Sedimentary DNA and Molecular Evidence for Early Human Occupation of the Faroe Islands

The Faroe Islands, a North Atlantic archipelago between Norway and Iceland, were settled by Viking explorers in the mid-9th century CE. However, several indirect lines of evidence suggest earlier occupation of the Faroes by people from the British Isles. Here, we present sedimentary ancient DNA and molecular fecal biomarker evidence from a lake sediment core proximal to a prominent archaeological site in the Faroe Islands to establish the earliest date for the arrival of people in the watershed. Our results reveal an increase in fecal biomarker concentrations and the first appearance of sheep DNA at 500 CE (95% confidence interval 370-610 CE), pre-dating Norse settlements by 300 years. Sedimentary plant DNA indicates an increase in grasses and the disappearance of woody plants, likely due to livestock grazing. This provides unequivocal evidence for human arrival and livestock disturbance in the Faroe Islands centuries before Viking settlement in the 9th century

Sedimentary DNA and molecular evidence for early human occupation of the Faroe Islands

The Faroe Islands, a North Atlantic archipelago between Norway and Iceland, were settled by Viking explorers in the mid-9th century CE. However, several indirect lines of evidence suggest earlier occupation of the Faroes by people from the British Isles. Here, we present sedimentary ancient DNA and molecular fecal biomarker evidence from a lake sediment core proximal to a prominent archaeological site in the Faroe Islands to establish the earliest date for the arrival of people in the watershed. Our results reveal an increase in fecal biomarker concentrations and the first appearance of sheep DNA at 500 CE (95% confidence interval 370-610 CE), pre-dating Norse settlements by 300 years. Sedimentary plant DNA indicates an increase in grasses and the disappearance of woody plants, likely due to livestock grazing. This provides unequivocal evidence for human arrival and livestock disturbance in the Faroe Islands centuries before Viking settlement in the 9th century

Climate and Human History of the North Atlantic: Perspectives from Lipid Biomarkers in Lake Sediments

As our global community grapples with the ongoing challenges of climate change mitigation and adaptation, records of past climate changes provide important benchmarks for climate models and insights into the interactions between climate changes, human societies, and the landscape. In this dissertation, I reconstruct past changes in climate and redefine the human settlement history of the North Atlantic region. Understanding the human and climate history of the North Atlantic is particularly important because the region is especially sensitive to changes in climate, and climate and oceanographic changes in the region have global ramifications. I focus on the Faroe Islands and Iceland. These islands are close to oceanographic and atmospheric fronts and are sensitive to small changes in the climate system. Furthermore, the Faroes and Iceland were not settled by humans until the the first millennium CE, and as such, provide climate records that are unaltered by human land use activities for most of the Holocene, and are important test cases for understanding human-climate-landscape interactions after human settlement. In this work, I use lake sediment cores to reconstruct continuous climate records for the Holocene period, and in some cases, snapshots of previous interglacials. Lipid biomarkers are a group of molecules that accumulate in lake sediment and can be traced back to organisms in the lake or its watershed. I use these molecules and their isotopic compositions to quantify past changes in temperature and precipitation isotopes, which provide constraints on past climate and atmospheric circulation. I use fecal biomarkers, which are produced by the gut bacteria of humans and livestock, to determine when humans first settled in a lake’s watershed, and the impact they had on the environment. Ancient DNA stored in lake sediment can also be used to trace past changes in vegetation and to determine if livestock were present in the watershed, enhancing our understanding of agricultural impacts on the landscape. By combining these molecular tools, in Chapter 2, I reconstruct the Holocene and Last Interglacial climate in the Faroe Islands using the hydrogen and carbon isotopes of leaf waxes. In this case, I found that the Faroe Islands slowly transitioned over the Holocene from a climate that was warmer and wetter than present conditions, to a climate that is cooler and drier. In the Faroes, the Last Interglacial climate was similar to the early Holocene. In Chapter 3, I use fecal biomarkers and sedimentary ancient DNA to determine that humans arrived 300 years prior than previously thought. Human settlement caused erosion in the catchment and a shift in the vegetation community. In Chapter 4, I use the hydrogen isotopic composition of leaf waxes in conjunction with a biomarker-based temperature reconstruction from a lake in Iceland to determine past shifts in regional atmospheric circulation. I found that a shift towards more northerly-sourced precipitation, consistent with conditions similar to a positive NAO, occurred at the same time as regional neoglaciation and expansion of sea ice. All together, these records advance our understanding of Holocene and Last Interglacial climate change, the human settlement histor

