suggesting that such climate perturbations may have recurred during the Cretaceous with concomitant consequences for biota and the marine environment.

Quantitative coccolithophore analyses in sediment core MD01-2446

Quantitative coccolithophore analyses were performed in core MD01-2446, located in the mid-latitude North Atlantic, to reconstruct climatically induced sea-surface water conditions throughout Marine Isotope Stages (MIS) 14-9. The data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby North Atlantic records that support the coccolithophore signature at glacial-interglacial to millennial climate scale. Total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations. Coccolithophore warm-water taxa (wwt) indicate that MIS11c and MIS9e experienced warmer and more stable conditions throughout the whole photic zone compared to MIS13. MIS11 was a long-lasting warmer and stable interglacial characterized by a climate optimum during MIS11c when a more prominent influence of the subtropical front at the site is inferred. The wwt pattern also suggests distinct interstadial and stadial events lasting about 4-10 kyr. The glacial increases of Gephyrocapsa margereli-G. muellerae 3-4 µm along with higher values of Corg, additionally supported by the total alkenone abundance at Site U1313, indicate more productive surface waters, likely reflecting the migration of the polar front into the mid-latitude North Atlantic. Distinctive peaks of G. margereli-muellerae (> 4 µm), C. pelagicus pelagicus, Neogloboquadrina pachyderma left coiling, and reworked nannofossils, combined with minima in total nannofossil accumulation rate, are tracers of Heinrich-type events during MIS12 and MIS10. Additional Heinrich-type events are suggested during MIS12 and MIS14 based on biotic proxies, and we discuss possible iceberg sources at these times. Our results improve the understanding of mid-Brunhes paleoclimate and the impact on phytoplankton diversity in the mid-latitude North Atlantic region.

Evaluation of long chain 1,14-alkyl diols in marine sediments as indicators for upwelling and temperature

Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but also revealed uncertainties about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors like sea surface temperature (SST), salinity and nutrient concentrations. Previous cultivation efforts indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified in the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices in surface sediments show no relationship with annual mean SST of the overlying water. It remains unknown what determines the DSI, although our data suggests that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions of algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15-diols have previously been applied as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28 + C30 1,14-diols]/[(C28 + C30 1,13-diols) + (C28 + C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.

Characteristics, pyrolysis, age, lithology, sedimentation rate, organic matter, and thermal alteration index at DSDP Leg 67 Holes

Marine-derived amorphous organic matter dominates hemipelagic and trench sediments in and around the Middle America Trench. These sediments contain, on the average, 1% to 2% total organic carbon (TOC), with a maximum of 4.8%. Their organic facies and richness reflect (1) the small land area of Guatemala, which contributes small amounts of higher land plant remains, and (2) high levels of marine productivity and regionally low levels of dissolved oxygen, which encourage deposition and preservation of marine organic remains. These sediments have good potential for oil but are now immature. For this reason, gaseous hydrocarbons like the ethane identified in the deep parts of the section, as at Sites 496 and 497, are probably migrating from a mature section at depth. The pelagic sediments of the downgoing Cocos Plate are lean in organic carbon and have no petroleum potential

Marine and terrigenous lipids in ODP Leg 175 holes

Lipid compositions of sediments recovered during Ocean Drilling Program Leg 175 in the eastern South Atlantic reflect a variety of oceanographic and climatological environments. Most of the identified lipids can be ascribed to marine sources, notably haptophytes, eustigmatophytes, dinoflagellates, archaea, and diatoms. Elevated concentrations of cholesterol suggest zooplankton herbivory, characteristic for sites influenced by upwelling. At these sites, sulfurized highly branched isoprenoids from diatoms are also present in high amounts. Sterols, sterol ethers, hopanoids, and midchain hydroxy fatty acids could also be detected. Terrigenous lipids are n-alkanes, fatty acids, n-alcohols, and triterpenoid compounds like taraxerol and -amyrine. n-Alkanes, fatty acids, and n-alcohols are derived from leaf waxes of higher land plants and transported to the sea by airborne dust or fresh water. Triterpenoid compounds are most probably derived from mangroves and transported solely by rivers. Lipid compositions below the Congo low-salinity plume are strongly influenced by terrigenous material from the Congo River. Elevated organic carbon contents and predominantly marine lipid distributions at the Angola margin may indicate a highly productive plankton population, probably sustained by the Angola Dome. Sedimentary lipids in the Walvis Basin contain an upwelling signal, likely transported by the Benguela Current. Sedimentary lipids off Lüderitz Bay and in the southern Cape Basin are dominated by plankton lipids in high to intermediate amounts, reflecting persistent and seasonal upwelling, respectively.

Occurrence and Range-through database of functional diversity of marine ecosystems after the Late Permian mass extinction event

The Late Permian mass extinction event about 252 million years ago was the most severe biotic crisis of the past 500 million years and occurred during an episode of global warming. The loss of around two-thirds of marine genera is thought to have had substantial ecological effects, but the overall impacts on the functioning of marine ecosystems and the pattern of marine recovery are uncertain. Here we analyse the fossil occurrences of all known benthic marine invertebrate genera from the Permian and Triassic periods, and assign each to a functional group based on their inferred lifestyle. We show that despite the selective extinction of 62-74% of these genera, all but one functional group persisted through the crisis, indicating that there was no significant loss of functional diversity at the global scale. In addition, only one new mode of life originated in the extinction aftermath. We suggest that Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed. Functional diversity was, however, reduced in particular regions and habitats, such as tropical reefs; at these smaller scales, recovery varied spatially and temporally, probably driven by migration of surviving groups. We find that marine ecosystems did not return to their pre-extinction state, and by the Middle Triassic greater functional evenness is recorded, resulting from the radiation of previously subordinate groups such as motile, epifaunal grazers.