Papers by Francesca Sangiorgi
2014 AGU Fall Meeting, Dec 18, 2014
Pages (Bern), Jun 1, 2009
Palynological analyses performed on long sedimentary records from the crest of the Lomonosov Ridg... more Palynological analyses performed on long sedimentary records from the crest of the Lomonosov Ridge (Arctic Ocean) indicates that the Arctic developed from a warmer-than-expected, semi-isolated, shallow, freshwater dominated, eutrophic basin during the early Paleogene, to a sea-ice and iceberg dominated ocean during most of the Neogene. During the Eocene, the environmental changes were orbitally paced, with a biological response strongly affected by obliquity.
The TEX86H paleothermometer based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) ... more The TEX86H paleothermometer based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) has widely been applied in various marine settings to reconstruct past sea surface temperatures (SSTs). However, it still remains uncertain how well this proxy reconstructs annual mean SSTs. Here, we assess environmental factors governing the TEX86H paleothermometer in the Mediterranean Sea, by studying the distribution of isoGDGTs in surface sediments, suspended particulate matter (SPM), and two sediment cores. A redundancy analysis using the fractional abundance of the six major isoGDGTs indicates that the sedimentary isoGDGTs are mostly influenced by three environmental factors explaining a large part (74%) of the variance in isoGDGT distribution. In order of decreasing significance, these factors are annual mean SST, continental organic matter input as indicated by the BIT index, and water depth. However, when considering only the four isoGDGTs that are used for the TEX86H proxy, water depth is the most significant parameter, explaining 63% of the variance. Indeed, a strong positive relationship between water depth and TEX86H is observed in both surface sediments and SPM from the Mediterranean Sea. This is driven by an increase in fractional abundances of GDGT-2 and crenarchaeol regio-isomer and a decrease in the fractional abundances of GDGT-1 and GDGT-3 with increasing water depth, leading to a bias to higher temperatures of TEX86H in deep-water surface sediments. The fact that the water-depth trend is also apparent in SPM suggests that this change might be due to a change in thaumarchaeotal community thriving below surface mixed-layer waters and that this signal is, at least partly, incorporated into sedimentary isoGDGTs. Interestingly, surface-sediment TEX86H values from >1000 m water depth do not show a correlation with water depth anymore and instead are correlated to annual mean SSTs. A composite deep-water TEX86H dataset of surface sediments from both the Mediterranean Sea and the Red Sea, interconnecte [...]
Organic Geochemistry, Apr 1, 2021
Abstract The fractional abundance of branched glycerol dialkyl glycerol tetraether (brGDGT) membr... more Abstract The fractional abundance of branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids in coastal marine sediments has been posited as a proxy for the reconstruction of terrestrial temperatures on the nearby land, based on the assumption that they are produced in soils and delivered to the marine realm by rivers following erosion. Here, we test the suitability of brGDGTs as a continental paleothermometer in Pliocene age sediments from the northern Gulf of Mexico (GoM; speculated Mississippi River input) and the Ceara Rise (speculated Amazon River input). Low branched to isoprenoid tetraether (BIT) index values of 0.00–0.13 and the near absence of pollen and long-chain plant waxes in the GoM sediments suggest that the Mississippi River did not have a strong influence on the delivery of terrestrial organic matter to the site during the Pliocene and soil input was limited. Indeed, the high weighted average of cyclopentane-containing tetramethylated brGDGTs (#ringstetra) in the GoM sediments (0.50 ± 0.09) relative to that of modern soils from the Mississippi catchment (0.25 ± 0.16) indicates that the brGDGTs in the GoM sediments were mostly produced in situ in the marine realm, hampering reliable land temperature reconstruction using the global soil transfer function. In contrast, high BIT index values (0.46 ± 0.21) and low #ringstetra (0.25 ± 0.15) in sediments from the Ceara Rise suggest that these brGDGTs are primarily derived from soils. However, reconstructed temperatures were 11–18 °C lower than modern Amazon catchment temperatures. The relative abundance of 6-methylated brGDGTs (Isomerisation Ratio; IR) in the sediments is 0.82 ± 0.10, which resembles that of suspended particulate matter (SPM) in the modern Amazon River more than that of catchment soils (IR = 0.18 ± 0.18). This reveals that brGDGTs in the Ceara Rise sediments likely have a freshwater, riverine origin. Thus, the majority of the brGDGTs in both the GoM and Ceara Rise sediments are produced in situ, in the marine or river realms, which precludes application of the brGDGT paleothermometer. Our study shows that the sources of brGDGTs in coastal marine sediment archives must be critically evaluated prior to using the proxy for paleoclimate reconstruction.
Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2002
A high-resolution study of sea surface temperature (SST) and primary productivity changes during ... more A high-resolution study of sea surface temperature (SST) and primary productivity changes during the last deglaciation in the South Adriatic Sea is presented on the basis of organic-walled dinoflagellate cysts (dinocysts), compared with stable oxygen and carbon isotope records derived from Globigerina bulloides. Two more defined warming phases between 14.75 and 14.10 cal kyr BP (GI-1e) and between 13.85 and 13.25 cal kyr BP (GI-1c), and perhaps a mild one between 12.95 and 12.60 cal kyr BP (GI-1a), interrupted by two cold ...
The upper 200 m of the sediments recovered during IODP Leg 302, the Arctic Coring Expedition (ACE... more The upper 200 m of the sediments recovered during IODP Leg 302, the Arctic Coring Expedition (ACEX), to the Lomonosov Ridge in the central Arctic Ocean consist almost exclusively of detrital material. The scarcity of biostratigraphic markers severely complicates the establishment of a reliable chronostratigraphic framework for these sediments, which contain the first continuous record of the Neogene environmental and climatic evolution of the Arctic region. Here we present profiles of cosmogenic 10Be together with the seawater-derived fraction of stable 9Be obtained from the ACEX cores. The down-core decrease of 10Be/9Be provides an average sedimentation rate of 14.5 ± 1 m/Ma for the uppermost 151 m of the ACEX record and allows the establishment of a chronostratigraphy for the past 12.3 Ma. The age-corrected 10Be concentrations and 10Be/9Be ratios suggest the existence of an essentially continuous sea ice cover over the past 12.3 Ma.
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Papers by Francesca Sangiorgi