Geochemistry of Auckland Island Lake Sediments: Assessing Recent Sub-Antarctic Climate Change

The Southern Hemisphere Westerly Winds (SHWW) are one of the primary controllers of air-ocean CO2 flux in the Southern Ocean. As the winds shift poleward and intensify with an increasingly positive Southern Annular Mode (SAM), upwelling of CO2-rich deep ocean water is enhanced, and the ocean's role in reducing the rate at which anthropogenic CO2 accumulates in the atmosphere is diminished. Furthermore, the strength and latitudinal position of the SHWW control storm tracks in the Southern Hemisphere and directly influence precipitation patterns in the South Island of New Zealand and throughout the Southern Hemisphere mid-latitudes. Despite their global significance, past variability of the SHWW is poorly understood. There are few terrestrial paleoclimate records of past SHWW variability, particularly at Sub-Antarctic latitudes where landmasses are scarce and the modern westerly maximum is located. Lake sediment cores from the Auckland Islands (50 deg S) provide an opportunity to study Holocene SHWW variability in this crucial gap. A high-resolution record of environmental change on the Auckland Islands over the last 550 years has been compiled from short sediment cores from three lakes using multiple physical and geochemical methods. The sediments collected are diatom- and plant macrofossil-rich and contain no carbonate. Down-core variations in the bulk sediment C/N ratio, magnetic susceptibility, and n-alkane distributions show an increase in terrestrial components of the sediment at about 300 years BP, while an overall decrease in the biogenic silica component of the sediment reveals a decline in lake productivity. These changes are indicative of an increase in precipitation causing additional influx of terrestrial material from the watershed and increased wind-driven mixing of the lake water column during a period of stronger westerly flow. Observed changes are broadly correlated with shifts in the SAM index as reconstructed by Abram et al. (2014). The dD of the C29 n-alkanes in modern lake sediment obtained from core tops appears to reflect local mean annual precipitation dD, and can potentially be applied as a proxy for the isotopic composition of precipitation, which likely reflects middle to high latitude temperature change and changes in the precipitation source region. When this record is compared to records from the South Island of New Zealand, wind strength appears to have an anti-phase relationship to that inferred in other studies, suggesting that the changes at the Auckland Islands may be due, in part, to latitudinal shifts in the westerly maximum, and not just changes in strength. Longer sediment cores from lakes on the Auckland Islands have the potential to produce high-resolution and continuous records of wind strength and temperature change throughout the Holocene, which will provide a useful comparison to records from the South Island and across the Southern Hemisphere for constructing new regional perspectives of Holocene shifts in the SHWW

Quantification of Low Molecular Weight N-Alkanes in Lake Sediment Cores for Paleoclimate Studies.

Organic biomarkers, such as n-alkanes, can be used as proxies in a range of paleoclimate and paleoenvironmental investigations. n-Alkanes accumulate in lacustrine sediments and can therefore be used to determine past terrestrial conditions by investigating chain length ratios and compound specific isotope signatures. Analytical methods for their quantification in sediments have been described previously; however, method validation has not been rigorously reported for the low molecular weight (LMW) n-alkanes, which have recently been gaining attention as useful proxies. Using spike and recovery experiments with a simple sand matrix, we found that LMW n-alkanes are prone to low recovery due to volatilization when following common protocols for quantification. This is alarming because low recovery can lead to misinterpretation of n-alkane results. On the other hand, we found that isotope fractionation was fortunately not observed even when volatilization loss was high. We addressed the problem of LMW n-alkane volatilization by developing an alternative extraction and sample preparation method. The optimized method, which employs pressurized liquid extraction, was tested by using it to extract n-alkanes from sediments from three Southern New Zealand lakes (Hinemoa, Ohau and Thomas) with different properties. Recovery of the C15-C40n-alkanes ranged from 32–66% for Lake Hinemoa, 54–85% for Lake Thomas and 61–89% for Lake Ohau. Variation in n-alkane recovery from the three lakes was attributed to differences in sediment properties, notably organic matter and particle size, and an approach for calculating ‘adjusted concentration’ with a sediment-specific adjustment factor for each n-alkane is suggested

Holocene and Last Interglacial climate of the Faroe Islands from sedimentary plant wax hydrogen and carbon isotopes

