Holocene environmental changes disclosed from anoxic fjord sediments by biomarkers and their radiocarbon content

The power and validity of compound-specific radiocarbon dating was evaluated using sediments from Saanich Inlet, Canada, in age ranging from recent to 5000 yr BP. Compounds characteristic of higher plants, phytoplankton and archaea, were isolated by preparative GC and semi-preparative HPLC. For preparative HPLC a new method was designed, to be able to rapidly isolate relatively polar and high molecular weight biomarkers. After radiocarbon analysis, compound 14C ages were calibrated to produce calendar ages, for comparison with the sediment ages and the age of the total organic carbon (TOC). Phytoplanktonic and archaeal lipids showed on average age differences with the sediment of ~800 years, consistent with published DIC reservoir ages. Because the sediment ages were known, specific reservoir ages could be determined and compared with model reservoir ages. Planktonic biomarkers showed considerable variation, while crenarchaeol, from ubiquitously occurring marine archaea, showed minor variations in reservoir age. This indicates that compound specific 14C dating of crenarchaeol proves to be a promising new dating method for marine, carbonate-poor sediments, because it was relatively easy to isolate in sufficient amounts and consistent regarding reservoir effects. An increasing relative age of the terrestrial biomarker towards recent times pointed towards an ongoing aging of the soil in the fjord environs, due to the ongoing accumulation of the refractory soil organic carbon after deglaciation of the area. The results suggest that the terrigenous organic carbon pool in temperate regions may still be increasing as a long-term response to the end of the last ice-age. A 400 year sedimentary record of the anoxic Kyllaren Fjord (West Norway) was investigated using organic geochemical, geochemical and sedimentological approaches in order to reconstruct environmental changes. The results show that in the first half of the 19th century an environmental change occurred, likely caused by a change in the precipitation regime, vegetation and/or land use. In the last century a distinct increase in primary productivity is observed, likely caused by 'natural' eutrophication due to the transformation of the fjord from an open to a confined system by the building of a partially open dam in 1954, possibly combined with anthropogenic eutrophication. Decreased delta-13C values of several biomarkers point towards enhanced carbon recycling in the fjord over the last century. The results of a similar biogeochemical study on the South Norwegian Drammensfjord, covering the last millenium, show that eutrophication already started halfway the 19th century. This was concurrent with the industrialization of sawmills and papermills along the river Drammen and upstream water bodies, which could be traced by 'coniferous' biomarkers in the sediment. The concurrent disappearance of a suite of (bi)cyclobotryococcenes from the upper fjord sediments also revealed that eutrophication likely caused the demise and eventual disappearance of the alga Botryococcus braunii from the fjord. Because of the preference of this alga for oligotrophic and slightly brackish conditions, and the possibility to easily trace these specific biomarkers, it is argued that the disappearance of this alga from a sedimentary record can serve as an palaeoenvironmental indicator for early eutrophication

An interlaboratory study of TEX86 and BIT analysis of sediments, extracts and standard mixtures.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3-4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the "true" (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values

Chemotaxonomy in some Mediterranean plants and implications for fossil biomarker records

The increasing utilization of n-alkanes as plant-derived paleo-environmental proxies calls for improved chemotaxonomic control of the modern flora in order to calibrate fossil sediment records to modern analogues. Several recent studies have investigated long-chain n-alkane concentrations and chain-length distributions in species from various vegetation biomes, but up to date, the Mediterranean flora is relatively unexplored in this respect. Here, we analyse the n-alkane concentrations and chain-length distributions in some of the most common species of the modern macchia and phrygana vegetation in south western Peloponnese, Greece. We show that the drought adapted phrygana herbs and shrubs, as well as some of the sclerophyll and gymnosperm macchia components, produce high concentrations of n-alkanes, on average more than double n-alkane production in local wetland reed vegetation. Furthermore, the chain-length distribution in the analysed plants is related to plant functionality, with longer chain lengths associated with higher drought adaptive capacities, probably as a response to long-term evolutionary processes in a moisture limited environment. Furthermore, species with relatively higher average chain lengths (ACL) showed more enriched carbon isotope composition in their tissues (δ13Cplant), suggesting a dual imprint from both physiological and biochemical drought adaptation. The findings have bearings on interpretation of fossil sedimentary biomarker records in the Mediterranean region, which is discussed in relation to a case study from Agios Floros fen, Messenian plain, Peloponnese. The 6000 year long n-alkane record from Agios Floros (ACL, δ13Cwax) is linked to the modern analogue and then evaluated through a comparison with other regional-wide as well as local climate and vegetation proxy-data. The high concentration of long chain n-alkanes in phrygana vegetation suggests a dominating imprint from this vegetation type in sedimentary archives from this ecotone. © 2017 The Author(s

Rapid isolation of biomarkers for compound specific radiocarbon dating using high-performance liquid chromatography and flow injection analysis-atmospheric pressure chemical ionisation mass spectrometry

Repeated semi-preparative normal-phase HPLC was performed to isolate selected biomarkers from sediment extracts for radiocarbon analysis. Flow injection analysis mass spectrometry was used for rapid analysis of collected fractions to evaluate the separation procedure, taking only 1 min per fraction. In this way 100 1000 g of glycerol dialkyl glycerol tetraethers, sterol fractions and chlorophyll-derived phytol were isolated from typically 100 g of marine sediment, i.e., in sufficient quantities for radiocarbon analysis, without significant carbon isotopic fractionation or contamination

Ongoing buildup of refractory organic carbon in boreal soils during the Holocene

Radiocarbon ages of vascular plant wax–derived n-alkanes preserved in well-dated Holocene sediments in an anoxic fjord (Saanich Inlet, Canada) were found to be not only substantially older than the depositional age but increasingly so during the Holocene. Assuming that n-alkanes serve as a proxy for recalcitrant terrigenous organic matter, this indicates that the accumulation of refractory organic carbon in soils that developed after the deglaciation of the American Pacific Northwest is ongoing and may still be far from equilibrium with mineralization and erosion rates

A 400 year record of environmental change in an euxinic fjord as revealed by the sedimentary biomarker record

A 400-year sedimentary record of the euxinic Kyllaren Fjord was investigated using organic biogeochemical, geochemical and sedimentological approaches. Accumulation rates of a suite of biomarkers, and in some cases their stable carbon isotopic composition, were determined. Biomarkers were separated into three different groups: terrestrial derived, general aquatic/marine derived, and aquatic/marine derived but related to high primary productivity. Variations in bulk sediment parameters and biomarker accumulation rates with depth were used to interpret the sedimentary record. We infer that in the first half of the 19th century an environmental change occurred, caused by a change in either the precipitation regime, vegetation and/or land use. The data also show that in the last century, and especially in the last decades, a distinct increase in primary productivity occurred. Most likely this is caused by a natural eutrophication due to the transformation of the fjord from an open to a confined system by the building of a partially open dam in 1954, possibly combined with anthropogenic eutrophication. A concurrent shoaling of the fjord chemocline may have had a mediating effect in the change towards a higher productivity by enhancing nutrient and carbon recycling. Enhanced carbon recycling is reflected by decreased 13C values of several biomarkers

Evaluation of anhydrosugars as a molecular proxy for paleofire activity: A case study on a Holocene sediment core from Agios Floros, Peloponnese, Greece

The anhydrosugars, levoglucosan, mannosan and galactosan, are regarded as suitable molecular indicators of natural biomass combustion. Here, we evaluate summed anhydrosugars (SAS) as a paleofire indicator in a 6000 year-long fossil core from Agios Floros fen, Peloponnese, Greece, by analyzing charcoal fragments in parallel, throughout the sediment sequence. Modern surface soil samples from the same region were analysed for the presence of SAS, confirming the biomarker as an indicator of recent fire activity. The highest SAS concentrations in the fossil core were found in sections representing periods of wet conditions, both on local and regional scales and regionally widespread arboreal vegetation. Low amounts, or the absence, of SAS in the fossil core were associated with periods of dryness, regional dominance of non-arboreal vegetation and the presence of a fen rather than a lake ecosystem at the site. Micro-charcoal fragments were generally more abundant under these conditions. This suggests that SAS yield and deposition may vary with fuel availability and fire behavior, which in turn is affected by climate, local moisture and vegetation type. Forest fires result in more SAS compared to grass fires. SAS yield is also favored by low-temperature fires sustained under wet climate conditions. Preservation of SAS is likely to be compromised in the only seasonally wet fen ecosystem under the dry and warm Mediterranean climate conditions. The moist and shallow conditions in the wetland during hot summer months probably promote oxidation and biodegradation of the labile SAS molecules, compared to the more robust charcoal fragments. Thus, a multiproxy approach - using several proxies, both for fire, hydroclimate and vegetation change - is preferred when aiming to reconstruct past biomass burning from wetland ecosystems in a Mediterranean environment. The micro-charcoal record from Agios Floros reveals significant fire activity between 4400 and 2800 cal yr BP. This partly overlaps the Bronze Age period, associated with intense human environmental interaction and climate change in this area of Peloponnese, Greece. © 2021 The Author

Pre- and post-industrial environmental changes as revealed by the biogeochemical sedimentary record of Drammensfjord, Norway

The biogeochemical sedimentary record of the anoxic Drammensfjord, Norway, was investigated on a decadal to centennial time scale over the last millennium, in order to reconstruct the pre-industrial fjord environment and ecosystem and human-induced environmental changes. The sediments were dated by a combination of 14C and 210Pb analysis and varve counting. Analysis of the bulk sedimentary parameters and of the biomarker distribution revealed that the sedimentary organic matter of the fjord is primarily of terrigenous origin, indicating that the fjord was oligotrophic or mesotrophic. The fjord's bottom water has been continuously euxinic since at least 1000 AD, but photic zone euxinia occurred only irregularly in the fjord. The organic matter flux and composition remained virtually invariable until the 18th century. After that time, the flux of material derived from coniferous trees started to increase, indicated by elevated concentrations of dehydroabietic acid and related compounds, but also by raising levels of C24 n-alcohols and fatty acids. This marked the onset of sawmill activities in the hinterland. After the beginning of the industrial revolution, around 1850, the flux of organic waste from sawmills and paper mills increased substantially. It is suggested that slow bacterial degradation of this relatively nutrient-poor organic waste caused a gradual eutrophication trend, which is reflected in substantial increased bacterial and moderately increased other aquatic biomarker accumulation rates. After the industrial revolution, this trend accelerated and was possibly enhanced by a growing population of the area with accompanying agricultural and domestic waste. This promoted primary productivity and changed the phytoplankton composition in the fjord