The Last Interglacial period (LIG) is Earth\u27s most recent globally warm period and is analogous in some ways to projected future global warming. However, questions remain regarding the state of the climate during the LIG in the North Atlantic, a region that is extremely sensitive to changes in oceanic and atmospheric circulation. Here, we present hydrogen and carbon isotope (δD and δ13C) records from a suite of plant wax biomarkers preserved in Holocene and LIG lacustrine sediments from the North Atlantic Faroe Islands and interpret them as qualitative proxies for temperature and hydroclimate variability. These data are used to directly compare LIG and Holocene climate using the same proxy approaches from the same terrestrial location. Measuring multiple isotopes on multiple types of waxes elucidates the sources of homologous plant waxes. We deduce that the δD values of long-chain n-alkanes (C27–C33) and mid-chain n-alkanes (C23–C25) in these sedimentary archives reflect leaf water and lake water δD values, respectively, while the δD values for both long-chain (C28–C30) and mid-chain n-alkanoic acids (C24–C26) primarily represent lake water δD values. Plant wax-inferred δD values of precipitation during the early Holocene (10,100 to 8,200 cal yr BP) are ∼35‰ more positive than late Holocene values, and decline over the Holocene. δD-inferred hydrologic change and δ13C -inferred plant water use efficiency both indicate that the Faroe Islands became drier throughout the Holocene. Comparison with measurements from LIG plant waxes indicates that late LIG in the Faroe Islands was hydrologically similar to the early-to mid-Holocene (8,200 to 4,000 cal yr BP), with enriched precipitation isotopes and reduced evapotranspiration indicating a warmer, wetter environment

Northern Norway paleofire records reveal two distinct phases of early human impacts on fire activity

Paleofire records document fire’s response to climate, ecosystem changes, and human-activity, offering insights into climate-fire-human relationships and the potential response of fire to anthropogenic climate change. We present three new lake sediment PAH records and a charcoal record from the Lofoten Islands, Norway to evaluate the Holocene fire history of northern Norway and examine human impacts on fire in this region. All three datasets show an increase in PAH accumulation rate over the past c. 7500 cal years BP, with an increase c. 5000 cal years BP that signals initial human impacts on fire activity. More significant increases c. 3500 cal years BP reach a maximum c. 2000 cal years BP that correlates with the establishment and expansion of agricultural settlements in Lofoten during the Late Bronze Age and Pre-Roman Iron Age. Decreased PAH accumulation rates c. 1500–900 cal years BP reflect less burning during the Late Iron Age and early medieval period. A shift toward higher molecular weight PAHs and increasing PAHs overall from c. 1000 cal years BP to present, reflects intensified human activity. Sedimentary charcoal (>125 and 63–125 µm) in the Lauvdalsvatnet record does not vary until an increase in the last 900 years, showing a proxy insensitivity to human-caused fire. The Late-Holocene increase in fire activity in Lofoten follows trends in regional charcoal records, but exhibits two distinct phases of increased fire that reflect the intensity of burning due to human landscape changes that overwhelm the signal of natural variations in regional fire activity

Sedimentary ancient DNA, fecal biomarker, and tephrochronology from Eidisvatn, Faroe Islands

This dataset includes sedimentary ancient DNA, lipid biomarker, and tephra geochemical data from a lake sediment core from the Faroe Islands. The purpose of the study was to characterize the signature of human influence on the landscape via lake sediment analysis, and to determine the timing of human arrival to the Faroe Islands. To achieve this, we analyzed fecal sterols, which are lipid biomarkers that are produced by the mammalian gut microbiome and deposited on the land surface in feces. We also used metabarcoding techniques to determine the first appearance of ancient sheep DNA in the lake sedimentary sequence. The lake sediment core was recovered from Eidisvatn on the island of Esturoy (62.286194, -7.057611) in August of 2015. Radiocarbon and tephrochronology were used to constrain sediment core chronology. Radiocarbon samples were analyzed via accelerator mass spectrometry at either the Woods Hole NOSAMS facility or the University of California Irvine Keck AMS facility. We analyzed the geochemistry of five tephra layers using microprobe. We extracted lipid biomarkers from 68 core subsamples, and following column chromatography, fecal biomarkers were identified and quantified via GC-MSD at the Lamont-Doherty Earth Observatory. 14 sediment samples were analyzed in the University of California Santa Cruz Paleogenomics Center. Plant and mammal DNA were amplified from each sample, and libraries were sequenced via an Illumina NextSeq